TGF-beta 1 in colonic neoplasia. A genetic molecular and immunohistochemical study

Transforming growth factor-beta proteins are key regulators of cellular growth and differentiation. To understand the role of TGF-beta in colonic tumour progression, 47 paraffin-embedded samples from colonic tumours (13 adenomas, and 34 adenocarcinomas) were studied. Gene mutations in the region coding for the active protein were studied by PCRSSCP analysis of exons 5, 6, and 7. TGF-beta 1 mRNA expression and localization were studied by NISH using cDNA probes generated by RT-PCR. Protein distribution was investigated by immunohistochemistry using antibodies against both intracellular and extracellular forms. Three mutations were found: one in exon 5 (Dukes C) and two in exon 7 (Dukes C and A). mRNA TGF-beta 1 was observed in 9 (69%) of 13 adenomas and in 30 (88%) of 34 adenocarcinomas. Levels of TGF-beta 1 mRNA and proteins were higher in colorectal carcinomas than in colorectal adenomas. Tubular adenomas associated with dysplasia showed greater expression of TGF-beta 1 than adenomas without dysplasia and than non neoplastic colonic mucosa. In dysplasia and cancer, epithelial neoplastic cells and stromal cells were positive for TGF-beta 1. In normal tissue endothelial cells and granulocytes sporadically showed immunoreactivity for TGF-beta 1, whereas epithelial cells were all negative. The three mutations in TGF-beta 1 exons 5, 6 and 7 found in colorectal adenocarcinomas suggest that TGF-beta 1 mutation may play a role in colorectal carcinogenesis and that the presence of the mutant form contributes to the transformed state. Our two other findings, the loss of staining gradient in normal colonic mucosa and the higher levels of TGF-beta 1 mRNA and proteins in colorectal carcinomas than in colorectal adenomas, indicate that the deregulation of TGF-beta 1 expression may occur as an early event in colorectal carcinogenesis. Although TGF-beta 1 expression is generally a reflection of cellular differentiation, tumour grade is not associated with mRNA TGF-beta 1 expression. As well as being present in the epithelial cells of the colonic tumours, mRNA TGF-beta 1 also occurred in the stroma. Its localization in the macrophages adjacent to tumour strongly suggests that TGF-beta 1 could be secreted by macrophages. This hypothesis should lead to new therapeutic strategies for colorectal carcinoma.