Replication stress induces mitotic cell death through cohesion fatigue and telomere deprotection

Inducing DNA replication stress or targeting pathways that respond to replication stress is a prominent approach for chemotherapeutic cancer treatment. Lethal replication stress has previously been associated with “mitotic catastrophe”, a broad descriptor encompassing the complex and poorly understood mechanisms that connect genomic insult to mitotic disruption and cell death. While low dosages of replication stress drive genome instability through the passage of damaged DNA and chromosome segregation errors during mitosis, direct mechanisms connecting lethal replication stress to cell death remain unclear. In this thesis, I identify that lethal replication stress induces mitotic cell death, in the same cell cycle, through the two parallel pathways of cohesion fatigue and telomere deprotection. p53 compromised cells treated with pharmacological replication stress-inducing compounds, undergo a prolonged S/G2 phase followed by spindle assembly checkpoint (SAC)-dependent mitotic arrest. The SAC is engaged because WAPL promotes impaired centromeric cohesion during the prolonged S/G2, which is then passed into mitosis. Continued mitotic arrest then drives WAPL-dependent cohesion fatigue, which activates Bax, Bak dependent apoptotic cell death. This WAPL dependent apoptosis signalling is determined to be the major pathway of replication stress induced mitotic cell death. Evasion of mitotic cell death by WAPL knockdown or by Bax, Bak double knock out caused increased genome instability, respectively, through chromosome segregation errors or mitotic slippage

The long lifespan of two bat species is correlated with resistance to protein oxidation and enhanced protein homeostasis

Altered structure, and hence function, of cellular macromolecules caused by oxidation can contribute to loss of physiological function with age. Here, we tested whether the lifespan of bats, which generally live far longer than predicted by their size, could be explained by reduced protein damage relative to short-lived mice. We show significantly lower protein oxidation (carbonylation) in Mexican free-tailed bats (Tadarida brasiliensis) relative to mice, and a trend for lower oxidation in samples from cave myotis bats (Myotis velifer) relative to mice. Both species of bat show in vivo and in vitro resistance to protein oxidation under conditions of acute oxidative stress. These bat species also show low levels of protein ubiquitination in total protein lysates along with reduced proteasome activity, suggesting diminished protein damage and removal in bats. Lastly, we show that bat-derived protein fractions are resistant to urea-induced protein unfolding relative to the level of unfolding detected in fractions from mice. Together, these data suggest that long lifespan in some bat species might be regulated by very efficient maintenance of protein homeostasis.—Salmon, A. B., Leonard, S., Masamsetti, V., Pierce, A., Podlutsky, A. J., Podlutskaya, N., Richardson, A., Austad, S. N., Chaudhuri, A. R. The long lifespan of two bat species is correlated with resistance to protein oxidation and enhanced protein homeostasis