GPA-12 is a heterotrimeric guanine-nucleotide-binding protein (G protein) alpha subunit of the Galpha-12/13 subfamily, the C. elegans homolog of mammalian Galpha-12/Galpha-13. It has a canonical Galpha domain with intact G1-G5 nucleotide-binding motifs and functions as a GTP/GDP-regulated molecular switch that, in its GTP-bound state, engages downstream effectors to relay signals from the cell surface. Its best-characterized physiological role is in the epidermis (hypodermis), where GPA-12 signaling acts upstream of protein kinase C delta (TPA-1) and a conserved p38 MAPK cassette (TIR-1, NSY-1, SEK-1, PMK-1) and the STAT-like factor STA-2 to drive induction of antimicrobial peptide genes of the NLP (nlp-29 cluster) and CNC families in response to fungal infection and wounding. A constitutively active form (GPA-12 Q205L / G12QL) is sufficient to drive constitutive antimicrobial peptide gene expression, and, when hyperactivated more broadly, causes a developmental growth arrest through a pharyngeal-pumping (feeding) defect that also depends on TPA-1. gpa-12 loss-of-function animals are viable.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003925 G protein activity | IBA GO_REF:0000033 | ACCEPT | Summary: Correct and core molecular function. GPA-12 is a heterotrimeric G protein alpha subunit (Galpha-12/13 subfamily) that cycles between GTP- and GDP-bound states to act as a signal-transducing molecular switch. GO:0003925 is the appropriate MF for such subunits, and its behavior is supported experimentally in worm by the constitutively active Q205L (catalytic-glutamine) mutant. Reason: Best and most specific molecular-function term for a Galpha subunit; consistent with family membership, intact G1-G5 motifs, and the behavior of activated GPA-12. Supporting Evidence: PMID:12646136 We characterized a C. elegans Galpha subunit gene, gpa-12, which is a homolog of mammalian G(12)/G(13)alpha, and found that animals defective in gpa-12 are viable |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) localization to cytoplasm, independently corroborated by the experimental IDA cytoplasm annotation from PMID:12646136. This is a reasonable functional cellular compartment for a peripheral, membrane-associated Galpha subunit that cycles at the cytoplasmic face of the plasma membrane. Reason: Consistent, independently corroborated cellular localization for a Galpha subunit; accepted as the cellular compartment in which GPA-12 acts. |
| GO:0007188 adenylate cyclase-modulating G protein-coupled receptor signaling pathway | IBA GO_REF:0000033 | REMOVE | Summary: Over-propagation from the pan-Galpha PANTHER family node. Adenylate cyclase/cAMP modulation is the defining function of the Gs (stimulatory) and Gi (inhibitory) subfamilies, not of the Galpha-12/13 subfamily to which GPA-12 belongs. There is no evidence that GPA-12 modulates adenylate cyclase, and this pathway type is biologically inappropriate for a G12/13 protein. Reason: Biologically incorrect for the G12/13 subfamily; the term propagated electronically from Gs/Gi paralogs in the broad pan-Galpha tree and should not transfer to GPA-12. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000026392 Β· pan-Galpha family node SUPPORTS SOURCE BUT NOT TARGET |
| GO:0007266 Rho protein signal transduction | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Canonical mammalian Galpha-12/13 signaling activates RhoGEFs to relay signals through Rho GTPases, so this term is biologically apt at the family level and propagates from the G12/13 node (mouse Gna12/Gna13). However, the Rho effector arm has not been demonstrated for C. elegans GPA-12; the experimentally defined worm effector arm runs through phospholipase (PLC-3) and PKCdelta (TPA-1). Retained as a homology-based, non-core inference. Reason: Homology-supported canonical G12/13 function, but not experimentally established in worm, where the demonstrated downstream arm is PLC/PKCdelta rather than Rho. |
| GO:0005834 heterotrimeric G-protein complex | IBA GO_REF:0000033 | ACCEPT | Summary: Correct. As a Galpha subunit, GPA-12 assembles into a heterotrimeric G protein (Galpha-beta-gamma) complex; in the epidermal immune pathway it partners with the Gbeta RACK-1. Reason: Accurate and well-supported complex membership for a Galpha subunit. Supporting Evidence: PMID:22470487 Wounding and infection require G-protein signaling, involving the GΞ± protein GPA-12 and the GΓ RACK-1, while infection specifically involves the Tribbles-like kinase NIPI-3 |
| GO:0031526 brush border membrane | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Over-specific location propagated from mammalian (rat) orthologs. Brush border membrane is the plasma membrane of intestinal microvilli; GPA-12's demonstrated site of action is the epidermis/hypodermis. There is no C. elegans evidence for brush border localization. Reason: Narrow mammalian-tissue location transferred by phylogenetic inference; not supported for the worm protein and inconsistent with its known site of action. Propagation Review Root cause: PROPAGATION BAD Failure modes: CONTEXT OR TISSUE MISMATCH COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000026689 Β· Galpha-12/13 node SUPPORTS SOURCE BUT NOT TARGET |
| GO:0031752 D5 dopamine receptor binding | IBA GO_REF:0000033 | REMOVE | Summary: Hyper-specific molecular function propagated from a single mammalian ortholog annotation. Binding to a D5 dopamine receptor is not a plausible or supported activity for C. elegans GPA-12 (worms lack a D5 dopamine receptor ortholog), and there is no worm evidence for it. Reason: Over-propagated, organism-specific receptor-binding annotation with no relevance or evidence for the worm protein. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG CONTEXT OR TISSUE MISMATCH Sources checked: PANTHER:PTN000026689 Β· Galpha-12/13 node SUPPORTS SOURCE BUT NOT TARGET |
| GO:0001664 G protein-coupled receptor binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Generic InterPro-based inference. Galpha subunits are activated by, and physically couple to, GPCRs, so GPCR binding is a defensible general molecular function. However, the specific cognate receptor for GPA-12 is not established, so this remains a generic, non-core capability. Reason: True general Galpha property (more informative than 'protein binding') but generic; the actual GPA-12 receptor is unknown. |
| GO:0003924 GTPase activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Galpha subunits have intrinsic GTPase activity that terminates signaling by returning the switch to the GDP-bound state. Correct for GPA-12, whose G-box motifs are intact and whose catalytic-glutamine (Q205L) mutant behaves as a GTP-hydrolysis-defective, constitutively active protein. The more specific GO:0003925 (G protein activity) better captures the defining signaling-switch role, so this generic GTPase term is retained as a supporting, non-core activity. Reason: Correct enzymatic capability for a Galpha subunit, but a supporting activity underlying the switch rather than the defining core function, which is better represented by GO:0003925 (G protein activity). |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: High-level, generic biological process. True (GPA-12 is a signal transducer) but far less informative than the specific GPCR-signaling and immune-signaling processes it participates in. Reason: Correct but uninformatively general; subsumed by more specific process terms. |
| GO:0007186 G protein-coupled receptor signaling pathway | IEA GO_REF:0000002 | ACCEPT | Summary: Appropriate mechanistic process term: Galpha subunits are the canonical transducers of GPCR signaling. This captures the pathway type through which GPA-12 relays signals in the epidermis, even though the specific receptor is not yet identified. Reason: Accurate, mechanism-defining process for a Galpha subunit. |
| GO:0007266 Rho protein signal transduction | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro-based duplicate of the IBA Rho protein signal transduction annotation, reflecting the canonical G12/13 -> RhoGEF -> Rho effector arm. As with the IBA version, this is homology-based and not experimentally demonstrated for worm GPA-12. Reason: Redundant with the IBA annotation; homology-supported canonical function not demonstrated in worm. |
| GO:0019001 guanyl nucleotide binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct supporting molecular function: GPA-12 binds guanine nucleotides (GTP/GDP) via its intact G-box motifs. This underlies the G protein switch but is a component capability rather than the core function. Reason: Accurate binding activity underpinning the GTPase/G-protein switch; supporting rather than core. |
| GO:0031683 G-protein beta/gamma-subunit complex binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct: the Galpha subunit binds the Gbeta/gamma dimer to form the inactive heterotrimer, releasing it upon GTP loading. Consistent with the curated GO-CAM (gomodel:5b91dbd100002057), which models GPA-12's molecular function as Gbeta/gamma-subunit complex binding, partnered with the Gbeta RACK-1. Reason: Accurate Galpha-Gbetagamma interaction supporting heterotrimer assembly; supporting rather than the core signaling function. |
| GO:0010628 positive regulation of gene expression | IMP PMID:22470487 The pseudokinase NIPI-4 is a novel regulator of antimicrobia... | ACCEPT | Summary: Experimentally supported: epidermis-restricted active GPA-12* drives a marked constitutive increase in antimicrobial peptide gene expression (nlp-29, nlp-31, nlp-34 and cnc-1, cnc-4), an effect abolished in a nipi-4 mutant. This is the transcriptional-induction readout of GPA-12's epidermal immune signaling. Reason: Directly supported by loss/gain-of-function transcriptional data; captures GPA-12's role in up-regulating immune-effector gene expression. Supporting Evidence: PMID:22470487 In uninfected transgenic worms carrying the Pcol-19::GPA-12* construct, we observed a very marked increase in the expression of Pnlp-29::GFP in the epidermis from the late L4 stage onwards PMID:22470487 the transgenic strain exhibited an elevated constitutive expression of nlp-29, nlp-31 and nlp-34, and cnc-1, cnc-4 |
| GO:0050832 defense response to fungus | IMP PMID:22470487 The pseudokinase NIPI-4 is a novel regulator of antimicrobia... | ACCEPT | Summary: Experimentally supported core biological process. GPA-12 signaling is required for the epidermal antifungal defense program (nlp/cnc antimicrobial peptide induction) against the natural fungal pathogen Drechmeria coniospora. Reason: Well-supported IMP annotation reflecting GPA-12's core physiological role in antifungal defense. Supporting Evidence: PMID:22470487 When we crossed the Pcol-19::GPA-12* transgene into nipi-4(fr106) mutant, the elevated expression of the Pnlp-29::GFP reporter provoked by the active form of GPA-12 was abrogated |
| GO:0061760 antifungal innate immune response | IMP PMID:19380113 Antifungal innate immunity in C. elegans: PKCdelta links G p... | ACCEPT | Summary: Experimentally supported and the most specific immune process term for GPA-12. Epidermal antifungal innate immunity (nlp-29 induction) requires G protein signaling acting through PKCdelta and the p38 MAPK cascade, with GPA-12 as the Galpha subunit; this is the same activity modeled in the curated GO-CAM (gomodel:5b91dbd100002057). Reason: Core, well-supported immune process; most specific and informative BP term for this gene. Supporting Evidence: PMID:19380113 This involves G protein signaling and specific C-type phospholipases acting upstream of PKCdelta PMID:19380113 C. elegans PKC acts through the p38 MAPK pathway to regulate nlp-29 |
| GO:0005634 nucleus | IDA PMID:12646136 Hyperactivation of the G12-mediated signaling pathway in Cae... | KEEP AS NON CORE | Summary: WormBase IDA nuclear localization from PMID:12646136. Nuclear localization is unusual for a Galpha subunit, and the primary imaging data are in the full text, which is not in the cache (abstract-only). Per curation guidance I do not overrule an experimental IDA I cannot fully verify; I retain it as a non-core localization and defer to the WormBase curator. Reason: Experimental IDA from the curator (full text unavailable to verify); unusual for a Galpha and not a core function, but not to be removed on incomplete evidence. |
| GO:0005737 cytoplasm | IDA PMID:12646136 Hyperactivation of the G12-mediated signaling pathway in Cae... | ACCEPT | Summary: WormBase IDA cytoplasmic localization from PMID:12646136, consistent with the expected peripheral/cytoplasmic disposition of a membrane-associated Galpha subunit and with the IBA cytoplasm annotation. Accepted as the cellular compartment in which GPA-12 acts. Reason: Experimentally curated localization for a Galpha, corroborated by phylogenetic inference; accepted as GPA-12's cellular compartment of action. |
| GO:0050832 defense response to fungus | IMP PMID:19380113 Antifungal innate immunity in C. elegans: PKCdelta links G p... | ACCEPT | Summary: Experimentally supported core process (duplicate term with a distinct primary reference). GPA-12 is required for the epidermal antifungal defense response, as shown by its position upstream of PKCdelta and the p38 cascade controlling nlp-29 induction after fungal infection. Reason: Well-supported IMP annotation from the Ziegler et al. study; reinforces the core antifungal-defense role. Supporting Evidence: PMID:19380113 This involves G protein signaling and specific C-type phospholipases acting upstream of PKCdelta |
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Download this section (compressed HTML)What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The cognate receptor and activating input for GPA-12 are not biochemically defined. It is unknown which cell-surface receptor couples to GPA-12 to initiate epidermal immune signaling, what ligand/damage cue activates it, and whether GPA-12 engages such a receptor directly.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Established: GPA-12 is a Galpha-12/13 subunit that acts upstream of PKCdelta (TPA-1) and the p38 MAPK cascade to drive antimicrobial peptide expression after fungal infection and wounding, and its activity is required for this response. Unknown: the identity of the activating receptor and whether coupling is direct.
Significance: Identifying the receptor that switches on GPA-12 would define the sensing step of epidermal surveillance immunity and connect damage/infection detection to the p38/PMK-1 defense program.
Provenance (the field's own admissions):
Gap: The immediate downstream effector of GPA-12 is undetermined. Genetic epistasis places GPA-12 upstream of phospholipase (PLC-3) and PKCdelta (TPA-1), but it is not known whether GPA-12 directly activates a phospholipase, a RhoGEF/Rho module (the canonical mammalian Galpha-12/13 effector arm), or another target.
OPEN BIOLOGY MF_DARK
What is known: Established: GPA-12/G-protein signaling acts genetically upstream of C-type phospholipases and PKCdelta, and activated GPA-12 drives the p38-dependent antimicrobial peptide program. Unknown: the direct biochemical effector; the canonical G12/13 -> RhoGEF -> Rho arm has not been demonstrated in worm.
Significance: Whether worm GPA-12 signals through a Rho arm (like mammalian G12/13) or through a phospholipase/PKCdelta arm (more Gq-like) determines how this subfamily was wired into nematode epidermal immunity and would resolve an apparent divergence from the mammalian paradigm.
Provenance (the field's own admissions):
Gap: The full endogenous tissue and physiological repertoire of GPA-12 is unresolved. Its immune requirement is epidermis/cell-type restricted, and hyperactive G12 separately perturbs pharyngeal pumping/feeding and growth, but why the immune requirement is tissue-restricted and what other endogenous processes GPA-12 normally controls are not defined.
OPEN BIOLOGY BP_DARK
What is known: Established: active GPA-12 drives antimicrobial peptide expression in the epidermis and, when broadly hyperactivated, causes a growth arrest via a pharyngeal-pumping defect (with TPA-1 downstream); loss-of-function animals are viable. Unknown: the complete set of tissues/behaviors in which endogenous GPA-12 acts, and the basis of its tissue-restricted immune role.
Significance: Mapping GPA-12's endogenous functions would distinguish its dedicated immune role from its developmental/feeding role and clarify how one Galpha subunit is deployed across contexts.
Provenance (the field's own admissions):
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