DEPTOR suppresses lymphomagenesis by promoting EGFR degradation via HUWE1 E3 ligase

Abstract

DEPTOR, a naturally occurring inhibitor of mTOR, plays crucial roles in tumorigenesis and is frequently dysregulated in a variety of human cancers. Interestingly, DEPTOR could act either as a tumor suppressor or as an oncogene in a manner dependent of cellular context or tissue environment. Whether and how DEPTOR regulates lymphomagenesis remains elusive. In this study, we report that in a mouse lymphoma model induced by heterozygous Pten loss, Deptor knockout (KO) markedly accelerates lymphomagenesis, whereas degradation-resistant Deptor^S275A knock-in (KI) variant significantly inhibits it. Furthermore, Deptor KO mice spontaneously developed lymphomas in the later stages of their lifespan, and Deptor KO further shortened overall lifespan in Pten^fl/fl;MMTV-Cre mice. Consistently, DEPTOR protein levels are significantly lower in human lymphoma tissues, as compared to normal lymph nodes. Mechanistically, DEPTOR, on one hand, enhances the interaction of EGFR to HUWE1 E3 ubiquitin ligase for targeted ubiquitination and proteasomal degradation, and subsequent inactivation of the MAPK signal. On the other hand, DEPTOR inactivates both mTORC1 and mTORC2 signals. Collectively, our study demonstrated that DEPTOR is a tumor suppressor that inhibits lymphomagenesis upon Pten-loss. The strategy that reactivates DEPTOR could be a promising approach for the treatment of lymphoma.