C-peptide stimulates Na+, K+-ATPase via activation of ERK1/2 MAP kinases in human renal tubular cells

Proinsulin-connecting peptide (C-peptide) exerts physiological effects partially via stimulation of Na⁺, K⁺-ATPase. We determined the molecular mechanism by which C-peptide stimulates Na⁺, K⁺-ATPase in primary human renal tubular cells (HRTCs). Incubation of the cells with 5 nM human C-peptide at 37°C for 10 min stimulated ⁸⁶Rb⁺ uptake by 40% (p<0.01). The carboxy-terminal pentapeptide was found to elicit 57% of the activity of the intact molecule. In parallel with ouabain-sensitive ⁸⁶Rb⁺ uptake, C-peptide increased subunit phosphorylation and basolateral membrane (BLM) abundance of the Na⁺, K⁺-ATPase ₁ and ₁ subunits. The increase in BLM abundance of the Na⁺, K⁺-ATPase ₁ and ₁ subunits was accompanied by depletion of ₁ and ₁ subunits from the endosomal compartments. C-peptide action on Na⁺, K⁺-ATPase was ERK1/2-dependent in HRTCs. C-peptide-stimulated Na⁺, K⁺-ATPase activation, phosphorylation of ₁-subunit and translocation of ₁ and ₁ subunits to the BLM were abolished by a MEK1/2 inhibitor (20 M PD98059). C-peptide stimulation of ⁸⁶Rb⁺ uptake was also abolished by preincubation of HRTCs with an inhibitor of PKC (1 M GF109203X). C-peptide stimulated phosphorylation of human Na⁺, K⁺-ATPase subunit on Thr-Pro amino acid motifs, which form specific ERK substrates. In conclusion, C-peptide stimulates sodium pump activity via ERK1/2-induced phosphorylation of Thr residues on the subunit of Na⁺, K⁺-ATPase.Received 15 June 2004; received after revision 14 September 2004; accepted 14 September 2004