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Protein kinase C-dependent phosphorylation regulates osteoclast calcium-sensing
L Argentino1, S Colucci, M Grano
1Istituto di Anatomia Umana Normale, Università di Bari.
Summary
Protein kinase C (PKC) plays a key role in osteoclast calcium-sensing, enhancing bone resorption inhibition. This finding suggests PKC and PKA synergistically regulate osteoclast activity through phosphorylation.
Area of Science:
- Cell Biology
- Biochemistry
- Bone Biology
Background:
- Osteoclasts possess a membrane calcium-sensing mechanism that regulates bone resorption.
- Extracellular calcium concentration ([Ca2+]o) influences intracellular calcium ([Ca2+]i) and osteoclast activity.
- Protein kinase C (PKC) is hypothesized to be involved in this calcium-sensing pathway.
Purpose of the Study:
- To investigate the role of PKC in regulating osteoclast calcium-sensing and activity.
- To determine if PKC activation or inhibition affects the osteoclast response to extracellular calcium.
- To elucidate the contribution of PKC to the modulation of bone resorption.
Main Methods:
- Experiments were conducted on single rabbit osteoclasts.
- Intracellular calcium ([Ca2+]i) was measured using fura 2-loaded cells.
- Osteoclasts were treated with PKC activators (phorbol esters) and inhibitors (H7, staurosporine, sphingosine).
Main Results:
- PKC activation by phorbol esters doubled the [Ca2+]o-induced [Ca2+]i elevation.
- PKC inhibition by H7, staurosporine, or sphingosine completely blocked the osteoclast response to elevated [Ca2+]o.
- A control inactive agent, 4Aphorbol, did not alter the cellular response.
Conclusions:
- PKC plays a synergistic role in the regulation of osteoclast calcium-sensing.
- The findings support a model where both PKA and PKC-dependent phosphorylations positively feedback on osteoclast calcium-sensing.
- PKC is a critical mediator in the control of osteoclast function and bone resorption.