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A Growth-stimulating Factor Released by Cultured Mouse Mammary Tumor Cells¹

Department of Zoology and its Cancer Research Laboratory, University of California, Berkeley, California 94720

Medium from mouse mammary tumor cell cultures contained a growth-stimulating factor. The assay for growth-stimulating factor was performed on density-inhibited cultures of mouse embryo cells. Addition of nondialyzed or dialyzed mouse mammary tumor cell culture medium caused an increase in DNA synthesis and mitosis in density-inhibited cells. Dialyzed medium was more active than non-dialyzed medium in stimulating growth. Normal mouse mammary cell culture medium also showed similar growth-stimulatory activity, but to a lesser extent than that showed by tumor cell culture medium. The growth-stimulating factor was precipitated from the culture medium with 60% saturated ammonium sulfate.

¹ This work was supported by USPHS Grants CA-05388 and CA 05045 from the National Cancer Institute.

² Present address: Department of Community and Environmental Medicine, University of California, Irvine, College of Medicine, Irvine, Calif. 92664.

Received 4/27/73. Accepted 7/19/73.