CELL-SPECIFIC EXPRESSION OF HELIX-LOOP-HELIX TRANSCRIPTION FACTORS ENCODED BY THE E2A GENE

The E2A gene encodes transcription factors of the helix-loop-helix fam ily that are implicated in cell-specific gene expression as part of di meric complexes that interact with E box enhancer elements. It has pre viously been shown that transcripts of the E2A gene can be detected in a wide range of cell types. We have now examined expression of the mo use E2A gene at the protein level using polyclonal antisera directed a gainst distinct portions of the E2A protein to probe blots of cellular extracts. A 73 kDa protein was identified by this analysis: this prot ein is highly enriched in cell lines of B lymphoid origin as compared to pancreatic beta-cells and fibroblast cells. The detection of this p rotein selectively in extracts of lymphoid cells correlates with the p resence of the E box-binding activity LEF1/BCF1 in these cells; this b inding activity was previously shown to be efficiently recognized by a ntiserum directed against E2A gene products. Transfection of cells wit h full length E2A cDNA leads to appearance of protein co-migrating wit h the 73 kDa protein on SDS gel electrophoresis and co-migrating with LEF1/BCF1 on mobility shift analysis. Our results are consistent with the view that the DNA-binding activity LEF1/BCF1 is a homodimer of E2A proteins; the selective appearance of this putative cell-specific tra nscription factor in B lymphoid cells seems to be attributable, at lea st in part, to the elevated E2A protein concentrations in these cells.