Calcium/calmodulin‐dependent kinase II regulates notch‐1 signaling in prostate cancer cells

Notch signaling is associated with prostate osteoblastic bone metastases and calcium/calmodulin‐dependent kinase II (CaMKII) is associated with osteoblastogenesis of human mesenchymal stem cells. Here we show that prostate cancer cell lines C4‐2B and PC3, both derived from bone metastases and express Notch‐1, have all four isoforms of CaMKII (α, β, γ, δ). In contrast, prostate cancer cell lines LNcaP and DU145, which are not derived from bone metastases and lack the Notch‐1 receptor, both lack the alpha isoform of CaMKII. In addition, DU145 cells also lack the β‐isoform. In C4‐2B cells, inhibition of CaMKII by KN93 or γ‐secretase by L‐685,458 inhibited the formation of the cleaved form of Notch‐1 thus inhibiting Notch signaling. KN93 inhibited down stream Notch‐1 signaling including Hes‐1 gene expression, Hes‐1 promoter activity, and c‐Myc expression. In addition, both KN93 and L‐685,458 inhibited proliferation and Matrigel invasion by C4‐2B cells. The activity of γ‐secretase was unaffected by KN93 but markedly inhibited by L‐685,458. Inhibition of the expression of α, β, or γ‐isoform by siRNA did not affect Hes‐1 gene expression, however when expression of one isoform was inhibited by siRNA, there were compensatory changes in the expression of the other isoforms. Over‐expression of CaMKII‐α increased Hes‐1 expression, consistent with Notch‐1 signaling being at least partially dependent upon CaMKII. This unique crosstalk between CaMKII and Notch‐1 pathways provides new insight into Notch signaling and potentially provides new targets for pharmacotherapeutics. J. Cell. Biochem. 106: 25–32, 2009. © 2008 Wiley‐Liss, Inc.