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 Ras. RGL shares 50% amino acid identity with Ral GDP dissociation stimulator and contains the CDC25-like domain in the central region and the Ras-interacting domain in the C-terminal region. Since the modes of activation and action of RGL have not yet been clarified, in this paper we have analyzed the functions of RGL. In COS cells, RGL interacted with RasG12V/E37G (a Ras mutant in which Gly-12 and Glu-37 were changed to Val and Gly, respectively) which failed to bind to Raf, but not with RasG12V/T35S which bound to Raf. Raf did not inhibit the binding of RGL to RasG12V/E37G under the condition that Raf inhibited that of RGL to RasG12V. Expression of either RGL or Raf into NIH3T3 cells slightly activated c-fos promoter, while coexpression of both proteins greatly stimulated the c-fos promoter 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 Ras, Rac, CDC42, Rap, or Rho. Furthermore, this action of RGL to stimulate the GDP/GTP exchange of Ral was dependent on Ras in COS cells. These results suggest that RGL constitutes another Ras-signaling pathway which is distinct from the Raf pathway and indicate that the RGL pathway regulates the c-fos promoter activity and the GDP/GTP exchange of Ral.