Cell cycle progression defects and impaired DNA damage signaling drive enlarged cells into senescence

Abstract

Cellular senescence plays an important role in development, ageing, and cancer biology. Senescence is associated with increased cell size, but how this contributes to permanent cell cycle exit is poorly understood. Using reversible G1 cell cycle arrests combined with growth rate modulation, we examined the effects of excess cell size on cell cycle progression in human cells. We show that enlarged cells paradoxically have high levels of G1/S regulators relative to cells that were maintained at physiological size but also induce p21, which restrains cell cycle entry and protects against cell division failure. Furthermore, we find that enlarged cells bear an increased propensity for DNA breakage and concomitant DNA damage repair defects that are established during G1. Based on these observations, we propose that impaired DNA damage repair pathways prime enlarged cells for persistent replication-acquired damage, ultimately leading to catastrophic cell cycle failure and permanent cell cycle exit.

Cell overgrowth during G1 arrest triggers an osmotic stress response and chronic p38 activation to promote cell cycle exit

“…The lack of apparent DNA damage from cells withdrawing from G0/G1 is crucial (Crozier et al, 2022; Manohar et al, 2022; Wang et al, 2022) ( Supplementary Figure 4A ). Cells that enter S-phase and undergo replication stress will trigger a DNA damage response, which was demonstrated to activate NF-kappa-B and induce a secretory phenotype that promotes proliferation and migration of tumour cells (Chien et al, 2011; Rodier et al, 2009).…”

“…However, we hypothesise that increased nuclear area, together with subscaling of DNA replication licensing factors ( Supplementary Table 1 ) (Crozier et al, 2022), could cause an overall decreased concentration of nuclear proteins leading to lower efficiency in DNA origin licensing. In addition, in recent work, it has been shown that cellular overgrowth makes cells more sensitive to DNA damage during the G0/G1 arrest (Manohar et al, 2022). This was, at least in part, attributed to a reduced capacity for p53 to respond to DNA damage occurring in these arrested cells.…”

“…A recent study proposed a model whereby excessive growth produces a diluted cytoplasm that limits cellular functions (Neurohr et al, 2019). Downstream, permanent cell cycle arrest after prolonged CDK4/6i treatment has been demonstrated to be p53-dependent (Crozier et al, 2022; Manohar et al, 2022; Wang et al, 2022), but the molecular pathways that link excessive cell growth to p53 activation are not understood.…”

Oncogenic signals prime cancer cells for toxic cell growth during a G1 cell cycle arrest

“…Thirdly, some cells can escape this G1 arrest, but these cells experience significant replication stress during the proceeding S-phase, which is associated with dilution of replisome components that subscale with size (Crozier et al, 2022a; Crozier et al, 2022b). Very recent data suggest that the DNA damage response is also impaired in enlarged cells, and the DNA itself may be prone to damage (Manohar et al, 2022). As a result of these replication-associated problems, p21 protein is induced again as cells enter G2, causing further cell cycle exit (Crozier et al, 2022a).…”

“…As a result of these replication-associated problems, p21 protein is induced again as cells enter G2, causing further cell cycle exit (Crozier et al, 2022a). Finally, cells that fail to exit the cell cycle from G2, in particular p53-deficient cells that cannot induce p21, enter mitosis and experience even further damage due to catastrophic chromosome segregation errors, promoting further cell cycle withdrawals (Crozier et al, 2022a; Crozier et al, 2022b; Manohar et al, 2022; Wang et al, 2022). Future research will be important to determine how much these various routes to genotoxic stress contribute to cell cycle exit in cancer cells with different oncogenic mutations.…”