A common downstream signaling activity of osteoclast survival factors thatprevent nitric oxide-promoted osteoclast apoptosis

Treatment with NO-releaser NOC18 significantly promoted apoptosis in murine osteoclast-like cells, with a transient increase in caspase-3-like proteas e activity. In contrast, the apoptosis was protected against by caspase inh ibitors, most efficiently with the broadly acting caspase specific inhibito r z-Asp-CH2-DCB, indicating involvement of multiple caspases in progression of the apoptosis. Among osteoclast survival factors examined, calcitonin c ompletely protected against morphologically defined-apoptosis and the incre ase of caspase-3-like protease activity. The effect of calcitonin was mimic ked by treatment of cells with (Bu)(2)cAMP and forskolin, and abolished by protein kinase-A inhibitor H-89. Independently from the PKA activation, col ony stimulating factor-1, interleukin-1 beta and the receptor activator of NF-kappa B ligand also protected against the apoptosis but were less effect ive than calcitonin. All survival factors investigated inhibited conversion of procaspases-3 and -9 to their mature forms in the cells. Thus, downstre am antiapoptotic signaling activity from each factor overlapped in inhibiti on of caspases. However, how this was attained seemed to be different from each other. Typically, only colony stimulating factor-1 up-regulated expres sion of endogenous caspase inhibitor protein, X-linked inhibitor of apoptos is (XIAP), in the osteoclast-like cells.