Submitted on March 21, 2008
Revised on April 22, 2008
Accepted on April 22, 2008
Collagen phagocytosis is regulated by the guanine nucleotide exchange factor Vav2
Pamela D Arora1, Paola Marignani2, and Christopher A. G. McCulloch1*
1 University of Toronto
2 Dept. of Biochemistry
* To whom correspondence should be addressed. E-mail: christopher.mcculloch{at}utoronto.ca.
Collagen phagocytosis is a crucial, 
2
1 integrin-dependent process that mediates extracellular matrix remodeling by fibroblasts. We showed previously that after initial contact with collagen, activated Rac1 accelerates collagen phagocytosis but the Rac guanine nucleotide exchange factors (GEFs) that regulate Rac are not defined. We examined here the GEFs that regulate collagen phagocytosis in mouse fibroblasts. Collagen binding enhanced Rac1 activity (5-20 mins) but not Cdc42 or RhoA. Analysis of collagen bead-associated proteins showed enrichment with Vav2, which correlated temporally with increased Rac1 activity. Knockdown of Vav2 prevented Rac activation, recruitment of Rac1 to collagen bead binding sites and collagen bead binding but knockdown of Sos-1 or -Pix had no effect on Rac activation or collagen binding. Vav2 associated with the nucleotide-free Rac1 mutant (G15ARac1) after collagen binding. Collagen bead binding promoted phosphorylation of Vav2 which temporally correlated with Rac1 activation and which required Src kinase activity. Blockage of Src activity prevented collagen bead-induced Rac activation and collagen bead binding. Collectively these data indicate that Vav2 regulates the Rac1 activity associated with the binding step of collagen phagocytosis.
