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Evidence that c-src is involved in the process of osteoclastic bone resorption
T J Hall1, M Schaeublin, M Missbach
1Ciba-Geigy Ltd., Research Department, Basel, Switzerland.
Abstract:
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 inhibitors that are known to inhibit c-src, on osteoclast activity in the bone slice assay. Geldanamycin, herbimycin A and monorden (0.001-10 microM) all dose-dependently inhibited bone resorption with IC50 values of 8, 70 and 86 nM, respectively. At concentrations of 0.001-1 microM, the compounds were not cytotoxic as judged by osteoclast morphology and survival 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 performed kinetic experiments using human calcitonin as a positive control. Calcitonin inhibited all bone resorption subsequent to its addition at t = 0, 3 or 6 hr (100%, approximately 90% and approximately 50% inhibition, respectively), after the start of the 24 hr bone slice assay. Similar results were obtained with herbimycin A and geldanamycin (1 microM) added at t = 0, 3 or 6 hr, and with monorden (1 microM) added at t = 0 and 6 hr. These results indicate that c-src plays a crucial and continuous role in the process of osteoclastic bone resorption, most likely related to the translocation and/or fusion of exocytic vesicles to the ruffled border membrane.
Insights
The protein tyrosine kinase c-src (cell survival region) is crucial for osteoclast function and bone resorption. Inhibiting c-src effectively reduces bone resorption without harming osteoclasts.
Area of Science:
- Biochemistry
- Cell Biology
- Bone Biology
Background:
- Transgenic mice lacking functional c-src exhibit osteopetrosis, indicating a role for c-src in osteoclast activity.
- Osteopetrosis is a bone disorder characterized by impaired osteoclast function.
Purpose of the Study:
- To investigate the effects of selective protein tyrosine kinase inhibitors, known to inhibit c-src, on osteoclast activity.
- To determine if c-src is involved in osteoclast activation or the bone resorption process itself.
Main Methods:
- Utilized a bone slice assay to assess osteoclast activity.
- Administered selective c-src inhibitors (Geldanamycin, Herbimycin A, Monorden) and human calcitonin at various time points.
- Evaluated dose-dependent inhibition and cytotoxicity of compounds.
Main Results:
- Geldanamycin, Herbimycin A, and Monorden dose-dependently inhibited bone resorption with low IC50 values.
- Compounds were not cytotoxic at effective concentrations.
- Kinetic experiments demonstrated that c-src inhibition affects ongoing bone resorption, similar to calcitonin.
Conclusions:
- c-src plays a critical and continuous role in osteoclastic bone resorption.
- The role of c-src is likely associated with exocytic vesicle translocation and fusion at the ruffled border membrane.