REVERSION OF A HUMAN TUMOR-CELL LINE CONTAINING ONCOGENIC P21(RAS) ISASSOCIATED WITH A DEFECT IN THE POSTTRANSLATIONAL PROCESSING OF THE RAS PROTEIN

Correct post-translational modifications of the ras proteins are essen tial for their membrane localisation and functioning. The flat reverta nt cell lines 1aCB and 8b, derived from the human bladder carcinoma ce ll line EJ, contain the transforming gene V12Ha-ras and are resistant to retransformation by vas protein or DNA, but still do require the pr esence of ras for proliferation. Both revertant cell lines demonstrate d reduced levels of membrane associated p21(ras) when compared to thei r parental EJ cell lines. This reduced level in 1aCB was reflected by an increase in nuclear associated p21(ras), as seen by immunofluoresce nce of endogenous and introduced ras. In addition, 1aCB had a reduced ratio of ras in the detergent to aqueous phases after triton X114 part itioning, suggesting a defect in Step I processing of the p21(ras) in the cell line. This was not however due to defects in the Step I enzym es farnesyltransferase or carboxymethyltransferase whose activities we re not reduced.