The Role of Chromosomal Instability and Epigenetics in Colorectal Cancers Lackingβ-Catenin/TCF Regulated Transcription

Abstract

All colorectal cancer cell lines except RKO displayed activeβ-catenin/TCF regulated transcription. This feature of RKO was noted in familial colon cancers; hence our aim was to dissect its carcinogenic mechanism. MFISH and CGH revealed distinct instability of chromosome structure in RKO. Gene expression microarray of RKO versus 7 colon cancer lines (with active Wnt signaling) and 3 normal specimens revealed 611 differentially expressed genes. The majority of the tested gene loci were susceptible to LOH in primary tumors with variousβ-catenin localizations as a surrogate marker forβ-catenin activation. The immunohistochemistry of selected genes (IFI16,RGS4,MCTP1,DGKI,OBCAM/OPCML, andGLIPR1) confirmed that they were differentially expressed in clinical specimens. Since epigenetic mechanisms can contribute to expression changes, selected target genes were evaluated for promoter methylation in patient specimens from sporadic and hereditary colorectal cancers.CMTM3,DGKI, andOPCMLwere frequently hypermethylated in both groups, whereasKLK10,EPCAM, andDLC1displayed subgroup specificity. The overall fraction of hypermethylated genes was higher in tumors with membranousβ-catenin. We identified novel genes in colorectal carcinogenesis that might be useful in personalized tumor profiling. Tumors with inactive Wnt signaling are a heterogeneous group displaying interaction of chromosomal instability, Wnt signaling, and epigenetics.