E2A EXPRESSION, NUCLEAR-LOCALIZATION, AND IN-VIVO FORMATION OF DNA-BINDING AND NON-DNA-BINDING SPECIES DURING B-CELL DEVELOPMENT

A monoclonal antibody (Yae) was characterized and shown to specifically recognize E2A proteins in vivo, including the E2A-Pbx1 fusion gene products, p77E2A-Pbx1 and p85E2A-Pbx1. E2A proteins of a predominant molecular mass of 72 kDa, which comigrated with in vitro-produced rat E12 and rat E47, were detected in human pro-B, pre-B, mature B, and plasma cell lines. The Yae antibody detected an E2A-containing muE2 enhancer element-binding complex (BCF-1) in pre-B- and mature B-cell lines in electrophoretic mobility shift assays which displayed a migration rate similar to that of in vitro-produced rat E12 and rat E47. A new E2A-containing muE2-binding species (P-E2A) was identified in plasma cells by using electrophoretic mobility shift assays. E2A proteins were detected in pro-B cells but were unable to bind the muE2 site. These observations suggest that the muE2 site is the target of stage-specific E2A regulatory complexes during B-cell development. Immunostaining analyses demonstrated the predominant nuclear localization of E2A proteins. Finally, we have identified an E2A form, designated I-E2A, which is unable to bind DNA. Our observations demonstrate novel in vivo mechanisms for the regulation of transcription by E2A proteins during B-cell development.