title: C-peptide stimulates ERK1/2 and JNK MAP kinases via activation of protein kinase C in human renal tubular cells.
abstract: OBJECTIVE
  Accumulating evidence indicates that replacement of C-peptide in type 1 diabetes ameliorates nerve and kidney dysfunction, but the molecular mechanisms involved are incompletely understood. C-peptide shows specific binding to a G-protein-coupled membrane binding site, resulting in Ca(2+) influx, activation of mitogen-activated protein kinase signalling pathways, and stimulation of Na(+), K(+)-ATPase and endothelial nitric oxide synthase. This study examines the intracellular signalling pathways activated by C-peptide in human renal tubular cells.
  
  
  METHODS
  Human renal tubular cells were cultured from the outer cortex of renal tissue obtained from patients undergoing elective nephrectomy. Extracellular-signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and Akt/protein kinase B (PKB) activation was determined using phospho-specific antibodies. Protein kinase C (PKC) and RhoA activation was determined by measuring their translocation to the cell membrane fraction using isoform-specific antibodies.
  
  
  RESULTS
  Human C-peptide increases phosphorylation of ERK1/2 and Akt/PKB in a concentration- and time-dependent manner in renal tubular cells. The C-terminal pentapeptide of C-peptide is equipotent with the full-length C-peptide, whereas scrambled C-peptide has no effect. C-peptide stimulation also results in phosphorylation of JNK, but not of p38 mitogen-activated protein kinase. MEK1/2 inhibitor PD98059 blocks the C-peptide effect on ERK1/2 phosphorylation. C-peptide causes specific translocation of PKC isoforms delta and epsilon to the membrane fraction in tubular cells. All stimulatory effects of C-peptide were abolished by pertussis toxin. The isoform-specific PKC-delta inhibitor rottlerin and the broad-spectrum PKC inhibitor GF109203X both abolish the C-peptide effect on ERK1/2 phosphorylation. C-peptide stimulation also causes translocation of the small GTPase RhoA from the cytosol to the cell membrane. Inhibition of phospholipase C abolished the stimulatory effect of C-peptide on phosphorylation of ERK1/2, JNK and PKC-delta.
  
  
  CONCLUSIONS
  C-peptide signal transduction in human renal tubular cells involves the activation of phospholipase C and PKC-delta and PKC-epsilon, as well as RhoA, followed by phosphorylation of ERK1/2 and JNK, and a parallel activation of Akt.
authors.affiliation: Section of Clinical Physiology, Department of Surgical Sciences, Karolinska Institute, Stockholm, Sweden.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhong
authors.forename: A
authors.initials: A
authors.lastname: Davidescu
authors.forename: I
authors.initials: I
authors.lastname: Ehrén
authors.forename: K
authors.initials: K
authors.lastname: Ekberg
authors.forename: H
authors.initials: H
authors.lastname: Jörnvall
authors.forename: J
authors.initials: J
authors.lastname: Wahren
authors.forename: A V
authors.initials: AV
authors.lastname: Chibalin
mesh_terms: D002096:C-Peptide / Q000494:pharmacology*; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D007672:Kidney Cortex / Q000201:enzymology; D007684:Kidney Tubules / Q000201:enzymology*; D007700:Kinetics; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D002096:C-Peptide; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000254:Sodium-Potassium-Exchanging ATPase