RAS-INTERACTING DOMAIN OF RAL GDP DISSOCIATION STIMULATOR LIKE (RGL) REVERSES V-RAS-INDUCED TRANSFORMATION AND RAF-1 ACTIVATION IN NIH3T3 CELLS

Ral GDP dissociation stimulator (RalGDS) and RalGDS like (RGL) are put ative effector proteins of Ras and contain the Ras-interacting domain (RID) at their C-terminal regions, v-Ras is known to activate c-fos pr omoter/enhancer and Raf-1 and to transform NIH3T3 cells. It is also kn own that v-Raf activates c-fos promoter/enhancer and transforms NIH3T3 cells. In this study, we examined the effect of RID on the phenotype of the cells transformed by v-Ras and v-Raf. Overexpression of RID gre atly reduced cell growth in low serum, colony-forming activity in soft agar, c-fos promoter/enhancer activity, and Raf-1 activity of v-Ras-t ransformed cells. However, overexpression of RID did not affect the ph enotype of v-Raf-transformed cells. These results clearly indicate tha t RID of RGL specifically binds to Ras in mammalian cells, that it blo cks the signal from Ras to Raf-1, and that it reverses v-Ras-induced m alignant phenotype. It has been reported that Ras-binding domains of R af-1 and neurofibromatosis type 1 (NF1) reverse v-Ras-induced malignan t phenotype, Since there is no homology in primary structures of RGL, Raf-1, and NF1, there may be a similarity of secondary or tertiary str ucture among RID of RGL and Ras-binding domains of Raf-1 and NF1, and the structure might be useful for developing a potential medicine for human cancers caused by Ras.