ArgBP2γ interacts with akt and p21 activated kinase-1 and promotes cell survival

Akt/protein kinase B is a major cell survival pathway through phosphorylation of proapoptotic proteins Bad and Bax and of additional apoptotic pathways linked to Forkhead proteins glycogen synthase kinase-3 beta and ASK1. To further explore the mechanism by which Akt regulates cell survival, we identified an Akt interaction protein by yeast two-hybrid screening. It is highly homologous to ARG-binding protein 2 ( ArgBP2) with splicing exon 8 of the coding region of the ArgBP2. As two splicing isoforms (ArgBP2 alpha and -beta) of ArgBP2 have been identified (Wang, B., Golemis, E. A., and Kruh, G. D. ( 1997) J. Biol. Chem. 272, 17542 - 17550), it was named ArgBP2 gamma. ArgBP2 gamma contains four Akt phosphorylation consensus sites, a SoHo motif, and three Src homology (SH) 3 domains and binds to C-terminal proline-rich motifs of Akt through its first and second SH3 domains. It also interacts with p21-activated protein kinase ( PAK1) via its first and third SH3 domains, indicating the SH3 domains of ArgBP2 gamma as docking sites for Akt and PAK1. Akt phosphorylates ArgBP2 gamma in vitro and in vivo. Expression of ArgBP2 gamma induces PAK1 activity and overrides apoptosis induced by ectopic expression of Bad or DNA damage. Nonphosphorylatable ArgBP2 gamma-4A and SH3 domain-truncated mutant ArgBP2 inhibit Akt-induced PAK1 activation and reduce Akt and PAK1 phosphorylation of Bad and antiapoptotic function. These data indicate that ArgBP2 gamma is a physiological substrate of Akt, functions as an adaptor for Akt and PAK1, and plays a role in Akt/PAK1 cell survival pathway.