Mammalian Diaphanous (mDia) may be involved in the signal transduction of sphingosine-1-phosphate on developing actin stress fiber of human fibroblasts

Sphingosine 1-phosphate (S1P) is a biologically active lipid mediator with many pivotal roles in the regulation of cell growth, migration, differentiation, and apoptosis. However, signal transduction mediated by S1P in human fibroblasts is still unclear. We investigated signal transduction by S1P in human fibroblasts using collagen matrix contraction in order to explore whether or not S1P could be applied for the treatment of skin wound healing. We found that S1P promoted floating collagen matrices' contraction, for the in vitro model of initial phase wound contraction, in which some kinds of G protein, such as Gi alpha, Rac 1, and Rho, were involved. However, Rho-associated coiled-coil forming kinase (ROCK) was partially involved in S1P-promoting floating collagen matrices contraction. Mammalian Diaphanous (mDia) as well as ROCK have been identified to be putative downstream target molecules of Rho. In mDia-silenced cells, the ROCK inhibitor suppressed actin stress fiber formation regardless of the presence or absence of S1P. Our results indicate that mDia as well as ROCK may be situated downstream of Gi alpha, Rac1, and Rho to induce actin stress fiber development by human fibroblasts stimulated with SIP.