Proinsulin C-peptide rapidly stimulates mitogen-activated protein kinases in Swiss 3T3 fibroblasts: requirement of protein kinase C, phosphoinositide 3-kinase and pertussis toxin-sensitive G-protein

Biochem J. 2001 Apr 1;355(Pt 1):123-9. doi: 10.1042/0264-6021:3550123.


It has been demonstrated that proinsulin C-peptide possesses several biological activities and that its specific binding sites are present on the surface of cell membranes. However, the molecular and cellular mechanisms of C-peptide actions are poorly known. In the present study we examined the possible involvement of the mitogen-activated protein kinase (MAPK) pathway in C-peptide effects. C-peptide induced the phosphorylation of MAPK [p44 extracellular signal-regulated kinase 1 (ERK1) and p42 ERK2] in Swiss 3T3 and 3T3-F442A fibroblasts but not in 3T3-L1 fibroblasts and some other cell lines such as L(6)E(9) muscle cells. In Swiss 3T3 cells, C-peptide-induced phosphorylation of MAPK was dependent on time and concentration, being maximal at 1 min and at 1 nM C-peptide and was accompanied by an increase in MAPK activity and MAPK kinase (MEK) phosphorylation. The MAPK phosphorylation by C-peptide was abolished by treatment with pertussis toxin (PTX) and also with a MEK inhibitor, PD 98059. In addition, MAPK phosphorylation was attenuated by treatment with a phosphoinositide 3-kinase (PI-3K) inhibitor, wortmannin, and with a protein kinase C (PKC) inhibitor, GF109203X, and by down-regulation of PKC by prolonged treatment with PMA. Similar effects of the inhibitors and PTX were found on the MAPK phosphorylation induced by neuropeptide Y. These results suggest that C-peptide activates MAPK through a putative G(i)/G(o)-linked receptor for C-peptide and through PI-3K-dependent and PKC-dependent pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Blotting, Western
  • C-Peptide / physiology*
  • Enzyme Activation
  • GTP-Binding Proteins / metabolism*
  • Mice
  • Mitogen-Activated Protein Kinases / metabolism*
  • Pertussis Toxin*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphorylation
  • Protein Kinase C / metabolism*
  • Virulence Factors, Bordetella / pharmacology*


  • C-Peptide
  • Virulence Factors, Bordetella
  • Pertussis Toxin
  • Phosphatidylinositol 3-Kinases
  • Protein Kinase C
  • Mitogen-Activated Protein Kinases
  • GTP-Binding Proteins