Transcriptional regulation of immunoglobulin expression in a chronic lymphocytic leukemia cell line.

A cell line derived from a B-type chronic lymphocytic leukemia, Corinna II, was found to down-regulate its steady-state level of IgM mRNA after treatment with phorbol 12-myristate 13-acetate while the proliferative capacity of the cell line was unaffected. No changes in the splicing pattern of the IgM transcript could be observed after treatment. The down-regulatory effect on IgM RNA expression was found to be inhibited by cycloheximide, suggesting that functional protein synthesis was needed for the effect. Transfection experiments showed that the down-regulatory effect of phorbol myristate acetate was exerted at the level of transcriptional initiation. The DNA element mediating the down-regulatory effect was found to be present within 140 bp 5' of the mRNA cap site in an immunoglobulin promoter.