{"gene":"ATP2C1","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2000,"finding":"ATP2C1 encodes a P-type Ca2+-transport ATPase that sequesters calcium into the Golgi apparatus; heterozygous loss-of-function mutations in ATP2C1 cause Hailey-Hailey disease, associated with impaired cytoplasmic calcium regulation in keratinocytes and attenuation of the normal epidermal calcium gradient in vivo.","method":"Positional cloning, mutation identification in 21 HHD kindreds, Ca2+ signaling measurements in cultured keratinocytes, in vivo calcium gradient analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — positional cloning plus functional calcium measurements in patient keratinocytes, independently replicated in a second contemporaneous study (PMID:10767338)","pmids":["10615129","10767338"],"is_preprint":false},{"year":2003,"finding":"Human ATP2C1 (SPCA1) protein (~115 kDa) localizes to the Golgi apparatus in keratinocytes and is responsible for maintaining Golgi Ca2+ stores; Hailey-Hailey disease keratinocytes show slower Golgi Ca2+ refill and a lower maximum Golgi Ca2+ concentration, demonstrating the physiological role of ATP2C1 in controlling intraorganelle Ca2+ levels.","method":"Immunofluorescence localization, Golgi-targeted aequorin Ca2+ measurements, comparison of HHD vs. normal keratinocytes in vitro and in vivo","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct subcellular localization with functional consequence demonstrated by organelle-targeted luminescent Ca2+ sensor, corroborated by in vivo data","pmids":["14632183"],"is_preprint":false},{"year":2003,"finding":"SPCA1 mediates Ca2+ uptake into a subfraction of the Golgi apparatus in HeLa cells; RNAi-mediated knockdown of SPCA1 reduces Golgi Ca2+ accumulation and decreases frequency of baseline cytosolic Ca2+ oscillations in response to histamine, demonstrating SPCA1's contribution to cytosolic Ca2+ signal shaping.","method":"RNAi knockdown, Golgi-targeted aequorin Ca2+ measurements, cytosolic Ca2+ imaging","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — RNAi with two orthogonal readouts (organelle Ca2+ measurement and cytosolic oscillation frequency), single lab","pmids":["12804581"],"is_preprint":false},{"year":2003,"finding":"Keratinocytes rely predominantly on SPCA1 (rather than SERCA) to load the Golgi with Ca2+, whereas in COS-1 cells SERCA is the predominant Golgi Ca2+ pump; SPCA1-overexpressing COS-1 cells recapitulate the Ca2+ signaling phenotype of keratinocytes including prolonged latency of cytosolic Ca2+ signals, reflecting extra Ca2+ buffering by the SPCA1-containing store.","method":"SPCA1 overexpression in COS-1 cells, ER- and Golgi-targeted aequorin measurements, cytosolic Ca2+ imaging with capacitative Ca2+ entry","journal":"Cell calcium","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal Ca2+ measurement methods, single lab","pmids":["12810057"],"is_preprint":false},{"year":2004,"finding":"SPCA1 (ATP2C1) transports both Ca2+ and Mn2+ into the Golgi lumen and plays a role in cytosolic and intra-Golgi Ca2+ and Mn2+ homeostasis; it is distinct from SERCA and is thapsigargin-insensitive.","method":"Review consolidating functional transport assays and mutant analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — review summarizing multiple experimental studies; Ca2+/Mn2+ dual-transport established by cited in vitro transport assays","pmids":["15336968"],"is_preprint":false},{"year":2004,"finding":"ATP2C1 (PMR1 in beta cells) localizes to both microsomal and dense-core secretory vesicle fractions in pancreatic beta cells; siRNA-mediated depletion inhibits Ca2+ uptake into ER and secretory vesicles (~20%), markedly enhances L-type Ca2+ channel flux, augments glucose-stimulated insulin secretion, and alters cytosolic Ca2+ oscillation kinetics, demonstrating a role partially non-overlapping with SERCA in beta-cell Ca2+ homeostasis and insulin secretion.","method":"Subcellular fractionation, organelle-targeted aequorin Ca2+ measurements, siRNA knockdown, patch-clamp/Ca2+ imaging, insulin secretion assay","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, organelle Ca2+, functional insulin secretion) in a single well-controlled study","pmids":["14747290"],"is_preprint":false},{"year":2004,"finding":"ATP2C1 knockdown by siRNA impairs post-translational processing of thyroglobulin (a secretory glycoprotein) and ER-associated degradation of mutant thyroglobulin, while degradation of a nonglycosylated misfolded substrate is unaffected; ATP2C1 deficiency also renders cells hypersensitive to ER stress without basally elevating ER chaperones or activating the UPR (PERK, ATF6, or Ire1/XBP1).","method":"siRNA knockdown, pulse-chase protein processing assays, ER stress sensitivity assays, UPR marker analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockdown with multiple functional readouts (glycoprotein processing, ERAD, ER stress sensitivity) in a single rigorous study","pmids":["15623514"],"is_preprint":false},{"year":2005,"finding":"SPCA1, not SERCA, is the primary intracellular Ca2+ pump mediating progesterone-induced Ca2+ oscillations in human spermatozoa; SPCA1 protein localizes to the region behind the nucleus extending into the midpiece of sperm, whereas SERCA is undetectable in these cells.","method":"Pharmacological inhibition (thapsigargin, cyclopiazonic acid, bis-phenol), Western blotting, immunolocalization","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological evidence combined with localization, single lab, but selectivity of inhibitors partially limits interpretation","pmids":["15811949"],"is_preprint":false},{"year":2006,"finding":"ATP2C1 is specifically expressed in the basal layer of normal epidermis; siRNA-mediated knockdown of ATP2C1 induces keratinocyte differentiation markers (K10 keratin and involucrin), while a manganese-selective ionophore (Br-A23187) but not a calcium ionophore (A23187) recapitulates this effect, suggesting ATP2C1 maintains basal keratinocytes in an undifferentiated state primarily through Mn2+ sequestration in the Golgi.","method":"Immunohistochemistry, siRNA knockdown, differentiation marker expression assays, ionophore treatment","journal":"Journal of dermatological science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown plus ionophore pharmacology with specific marker readouts, single lab","pmids":["16621454"],"is_preprint":false},{"year":2007,"finding":"Complete loss of Atp2c1 (Spca1-/-) in mice causes lethal Golgi stress with dilated Golgi membranes, reduced Golgi stacking, increased Golgi-associated vesicles, increased apoptosis, and embryonic death by gestational day 10.5; heterozygous adult mice develop squamous cell tumors of keratinized epithelia, demonstrating that SPCA1 is essential for Golgi homeostasis and that haploinsufficiency predisposes to cancer.","method":"Targeted gene knockout in mice, electron microscopy of Golgi ultrastructure, apoptosis assays, tumor incidence in aged heterozygotes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function in vivo with multiple orthogonal ultrastructural and cellular readouts","pmids":["17597066"],"is_preprint":false},{"year":2009,"finding":"SPCA1 knockdown in N2a neuroblastoma cells and primary hippocampal neurons impairs Golgi Ca2+ homeostasis, disrupts trafficking of Golgi-resident and plasma membrane-targeted proteins, delays neuronal differentiation (fewer and shorter neurites), and causes cell death upon complete suppression, establishing SPCA1 as required for neural polarity and differentiation.","method":"siRNA knockdown in N2a and primary neurons, Ca2+ imaging, immunocytochemical trafficking assays, morphological differentiation analysis","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockdown in two independent cell systems with multiple functional readouts including Ca2+ imaging and protein trafficking","pmids":["19793975"],"is_preprint":false},{"year":2010,"finding":"SPCA1 localizes predominantly to the lateral rims of Golgi cisternae, tubular non-compact zones connecting Golgi stacks, and tubular trans-Golgi network regions; SPCA1 knockdown causes Golgi fragmentation (loss of cis-most and trans-most cisternae), inhibits exit of VSV-G protein from the Golgi, and delays retrograde redistribution of Golgi glycosylation enzymes to the ER induced by brefeldin A, demonstrating SPCA1 is required for intra-Golgi transport and Golgi ribbon maintenance.","method":"Immunofluorescence/electron microscopy localization, siRNA knockdown, VSV-G trafficking assay, brefeldin A retrograde transport assay","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 / Strong — precise localization combined with functional knockdown using multiple transport readouts in a single study","pmids":["20604898"],"is_preprint":false},{"year":2010,"finding":"SPCA1 inhibition in MDA-MB-231 basal-like breast cancer cells alters processing of IGF1R by proprotein convertases in the secretory pathway (accumulation of inactive pro-IGF1R in the TGN, reduced functional IGF1Rβ), without altering global cytosolic Ca2+ signaling or ER stress, demonstrating SPCA1 controls Ca2+-dependent enzyme activity in the Golgi lumen to regulate proprotein processing.","method":"SPCA1 inhibition, Western blot for IGF1R processing, 3D proliferation/morphology assays, ER stress assays, Ca2+ imaging","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal readouts (protein processing, morphology, Ca2+) but pharmacological inhibition rather than clean genetic loss-of-function, single lab","pmids":["20837466"],"is_preprint":false},{"year":2012,"finding":"ATP2C1/SPCA1 knockdown in keratinocytes up-regulates tight junction proteins claudins 1 and 4 even at low extracellular Ca2+, and causes delayed translocation of desmoplakin and desmoglein 3 with increased intracellular accumulation, indicating SPCA1 specifically regulates claudin expression and desmosomal/tight junction protein trafficking.","method":"siRNA knockdown, qPCR, Western blot, indirect immunofluorescence in low and high Ca2+ conditions","journal":"Experimental dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean siRNA knockdown with multiple junction protein readouts, single lab","pmids":["22639968"],"is_preprint":false},{"year":2012,"finding":"Bis-phenol selectively inhibits human SPCA1d Ca2+-ATPase activity (IC50 ~0.13 µM) with 62-fold greater potency than hSERCA2b (IC50 ~8.1 µM), and can mobilize Ca2+ from thapsigargin-insensitive stores in intact cells, establishing bis-phenol as a selective SPCA1 inhibitor.","method":"Overexpression of SPCA1d and SERCA2b in COS-7 cells, Ca2+-dependent ATPase activity assays, Ca2+ mobilization assays in intact cells","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct enzymatic assay with dose-response and selectivity comparison plus intact-cell functional validation, single lab","pmids":["22796571"],"is_preprint":false},{"year":2013,"finding":"PMR-1 (C. elegans ortholog of SPCA1/ATP2C1) is required for embryonic cell migration; pmr-1 mutant embryos show reduced migration rates of ventral neuroblasts and other blastomeres, and genetic interaction experiments show that changing activity of IP3R (itr-1) or RyR (unc-68) modulates lethality, placing pmr-1 in a Ca2+ channel network regulating cell migration.","method":"Forward genetic screen, time-lapse imaging of cell migration, genetic epistasis with itr-1 and unc-68","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with live imaging plus epistasis experiments, ortholog in established model organism","pmids":["23696750"],"is_preprint":false},{"year":2014,"finding":"Cofilin-1 (CFL-1) recruits F-actin to the phosphorylation domain (P-domain) of SPCA1 at the TGN; a 132-amino-acid portion of the SPCA1 P-domain interacts with actin in a CFL-1-dependent manner. Mutagenesis of four residues constituting the CFL-1 binding site in SPCA1 impairs Ca2+ import into the TGN and secretory cargo sorting.","method":"In vitro binding assay with purified proteins, Ni-NTA pulldown with P-domain fragment, mutagenesis, TGN Ca2+ imaging, cargo sorting assay in HeLa cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified proteins plus mutagenesis plus cellular functional assays, multiple orthogonal methods","pmids":["25179631"],"is_preprint":false},{"year":2016,"finding":"ATP2C1 inactivation in keratinocytes increases oxidative stress and activates Notch1; RNA-seq of HHD patient lesional keratinocytes shows consistent down-regulation of the DNA damage response (DDR); Notch1 activation downstream of oxidative stress induced by ATP2C1 loss drives keratinocyte differentiation and represses DDR gene expression, identifying an ATP2C1/NOTCH1 axis in epidermal homeostasis.","method":"siRNA knockdown, RNA-seq, oxidative stress assays, Notch1 activation assays in cultured keratinocytes and HHD patient lesions","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transcriptome-level evidence combined with functional knockdown and pathway analysis, single lab","pmids":["27528123"],"is_preprint":false},{"year":2017,"finding":"Genome-wide haploid knockout screen identifies SPCA1 as required for maturation and spread of viruses from Paramyxoviridae, Flaviviridae, and Togaviridae families; SPCA1 Ca2+ transport activity is required because it activates proprotein convertases in the TGN that cleave viral glycoproteins; SPCA1-deficient cells accumulate uncleaved, non-functional viral glycoproteins and fail to support viral spread.","method":"Genome-wide CRISPR/haploid cell knockout screen, glycoprotein processing assays, protease activity assays, viral spread assays in SPCA1-KO cells","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide unbiased screen validated by clean KO with multiple orthogonal mechanistic readouts (protease activity, glycoprotein processing, viral spread) across diverse viral families","pmids":["29024641"],"is_preprint":false},{"year":2017,"finding":"In zebrafish, ATP2C1 expression provides compensatory Mn2+ transport protection in embryos lacking the Mn efflux transporter Slc30a10; wild-type or mutant SLC30A10 expression can inhibit the protective effect of ATP2C1 in response to Mn challenge in both zebrafish and HeLa cells, indicating ATP2C1 functions as a Mn2+ transport buffer that can substitute for SLC30A10.","method":"CRISPR/Cas9 zebrafish knockout, rescue experiments with ATP2C1 expression constructs, HeLa cell Mn challenge assays","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic rescue/epistasis in two systems (zebrafish and HeLa), single lab","pmids":["28692648"],"is_preprint":false},{"year":2018,"finding":"SPCA1 activity couples secretory protein sorting to sphingomyelin synthesis in the TGN: sphingomyelin in the TGN membrane promotes SPCA1-mediated Ca2+ flux into the TGN lumen, which drives Ca2+-dependent oligomerization of the secreted Ca2+-binding protein Cab45, enabling Cab45 to package client secreted proteins into sphingomyelin-enriched vesicular carriers for export to the cell surface.","method":"SPCA1 activity assays, sphingomyelin manipulation, Cab45 oligomerization assays, Ca2+ flux measurements, vesicle trafficking assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — mechanistic reconstitution of lipid-Ca2+-protein coupling with multiple orthogonal experimental approaches in a single rigorous study","pmids":["30393074"],"is_preprint":false},{"year":2018,"finding":"Loss of Spca1 in mice impairs neuroepithelial cell apical constriction during neural tube closure, not primarily through apoptosis; SPCA1 promotes apical constriction by regulating myosin II localization and actin dynamics through cofilin-1, with cofilin-1 acting as a downstream effector of SPCA1 function.","method":"Novel Spca1 allele characterization in mice, apical constriction imaging, myosin II localization by immunofluorescence, actin dynamics assays, cofilin-1 localization analysis","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic evidence with multiple cellular mechanism readouts (apical constriction, myosin II, cofilin localization) in a single study","pmids":["30228103"],"is_preprint":false},{"year":2018,"finding":"SPCA1 overexpression induces STIM1-independent, Orai1-dependent cytosolic Ca2+ influx (store-independent Ca2+ entry, SICE) and co-localizes with Orai1 near the plasma membrane as shown by TIRF microscopy; this functional coupling elevates Ca2+ in non-ER stores and induces Golgi swelling with nuclear translocation of TFE3 (Golgi stress marker); HHD-associated SPCA1 mutations differentially impair Ca2+ transport, Orai1 activation, or both.","method":"SPCA1/SPCA2 overexpression, Orai1 knockdown, TIRF microscopy co-localization, cytosolic Ca2+ measurements, Golgi swelling assay, TFE3 nuclear translocation assay, HHD mutant functional analysis","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple localization and functional readouts, single lab, overexpression system","pmids":["29555205"],"is_preprint":false},{"year":2019,"finding":"SPCA1a has an N-terminal EF-hand-like motif that binds Ca2+ and regulates pump activity: Ca2+ binding to this motif promotes autophosphorylation and SPCA1a activity, modulates substrate ion affinity, and accounts for a biphasic activation curve and lower apparent Ca2+ affinity relative to SPCA2. SPCA1a has lower Ca2+ affinity and a ~2-fold higher Ca2+ turnover rate compared with Mn2+; mutation of the EF-hand-like motif lowers Ca2+ turnover rate and increases substrate affinity.","method":"Yeast recombinant expression and purification of SPCA1a and SPCA2, biochemical reconstitution, Ca2+/Mn2+ transport assays, autophosphorylation assays, EF-hand mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified proteins, mutagenesis, and multiple enzymatic assays in a single rigorous biochemical study","pmids":["30923126"],"is_preprint":false},{"year":2019,"finding":"TMEM165 stability depends on SPCA1's Mn2+ pumping activity: TMEM165 is constitutively degraded in lysosomes in the absence of SPCA1; among SPCA1 mutants, only Q747A (which favors Mn2+ over Ca2+ transport) rescues TMEM165 abundance and Golgi localization; SERCA2b overexpression also rescues TMEM165, indicating Mn2+ homeostasis in the Golgi lumen governs TMEM165 stability.","method":"SPCA1-deficient Hap1 cells, SPCA1 complementation with transport-selective mutants, lysosomal inhibitors, Western blot, immunofluorescence","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic loss-of-function with selective mutant complementation establishing Mn2+ transport as the mechanistic requirement, multiple methods","pmids":["31652305"],"is_preprint":false},{"year":2019,"finding":"In yeast complementation assays, fourteen HHD-associated ATP2C1 missense mutations preferentially impair Mn2+ transport over Ca2+ transport (12/14 fail to complement Mn2+ sensitivity; 13/14 partially complement high-Ca2+ requirement); nine mutations show cold-sensitive complementation; twelve mutations induce the unfolded protein response (UPR) in the absence of wild-type ATP2C1, and four cause hSPCA1 mis-localization to the vacuolar membrane; co-expression of wild-type ATP2C1 or ATP2A2 prevents UPR induction and mis-localization.","method":"Yeast complementation system, Mn2+/Ca2+ sensitivity growth assays, UPR reporter assays, fluorescence localization of hSPCA1 variants","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro yeast reconstitution system with multiple functional readouts but heterologous expression system","pmids":["31455819"],"is_preprint":false},{"year":2021,"finding":"UVA irradiation increases SPCA1 expression in human dermal fibroblasts via MAPK/c-jun pathway; c-jun binds the SPCA1 promoter and transcriptionally up-regulates SPCA1; SPCA1 knockdown aggravates UVA-induced senescence by elevating intracellular Ca2+, increasing ROS, and increasing MAPK activity, while SPCA1 overexpression reduces Ca2+ overload, lowers ROS, and suppresses MAPK, establishing a negative feedback loop.","method":"Dual-luciferase reporter assay, chromatin immunoprecipitation (ChIP), siRNA knockdown, SPCA1 overexpression, ROS/Ca2+/senescence assays","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus reporter assay for transcriptional mechanism, combined with gain/loss-of-function functional assays, single lab","pmids":["34239867"],"is_preprint":false},{"year":2022,"finding":"SPCA1 knockdown in brain microvascular endothelial cells increases cytoplasmic Ca2+, which in turn increases plasma membrane localization of ZIP8 and ZIP14 metal transporters (via surface biotinylation and immunofluorescence), resulting in enhanced Mn2+ uptake; conversely, SPCA1 overexpression or gain-of-function mutant decreases cytoplasmic Ca2+ and reduces Mn2+ accumulation, demonstrating that SPCA1 regulates ZIP-mediated Mn2+ uptake through cytoplasmic Ca2+ control of transporter membrane trafficking.","method":"siRNA knockdown, SPCA1 overexpression with gain-of-function mutant, surface protein biotinylation, indirect immunofluorescence, GFP-tagged transporter localization, 54Mn2+ uptake assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain and loss-of-function with multiple orthogonal methods (biotinylation, imaging, isotope uptake), mechanistic pathway established","pmids":["35787370"],"is_preprint":false},{"year":2023,"finding":"Six cryo-EM structures of human SPCA1 in a near-complete conformational cycle reveal unique conformational changes during ATP binding and phosphorylation compared to other P-type II ATPases; transmembrane helix 4L and 6 separation causes conformational distortion of the Ca2+-binding site constituting a distinct Ca2+ release mechanism; the CaE2P intermediate state is resolved, providing the structural basis for Ca2+ entry and release in hSPCA1.","method":"Cryo-electron microscopy structure determination (6 conformational states), molecular dynamics simulations","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple high-resolution cryo-EM structures spanning the catalytic cycle, supported by MD simulations, in a single rigorous structural study","pmids":["37258749"],"is_preprint":false},{"year":2005,"finding":"Transcription factors Sp1 and YY1 directly bind the region +21/+57 of the ATP2C1 promoter and transactivate it; Ca2+ stimulation increases nuclear Sp1 and ATP2C1 mRNA in normal keratinocytes, but both increases are suppressed in HHD patient keratinocytes, indicating impaired transcriptional upregulation contributes to keratinocyte-specific pathogenesis.","method":"Transient reporter assay, EMSA, Sp1/YY1 overexpression, Ca2+ stimulation experiments in normal vs. HHD keratinocytes","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EMSA plus reporter assay with functional overexpression validation, single lab","pmids":["15955096"],"is_preprint":false},{"year":2020,"finding":"TMEM165 expression is more sensitive to MnCl2-induced degradation in HHD patient fibroblasts and keratinocytes (with partial SPCA1 deficiency) than in controls; ICP-MS and GPP130 Golgi Mn2+ sensor demonstrate cytosolic Mn2+ accumulation in MnCl2-supplemented HHD fibroblasts, linking SPCA1 Mn2+ pumping function to TMEM165 stability in a pathological context.","method":"HHD patient fibroblasts and keratinocytes, Western blot, ICP-MS, GPP130 as Golgi Mn2+ sensor, MnCl2 supplementation","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived cells with multiple quantitative readouts, single lab","pmids":["32335229"],"is_preprint":false}],"current_model":"ATP2C1 encodes SPCA1, a P-type Ca2+/Mn2+ ATPase localized to the Golgi apparatus (and TGN lateral rims) that pumps cytosolic Ca2+ and Mn2+ into the Golgi lumen; its activity controls intra-Golgi Ca2+ and Mn2+ homeostasis, drives secretory protein sorting via Ca2+-dependent Cab45 oligomerization coupled to sphingomyelin synthesis, regulates proprotein convertase activity for glycoprotein and receptor processing, maintains Golgi ribbon integrity for intra-Golgi transport, governs TMEM165 stability through Mn2+ transport, and supports cytoskeletal dynamics (via cofilin-1 and myosin II) required for neural tube closure and cell migration; haploinsufficiency causes Hailey-Hailey disease through impaired Ca2+/Mn2+ homeostasis in keratinocytes, and cryo-EM structures reveal a unique conformational cycle including a distinct Ca2+ release mechanism involving separation of transmembrane helices 4L and 6."},"narrative":{"mechanistic_narrative":"ATP2C1 encodes SPCA1, a thapsigargin-insensitive P-type ATPase that pumps cytosolic Ca2+ and Mn2+ into the Golgi lumen to govern intra-Golgi and cytosolic ion homeostasis and secretory pathway function [PMID:15336968, PMID:14632183]. In keratinocytes SPCA1 is the dominant Golgi Ca2+ pump, and heterozygous loss-of-function mutations cause Hailey-Hailey disease through impaired Golgi Ca2+ refill and reduced maximal luminal Ca2+ [PMID:10615129, PMID:10767338, PMID:14632183]; many disease alleles preferentially cripple Mn2+ over Ca2+ transport and can trigger UPR and mis-localization in complementation assays [PMID:31455819]. Luminal Ca2+ delivered by SPCA1 is functionally coupled to secretory sorting: sphingomyelin in the TGN membrane promotes SPCA1 Ca2+ flux that drives Ca2+-dependent oligomerization of Cab45 to package secretory cargo, and cofilin-1 recruits F-actin to the SPCA1 phosphorylation domain to support TGN Ca2+ import and cargo sorting [PMID:30393074, PMID:25179631]. SPCA1-supplied luminal Ca2+ also activates TGN proprotein convertases required to process glycoproteins and receptors such as IGF1R and viral envelope proteins, the latter making SPCA1 essential for maturation and spread of multiple enveloped virus families [PMID:20837466, PMID:29024641]. Through its Mn2+ pumping activity SPCA1 maintains Golgi Mn2+ homeostasis, stabilizing the Mn2+-handling protein TMEM165 against lysosomal degradation, and by controlling cytosolic Ca2+ it modulates surface trafficking of ZIP8/ZIP14 Mn2+ importers [PMID:31652305, PMID:35787370]. SPCA1 is required for Golgi ribbon integrity and intra-Golgi transport, and at the organism level its loss is embryonic-lethal with Golgi stress, while it drives neuronal differentiation and neuroepithelial apical constriction via myosin II and cofilin-1-dependent actin dynamics [PMID:20604898, PMID:17597066, PMID:19793975, PMID:30228103]. Cryo-EM structures spanning the catalytic cycle define a distinct Ca2+ release mechanism involving separation of transmembrane helices 4L and 6, and an N-terminal EF-hand-like motif binds Ca2+ to regulate autophosphorylation and ion turnover [PMID:37258749, PMID:30923126].","teleology":[{"year":2000,"claim":"Establishing the disease gene: positional cloning linked ATP2C1 mutations to Hailey-Hailey disease and tied the phenotype to disrupted keratinocyte calcium handling, defining SPCA1 as a Golgi Ca2+ pump with physiological importance in epidermis.","evidence":"Positional cloning in HHD kindreds with keratinocyte Ca2+ measurements and in vivo epidermal calcium gradient analysis","pmids":["10615129","10767338"],"confidence":"High","gaps":["Molecular transport mechanism and ion selectivity not resolved","Why haploinsufficiency manifests specifically in keratinocytes unexplained"]},{"year":2003,"claim":"Localizing the function: direct organelle Ca2+ measurements established SPCA1 as a Golgi-resident pump maintaining luminal Ca2+ stores and shaping cytosolic Ca2+ signals, with reduced refill in HHD cells.","evidence":"Immunofluorescence and Golgi-targeted aequorin in keratinocytes and HeLa cells with RNAi knockdown","pmids":["14632183","12804581","12810057"],"confidence":"High","gaps":["Relative contribution of SPCA1 vs SERCA is cell-type dependent and not generalized","Mn2+ transport not yet assayed in these systems"]},{"year":2004,"claim":"Defining substrate scope and downstream consequences: SPCA1 transports both Ca2+ and Mn2+, contributes to beta-cell Ca2+ homeostasis/insulin secretion, supports glycoprotein processing and ERAD, and maintains basal keratinocyte state via Mn2+ sequestration.","evidence":"Transport assays, siRNA in beta cells and keratinocytes, pulse-chase glycoprotein processing, ionophore pharmacology","pmids":["15336968","14747290","15623514","16621454"],"confidence":"High","gaps":["Mechanistic coupling between luminal ion levels and glycoprotein processing not yet defined","Distinction between Ca2+- and Mn2+-dependent effects incompletely separated"]},{"year":2005,"claim":"Transcriptional control: Sp1 and YY1 directly transactivate the ATP2C1 promoter and Ca2+ induces Sp1/ATP2C1 upregulation in normal but not HHD keratinocytes, adding a regulatory layer to disease pathogenesis.","evidence":"Reporter assays, EMSA, and Ca2+ stimulation in normal vs HHD keratinocytes","pmids":["15955096"],"confidence":"Medium","gaps":["Single lab; in vivo relevance of the transcriptional defect unconfirmed","Whether impaired upregulation is cause or consequence of HHD Ca2+ defect unclear"]},{"year":2007,"claim":"In vivo essentiality: complete Atp2c1 knockout causes Golgi stress and embryonic lethality while heterozygotes develop epithelial tumors, establishing SPCA1 as essential for Golgi homeostasis and a haploinsufficient tumor predisposition gene.","evidence":"Mouse targeted knockout with Golgi ultrastructure, apoptosis, and tumor incidence analysis","pmids":["17597066"],"confidence":"High","gaps":["Molecular trigger of Golgi stress not defined","Mechanism connecting haploinsufficiency to tumorigenesis unresolved"]},{"year":2010,"claim":"Defining the Golgi transport role: SPCA1 localizes to lateral rims and TGN tubules and is required for intra-Golgi transport, Golgi ribbon maintenance, and Ca2+-dependent proprotein convertase processing of receptors such as IGF1R.","evidence":"EM/IF localization, siRNA with VSV-G and brefeldin A transport assays, IGF1R processing in breast cancer cells","pmids":["20604898","20837466"],"confidence":"High","gaps":["IGF1R study used pharmacological inhibition rather than genetic loss","How luminal Ca2+ directly activates convertases not mechanistically reconstituted"]},{"year":2014,"claim":"Linking the pump to the cytoskeleton: cofilin-1 recruits F-actin to the SPCA1 phosphorylation domain at the TGN, and disrupting this interface impairs TGN Ca2+ import and cargo sorting, connecting actin dynamics to pump function.","evidence":"In vitro binding with purified proteins, pulldown, mutagenesis, and TGN Ca2+/cargo sorting assays in HeLa","pmids":["25179631"],"confidence":"High","gaps":["How actin/cofilin binding mechanistically enhances Ca2+ import unclear","Regulation of the interaction in vivo not addressed"]},{"year":2017,"claim":"Mechanism in viral pathogenesis: an unbiased genetic screen showed SPCA1 Ca2+ transport activates TGN proprotein convertases that cleave viral glycoproteins, making it required for maturation and spread of multiple enveloped virus families.","evidence":"Genome-wide haploid/CRISPR knockout screen with glycoprotein processing, protease activity, and viral spread assays","pmids":["29024641"],"confidence":"High","gaps":["Whether SPCA1 is broadly required across all enveloped viruses unknown","Direct biochemical link between luminal Ca2+ and convertase catalysis not isolated"]},{"year":2018,"claim":"Coupling ion transport to secretion and morphogenesis: sphingomyelin-promoted SPCA1 Ca2+ flux drives Cab45 oligomerization for cargo sorting, and SPCA1 loss disrupts neural tube apical constriction via myosin II and cofilin-1, integrating pump activity with lipid signaling and tissue morphogenesis.","evidence":"SM manipulation with Cab45 oligomerization/vesicle assays; mouse Spca1 allele with apical constriction and cytoskeletal imaging; Orai1-coupled Ca2+ entry overexpression studies","pmids":["30393074","30228103","29555205"],"confidence":"High","gaps":["Orai1 coupling shown only in overexpression and unconfirmed at endogenous levels","How cytoskeletal effects relate to luminal vs cytosolic Ca2+ not fully separated"]},{"year":2019,"claim":"Resolving Mn2+-specific functions and intrinsic regulation: SPCA1 Mn2+ pumping stabilizes TMEM165 against lysosomal degradation, an N-terminal EF-hand-like motif tunes autophosphorylation and ion turnover, and HHD alleles preferentially impair Mn2+ transport, refining the disease mechanism toward Mn2+ handling.","evidence":"Selective-mutant complementation in SPCA1-deficient cells, yeast reconstitution with purified pump and EF-hand mutagenesis, yeast complementation of HHD missense alleles","pmids":["31652305","30923126","31455819","28692648"],"confidence":"High","gaps":["Yeast/heterologous systems may not fully model human pump behavior","Relative pathogenic weight of Ca2+ vs Mn2+ defects in HHD epidermis unresolved"]},{"year":2022,"claim":"Extending Mn2+ homeostasis control to the cell surface: SPCA1-set cytosolic Ca2+ regulates plasma membrane trafficking of ZIP8/ZIP14 Mn2+ importers, positioning SPCA1 within a broader Mn2+ buffering network alongside its TMEM165-stabilizing role in patient cells.","evidence":"Gain/loss-of-function with surface biotinylation, imaging, and 54Mn2+ uptake in endothelial cells; patient fibroblast ICP-MS/GPP130 Mn2+ sensing","pmids":["35787370","32335229"],"confidence":"High","gaps":["In vivo systemic Mn2+ handling role not established","Single-lab mechanism for ZIP trafficking control"]},{"year":2023,"claim":"Structural basis of transport: cryo-EM structures across the catalytic cycle reveal a distinct Ca2+ release mechanism via separation of transmembrane helices 4L and 6, explaining how SPCA1 differs from other P-type II ATPases.","evidence":"Six cryo-EM conformational states with molecular dynamics simulations","pmids":["37258749"],"confidence":"High","gaps":["Structural basis for Mn2+ versus Ca2+ selectivity not resolved","Structures of disease mutants not determined"]},{"year":null,"claim":"How SPCA1 achieves and switches between Ca2+ and Mn2+ selectivity, and how this dictates tissue-specific disease manifestation, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["Structural/biochemical determinants of Ca2+ vs Mn2+ selectivity unknown","Why haploinsufficiency causes epidermis-restricted disease despite ubiquitous expression unexplained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[4,23,14]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,4,24]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[14,23]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1,11]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[11,20]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[6,12,18]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[4,24,27]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,25]}],"complexes":[],"partners":["CFL1","ORAI1","TMEM165","CAB45/SDF4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P98194","full_name":"Calcium-transporting ATPase type 2C member 1","aliases":["ATP-dependent Ca(2+) pump PMR1","Ca(2+)/Mn(2+)-ATPase 2C1","Secretory pathway Ca(2+)-transporting ATPase type 1","SPCA1"],"length_aa":919,"mass_kda":100.6,"function":"ATP-driven pump that supplies the Golgi apparatus with Ca(2+) and Mn(2+) ions, both essential cofactors for processing and trafficking of newly synthesized proteins in the secretory pathway (PubMed:12707275, PubMed:16192278, PubMed:20439740, PubMed:21187401, PubMed:30923126). Within a catalytic cycle, acquires Ca(2+) or Mn(2+) ions on the cytoplasmic side of the membrane and delivers them to the lumenal side. The transfer of ions across the membrane is coupled to ATP hydrolysis and is associated with a transient phosphorylation that shifts the pump conformation from inward-facing to outward-facing state (PubMed:16192278, PubMed:16332677, PubMed:30923126). Plays a primary role in the maintenance of Ca(2+) homeostasis in the trans-Golgi compartment with a functional impact on Golgi and post-Golgi protein sorting as well as a structural impact on cisternae morphology (PubMed:14632183, PubMed:20439740). Responsible for loading the Golgi stores with Ca(2+) ions in keratinocytes, contributing to keratinocyte differentiation and epidermis integrity (PubMed:10615129, PubMed:14632183, PubMed:20439740). Participates in Ca(2+) and Mn(2+) ions uptake into the Golgi store of hippocampal neurons and regulates protein trafficking required for neural polarity (By similarity). May also play a role in the maintenance of Ca(2+) and Mn(2+) homeostasis and signaling in the cytosol while preventing cytotoxicity (PubMed:21187401)","subcellular_location":"Golgi apparatus, trans-Golgi network membrane; Golgi apparatus, Golgi stack membrane","url":"https://www.uniprot.org/uniprotkb/P98194/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATP2C1","classification":"Not Classified","n_dependent_lines":103,"n_total_lines":1208,"dependency_fraction":0.08526490066225166},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"GORASP2","stoichiometry":0.2},{"gene":"TMED10","stoichiometry":0.2},{"gene":"YIPF5","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ATP2C1","total_profiled":1310},"omim":[{"mim_id":"620693","title":"ASTEROID HOMOLOG 1; ASTE1","url":"https://www.omim.org/entry/620693"},{"mim_id":"613082","title":"ATPase, Ca(2+)-TRANSPORTING, TYPE 2C, MEMBER 2; ATP2C2","url":"https://www.omim.org/entry/613082"},{"mim_id":"606805","title":"GOLGI INTEGRAL MEMBRANE PROTEIN 4; GOLIM4","url":"https://www.omim.org/entry/606805"},{"mim_id":"604384","title":"ATPase, Ca(2+)-TRANSPORTING, TYPE 2C, MEMBER 1; ATP2C1","url":"https://www.omim.org/entry/604384"},{"mim_id":"169600","title":"HAILEY-HAILEY DISEASE; HHD","url":"https://www.omim.org/entry/169600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATP2C1"},"hgnc":{"alias_symbol":["KIAA1347","ATP2C1A","PMR1","SPCA1"],"prev_symbol":["BCPM"]},"alphafold":{"accession":"P98194","domains":[{"cath_id":"2.70.150.10","chopping":"2-251","consensus_level":"medium","plddt":76.2227,"start":2,"end":251},{"cath_id":"1.20.1110.10","chopping":"300-313_701-911","consensus_level":"high","plddt":86.0042,"start":300,"end":911},{"cath_id":"3.40.50.1000","chopping":"332-357_549-681","consensus_level":"medium","plddt":87.4577,"start":332,"end":681},{"cath_id":"3.40.1110.10","chopping":"364-543","consensus_level":"high","plddt":90.505,"start":364,"end":543}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P98194","model_url":"https://alphafold.ebi.ac.uk/files/AF-P98194-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P98194-F1-predicted_aligned_error_v6.png","plddt_mean":83.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATP2C1","jax_strain_url":"https://www.jax.org/strain/search?query=ATP2C1"},"sequence":{"accession":"P98194","fasta_url":"https://rest.uniprot.org/uniprotkb/P98194.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P98194/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P98194"}},"corpus_meta":[{"pmid":"10615129","id":"PMC_10615129","title":"Mutations 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that sequesters calcium into the Golgi apparatus; heterozygous loss-of-function mutations in ATP2C1 cause Hailey-Hailey disease, associated with impaired cytoplasmic calcium regulation in keratinocytes and attenuation of the normal epidermal calcium gradient in vivo.\",\n      \"method\": \"Positional cloning, mutation identification in 21 HHD kindreds, Ca2+ signaling measurements in cultured keratinocytes, in vivo calcium gradient analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — positional cloning plus functional calcium measurements in patient keratinocytes, independently replicated in a second contemporaneous study (PMID:10767338)\",\n      \"pmids\": [\"10615129\", \"10767338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human ATP2C1 (SPCA1) protein (~115 kDa) localizes to the Golgi apparatus in keratinocytes and is responsible for maintaining Golgi Ca2+ stores; Hailey-Hailey disease keratinocytes show slower Golgi Ca2+ refill and a lower maximum Golgi Ca2+ concentration, demonstrating the physiological role of ATP2C1 in controlling intraorganelle Ca2+ levels.\",\n      \"method\": \"Immunofluorescence localization, Golgi-targeted aequorin Ca2+ measurements, comparison of HHD vs. normal keratinocytes in vitro and in vivo\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct subcellular localization with functional consequence demonstrated by organelle-targeted luminescent Ca2+ sensor, corroborated by in vivo data\",\n      \"pmids\": [\"14632183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SPCA1 mediates Ca2+ uptake into a subfraction of the Golgi apparatus in HeLa cells; RNAi-mediated knockdown of SPCA1 reduces Golgi Ca2+ accumulation and decreases frequency of baseline cytosolic Ca2+ oscillations in response to histamine, demonstrating SPCA1's contribution to cytosolic Ca2+ signal shaping.\",\n      \"method\": \"RNAi knockdown, Golgi-targeted aequorin Ca2+ measurements, cytosolic Ca2+ imaging\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi with two orthogonal readouts (organelle Ca2+ measurement and cytosolic oscillation frequency), single lab\",\n      \"pmids\": [\"12804581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Keratinocytes rely predominantly on SPCA1 (rather than SERCA) to load the Golgi with Ca2+, whereas in COS-1 cells SERCA is the predominant Golgi Ca2+ pump; SPCA1-overexpressing COS-1 cells recapitulate the Ca2+ signaling phenotype of keratinocytes including prolonged latency of cytosolic Ca2+ signals, reflecting extra Ca2+ buffering by the SPCA1-containing store.\",\n      \"method\": \"SPCA1 overexpression in COS-1 cells, ER- and Golgi-targeted aequorin measurements, cytosolic Ca2+ imaging with capacitative Ca2+ entry\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal Ca2+ measurement methods, single lab\",\n      \"pmids\": [\"12810057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SPCA1 (ATP2C1) transports both Ca2+ and Mn2+ into the Golgi lumen and plays a role in cytosolic and intra-Golgi Ca2+ and Mn2+ homeostasis; it is distinct from SERCA and is thapsigargin-insensitive.\",\n      \"method\": \"Review consolidating functional transport assays and mutant analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — review summarizing multiple experimental studies; Ca2+/Mn2+ dual-transport established by cited in vitro transport assays\",\n      \"pmids\": [\"15336968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ATP2C1 (PMR1 in beta cells) localizes to both microsomal and dense-core secretory vesicle fractions in pancreatic beta cells; siRNA-mediated depletion inhibits Ca2+ uptake into ER and secretory vesicles (~20%), markedly enhances L-type Ca2+ channel flux, augments glucose-stimulated insulin secretion, and alters cytosolic Ca2+ oscillation kinetics, demonstrating a role partially non-overlapping with SERCA in beta-cell Ca2+ homeostasis and insulin secretion.\",\n      \"method\": \"Subcellular fractionation, organelle-targeted aequorin Ca2+ measurements, siRNA knockdown, patch-clamp/Ca2+ imaging, insulin secretion assay\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, organelle Ca2+, functional insulin secretion) in a single well-controlled study\",\n      \"pmids\": [\"14747290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ATP2C1 knockdown by siRNA impairs post-translational processing of thyroglobulin (a secretory glycoprotein) and ER-associated degradation of mutant thyroglobulin, while degradation of a nonglycosylated misfolded substrate is unaffected; ATP2C1 deficiency also renders cells hypersensitive to ER stress without basally elevating ER chaperones or activating the UPR (PERK, ATF6, or Ire1/XBP1).\",\n      \"method\": \"siRNA knockdown, pulse-chase protein processing assays, ER stress sensitivity assays, UPR marker analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockdown with multiple functional readouts (glycoprotein processing, ERAD, ER stress sensitivity) in a single rigorous study\",\n      \"pmids\": [\"15623514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SPCA1, not SERCA, is the primary intracellular Ca2+ pump mediating progesterone-induced Ca2+ oscillations in human spermatozoa; SPCA1 protein localizes to the region behind the nucleus extending into the midpiece of sperm, whereas SERCA is undetectable in these cells.\",\n      \"method\": \"Pharmacological inhibition (thapsigargin, cyclopiazonic acid, bis-phenol), Western blotting, immunolocalization\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological evidence combined with localization, single lab, but selectivity of inhibitors partially limits interpretation\",\n      \"pmids\": [\"15811949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ATP2C1 is specifically expressed in the basal layer of normal epidermis; siRNA-mediated knockdown of ATP2C1 induces keratinocyte differentiation markers (K10 keratin and involucrin), while a manganese-selective ionophore (Br-A23187) but not a calcium ionophore (A23187) recapitulates this effect, suggesting ATP2C1 maintains basal keratinocytes in an undifferentiated state primarily through Mn2+ sequestration in the Golgi.\",\n      \"method\": \"Immunohistochemistry, siRNA knockdown, differentiation marker expression assays, ionophore treatment\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown plus ionophore pharmacology with specific marker readouts, single lab\",\n      \"pmids\": [\"16621454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Complete loss of Atp2c1 (Spca1-/-) in mice causes lethal Golgi stress with dilated Golgi membranes, reduced Golgi stacking, increased Golgi-associated vesicles, increased apoptosis, and embryonic death by gestational day 10.5; heterozygous adult mice develop squamous cell tumors of keratinized epithelia, demonstrating that SPCA1 is essential for Golgi homeostasis and that haploinsufficiency predisposes to cancer.\",\n      \"method\": \"Targeted gene knockout in mice, electron microscopy of Golgi ultrastructure, apoptosis assays, tumor incidence in aged heterozygotes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function in vivo with multiple orthogonal ultrastructural and cellular readouts\",\n      \"pmids\": [\"17597066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SPCA1 knockdown in N2a neuroblastoma cells and primary hippocampal neurons impairs Golgi Ca2+ homeostasis, disrupts trafficking of Golgi-resident and plasma membrane-targeted proteins, delays neuronal differentiation (fewer and shorter neurites), and causes cell death upon complete suppression, establishing SPCA1 as required for neural polarity and differentiation.\",\n      \"method\": \"siRNA knockdown in N2a and primary neurons, Ca2+ imaging, immunocytochemical trafficking assays, morphological differentiation analysis\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockdown in two independent cell systems with multiple functional readouts including Ca2+ imaging and protein trafficking\",\n      \"pmids\": [\"19793975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SPCA1 localizes predominantly to the lateral rims of Golgi cisternae, tubular non-compact zones connecting Golgi stacks, and tubular trans-Golgi network regions; SPCA1 knockdown causes Golgi fragmentation (loss of cis-most and trans-most cisternae), inhibits exit of VSV-G protein from the Golgi, and delays retrograde redistribution of Golgi glycosylation enzymes to the ER induced by brefeldin A, demonstrating SPCA1 is required for intra-Golgi transport and Golgi ribbon maintenance.\",\n      \"method\": \"Immunofluorescence/electron microscopy localization, siRNA knockdown, VSV-G trafficking assay, brefeldin A retrograde transport assay\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — precise localization combined with functional knockdown using multiple transport readouts in a single study\",\n      \"pmids\": [\"20604898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SPCA1 inhibition in MDA-MB-231 basal-like breast cancer cells alters processing of IGF1R by proprotein convertases in the secretory pathway (accumulation of inactive pro-IGF1R in the TGN, reduced functional IGF1Rβ), without altering global cytosolic Ca2+ signaling or ER stress, demonstrating SPCA1 controls Ca2+-dependent enzyme activity in the Golgi lumen to regulate proprotein processing.\",\n      \"method\": \"SPCA1 inhibition, Western blot for IGF1R processing, 3D proliferation/morphology assays, ER stress assays, Ca2+ imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal readouts (protein processing, morphology, Ca2+) but pharmacological inhibition rather than clean genetic loss-of-function, single lab\",\n      \"pmids\": [\"20837466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ATP2C1/SPCA1 knockdown in keratinocytes up-regulates tight junction proteins claudins 1 and 4 even at low extracellular Ca2+, and causes delayed translocation of desmoplakin and desmoglein 3 with increased intracellular accumulation, indicating SPCA1 specifically regulates claudin expression and desmosomal/tight junction protein trafficking.\",\n      \"method\": \"siRNA knockdown, qPCR, Western blot, indirect immunofluorescence in low and high Ca2+ conditions\",\n      \"journal\": \"Experimental dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean siRNA knockdown with multiple junction protein readouts, single lab\",\n      \"pmids\": [\"22639968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Bis-phenol selectively inhibits human SPCA1d Ca2+-ATPase activity (IC50 ~0.13 µM) with 62-fold greater potency than hSERCA2b (IC50 ~8.1 µM), and can mobilize Ca2+ from thapsigargin-insensitive stores in intact cells, establishing bis-phenol as a selective SPCA1 inhibitor.\",\n      \"method\": \"Overexpression of SPCA1d and SERCA2b in COS-7 cells, Ca2+-dependent ATPase activity assays, Ca2+ mobilization assays in intact cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct enzymatic assay with dose-response and selectivity comparison plus intact-cell functional validation, single lab\",\n      \"pmids\": [\"22796571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PMR-1 (C. elegans ortholog of SPCA1/ATP2C1) is required for embryonic cell migration; pmr-1 mutant embryos show reduced migration rates of ventral neuroblasts and other blastomeres, and genetic interaction experiments show that changing activity of IP3R (itr-1) or RyR (unc-68) modulates lethality, placing pmr-1 in a Ca2+ channel network regulating cell migration.\",\n      \"method\": \"Forward genetic screen, time-lapse imaging of cell migration, genetic epistasis with itr-1 and unc-68\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with live imaging plus epistasis experiments, ortholog in established model organism\",\n      \"pmids\": [\"23696750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cofilin-1 (CFL-1) recruits F-actin to the phosphorylation domain (P-domain) of SPCA1 at the TGN; a 132-amino-acid portion of the SPCA1 P-domain interacts with actin in a CFL-1-dependent manner. Mutagenesis of four residues constituting the CFL-1 binding site in SPCA1 impairs Ca2+ import into the TGN and secretory cargo sorting.\",\n      \"method\": \"In vitro binding assay with purified proteins, Ni-NTA pulldown with P-domain fragment, mutagenesis, TGN Ca2+ imaging, cargo sorting assay in HeLa cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified proteins plus mutagenesis plus cellular functional assays, multiple orthogonal methods\",\n      \"pmids\": [\"25179631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ATP2C1 inactivation in keratinocytes increases oxidative stress and activates Notch1; RNA-seq of HHD patient lesional keratinocytes shows consistent down-regulation of the DNA damage response (DDR); Notch1 activation downstream of oxidative stress induced by ATP2C1 loss drives keratinocyte differentiation and represses DDR gene expression, identifying an ATP2C1/NOTCH1 axis in epidermal homeostasis.\",\n      \"method\": \"siRNA knockdown, RNA-seq, oxidative stress assays, Notch1 activation assays in cultured keratinocytes and HHD patient lesions\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transcriptome-level evidence combined with functional knockdown and pathway analysis, single lab\",\n      \"pmids\": [\"27528123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Genome-wide haploid knockout screen identifies SPCA1 as required for maturation and spread of viruses from Paramyxoviridae, Flaviviridae, and Togaviridae families; SPCA1 Ca2+ transport activity is required because it activates proprotein convertases in the TGN that cleave viral glycoproteins; SPCA1-deficient cells accumulate uncleaved, non-functional viral glycoproteins and fail to support viral spread.\",\n      \"method\": \"Genome-wide CRISPR/haploid cell knockout screen, glycoprotein processing assays, protease activity assays, viral spread assays in SPCA1-KO cells\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide unbiased screen validated by clean KO with multiple orthogonal mechanistic readouts (protease activity, glycoprotein processing, viral spread) across diverse viral families\",\n      \"pmids\": [\"29024641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In zebrafish, ATP2C1 expression provides compensatory Mn2+ transport protection in embryos lacking the Mn efflux transporter Slc30a10; wild-type or mutant SLC30A10 expression can inhibit the protective effect of ATP2C1 in response to Mn challenge in both zebrafish and HeLa cells, indicating ATP2C1 functions as a Mn2+ transport buffer that can substitute for SLC30A10.\",\n      \"method\": \"CRISPR/Cas9 zebrafish knockout, rescue experiments with ATP2C1 expression constructs, HeLa cell Mn challenge assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue/epistasis in two systems (zebrafish and HeLa), single lab\",\n      \"pmids\": [\"28692648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SPCA1 activity couples secretory protein sorting to sphingomyelin synthesis in the TGN: sphingomyelin in the TGN membrane promotes SPCA1-mediated Ca2+ flux into the TGN lumen, which drives Ca2+-dependent oligomerization of the secreted Ca2+-binding protein Cab45, enabling Cab45 to package client secreted proteins into sphingomyelin-enriched vesicular carriers for export to the cell surface.\",\n      \"method\": \"SPCA1 activity assays, sphingomyelin manipulation, Cab45 oligomerization assays, Ca2+ flux measurements, vesicle trafficking assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mechanistic reconstitution of lipid-Ca2+-protein coupling with multiple orthogonal experimental approaches in a single rigorous study\",\n      \"pmids\": [\"30393074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of Spca1 in mice impairs neuroepithelial cell apical constriction during neural tube closure, not primarily through apoptosis; SPCA1 promotes apical constriction by regulating myosin II localization and actin dynamics through cofilin-1, with cofilin-1 acting as a downstream effector of SPCA1 function.\",\n      \"method\": \"Novel Spca1 allele characterization in mice, apical constriction imaging, myosin II localization by immunofluorescence, actin dynamics assays, cofilin-1 localization analysis\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic evidence with multiple cellular mechanism readouts (apical constriction, myosin II, cofilin localization) in a single study\",\n      \"pmids\": [\"30228103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SPCA1 overexpression induces STIM1-independent, Orai1-dependent cytosolic Ca2+ influx (store-independent Ca2+ entry, SICE) and co-localizes with Orai1 near the plasma membrane as shown by TIRF microscopy; this functional coupling elevates Ca2+ in non-ER stores and induces Golgi swelling with nuclear translocation of TFE3 (Golgi stress marker); HHD-associated SPCA1 mutations differentially impair Ca2+ transport, Orai1 activation, or both.\",\n      \"method\": \"SPCA1/SPCA2 overexpression, Orai1 knockdown, TIRF microscopy co-localization, cytosolic Ca2+ measurements, Golgi swelling assay, TFE3 nuclear translocation assay, HHD mutant functional analysis\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple localization and functional readouts, single lab, overexpression system\",\n      \"pmids\": [\"29555205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPCA1a has an N-terminal EF-hand-like motif that binds Ca2+ and regulates pump activity: Ca2+ binding to this motif promotes autophosphorylation and SPCA1a activity, modulates substrate ion affinity, and accounts for a biphasic activation curve and lower apparent Ca2+ affinity relative to SPCA2. SPCA1a has lower Ca2+ affinity and a ~2-fold higher Ca2+ turnover rate compared with Mn2+; mutation of the EF-hand-like motif lowers Ca2+ turnover rate and increases substrate affinity.\",\n      \"method\": \"Yeast recombinant expression and purification of SPCA1a and SPCA2, biochemical reconstitution, Ca2+/Mn2+ transport assays, autophosphorylation assays, EF-hand mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified proteins, mutagenesis, and multiple enzymatic assays in a single rigorous biochemical study\",\n      \"pmids\": [\"30923126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TMEM165 stability depends on SPCA1's Mn2+ pumping activity: TMEM165 is constitutively degraded in lysosomes in the absence of SPCA1; among SPCA1 mutants, only Q747A (which favors Mn2+ over Ca2+ transport) rescues TMEM165 abundance and Golgi localization; SERCA2b overexpression also rescues TMEM165, indicating Mn2+ homeostasis in the Golgi lumen governs TMEM165 stability.\",\n      \"method\": \"SPCA1-deficient Hap1 cells, SPCA1 complementation with transport-selective mutants, lysosomal inhibitors, Western blot, immunofluorescence\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic loss-of-function with selective mutant complementation establishing Mn2+ transport as the mechanistic requirement, multiple methods\",\n      \"pmids\": [\"31652305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In yeast complementation assays, fourteen HHD-associated ATP2C1 missense mutations preferentially impair Mn2+ transport over Ca2+ transport (12/14 fail to complement Mn2+ sensitivity; 13/14 partially complement high-Ca2+ requirement); nine mutations show cold-sensitive complementation; twelve mutations induce the unfolded protein response (UPR) in the absence of wild-type ATP2C1, and four cause hSPCA1 mis-localization to the vacuolar membrane; co-expression of wild-type ATP2C1 or ATP2A2 prevents UPR induction and mis-localization.\",\n      \"method\": \"Yeast complementation system, Mn2+/Ca2+ sensitivity growth assays, UPR reporter assays, fluorescence localization of hSPCA1 variants\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro yeast reconstitution system with multiple functional readouts but heterologous expression system\",\n      \"pmids\": [\"31455819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"UVA irradiation increases SPCA1 expression in human dermal fibroblasts via MAPK/c-jun pathway; c-jun binds the SPCA1 promoter and transcriptionally up-regulates SPCA1; SPCA1 knockdown aggravates UVA-induced senescence by elevating intracellular Ca2+, increasing ROS, and increasing MAPK activity, while SPCA1 overexpression reduces Ca2+ overload, lowers ROS, and suppresses MAPK, establishing a negative feedback loop.\",\n      \"method\": \"Dual-luciferase reporter assay, chromatin immunoprecipitation (ChIP), siRNA knockdown, SPCA1 overexpression, ROS/Ca2+/senescence assays\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus reporter assay for transcriptional mechanism, combined with gain/loss-of-function functional assays, single lab\",\n      \"pmids\": [\"34239867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SPCA1 knockdown in brain microvascular endothelial cells increases cytoplasmic Ca2+, which in turn increases plasma membrane localization of ZIP8 and ZIP14 metal transporters (via surface biotinylation and immunofluorescence), resulting in enhanced Mn2+ uptake; conversely, SPCA1 overexpression or gain-of-function mutant decreases cytoplasmic Ca2+ and reduces Mn2+ accumulation, demonstrating that SPCA1 regulates ZIP-mediated Mn2+ uptake through cytoplasmic Ca2+ control of transporter membrane trafficking.\",\n      \"method\": \"siRNA knockdown, SPCA1 overexpression with gain-of-function mutant, surface protein biotinylation, indirect immunofluorescence, GFP-tagged transporter localization, 54Mn2+ uptake assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain and loss-of-function with multiple orthogonal methods (biotinylation, imaging, isotope uptake), mechanistic pathway established\",\n      \"pmids\": [\"35787370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Six cryo-EM structures of human SPCA1 in a near-complete conformational cycle reveal unique conformational changes during ATP binding and phosphorylation compared to other P-type II ATPases; transmembrane helix 4L and 6 separation causes conformational distortion of the Ca2+-binding site constituting a distinct Ca2+ release mechanism; the CaE2P intermediate state is resolved, providing the structural basis for Ca2+ entry and release in hSPCA1.\",\n      \"method\": \"Cryo-electron microscopy structure determination (6 conformational states), molecular dynamics simulations\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple high-resolution cryo-EM structures spanning the catalytic cycle, supported by MD simulations, in a single rigorous structural study\",\n      \"pmids\": [\"37258749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Transcription factors Sp1 and YY1 directly bind the region +21/+57 of the ATP2C1 promoter and transactivate it; Ca2+ stimulation increases nuclear Sp1 and ATP2C1 mRNA in normal keratinocytes, but both increases are suppressed in HHD patient keratinocytes, indicating impaired transcriptional upregulation contributes to keratinocyte-specific pathogenesis.\",\n      \"method\": \"Transient reporter assay, EMSA, Sp1/YY1 overexpression, Ca2+ stimulation experiments in normal vs. HHD keratinocytes\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EMSA plus reporter assay with functional overexpression validation, single lab\",\n      \"pmids\": [\"15955096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TMEM165 expression is more sensitive to MnCl2-induced degradation in HHD patient fibroblasts and keratinocytes (with partial SPCA1 deficiency) than in controls; ICP-MS and GPP130 Golgi Mn2+ sensor demonstrate cytosolic Mn2+ accumulation in MnCl2-supplemented HHD fibroblasts, linking SPCA1 Mn2+ pumping function to TMEM165 stability in a pathological context.\",\n      \"method\": \"HHD patient fibroblasts and keratinocytes, Western blot, ICP-MS, GPP130 as Golgi Mn2+ sensor, MnCl2 supplementation\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived cells with multiple quantitative readouts, single lab\",\n      \"pmids\": [\"32335229\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP2C1 encodes SPCA1, a P-type Ca2+/Mn2+ ATPase localized to the Golgi apparatus (and TGN lateral rims) that pumps cytosolic Ca2+ and Mn2+ into the Golgi lumen; its activity controls intra-Golgi Ca2+ and Mn2+ homeostasis, drives secretory protein sorting via Ca2+-dependent Cab45 oligomerization coupled to sphingomyelin synthesis, regulates proprotein convertase activity for glycoprotein and receptor processing, maintains Golgi ribbon integrity for intra-Golgi transport, governs TMEM165 stability through Mn2+ transport, and supports cytoskeletal dynamics (via cofilin-1 and myosin II) required for neural tube closure and cell migration; haploinsufficiency causes Hailey-Hailey disease through impaired Ca2+/Mn2+ homeostasis in keratinocytes, and cryo-EM structures reveal a unique conformational cycle including a distinct Ca2+ release mechanism involving separation of transmembrane helices 4L and 6.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATP2C1 encodes SPCA1, a thapsigargin-insensitive P-type ATPase that pumps cytosolic Ca2+ and Mn2+ into the Golgi lumen to govern intra-Golgi and cytosolic ion homeostasis and secretory pathway function [#4, #1]. In keratinocytes SPCA1 is the dominant Golgi Ca2+ pump, and heterozygous loss-of-function mutations cause Hailey-Hailey disease through impaired Golgi Ca2+ refill and reduced maximal luminal Ca2+ [#0, #1]; many disease alleles preferentially cripple Mn2+ over Ca2+ transport and can trigger UPR and mis-localization in complementation assays [#25]. Luminal Ca2+ delivered by SPCA1 is functionally coupled to secretory sorting: sphingomyelin in the TGN membrane promotes SPCA1 Ca2+ flux that drives Ca2+-dependent oligomerization of Cab45 to package secretory cargo, and cofilin-1 recruits F-actin to the SPCA1 phosphorylation domain to support TGN Ca2+ import and cargo sorting [#20, #16]. SPCA1-supplied luminal Ca2+ also activates TGN proprotein convertases required to process glycoproteins and receptors such as IGF1R and viral envelope proteins, the latter making SPCA1 essential for maturation and spread of multiple enveloped virus families [#12, #18]. Through its Mn2+ pumping activity SPCA1 maintains Golgi Mn2+ homeostasis, stabilizing the Mn2+-handling protein TMEM165 against lysosomal degradation, and by controlling cytosolic Ca2+ it modulates surface trafficking of ZIP8/ZIP14 Mn2+ importers [#24, #27]. SPCA1 is required for Golgi ribbon integrity and intra-Golgi transport, and at the organism level its loss is embryonic-lethal with Golgi stress, while it drives neuronal differentiation and neuroepithelial apical constriction via myosin II and cofilin-1-dependent actin dynamics [#11, #9, #10, #21]. Cryo-EM structures spanning the catalytic cycle define a distinct Ca2+ release mechanism involving separation of transmembrane helices 4L and 6, and an N-terminal EF-hand-like motif binds Ca2+ to regulate autophosphorylation and ion turnover [#28, #23].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the disease gene: positional cloning linked ATP2C1 mutations to Hailey-Hailey disease and tied the phenotype to disrupted keratinocyte calcium handling, defining SPCA1 as a Golgi Ca2+ pump with physiological importance in epidermis.\",\n      \"evidence\": \"Positional cloning in HHD kindreds with keratinocyte Ca2+ measurements and in vivo epidermal calcium gradient analysis\",\n      \"pmids\": [\"10615129\", \"10767338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular transport mechanism and ion selectivity not resolved\", \"Why haploinsufficiency manifests specifically in keratinocytes unexplained\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Localizing the function: direct organelle Ca2+ measurements established SPCA1 as a Golgi-resident pump maintaining luminal Ca2+ stores and shaping cytosolic Ca2+ signals, with reduced refill in HHD cells.\",\n      \"evidence\": \"Immunofluorescence and Golgi-targeted aequorin in keratinocytes and HeLa cells with RNAi knockdown\",\n      \"pmids\": [\"14632183\", \"12804581\", \"12810057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of SPCA1 vs SERCA is cell-type dependent and not generalized\", \"Mn2+ transport not yet assayed in these systems\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defining substrate scope and downstream consequences: SPCA1 transports both Ca2+ and Mn2+, contributes to beta-cell Ca2+ homeostasis/insulin secretion, supports glycoprotein processing and ERAD, and maintains basal keratinocyte state via Mn2+ sequestration.\",\n      \"evidence\": \"Transport assays, siRNA in beta cells and keratinocytes, pulse-chase glycoprotein processing, ionophore pharmacology\",\n      \"pmids\": [\"15336968\", \"14747290\", \"15623514\", \"16621454\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic coupling between luminal ion levels and glycoprotein processing not yet defined\", \"Distinction between Ca2+- and Mn2+-dependent effects incompletely separated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Transcriptional control: Sp1 and YY1 directly transactivate the ATP2C1 promoter and Ca2+ induces Sp1/ATP2C1 upregulation in normal but not HHD keratinocytes, adding a regulatory layer to disease pathogenesis.\",\n      \"evidence\": \"Reporter assays, EMSA, and Ca2+ stimulation in normal vs HHD keratinocytes\",\n      \"pmids\": [\"15955096\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; in vivo relevance of the transcriptional defect unconfirmed\", \"Whether impaired upregulation is cause or consequence of HHD Ca2+ defect unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"In vivo essentiality: complete Atp2c1 knockout causes Golgi stress and embryonic lethality while heterozygotes develop epithelial tumors, establishing SPCA1 as essential for Golgi homeostasis and a haploinsufficient tumor predisposition gene.\",\n      \"evidence\": \"Mouse targeted knockout with Golgi ultrastructure, apoptosis, and tumor incidence analysis\",\n      \"pmids\": [\"17597066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger of Golgi stress not defined\", \"Mechanism connecting haploinsufficiency to tumorigenesis unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defining the Golgi transport role: SPCA1 localizes to lateral rims and TGN tubules and is required for intra-Golgi transport, Golgi ribbon maintenance, and Ca2+-dependent proprotein convertase processing of receptors such as IGF1R.\",\n      \"evidence\": \"EM/IF localization, siRNA with VSV-G and brefeldin A transport assays, IGF1R processing in breast cancer cells\",\n      \"pmids\": [\"20604898\", \"20837466\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IGF1R study used pharmacological inhibition rather than genetic loss\", \"How luminal Ca2+ directly activates convertases not mechanistically reconstituted\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linking the pump to the cytoskeleton: cofilin-1 recruits F-actin to the SPCA1 phosphorylation domain at the TGN, and disrupting this interface impairs TGN Ca2+ import and cargo sorting, connecting actin dynamics to pump function.\",\n      \"evidence\": \"In vitro binding with purified proteins, pulldown, mutagenesis, and TGN Ca2+/cargo sorting assays in HeLa\",\n      \"pmids\": [\"25179631\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How actin/cofilin binding mechanistically enhances Ca2+ import unclear\", \"Regulation of the interaction in vivo not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Mechanism in viral pathogenesis: an unbiased genetic screen showed SPCA1 Ca2+ transport activates TGN proprotein convertases that cleave viral glycoproteins, making it required for maturation and spread of multiple enveloped virus families.\",\n      \"evidence\": \"Genome-wide haploid/CRISPR knockout screen with glycoprotein processing, protease activity, and viral spread assays\",\n      \"pmids\": [\"29024641\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SPCA1 is broadly required across all enveloped viruses unknown\", \"Direct biochemical link between luminal Ca2+ and convertase catalysis not isolated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Coupling ion transport to secretion and morphogenesis: sphingomyelin-promoted SPCA1 Ca2+ flux drives Cab45 oligomerization for cargo sorting, and SPCA1 loss disrupts neural tube apical constriction via myosin II and cofilin-1, integrating pump activity with lipid signaling and tissue morphogenesis.\",\n      \"evidence\": \"SM manipulation with Cab45 oligomerization/vesicle assays; mouse Spca1 allele with apical constriction and cytoskeletal imaging; Orai1-coupled Ca2+ entry overexpression studies\",\n      \"pmids\": [\"30393074\", \"30228103\", \"29555205\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Orai1 coupling shown only in overexpression and unconfirmed at endogenous levels\", \"How cytoskeletal effects relate to luminal vs cytosolic Ca2+ not fully separated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Resolving Mn2+-specific functions and intrinsic regulation: SPCA1 Mn2+ pumping stabilizes TMEM165 against lysosomal degradation, an N-terminal EF-hand-like motif tunes autophosphorylation and ion turnover, and HHD alleles preferentially impair Mn2+ transport, refining the disease mechanism toward Mn2+ handling.\",\n      \"evidence\": \"Selective-mutant complementation in SPCA1-deficient cells, yeast reconstitution with purified pump and EF-hand mutagenesis, yeast complementation of HHD missense alleles\",\n      \"pmids\": [\"31652305\", \"30923126\", \"31455819\", \"28692648\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Yeast/heterologous systems may not fully model human pump behavior\", \"Relative pathogenic weight of Ca2+ vs Mn2+ defects in HHD epidermis unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extending Mn2+ homeostasis control to the cell surface: SPCA1-set cytosolic Ca2+ regulates plasma membrane trafficking of ZIP8/ZIP14 Mn2+ importers, positioning SPCA1 within a broader Mn2+ buffering network alongside its TMEM165-stabilizing role in patient cells.\",\n      \"evidence\": \"Gain/loss-of-function with surface biotinylation, imaging, and 54Mn2+ uptake in endothelial cells; patient fibroblast ICP-MS/GPP130 Mn2+ sensing\",\n      \"pmids\": [\"35787370\", \"32335229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo systemic Mn2+ handling role not established\", \"Single-lab mechanism for ZIP trafficking control\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structural basis of transport: cryo-EM structures across the catalytic cycle reveal a distinct Ca2+ release mechanism via separation of transmembrane helices 4L and 6, explaining how SPCA1 differs from other P-type II ATPases.\",\n      \"evidence\": \"Six cryo-EM conformational states with molecular dynamics simulations\",\n      \"pmids\": [\"37258749\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for Mn2+ versus Ca2+ selectivity not resolved\", \"Structures of disease mutants not determined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SPCA1 achieves and switches between Ca2+ and Mn2+ selectivity, and how this dictates tissue-specific disease manifestation, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural/biochemical determinants of Ca2+ vs Mn2+ selectivity unknown\", \"Why haploinsufficiency causes epidermis-restricted disease despite ubiquitous expression unexplained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [4, 23, 14]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 4, 24]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [14, 23]},\n      {\"term_id\": \"GO:0046872\", \"supporting_discovery_ids\": [23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1, 11]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [11, 20]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [6, 12, 18]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [4, 24, 27]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CFL1\", \"ORAI1\", \"TMEM165\", \"CAB45/SDF4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}