Thrombin signal transduction mechanisms in human glomerular epithelial cells

J Cell Physiol. 1992 Mar;150(3):475-83. doi: 10.1002/jcp.1041500307.


We have previously shown that alpha-thrombin exerted a mitogenic effect on human glomerular epithelial cells and stimulated the synthesis of urokinase-type (u-PA) and tissue-type plasminogen activator (t-PA) and of their inhibitor, plasminogen activator inhibitor 1 (PAI-1). In the present study, we investigate the signal transduction mechanisms of thrombin in these cultured cells. Thrombin induced an increase in intracellular free calcium concentrations ([Ca2+]i) in a dose-dependent manner, a plateau being reached at 1 U/ml thrombin. A 60% inhibition of this effect was produced by 300 nM nicardipine, a dihydroperidine agent, or by 4 mM EGTA, indicating that increase in [Ca2+]i was due in part to extracellular Ca2+ entry through L-type voltage-sensitive calcium channels. Thrombin also induced an increase in inositol trisphosphate (IP3), suggesting that phospholipase C activation and phosphatidylinositides breakdown were stimulated. Interestingly thrombin-stimulated cell proliferation measured by 3H thymidine incorporation was inhibited by 300 nM nicardipine, and restored by addition of 10(-8) M ionomycin, indicating that calcium entry was critical for the mitogenic signal of thrombin. Conversely, nicardipine did not modify thrombin-stimulated synthesis of u-PA, t-PA, and PAI-1. Both thrombin-stimulated cell proliferation and protein synthesis required protein kinase C activation since these effects were blocked by 10 microM H7, an inhibitor of protein kinases, and by desensitization of protein kinase C by phorbol ester pretreatment of the cells. Interestingly, DFP-inactivated thrombin which binds the thrombin receptor and gamma-thrombin, which has some enzymatic activity but does not bind to thrombin receptor, had no effect when used alone. Simultaneous addition of these two thrombin derivatives had no effect on [Ca2+]i, and 3H thymidine incorporation but stimulated u-PA, t-PA, and PAI-1 synthesis although to a lesser extent than alpha-thrombin. This effect also required protein kinase C activation to occur, presumably by a pathway distinct from phosphoinositoside turnover since it was not associated with IP3 generation. In conclusion, multiple signalling pathways can be activated by alpha-thrombin in glomerular epithelial cells: 1) Ca2+ influx through a dihydroperidine-sensitive calcium channel, which seems critical for mitogenesis; 2) protein kinase C activation by phosphoinositide breakdown, which stimulates both mitogenesis and synthesis of u-PA, t-PA, and PAI-1; 3) protein kinase C activation by other phospholipid breakdown can stimulate u-PA, t-PA, and PAI-1 synthesis but not mitogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism
  • Calcium Channel Blockers / pharmacology
  • Cell Division
  • Enzyme Activation
  • Epithelial Cells
  • Epithelium / enzymology
  • Epithelium / metabolism
  • Glomerular Mesangium / cytology
  • Glomerular Mesangium / enzymology
  • Glomerular Mesangium / metabolism*
  • Humans
  • Inositol 1,4,5-Trisphosphate / metabolism
  • Ionomycin / pharmacology
  • Kinetics
  • Nicardipine / pharmacology
  • Plasminogen Inactivators / metabolism
  • Protein Kinase C / metabolism
  • Signal Transduction*
  • Thrombin / physiology*
  • Tissue Plasminogen Activator / biosynthesis
  • Urokinase-Type Plasminogen Activator / biosynthesis


  • Calcium Channel Blockers
  • Plasminogen Inactivators
  • Ionomycin
  • Inositol 1,4,5-Trisphosphate
  • Nicardipine
  • Protein Kinase C
  • Thrombin
  • Tissue Plasminogen Activator
  • Urokinase-Type Plasminogen Activator
  • Calcium