1. ¹Max Planck Institute for Infection Biology, Department of Molecular Biology, Campus Charité Mitte, Charitéplatz 1, Berlin 10 117, Germany
2. ²Laboratory of Cellular Oncology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA

Correspondence: Thomas Rudel, Tel: +49-30-28460-415; Fax: +49-30-28460-401 E-mail: rudel@mpiib-berlin.mpg.de

Received 24 February 2006; Revised 30 July 2006; Accepted 31 July 2006.

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 PIX, 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 PIX using the yeast two-hybrid system, in vitro pull-down assays, and in vivo co-immunoprecipitation experiments. In vitro, the C-terminal fragment of PIX interacted with Abi-1, while in vivo the N-terminal fragment of PIX interacted with Abi-1. The biological function of this interaction was investigated in mouse fibroblasts in response to PDGF stimulation. Abi-1 and PIX 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 PIX in mouse fibroblasts blocked PDGF-induced membrane dorsal ruffles. Together, these results show that the interaction between Abi-1 and PIX is involved in the formation of growth factor-induced membrane dorsal ruffles.