The immunoglobulin J chain gene is inducibly transcribed in mature B cells upon antigen recognition and a signal from interleukin-2 (IL-2). B cell-specific activator protein (BSAP), a transcription factor that silences J chain transcription, has been identified as a nuclear target of the IL-2 signal. The levels of BSAP progressively decrease in response to IL-2 and this change correlates with the differentiation of B cells into antibody secreting plasma cells. Here we report the binding of the upstream stimulatory factor (USF) to an E-box motif immediately upstream from the BSAP site on the J chain promoter. Mutations in the USF binding motif significantly decrease J chain promoter activity in J chain expressing B cell lines. We also show that a functional relationship exists between USF and a second J chain positive-regulating factor, B-MEF2, using co- immunoprecipitation assays and transfections. Finally, we provide evidence that the binding of BSAP prevents USF and B-MEF2 from interacting with the J chain promoter during the antigen-independent stages of B cell development. It is not until the levels of BSAP decrease during the antigen-driven stages of B cell development that both USF and B-MEF2 are able to bind to their respective promoter elements and activate J chain transcription.
CITATION STYLE
Wallin, J. J., Rinkenberger, J. L., Rao, S., Gackstetter, E. R., Koshland, M. E., & Zwollo, P. (1999). B cell-specific activator protein prevents two activator factors from binding to the immunoglobulin J chain promoter until the antigen-driven stages of B cell development. Journal of Biological Chemistry, 274(22), 15959–15965. https://doi.org/10.1074/jbc.274.22.15959
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