A new interaction between Abi-1 and βPIX involved in PDGF-activated actin cytoskeleton reorganisation

Abstract

Members of the Rho family of GTPases are key regulators of the actin cytoskeleton. In particular, activated Rac1 stimulates membrane dorsal ruffle formation in response to platelet-derived growth factor (PDGF). Abl-interactor (Abi)-1 and βPIX, a guanine nucleotide exchange factor for Rac1, localise at these Rac1-induced actin structures and play important roles in the induction of membrane dorsal ruffling in response to PDGF in fibroblasts. Here, we demonstrate a novel interaction between Abi-1 and βPIX using the yeast two-hybrid system, in vitro pull-down assays, and in vivo co-immunoprecipitation experiments. In vitro, the C-terminal fragment of βPIX interacted with Abi-1, while in vivo the N-terminal fragment of βPIX interacted with Abi-1. The biological function of this interaction was investigated in mouse fibroblasts in response to PDGF stimulation. Abi-1 and βPIX co-localised in the cytoplasm and to membrane dorsal ruffles after PDGF treatment. We show that the co-expression of Abi-1 and truncated forms of βPIX in mouse fibroblasts blocked PDGF-induced membrane dorsal ruffles. Together, these results show that the interaction between Abi-1 and βPIX is involved in the formation of growth factor-induced membrane dorsal ruffles. © 2006 IBCB, SIBS, CAS. All rights reserved.