Munawar, S. Y. | 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↗

bioRxiv2025

Patient-derived organoids reveal hypoxia-driven plasticity and therapeutic vulnerabilities in pheochromocytomas and paragangliomas

Pheochromocytomas and paragangliomas (PPGLs) are rare chromaffin cell-derived neuroendocrine tumors of sympathetic (catecholamine-producing) or parasympathetic (nonsecretory) origin, frequently driven by dysregulation of hypoxia-inducible factor (HIF) signaling, particularly HIF-2. Although often benign, PPGLs can metastasize unpredictably, with limited therapeutic options once disseminated. Progress has been hindered by the lack of robust preclinical models, especially those that capture their molecular complexity and microenvironmental influences. To address this gap, we established patient-derived tumor organoids (PDOs) from 35 PPGLs, encompassing a broad spectrum of clinical and molecular phenotypes. The organoids retained key immunohistochemical, genomic, transcriptomic, and catecholamine-secretory features of their parental tumors. PPGL organoids cultured under hypoxic conditions generally exhibited enhanced viability, supporting hypoxia as a driver of cell survival. Hypoxia activated HIF-1 and expanded ASCL1+ cell populations, suggesting a lineage shift toward an immature chromaffin state. In contrast, long-term normoxic cultures activated hypoxia inducible factor 2 (HIF-2) and acquired a hybrid sympathoblast-mesenchymal identity in subpopulations with upregulation of extracellular matrix and cell cycle markers, independent of genotype. These features resemble high-risk neuroblastoma subtypes and establish a molecular parallel suggestive of shared lineage plasticity and pathogenic programs, detectable in primary PPGLs. Drug screening across a library of up to 51 drugs and combinations revealed both shared and unique vulnerabilities, with response rates to approved therapies matching clinical observations. The CDK4/6 inhibitor abemaciclib, previously unexplored in PPGLs, elicited the strongest activity. Abemaciclib-responsive PDOs and their matched tumors, including a metastatic sample, exhibited epithelial mesenchyme transition enrichment, nominating potential biomarkers for patient stratification. Our results establish PDOs as a novel platform for modeling neuroendocrine tumor biology, reveal microenvironment-driven plasticity in PPGLs, with potential translational relevance, and identify actionable vulnerabilities in a disease with few effective systemic therapies. Main findingsO_LIPDOs can be successfully generated from PPGLs of various genetic backgrounds and reflect parental tumor properties C_LIO_LIPDO cultures grown in hypoxia retain main molecular features of parental tumors, have increased viability and a more immature developmental/biosynthetic profile C_LIO_LILong term PDOs grown for 4 weeks in normoxia activate HIF2, drift toward a hybrid sympathoblast-mesenchymal-like identity resembling relapsed/therapy resistant neuroblastomas, features that can be detected in primary tumors C_LIO_LIA subset of PDOs respond to Abemaciclib, a drug class not previously used therapeutically in PPGLs C_LI

cancer biology↗