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Mitochondrial E3 ubiquitin ligase MARCHF5 controls BAK function independently of BH3-only proteins

ABSTRACT: Intrinsic apoptosis is principally regulated by the BCL-2 family of proteins, but some non-BCL-2 proteins also serve as important regulators. To identify novel apoptosis regulators, we performed a genome-wide CRISPR-Cas9 library screen, and it identified the mitochondrial E3 ubiquitin ligase MARCHF5/MITOL/RNF153 as an important regulator of BAK apoptotic function. Deleting MARCHF5 in multiple BAX-deficient cell lines conferred profound resistance to BH3-mimetic drugs. The loss of MARCHF5 or its E3 ubiquitin ligase activity surprisingly drove BAK to adopt an active conformation, with resistance to BH3-mimetics afforded by the formation of inhibitory complexes with pro-survival proteins MCL-1 and BCL-XL. Importantly, these changes to BAK conformation and pro-survival association occurred independently of BH3-only proteins. This study identifies a mechanism by which MARCHF5 regulates apoptotic cell death and provides new insight into how cancer cells respond to BH3-mimetic drugs. These data also highlight the emerging role of ubiquitin signalling in apoptosis that may be exploited therapeutically.

INSTRUMENT(S): Q Exactive Plus

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Cell Culture

SUBMITTER: David Stroud

LAB HEAD: David Stroud

PROVIDER: PXD030246 | Pride | 2022-09-25

REPOSITORIES: Pride

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Project description:Amyloid light chain amyloidosis (AL) is an incurable protein misfolding disorder characterized by the production of amyloidogenic immunoglobulin light chains by clonal populations of plasma cells. These abnormal light chains accumulate as amyloid fibrils in vital organs and cause multi-organ dysfunction that can be rapidly fatal. Current treatment regimens, which include proteasome inhibitors, were developed for the treatment of the more common plasma cell disease multiple myeloma and have demonstrated efficacy in AL amyloidosis. However, use of these agents is frequently limited due to multi-organ dysfunction at presentation, resulting in a median survival of 2-3 years and underscoring the need for novel therapies. By analyzing bone marrow-derived plasma cells from 44 patients with AL amyloidosis, we find that clonal plasma cells are highly primed to undergo apoptosis and exhibit strong dependencies on pro-survival BCL-2 family proteins that can potentially be targeted by recently-developed BH3 mimetics. In particular, we find that clonal plasma cells are highly dependent on the pro-survival MCL-1 and undergo apoptosis in response to single-agent treatment with an MCL-1 inhibitor. Notably, this MCL-1 dependency is indirectly targeted by the proteasome inhibitor bortezomib, which is currently the standard of care for this disease, via the stabilization of Noxa and its direct inhibitory binding to MCL-1. BCL-2 inhibition with the FDA-approved inhibitor venetoclax (ABT-199) sensitizes plasma cells to bortezomib treatment and other front-line therapies, which can be observed in vitro and in vivo. Mass spectrometry-based proteomic analysis reveals changes in signaling pathways regulating apoptosis, proliferation and mitochondrial metabolism between isogenic AL amyloidosis and multiple myeloma cells that divergently alter their sensitivity to therapy. Overall, our results indicate that BH3 mimetics may be highly effective therapies for AL amyloidosis that exploit inherent and induced dependencies on pro-survival proteins.

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Mitochondrial E3 ubiquitin ligase MARCHF5 controls BAK function independently of BH3-only proteins

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