The small GTP-binding protein Rab4 has been involved in the recycling of alphavbeta3 integrins in response to platelet-derived growth factor (PDGF) stimulation suggesting a role for Rab4 in cell adhesion and migration. In this study, we explored the role of Rabip4 and Rabip4', two Rab4 effector proteins, in migration of NIH 3T3 fibroblasts. In these cells, Rabip4 and Rabip4', collectively named Rabip4s, were partially co-localized with the early endosomal marker EEA1. PDGF treatment re-distributed endogenous Rabip4s toward the cell periphery where they colocalized with F-actin. In cells expressing green fluorescent protein (GFP)-Rabip4 or GFP-Rabip4', constitutive appearance of GFP-Rabip4s at the cell periphery was accompanied by local increase in cortical F-actin in membrane ruffles at the leading edge. The expression of GFP-Rabip4 induced an increased migration compared with control cells expressing GFP alone, even in the absence of PDGF stimulation. On the contrary, in cells expressing a mutated form of Rabip4s unable to interact with Rab4, lack of typical leading edge was observed. Furthermore, PDGF treatment did not stimulate the migration of these cells. Furthermore, down-regulation of the expression of Rabip4s inhibited PDGF-stimulated cell migration. Endogenous Rabip4s were localized with alphav integrins at the leading edge following PDGF treatment, whereas in cells expressing GFP-Rabip4s, alphav integrins, together with GFP-Rabip4s, were constitutively localized at the leading edge. In contrast, reduction in Rabip4s expression levels using small interfering RNA was associated with impaired PDGF-induced translocation of alphav integrins toward the leading edge. Taken together, our data provide evidence that Rabip4s, possibly via their interaction with Rab4, regulate integrin trafficking and are involved in the migration of NIH 3T3 fibroblasts.
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