Induction of plasminogen activator in a human diploid fibroblast cell line (MRC-5) by conditions which cause induction of interferon: the role of calcium ions

The human diploid fibroblast cell line, MRC-5, derived from embryo lung tissue produced only small quantities of plasminogen activator (PA) when harvested using a standard nutrient medium (Eagle's Minimal Essential Medium, MEM). Use of a schedule designed to induce high concentrations of fibroblast interferon in these cells also resulted in production of considerably enhanced levels of PA. The kinetics of PA production differed from those of interferon production; specifically, PA was produced for at least 6 days following induction despite the toxicity of the inducers whereas interferon synthesis continued for only 1 day. Further investigation of the induction conditions for PA revealed that double-stranded RNA which was absolutely required for interferon production was not required for induction of PA. Indeed, the stimulus for enhancement of PA production appeared to be solely an elevated concentration of calcium ions in the extracellular medium. The possible physiological relevance of this induction of PA by elevated concentrations of calcium ions is discussed.