{"gene":"PRKACA","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2014,"finding":"A ~400-kb deletion on chromosome 19 creates a chimeric DNAJB1-PRKACA transcript encoding a fusion protein containing the DNAJB1 J-domain fused in-frame to the PRKACA catalytic domain; immunoprecipitation and Western blot confirmed expression in FL-HCC tumor tissue, and cell culture assay demonstrated the fusion protein retains kinase activity.","method":"RNA sequencing, RT-PCR, immunoprecipitation, Western blot, cell-based kinase assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (IP, WB, kinase assay), replicated across subsequent studies","pmids":["24578576"],"is_preprint":false},{"year":2014,"finding":"Somatic PRKACA p.Leu206Arg (L206R) substitution directly disrupts interaction with the regulatory subunit PRKAR1A, causing constitutive catalytic activity, increased phosphorylation of downstream PKA targets, and autonomous cortisol production driving adrenal adenoma development.","method":"Exome sequencing, in vitro kinase/binding assays, functional characterization of PRKAR1A binding loss","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — binding disruption and kinase activity confirmed in vitro, independently replicated by multiple groups (PMIDs 24700472, 25069672, 25750087)","pmids":["24747643","24700472"],"is_preprint":false},{"year":2014,"finding":"The PRKACA L205R/L206R mutation locates in the P+1 loop of the PKA catalytic subunit, promotes PKA substrate phosphorylation and downstream target gene expression, conferring constitutive kinase activity.","method":"Whole-exome sequencing, RNA sequencing, in vitro phosphorylation assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional phosphorylation assays, independently replicated across multiple cohorts and labs","pmids":["24700472","24747643"],"is_preprint":false},{"year":2017,"finding":"Expression of the endogenous DNAJB1-PRKACA fusion protein (but not overexpression of wild-type PRKACA alone) in mouse liver via CRISPR-Cas9 is sufficient to drive formation of tumors resembling FL-HCC, establishing the fusion as an oncogenic driver beyond simple PRKACA overexpression; tumorigenesis is significantly enhanced by β-catenin activation.","method":"CRISPR/Cas9 genome editing, somatic gene transfer, histology, IHC, RNA sequencing, whole-exome sequencing","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss/gain-of-function in two independent mouse model studies (PMIDs 29162699, 28923495) with rigorous controls","pmids":["29162699","28923495"],"is_preprint":false},{"year":2017,"finding":"CRISPR/Cas9-induced Dnajb1-Prkaca fusion gene in wild-type mice is sufficient to initiate liver tumor formation with FL-HCC features in the absence of other genetic alterations or carcinogens, confirming the fusion as a standalone oncogenic driver.","method":"CRISPR/Cas9 hydrodynamic tail-vein injection, histology, IHC, RNA sequencing, whole-exome sequencing","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis with rigorous controls, replicated concept across two independent mouse model papers","pmids":["28923495"],"is_preprint":false},{"year":2017,"finding":"PRKACA microinsertions (in-frame, 18-33 bp) in exons 7 and 8 cause the mutant PRKACA protein to lose binding to PRKAR1A regulatory subunit, leading to constitutive PKA pathway activation in sporadic cardiac myxoma.","method":"Sanger sequencing, functional binding assays (PRKAR1A interaction loss), PKA pathway activation assays","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding loss demonstrated in vitro, single lab, two orthogonal methods","pmids":["28369983"],"is_preprint":false},{"year":2018,"finding":"NMR and molecular dynamics simulations of the DNAJB1-PRKACA chimeric kinase reveal an ensemble of conformations in which the J-domain can be tucked under the large lobe or swing free in solution, with no obvious steric interaction with RIIβ holoenzyme components.","method":"Molecular dynamics simulations, NMR spectroscopy, structural modeling","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — NMR with MD simulation in single lab, conformational states experimentally captured","pmids":["29335433"],"is_preprint":false},{"year":2018,"finding":"Loss of PRKAR1A (regulatory subunit of PKA) expression due to inactivating PRKAR1A mutations in Carney complex patients leads to PKA activation and fibrolamellar carcinoma formation, providing an alternative mechanism to DNAJB1-PRKACA fusion for PKA deregulation in FL-HCC.","method":"FISH (negative for PRKACA rearrangement), PRKAR1A sequencing, IHC (loss of PRKAR1A protein)","journal":"Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct sequencing and IHC protein loss, multiple cases, single lab","pmids":["29222914"],"is_preprint":false},{"year":2019,"finding":"GPER1 (G protein-coupled estrogen receptor 1) activates PRKACA, which in turn phosphorylates MORC2 at threonine 582, protecting MORC2 from chaperone-mediated autophagy (CMA)-mediated lysosomal degradation and contributing to estrogen-induced cell proliferation and antiestrogen resistance in breast cancer cells.","method":"Knockdown/overexpression, phosphorylation-deficient mutant (T582A), co-immunoprecipitation, functional cell proliferation assays","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal functional validation with phospho-dead mutant and KD, single lab","pmids":["32401166"],"is_preprint":false},{"year":2014,"finding":"PRKACA expression rescues HER2-amplified breast cancer cells from HER2 inhibition not by restoring MAPK or PI3K signaling, but by inactivating the pro-apoptotic protein BAD, permitting survival signaling through BCL-XL.","method":"Kinase ORF screen, pharmacological BCL-XL/BCL-2 blockade, signaling pathway analysis (MAPK, PI3K readouts negative)","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional screen plus pathway dissection, single lab, multiple readouts","pmids":["24909179"],"is_preprint":false},{"year":2020,"finding":"Germline or mosaic missense variants in PRKACA produce PKA holoenzymes that are more sensitive to cAMP activation than wild-type, and expression of PRKACA variants inhibits hedgehog signaling in NIH 3T3 fibroblasts, providing a mechanism for the developmental defects (atrioventricular septal defects, polydactyly, skeletal/ectodermal abnormalities) observed in affected individuals.","method":"Computational structural analysis, cAMP-sensitivity assays, hedgehog signaling reporter assays in NIH 3T3 cells","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based functional assays with multiple variants, single lab, two orthogonal methods","pmids":["33058759"],"is_preprint":false},{"year":2008,"finding":"PRKACA regulates G2/M transition in mouse fertilized eggs by phosphorylating CDC25B at Ser321 (but not Ser229); unphosphorylatable CDC25B-S321A mutant overrides G2 arrest even under elevated cAMP by directly dephosphorylating CDC2A-Tyr15 to activate MPF.","method":"Microinjection of CDC25B mutants, Western blot with phospho-Ser321 antibody, MPF activation assay, cAMP treatment","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-specific mutagenesis with functional rescue, phospho-specific antibody validation, single lab","pmids":["18633139"],"is_preprint":false},{"year":2023,"finding":"Continued DNAJB1-PRKACA expression is required not only for FL-HCC tumor maintenance but its inhibition causes tumor cell death (oncogene addiction); shRNA-mediated knockdown of the fusion in patient-derived xenografts inhibits tumor growth in vivo with no effect on hepatocellular carcinoma cells not expressing the fusion.","method":"shRNA knockdown, patient-derived xenograft (PDX) models in vivo, cell viability assays","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular phenotype in PDX models, single lab","pmids":["36302174"],"is_preprint":false},{"year":2025,"finding":"DNAJB1-PRKACA fusion drives FL-HCC through inactivation of SIK (salt-inducible kinase), which stimulates CRTC2-p300-mediated transcriptional reprogramming to drive tumor growth.","method":"Functional studies in model systems, examination of human tumor specimens, pathway analysis","journal":"Cancer discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional studies in models plus human tumor validation, single lab","pmids":["39326063"],"is_preprint":false},{"year":2025,"finding":"Nsun2 methylates PRKACA mRNA at specific sites, promoting PRKACA translation in a YBX1-dependent manner; cardiac-specific Nsun2 knockout markedly reduces PKA activity, impairs substrate phosphorylation, myocyte contraction/relaxation, and calcium transients, while Nsun2 overexpression sensitizes the heart to hypertrophic stimuli in a PRKACA-dependent manner.","method":"m5C-RIP-seq, RNA pulldown, polysome profiling, cardiac-specific KO (Cre/LoxP), rAAV9 overexpression, IonOptix calcium measurement, reporter gene analysis","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (RIP-seq, polysome profiling, KO with functional phenotype), single lab","pmids":["39990213"],"is_preprint":false},{"year":1996,"finding":"The PRKACA gene encoding the catalytic subunit Cα of cAMP-dependent protein kinase was localized to human chromosome region 19p13.1 by PCR and Southern blot analysis of somatic cell hybrid mapping panels, confirmed by two-color FISH.","method":"PCR, Southern blot, somatic cell hybrid panel, two-color FISH","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal cytogenetic methods, consistent localization","pmids":["8884279"],"is_preprint":false},{"year":2021,"finding":"Integrated cell-based and in vitro phosphoproteomics identified direct substrates of PRKACA and the DNAJB1-PRKACA chimeric kinase, revealing the chimera targets overlapping but distinct substrate sets and altered pathways compared to wild-type PRKACA, with some substrates persisting under PKA inhibitor treatment.","method":"Cell-based phosphoproteomics, in vitro rephosphorylation with recombinant enzymes, PKA inhibitor treatment (rpcAMPs and PKI), mass spectrometry","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — integrated cell-based and in vitro phosphoproteomics, single lab, two orthogonal approaches","pmids":["34436901"],"is_preprint":false},{"year":2025,"finding":"The PRKACA L205R Cushing's syndrome mutation locally disrupts the P+1 hydrophobic pocket (displacing the P+1-residue and altering substrate specificity) and has long-range allosteric effects on the linker connecting the A helix to β strand 1 and on the phosphoryl transfer site, as revealed by MD simulations and protein residue network analysis; some distal changes are not captured in the crystal structure.","method":"Molecular dynamics simulations, protein residue network (LSP) analysis, crystal structure comparison","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — computational MD with structural comparison, single lab, no experimental mutagenesis validation reported in abstract","pmids":["40504162"],"is_preprint":false},{"year":2025,"finding":"A fusion-protein-specific peptide degrader selectively eliminates DNAJB1::PRKACA (and ATP1B1::PRKACA) without affecting native PRKACA; specificity reflects structural properties of the fusion. Combining the degrader with siRNA against the fusion transcript in a single mRNA accelerates degradation and is lethal to FLC tumor cells in preclinical models with no toxicity to non-FLC cells.","method":"mRNA-delivered peptide degrader, siRNA combination, FLC cell/PDX models in vitro and in vivo, selectivity controls","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — preprint, functional in vivo data with selectivity controls, single lab","pmids":[],"is_preprint":true},{"year":2025,"finding":"PRKACA (PKA catalytic α subunit) phosphorylates huntingtin at S421 (pS421-HTT) in human cells, as demonstrated by an ultrasensitive immunoassay showing that PRKACA activity regulates endogenous S421-HTT phosphorylation levels.","method":"Ultrasensitive immunoassay, cell-based PRKACA activity modulation, endogenous pS421-HTT detection","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, single method approach for the specific PRKACA-HTT substrate relationship","pmids":[],"is_preprint":true},{"year":2016,"finding":"Functional analysis of the novel PRKACA p.His88Asp variant found in an aldosterone-producing adenoma showed it was NOT associated with gain of function (negative finding), distinguishing it mechanistically from the p.Leu206Arg gain-of-function mutation.","method":"In vitro enzymatic activity assay of PRKACA variants, immunofluorescence for CYP11B2/CYP11B1","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vitro kinase activity assay with negative result clearly reported, single lab","pmids":["27270477"],"is_preprint":false},{"year":2022,"finding":"DNAJB1-PRKACA-derived HLA class I and class II ligands are naturally processed and presented on tumor cells as confirmed by mass spectrometry-based immunopeptidome analysis, and induce multifunctional cytotoxic CD8+ and T-helper 1 CD4+ T cell responses, establishing the fusion junction as a bona fide neoantigen.","method":"Mass spectrometry immunopeptidome analysis, T cell functional assays, single-cell RNA sequencing of TCRs","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-confirmed antigen presentation plus functional T cell assays, single institution","pmids":["36302754"],"is_preprint":false}],"current_model":"PRKACA encodes the catalytic α subunit (Cα) of cAMP-dependent protein kinase A (PKA), which is held inactive in a regulatory (PRKAR) subunit-bound holoenzyme and released upon cAMP binding; activating mutations (most commonly L205R/L206R) or oncogenic gene fusions (DNAJB1-PRKACA) disrupt the Cα–regulatory subunit interaction to produce constitutive kinase activity that phosphorylates downstream substrates including BAD (anti-apoptotic signaling), CDC25B-Ser321 (cell cycle G2/M control), MORC2-Thr582 (autophagy resistance), and SIK (transcriptional reprogramming via CRTC2-p300), while the DNAJB1-PRKACA fusion is both necessary and sufficient to drive fibrolamellar hepatocellular carcinoma and related oncocytic pancreatobiliary neoplasms through continued oncogene-addicted kinase signaling."},"narrative":{"mechanistic_narrative":"PRKACA encodes the catalytic α subunit (Cα) of cAMP-dependent protein kinase A, a serine/threonine kinase whose activity is normally restrained by binding to PRKAR regulatory subunits; releasing this restraint converts PRKACA into a constitutive driver of endocrine and oncogenic phenotypes [PMID:24747643, PMID:24700472]. Activating point mutations cluster in the P+1 loop of the catalytic subunit—most prominently L205R/L206R—and act by disrupting the interaction with the PRKAR1A regulatory subunit, producing autonomous kinase activity, increased substrate phosphorylation, and downstream target gene expression that drives adrenal adenoma and Cushing's syndrome [PMID:24747643, PMID:24700472, PMID:40504162]; in-frame microinsertions in exons 7–8 similarly abolish PRKAR1A binding in cardiac myxoma [PMID:28369983], and loss of PRKAR1A itself provides an alternative route to PKA deregulation [PMID:29222914]. The DNAJB1-PRKACA fusion, created by a ~400-kb chromosome 19 deletion that joins the DNAJB1 J-domain to the PRKACA catalytic domain, retains kinase activity and is both necessary and sufficient to drive fibrolamellar hepatocellular carcinoma, with continued expression required for tumor maintenance (oncogene addiction) [PMID:24578576, PMID:29162699, PMID:28923495, PMID:36302174]; the fusion phosphorylates an overlapping but distinct substrate set relative to wild-type Cα and reprograms transcription through SIK inactivation and CRTC2-p300 signaling [PMID:39326063, PMID:34436901]. Beyond these oncogenic contexts, PRKACA phosphorylates specific substrates to control discrete cellular programs: BAD to enable BCL-XL survival signaling under HER2 inhibition [PMID:24909179], MORC2-Thr582 to protect it from chaperone-mediated autophagy and confer antiestrogen resistance downstream of GPER1 [PMID:32401166], and CDC25B-Ser321 to regulate the G2/M transition [PMID:18633139]. Germline PRKACA variants that increase cAMP sensitivity and inhibit hedgehog signaling cause a developmental syndrome with septal and skeletal defects [PMID:33058759]. The fusion junction itself is processed and presented as an HLA-restricted neoantigen, establishing an immunotherapeutic axis [PMID:36302754].","teleology":[{"year":1996,"claim":"Establishing the chromosomal position of the PKA catalytic α subunit gene provided the genomic anchor later required to interpret rearrangements and copy-number events at this locus.","evidence":"PCR, Southern blot, somatic cell hybrid mapping and two-color FISH localizing PRKACA to 19p13.1","pmids":["8884279"],"confidence":"High","gaps":["Does not address kinase function or regulation","No link to disease at this stage"]},{"year":2008,"claim":"Identifying CDC25B-Ser321 as a PRKACA phosphorylation site explained how cAMP/PKA imposes G2 arrest, linking the kinase to direct cell-cycle control.","evidence":"Microinjection of CDC25B mutants, phospho-Ser321 Western blot, and MPF activation assay in mouse fertilized eggs","pmids":["18633139"],"confidence":"Medium","gaps":["Demonstrated in oocyte/embryo system, generality to somatic cells untested","Single lab"]},{"year":2014,"claim":"Discovery of the DNAJB1-PRKACA chimeric transcript answered what genetic lesion defines fibrolamellar HCC and showed the fusion retains kinase activity.","evidence":"RNA-seq, RT-PCR, immunoprecipitation, Western blot and cell-based kinase assay on FL-HCC tumor tissue","pmids":["24578576"],"confidence":"High","gaps":["Did not prove the fusion is sufficient to cause tumors","Downstream substrate program undefined"]},{"year":2014,"claim":"The L205R/L206R substitution was shown to disrupt PRKAR1A binding and produce constitutive activity, defining the molecular basis of cortisol-producing adrenal adenomas.","evidence":"Exome/RNA sequencing plus in vitro kinase and PRKAR1A-binding assays","pmids":["24747643","24700472"],"confidence":"High","gaps":["Full downstream substrate set not mapped at this stage","Structural mechanism of disruption inferred from mutation location"]},{"year":2014,"claim":"A kinase ORF screen revealed PRKACA promotes survival under HER2 inhibition through BAD inactivation rather than MAPK/PI3K restoration, defining a distinct PKA survival axis.","evidence":"Kinase ORF screen, pharmacological BCL-XL/BCL-2 blockade, MAPK/PI3K readouts in HER2-amplified breast cancer cells","pmids":["24909179"],"confidence":"Medium","gaps":["Direct phosphorylation of BAD by PRKACA not biochemically isolated here","Single lab"]},{"year":2017,"claim":"In vivo modeling answered whether the fusion is causal: endogenous DNAJB1-PRKACA, but not wild-type PRKACA overexpression, was sufficient to drive FL-HCC-like tumors in mice.","evidence":"CRISPR/Cas9 genome editing and hydrodynamic somatic gene transfer in mouse liver with histology, IHC, RNA-seq, WES","pmids":["29162699","28923495"],"confidence":"High","gaps":["Mechanistic distinction between fusion and wild-type signaling not yet resolved","β-catenin cooperation noted but not fully dissected"]},{"year":2017,"claim":"PRKACA microinsertions in cardiac myxoma were shown to abolish PRKAR1A binding, extending the loss-of-regulation mechanism beyond point mutations to another tumor type.","evidence":"Sanger sequencing with functional PRKAR1A-interaction and PKA pathway activation assays","pmids":["28369983"],"confidence":"Medium","gaps":["Single lab","Downstream substrate consequences not characterized"]},{"year":2018,"claim":"Structural studies addressed how the J-domain affects the chimeric kinase, finding it adopts an ensemble of conformations without obvious steric clash with holoenzyme components.","evidence":"NMR spectroscopy and molecular dynamics simulations of the DNAJB1-PRKACA chimera","pmids":["29335433"],"confidence":"Medium","gaps":["Functional consequence of J-domain conformations on substrate selection unresolved","Single lab, computational/biophysical only"]},{"year":2018,"claim":"PRKAR1A loss in Carney complex patients was shown to cause FL-HCC, establishing an alternative route to PKA deregulation independent of the fusion.","evidence":"FISH (negative for PRKACA rearrangement), PRKAR1A sequencing and IHC showing protein loss","pmids":["29222914"],"confidence":"Medium","gaps":["Single lab","Does not establish identical downstream program as the fusion"]},{"year":2019,"claim":"Identifying MORC2-Thr582 as a PRKACA substrate downstream of GPER1 linked the kinase to autophagy escape and antiestrogen resistance in breast cancer.","evidence":"Knockdown/overexpression, T582A phospho-dead mutant, co-IP and proliferation assays","pmids":["32401166"],"confidence":"Medium","gaps":["Single lab","Direct kinase-substrate biochemistry vs cellular correlation"]},{"year":2020,"claim":"Germline PRKACA variants were shown to raise cAMP sensitivity and inhibit hedgehog signaling, providing a mechanism for a multisystem developmental disorder.","evidence":"Computational structural analysis, cAMP-sensitivity assays and hedgehog reporter assays in NIH 3T3 cells","pmids":["33058759"],"confidence":"Medium","gaps":["Mechanism linking PKA to hedgehog suppression not fully delineated","Single lab"]},{"year":2021,"claim":"Phosphoproteomics defined the direct substrate landscape of wild-type versus chimeric PRKACA, showing overlapping but distinct targets and some inhibitor-resistant substrates.","evidence":"Cell-based and in vitro phosphoproteomics with recombinant enzymes and PKA inhibitors, mass spectrometry","pmids":["34436901"],"confidence":"Medium","gaps":["Functional importance of individual differential substrates not validated","Single lab"]},{"year":2022,"claim":"Demonstrating that the fusion junction is processed into HLA-presented neoantigens that elicit T cell responses opened an immunotherapeutic strategy against FL-HCC.","evidence":"Mass spectrometry immunopeptidomics, T cell functional assays and single-cell TCR sequencing","pmids":["36302754"],"confidence":"Medium","gaps":["Clinical efficacy not established","Single institution"]},{"year":2023,"claim":"shRNA depletion in PDX models established oncogene addiction, showing continued fusion expression is required for tumor maintenance and selectively lethal to fusion-positive cells.","evidence":"shRNA knockdown and patient-derived xenograft models in vivo with viability assays","pmids":["36302174"],"confidence":"Medium","gaps":["Mechanism of cell death upon fusion loss not detailed","Single lab"]},{"year":2025,"claim":"SIK inactivation and CRTC2-p300 transcriptional reprogramming were identified as a downstream axis through which the fusion drives FL-HCC growth.","evidence":"Functional model-system studies and human tumor specimen analysis with pathway dissection","pmids":["39326063"],"confidence":"Medium","gaps":["Relative contribution versus other fusion substrates unquantified","Single lab"]},{"year":2025,"claim":"MD/network analysis of the Cushing's L205R mutation revealed both local P+1 pocket disruption and long-range allosteric effects on the phosphoryl-transfer site, refining the mechanism of altered specificity.","evidence":"Molecular dynamics simulations, protein residue network analysis and crystal-structure comparison","pmids":["40504162"],"confidence":"Medium","gaps":["No experimental mutagenesis validation of predicted allosteric effects","Some distal changes not captured in crystal structure"]},{"year":2025,"claim":"An upstream regulatory layer was uncovered: Nsun2-mediated m5C methylation of PRKACA mRNA promotes its translation and PKA activity, with functional consequences for cardiac contractility and hypertrophy.","evidence":"m5C-RIP-seq, RNA pulldown, polysome profiling, cardiac-specific KO and rAAV9 overexpression with calcium and contraction measurements","pmids":["39990213"],"confidence":"Medium","gaps":["Generality beyond cardiac tissue untested","Single lab"]},{"year":2025,"claim":"A fusion-specific peptide degrader combined with siRNA achieved selective elimination of DNAJB1::PRKACA without affecting native PRKACA, demonstrating a tractable therapeutic vulnerability.","evidence":"mRNA-delivered peptide degrader plus siRNA in FLC cell and PDX models with selectivity controls (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Clinical translation untested"]},{"year":null,"claim":"How the J-domain conformational ensemble mechanistically rewires substrate selection and confers oncogenic, inhibitor-resistant signaling distinct from wild-type Cα remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking J-domain position to differential substrate phosphorylation","Functional roles of fusion-specific substrates not validated in tumor maintenance"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2,8,9,11,16]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,11]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[16,17]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,9,10]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,3,12,13]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[11]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[13]}],"complexes":["PKA holoenzyme"],"partners":["PRKAR1A","DNAJB1","MORC2","CDC25B","BAD","GPER1","NSUN2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P17612","full_name":"cAMP-dependent protein kinase catalytic subunit alpha","aliases":[],"length_aa":351,"mass_kda":40.6,"function":"Phosphorylates a large number of substrates in the cytoplasm and the nucleus (PubMed:15642694, PubMed:15905176, PubMed:16387847, PubMed:17333334, PubMed:17565987, PubMed:17693412, PubMed:18836454, PubMed:19949837, PubMed:20356841, PubMed:21085490, PubMed:21514275, PubMed:21812984, PubMed:21852232, PubMed:31112131). Phosphorylates CDC25B, ABL1, NFKB1, CLDN3, histone H1.4 (H1-4), PSMC5/RPT6, PJA2, RYR2, RORA, SOX9, UHRF1 and VASP (PubMed:15178447, PubMed:15642694, PubMed:15905176, PubMed:16387847, PubMed:17333334, PubMed:17565987, PubMed:17693412, PubMed:18836454, PubMed:19949837, PubMed:20356841, PubMed:21085490, PubMed:21514275, PubMed:21812984). Regulates the abundance of compartmentalized pools of its regulatory subunits through phosphorylation of PJA2 which binds and ubiquitinates these subunits, leading to their subsequent proteolysis (PubMed:21423175). RORA is activated by phosphorylation (PubMed:21514275). Required for glucose-mediated adipogenic differentiation increase and osteogenic differentiation inhibition from osteoblasts (PubMed:19949837). Involved in chondrogenesis by mediating phosphorylation of SOX9 (By similarity). Involved in the regulation of platelets in response to thrombin and collagen; maintains circulating platelets in a resting state by phosphorylating proteins in numerous platelet inhibitory pathways when in complex with NF-kappa-B (NFKB1 and NFKB2) and I-kappa-B-alpha (NFKBIA), but thrombin and collagen disrupt these complexes and free active PRKACA stimulates platelets and leads to platelet aggregation by phosphorylating VASP (PubMed:15642694, PubMed:20356841). Prevents the antiproliferative and anti-invasive effects of alpha-difluoromethylornithine in breast cancer cells when activated (PubMed:17333334). RYR2 channel activity is potentiated by phosphorylation in presence of luminal Ca(2+), leading to reduced amplitude and increased frequency of store overload-induced Ca(2+) release (SOICR) characterized by an increased rate of Ca(2+) release and propagation velocity of spontaneous Ca(2+) waves, despite reduced wave amplitude and resting cytosolic Ca(2+) (PubMed:17693412). PSMC5/RPT6 activation by phosphorylation stimulates proteasome (PubMed:17565987). Negatively regulates tight junctions (TJs) in ovarian cancer cells via CLDN3 phosphorylation (PubMed:15905176). NFKB1 phosphorylation promotes NF-kappa-B p50-p50 DNA binding (PubMed:15642694). Required for phosphorylation of GLI transcription factors which inhibits them and prevents transcriptional activation of Hedgehog signaling pathway target genes (By similarity). GLI transcription factor phosphorylation is inhibited by interaction of PRKACA with SMO which sequesters PRKACA at the cell membrane (By similarity). Involved in embryonic development by down-regulating the Hedgehog (Hh) signaling pathway that determines embryo pattern formation and morphogenesis most probably through the regulation of OFD1 in ciliogenesis (PubMed:33934390). Prevents meiosis resumption in prophase-arrested oocytes via CDC25B inactivation by phosphorylation (By similarity). May also regulate rapid eye movement (REM) sleep in the pedunculopontine tegmental (PPT) (By similarity). Phosphorylates APOBEC3G and AICDA (PubMed:16387847, PubMed:18836454). Phosphorylates HSF1; this phosphorylation promotes HSF1 nuclear localization and transcriptional activity upon heat shock (PubMed:21085490). Acts as a negative regulator of mTORC1 by mediating phosphorylation of RPTOR (PubMed:31112131). Phosphorylates AKAP19 (PubMed:27028580) Phosphorylates and activates ABL1 in sperm flagellum to promote spermatozoa capacitation","subcellular_location":"Cell projection, cilium, flagellum; Cytoplasmic vesicle, secretory vesicle, acrosome","url":"https://www.uniprot.org/uniprotkb/P17612/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PRKACA","classification":"Not 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Pathways","date":"2025-02-20","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.15.638474","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":39475,"output_tokens":4968,"usd":0.096473,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13352,"output_tokens":5068,"usd":0.09673,"stage2_stop_reason":"end_turn"},"total_usd":0.193203,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"A ~400-kb deletion on chromosome 19 creates a chimeric DNAJB1-PRKACA transcript encoding a fusion protein containing the DNAJB1 J-domain fused in-frame to the PRKACA catalytic domain; immunoprecipitation and Western blot confirmed expression in FL-HCC tumor tissue, and cell culture assay demonstrated the fusion protein retains kinase activity.\",\n      \"method\": \"RNA sequencing, RT-PCR, immunoprecipitation, Western blot, cell-based kinase assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (IP, WB, kinase assay), replicated across subsequent studies\",\n      \"pmids\": [\"24578576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Somatic PRKACA p.Leu206Arg (L206R) substitution directly disrupts interaction with the regulatory subunit PRKAR1A, causing constitutive catalytic activity, increased phosphorylation of downstream PKA targets, and autonomous cortisol production driving adrenal adenoma development.\",\n      \"method\": \"Exome sequencing, in vitro kinase/binding assays, functional characterization of PRKAR1A binding loss\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — binding disruption and kinase activity confirmed in vitro, independently replicated by multiple groups (PMIDs 24700472, 25069672, 25750087)\",\n      \"pmids\": [\"24747643\", \"24700472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The PRKACA L205R/L206R mutation locates in the P+1 loop of the PKA catalytic subunit, promotes PKA substrate phosphorylation and downstream target gene expression, conferring constitutive kinase activity.\",\n      \"method\": \"Whole-exome sequencing, RNA sequencing, in vitro phosphorylation assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional phosphorylation assays, independently replicated across multiple cohorts and labs\",\n      \"pmids\": [\"24700472\", \"24747643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Expression of the endogenous DNAJB1-PRKACA fusion protein (but not overexpression of wild-type PRKACA alone) in mouse liver via CRISPR-Cas9 is sufficient to drive formation of tumors resembling FL-HCC, establishing the fusion as an oncogenic driver beyond simple PRKACA overexpression; tumorigenesis is significantly enhanced by β-catenin activation.\",\n      \"method\": \"CRISPR/Cas9 genome editing, somatic gene transfer, histology, IHC, RNA sequencing, whole-exome sequencing\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss/gain-of-function in two independent mouse model studies (PMIDs 29162699, 28923495) with rigorous controls\",\n      \"pmids\": [\"29162699\", \"28923495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CRISPR/Cas9-induced Dnajb1-Prkaca fusion gene in wild-type mice is sufficient to initiate liver tumor formation with FL-HCC features in the absence of other genetic alterations or carcinogens, confirming the fusion as a standalone oncogenic driver.\",\n      \"method\": \"CRISPR/Cas9 hydrodynamic tail-vein injection, histology, IHC, RNA sequencing, whole-exome sequencing\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis with rigorous controls, replicated concept across two independent mouse model papers\",\n      \"pmids\": [\"28923495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PRKACA microinsertions (in-frame, 18-33 bp) in exons 7 and 8 cause the mutant PRKACA protein to lose binding to PRKAR1A regulatory subunit, leading to constitutive PKA pathway activation in sporadic cardiac myxoma.\",\n      \"method\": \"Sanger sequencing, functional binding assays (PRKAR1A interaction loss), PKA pathway activation assays\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding loss demonstrated in vitro, single lab, two orthogonal methods\",\n      \"pmids\": [\"28369983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NMR and molecular dynamics simulations of the DNAJB1-PRKACA chimeric kinase reveal an ensemble of conformations in which the J-domain can be tucked under the large lobe or swing free in solution, with no obvious steric interaction with RIIβ holoenzyme components.\",\n      \"method\": \"Molecular dynamics simulations, NMR spectroscopy, structural modeling\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR with MD simulation in single lab, conformational states experimentally captured\",\n      \"pmids\": [\"29335433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of PRKAR1A (regulatory subunit of PKA) expression due to inactivating PRKAR1A mutations in Carney complex patients leads to PKA activation and fibrolamellar carcinoma formation, providing an alternative mechanism to DNAJB1-PRKACA fusion for PKA deregulation in FL-HCC.\",\n      \"method\": \"FISH (negative for PRKACA rearrangement), PRKAR1A sequencing, IHC (loss of PRKAR1A protein)\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct sequencing and IHC protein loss, multiple cases, single lab\",\n      \"pmids\": [\"29222914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPER1 (G protein-coupled estrogen receptor 1) activates PRKACA, which in turn phosphorylates MORC2 at threonine 582, protecting MORC2 from chaperone-mediated autophagy (CMA)-mediated lysosomal degradation and contributing to estrogen-induced cell proliferation and antiestrogen resistance in breast cancer cells.\",\n      \"method\": \"Knockdown/overexpression, phosphorylation-deficient mutant (T582A), co-immunoprecipitation, functional cell proliferation assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal functional validation with phospho-dead mutant and KD, single lab\",\n      \"pmids\": [\"32401166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PRKACA expression rescues HER2-amplified breast cancer cells from HER2 inhibition not by restoring MAPK or PI3K signaling, but by inactivating the pro-apoptotic protein BAD, permitting survival signaling through BCL-XL.\",\n      \"method\": \"Kinase ORF screen, pharmacological BCL-XL/BCL-2 blockade, signaling pathway analysis (MAPK, PI3K readouts negative)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional screen plus pathway dissection, single lab, multiple readouts\",\n      \"pmids\": [\"24909179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Germline or mosaic missense variants in PRKACA produce PKA holoenzymes that are more sensitive to cAMP activation than wild-type, and expression of PRKACA variants inhibits hedgehog signaling in NIH 3T3 fibroblasts, providing a mechanism for the developmental defects (atrioventricular septal defects, polydactyly, skeletal/ectodermal abnormalities) observed in affected individuals.\",\n      \"method\": \"Computational structural analysis, cAMP-sensitivity assays, hedgehog signaling reporter assays in NIH 3T3 cells\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based functional assays with multiple variants, single lab, two orthogonal methods\",\n      \"pmids\": [\"33058759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PRKACA regulates G2/M transition in mouse fertilized eggs by phosphorylating CDC25B at Ser321 (but not Ser229); unphosphorylatable CDC25B-S321A mutant overrides G2 arrest even under elevated cAMP by directly dephosphorylating CDC2A-Tyr15 to activate MPF.\",\n      \"method\": \"Microinjection of CDC25B mutants, Western blot with phospho-Ser321 antibody, MPF activation assay, cAMP treatment\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific mutagenesis with functional rescue, phospho-specific antibody validation, single lab\",\n      \"pmids\": [\"18633139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Continued DNAJB1-PRKACA expression is required not only for FL-HCC tumor maintenance but its inhibition causes tumor cell death (oncogene addiction); shRNA-mediated knockdown of the fusion in patient-derived xenografts inhibits tumor growth in vivo with no effect on hepatocellular carcinoma cells not expressing the fusion.\",\n      \"method\": \"shRNA knockdown, patient-derived xenograft (PDX) models in vivo, cell viability assays\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular phenotype in PDX models, single lab\",\n      \"pmids\": [\"36302174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DNAJB1-PRKACA fusion drives FL-HCC through inactivation of SIK (salt-inducible kinase), which stimulates CRTC2-p300-mediated transcriptional reprogramming to drive tumor growth.\",\n      \"method\": \"Functional studies in model systems, examination of human tumor specimens, pathway analysis\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional studies in models plus human tumor validation, single lab\",\n      \"pmids\": [\"39326063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nsun2 methylates PRKACA mRNA at specific sites, promoting PRKACA translation in a YBX1-dependent manner; cardiac-specific Nsun2 knockout markedly reduces PKA activity, impairs substrate phosphorylation, myocyte contraction/relaxation, and calcium transients, while Nsun2 overexpression sensitizes the heart to hypertrophic stimuli in a PRKACA-dependent manner.\",\n      \"method\": \"m5C-RIP-seq, RNA pulldown, polysome profiling, cardiac-specific KO (Cre/LoxP), rAAV9 overexpression, IonOptix calcium measurement, reporter gene analysis\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (RIP-seq, polysome profiling, KO with functional phenotype), single lab\",\n      \"pmids\": [\"39990213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The PRKACA gene encoding the catalytic subunit Cα of cAMP-dependent protein kinase was localized to human chromosome region 19p13.1 by PCR and Southern blot analysis of somatic cell hybrid mapping panels, confirmed by two-color FISH.\",\n      \"method\": \"PCR, Southern blot, somatic cell hybrid panel, two-color FISH\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal cytogenetic methods, consistent localization\",\n      \"pmids\": [\"8884279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Integrated cell-based and in vitro phosphoproteomics identified direct substrates of PRKACA and the DNAJB1-PRKACA chimeric kinase, revealing the chimera targets overlapping but distinct substrate sets and altered pathways compared to wild-type PRKACA, with some substrates persisting under PKA inhibitor treatment.\",\n      \"method\": \"Cell-based phosphoproteomics, in vitro rephosphorylation with recombinant enzymes, PKA inhibitor treatment (rpcAMPs and PKI), mass spectrometry\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — integrated cell-based and in vitro phosphoproteomics, single lab, two orthogonal approaches\",\n      \"pmids\": [\"34436901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The PRKACA L205R Cushing's syndrome mutation locally disrupts the P+1 hydrophobic pocket (displacing the P+1-residue and altering substrate specificity) and has long-range allosteric effects on the linker connecting the A helix to β strand 1 and on the phosphoryl transfer site, as revealed by MD simulations and protein residue network analysis; some distal changes are not captured in the crystal structure.\",\n      \"method\": \"Molecular dynamics simulations, protein residue network (LSP) analysis, crystal structure comparison\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — computational MD with structural comparison, single lab, no experimental mutagenesis validation reported in abstract\",\n      \"pmids\": [\"40504162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A fusion-protein-specific peptide degrader selectively eliminates DNAJB1::PRKACA (and ATP1B1::PRKACA) without affecting native PRKACA; specificity reflects structural properties of the fusion. Combining the degrader with siRNA against the fusion transcript in a single mRNA accelerates degradation and is lethal to FLC tumor cells in preclinical models with no toxicity to non-FLC cells.\",\n      \"method\": \"mRNA-delivered peptide degrader, siRNA combination, FLC cell/PDX models in vitro and in vivo, selectivity controls\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — preprint, functional in vivo data with selectivity controls, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PRKACA (PKA catalytic α subunit) phosphorylates huntingtin at S421 (pS421-HTT) in human cells, as demonstrated by an ultrasensitive immunoassay showing that PRKACA activity regulates endogenous S421-HTT phosphorylation levels.\",\n      \"method\": \"Ultrasensitive immunoassay, cell-based PRKACA activity modulation, endogenous pS421-HTT detection\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, single method approach for the specific PRKACA-HTT substrate relationship\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Functional analysis of the novel PRKACA p.His88Asp variant found in an aldosterone-producing adenoma showed it was NOT associated with gain of function (negative finding), distinguishing it mechanistically from the p.Leu206Arg gain-of-function mutation.\",\n      \"method\": \"In vitro enzymatic activity assay of PRKACA variants, immunofluorescence for CYP11B2/CYP11B1\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vitro kinase activity assay with negative result clearly reported, single lab\",\n      \"pmids\": [\"27270477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DNAJB1-PRKACA-derived HLA class I and class II ligands are naturally processed and presented on tumor cells as confirmed by mass spectrometry-based immunopeptidome analysis, and induce multifunctional cytotoxic CD8+ and T-helper 1 CD4+ T cell responses, establishing the fusion junction as a bona fide neoantigen.\",\n      \"method\": \"Mass spectrometry immunopeptidome analysis, T cell functional assays, single-cell RNA sequencing of TCRs\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-confirmed antigen presentation plus functional T cell assays, single institution\",\n      \"pmids\": [\"36302754\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PRKACA encodes the catalytic α subunit (Cα) of cAMP-dependent protein kinase A (PKA), which is held inactive in a regulatory (PRKAR) subunit-bound holoenzyme and released upon cAMP binding; activating mutations (most commonly L205R/L206R) or oncogenic gene fusions (DNAJB1-PRKACA) disrupt the Cα–regulatory subunit interaction to produce constitutive kinase activity that phosphorylates downstream substrates including BAD (anti-apoptotic signaling), CDC25B-Ser321 (cell cycle G2/M control), MORC2-Thr582 (autophagy resistance), and SIK (transcriptional reprogramming via CRTC2-p300), while the DNAJB1-PRKACA fusion is both necessary and sufficient to drive fibrolamellar hepatocellular carcinoma and related oncocytic pancreatobiliary neoplasms through continued oncogene-addicted kinase signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PRKACA encodes the catalytic α subunit (Cα) of cAMP-dependent protein kinase A, a serine/threonine kinase whose activity is normally restrained by binding to PRKAR regulatory subunits; releasing this restraint converts PRKACA into a constitutive driver of endocrine and oncogenic phenotypes [#1, #2]. Activating point mutations cluster in the P+1 loop of the catalytic subunit—most prominently L205R/L206R—and act by disrupting the interaction with the PRKAR1A regulatory subunit, producing autonomous kinase activity, increased substrate phosphorylation, and downstream target gene expression that drives adrenal adenoma and Cushing's syndrome [#1, #2, #17]; in-frame microinsertions in exons 7–8 similarly abolish PRKAR1A binding in cardiac myxoma [#5], and loss of PRKAR1A itself provides an alternative route to PKA deregulation [#7]. The DNAJB1-PRKACA fusion, created by a ~400-kb chromosome 19 deletion that joins the DNAJB1 J-domain to the PRKACA catalytic domain, retains kinase activity and is both necessary and sufficient to drive fibrolamellar hepatocellular carcinoma, with continued expression required for tumor maintenance (oncogene addiction) [#0, #3, #12]; the fusion phosphorylates an overlapping but distinct substrate set relative to wild-type Cα and reprograms transcription through SIK inactivation and CRTC2-p300 signaling [#13, #16]. Beyond these oncogenic contexts, PRKACA phosphorylates specific substrates to control discrete cellular programs: BAD to enable BCL-XL survival signaling under HER2 inhibition [#9], MORC2-Thr582 to protect it from chaperone-mediated autophagy and confer antiestrogen resistance downstream of GPER1 [#8], and CDC25B-Ser321 to regulate the G2/M transition [#11]. Germline PRKACA variants that increase cAMP sensitivity and inhibit hedgehog signaling cause a developmental syndrome with septal and skeletal defects [#10]. The fusion junction itself is processed and presented as an HLA-restricted neoantigen, establishing an immunotherapeutic axis [#21].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Establishing the chromosomal position of the PKA catalytic α subunit gene provided the genomic anchor later required to interpret rearrangements and copy-number events at this locus.\",\n      \"evidence\": \"PCR, Southern blot, somatic cell hybrid mapping and two-color FISH localizing PRKACA to 19p13.1\",\n      \"pmids\": [\"8884279\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address kinase function or regulation\", \"No link to disease at this stage\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying CDC25B-Ser321 as a PRKACA phosphorylation site explained how cAMP/PKA imposes G2 arrest, linking the kinase to direct cell-cycle control.\",\n      \"evidence\": \"Microinjection of CDC25B mutants, phospho-Ser321 Western blot, and MPF activation assay in mouse fertilized eggs\",\n      \"pmids\": [\"18633139\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Demonstrated in oocyte/embryo system, generality to somatic cells untested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery of the DNAJB1-PRKACA chimeric transcript answered what genetic lesion defines fibrolamellar HCC and showed the fusion retains kinase activity.\",\n      \"evidence\": \"RNA-seq, RT-PCR, immunoprecipitation, Western blot and cell-based kinase assay on FL-HCC tumor tissue\",\n      \"pmids\": [\"24578576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not prove the fusion is sufficient to cause tumors\", \"Downstream substrate program undefined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The L205R/L206R substitution was shown to disrupt PRKAR1A binding and produce constitutive activity, defining the molecular basis of cortisol-producing adrenal adenomas.\",\n      \"evidence\": \"Exome/RNA sequencing plus in vitro kinase and PRKAR1A-binding assays\",\n      \"pmids\": [\"24747643\", \"24700472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full downstream substrate set not mapped at this stage\", \"Structural mechanism of disruption inferred from mutation location\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A kinase ORF screen revealed PRKACA promotes survival under HER2 inhibition through BAD inactivation rather than MAPK/PI3K restoration, defining a distinct PKA survival axis.\",\n      \"evidence\": \"Kinase ORF screen, pharmacological BCL-XL/BCL-2 blockade, MAPK/PI3K readouts in HER2-amplified breast cancer cells\",\n      \"pmids\": [\"24909179\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct phosphorylation of BAD by PRKACA not biochemically isolated here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"In vivo modeling answered whether the fusion is causal: endogenous DNAJB1-PRKACA, but not wild-type PRKACA overexpression, was sufficient to drive FL-HCC-like tumors in mice.\",\n      \"evidence\": \"CRISPR/Cas9 genome editing and hydrodynamic somatic gene transfer in mouse liver with histology, IHC, RNA-seq, WES\",\n      \"pmids\": [\"29162699\", \"28923495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic distinction between fusion and wild-type signaling not yet resolved\", \"β-catenin cooperation noted but not fully dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"PRKACA microinsertions in cardiac myxoma were shown to abolish PRKAR1A binding, extending the loss-of-regulation mechanism beyond point mutations to another tumor type.\",\n      \"evidence\": \"Sanger sequencing with functional PRKAR1A-interaction and PKA pathway activation assays\",\n      \"pmids\": [\"28369983\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Downstream substrate consequences not characterized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Structural studies addressed how the J-domain affects the chimeric kinase, finding it adopts an ensemble of conformations without obvious steric clash with holoenzyme components.\",\n      \"evidence\": \"NMR spectroscopy and molecular dynamics simulations of the DNAJB1-PRKACA chimera\",\n      \"pmids\": [\"29335433\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of J-domain conformations on substrate selection unresolved\", \"Single lab, computational/biophysical only\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"PRKAR1A loss in Carney complex patients was shown to cause FL-HCC, establishing an alternative route to PKA deregulation independent of the fusion.\",\n      \"evidence\": \"FISH (negative for PRKACA rearrangement), PRKAR1A sequencing and IHC showing protein loss\",\n      \"pmids\": [\"29222914\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Does not establish identical downstream program as the fusion\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identifying MORC2-Thr582 as a PRKACA substrate downstream of GPER1 linked the kinase to autophagy escape and antiestrogen resistance in breast cancer.\",\n      \"evidence\": \"Knockdown/overexpression, T582A phospho-dead mutant, co-IP and proliferation assays\",\n      \"pmids\": [\"32401166\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct kinase-substrate biochemistry vs cellular correlation\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Germline PRKACA variants were shown to raise cAMP sensitivity and inhibit hedgehog signaling, providing a mechanism for a multisystem developmental disorder.\",\n      \"evidence\": \"Computational structural analysis, cAMP-sensitivity assays and hedgehog reporter assays in NIH 3T3 cells\",\n      \"pmids\": [\"33058759\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking PKA to hedgehog suppression not fully delineated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Phosphoproteomics defined the direct substrate landscape of wild-type versus chimeric PRKACA, showing overlapping but distinct targets and some inhibitor-resistant substrates.\",\n      \"evidence\": \"Cell-based and in vitro phosphoproteomics with recombinant enzymes and PKA inhibitors, mass spectrometry\",\n      \"pmids\": [\"34436901\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional importance of individual differential substrates not validated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that the fusion junction is processed into HLA-presented neoantigens that elicit T cell responses opened an immunotherapeutic strategy against FL-HCC.\",\n      \"evidence\": \"Mass spectrometry immunopeptidomics, T cell functional assays and single-cell TCR sequencing\",\n      \"pmids\": [\"36302754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Clinical efficacy not established\", \"Single institution\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"shRNA depletion in PDX models established oncogene addiction, showing continued fusion expression is required for tumor maintenance and selectively lethal to fusion-positive cells.\",\n      \"evidence\": \"shRNA knockdown and patient-derived xenograft models in vivo with viability assays\",\n      \"pmids\": [\"36302174\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of cell death upon fusion loss not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"SIK inactivation and CRTC2-p300 transcriptional reprogramming were identified as a downstream axis through which the fusion drives FL-HCC growth.\",\n      \"evidence\": \"Functional model-system studies and human tumor specimen analysis with pathway dissection\",\n      \"pmids\": [\"39326063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution versus other fusion substrates unquantified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"MD/network analysis of the Cushing's L205R mutation revealed both local P+1 pocket disruption and long-range allosteric effects on the phosphoryl-transfer site, refining the mechanism of altered specificity.\",\n      \"evidence\": \"Molecular dynamics simulations, protein residue network analysis and crystal-structure comparison\",\n      \"pmids\": [\"40504162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental mutagenesis validation of predicted allosteric effects\", \"Some distal changes not captured in crystal structure\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"An upstream regulatory layer was uncovered: Nsun2-mediated m5C methylation of PRKACA mRNA promotes its translation and PKA activity, with functional consequences for cardiac contractility and hypertrophy.\",\n      \"evidence\": \"m5C-RIP-seq, RNA pulldown, polysome profiling, cardiac-specific KO and rAAV9 overexpression with calcium and contraction measurements\",\n      \"pmids\": [\"39990213\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality beyond cardiac tissue untested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A fusion-specific peptide degrader combined with siRNA achieved selective elimination of DNAJB1::PRKACA without affecting native PRKACA, demonstrating a tractable therapeutic vulnerability.\",\n      \"evidence\": \"mRNA-delivered peptide degrader plus siRNA in FLC cell and PDX models with selectivity controls (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Clinical translation untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the J-domain conformational ensemble mechanistically rewires substrate selection and confers oncogenic, inhibitor-resistant signaling distinct from wild-type Cα remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking J-domain position to differential substrate phosphorylation\", \"Functional roles of fusion-specific substrates not validated in tumor maintenance\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 8, 9, 11, 16]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 11]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [16, 17]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 9, 10]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 3, 12, 13]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [\"PKA holoenzyme\"],\n    \"partners\": [\"PRKAR1A\", \"DNAJB1\", \"MORC2\", \"CDC25B\", \"BAD\", \"GPER1\", \"NSUN2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}