Mitochondrial E3 Ubiquitin Ligase MARCH5 Coordinates Mitochondrial Membrane Dynamics in the Outer Mitochondrial Membrane Associated Degradation (OMMAD) Pathway

Abstract

The molecular mechanisms of the pathway governing mitochondrial and cellular homeostasis via outer mitochondrial membrane (OMM)- associated degradation (OMMAD) are not clear. We found that stability of OMM proteins MiD49, a mitochondrial fission factor, and Mcl1, an anti-apoptotic Bcl-2 family protein, is controlled by OMM-associated E3 ubiquitin ligase MARCH5. Accumulation of MiD49 and Mcl1, but not other proteins, and selective inhibition of proteasome-dependent degradation was seen in MARCH5 knockout cells. Through immunofluorescence, mitochondrial fusion, and biochemical assays, we found that MARCH5 governs Mcl1 turnover indirectly, but regulates MiD49 directly through ubiquitination. Furthermore, factors inducing stress-dependent apoptosis and mitochondrial toxins induced MARCH5-dependent MiD49 degradation, showing MARCH5 control of MiD49 stability as a novel stress response mechanism. Accordingly, MARCH5 depleted cells were more sensitive to stress-induced apoptosis. These findings provided evidence supporting a central role of MARCH5 in Mcl1 and MiD49 turnover and coordination of the OMMAD pathway with the mitochondrial and cellular stress response.