Targeting Cullin-RING ligases by MLN4924 induces autophagy via modulating the HIF1-REDD1-TSC1-mTORC1-DEPTOR axis

Y Zhao,Y Sun,X Xiong,L Jia

doi:10.1038/cddis.2012.125

Abstract

MLN4924, a newly discovered small molecule inhibitor of NEDD8-activating enzyme (NAE), inactivates Cullin-RING E3 ubiquitin Ligases (CRLs) by blocking cullin neddylation. As a result, MLN4924 causes accumulation of several key substrates of CRLs and effectively suppresses tumor cell growth by inducing apoptosis and senescence. However, the role of MLN4924 in induction of autophagy and its biological significance are totally unknown. Here we showed that MLN4924 effectively induces autophagy in both time- and dose-dependent manners in multiple human cancer lines, indicating a general phenomenon. Mechanistically, by inactivating CRLs, MLN4924 causes accumulation of DEPTOR and HIF1α. The siRNA knockdown and gene KO studies showed that DEPTOR and the HIF1-REDD1-TSC1 axis are responsible for MLN4924-induced autophagy via inhibiting mTORC1. Biologically, autophagy is a survival signal to tumor cells, and blockage of autophagy via siRNA knockdown, gene KO and small molecule inhibitor remarkably enhanced MLN4924-induced apoptosis. Our study reveals an uncharacterized mechanism of MLN4924 action and provides the proof-of-concept evidence for strategic drug combination of MLN4924 with an autophagy inhibitor for maximal killing of tumor cells via enhancing apoptosis.

Highlights

IntroductionSKP1 and an F-box protein at the N-terminus, and a RING protein, RBX1 or RBX2 ( known as ROC2 or SAG) at the
SKP1 and an F-box protein at the N-terminus, and a RING protein, RBX1 or RBX2 at the
We have recently shown that DEPTOR, a naturally occurring inhibitor of mTORC1 and mTORC2,21 is a physiological substrate of SCFbTrCP E3 ubiquitin ligase and that DEPTOR accumulation in response to glucose deprivation inhibited mTORC1 to induce autophagy.[22]

Summary

Introduction

SKP1 and an F-box protein at the N-terminus, and a RING protein, RBX1 or RBX2 ( known as ROC2 or SAG) at the. MLN4924 is a newly discovered investigational small molecule inhibitor of NAE.[9] MLN4924 binds to NAE to create a covalent NEDD8–MLN4924 adduct, which cannot be further utilized in subsequent intraenzyme reactions, blocking NAE enzymatic activity.[10] By blocking cullin neddylation, MLN4924 inactivates CRLs/SCF E3 ligase and causes accumulation of CRLs/SCF E3 substrates to suppress tumor cell growth both in vitro and in vivo.[9,10] A potential advantage of MLN4924 over bortezomib, the first and only FDA-. Mechanistic studies of MLN4924 action in growth suppression of tumor cells revealed that MLN4924 effectively induced apoptosis[9,14,15,16,17] and senescence[18,19,20] in several human cancer cell lines. Our study provides proof-of-concept evidence for a novel drug combination of MLN4924 with an autophagy inhibitor for more effective cancer therapy

Methods

Results

Conclusion