Phorbol ester induces class II gene expression in pre-B cell lines

The effect of phorbol myristate acetate on the induction of major histocompatibility complex class II gene expression was studied in four Abelson murine leukemia virus-transformed pre-B cell lines. In three cell lines, low concentrations of PMA (0.1-10 ng/ml) induced the expression of high levels of surface Ia molecules, and this effect was mediated at the transcriptional level. PMA induced a program of coordinated transcription of all four genes involved in the biosynthesis of Ia molecules. A spontaneous Ia-positive variant pre-B cell line was derived from an Ia-negative parental cell line. This variant was highly sensitive to the toxic effects of PMA, and highly responsive to the Ia-inductive effects of phorbol ester. Our findings suggest that in pre-B cells the appearance of Ia molecules and the regulation of their expression are controlled, at least partially, by variations in the activity of protein kinase C, which is the cellular receptor for phorbol esters.