Inducible overproduction of the mouse c-myc protein in mammalian cells.

Abstract
We have made Chinese hamster ovary (CHO) cell lines that contain up to 2000 copies of the coding region of the mouse c-myc gene fused to the promoter of the Drosophila gene (hsp70) encoding a Mr 70,000 heat shock protein. Incubation these cells at 43.degree. C results in an estimated 100-fold induction of c-myc mRNA. Translation of this mRNA occurs when the cells are returned to 37.degree. C, during the first 3 hr of recovery at 37.degree. C, the c-myc protein is one of the most abundantly synthesized proteins in the cells. The products of the induced c-myc gene are phosphoproteins of apparent Mr 64,000, 66,000, and 75,000. Induced cells die, suggesting that elevated levels of c-myc are cytotoxic. Amplification of genes placed under control of the Drosophila hsp70 promoter may provide a general method for inducibly overexpressing proteins in mammalian cells.