Role of Protein Kinase C in Endothelin Converting Enzyme-1 trafficking and shedding from endothelial cells.

This study aimed to determine the consequences of Protein Kinase C (PKC) mediated Endothelin Converting Enzyme-1 (ECE-1) phosphorylation and its relationship to ECE-1 expression and shedding. The proteins on the surface of EA.hy926 cells were labelled with EZ-Link NHS-SS-Biotin both prior to (control) and following stimulation by 2 microM phorbol 12-myristate 13-acetate (PMA) which activates PKC. The biotinylated proteins were isolated using neutravidin beads, resolved by gel electrophoresis and analysed by western blotting using anti-ECE-1 antibodies. Significant increase in ECE-1 expression at the cell surface was observed following stimulation by PMA, compared to unstimulated control cells (170+/-32.3% of control, n=5). The ECE-1 activity (expressed as microM substrate cleaved/min) was determined by monitoring the cleavage of a quenched fluorescent substrate. The specificity of cleavage was confirmed using the ECE-1 inhibitor CGS35066. The stimulation of cells by PMA (1 microM, 6 h) significantly increased the ECE-1 activity (0.28+/-0.02; n=3) compared to the control (0.07+/-0.02; n=3). This increase was prevented by prior incubation with the PKC inhibitor bisindolymaleimide (BIM; 2 microM for 1 h; 0.10+/-0.01; n=3). Treatment with PMA also increased the activity of ECE-1 in the media (0.18+/-0.01; n=3) compared to control (0.08+/-0.01; n=3). In addition, this study confirmed by western immunoblotting that only the extracellular region of ECE-1 is released from the cell surface. These data indicate for the first time that PKC activation induces the trafficking and shedding of ECE to and from the cell surface, respectively. Crown Copyright (c) 2010. Published by Elsevier Inc. All rights reserved.