Affinage

PRKX

cAMP-dependent protein kinase catalytic subunit PRKX · UniProt P51817

Length
358 aa
Mass
40.9 kDa
Annotated
2026-06-10
20 papers in source corpus 11 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/7 claims corpus-supported (86%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PRKX is a cAMP-dependent serine/threonine protein kinase that is structurally and regulatorily distinct from classical PKA and drives epithelial morphogenesis, cell migration, and angiogenesis (PMID:10026146, PMID:12082174, PMID:21684272). It phosphorylates the model substrate Kemptide and is held inactive by high-affinity binding to type I regulatory subunit RIα and to the heat-stable protein kinase inhibitor PKI, while binding RIIα only weakly; this RIα-mediated inhibition is relieved by nanomolar cAMP, which also permits nuclear translocation (PMID:10026146). Its selectivity for RI over RII regulatory subunits is dictated by the αH-αI loop residue Arg-283, since an R283L mutant gains the ability to form holoenzymes with RII, a determinant conserved across PrKX-like kinases (PMID:20819953). Through its kinase activity PRKX promotes renal epithelial cell migration and branching morphogenesis of MDCK cells, effects that require an intact catalytic function and are not reproduced by PKA (PMID:12082174). PRKX binds and phosphorylates the polycystin-1 C-terminal tail at Ser-4166, and constitutively active PRKX rescues adhesion, migration, and branching defects caused by PKD1 deficiency, linking the kinase to renal tubular morphogenesis (PMID:17980165). In innate immunity, PRKX phosphorylates TAK1 at Ser-412 to enable full TAK1 activation and downstream NF-κB signaling in response to proinflammatory stimuli (PMID:25028512), and in a teleost ortholog it instead promotes lysosome-dependent degradation of TAK1 to suppress IFN signaling (PMID:36713382). PRKX kinase activity is competitively inhibited by AAV Rep proteins (Rep78/Rep52) through a PKI-like pseudosubstrate domain that raises the substrate Km without altering Vmax, an inhibition required for AAV interference with adenovirus replication (PMID:9742109, PMID:11773379, PMID:12660177).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1998 High

    Established that the viral AAV Rep proteins physically engage and inhibit PRKX, defining the first regulatory partners of the kinase and a route by which a virus could subvert cAMP signaling.

    Evidence Yeast two-hybrid, pull-down/Co-IP, in vitro kinase assay, and reporter assays with Rep78/Rep52 versus Rep68

    PMID:9733829 PMID:9742109

    Open questions at the time
    • Did not resolve the precise inhibitory domain or kinetic mechanism
    • CREB-dependent transcriptional output not tied to specific endogenous targets
  2. 1999 High

    Defined PRKX as a bona fide cAMP-dependent kinase with distinct regulatory-subunit preference, answering how it is held inactive and activated.

    Evidence Surface plasmon resonance, in vitro Kemptide kinase assay, and microinjection of fluorescent R subunits

    PMID:10026146

    Open questions at the time
    • Physiological substrates beyond Kemptide not identified
    • Mechanistic basis for RI versus RII selectivity not yet defined
  3. 2002 High

    Showed PRKX kinase activity drives renal epithelial migration and branching morphogenesis distinct from PKA, establishing a cellular role.

    Evidence Overexpression in renal epithelial and MDCK cells with migration and collagen-gel branching assays and a kinase-dead control

    PMID:12082174

    Open questions at the time
    • Endogenous substrates mediating the morphogenetic effect not identified
    • Differences from PKA at the molecular level unexplained
  4. 2002 Medium

    Defined Rep78 inhibition as a competitive pseudosubstrate mechanism homologous to PKI, explaining how the virus blocks the kinase.

    Evidence Deletion mapping and steady-state kinetic analysis of inhibition with sequence homology analysis

    PMID:11773379

    Open questions at the time
    • Single-lab kinetic characterization
    • Did not establish in vivo consequences of inhibition
  5. 2003 Medium

    Linked Rep-mediated PRKX/PKA inhibition to AAV interference with adenovirus replication, giving the inhibition a biological purpose.

    Evidence Mutant AAV2 lacking the Rep kinase-inhibitory domain and adenovirus replication assays

    PMID:12660177

    Open questions at the time
    • Relative contribution of PRKX versus PKA inhibition not separated
    • Downstream effectors of the interference not mapped
  6. 2007 Medium

    Identified polycystin-1 Ser-4166 as a PRKX substrate and placed PRKX downstream/parallel to PKD1 in renal tubular morphogenesis.

    Evidence In vitro kinase assay on the polycystin-1 C-terminal peptide, ADPKD cell rescue, and embryonic kidney organ-culture injection

    PMID:17980165

    Open questions at the time
    • In vivo phosphorylation of full-length polycystin-1 not demonstrated
    • Functional output of Ser-4166 phosphorylation not defined
  7. 2010 High

    Pinpointed Arg-283 in the αH-αI loop as the determinant of RI-over-RII selectivity, explaining the divergent regulation of PRKX from PKA.

    Evidence BRET in living cells, SPR, and reciprocal site-directed mutagenesis (R283L PrKX, L277R PKA Cα) tested across species

    PMID:20819953

    Open questions at the time
    • Physiological significance of RI selectivity in cells not established
    • Structural model of the holoenzyme interface not resolved
  8. 2011 Medium

    Extended PRKX function to angiogenesis and named candidate protein partners, broadening its biological scope beyond renal cells.

    Evidence Endothelial proliferation, migration, and tube-formation assays with PKA comparison and binding assays for Pin-1, Magi-1, Bag-3

    PMID:21684272

    Open questions at the time
    • Binding partners not validated by reciprocal or structural studies
    • No substrate connecting PRKX to the angiogenic phenotype identified
  9. 2014 High

    Identified TAK1 Ser-412 as a PRKX substrate required for NF-κB activation, embedding PRKX in proinflammatory signaling.

    Evidence In vitro kinase assay, shRNA knockdown with phospho-specific immunoblot, and zebrafish morpholino knockdown/rescue

    PMID:25028512

    Open questions at the time
    • Stimulus-specific regulation of PRKX upstream of TAK1 not defined
    • Shared activity with PKACα not fully deconvoluted
  10. 2023 Medium

    Revealed an opposing, lysosome-dependent mechanism in which a PRKX ortholog degrades TAK1 to suppress IFN signaling, indicating context-dependent regulation of TAK1.

    Evidence Co-IP, immunofluorescence, luciferase reporter, shRNA knockdown, and chloroquine versus MG-132 inhibitor treatment in black carp

    PMID:36713382

    Open questions at the time
    • Demonstrated in fish ortholog only
    • Mechanism reconciling activation versus degradation of TAK1 not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How PRKX selects among its substrates in different tissues and how its activation versus degradation of TAK1 is controlled remains unresolved.
  • No structural model of substrate recognition
  • Upstream signals controlling PRKX activation in vivo unknown
  • Reconciliation of pro-inflammatory and IFN-suppressive roles unestablished

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 4 GO:0140096 catalytic activity, acting on a protein 3 GO:0140657 ATP-dependent activity 1
Localization
GO:0005634 nucleus 1
Pathway
R-HSA-1266738 Developmental Biology 3 R-HSA-162582 Signal Transduction 2 R-HSA-168256 Immune System 2
Partners
MAGI1PIN1PKD1PKIAPRKAR1AREP52REP78TAK1

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 PrKX is a catalytic subunit of cAMP-dependent protein kinase that phosphorylates the heptapeptide Kemptide, binds with high affinity to regulatory subunit type I (RIα, KD=10 nM) and heat-stable protein kinase inhibitor (KD=15 nM), but not to RIIα under physiological conditions (KD=2.3 µM). RIα inhibition of PrKX is reversed by nanomolar cAMP (Ka=40 nM). Microinjection data showed that RIα but not RIIα binds PrKX in vivo, preventing nuclear translocation in the absence of cAMP. RIIα is phosphorylated by PrKX in a cAMP-independent manner. Surface plasmon resonance, in vitro kinase assay (Kemptide phosphorylation), autophosphorylation assay, microinjection with fluorescent R subunits The Journal of biological chemistry High 10026146
1998 AAV type 2 Rep78 interacts with PRKX via a C-terminal zinc finger-like domain of Rep78 (Rep68, which lacks this domain, does not interact). This interaction inhibits PRKX autophosphorylation and kinase activity. PRKX was shown to activate CREB-dependent transcription when expressed in transfected cells, and this activation was suppressed by Rep78. Yeast two-hybrid screen, pMal-Rep pull-down assay, in vitro kinase assay, transfection/reporter assay Journal of virology Medium 9733829
1998 AAV Rep78 and Rep52 (but not Rep68) form stable complexes with PrKX and inhibit its kinase activity; Rep52 inhibits PrKX trans- and autophosphorylation with a Ki of ~167 nM, as determined by surface plasmon resonance. Rep52 also inhibits PKA with Ki ~300 nM. Interaction was confirmed by coimmunoprecipitation in vitro and in vivo. Yeast two-hybrid, coimmunoprecipitation (in vitro and in vivo), surface plasmon resonance, in vitro kinase assay Molecular and cellular biology High 9742109
2002 PRKX activates migration of cultured renal epithelial cells in the presence of cAMP (blocked by H89); this effect was not observed with PKA. PRKX also activates branching morphogenesis of MDCK cells in collagen gels even without cAMP or HGF, an effect not seen with PKA or with a kinase-inactivated PRKX mutant, establishing kinase activity as essential. Transfection/overexpression in renal epithelial cells, migration assay, MDCK branching morphogenesis assay in collagen gels, kinase-dead mutant control Proceedings of the National Academy of Sciences of the United States of America High 12082174
2002 AAV2 Rep78 inhibition of PKA and PRKX is mapped to amino acids 526–561 (for PRKX) and 526–621 (for PKA). Steady-state kinetic analysis showed Rep78 increases the Km for the peptide substrate without affecting Vmax, indicating competitive (pseudosubstrate) inhibition. Homology was detected between the Rep78 inhibitory domain and the cellular pseudosubstrate inhibitor PKI. Deletion mapping, steady-state kinetic analysis of kinase inhibition, sequence homology analysis Journal of virology Medium 11773379
2003 AAV2 Rep78/Rep52 proteins contain a PKA/PrKX inhibitory domain homologous to the heat-stable PKA inhibitor PKI. Adenovirus replication was shown to be sensitive to PKA activity, and a mutant AAV2 lacking the Rep kinase-inhibitory domain failed to inhibit adenovirus replication, establishing that PKA/PrKX inhibition by Rep is required for AAV interference with adenovirus. Mutant virus construction, adenovirus replication assay, PKA activity modulation The EMBO journal Medium 12660177
2007 PRKX binds and phosphorylates the C-terminal tail of polycystin-1 (PKD1 gene product) at Ser-4166 in vitro. Expression of constitutively active PRKX in human ADPKD epithelial cells rescued adhesion and migration defects caused by PKD1 deficiency. Co-injection of constitutively active PRKX with inhibitory PKD1 construct into mouse embryonic kidney ureteric buds restored normal branching morphogenesis. In vitro kinase assay with polycystin-1 C-terminal peptide, transfection/rescue assay in ADPKD cell lines, embryonic kidney organ culture injection Biochimica et biophysica acta Medium 17980165
2010 The αH-αI loop residue Arg-283 in PrKX is crucial for its preferential interaction with RI over RII regulatory subunits. A R283L mutant of PrKX was able to form holoenzyme complexes with wild-type RII subunits. Conversely, the reciprocal L277R mutation in PKA Cα destabilized RII-containing holoenzymes and facilitated cAMP-mediated activation. This RI preference is evolutionarily conserved across PrKX-like kinases from human to Trypanosoma brucei. Bioluminescence resonance energy transfer (BRET) in living cells, surface plasmon resonance, site-directed mutagenesis The Journal of biological chemistry High 20819953
2011 PRKX stimulates endothelial cell proliferation, migration, and vascular-like structure formation (three essential processes for angiogenesis), whereas PKA had an inhibitory effect on vascular-like structure formation. PRKX was found to interact (bind) with Pin-1, Magi-1, and Bag-3. Overexpression in endothelial cells, proliferation assay, migration assay, tube formation assay, co-immunoprecipitation/binding assay for Pin-1/Magi-1/Bag-3 Developmental biology Medium 21684272
2014 PRKX (together with PKACα) phosphorylates TAK1 at Ser-412, which is required for full TAK1 activation in response to proinflammatory stimuli (TNF-α, LPS, IL-1β). shRNA-based knockdown of PRKX reduced TAK1 Ser-412 phosphorylation and impaired downstream NF-κB signaling and proinflammatory cytokine induction. The corresponding site in zebrafish TAK1 (Ser-391) was shown by morpholino knockdown and rescue to play a conserved role in NF-κB activation. In vitro kinase assay, shRNA knockdown, phospho-specific immunoblot, zebrafish morpholino knockdown and rescue The Journal of biological chemistry High 25028512
2023 In black carp, PRKX (bcPRKX) interacts with TAK1 (bcTAK1), suppresses bcTAK1/bcIRF7/IFN signaling, and promotes lysosome-dependent (not proteasome-dependent) degradation of bcTAK1. Chloroquine (lysosome inhibitor) prevented bcTAK1 degradation mediated by bcPRKX, whereas the proteasome inhibitor MG-132 did not. Co-immunoprecipitation, immunofluorescence, luciferase reporter assay, shRNA knockdown, inhibitor treatment (chloroquine vs MG-132), plaque assay Frontiers in immunology Medium 36713382

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1997 Abnormal XY interchange between a novel isolated protein kinase gene, PRKY, and its homologue, PRKX, accounts for one third of all (Y+)XX males and (Y-)XY females. Human molecular genetics 97 9302280
1999 PrKX is a novel catalytic subunit of the cAMP-dependent protein kinase regulated by the regulatory subunit type I. The Journal of biological chemistry 82 10026146
1998 Adeno-associated virus Rep78 protein interacts with protein kinase A and its homolog PRKX and inhibits CREB-dependent transcriptional activation. Journal of virology 56 9733829
2014 Transforming growth factor (TGF)-β-activated kinase 1 (TAK1) activation requires phosphorylation of serine 412 by protein kinase A catalytic subunit α (PKACα) and X-linked protein kinase (PRKX). The Journal of biological chemistry 53 25028512
2012 PRKX, TTBK2 and RSK4 expression causes Sunitinib resistance in kidney carcinoma- and melanoma-cell lines. International journal of cancer 52 22020623
1995 The human protein kinase gene PKX1 on Xp22.3 displays Xp/Yp homology and is a site of chromosomal instability. Human molecular genetics 50 7633447
1998 Inhibition of PrKX, a novel protein kinase, and the cyclic AMP-dependent protein kinase PKA by the regulatory proteins of adeno-associated virus type 2. Molecular and cellular biology 48 9742109
2003 PKA/PrKX activity is a modulator of AAV/adenovirus interaction. The EMBO journal 45 12660177
2002 PRKX, a phylogenetically and functionally distinct cAMP-dependent protein kinase, activates renal epithelial cell migration and morphogenesis. Proceedings of the National Academy of Sciences of the United States of America 43 12082174
2016 PRKX, a Novel cAMP-Dependent Protein Kinase Member, Plays an Important Role in Development. Journal of cellular biochemistry 23 26252946
2011 PRKX critically regulates endothelial cell proliferation, migration, and vascular-like structure formation. Developmental biology 23 21684272
2010 Regulation of cAMP-dependent protein kinases: the human protein kinase X (PrKX) reveals the role of the catalytic subunit alphaH-alphaI loop. The Journal of biological chemistry 21 20819953
2007 Protein kinase X (PRKX) can rescue the effects of polycystic kidney disease-1 gene (PKD1) deficiency. Biochimica et biophysica acta 18 17980165
2005 Profiles of PrKX expression in developmental mouse embryo and human tissues. The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society 16 15879576
1997 FISH localization of the human Y-homolog of protein kinase PRKX (PRKY) to Yp11.2 and two pseudogenes to 15q26 and Xq12-->q13. Cytogenetics and cell genetics 16 9154127
2002 Adeno-associated virus type 2 Rep78 inhibition of PKA and PRKX: fine mapping and analysis of mechanism. Journal of virology 14 11773379
2022 Long non-coding RNA NRSN2-AS1 facilitates tumorigenesis and progression of ovarian cancer via miR-744-5p/PRKX axis. Biology of reproduction 13 34791059
2016 Altered Expression of PRKX, WNT3 and WNT16 in Human Nodular Basal Cell Carcinoma. Anticancer research 11 27630294
2013 Critical role of Yp inversion in PRKX/PRKY-mediated Xp;Yp translocation in a patient with 45,X testicular disorder of sex development. Endocrine journal 7 24088663
2023 PRKX down-regulates TAK1/IRF7 signaling in the antiviral innate immunity of black carp Mylopharyngodon piceus. Frontiers in immunology 6 36713382

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