Rapid selective effects by a growth inhibitor and epidermal growth factor on the incorporation of [35S]methionine into proteins secreted by African green monkey (BSC-1) cells

Abstract

Confluent African green monkey kidney (BSC-1) cells secrete a protein (Mr approximately equal to 24,000) that inhibits DNA synthesis and growth of the same cells. Using [35S]methionine to metabolically label proteins, we have found that this growth inhibitor selectively induces the BSC-1 cells to synthesize and secrete another protein with a relative Mr of 48,000 on NaDodSO4/polyacrylamide gels. We have called this protein "inhibitor-inducible protein" (IIP48). The maximal increase in rate of labeling of IIP48 due to treatment with the growth inhibitor averages 12-fold over the control. IIP48 is an N-glycosidically linked glycoprotein, and it is not a major intracellular protein. This protein is maximally induced within 4 to 6 hr of adding the growth inhibitor to the cells. This is an early response of these cells to the growth inhibitor and may represent a primary response to the growth inhibitor. Epidermal growth factor (EGF) increases the rate of labeling of three other secreted proteins (MrS 28,000, 59,000, and 61,000), which we have called "mitogen-inducible proteins" (MIP28, MIP59, and MIP61). The specific effects of both EGF and the growth inhibitor on the secreted levels of these proteins are inhibited if actinomycin D is added with the growth effectors. Thus, RNA synthesis appears necessary for the inductions. EGF and the growth inhibitor induce these secreted proteins by independent and noninteracting pathways.