Jaafar, C. | bioRxiv Science

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↗

bioRxiv2023

IRF8-mutant B cell lymphoma evades immunity through a CD74-dependent deregulation of antigen processing and presentation in MHC CII complexes

In diffuse large B-cell lymphoma (DLBCL), the transcription factor IRF8 is the target of a series of potentially oncogenic events, including, chromosomal translocation, focal amplification, and super-enhancer perturbations. IRF8 is also frequently mutant in DLBCL, but how these variants contribute to lymphomagenesis is unknown. We modeled IRF8 mutations in DLBCL and found that they did not meaningfully impact cell fitness. Instead, IRF8 mutants, mapping either to the DNA-binding domain (DBD) or c-terminal tail, displayed diminished transcription activity towards CIITA, a direct IRF8 target. In primary DLBCL, IRF8 mutations were mutually exclusive with mutations in genes involved in antigen presentation. Concordantly, expression of IRF8 mutants in murine B cell lymphomas uniformly suppressed CD4, but not CD8, activation elicited by antigen presentation. Unexpectedly, IRF8 mutation did not modify MHC CII expression on the cell surface, rather it downmodulated CD74 and HLA- DM, intracellular regulators of antigen peptide processing/loading in the MHC CII complex. These changes were functionally relevant as, in comparison to IRF8 WT, mice harboring IRF8 mutant lymphomas displayed a significantly higher tumor burden, in association with a substantial remodeling of the tumor microenvironment (TME), typified by depletion of CD4, CD8, Th1 and NK cells, and increase in T-regs and Tfh cells. Importantly, the clinical and immune phenotypes of IRF8-mutant lymphomas were rescued in vivo by ectopic expression of CD74. Deconvolution of bulk RNAseq data from primary human DLBCL recapitulated part of the immune remodeling detected in mice and pointed to depletion of dendritic cells as another feature of IRF8 mutant TME. We concluded that IRF8 mutations contribute to DLBCL biology by facilitating immune escape.

cancer biology↗