Phosphotyrosine, p62 c-myc and p21 c-Ha-ras proteins in colonic epithelium of normal and dimethylhydrazine-treated rats: an immunohistochemical analysis.

In the present study we used monoclonal antibodies to investigate the expression of phosphotyrosine, c-myc and c-Ha-ras proteins along the crypt continuum of normal and transformed rat colon tissue. Colon cancer was induced by administration of dimethylhydrazine. Particular attention was focused on the immunohistochemical pattern of murine colon mucosa during preneoplastic stages so as to permit the identification of putative changes in the expression/location of the oncoproteins prior to frank neoplasia. The immunohistochemical analysis of tyrosinephosphorylated proteins in the normal rat indicated that positive staining was mostly restricted to the lower colonic crypt zones. The carcinogenetic insult altered the magnitude and positional profile of phosphotyrosine along the colon crypt axis during the preneoplastic period. An intense positive reaction was observed in the upper crypt regions. Four weeks following the last DHM administration, viz. before tumor appearance, positive staining was evident in invasive adenocarcinoma tissue. In contrast to phosphotyrosine, the feeble c-myc immunohistochemical staining of normal rat colonic did not exhibit a focal topology. However, following DMH administration and prior to frank neoplasia, a substantial increase in the staining intensity for c-myc was noted, confined mostly to the supranuclear region of luminal cells. Invasive adenocarcinomas displayed intense cytoplasmic c-myc immunoreactivity. p21 c-Ha-ras expression and location along the colon crypt axis showed a different pattern when compared to p62 c-myc and phosphotyrosine. The p21 c-Ha-ras protein was prominently expressed in surface epithelium of normal and DMH-treated rats. Midcrypt colonocytes exhibited moderate p21 ras staining; in contrast, proliferating colonic cells resident in the lower crypt regions were consistently negative. These results suggest that c-Ha-ras gene product plays an important contributory role in determining the differentiated phenotype of the colonic cell.