Suppression of Genome Instability in pRB-Deficient Cells by Enhancement of Chromosome Cohesion

Abstract

Chromosome instability (CIN), a common feature of solid tumors, promotes tumor evolution and increases drug resistance during therapy. We previously demonstrated that loss of the pRB tumor suppressor causes changes in centromere structure and generates CIN. However, the reason for, and significance of, this change was unclear. Here we show that defects in cohesion are key to the pRB-loss phenotype. pRB loss alters H4K20 methylation, a prerequisite for efficient establishment of cohesion at centromeres. Changes in cohesin regulation are first evident during S-phase where they compromise replication and increase DNA damage. Ultimately such changes compromise mitotic fidelity in pRB-deficient cells. Remarkably, increasing cohesion suppressed all of these phenotypes and dramatically reduced CIN in cancer cells lacking functional pRB. These data explain how loss of pRB undermines genomic integrity. Given the frequent functional inactivation of pRB in cancer, conditions that increase cohesion may provide a general strategy to suppress CIN.

Escape from Mitotic Arrest: An Unexpected Connection Between Microtubule Dynamics and Epigenetic Regulation of Centromeric Chromatin in Schizosaccharomyces pombe

“…Our studies of Msc1, the fission yeast homolog of the KDM5 family of proteins, are consistent with a role for Msc1 in mediating chromosome segregation, perhaps by modifying the chromatin landscape at the centromere. Mitotic defects in cells lacking the tumor suppressor Rb, including merotelic attachments and lagging chromosomes (Manning et al 2010), suggest that Rb itself contributes to proper chromosome segregation (Manning and Dyson 2012), perhaps via effects on chromosome cohesion (Manning et al 2014). These results, along with the observations reported here, suggest that an examination of the role of KDM5 proteins in chromosome segregation is warranted as well.…”

Haploinsufficiency of an RB–E2F1–Condensin II Complex Leads to Aberrant Replication and Aneuploidy

“…Intriguingly, augmentation of Cohesin function can suppress replication and chromosomal abnormalities caused by loss of RB1 function. This suggests that these chromosomal defects may potentially be suppressed therapeutically ( 48 ).…”

RB1: a prototype tumor suppressor and an enigma

“…These changes promote aneuploidy, particularly when combined with mutations in p53 (Zheng et al 2002;Manning et al 2014a). The mitotic phenotypes resulting from pRB loss have been linked to the altered expression of mitotic proteins (Hernando et al 2004), reduced loading of the Condensin II protein CapD3 (Longworth et al 2008;Coschi et al 2010;Manning et al 2010), reduced chromosomal cohesion (Manning et al 2010;van Harn et al 2010), and altered accumulation of cohesin complexes at pericentromeric chromatin (Manning et al 2014b).…”

“…Thus, the mitotic defects resulting from pRB inactivation may be relevant in many cancers. Significantly, the mitotic defects associated with pRB loss can be suppressed by knockdown of the checkpoint protein Mad2 (Hernando et al 2004;Sotillo et al 2010;Schvartzman et al 2011), depletion of Wapl (to increase cohesin loading) (Manning et al 2014b), addition of nucleosides (which improves replication dynamics and chromosome cohesion) (Bester et al 2011;Burrell et al 2013;Manning et al 2014a), or manipulations that change chromatin marks at centromeric and pericentromeric heterochromatin (Manning et al 2014b;Tanno et al 2015). These raise the intriguing idea that it may be possible to reduce genome instability caused by RB1 mutation.…”