Protein Kinase C regulation of the Na, K‐ATPase α3 isoform in highly metastatic human prostate cells

Abstract

The Na,K-ATPase is a membrane spanning protein complex that plays a central role in maintaining cellular homeostasis via the exchange of Na+ and K+ ions while consuming energy in the form of cellular ATP. The catalytic subunit of the pump exists in four isoforms (α1, α2, α3, and α4) of which the physiological significance is unknown. One distinction between the α-isoforms may be their regulation by Protein Kinase C (PKC). In many cell types, the α1-isoform typically responds with increased transport when treated with the PKC activator phorbol myristate acetate (PMA). This also appears to be the situation for human prostate cells in culture. In a highly metastatic line (PC3), however, the response of the ATPase-mediated transport to PKC activation over a five minute period is a decrease in activity (−16%). Moreover, PC3 cells express both the α1- and α3-isoforms, but it is unclear which isoforms are being regulated. To address this issue, we expressed exogenous α3 in PC3 cells under conditions in which the endogenous isoforms were inhibited with ouabain. When challenged with PMA, the transfected PC3 cells displayed a decrease in transport indistinguishable from that of the endogenous enzymes (−19%). This indicates that the α3 does indeed respond to PKC stimulation. In addition, it is tempting to suggest that the metastatic state of the PC3 cells may contribute to the altered regulatory response to PKC stimulation. [This project was supported in part by NIH RR-19799 and a Howard Hughes Medical Institute grant through the Undergraduate Science Education Program to Texas Tech University.]