Morphological transformation of cells induced by Kirsten sarcoma virus transforming factor is independent of serine proteases.

Reports from several laboratories have suggested that the virus transformed state may be maintained either by ectopically produced growth factors or alternatively by ectopically produced serine proteases including plasminogen activator. Here we show that the maintenance of transformation induced by Kirsten sarcoma virus induced growth factor(s) is independent of serine proteases in that 1) the factors are not themselves serine proteases, and 2) the growth factors do not induce the expression of detectable serine proteases or plasminogen activator.