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Cohesion Complex Members Validated as CIN Genes in Colorectal Cancer

Tarik Leylek

Max Rady College of Medicine, University of Manitoba

Introduction: Colorectal Cancer (CRC) is the second leading cause of cancer-related deaths globally. Over the next two decades, the World Health Organization indicates that CRC morbidity and mortality rates are predicted to increase by up to 150%, further underscoring the critical need for a greater understanding of the molecular origins of CRC. Up to 85% of all CRCs are associated with chromosome instability (CIN) which is defined as an increased rate at which whole chromosomes or large parts thereof are gained or lost. CIN is associated with early disease development, metastasis and poor patient outcome. Despite these associations, the aberrant genes and pathways causing CIN remain poorly understood. An emerging body of evidence has suggested aberrant cohesion may be a pathogenic event that contributes to the etiology of CRC. Methods: A comprehensive assessment of 10 cohesion-related genes was performed to determine the impact aberrant cohesion has on CIN and the development of CRC. Evaluation of candidate CIN genes was performed in two distinct karyotypically stable cell lines, HCT116 and hTERT, using siRNA-based approaches. Quantitative imaging microscopy was employed to evaluate two surrogate markers of CIN, changes in nuclear areas and micronucleus formation, relative to controls. To determine whether the CIN-associated phenotypes identified arise due to chromosomal defects, mitotic chromosome spreads were quantitatively assessed in HCT116 cells. Kolmogorov-Smirnov Tests (KS test) were employed to identify statistical significance. Results: Our high-content microscopy screen identified all 10 Cohesion complex member genes as putative CIN genes, of which SMC3, RAD21, NIPBL and ESCO2 induced the strongest CIN phenotypes. Mitotic chromosome spreads in HCT116 revealed statistically significant changes in cumulative distribution frequencies of chromosome numbers for RAD21, NIPBL and ESCO2 silenced conditions relative to control (siGAPDH; KS tests, p-value <0.05). Quantitative analysis identified large increases (12-17-fold) in cohesion defects following SMC3, RAD21, NIPBL and ESCO2 silencing relative to controls. Conclusions: Our data suggest all 10 cohesion-related genes are CIN genes with four genes, SMC3, RAD21, NIPBL and ESCO2, validated as CIN genes implicating them in CRC pathogenesis. These genes represent novel therapeutic targets that could be exploited through precision medicine strategies to better combat CRC.

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