Protein kinase C-induced phosphorylation modulates the Na+-ATPase activity from proximal tubules

Abstract

This study describes the modulation of the ouabain-insensitive Na(+)-ATPase activity from renal proximal tubule basolateral membranes (BLM) by protein kinase C (PKC). Two PKC isoforms were identified in BLM, one of 75 kDa and the other of 135 kDa. The former correlates with the PKC isoforms described in the literature but the latter seems to be a novel isoform, not yet identified. Both PKC isoforms of BLM are functional since a protein kinase C activator, TPA, increased the total hydroxylamine-resistant 32P(i) incorporation from [gamma-32P]ATP into the BLM. In parallel, TPA stimulated the Na(+)-ATPase activity from BLM in a dose-dependent manner, the effect being reversed by the PKC inhibitor sphingosine. The stimulatory effect of TPA on Na(+)-ATPase involved an increase in the V(max) (from 13.4+/-0.6 nmol P(i) mg(-1) min(-1) to 25.2+/-1.4 nmol P(i) mg(-1) min(-1), in the presence of TPA, P<0.05) but did not change the apparent affinity for Na(+) (K(0.5)=14.5+/-2.1 mM in control and 10.0+/-2.1 mM in the presence of TPA, P>0.07). PKC involvement was further confirmed by stimulation of the Na(+)-ATPase activity by the catalytic subunit of PKC (PKC-M). Finally, the phosphorylation of an approx. 100 kDa protein in the BLM (the suggested molecular mass of Na(+)-ATPase [1]) was induced by TPA. Taken together, these findings indicate that PKCs resident in BLM stimulate Na(+)-ATPase activity which could represent an important mechanism of regulation of proximal tubule Na(+) reabsorption.

Na+,K+‐ATPase is modulated by angiotensin II in diabetic rat kidney – another reason for diabetic nephropathy?

“…Besides the protein amount, phosphorylation takes a major part in the regulation of NKA enzyme activity and subcellular distribution. Previous studies demonstrated that in the proximal tubule ANGII action is mediated by PKC (Rangel et al 2001; Rangel et al 2002). The Ser23 phosphorylation site is within a PKC motif in the NH2 terminus of α‐1 and it is not phosphorylated by any other known kinases (Feschenko & Sweadner, 1995).…”

The second sodium pump: from the function to the gene

“…Angiotensin II (Ang II) stimulates the Na + -ATPase activity in outer kidney cortex kidney [130], mediated by AT1 receptors through the PI-PLCβ/PKC pathway [40, 131–133]. Additionally, it has been shown, in inner kidney cortex, that Ang II inhibits the Na + -ATPase activity, mediated by AT2 receptors through a cholera toxin-sensitive PKA pathway [37].…”

“…These receptors are differentially distributed throughout the nephron, from outer to inner renal cortex, leading to a preferential binding of Ang II either to AT1 or AT2 receptors, respectively. Therefore, the predominant effect of Ang II on the Na + -ATPase in outer cortex would be stimulatory [40, 131–133], while in the inner cortex this peptide would have an inhibitory effect [37]. …”

Effect of adenosine triphosphate on phosphate uptake in renal proximal tubule cells: Involvement of PKC and p38 MAPK

“…The activation of PKC by purinoceptors was reported in mesangial cells and collecting duct (Koster et al, 1996;Pfeilschifter and Huwiler, 1996). Indeed, PKC has a significant role in signal transduction of several biologically active substances that regulate a variety of renal cellular functions including apical transporters (Yamada et al, 1996; Singh and Linas, 1997; Rangel et al, 2001). Activation of P2X and P2Y receptors has been reported to stimulate mitogen activated protein kinase (MAPK) families [p44/42 MAPK, p38 MAPK, and c-jun N-terminal kinase (JNK)] in various cell types (Harden et al, 1995;Ralevic and Burnstock, 1998).…”