Genes with dual proto-oncogene and tumor suppressor gene activities are frequently altered by protein losses in colon cancers.

Cancer genes are largely categorized into tumor suppressor gene (TSG) and proto-oncogene, but many have dual activities depending on the cellular context. In the present study, we analyzed DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F genes known to possess the dual activities in sporadic colon cancers (CCs). By the mutation analysis, we identified DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F frameshift mutations in 2, 2, 3, 3, and 1 CCs in instability-high (MSI-H) cases (1.1-3.2% of MSI-H CCs), respectively, but not microsatellite stable (MSS) cases. One CC showed regional heterogeneous mutations (RHM) of ESRP1 mutation. Immunohistochemistry identified protein expression of ESRP1, MTSS1, and ADAMTS1 in the CCs, revealing that approximately 30% of CCs lost the protein expression irrespective of the MSI status. Our study showed that dual TSG and proto-oncogene genes DYRK1B, ESRP1, MTSS1, ADAMTS1, and INPP5F harbored low incidences of inactivating mutations, but that the protein losses were frequent in CCs. Our study suggests a possibility that the dual-function genes could be altered mainly at the expression level, which might contribute to CC pathogenesis.