A role for gelsolin in stress fiber-dependent cell contraction

Gelsolin is an abundant actin binding protein that mediates the rapid remod eling of cortical actin filaments through severing, capping, and nucleating activities. Most of the attention on the intracellular function of gelsoli n has focused on the remodeling of the cortical actin meshwork but the loca lization of gelsolin to other regions of the cell suggests that it may have other important functions elsewhere. In cultured fibroblasts, gelsolin is heavily enriched in stress fibers, where its function in these contractile organelles is unknown. To study gelsolin function during stress fiber forma tion and cell contraction, we first assessed gelsolin levels in stress fibe r preparations from lysophosphatidic acid (LPA)-treated human fibroblasts. LPA induced a large, time-dependent, calcium-independent increase of actin, gelsolin, alpha-actinin, and tropomyosin in stress fiber preparations. A m icroinjected gelsolin antibody that inhibits severing by gelsolin reduced s tress fibers. Anti-sense-transfected gelsolin-depleted 3T3 cell lines treat ed with LPA after serum starvation required similar to 6 h to form stress f ibers and focal adhesions, in contrast to control lines transfected with ve ctor only, which formed stress fibers 15 min after addition of LPA. In cell s microinjected with the gelsolin antibody that inhibits severing, Mg-ATP-i nduced cell contraction was greatly reduced in similar to 90% of injected c ells compared to cells injected with an irrelevant antibody. Gelsolin-deple ted cells were incapable of collagen gel contraction and showed no apparent Mg-ATP induced cell contraction compared to cell lines transfected with ve ctor only. The involvement of gelsolin in cell contraction and remodeling o f collagen gels suggests a novel role for gelsolin in stress fiber-dependen t cell function. (C) 1999 Academic Press.