TGF-BETA-1 IN COLONIC NEOPLASIA - A GENETIC MOLECULAR AND IMMUNOHISTOCHEMICAL STUDY

Transforming growth factor-beta proteins are key regulators of cellula r growth and differentiation. To understand the role of TGF-P in colon ic tumour progression, 47 paraffin embedded samples from colonic tumou rs (13 adenomas, and 34 adenocarcinomas) were studied. Gene mutations in the region coding for the active protein were studied by PCR SSCP a nalysis of exons 5, 6, and 7. TGF-beta 1 mRNA expression and localizat ion were studied by NISH using cDNA probes generated by RT-PCR, Protei n distribution was investigated by immunohistochemistry using antibodi es 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) . TGF-beta 1 mRNA 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 a denomas associated with dysplasia showed greater expression of TGF-bet a 1 than adenomas without dysplasia and than non-neoplastic colonic mu cosa. In dysplasia and cancer, epithelial neoplastic cells and stromal cells were positive for TGF-beta 1. In normal tissue endothelial cell s and granulocytes sporadically showed immunoreactivity for TGF-beta 1 , whereas epithelial cells were all negative. The three mutations in T GF-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 transform ed state. Our two other findings, the loss of staining gradient in nor mal colonic mucosa and the higher levels of TGF-beta 1 mRNA and protei ns in colorectal carcinomas than in colorectal adenomas, indicate that the de-regulation of TCF-beta 1 expression may occur as an early even t in colorectal carcinogenesis. Although TGF-beta 1 expression is gene rally a reflection of cellular differentiation, tumour grade is not as sociated with TGF-beta 1 expression. Beside being present in the epith elial cells of the colonic tumours, TGF-beta 1 mRNA also occurred in t he stroma: its localization in the macrophages adjacent to tumour stro ngly suggests that TGF-beta 1 could be secreted by macrophages. This h ypothesis should lead to new therapeutic strategies for colorectal car cinoma.