DRP-1 functions independently of mitochondrial structural perturbations to facilitate BH3 mimetic-mediated apoptosis

Abstract

Maintenance of mitochondrial integrity is critical for normal cellular homoeostasis. Most cells respond to stress stimuli and undergo apoptosis by perturbing mitochondrial structure and function to release proteins, such as cytochrome c , which are essential for the execution of the intrinsic apoptotic cascade. Cancer cells evade these events by overexpressing the anti-apoptotic BCL-2 family of proteins on mitochondrial membranes. Inhibitors of the anti-apoptotic BCL-2 family proteins, also known as BH3 mimetics, antagonise the pro-survival functions of these proteins and result in rapid apoptosis. Although the precise mechanism by which BH3 mimetics induce apoptosis has been well characterised, not much is known in terms of the structural changes that occur in mitochondria during apoptosis. Using a panel of highly selective BH3 mimetics and a wide range of cell lines, we demonstrate that BH3 mimetics induce extensive mitochondrial fission, accompanied by swelling of the mitochondrial matrix and rupture of the outer mitochondrial membrane. These changes occur in a BAX/ BAK-dependent manner. Although a major mitochondrial fission GTPase, DRP-1, has been implicated in mitochondrial apoptosis, our data demonstrate that DRP-1 might function independently/downstream of BH3 mimetic-mediated mitochondrial fission to facilitate the release of cytochrome c and apoptosis. Moreover, downregulation of DRP-1 prevented cytochrome c release and apoptosis even when OPA1, a protein mediating mitochondrial fusion, was silenced. Although BH3 mimetic-mediated displacement of BAK and other BH3-only proteins from BCL-X L and MCL-1 was unaffected by DRP-1 downregulation, it prevented BAK activation significantly, thus placing DRP-1 as one of the most critical players, along with BAX and BAK, that governs BH3 mimetic-mediated cytochrome c release and apoptosis.

The BH3 mimetic (±) gossypol induces ROS-independent apoptosis and mitochondrial dysfunction in human A375 melanoma cells in vitro

“…release of proteins, changes in mitochondrial morphology, loss of ΔΨ m ), only a few studies have investigated the role of Drp1 in mitochondria integrity. Milani and coworkers showed that several BH3 mimetics (ABT-199, A1331852, A1210477) induced mitochondrial fission and apoptosis in a Drp1dependent manner (Milani et al 2019(Milani et al , 2017. Appropriately, the treatment of human cardiomyocytes with the MCL-1 inhibitor S63845 resulted in Drp1-dependent mitochondrial fragmentation (Rasmussen et al 2020).…”

The multiple mechanisms of MCL1 in the regulation of cell fate

“…While the stability of OPA-1 is decreased and fusion is repressed, MCL1 does not abolish its activity as mitochondria can still undergo fusion when MCL1 is inhibited 128 . Subsequent studies have since shown that MCL1-specific BH3 mimetics display fragmented mitochondrial networks, highlighting the shift in mitochondrial dynamics toward enhanced organelle fragmentation through fission 117,131,132 (Fig. 4c).…”

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

“…Both proteins can be co-localized with Bax at the MOM, with Drp1 being recruited by Bax after apoptosis induction, promoting fission; and Mfn2 binding to Bax, leading to mitochondrial fusion inhibition [52,53,66,67]. Furthermore, Drp1 plays an essential role in cytochrome c release and in pro-apoptotic Bak activation [51,68]. Downregulation or blocking of Drp1 has been shown to have anti-apoptotic effect in different in vitro models [53,[68][69][70].…”

“…Furthermore, Drp1 plays an essential role in cytochrome c release and in pro-apoptotic Bak activation [51,68]. Downregulation or blocking of Drp1 has been shown to have anti-apoptotic effect in different in vitro models [53,[68][69][70]. Of note, apoptosis can occur without mitochondrial fragmentation, with some studies showing that blocking fission only slows down apoptosis rather than entirely preventing it [53,68,71,72].…”