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Identification of Somatomedin-like Polypeptides Produced by Mammary Tumors of BALB/c Mice¹

School of of Life Sciences, University of Nebraska, Lincoln, Nebraska 68588

A transplantable mammary tumor derived from an outgrowth of nodule-like alveolar lesions induced by 7,12-dimethylbenz[a]anthracene in cultures of whole mammary gland was shown to produce a family of somatomedin-like polypeptides when cultured in vitro. Minced mammary tumor tissue as well as monolayer cultures of tumor cells produced similar polypeptides when incubated in serum- and hormone-free medium. The polypeptides released into the medium ranged in molecular weight from 20,000 to 7,000 as determined by Sephadex G-50 chromatography under acidic conditions and analytical gel electrophoresis in acetic acid:urea. Because of their relative abundance, the M.W. 7000 polypeptides were partially purified and characterized. This preparation markedly stimulated DNA synthesis in chicken embryo fibroblast cultures and competed for the binding of ¹²⁵I-labeled multiplication-stimulating activity to these cells. The binding of ¹²⁵I-labeled epidermal growth factor to the surface of mouse embryo fibroblasts, in contrast, was not affected.

¹ Supported in part by USPHS Research Grants CA 11058, CA 25304, and CA 17620 from the National Cancer Institute.

² To whom requests for reprints should be addressed.

Received 6/13/80. Accepted 8/29/80.