Loss of cohesin deacetylation through KDAC8 inactivation leads to altered cohesin complex expression and chromosomal instability

The cohesin complex is critical for both proper gene expression and for pairing sister chromatids during mitosis to ensure proper chromosome segregation. Acetylation and deacetylation of SMC3, a component of cohesin, is a critical regulatory mechanism controlling stability and reformation of the complex. Patients with Cornelia de Lange Syndrome have been observed to have mutations in cohesin-related genes, including in the lysine deacetylase KDAC8 (HDAC8), leading to disruption of complex formation and recycling. To further understand the cellular consequences of disrupting the SMC3 acetylation cycle, we utilized cell lines in which KDAC8 is replaced by a catalytically-inactive variant (8CDm) or knocked-out (8KO). Although the 8CDm cell line completes mitosis at the same rate as wild-type cells, 8CDm cells display severe chromosomal instability, characterized by increased presence of micronuclei and a significant subpopulation of cycling tetraploid cells. These defects were not observed in 8KO cells. Although total SMC3 protein levels are similar in all cell lines, SMC3 and other cohesin-associated genes are differentially expressed in the mutant cell lines. We hypothesize a model in which 8KO cells compensate for the inability to deacetylate SMC3 by increasing both SMC3 turnover and gene expression, and 8CDm mediated suppression of SMC3 turnover and expression results in fewer functional cohesin complexes and the severe chromosomal instability phenotype. Overall, these observations provide a greater understanding of the importance of SMC3 deacetylation by KDAC8 and insight into the phenotypic range observed in Cornelia de Lange Syndrome patients.