Amplification of P450c21 expression in cultured mammalian cells.

We describe in this paper an investigation of mammalian expression systems for P450c21 (21-hydroxylase). Four different promoters, the SV40 early and late promoters, MMTV-LTR, and CMV immediate early promoter were tested for their ability to drive the expression of P450c21 in cultured COS-1 cells. With the exception of MMTV-LTR, all drove the expression of similar levels of functional 21-hydroxylase. In addition, the Rat-1 cell line was tested and shown to be suitable for the stable expression of functional P450c21. We have established cell lines derived from Rat-1 either normal or mutant P450c21 stably expressed together with amplifiable markers. The expression of P450c21 was further increased by selection in methotrexate.