Atypical APC/C‐dependent degradation of Mcl‐1 provides an apoptotic timer during mitotic arrest

Abstract

The initiation of apoptosis in response to the disruption of mitosis provides surveillance against chromosome instability. Here, we show that proteolytic destruction of the key regulator Mcl‐1 during an extended mitosis requires the anaphase‐promoting complex or cyclosome (APC/C) and is independent of another ubiquitin E3 ligase, SCFFbw7. Using live‐cell imaging, we show that the loss of Mcl‐1 during mitosis is dependent on a D box motif found in other APC/C substrates, while an isoleucine‐arginine (IR) C‐terminal tail regulates the manner in which Mcl‐1 engages with the APC/C, converting Mcl‐1 from a Cdc20‐dependent and checkpoint‐controlled substrate to one that is degraded independently of checkpoint strength. This mechanism ensures a relatively slow but steady rate of Mcl‐1 degradation during mitosis and avoids its catastrophic destruction when the mitotic checkpoint is satisfied, providing an apoptotic timer that can distinguish a prolonged mitotic delay from normal mitosis. Importantly, we also show that inhibition of Cdc20 promotes mitotic cell death more effectively than loss of APC/C activity through differential effects on Mcl‐1 degradation, providing an improved strategy to kill cancer cells.

Boosting the apoptotic response of high‐grade serous ovarian cancers with CCNE1 amplification to paclitaxel in vitro by targeting APC/C and the pro‐survival protein MCL‐1

“…The activation of the intrinsic pathway in cells exhibiting mitotic catastrophe induced by paclitaxel aims at inducing mitotic cell death. Accordingly, the pro‐survival factor MCL‐1 has been proposed to play an important role in defining the cell fate in cancers . To directly test this, we first incubated OVCAR‐3 cells with the combination paclitaxel/proTAME, and after 6–8 hr, we added the potent MCL‐1 inhibitor A1210477 that acts as BH3 mimetic specifically targeting MCL‐1 and disrupts the MCL‐1/BIM complex .…”

“…Accordingly, the pro-survival factor MCL-1 has been proposed to play an important role in defining the cell fate in cancers. 18,21 To directly test this, we first incubated OVCAR-3 cells with the combination paclitaxel/proTAME, and after 6-8 hr, we added the potent MCL-1 inhibitor A1210477 that acts as BH3 mimetic specifically targeting MCL-1 and disrupts the MCL-1/ BIM complex. 30 Time-lapse microscopy showed that while control cells completed mitosis normally (2.26 hr), paclitaxel significantly increased the average mitosis duration up to 13.7 hr, which was followed by mitosis escape and the formation of tetraploid cells ( Figs.…”

“…Interestingly, several studies linked the activation of the apoptotic machinery with the duration of mitosis. Hereby, the induced myeloid leukemia cell differentiation protein (MCL‐1) was identified as the protein linking the time of mitosis to the induction of apoptosis . The pro‐survival function of MCL‐1 lies in its ability to bind and sequester BAX and BAK preventing them from forming pores in the mitochondrial membrane thereby triggering apoptosis .…”

“…Hereby, the induced myeloid leukemia cell differentiation protein (MCL-1) was identified as the protein linking the time of mitosis to the induction of apoptosis. 15,[18][19][20][21][22] The pro-survival function of MCL-1 lies in its ability to bind and sequester BAX and BAK preventing them from forming pores in the mitochondrial membrane thereby triggering apoptosis. 17 Interestingly, the expression of MCL-1 appears to increase only when cells are facing insults including the treatment with microtubule targeting drugs.…”

MARCH5-dependent degradation of MCL1/NOXA complexes defines susceptibility to antimitotic drug treatment

“…The controversy still exists as to which E3-ligases control MCL1 levels in response to different types of stress including mitotic arrest [8,20]. One E3-ligase that has been shown to regulate BCL2 family proteins is membrane associated RING finger protein 5 (MARCH5) [21,22].…”