B lymphocyte specific transcriptional regulation of the immunoglobulin heavy chain enhancer

Chun-Pyn Shen, University of Pennsylvania


Activity of the immunoglobulin heavy chain (IgH) enhancer is B cell specific, and developmentally regulated. Both repressors and transcription activators have been implicated to restrict enhancer function to B cells. BCF-1 binds to the $\mu$E5 and $\mu$E4 sites of the enhancer. The presence of BCF-1 correlates well with enhancer activity. The DNA binding profile of BCF-1 suggests that it is the positive factor in B cells that displaces ZEB, a repressor that keeps the enhancer off. E2A gene products, widely expressed bHLH proteins, are integral component of BCF-1. Gene knockouts approach from others have shown that E2A is required for the B cell lineage. The restriction of BCF-1 to B cells is not due to the relative levels of the E2A proteins nor to the relative expression of different splicing isoforms of E2A transcripts. The results of UV-crosslinking, SDS-PAGE-fractionation-reconstitution, and forced-heterodimerization experiments indicate that BCF-1 comprises an E2A homodimer and suggest a porttranslational regulation of E2A DNA binding activity. Casein kinase II inhibits the transactivation function of E2-5 indirectly by targeting the C-terminal one third of the protein, arguing that phosphorylation may be involved. Results from the analysis of B X T hybrids suggest that BCF-1, PU.1, Oct-2, and OCA-B are required to maintain high-level expression of the IgH enhancer. However, PU.1 is dispensable for initiating enhancer activity. When various enhancer binding proteins are transiently expressed in NIH3T3 cells, only E2A proteins can activate the endogenous IgH enhancer to produce the sterile transcripts. Neither E2-2 nor MyoD, which bind the same sites on the enhancer of E2A in vitro were unable to do so. These results suggest a hierarchy among the various enhancer-binding proteins that activate the IgH enhancer. In conclusion, this work demonstrates that E2A proteins play a pivotal role in conferring the IgH enhancer's B cell specificity and may participate the commitment step of B cell development.

Subject Area

Molecular biology|Immunology|Genetics

Recommended Citation

Shen, Chun-Pyn, "B lymphocyte specific transcriptional regulation of the immunoglobulin heavy chain enhancer" (1995). Dissertations available from ProQuest. AAI9532277.