RHBDF1

RHBDF1 (iRhom1) is a catalytically inactive rhomboid pseudoprotease that functions as a central regulatory cofactor of ADAM17 and an integrator of ER proteostasis. Its transmembrane helix and a conserved cytoplasmic re-entry loop form a molecular relay—resolved by cryo-EM—that promotes ADAM17 maturation, ER-to-surface trafficking, and sheddase activation, controlling release of EGFR ligands (TGF-α), TNF receptors, and neuronal substrates such as MEGF10, while its extended N-terminal cytoplasmic domain negatively tunes ADAM17 activity (PMID:15965977, PMID:26535007, PMID:34613632, PMID:42024498). Beyond ADAM17 regulation, RHBDF1 maintains ER homeostasis by stabilizing the chaperone BiP and by promoting proteasome assembly through interaction with PAC1/PAC2, and it modulates glycolysis by competitively shielding GPI from TRIM32-mediated ubiquitination (PMID:26109405, PMID:37798352, PMID:37979663). RHBDF1 additionally facilitates PKCζ nuclear import via importin β1, disrupting the Par apicobasal polarity complex and tight/adherens junctions in epithelial cells (PMID:39582014).

1. 2005 High

   Identification of RHBDF1 as a catalytically dead, ER/Golgi-resident rhomboid-family protein that dimerizes and physically engages TGF-α established the gene as a pseudoprotease with a potential role in EGFR ligand processing.

   Evidence cDNA cloning, subcellular fractionation, co-immunoprecipitation, active-site sequence analysis, and Drosophila functional assay

   PMID:15965977

   Open questions at the time

   • Whether RHBDF1 promotes TGF-α shedding or only intracellular trafficking was unresolved
   • Identity of the metalloprotease partner was unknown
   • No structure of the RHBDF1 transmembrane domain
2. 2008 High

   Demonstrating that RHBDF1 is required for GPCR-induced TGF-α shedding and subsequent EGFR transactivation positioned it as a specific gatekeeper of ligand release rather than ligand production.

   Evidence siRNA knockdown and overexpression in cells with EGFR/MAPK/AKT phosphorylation readouts and TGF-α secretion assays

   PMID:18832597

   Open questions at the time

   • The shedding enzyme mediating TGF-α release downstream of RHBDF1 was not identified
   • Whether RHBDF1 acts at the ER or at the cell surface was unclear
3. 2015 High

   Linking RHBDF1 directly to ADAM17 maturation and showing that the N-terminal cytoplasmic domain is an inhibitory module unified prior observations into a model where iRhom1 is an essential ADAM17 regulatory subunit, while the parallel discovery of PAC1/PAC2 interaction revealed an ADAM17-independent role in ER-stress-induced proteasome assembly.

   Evidence ΔN-mutant genetic screen with ADAM17 inhibitor rescue and TNFR shedding assays; genome-wide cDNA screen with co-IP, native-gel proteasome analysis, and Drosophila rescue

   PMID:26109405 PMID:26535007

   Open questions at the time

   • Structural basis of the iRhom1–ADAM17 interaction was unknown
   • Whether proteasome-stimulatory and ADAM17-regulatory functions are coordinated was untested
   • Redundancy with iRhom2 complicated tissue-specific loss-of-function interpretation
4. 2020 Medium

   Showing that endogenous iRhom1 reaches the cell surface and that its stability is ADAM17-independent (unlike iRhom2) clarified that iRhom1 has autonomous functions and distinct regulation from its paralog; transcriptional induction by shear stress via KLF2 placed it in vascular mechano-sensing.

   Evidence Cell-surface biotinylation in ADAM17-KO MEFs; primary endothelial cells under shear stress with qPCR and ADAM17 maturation assays

   PMID:32060096 PMID:33335915

   Open questions at the time

   • Both findings from single laboratories, awaiting independent replication
   • Function of surface-localized iRhom1 pool was not determined
   • Downstream vascular phenotype of iRhom1 loss in shear-stress context was unexplored
5. 2021 High

   In vivo secretome profiling of iRhom1-knockout mouse neurons identified MEGF10 as a physiological, nervous-system-specific ADAM17 substrate controlled by iRhom1, extending its functional scope beyond EGFR ligands.

   Evidence iRhom1-KO mouse model with hiSPECS secretome proteomics, CSF proteomics, and ADAM17-KO MEF validation

   PMID:34613632

   Open questions at the time

   • Functional consequence of reduced MEGF10 shedding in the CNS was not addressed
   • Full catalogue of iRhom1-specific versus iRhom2-dependent substrates in vivo remains incomplete
6. 2022 Medium

   Discovery of the alternative splice variant RHX6 that antagonizes RHBDF1 by blocking ADAM17 maturation and TGF-α trafficking revealed a built-in post-transcriptional brake on iRhom1 function, regulated by the splicing factor RBM4.

   Evidence Overexpression of RHX6 splicing variant with TACE maturation, pro-TGF-α trafficking, and proliferation/migration assays; RBM4 knockdown

   PMID:35595096

   Open questions at the time

   • Physiological tissue contexts where RHX6 predominates are not defined
   • Mechanism by which RHX6 interferes with ADAM17 at the molecular level is not resolved
7. 2023 Medium

   Two ADAM17-independent functions were delineated: RHBDF1 stabilizes BiP to maintain ER protein homeostasis, and it competitively shields GPI from TRIM32-mediated K27/K63 ubiquitination to sustain glycolysis, broadening its role to metabolic and proteostasis regulation.

   Evidence Co-IP and SPR for BiP binding with RHBDF1-KO unfolded protein aggregation assay; co-IP, ubiquitination assays, mutagenesis (R747, Y799), and in vivo mouse melanoma model for TRIM32/GPI axis

   PMID:37798352 PMID:37979663

   Open questions at the time

   • BiP interaction and TRIM32 competition each demonstrated in single labs
   • Whether these functions depend on iRhom1 pseudoprotease fold or only its transmembrane domain is unknown
   • Relative importance of ADAM17-dependent versus -independent functions in normal tissue physiology is unclear
8. 2024 Medium

   Identification of RHBDF1 as a facilitator of PKCζ nuclear translocation via importin β1, leading to disruption of apicobasal polarity, provided a mechanistic route linking RHBDF1 to epithelial-to-mesenchymal transition-like phenotypes.

   Evidence Co-IP of RHBDF1 with importin β1 and PKCζ, nuclear fractionation, PKCζ inhibitor rescue, and polarity/junction marker analysis in mammary epithelial cells

   PMID:39582014

   Open questions at the time

   • Single-lab study; independent confirmation needed
   • Whether PKCζ transport function is separable from ADAM17 regulatory function is unknown
   • In vivo relevance for mammary tissue polarity not demonstrated
9. 2026 High

   The cryo-EM structure of the ADAM17 zymogen–iRhom1 complex revealed the transmembrane helix and cytoplasmic re-entry loop as a signal relay, and a cardiomyopathy-associated human iRhom1 mutation that disrupts ADAM17 maturation linked the structural mechanism to human disease.

   Evidence Cryo-EM structure determination, all-atom MD simulations, disease-associated mutant analysis of ADAM17 maturation/trafficking

   PMID:42024498

   Open questions at the time

   • Full-length structure including the N-terminal inhibitory domain is lacking
   • Structural basis for iRhom1-specific versus iRhom2-specific substrate selectivity remains unresolved
   • Whether the cardiomyopathy phenotype is solely ADAM17-dependent or involves other iRhom1 partners is not established

• How iRhom1 coordinates its multiple partner interactions (ADAM17, BiP, PAC1/PAC2, TRIM32/GPI, importin β1/PKCζ) spatiotemporally within the ER and beyond, and which functions dominate in specific tissues, remains an open question.
• No integrative study has examined all iRhom1 functions in a single model system
• Full-length iRhom1 structure including the disordered N-terminal domain is needed
• Conditional tissue-specific knockout phenotyping beyond the nervous system is limited