Submitted on January 7, 2008
Accepted on February 20, 2008
Protein Kinase C Inhibits Caveolae-Mediated Endocytosis of TRPV5
Seung-Kuy Cha1, Tao Wu1, and Chou-Long Huang1*
1 Internal Medicine, UT Southwestern Medical Center, Dallas, Texas, United States
* To whom correspondence should be addressed. E-mail: chou-long.huang{at}utsouthwestern.edu.
TRPV5 constitutes the apical entry pathways for transepithelial Ca2+ reabsorption in kidney. Many hormones alter renal Ca2+ reabsorption at least partly by regulating TRPV5. The mechanism for acute regulation of TRPV5 by phospholipase C-coupled hormones is largely unknown. Here, we found that protein kinase C (PKC) activator 1-oleoyl-acetyl-sn-glycerol (OAG) increased TRPV5 current density and surface abundance in cultured cells. The OAG-mediated increase of TRPV5 was prevented by preincubation with specific PKC inhibitors. Coexpression with a dominant-negative dynamin increased the basal TRPV5 current density and prevented the increase by OAG. Knockdown of caveolin-1 by small interference RNA (siRNA) prevented the increase of TRPV5 by OAG. In contrast, knockdown of clathrin heavy chain had no effects. OAG had no effect on TRPV5 expressed in caveolin-1 null cells derived from caveolin-1 knockout mice. Forced expression of recombinant caveolin-1 restored the regulation of TRPV5 by OAG in caveolin-1 knockout cells. Mutations of serine-299 and/or serine-654 of TRPV5 (consensus residues for phosphorylation by PKC) abolished the regulation by OAG. Parathyroid hormone (PTH) increased TRPV5 current density in cells coexpressing TRPV5 and type 1 PTH receptor. The increase caused by PTH was prevented by PKC inhibitor, mutation of serine-299/serine-654 or by knockdown of caveolin-1. Thus, TRPV5 undergoes constitutive caveolae-mediated endocytosis. Activation of PKC increases cell-surface abundance of TRPV5 by inhibiting the endocytosis. This mechanism of regulation by PKC may contribute to the acute stimulation of TRPV5 and renal Ca2+ reabsorption by PTH.
