Epithelial and stromal genetic instability linked to tumor suppressor genes in ulcerative colitis-associated tumorigenesis

Abstract

Objective. We have previously documented not only epithelial but also stromal genetic instability in ulcerative colitis (UC)-associated lesions, including adenocarcinomas, using microsatellite markers close to the p53 gene on chromosome 17 (Chr.17). However, about half of the UC-associated tumors do not have p53 gene alterations. The purpose of this study was to detect early genetic instability (loss of heterozygosity (LOH) and microsatellite instability (MSI)) of both epithelial and stromal cells in UC-associated tumorigenesis, using different microsatellite markers from the p53 gene. Material and methods. The laser-captured microdissection-PCR-GeneScan method was applied to investigate genetic instability in both the epithelial and stromal elements of early UC-associated lesions (regenerative mucosa and dysplasia) and carcinomas using multiple microsatellite markers, chiefly close to tumor suppressor genes (TSGs: p16INK4A, Rb, Smad4 and fragile histidine triad (FHIT)). Furthermore, expression of their gene products was analyzed by immunohistochemistry. Results. In epithelium, although LOH for Chr.17 markers increased along with histological progression, the frequencies of LOH or MSI for TSG markers were found to be almost constantly increased in both stromal and epithelial components of all lesion types. In contrast, genetic instability of National Cancer Institute (NCI)-recommended standard markers was not found to be significantly correlated with UC-associated tumorigenesis. Immunohistochemically, epithelial p16INK4A expression tended to be decreased in LOH-positive lesions (p=0.0780) and Smad4 expression was significantly decreased (p<0.05). Conclusions. These results suggest that genetic instability in the stroma, especially regarding TSG markers, may play an important role in early-phase, UC-associated tumorigenesis. In addition, decreased expression of TSG due to genetic alteration might contribute to tumorigenesis.