Prolonged mitotic arrest induces a caspase-dependent DNA damage response at telomeres that determines cell survival

Abstract

A delay in the completion of metaphase induces a stress response that inhibits further cell proliferation or induces apoptosis. This response is thought to protect against genomic instability and is important for the effects of anti-mitotic cancer drugs. Here, we show that mitotic arrest induces a caspase-dependent DNA damage response (DDR) at telomeres in non-apoptotic cells. This pathway is under the control of Mcl-1 and other Bcl-2 family proteins and requires caspase-9, caspase-3/7 and the endonuclease CAD/DFF40. The gradual caspase-dependent loss of the shelterin complex protein TRF2 from telomeres promotes a DDR that involves DNA-dependent protein kinase (DNA-PK). Suppression of mitotic telomere damage by enhanced expression of TRF2, or the inhibition of either caspase-3/7 or DNA-PK during mitotic arrest, promotes subsequent cell survival. Thus, we demonstrate that mitotic stress is characterised by the sub-apoptotic activation of a classical caspase pathway, which promotes telomere deprotection, activates DNA damage signalling, and determines cell fate in response to a prolonged delay in mitosis.

The caspase‐activated DNase: apoptosis and beyond

“…Indeed, CAD‐induced DNA breaks that appear during prolonged mitotic arrest localize to telomeric regions. This telomeric localization likely reflects chromatin accessibility of mitotic cells, which would restrict CAD's activity . The specificity of CAD‐induced DNA breaks in an interphase cell is apparent during skeletal muscle differentiation, here the breaks appear restricted to euchromatic regions.…”

“…Hain et al . recently explored the significance of the CAD‐induced telomeric DNA damage, and demonstrated this promoted a DNA‐PK‐dependent loss of TRF2 from the telomeres, further signaling dysfunction.…”

“…Strikingly, CAD has a pronounced impact on cell fate decisions both during mitotic arrest and in the subsequent interphase following slippage . Topham et al .…”

Cell death response to anti-mitotic drug treatment in cell culture, mouse tumor model and the clinic

“…For some cancer cell lines, e.g., U-2 OS, apoptosis after mitotic slippage is the major cell death response to anti-mitotic drug treatment and highly effective (~90% death after slippage) [18]. The key pro-apoptotic signal that activates cell death after slippage was identified to be DNA damage [22, 54–59] (Fig. 3).…”

“…3). Several studies have shown that caspase activities, which were partially activated during prolonged mitotic arrest, engender DNA fragmentation in the post-slippage cells and thus induce p53-mediated DNA damage response [56–59]. Our own results confirmed the involvement of DNA damage in post-slippage cell death and further illustrated that the degree of DNA damage induced by microtubule-targeting drugs, e.g., paclitaxel, is substantially higher than the spindle-targeting Kinesin-5 inhibitor [22].…”