NORMAL AND TRANSFORMING RAS ARE DIFFERENTLY REGULATED FOR POSTTRANSLATIONAL MODIFICATIONS

Point mutation of the c-H-ras gene significantly increases cellular tr ansforming activities of Pas. Since posttranslational modification and subsequent membrane localization are essential for the biological act ivities of Ras, we examined whether or not the mutation also affects t hese two factors. The normal (Gly(12)) or the transforming (Val(12)) c -H-ras gene was expressed in NIH3T3 cells using a metallothionein prom oter. Expression of either type of Ras was efficiently induced by the cadmium treatment of these cells, and immunoprecipitation of metabolic ally labeled cell extracts revealed that both normal and transforming Ras were expressed as four differently migrating forms on SDS-polyacry lamide gels, two of which were slower migrating cytosolic precursors a nd the other two were faster migrating membrane-bound forms. There was no significant difference in half lives between normal and transformi ng Ras; however, posttranslational modification was quite different be tween the two types of Ras. Transforming Ras was processed and became membrane-bound forms much more efficiently than normal Ras. Interestin gly, posttranslational modification and membrane localization of Ras w as significantly inhibited when the c-myc oncogene was co-expressed wi th Ras. In contrast to the c-myc oncogene, expression of either wild t ype or mutant p53 did not affect the posttranslational modification of Ras, suggesting that the c-myc oncogene specifically impairs the post translational modification of Ras. (C) 1996 Wiley-Liss, Inc.