Frameshift Mutations and Loss of Expression of CLCA4 Gene are Frequent in Colorectal Cancers With Microsatellite Instability

Chloride channel calcium-activated (CLCA) genes encode regulators for chloride transport across the cell membrane. As for cancer development, some CLCA genes are considered putative tumor suppressor genes. The aim of this study was to explore whetherCLCA4gene would have mutations in its nucleotide repeats in colorectal cancer (CRC). In a public database, we found thatCLCA4gene had mononucleotide repeats in the coding sequences that might be mutational targets in the cancers with microsatellite instability. For this, the current study studied 146 CRCs for mutation and expression analyses by single-strand conformation polymorphism analysis, DNA sequencing, and immunohistochemistry. Overall, we foundCLCA4frameshift mutations in 12/101 (11.8%) CRCs with high-microsatellite instability (MSI-H), but none in microsatellite stable CRCs (0/45) (P<0.01). In addition, we analyzed intratumoral heterogeneity of theCLCA4frameshift mutations and found that 1 CRC harbored regional intratumoral heterogeneity of theCLCA4frameshift mutation. Loss of CLCA4 protein expression was identified in 50% of CRCs. Also, cancers with MSI-H harboringCLCA4frameshift mutations showed lower CLCA4 immunostaining than those with the wild-type. Our data indicate that theCLCA4gene harbors alterations both in somatic mutation and expression, suggesting their roles in tumorigenesis of CRC with MSI-H.