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 (MW .apprxeq. 24,000) that inhibits DNA synthesis and growth of the same cells. Using [35S]methionine to metabolically label proteins, it was found that this growth inhibitor selectively induces the BSC-1 cells to synthesize and secrete another protein with a relative MW of 48,000 on NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gels. This protein was called "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 4-6 h 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 3 other secreted proteins (MW 28,000, 59,000 and 61,000), called "mitogen-inducible protein" (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. RNA synthesis appears necessary for the inductions. EGF and the growth inhibitor induce these secreted proteins by independent and noninteracting pathways.