Cyr61 downmodulation potentiates the anticancer effects of zoledronic acid in androgen-independent prostate cancer cells

We have analyzed the gene modulation induced by zoledronic acid (ZOL) in androgen-resistant prostate cancer PC3 cells with cDNA microarray platform to identify new molecular targets of ZOL in prostate cancer. The gene coding for cysteine-rich, angiogenic inducer, 61 (CYR61) resulted highly downregulated with a fold change of 5.58. Therefore, we have studied the effects of ZOL on CYR61 protein product, and we have found that CYR61 protein expression was decreased significantly after exposure to ZOL. The effect of ZOL on CYR61 expression was dose and time dependent was due to a reduced transcriptional activity of CYR61 promoter. Moreover, the effects induced by ZOL were paralleled by decreased activation of Ras-Raf-1- and Akt-dependent pathways that was dependent from isoprenylation inhibition, since it was antagonized by the addition of geranylgeraniol. Finally, we have investigated the role of CYR61 in the regulation of growth inhibition and invasion/motility of PC3 cells using a shRNA for CYR61 to downregulate the expression of CYR61 protein. The enhanced inhibition of proliferation and motility/invasion induced by ZOL by S-phase accumulation. In the same experimental conditions, CYR61 protein downregulation potentiated the inactivation of the Ras-dependent proliferation pathway and cell cycle inhibitors p21 and p27 expression.