RHBDD1

RHBDD1 is an ER-resident rhomboid-family serine protease that controls cell fate by cleaving transmembrane substrates and, in cancer, by potentiating growth-signaling pathways (PMID:18953687, PMID:37954160). Its proteolytic activity depends on the catalytic residues Gly142 and Ser144, which it uses to cleave the pro-apoptotic Bcl-2 protein BIK within its transmembrane region, thereby restraining BIK-driven apoptosis (PMID:18953687). The same activity cleaves the multi-pass membrane protein TSAP6 in its third transmembrane domain, and loss of RHBDD1 elevates non-classical exosome secretion in a TSAP6-dependent manner (PMID:22624035). RHBDD1 (also designated RHBDL4) further cleaves the lipogenic transcription factor SREBP-1c at the ER, with the residual membrane-embedded fragment extracted by the p97/VCP complex; this cleavage is enhanced by saturated fatty acids and inhibited by polyunsaturated fatty acids, and its genetic deletion in mice blunts SREBP-1c-driven lipogenic gene induction (PMID:37954160). Beyond direct proteolysis, RHBDD1 acts as a pro-tumorigenic regulator across multiple carcinomas: it physically associates with EGFR and drives c-Jun/AP-1-dependent EGFR transcription and EGFR/PI3K/AKT signaling (PMID:28445956, PMID:41759697), and it activates Wnt/β-catenin signaling through β-catenin Ser552/Ser675 phosphorylation while inducing ZEB1 to promote EMT and invasion (PMID:29426364, PMID:33515112). In TP53-mutant cells RHBDD1 promotes ERAD-dependent degradation of mutant p53 and DNA-PKcs, producing S-phase arrest while suppressing apoptosis to favor survival (PMID:41013641).

1. 2008 High

   Established RHBDD1 as a catalytically active rhomboid protease and identified its first substrate, linking it to apoptotic control.

   Evidence In vitro cleavage assay with active-site mutagenesis (G142, S144) and gain/loss-of-function apoptosis readout in HEK293T cells

   PMID:18953687

   Open questions at the time

   • Physiological context of BIK cleavage in tissues not defined
   • No structural model of the protease-substrate interaction
2. 2012 High

   Showed RHBDD1 cleaves a second transmembrane substrate (TSAP6) and thereby restrains non-classical exosome secretion, broadening its substrate repertoire and physiological output.

   Evidence In vitro proteolysis, MS-mapped cleavage site, endogenous genetic inactivation, and TSAP6-knockdown epistasis with exosome quantification in colon cancer cells

   PMID:22624035

   Open questions at the time

   • Functional consequence of altered exosome flux in vivo unresolved
   • Whether TSAP6 cleavage is regulated remains unknown
3. 2013 Low

   Implicated RHBDD1 as required for cell cycle progression in glioblastoma, the first link to a proliferative phenotype.

   Evidence Lentiviral shRNA knockdown with proliferation, colony formation, and cell cycle assays in U251/U87MG cells

   PMID:23883433

   Open questions at the time

   • No molecular mechanism or pathway placement identified
   • Single lab, descriptive phenotype only
4. 2017 Medium

   Defined a non-proteolytic transcriptional axis whereby RHBDD1 drives EGFR expression through c-Jun/AP-1 in colorectal cancer.

   Evidence Knockdown/inactivation with c-Jun overexpression and knockdown rescue, western blot, tumor models, tissue microarray

   PMID:28445956

   Open questions at the time

   • Whether protease activity is needed for AP-1/EGFR regulation not tested
   • Direct molecular link between RHBDD1 and c-Jun unclear
5. 2018 Medium

   Connected RHBDD1 to Wnt/β-catenin signaling and EMT via β-catenin phosphorylation and ZEB1 induction, explaining its pro-metastatic role.

   Evidence RNA-seq, TOP/FOP reporter, phospho-β-catenin western blot, phosphorylation rescue, Transwell and in vivo pleural metastasis

   PMID:29426364

   Open questions at the time

   • Kinase mediating β-catenin Ser552/Ser675 phosphorylation not identified
   • Mechanism linking protease to Wnt activation unresolved
6. 2021 Medium

   Extended the RHBDD1–ZEB1 and EGFR/AKT oncogenic axes to NSCLC and renal cell carcinoma, indicating these signaling roles generalize across tumor types.

   Evidence RNAi knockdown with ZEB1/AKT and gefitinib pharmacological rescue, phospho-signaling western blots, proliferation/invasion assays in NSCLC and RCC cells

   PMID:33515112 PMID:34581421

   Open questions at the time

   • Direct versus indirect engagement of EGFR/AKT not distinguished
   • No in vitro enzymatic or structural data in these contexts
7. 2023 High

   Identified SREBP-1c as a metabolically regulated substrate cleaved at the ER, with fatty acids tuning protease activity and p97/VCP completing membrane extraction, establishing RHBDD1 as a lipogenic regulator.

   Evidence In vitro cleavage, knockout mice on Western diet, lipogenic gene expression analysis, biochemical fractionation/p97 complex analysis

   PMID:37954160

   Open questions at the time

   • Molecular basis of fatty-acid sensing by the protease not defined
   • Relationship between metabolic and oncogenic functions unexplored
8. 2025 Medium

   Showed RHBDD1 directs ERAD of mutant p53 and DNA-PKcs in TP53-mutant cells, coupling its activity to cell cycle arrest and apoptosis suppression for survival.

   Evidence shRNA/overexpression in TP53-mutant vs wild-type NSCLC, immunofluorescence co-localization, ER stress markers, flow cytometry, pharmacological rescue with p53 activators and DNA-PKcs inhibitor

   PMID:41013641

   Open questions at the time

   • No in vitro reconstitution of RHBDD1-mediated ERAD of p53/DNA-PKcs
   • Direct versus indirect substrate engagement unresolved
9. 2026 Medium

   Demonstrated a direct physical RHBDD1–EGFR association driving EGFR/PI3K/AKT-dependent oncogenicity in cervical cancer, reinforcing EGFR as a recurring effector.

   Evidence Co-immunoprecipitation, knockdown/overexpression, pharmacological epistasis (gefitinib, LY294002, SC79), western blot, xenograft model

   PMID:41759697

   Open questions at the time

   • Whether EGFR is a proteolytic substrate or scaffold partner not determined
   • Reciprocal/structural validation of the interaction lacking

• How RHBDD1's catalytic proteolytic activity mechanistically connects to its many downstream signaling outputs (EGFR, Wnt, PI3K/AKT, ERAD) remains unresolved.
• No structural model of substrate recognition
• Unclear which signaling roles require catalytic activity versus scaffolding
• Integration of metabolic and oncogenic functions undefined