RASA4

RASA4 (CAPRI) is a Ca2+-dependent Ras GTPase-activating protein that couples elevated intracellular Ca2+ to inactivation of the Ras-MAPK pathway (PMID:11448776). Following stimuli that raise cytosolic Ca2+, its C2 domain drives fast translocation to the plasma membrane, where it accelerates GTP hydrolysis on Ras (PMID:11448776); sustained recruitment then becomes largely Ca2+-independent and depends on integration of the C2 domains with agonist-evoked PH-domain interaction sites, allowing different Ca2+ stimulus intensities to be converted into different durations of Ras activity (PMID:16009725). Ca2+ at physiological concentrations also drives homodimerization through a C-terminal hydrophobic helix, and this switches catalytic preference: monomeric RASA4 acts more strongly as a RasGAP while the dimer acts more strongly as a RapGAP, coordinating regulation of both Ras and Rap1 (PMID:21460216). In mast cells, this membrane translocation terminates the early phase of ERK2 activation and suppresses antigen-induced degranulation and cytokine production, with a GAP-domain mutant abolishing both translocation and suppression (PMID:16815298). In triple-negative breast cancer cells, Ca2+ influx through TRPC3 sustains plasma-membrane RASA4 to restrain MAPK signaling, proliferation, and apoptosis resistance (PMID:31003514). Isoform-specific promoter hypermethylation silences RASA4 in juvenile myelomonocytic leukemia, consistent with loss of its Ras-suppressive function in disease (PMID:25147919).

1. 2001 High

   Established RASA4/CAPRI as the molecular link between Ca2+ signals and Ras inactivation, defining how Ca2+ feeds back onto the Ras-MAPK pathway.

   Evidence Live-cell imaging of translocation, in vivo Ras activity assays, and C2 domain mutants

   PMID:11448776

   Open questions at the time

   • Did not resolve how membrane retention is sustained beyond the initial Ca2+ spike
   • Catalytic preference between Ras and Rap not addressed
2. 2005 High

   Showed RASA4 acts as a low-pass filter that translates Ca2+ stimulus intensity into Ras-activity duration, distinguishing it from oscillation-tracking relatives.

   Evidence FRET-based real-time Ras activity assay, live-cell imaging, and domain mutant analysis of Ca2+-dependent versus PH-dependent recruitment

   PMID:16009725

   Open questions at the time

   • Identity of the agonist-evoked PH-domain membrane interaction sites not defined
   • Whether filtering behavior holds in physiological cell types untested
3. 2006 Medium

   Demonstrated a cellular consequence of RASA4 action by showing it terminates early ERK2 activation and suppresses mast cell effector responses, tying membrane translocation to function.

   Evidence Overexpression and GAP-domain point mutant (R472S) in RBL mast cells with degranulation, cytokine, ERK2 localization, and Ca2+ readouts

   PMID:16815298

   Open questions at the time

   • Based on overexpression rather than endogenous loss-of-function
   • Single cell line and lab
4. 2011 High

   Resolved how a single GAP regulates two GTPases by showing Ca2+-driven dimerization switches catalytic preference between RasGAP and RapGAP activity.

   Evidence Reciprocal Co-IP, deletion/point mutagenesis of a C-terminal hydrophobic helix, and in vivo GAP assays for Ras and Rap1 with histamine stimulation

   PMID:21460216

   Open questions at the time

   • No structural model of the dimer interface
   • Downstream consequences of Rap1 regulation not characterized
5. 2014 Medium

   Connected RASA4 to malignant Ras dysregulation by identifying isoform-specific promoter hypermethylation as a silencing mechanism in JMML.

   Evidence Quantitative mass spectrometry-based DNA methylation profiling in 125 patients with genetic correlations

   PMID:25147919

   Open questions at the time

   • No functional rescue confirming silencing drives Ras activation
   • Causality versus correlation with PTPN11 mutation and monosomy 7 not established
6. 2019 Medium

   Defined an upstream channel input by showing TRPC3-mediated Ca2+ influx sustains plasma-membrane RASA4 to restrain MAPK-driven proliferation in breast cancer.

   Evidence Subcellular fractionation, immunocytochemistry, TRPC3 pharmacological and dominant-negative inhibition, with proliferation and apoptosis assays

   PMID:31003514

   Open questions at the time

   • Direct molecular link between TRPC3 and RASA4 retention not shown
   • Single cell line
7. 2021 Medium

   Implicated RASA4 in host-pathogen signaling by linking its upregulation to cytoskeletal and matrix remodeling in periodontal fibroblasts.

   Evidence mRNA quantification and functional assays (actin dynamics, adhesion, MMP-2 activity) on T. denticola/dentilisin-infected primary PDL cells

   PMID:34094999

   Open questions at the time

   • mRNA-level only without protein knockdown rescue
   • GAP activity not directly linked to actin/MMP-2 phenotype

• A structural basis for the dimerization-driven RasGAP-to-RapGAP switch and how it is coordinated with Ca2+- and PH-dependent membrane retention across cell types remains undefined.
• No structure of monomeric versus dimeric RASA4
• Physiological balance of Ras versus Rap1 regulation in vivo unknown
• Endogenous loss-of-function phenotypes largely uncharacterized