Serum levels of osteocalcin (OC), a bone matrix non-collagenous protein secreted by osteoblasts, are correlated with pathological bone remodeling such as the bone metastasis of cancer, as well as physiological bone turnover. The pathological roles in prostate cancer growth of the two existing types of serum OC, γ-carboxylated (GlaOC) and lower- (or un-) carboxylated (GluOC), have not yet been discriminatively examined. In the present study, we demonstrate that normal prostate epithelial cell growth was promoted by both types of OC, while growth of cancer cells in the prostate was accelerated by GlaOC but suppressed by GluOC. We suggest that OC regulates prostate cancer growth depending on the γ-carboxylation, in part by triggering reduced phosphorylation of receptor tyrosine kinases.
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