Protein kinases D2 and D3 are novel growth regulators in HCC1806 triple-negative breast cancer cells.

AIM The role of protein kinase D (PKD) in the context of breast cancer cell biology is not clear. MATERIALS AND METHODS The expression of PKD isoforms was assessed in various breast cancer cell lines and PKD isoform-specific siRNAs and selective inhibitors were used to study the role of PKD in breast cancer cell growth. RESULTS PKD2 and PKD3 were two major isoforms expressed at the highest levels in tumorgenic HCC1806 triple-negative breast cancer cells. Silencing PKD2 or PKD3 significantly inhibited HCC1806 cell proliferation, and PKD3 silencing had a higher inhibitory effect than PKD2 silencing on cell growth and PKD-mediated signaling. HCC1806 breast cancer cells were highly responsive to PKD inhibitors but not to a general protein kinase C (PKC) inhibitor. CONCLUSION We have identified PKD2 and PKD3, especially PKD3, as novel cell growth regulators in HCC1806 triple-negative breast cancer cells. Targeting PKD instead of all PKCs effectively inhibited cell proliferation in a number of breast cancer cell lines.