Rho-A is critical for osteoclast podosome organization, motility, and boneresorption

Rho plays a regulatory role in the formation of actin stress fibers and foc al adhesions, and it is also involved in integrin-mediated signaling events . To study the role of Rho in alpha(v)beta(3)/gelsolin-dependent signaling, the HIV-Tat peptide, hemagglutinin (HA)-taffged Rho(Val-14) (constitutivel y active) and Rho(Asn-19) (dominant negative) were transduced into avian os teoclasts. Protein transduction by HA-Tat was highly efficient, and 90-100% of the cells were transduced with HA-tagged proteins. We demonstrate here that Rho(Val-14) transduction (100 nM) stimulated gelsolin-associated phosp hatidylinositol 3-kinase activity, podosome assembly, stress fiber formatio n, osteoclast motility, and bone resorption, mimicking osteoclast stimulati on by osteopontin/alpha(v)beta(3). The effects of Rho(Val-14) transduction stimulation was time-dependent. C3 exoenzyme blocked the effects of Rho(Val -14) and induced podosome disassembly, loss of motility, and inhibition of bone resorption, Transduction of Rho(Asn-19) produced podosome disassembly, and blocked osteopontin stimulation. These data demonstrate that integrin- dependent activation of phosphoinositide synthesis, actin stress fiber form ation, podosome reorganization for osteoclast motility, and bone resorption require Rho stimulation.