Transformation-dependent secretion of a low molecular weight protein by murine fibroblasts.

Abstract

A protocol was devised to radiolabel proteins secreted by murine fibroblasts in vitro. A radiolabeled polypeptide of MW 35,000 is released into medium in relatively large amounts by transformed cells and smaller amounts by nontransformed fibroblasts. This major excreted polypeptide (MEP) is found in the medium of spontaneously transformed mouse cells and mouse cells transformed by a DNA tumor virus, RNA tumor viruses or methylcholanthrene. The appearance of MEP appears to be well correlated with anchorage independence in these transformed cells. MEP can be localized within the cytoplasm of transformed but not untransformed cells by indirect immunofluorescence. The presence of MEP within murine fibroblasts or their culture medium serves as a novel biochemical marker of transformation. A biological role for this protein was not assigned.