Novel protein-DNA interactions associated with increased immunoglobulin transcription in response to antigen plus interleukin-5.

Although much has been learned about basal levels of immunoglobulin (Ig) transcription, the regulatory effects of cytokines and antigen (Ag) upon Ig expression in lymphocytes have not been fully characterized. We previously reported that Ag plus interleukin-5 (IL-5) caused increased steady-state Ig mRNA levels in Ag-specific cell lines. In this study, we have identified a region between -250 and -125 bp 5' of the Ig transcription start site that is necessary for the induction of increased mu mRNA levels by Ag plus IL-5. Mobility shift and UV cross-linking studies indicated that IL-5 plus Ag induced increased protein binding to this region. Furthermore, this sequence was found to be closely related to another A + T-rich sequence at -525 bp 5' of the transcription start site. Both sequences exhibited similar B-cell-specific and inducible protein binding. Our data suggest that treatment with IL-5 plus Ag induces several DNA-binding proteins, some of which may participate in increasing Ig transcription above basal levels by binding to sequences 5' of the octamer motif.