EVIDENCE THAT C-SRC IS INVOLVED IN THE PROCESS OF OSTEOCLASTIC BONE-RESORPTION

Transgenic mice lacking a functional c-src gene have osteopetrosis, a bone disorder characterized by defective osteoclast function. We have investigated the effects of selective protein tyrosine kinase inhibito rs that are known to inhibit c-src, on osteoclast activity in the bone slice assay. Geldanamycin, herbimycin A and monorden (0.001 - 10 muM) all dose-dependently inhibited bone resorption with IC50 values of 8, 70 and 86 nM, respectively. At concentrations of 0.001 - 1 muM, the c ompounds were not cytotoxic as judged by osteoclast morphology and sur vival on bone slices. In order to determine whether c-src plays a role in signal transduction associated with osteoclast activation prior to bone resorption commencing, or in the resorptive process itself, we p erformed kinetic experiments using human calcitonin as a positive cont rol. Calcitonin inhibited all bone resorption subsequent to its additi on at t = 0, 3 or 6 hr (100%, approximately 90% and approximately 50% inhibition, respectively), after the start of the 24 hr bone slice ass ay. Similar results were obtained with herbimycin A and geldanamycin ( 1 muM) added at t = 0, 3 or 6 hr, and with monorden (1 muM) added at t = 0 and 6 hr. These results indicate that c-src plays a crucial and c ontinuous role in the process of osteoclastic bone resorption, most li kely related to the translocation and/or fusion of exocytic vesicles t o the ruff led border membrane. (C) 1994 Academic Press Inc.