Protein Kinase C Activation Downregulates Human Organic Anion Transporter 1-mediated Transport Through Carrier Internalization

Organic anion transport in intact renal proximal tubule cells in animal model systems is downregulated by treatments that activate protein kinase C (PKC). How this downregulation is achieved is not yet known. Stimulation of PKC with sn-1,2-dioctanoylglycerol resulted in strong inhibition of p-aminohippurate transport mediated by the cloned human organic anion transporter 1 (hOAT1) expressed in Xenopus oocytes and HEK293 cells, as well as hOAT1 internalization in both expression systems. The sn-1,2-dioctanoylglycerol-induced transport inhibition was partially prevented by staurosporine. It was independent of the conserved canonical PKC consensus sites in hOAT1, however, and was unaffected by agents that destabilize actin filaments or microtubules, which altered baseline hOAT1-mediated p-aminohippurate uptake activity in oocytes. It is concluded that PKC-induced hOAT1 downregulation is achieved through carrier retrieval from the cell membrane and does not involve phosphorylation of the predicted classic hOAT1 PKC consensus sites.