[Demonstration of molecular forms of Rap 1 in cells or tissues deriving from normal or pathological human colonic epithelium].
Mutations of the cK-ras gene which confer oncogenic properties to the corresponding encoded small G protein, occur in 30 to 50% of the human colonic adenocarcinomas. Overexpression of Rap 1A, a member of the Ras family, in K-ras transformed fibroblasts, reverts the transforming properties of the oncogene. This indicates that Rap 1A may exert antagonistic properties towards the K-Ras protein. In this respect, we have been interested in comparing Rap 1 expression in the human adenocarcinoma cell line HT29 and in safe or pathological tissues deriving from the human colonic epithelium. In the human adenocarcinoma cells HT29, several immunoreactive forms of Rap 1 of 71 kDa, 47 kDa, 40 kDa and 24 kDa are detected. Extraction in Triton X-114 allows separation of HT29 cell proteins on the basis of their differential hydrophobic properties. Parallelly, proteins were separated in crude cytosolic or membrane fractions. Most of the immunoreactive material corresponding to the 24 kDa band may contain hydrophobic and membrane associated components. The molecular nature of the higher size components is also discussed here. In the tissues, the 47 kDa form which is common in all of the safe and pathological samples considered, appears to be specifically expressed in the colon. Besides, the 71, 68 and 24 kDa were found in pathological tissues. High expression of Rap 1 was demonstrated to be correlated with cell differentiation in the safe colonic epithelium and in the adenomas. Cloning of the Rap 1A cDNA is now in progress in the laboratory, using PCR detection in an HT29 expression library.