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 α subunit phosphorylation and basolateral membrane (BLM) abundance of the Na⁺,K⁺-ATPase α₁ and β₁ subunits. The increase in BLM abundance of the Na ⁺,K⁺-ATPase α₁ and β₁ subunits was accompanied by depletion of α₁ and β₁ 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 α₁-subunit and translocation of α₁ and β₁ subunits to the BLM were abolished by a MEK1/2 inhibitor (20 μM PD98059). C-peptide stimulation of ⁸⁶Rb⁺ uptake was also abolished by preincubation of HRTCs with an inhibitor of PKC (1 μM GF109203X). C-peptide stimulated phosphorylation of human Na⁺,K⁺-ATPase α 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 α subunit of Na⁺,K⁺-ATPase.