Characterization of choline kinase in human endothelial cells.

High choline kinase- (Chk-) expression is frequently observed in cancer cells, making it a novel target for pharmacological and molecular inhibition. As inhibiting agents are delivered systemically, it is important to determine Chk- expression levels in endothelial cells that line both normal and tumor vasculature, and the effect of Chk- downregulation on these cells. Here, we characterized Chk- expression and the effect of its downregulation in human umbilical vein endothelial cells (HUVECs) relative to MDA-MB-231 human breast cancer cells. We used small interfering RNA (siRNA) to downregulate Chk- expression. Basal mRNA levels of Chk- were approximately three-fold lower in HUVECs relative to MDA-MB-231 breast cancer cells. Consistent with the differences in Chk- protein levels, phosphocholine levels were approximately 10-fold lower in HUVECs relative to MDA-MB-231 cells. Transient transfection with siRNA-Chk resulted in comparable levels of mRNA and protein in MDA-MB-231 breast cancer cells and HUVECs. However, there was a significant reduction in proliferation in MDA-MB-231 cells, but not in HUVECs. No significant difference in CD31 immunostaining was observed in tumor sections obtained from mice injected with control luciferase-short hairpin (sh)RNA or Chk-shRNA lentivirus. These data suggest that systemically delivered agents that downregulate Chk- in tumors will not affect endothelial cell proliferation during delivery, and further support the development of Chk- downregulation as a cancer-specific treatment. Copyright (c) 2013 John Wiley & Sons, Ltd.