RASSF4

RASSF4 is a GTP-dependent Ras effector and context-dependent tumor suppressor that couples RAS signaling to pro-apoptotic and growth-suppressive outputs (PMID:15574778). It binds activated K-Ras through its effector domain and induces Ras-dependent apoptosis, and its expression is frequently silenced in tumors by promoter hypermethylation (PMID:15574778, PMID:15375500). A central effector arm is the Hippo pathway: RASSF4 associates with the kinase MST1 and inhibits nuclear translocation of YAP, restraining the YAP/TEAD4/Bcl-2 axis to suppress proliferation and survival in colorectal cancer, and limiting hepatic steatosis, fibrosis, and hepatocellular carcinoma in vivo (PMID:29259009, PMID:38697356, PMID:35611809). RASSF4 additionally links RAS to the pro-death MST1/JNK/p38 kinases, driving G2 arrest and apoptosis (PMID:29259009), and stabilizes p53 via Chk2 activation under genotoxic stress to enforce tumor suppression (PMID:40259805). Beyond its kinase-scaffolding role, RASSF4 controls plasma-membrane phosphoinositide signaling by interacting with the small GTPase ARF6 and, together with PIP5KIγ, raising PI(4,5)P2 levels to promote STIM1 recruitment to ER-PM junctions and accelerate store-operated Ca2+ entry (PMID:28600435, PMID:31831523). RASSF4 is also required for early skeletal muscle differentiation, where it co-localizes with MTOC proteins and acts through MST1 (PMID:31508857), and it physically associates with the PKD2 ion channel to enhance channel activity by promoting the PKD2 N-C terminal intramolecular interaction while suppressing RAS/MAPK signaling (PMID:42141135).

1. 2004 Medium

   Established RASSF4 as a bona fide Ras effector by showing direct GTP-dependent binding to activated K-Ras and a pro-apoptotic function, answering whether this RASSF-family member engages active RAS at all.

   Evidence GTP-dependent pulldown binding assay and overexpression apoptosis readout in 293-T cells

   PMID:15574778

   Open questions at the time

   • Effector-domain residues mediating K-Ras binding not mapped
   • Downstream apoptotic machinery not defined at this stage
2. 2004 Medium

   Showed RASSF4 is epigenetically silenced in tumors, framing it as a candidate tumor suppressor whose loss is selected for in cancer.

   Evidence Bisulfite sequencing and demethylating-agent rescue with RT-PCR across tumor cell lines

   PMID:15375500 PMID:15574778

   Open questions at the time

   • Causal link between silencing and tumorigenesis not demonstrated in primary tumors
   • Which downstream pathway loss drives the phenotype unresolved
3. 2017 High

   Revealed an unexpected non-apoptotic role in membrane Ca2+ signaling, showing RASSF4 governs STIM1 translocation and ER-PM junction tethering and acts via ARF6 to control PI(4,5)P2.

   Evidence RASSF4 knockdown with live-cell STIM1 imaging, ER-PM junction and E-Syt tethering assays, ARF6 activity assays and PI(4,5)P2 measurement

   PMID:28600435

   Open questions at the time

   • Direct vs indirect nature of RASSF4-ARF6 regulation not fully dissected
   • Connection between Ca2+ signaling role and tumor suppression unclear
4. 2017 Medium

   Connected RASSF4 to pro-death kinase cascades, demonstrating it activates MST1, JNK, and p38 to enforce G2 arrest and apoptosis, defining the effector kinases downstream of RASSF4.

   Evidence Overexpression with kinome analysis, Western blot kinase activation, flow cytometry and in vivo confirmation in multiple myeloma

   PMID:29259009

   Open questions at the time

   • Order of MST1 vs JNK/p38 activation not established
   • Whether RAS binding is required for kinase activation not tested
5. 2019 Medium

   Extended RASSF4 function to developmental biology, showing it is required for myoblast differentiation and acts through MST1 at the MTOC.

   Evidence siRNA knockdown differentiation assay, immunofluorescence co-localization, RASSF4-MST1 Co-IP and MST1 rescue

   PMID:31508857

   Open questions at the time

   • Mechanism linking MTOC localization to myogenin induction unknown
   • Partial rescue indicates MST1-independent contributions remain
6. 2020 Medium

   Refined the membrane-Ca2+ mechanism by showing RASSF4 requires PIP5KIγ co-expression to raise PI(4,5)P2 and accelerate STIM1 mobilization, establishing it as a lipid-kinase cofactor rather than an autonomous PI(4,5)P2 producer.

   Evidence Mass spectrometry phosphoinositide quantification, KCNQ2/3 and PH-domain biosensor readouts, SOCE and STIM1 proximity imaging

   PMID:31831523

   Open questions at the time

   • Structural basis of RASSF4-PIP5KIγ functional cooperation unknown
   • Whether ARF6 and PIP5KIγ act in one continuous pathway not resolved
7. 2022 Medium

   Placed RASSF4 epistatically upstream of the YAP/TEAD4/Bcl-2 survival axis, showing YAP knockdown abolishes RASSF4 suppression of Bcl-2.

   Evidence Western blot, YAP-knockdown rescue, and ChIP for TEAD4 binding at the Bcl-2 promoter in colorectal cancer cells

   PMID:35611809

   Open questions at the time

   • Direct RASSF4-MST1-LATS-YAP biochemistry not reconstituted here
   • Generality beyond colorectal context untested in this study
8. 2024 Medium

   Provided in vivo genetic evidence that hepatocyte RASSF4-MST1 restrains YAP to suppress liver disease, and identified a paracrine TGF-β arm acting on stellate cells.

   Evidence RASSF4 knockout and overexpression mouse models, RASSF4-MST1 Co-IP, YAP localization Western blot, histopathology

   PMID:38697356

   Open questions at the time

   • How RASSF4 controls TGF-β secretion mechanistically unknown
   • Relative contribution of cell-autonomous vs paracrine effects not quantified
9. 2025 Medium

   Identified a Chk2-p53 stabilization arm, showing RASSF4 is induced by genotoxic stress and requires both Chk2 and p53 for its apoptotic and tumor-suppressive function.

   Evidence Cycloheximide chase, promoter reporter, immunoprecipitation, Chk2/p53 depletion epistasis, gastric xenograft

   PMID:40259805

   Open questions at the time

   • Whether RASSF4 directly activates Chk2 or acts indirectly unresolved
   • Integration with the parallel MST1/Hippo arm not defined
10. 2026 High

    Demonstrated a direct ion-channel regulatory function, showing RASSF4 binds PKD2 and enhances its activity by promoting the PKD2 N-C terminal intramolecular interaction while suppressing RAS/MAPK signaling.

    Evidence Proximity labeling/MS, Co-IP, BiFC, in vitro binding, two-electrode voltage clamp in oocytes, zebrafish rescue, and a blocking peptide (P134-S168)

    PMID:42141135

    Open questions at the time

    • Structural detail of the RASSF4-PKD2 interface beyond the P134-S168 region unknown
    • Whether channel regulation and tumor-suppressor functions share a common mechanism unresolved

• How RASSF4's distinct effector arms — Hippo/MST1-YAP, Chk2-p53, ARF6-PIP5K-SOCE, and PKD2 channel regulation — are integrated or selected in a given cell context, and which require K-Ras binding, remains unresolved.
• No unified model linking RAS binding to choice of downstream arm
• Tissue-specific determinants of which pathway dominates unknown
• No structural model of RASSF4 domain organization across functions