[Regulation of a small GTPase Rap2].

Rap2 is a member of Ras-family G proteins and related most closely to Rap1; however little is known about the regulation of Rap2 activity. In this study, I have compared the regulation and function of Rap2 with those of Rap1. In 293T cells, Rap2 was regulated by the same set of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) as those which regulated Rap1. Rap2 was localized at both plasma membrane and intracellular membrane compartments, as Rap1 was. Rap2 bound to the Ras-binding domain of Raf and inhibited Ras-dependent activation of Elk1 transcription factor. I have found that the GTP-bound form exceeds 50% of total Rap2 in the cells. This observation suggests that Rap2 suppresses Ras-mediated activation of ERK/MAP kinase cascade in quiescent cells.