Parathyroid hormone-mediated regulation of Na+-K+-ATPase requires ERK-dependent translocation of protein kinase Cα

Parathyroid hormone (PTH) inhibits Na+-K+-ATPase activity by serine phosphorylation of the alpha(1) subunit through protein kinase C (PKC)- and extracellular signal-regulated kinase (ERK)-dependent pathways. Based on previous studies we postulated that PTH regulates sodium pump activity through isoform-specific PKC-dependent activation of ERK. In the present work utilizing opossum kidney cells, a model of renal proximal tubule, PTH stimulated membrane translocation of PKCalpha by 102 +/- 16% and PKC betaI by 41 +/- 7% but had no effect on PKCbetaII and PKCzeta. Both PKCalpha and PKCbetaI phosphorylated the Na+-K+-ATPase alpha(1) subunit in vitro. PTH increased the activity of PKCalpha but not PKCbetaI. Coimmuno-precipitation assays demonstrated that treatment with PTH enhanced the association between Na+-K+-ATPase alpha(1) subunit and PKCalpha, whereas the association between Na+-K+-ATPase alpha(1) subunit and PKCbetaI remained unchanged. A PKCalpha inhibitory peptide blocked PTH-stimulated serine phosphorylation of the Na+-K+ ATPase alpha(1) subunit and inhibition of Na+-K+-ATPase activity. Pharmacologic inhibition of MEK-1 blocked PTH-stimulated translocation of PKCalpha, whereas transfection of constitutively active MEK-1 cDNA induced translocation of PKCalpha and increased phosphorylation of the Na+-K+-ATPase alpha(1) subunit. In contrast, PTH-stimulated ERK activation was not inhibited by pretreatment with the PKCalpha inhibitory peptide. Inhibition of PKCalpha expression by siRNA did not inhibit PTH-mediated ERK activation but significantly reduced PTH-mediated phosphorylation of the Na+-K+-ATPase alpha(1) subunit. Pharmacologic inhibition of phosphoinositide 3-kinase blocked PTH-stimulated ERK activation, translocation of PKCalpha, and phosphorylation of the Na+-K+-ATPase alpha(1) subunit. We conclude that PTH stimulates Na+-K+-ATPase phosphorylation and decreases the activity of Na+-K+-ATPase by ERK-dependent activation of PKCalpha.