Ca2+-sensing receptor expression and PTHrP secretion in PC-3 human prostate cancer cells

Prostate cancer metastasizes frequently to bone. Elevated extracellular cal cium concentrations ([Ca2+](o)) stimulate parathyroid hormone-related prote in (PTHrP) secretion from normal and malignant cells, potentially acting vi a the [Ca2+](o)-sensing receptor (CaR). Because prostate cancers produce PT HrP, if high [Ca2+](o) stimulates PTHrP secretion via the CaR, this could i nitiate a mechanism whereby osteolysis caused by bony metastases of prostat e cancer promotes further bone resorption. We investigated whether the pros tate cancer cell lines LnCaP and PC-3 express the CaR and whether polycatio nic CaR agonists stimulate PTHrP release. Both PC-3 and LnCaP prostate canc er cell lines expressed bona fide CaR transcripts by Northern analysis and RT-PCR and CaR protein by immunocytochemistry and Western analysis. The pol ycationic CaR agonists [Ca2+](o), neomycin, and spermine each concentration dependently stimulated PTHrP secretion from PC-3 cells, as measured by imm unoradiometric assay, with maximal, 3.2-, 3.6-, and 4.2-fold increases, res pectively. In addition, adenovirus-mediated infection of PC-3 cells with a dominant negative CaR construct attenuated high [Ca2+](o)-evoked PTHrP secr etion, further supporting the CaR's mediatory role in this process. Finally , pretreating PC-3 cells with transforming growth factor (TGF)-beta (1) aug mented both basal and high [Ca2+](o)-stimulated PTHrP secretion. Thus, in P THrP-secreting prostate cancers metastatic to bone, the CaR could initiate a vicious cycle, whereby PTHrP-induced bone resorption releases [Ca2+](o) a nd TGF-beta stored within bone, further increasing PTHrP release and osteol ysis.