CHARACTERIZATION OF RAL GDP DISSOCIATION STIMULATOR-LIKE (RGL) ACTIVITIES TO REGULATE C-FOS PROMOTER AND THE GDP GTP EXCHANGE OF RAL/

Ral GDP dissociation stimulator-like (RGL) has been identified to be a possible effector protein of has. RGL shares 50% amino acid identity with Ral GDP dissociation stimulator and contains the CDC25-like domai n in the central region and the Has-interacting domain in the C-termin al region. Since the modes of activation and action of RGL have not ye t been clarified, in this paper we have analyzed the functions of RGL. In COS cells, RGL interacted with Ras(G12V/E37G) (a pus mutant in whi ch Gly-12 and Glu-37 were changed to Val and Gly, respectively) which failed to bind to Raf, but not with Ras(G12V/T35S) which bound to Raf. Raf did not inhibit the binding of RGL to Ras(G12V/E37G) under the co ndition that Raf inhibited that of RGL to Ras(G12V). Expression of eit her RGL or Raf into NIH3T3 cells slightly activated c-fos promoter, wh ile coexpression of both proteins greatly stimulated the c-fos promote r activity. RGL stimulated the GDP/GTP exchange of Ral and this action was enhanced by the post-translational modification of Ral. However, RGL was not active on Has, Rac, CDC42, Rap, or Rho. Furthermore, this action of RGL to stimulate the GDP/GTP exchange of Ral was dependent o n Has in COS cells. These results suggest that RGL constitutes another Ras-signaling pathway which is distinct from the Raf pathway and indi cate that the RGL pathway regulates the c-fos promoter activity and th e GDP/GTP exchange of Ral.