Phosphorylation-dependent association of the Ras-related GTP-binding protein Rem with 14-3-3 proteins

Rem belongs to a subfamily of Ras-related GTPases that includes Rad, Gem, and Kir. These proteins are unique among the Ras superfamily since their expression is under transcriptional regulation and they contain distinct amino and carboxyl termini. To gain insight into the cellular function of Rem, we have undertaken an expression screen using a mouse embryo cDNA library to identify Rem-interacting proteins and find that Rem interacts with a series of 14-3-3 isoforms (epsilon, eta, theta, and zeta). Immunoprecipitation studies demonstrate an interaction that is independent of the nucleotide state of Rem. Rem is phosphorylated in vivo, and binding of Rem to 14-3-3zeta is abolished by pretreating Rem with protein phosphatase 1. Thus, the association of Rem and 14-3-3zeta is phosphorylation-dependent. Examination of the interaction between 14-3-3zeta and various Rem deletion mutants mapped a critical binding site to the C-terminus of Rem. Finally, we demonstrate the interaction of Rad but not the newly identified Rem2 protein with 14-3-3 proteins. These results suggest that 14-3-3 may allow the recruitment of distinct proteins that participate in Rem-mediated signal transduction pathways.