Gelsolin mediates collagen phagocytosis through a rac-dependent step.
The role of gelsolin, a calcium-dependent actin-severing protein, in mediating collagen phagocytosis, is not defined. We examined alpha 2 beta 1 integrin-mediated phagocytosis in fibroblasts from wild-type (WT) and gelsolin knockout (Gsn(-)) mice. After initial contact with collagen beads, collagen binding and internalization were 60% lower in Gsn(-) than WT cells. This deficiency was restored by transfection with gelsolin or with beta1 integrin-activating antibodies. WT cells showed robust rac activation and increased [Ca(2+)](i) during early contact with collagen beads, but Gsn(-) cells showed very limited responses. Transfected gelsolin in Gsn(-) cells restored rac activation after collagen binding. Transfection of Gsn(-) cells with active rac increased collagen binding to WT levels. Chelation of intracellular calcium inhibited collagen binding and rac activation, whereas calcium ionophore induced rac activation in WT and Gsn(-) cells. We conclude that the ability of gelsolin to remodel actin filaments is important for collagen-induced calcium entry; calcium in turn is required for rac activation, which subsequently enhances collagen binding to unoccupied alpha 2 beta 1 integrins.
Arora
Pamela D
PD
Canadian Institutes of Health Research Group in Matrix Dynamics, University of Toronto, Toronto, Ontario, Canada M5S 3E2.
Glogauer
Michael
M
Kapus
Andras
A
Kwiatkowski
David J
DJ
McCulloch
Christopher A
CA
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism*; D018260:Gelsolin / Q000378:metabolism*; D038982:Integrin alpha2beta1 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D010587:Phagocytosis / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt
D018260:Gelsolin; D038982:Integrin alpha2beta1; D003094:Collagen; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D002118:Calcium