TMEM127 suppresses tumor development by promoting RET ubiquitination, positioning, and degradation

The TMEM127 gene encodes a transmembrane protein of poorly known function that is mutated in pheochromocytomas, neural crest-derived tumors of adrenomedullary cells. Here, we report that, at single-nucleus resolution, TMEM127-mutant tumors share precursor cells and transcription regulatory elements with pheochromocytomas carrying mutations of the tyrosine kinase receptor RET. Additionally, TMEM127-mutant pheochromocytomas, human cells, and mouse knockout models of TMEM127 accumulate RET and increase its signaling. TMEM127 contributes to RET cellular positioning, trafficking, and lysosome-mediated degradation. Mechanistically, TMEM127 binds to RET and recruits the NEDD4 E3 ubiquitin ligase for RET ubiquitination and degradation via TMEM127 C-terminal PxxY motifs. Lastly, increased cell proliferation and tumor burden after TMEM127 loss can be reversed by selective RET inhibitors in vitro and in vivo. Our results define TMEM127 as a component of the ubiquitin system and identify aberrant RET stabilization as a likely mechanism through which TMEM127 loss-of-function mutations cause pheochromocytoma.

A RET::GRB2 fusion in pheochromocytoma defies the classic paradigm of RET oncogenic fusions

The RET kinase receptor is a target of mutations in neural crest tumors, including pheochromocytomas, and of oncogenic fusions in epithelial cancers. We report a RET::GRB2 fusion in a pheochromocytoma in which RET, functioning as the upstream partner, retains its kinase domain but loses critical C-terminal motifs and is fused to GRB2, a physiological RET interacting protein. RET::GRB2 is an oncogenic driver that leads to constitutive, ligand-independent RET signaling; has transforming capability dependent on RET catalytic function; and is sensitive to RET inhibitors. These observations highlight a new driver event in pheochromocytomas potentially amenable for RET-driven therapy.

Insights into Mechanisms of Pheochromocytomas and Paragangliomas Driven by Known or New Genetic Drivers

Simple Summary

Pheochromocytomas and paragangliomas are rare neuroendocrine tumors that are often hereditary. Although research has advanced considerably, significant gaps still persist in understanding risk factors, predicting metastatic potential and treating aggressive tumors. The study of rare mutations can provide new insights into how pheochromocytomas and paragangliomas develop. In this review, we provide examples of such rare events and how they can inform our understanding of the spectrum of mutations that can lead to these tumors and improve our ability to provide a genetic diagnosis.

Abstract

Pheochromocytomas and paragangliomas are rare tumors of neural crest origin. Their remarkable genetic diversity and high heritability have enabled discoveries of bona fide cancer driver genes with an impact on diagnosis and clinical management and have consistently shed light on new paradigms in cancer. In this review, we explore unique mechanisms of pheochromocytoma and paraganglioma initiation and management by drawing from recent examples involving rare mutations of hypoxia-related genes VHL, EPAS1 and SDHB, and of a poorly known susceptibility gene, TMEM127. These models expand our ability to predict variant pathogenicity, inform new functional domains, recognize environmental-gene connections, and highlight persistent therapeutic challenges for tumors with aggressive behavior.