RECOGNITION OF OSTEOPONTIN AND RELATED PEPTIDES BY AN ALPHA-V-BETA-3 INTEGRIN STIMULATES IMMEDIATE CELL SIGNALS IN OSTEOCLASTS

We have investigated the nature of immediate cell signals produced by occupancy of the chicken osteoclast alpha-v-beta-3 integrin. Synthetic osteopontin and peptides from the osteopontin and bone sialoprotein sequences containing Arg-Gly-Asp stimulated immediate reductions in osteoclast cytosolic Ca2+. The changes in cytosolic Ca2+ required the Arg-Gly-Asp sequence and were blocked by a monoclonal antibody to the alpha-v-beta-3 integrin, LM609. Osteoclast stimulation by the proteins through the integrin did not require immobilization since soluble peptides produced changes in cytosolic Ca2+ and inhibited osteoclast binding to bone particles and bone resorption. The decrease in cytosolic Ca2+ stimulated by osteopontin and related peptides appeared to be due to activation of a plasma membrane Ca2+-ATPase by calmodulin. Thus, the data suggest that ligand binding to the osteoclast alpha-v-beta-3 integrin results in calmodulin-dependent reduction in cytosolic Ca2+ which participates in regulation of osteoclast function.