MARCH5 requires MTCH2 to coordinate proteasomal turnover of the MCL1:NOXA complex

Tirta Mario Djajawi,Ming-Jie Luo,Jia-Nan Gong,Mark F Van Delft,Melissa J Call,David C S Huang,Zhen Xu,Allan Shuai Huang,Toru Okamoto,Lei Liu

doi:10.1038/s41418-020-0517-0

Abstract

MCL1, a BCL2 relative, is critical for the survival of many cells. Its turnover is often tightly controlled through both ubiquitin-dependent and -independent mechanisms of proteasomal degradation. Several cell stress signals, including DNA damage and cell cycle arrest, are known to elicit distinct E3 ligases to ubiquitinate and degrade MCL1. Another trigger that drives MCL1 degradation is engagement by NOXA, one of its BH3-only protein ligands, but the mechanism responsible has remained unclear. From an unbiased genome-wide CRISPR-Cas9 screen, we discovered that the ubiquitin E3 ligase MARCH5, the ubiquitin E2 conjugating enzyme UBE2K, and the mitochondrial outer membrane protein MTCH2 co-operate to mark MCL1 for degradation by the proteasome—specifically when MCL1 is engaged by NOXA. This mechanism of degradation also required the MCL1 transmembrane domain and distinct MCL1 lysine residues to proceed, suggesting that the components likely act on the MCL1:NOXA complex by associating with it in a specific orientation within the mitochondrial outer membrane. MTCH2 has not previously been reported to regulate protein stability, but is known to influence the mitochondrial localization of certain key apoptosis regulators and to impact metabolism. We have now pinpointed an essential but previously unappreciated role for MTCH2 in turnover of the MCL1:NOXA complex by MARCH5, further strengthening its links to BCL2-regulated apoptosis.

Highlights

Intrinsic apoptosis is a fundamental process that must be carefully balanced to maintain tissue homeostasis and preserve the well-being of multicellular organisms
MTCH2 may bridge interactions that take place within or adjacent to the mitochondrial outer membrane. We propose that these proteins come together in a specific orientation that allows MARCH5 to discharge ubiquitin onto K175/K178 of MCL1, thereby marking it for degradation. It has been recognized for some time that that the MCL1: NOXA complex is rapidly degraded by the proteasome, but the mechanism responsible has remained unclear [15, 16]
Using a genome-wide CRISPR-Cas9 screen we have identified that MARCH5 and MTCH2 are both required for this process and elucidated certain aspects of how they work together

Summary

Introduction

Intrinsic apoptosis is a fundamental process that must be carefully balanced to maintain tissue homeostasis and preserve the well-being of multicellular organisms. The most critical regulators of apoptosis are the members of the BCL2 protein family, which include BCL2 and its prosurvival relatives (MCL1, BCLxL, BCLW, and A1), the proapoptotic BH3-only proteins (NOXA, BIM, PUMA, BAD, and BID) and the effector proteins BAX and BAK. The balance of interactions between these proteins dictates whether BAX and BAK become activated to permeabilize the mitochondrial outer membrane and cause apoptosis [1, 2]. Precise control of apoptosis is achieved by regulating BCL2 proteins in multiple ways including through posttranslational modifications that impact their stability, localization, and/or propensity to interact [3, 4]. MCL1 is a prosurvival relative of BCL2 and has been implicated in tumorigenesis and the resistance of cancer cells to therapy [5].

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Conclusion