Differential transactivation potential of Oct1 and Oct2 is determined by additional B cell-specific activities.

Abstract

Cell type‐specific transcriptional regulation is generally believed to be mediated by sequence‐specific transcription factors that are specifically present in the corresponding cells. The interaction of the lymphoid‐specific Oct2 transcription factor has been thought to be responsible for the B cell‐specific activity of octamer‐containing promoter and enhancer elements. Here we show that physiological concentrations of Oct2 do not suffice to generate octamer‐dependent promoter activity in non‐B cell lines. Furthermore, we have tested the activity of octamer‐dependent promoter and enhancer elements in B cell lines that lack the endogenous Oct2 protein. Our results demonstrate that in these Oct2‐deficient B cells the ubiquitous endogenous Oct1 protein is able to stimulate octamer‐containing promoters to a level comparable with that of normal Oct2‐positive B cells. However, reporter constructs bearing the octamer motif in a distal enhancer position are not stimulated by the Oct1 protein, but do require the presence of Oct2. The B cell‐specific octamer‐dependent promoter activity mediated by Oct1 correlates with the presence of a novel B cell‐specific octamer‐binding complex containing the Oct1 protein. From these results we conclude that B cells contain two different activities: one that interacts with both Oct1 and Oct2 and mediates promoter proximal activity of the octamer motif and a second that specifically interacts with Oct2 to confer function from a remote enhancer position.