Aguiar, R. C. T. | Search bioRxiv

bioRxiv2026

The transmembrane protein TMEM127 regulates activation and fate of an MHC-I degradation complex by WWP2 modifications

TMEM127 is an adaptor protein that bridges substrates to E3 ubiquitin ligases of the HECT family. Among its interacting partners is the major histocompatibility class I (MHC-I), a critical component of the antigen presentation pathway and the adaptive immune response. MHC-I is ubiquitinated and fated for lysosome-mediated degradation by the WWP2 E3 ligase in a complex that involves TMEM127 and a second adaptor protein, SUSD6. However, the interacting dynamics among complex components remains to be determined, a key knowledge gap towards the development of pharmacological modulators. Here, using in vitro and in vivo models, we report that TMEM127-WWP2 interaction stabilizes the MHC-I degradation complex and reveals an asymmetric role of the two adaptor proteins. Specifically, we find that TMEM127 regulates WWP2 catalytic activity, abundance and localization through its canonical PY motif interaction with the WW domain of WWP2 with contribution of a TMEM127 endocytic motif, providing a mechanism to restrain complex activity. Further, we validate the impact of TMEM127 dosage in the endogenous complex assembly and regulation. Our results nominate TMEM127 as a critical member of the MHC-I degradation complex and highlight the TMEM127-WWP2 interaction as a target for augmenting MHC-I-mediated antigen presentation, a long sought goal in cancer immunology.

molecular biology↗

bioRxiv2020

Functional characterization of germline variants in the TMEM127 tumor suppressor reveals novel insights into its membrane topology and trafficking

PurposeTo better understand the function of the transmembrane protein TMEM127, a poorly known tumor suppressor gene associated with pheochromocytomas, paragangliomas and renal carcinomas, we evaluated patient-derived germline variants. MethodsSubcellular localization and steady-state levels of 21 tumor-associated, transiently expressed TMEM127 variants were compared to the wild-type protein using immunofluorescence and immunoblot analysis, respectively, in cells genetically modified to lack endogenous TMEM127. Membrane topology and endocytic mechanisms were also assessed. ResultsWe identified three subgroups of mutations and determined that 15 of the 21 variants (71%), including 9 of 15 missense variants (60%), are pathogenic or likely pathogenic, through loss of membrane binding ability, stability and/or internalization capability. Investigation into an N-terminal cluster of missense variants uncovered a previously unrecognized transmembrane domain, indicating that TMEM127 is a four-, not a three-, transmembrane domain-containing protein. Additionally, a C-terminal variant with predominant plasma membrane localization revealed an atypical, extended acidic, dileucine-based motif required for TMEM127 internalization through clathrin-mediated endocytosis. ConclusionWe characterized the functional deficits of several germline TMEM127 variants and identified novel structure-function features of TMEM127, namely, a fourth transmembrane domain and an endocytic motif. These findings will assist in TMEM127 variant interpretation and will help guide future studies investigating the cellular role of TMEM127.

genetics↗