Restoration ofin vitro growth control to malignant cells

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Abstract
A glycoprotein (molecular weight, ca. 160,000) from culture medium of contact-inhibited hamster melanocytes restores contact inhibition of growth to malignant melanocytes of man, mouse, and hamsters, and also effectively inhibits growth in vitro of a broad spectrum of malignant and normal cell types of ectodermal, mesodermal and endodermal origins, including human colon carcinomas. The melanocyte contact inhibitory factor (MCIF) produces G1 growth arrest in malignant melanocytes; inhibition of all cell types is reversible, does related, and nontoxic at concentrations below 200 microgram/ml, but selectively lethal to malignant cells at higher concentrations. An electrophoretically identical protein is present in culture media of contact-inhibited melanocytes, fibroblasts, and epidermal cells, but absent from those of colon carcinomas, HeLa cells and malignant melanomas. Nevertheless, an MCIF-like band is present in whole cell homogenates of human colon carcinomas and hamster melanomas. MCIF may permit normal surface interactions required for feedback inhibition of growth.