Tumor-specific inhibition of DNA synthesis and cell proliferation by a factor from bovine placenta--possible mechanism.

A polypeptide isolated from the maternal part of bovine placentas inhibits significantly the incorporation of thymidine into the DNA of tumor cells. When normal cells are used, this effect is found only to a very limited degree. Surface membrane components have been identified which are enriched on tumor cells and which are responsible for a better binding of the inhibitor to tumor cells than to normal cells. After internalization of the receptor-inhibitor complex, a decrease in the nuclear content of two proteins is observed, which might be a requirement for the inhibition of the DNA synthesis.