Dynamic Regulation of Long-Chain Fatty Acid Oxidation by a Noncanonical Interaction between the MCL-1 BH3 Helix and VLCAD

Abstract

MCL-1 is a BCL-2 family protein implicated in the development and chemoresistance of human cancer. Unlike its anti-apoptotic homologs, Mcl-1 deletion has profound physiologic consequences, indicative of a broader role in homeostasis. We report that the BCL-2 homology 3 (BH3) α helix of MCL-1 can directly engage very long-chain acyl-CoA dehydrogenase (VLCAD), a key enzyme of the mitochondrial fatty acid β-oxidation (FAO) pathway. Proteomic analysis confirmed that the mitochondrial matrix isoform of MCL-1 (MCL-1) interacts with VLCAD. Mcl-1 deletion, or eliminating MCL-1 alone, selectively deregulated long-chain FAO, causing increased flux through the pathway in response to nutrient deprivation. Transient elevation in MCL-1 upon serum withdrawal, a striking increase in MCL-1 BH3/VLCAD interaction upon palmitic acid titration, and direct modulation of enzymatic activity by the MCL-1 BH3 α helix are consistent with dynamic regulation. Thus, the MCL-1 BH3 interaction with VLCAD revealed a separable, gain-of-function role for MCL-1 in the regulation of lipid metabolism.

Regulation of apoptosis in health and disease: the balancing act of BCL-2 family proteins

“…The role of MCL1 in mammalian development is less clear than BCL-2 or BCL-X L due to the very early (at embryonic day 3.5) lethality of this knockout, which is associated with a trophectoderm defect that impairs implantation of the embryo 98 . Although this early lethality may be due to a strong requirement for MCL1 in counteracting apoptosis, it may alternatively be due to potential physiological roles of MCL1 beyond regulating apoptosis: it has been shown that an amino-terminally truncated isoform of MCL1 is imported into the mitochondrial matrix where it facilitates respiration and ATP production 99,100 . However, in cancer cells, the loss of MCL1 has no major impact on cell growth beyond regulating apoptosis 48 .…”

Ubiquitination and deubiquitination of MCL1 in cancer: deciphering chemoresistance mechanisms and providing potential therapeutic options

“…In addition, an amino-terminal truncated isoform of MCL1 has been reported to be anchored to the inner mitochondrial membrane (IMM) and exposed to the matrix where it retains the normal IMM structure, mitochondrial fusion, ATP production, membrane potential, and respiration 30 . This mitochondrial matrix form of MCL1 can also directly interact with and modulate very long-chain acyl-CoA dehydrogenase, a key enzyme in the mitochondrial fatty acid β-oxidation pathway, to engage in lipid metabolism 31 . Excluding the functions within mitochondria, MCL1 can be translocated into the nucleus to activate Chk1 and maintain genome integrity in response to DNA damage 32 , 33 .…”

Bid maintains mitochondrial cristae structure and function and protects against cardiac disease in an integrative genomics study

“…Our observation that Bid is found within the mitoplast ( Figure 3c and d ) raised the possibility that it is interacting with mitochondrial matrix proteins known to regulate cristae structure. In particular, the anti-apoptotic Bcl-2 family member Mcl-1 has been shown to have a matrix isoform involved in respiratory chain maintenance and mitochondrial metabolism ( Escudero et al, 2018 ; Perciavalle et al, 2012 ; Thomas et al, 2013 ; Wang et al, 2013 ). It is known that the BH3-domain of cBid associates with Mcl-1, to inhibit apoptosis ( Clohessy et al, 2006 ).…”

“…Our results indicating the presence of Bid in the matrix prompted us to determine if the M148T mutant would also impact a possible protein-protein interaction. A strong candidate is the anti-apoptotic Bcl-2 family member Mcl-1, which was rigorously shown to have a mitochondrial matrix isoform that mediated mitochondrial cristae structure and lipid metabolism independent of Mcl-1’s apoptotic function ( Escudero et al, 2018 ; Perciavalle et al, 2012 ). We find that this point mutant decreases the association between Bid with Mcl-1 Matrix compared to WT and D59A-mutanted Bid (rescue mutant).…”