Mitogenic effect of kallikrein from human urine on cultured human skin fibroblasts. Analysis of the combined action of kallikrein, insulin, and fibroblast growth factor on DNA and RNA synthesis.

Kallikrein isolated from human urine was capable of stimulating DNA and RNA synthesis in cultured human skin fibroblasts in media with a low serum content. The same concentration of kallikrein had a different effect on the DNA and RNA synthesis in different fibroblast lines, which was attributed to differences in the sensitivity of the cells to kallikrein. At a dose of 0.5 micrograms ml-1, kallikrein inactivated by heating at 100 degrees C caused an abrupt decrease in DNA synthesis in all the cell lines studied. When either active or inactivated kallikrein was added to the growth medium simultaneously with insulin there was a competitive effect on DNA and RNA synthesis. Preincubation of the cells with kallikrein prior to addition of insulin led to a reduction in the level of DNA synthesis compared to that seen upon simultaneous addition of kallikrein and insulin, suggesting that kallikrein and insulin competed for the same receptor. When kallikrein and fibroblast growth factor (FGF) were added simultaneously to the growth medium, there was a sharp decrease in both DNA and RNA synthesis in the cells compared to that seen on addition of FGF alone. Since heparin protected FGF from kallikrein inactivation, it is suggested that inactivation was caused by proteolytic degradation of part of the FGF molecule by kallikrein. It is concluded that kallikrein and insulin compete for the same receptor, possibly the insulin-like growth factor I (IGF-I), and that binding of kallikrein to this receptor is a prerequisite for mediation of the stimulatory effect of kallikrein on nucleic acid synthesis.