Modulation of proliferation of cultured human cells by urinary trypsin inhibitor

Several reports have indicated that proteinase inhibitors can act as both stimulators and inhibitors of the growth of cultured cells. To confirm and extend these reports, we have purified the trypsin inhibitor from human urine (UTI). We have demonstrated a biphasic effect of this protein on the proliferation of human fibroblasts, and have identified two types of cellular binding site which may be responsible for the stimulatory and inhibitory aspects of this effect. Both aspects of UTI action have also been observed in human tumour cell cultures, but they are not consistently associated in these cells.