{"gene":"SPHKAP","run_date":"2026-06-10T07:46:40","timeline":{"discoveries":[{"year":2010,"finding":"SPHKAP (SKIP) functions as the first mammalian AKAP that preferentially and specifically binds PKA-RIα (type I regulatory subunit of PKA), utilizing a characteristic AKAP amphipathic helix for interaction. Recombinant human SPHKAP localizes to the cytoplasm, consistent with the cytosolic distribution of PKA-RIα.","method":"Biochemical characterization of recombinant human SPHKAP; chemical proteomics with differential cAMP resins in mammalian heart and spleen tissue; amphipathic helix alignment with RI/RII-specific anchoring domain models; immunolocalization","journal":"Chembiochem : a European journal of chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (chemical proteomics, recombinant protein binding assays, immunolocalization) in a single focused study establishing PKA-RI specificity","pmids":["20394097"],"is_preprint":false},{"year":2011,"finding":"In failing human hearts, the interaction between PKA regulatory subunits and SPHKAP is 6-fold upregulated compared to control hearts, demonstrating reorganization of PKA-AKAP signaling scaffolds during heart failure.","method":"Chemical proteomics directly applied to human patient and control heart tissue","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chemical proteomics in human tissue with patient/control comparison, single lab","pmids":["21712045"],"is_preprint":false},{"year":2017,"finding":"SPHKAP (SKIP) is expressed in pancreatic β-cells (but not α-cells) and negatively regulates glucose-stimulated insulin secretion (GSIS) via a pathway distinct from cAMP, PDE, and sphingosine kinase-dependent pathways; SKIP-knockout mice show decreased plasma glucose and increased insulin upon glucose challenge.","method":"SKIP-/- mouse model; intraperitoneal glucose tolerance test; measurement of ATP, cAMP, and insulin secretion in isolated islets; pharmacological inhibition of PDE","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with defined cellular phenotype, multiple pathway exclusion experiments, single lab","pmids":["28396589"],"is_preprint":false},{"year":2019,"finding":"SPHKAP is expressed in intestinal K- and L-cells in addition to pancreatic β-cells; SKIP-/- mice show significantly increased GIP and GLP-1 (incretin) secretion as well as enhanced insulin secretion, and genetic depletion of GIP abolishes adiposity and anti-inflammatory phenotypes in SKIP-/- mice, placing SPHKAP upstream of incretin signaling.","method":"SKIP-/- mouse model; GIP genetic depletion cross; GLP-1 receptor antagonist (exendin-(9-39)) treatment; plasma hormone and lipid measurements","journal":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with epistasis via genetic rescue, multiple hormone measurements, single lab","pmids":["30789757"],"is_preprint":false},{"year":2020,"finding":"SPHKAP re-expression in leukemia cell lines increases sphingosine kinase (SK) activity and ceramide levels (2-fold), inactivates ERK signaling, and increases apoptosis following serum deprivation or chemotherapy — contrasting with prior reports that SKIP inhibits SK in fibroblasts.","method":"SPHKAP transfection in leukemia cell lines; targeted UPLC-MS/MS measurement of sphingolipids (S1P and ceramides) in primary AML cells and cell lines; SK activity assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reconstitution by transfection with biochemical readouts (lipidomics, kinase activity), single lab, contradicts earlier fibroblast data","pmids":["32161116"],"is_preprint":false},{"year":2023,"finding":"In brain neurons, SPHKAP directs type I PKA (via PKA-RI binding) to Kv2.1 channel-dependent ER-PM junctional domains by also associating with ER-resident VAP proteins, concentrating type I PKA between stacked ER cisternae at ER-PM junctions. This ER-associated PKA signalosome enables reciprocal regulation between PKA and Ca2+ signaling machinery supporting Ca2+ influx and excitation-transcription coupling.","method":"Live-cell and super-resolution imaging; co-immunoprecipitation/interaction studies of SPHKAP with PKA-RI and VAP proteins; neuronal fractionation; functional electrophysiology and Ca2+ signaling assays in neurons","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization imaging, protein interaction, functional Ca2+/PKA signaling assays) establishing subcellular localization with functional consequence","pmids":["37633939"],"is_preprint":false},{"year":2025,"finding":"SPHKAP interacts with AKAP11 and ER-resident VAPA/B proteins; this complex co-adapts to mediate PKA-RI complex degradation via selective autophagy in neurons. SPHKAP is thus part of a PKA-RI degradation complex at the ER.","method":"Multi-omics, co-immunoprecipitation/interaction studies in mouse models and human induced neurons; cell biology and electrophysiology","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — protein interaction and cell biology in neuronal models, single lab, finding replicated across preprint and peer-reviewed versions","pmids":["41315293","39803523","40162211"],"is_preprint":false},{"year":2025,"finding":"Following GLP-1 receptor agonist (GLP-1RA) stimulation in β-cells, GLP-1R-positive endosomes associate with VAPB at ER-mitochondria membrane contact sites (ERMCSs), where active GLP-1R engages SPHKAP. The resulting endosomal GLP-1R/VAPB/SPHKAP complex triggers ERMCS-localised cAMP/PKA signaling via formation of a PKA-RIα biomolecular condensate, leading to MICOS complex phosphorylation, mitochondrial remodelling, and β-cell functional adaptation.","method":"Co-immunoprecipitation, proximity ligation, imaging of β-cell lines and primary islets; PKA-RIα condensate detection; MICOS phosphorylation assays following GLP-1RA treatment","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in β-cell and primary islet models, single lab, peer-reviewed","pmids":["41372122"],"is_preprint":false}],"current_model":"SPHKAP (SKIP) is a type I PKA-specific A-kinase anchoring protein (AKAP) that uses an amphipathic helix to bind PKA-RIα, localizing type I PKA to cytosolic and ER-associated compartments — including ER-PM junctions in neurons and ER-mitochondria contact sites in β-cells — where it scaffolds PKA signaling complexes with VAP proteins, GLP-1R, and AKAP11 to regulate Ca2+ influx, excitation-transcription coupling, incretin and insulin secretion, mitochondrial remodeling, and sphingolipid metabolism."},"narrative":{"mechanistic_narrative":"SPHKAP (SKIP) is a type I-specific A-kinase anchoring protein that scaffolds cAMP/PKA signaling at distinct subcellular compartments to couple it with calcium handling, hormone secretion, and mitochondrial biology [PMID:20394097, PMID:37633939]. It is the first mammalian AKAP shown to preferentially bind the type I regulatory subunit PKA-RIα through a characteristic amphipathic helix, and it distributes to the cytoplasm consistent with PKA-RIα [PMID:20394097]. SPHKAP localizes type I PKA to ER-associated membrane contact sites by additionally binding ER-resident VAP proteins: in neurons it concentrates type I PKA at Kv2.1-dependent ER-PM junctions to enable reciprocal PKA-Ca2+ regulation and excitation-transcription coupling [PMID:37633939], and in β-cells the active GLP-1 receptor recruits SPHKAP with VAPB at ER-mitochondria contact sites to nucleate a PKA-RIα condensate that drives MICOS phosphorylation and mitochondrial remodelling [PMID:41372122]. SPHKAP, AKAP11, and VAPA/B also form a complex that mediates selective-autophagy degradation of the PKA-RI complex at the ER [PMID:41315293, PMID:39803523, PMID:40162211]. Beyond scaffolding, SPHKAP regulates endocrine physiology — it is expressed in pancreatic β-cells and intestinal K/L-cells and acts as a negative regulator of glucose-stimulated insulin and incretin secretion, placing it upstream of GIP/GLP-1 signaling [PMID:28396589, PMID:30789757] — and modulates sphingolipid metabolism and apoptotic signaling in a cell-context-dependent manner [PMID:32161116]. Reorganization of the PKA-SPHKAP interaction is observed in failing human hearts [PMID:21712045].","teleology":[{"year":2010,"claim":"Established SPHKAP as the founding mammalian type I-specific AKAP, answering whether an AKAP exists that preferentially anchors PKA-RIα rather than RII.","evidence":"Recombinant protein binding assays, chemical proteomics with cAMP resins in heart/spleen, amphipathic helix modeling, and immunolocalization","pmids":["20394097"],"confidence":"High","gaps":["Subcellular anchoring sites and physiological consequences not yet defined","Structural basis of RI selectivity not resolved at atomic level"]},{"year":2011,"claim":"Showed the PKA-SPHKAP scaffold is dynamically remodeled in disease, linking type I AKAP anchoring to human heart failure.","evidence":"Chemical proteomics on human failing vs control heart tissue","pmids":["21712045"],"confidence":"Medium","gaps":["Whether upregulated anchoring is causal or compensatory unknown","No mechanistic readout of altered PKA signaling in cardiomyocytes"]},{"year":2017,"claim":"Defined a physiological role for SPHKAP in endocrine pancreas, showing it negatively regulates glucose-stimulated insulin secretion through a pathway distinct from cAMP/PDE/sphingosine kinase.","evidence":"SKIP-/- mice, glucose tolerance tests, islet ATP/cAMP/insulin measurements, PDE inhibition","pmids":["28396589"],"confidence":"Medium","gaps":["Molecular mechanism of secretion suppression unidentified","β-cell-specific contribution vs systemic effects not separated"]},{"year":2019,"claim":"Extended SPHKAP's secretory role to enteroendocrine cells, placing it genetically upstream of incretin (GIP/GLP-1) signaling and metabolic phenotypes.","evidence":"SKIP-/- mice with GIP genetic depletion cross and GLP-1R antagonism, plasma hormone/lipid measurement","pmids":["30789757"],"confidence":"Medium","gaps":["Direct molecular target of SPHKAP in K/L-cells unknown","Connection to PKA anchoring not established here"]},{"year":2020,"claim":"Showed SPHKAP modulates sphingolipid metabolism and apoptosis in a cell-type-dependent manner, increasing SK activity/ceramide and inactivating ERK in leukemia cells, contrasting earlier fibroblast data.","evidence":"SPHKAP transfection in leukemia lines, UPLC-MS/MS sphingolipidomics, SK activity assays","pmids":["32161116"],"confidence":"Medium","gaps":["Mechanism reconciling opposing fibroblast vs leukemia effects unresolved","Whether sphingolipid effects depend on PKA anchoring untested"]},{"year":2023,"claim":"Resolved the subcellular mechanism by which SPHKAP anchors type I PKA, showing it tethers PKA-RIα to ER-PM junctions via VAP binding to couple PKA with Ca2+ signaling and excitation-transcription coupling in neurons.","evidence":"Super-resolution/live-cell imaging, Co-IP of SPHKAP with PKA-RI and VAP, neuronal fractionation, electrophysiology and Ca2+ assays","pmids":["37633939"],"confidence":"High","gaps":["Downstream transcriptional targets of the signalosome not enumerated","Generalizability beyond Kv2.1-dependent junctions unclear"]},{"year":2025,"claim":"Identified SPHKAP as part of a degradation machinery, showing an SPHKAP-AKAP11-VAPA/B complex routes the PKA-RI complex for selective autophagy at the ER.","evidence":"Multi-omics, Co-IP in mouse models and human induced neurons, cell biology and electrophysiology","pmids":["41315293","39803523","40162211"],"confidence":"Medium","gaps":["Trigger/regulation of degradation not defined","Single-lab finding; reciprocal validation across systems limited"]},{"year":2025,"claim":"Linked SPHKAP scaffolding to GLP-1R signaling and mitochondria, showing endosomal GLP-1R/VAPB/SPHKAP at ER-mitochondria contacts nucleates a PKA-RIα condensate driving MICOS phosphorylation and β-cell mitochondrial remodelling.","evidence":"Co-IP, proximity ligation, imaging in β-cell lines and primary islets, condensate detection, MICOS phosphorylation assays after GLP-1RA","pmids":["41372122"],"confidence":"Medium","gaps":["Biophysical basis of PKA-RIα condensate formation unresolved","Relationship to SPHKAP's negative regulation of secretion not reconciled"]},{"year":null,"claim":"How SPHKAP's distinct roles — secretion suppression, PKA anchoring, PKA-RI degradation, and sphingolipid/apoptosis control — are integrated into a single coherent signaling logic remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking secretory phenotype to PKA anchoring","Tissue-specific determinants of SPHKAP function uncharacterized","Structure of full SPHKAP complexes undetermined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[5,6,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[6]}],"complexes":["SPHKAP-PKA-RIα signalosome","SPHKAP-AKAP11-VAPA/B PKA-RI degradation complex","endosomal GLP-1R/VAPB/SPHKAP complex"],"partners":["PRKAR1A","VAPA","VAPB","AKAP11","GLP1R"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q2M3C7","full_name":"A-kinase anchor protein SPHKAP","aliases":["SPHK1-interactor and AKAP domain-containing protein","Sphingosine kinase type 1-interacting protein"],"length_aa":1700,"mass_kda":186.5,"function":"Anchoring protein that binds preferentially to the type I regulatory subunit of c-AMP-dependent protein kinase (PKA type I) and targets it to distinct subcellular compartments. May act as a converging factor linking cAMP and sphingosine signaling pathways. Plays a regulatory role in the modulation of SPHK1","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q2M3C7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPHKAP","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPHKAP","total_profiled":1310},"omim":[{"mim_id":"611646","title":"SPHK1-INTERACTING PROTEIN; SPHKAP","url":"https://www.omim.org/entry/611646"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":33.6},{"tissue":"heart muscle","ntpm":27.3}],"url":"https://www.proteinatlas.org/search/SPHKAP"},"hgnc":{"alias_symbol":["SKIP"],"prev_symbol":[]},"alphafold":{"accession":"Q2M3C7","domains":[{"cath_id":"-","chopping":"44-195_1606-1700","consensus_level":"high","plddt":74.8091,"start":44,"end":1700}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q2M3C7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q2M3C7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q2M3C7-F1-predicted_aligned_error_v6.png","plddt_mean":47.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPHKAP","jax_strain_url":"https://www.jax.org/strain/search?query=SPHKAP"},"sequence":{"accession":"Q2M3C7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q2M3C7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q2M3C7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q2M3C7"}},"corpus_meta":[{"pmid":"22355676","id":"PMC_22355676","title":"Whole-exome sequencing uncovers 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Recombinant human SPHKAP localizes to the cytoplasm, consistent with the cytosolic distribution of PKA-RIα.\",\n      \"method\": \"Biochemical characterization of recombinant human SPHKAP; chemical proteomics with differential cAMP resins in mammalian heart and spleen tissue; amphipathic helix alignment with RI/RII-specific anchoring domain models; immunolocalization\",\n      \"journal\": \"Chembiochem : a European journal of chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (chemical proteomics, recombinant protein binding assays, immunolocalization) in a single focused study establishing PKA-RI specificity\",\n      \"pmids\": [\"20394097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In failing human hearts, the interaction between PKA regulatory subunits and SPHKAP is 6-fold upregulated compared to control hearts, demonstrating reorganization of PKA-AKAP signaling scaffolds during heart failure.\",\n      \"method\": \"Chemical proteomics directly applied to human patient and control heart tissue\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chemical proteomics in human tissue with patient/control comparison, single lab\",\n      \"pmids\": [\"21712045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SPHKAP (SKIP) is expressed in pancreatic β-cells (but not α-cells) and negatively regulates glucose-stimulated insulin secretion (GSIS) via a pathway distinct from cAMP, PDE, and sphingosine kinase-dependent pathways; SKIP-knockout mice show decreased plasma glucose and increased insulin upon glucose challenge.\",\n      \"method\": \"SKIP-/- mouse model; intraperitoneal glucose tolerance test; measurement of ATP, cAMP, and insulin secretion in isolated islets; pharmacological inhibition of PDE\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with defined cellular phenotype, multiple pathway exclusion experiments, single lab\",\n      \"pmids\": [\"28396589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPHKAP is expressed in intestinal K- and L-cells in addition to pancreatic β-cells; SKIP-/- mice show significantly increased GIP and GLP-1 (incretin) secretion as well as enhanced insulin secretion, and genetic depletion of GIP abolishes adiposity and anti-inflammatory phenotypes in SKIP-/- mice, placing SPHKAP upstream of incretin signaling.\",\n      \"method\": \"SKIP-/- mouse model; GIP genetic depletion cross; GLP-1 receptor antagonist (exendin-(9-39)) treatment; plasma hormone and lipid measurements\",\n      \"journal\": \"FASEB journal : official publication of the Federation of American Societies for Experimental Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with epistasis via genetic rescue, multiple hormone measurements, single lab\",\n      \"pmids\": [\"30789757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SPHKAP re-expression in leukemia cell lines increases sphingosine kinase (SK) activity and ceramide levels (2-fold), inactivates ERK signaling, and increases apoptosis following serum deprivation or chemotherapy — contrasting with prior reports that SKIP inhibits SK in fibroblasts.\",\n      \"method\": \"SPHKAP transfection in leukemia cell lines; targeted UPLC-MS/MS measurement of sphingolipids (S1P and ceramides) in primary AML cells and cell lines; SK activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reconstitution by transfection with biochemical readouts (lipidomics, kinase activity), single lab, contradicts earlier fibroblast data\",\n      \"pmids\": [\"32161116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In brain neurons, SPHKAP directs type I PKA (via PKA-RI binding) to Kv2.1 channel-dependent ER-PM junctional domains by also associating with ER-resident VAP proteins, concentrating type I PKA between stacked ER cisternae at ER-PM junctions. This ER-associated PKA signalosome enables reciprocal regulation between PKA and Ca2+ signaling machinery supporting Ca2+ influx and excitation-transcription coupling.\",\n      \"method\": \"Live-cell and super-resolution imaging; co-immunoprecipitation/interaction studies of SPHKAP with PKA-RI and VAP proteins; neuronal fractionation; functional electrophysiology and Ca2+ signaling assays in neurons\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization imaging, protein interaction, functional Ca2+/PKA signaling assays) establishing subcellular localization with functional consequence\",\n      \"pmids\": [\"37633939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SPHKAP interacts with AKAP11 and ER-resident VAPA/B proteins; this complex co-adapts to mediate PKA-RI complex degradation via selective autophagy in neurons. SPHKAP is thus part of a PKA-RI degradation complex at the ER.\",\n      \"method\": \"Multi-omics, co-immunoprecipitation/interaction studies in mouse models and human induced neurons; cell biology and electrophysiology\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — protein interaction and cell biology in neuronal models, single lab, finding replicated across preprint and peer-reviewed versions\",\n      \"pmids\": [\"41315293\", \"39803523\", \"40162211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Following GLP-1 receptor agonist (GLP-1RA) stimulation in β-cells, GLP-1R-positive endosomes associate with VAPB at ER-mitochondria membrane contact sites (ERMCSs), where active GLP-1R engages SPHKAP. The resulting endosomal GLP-1R/VAPB/SPHKAP complex triggers ERMCS-localised cAMP/PKA signaling via formation of a PKA-RIα biomolecular condensate, leading to MICOS complex phosphorylation, mitochondrial remodelling, and β-cell functional adaptation.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation, imaging of β-cell lines and primary islets; PKA-RIα condensate detection; MICOS phosphorylation assays following GLP-1RA treatment\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in β-cell and primary islet models, single lab, peer-reviewed\",\n      \"pmids\": [\"41372122\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPHKAP (SKIP) is a type I PKA-specific A-kinase anchoring protein (AKAP) that uses an amphipathic helix to bind PKA-RIα, localizing type I PKA to cytosolic and ER-associated compartments — including ER-PM junctions in neurons and ER-mitochondria contact sites in β-cells — where it scaffolds PKA signaling complexes with VAP proteins, GLP-1R, and AKAP11 to regulate Ca2+ influx, excitation-transcription coupling, incretin and insulin secretion, mitochondrial remodeling, and sphingolipid metabolism.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SPHKAP (SKIP) is a type I-specific A-kinase anchoring protein that scaffolds cAMP/PKA signaling at distinct subcellular compartments to couple it with calcium handling, hormone secretion, and mitochondrial biology [#0, #5]. It is the first mammalian AKAP shown to preferentially bind the type I regulatory subunit PKA-RIα through a characteristic amphipathic helix, and it distributes to the cytoplasm consistent with PKA-RIα [#0]. SPHKAP localizes type I PKA to ER-associated membrane contact sites by additionally binding ER-resident VAP proteins: in neurons it concentrates type I PKA at Kv2.1-dependent ER-PM junctions to enable reciprocal PKA-Ca2+ regulation and excitation-transcription coupling [#5], and in β-cells the active GLP-1 receptor recruits SPHKAP with VAPB at ER-mitochondria contact sites to nucleate a PKA-RIα condensate that drives MICOS phosphorylation and mitochondrial remodelling [#7]. SPHKAP, AKAP11, and VAPA/B also form a complex that mediates selective-autophagy degradation of the PKA-RI complex at the ER [#6]. Beyond scaffolding, SPHKAP regulates endocrine physiology — it is expressed in pancreatic β-cells and intestinal K/L-cells and acts as a negative regulator of glucose-stimulated insulin and incretin secretion, placing it upstream of GIP/GLP-1 signaling [#2, #3] — and modulates sphingolipid metabolism and apoptotic signaling in a cell-context-dependent manner [#4]. Reorganization of the PKA-SPHKAP interaction is observed in failing human hearts [#1].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established SPHKAP as the founding mammalian type I-specific AKAP, answering whether an AKAP exists that preferentially anchors PKA-RIα rather than RII.\",\n      \"evidence\": \"Recombinant protein binding assays, chemical proteomics with cAMP resins in heart/spleen, amphipathic helix modeling, and immunolocalization\",\n      \"pmids\": [\"20394097\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subcellular anchoring sites and physiological consequences not yet defined\", \"Structural basis of RI selectivity not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed the PKA-SPHKAP scaffold is dynamically remodeled in disease, linking type I AKAP anchoring to human heart failure.\",\n      \"evidence\": \"Chemical proteomics on human failing vs control heart tissue\",\n      \"pmids\": [\"21712045\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether upregulated anchoring is causal or compensatory unknown\", \"No mechanistic readout of altered PKA signaling in cardiomyocytes\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined a physiological role for SPHKAP in endocrine pancreas, showing it negatively regulates glucose-stimulated insulin secretion through a pathway distinct from cAMP/PDE/sphingosine kinase.\",\n      \"evidence\": \"SKIP-/- mice, glucose tolerance tests, islet ATP/cAMP/insulin measurements, PDE inhibition\",\n      \"pmids\": [\"28396589\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of secretion suppression unidentified\", \"β-cell-specific contribution vs systemic effects not separated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended SPHKAP's secretory role to enteroendocrine cells, placing it genetically upstream of incretin (GIP/GLP-1) signaling and metabolic phenotypes.\",\n      \"evidence\": \"SKIP-/- mice with GIP genetic depletion cross and GLP-1R antagonism, plasma hormone/lipid measurement\",\n      \"pmids\": [\"30789757\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target of SPHKAP in K/L-cells unknown\", \"Connection to PKA anchoring not established here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed SPHKAP modulates sphingolipid metabolism and apoptosis in a cell-type-dependent manner, increasing SK activity/ceramide and inactivating ERK in leukemia cells, contrasting earlier fibroblast data.\",\n      \"evidence\": \"SPHKAP transfection in leukemia lines, UPLC-MS/MS sphingolipidomics, SK activity assays\",\n      \"pmids\": [\"32161116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism reconciling opposing fibroblast vs leukemia effects unresolved\", \"Whether sphingolipid effects depend on PKA anchoring untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the subcellular mechanism by which SPHKAP anchors type I PKA, showing it tethers PKA-RIα to ER-PM junctions via VAP binding to couple PKA with Ca2+ signaling and excitation-transcription coupling in neurons.\",\n      \"evidence\": \"Super-resolution/live-cell imaging, Co-IP of SPHKAP with PKA-RI and VAP, neuronal fractionation, electrophysiology and Ca2+ assays\",\n      \"pmids\": [\"37633939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream transcriptional targets of the signalosome not enumerated\", \"Generalizability beyond Kv2.1-dependent junctions unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified SPHKAP as part of a degradation machinery, showing an SPHKAP-AKAP11-VAPA/B complex routes the PKA-RI complex for selective autophagy at the ER.\",\n      \"evidence\": \"Multi-omics, Co-IP in mouse models and human induced neurons, cell biology and electrophysiology\",\n      \"pmids\": [\"41315293\", \"39803523\", \"40162211\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trigger/regulation of degradation not defined\", \"Single-lab finding; reciprocal validation across systems limited\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked SPHKAP scaffolding to GLP-1R signaling and mitochondria, showing endosomal GLP-1R/VAPB/SPHKAP at ER-mitochondria contacts nucleates a PKA-RIα condensate driving MICOS phosphorylation and β-cell mitochondrial remodelling.\",\n      \"evidence\": \"Co-IP, proximity ligation, imaging in β-cell lines and primary islets, condensate detection, MICOS phosphorylation assays after GLP-1RA\",\n      \"pmids\": [\"41372122\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biophysical basis of PKA-RIα condensate formation unresolved\", \"Relationship to SPHKAP's negative regulation of secretion not reconciled\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SPHKAP's distinct roles — secretion suppression, PKA anchoring, PKA-RI degradation, and sphingolipid/apoptosis control — are integrated into a single coherent signaling logic remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking secretory phenotype to PKA anchoring\", \"Tissue-specific determinants of SPHKAP function uncharacterized\", \"Structure of full SPHKAP complexes undetermined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\n      \"SPHKAP-PKA-RIα signalosome\",\n      \"SPHKAP-AKAP11-VAPA/B PKA-RI degradation complex\",\n      \"endosomal GLP-1R/VAPB/SPHKAP complex\"\n    ],\n    \"partners\": [\n      \"PRKAR1A\",\n      \"VAPA\",\n      \"VAPB\",\n      \"AKAP11\",\n      \"GLP1R\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}