Frameshift mutations of chromosome cohesion-related genes SGOL1 and PDS5B in gastric and colorectal cancers with high microsatellite instability.

Cohesin is a protein complex that regulates chromatid cohesion and plays a role in preventing aneuploidy and maintaining chromosomal stability. SGOL1 encodes a cohesin protector, and PDS5B encodes a regulatory cohesion factor. Both SGOL1 and PDS5B are considered putative tumor suppressor genes. The aim of this study was to explore whether SGOL1 and PDS5B genes are mutated and expressionally altered in gastric and colorectal cancers. A genome database indicated that both genes possessed mononucleotide repeats in coding sequences, which could be mutation targets in cancers with microsatellite instability. We analyzed mutations in 91 gastric cancers and 100 colorectal cancers with high microsatellite instability or stable/low microsatellite instability by single-strand conformation polymorphism analysis and DNA sequencing. We also analyzed SGOL1 and PDS5B expression by immunohistochemistry. Overall, we found 21 SGOL1 frameshift mutations in 21 cases and 18 PDS5B frameshift mutations in 16 cases. SGOL1 and PDS5B frameshift mutations were detected in 26.6% and 20.3%, respectively, of high microsatellite instability but not in stable/low microsatellite instability (0/112). By immunohistochemistry, losses of SGOL1 and PDS5B were identified in 19% to 47% of the gastric and colorectal cancers irrespective of microsatellite instability status. The losses were more common in those with frameshift mutations or high microsatellite instability than those without mutations or high microsatellite instability. The data indicate that frameshift mutations of SGOL1 and PDS5B and the loss of their expression may be a feature of gastric and colorectal cancers with high microsatellite instability. In addition, the data suggest that these alterations might contribute to cancer pathogenesis by deregulating cohesin-related functions.