HS1,2 enhancer regulation of germline epsilon and gamma 2b promoters in murine B lymphocytes: Evidence for specific promoter-enhancer interactions

During an immune response, activated B cells develop into high rate Ig-secr eting plasma cells. They also switch from production of IgM to IgG, IgA, or IgE. This process requires a DNA recombination event, which is regulated a t the transcriptional level by the production of isotype-specific, sterile germline (GL) transcripts. Induction of these transcripts is controlled by GL promoters and, possibly, by IgH 3' enhancers. We investigated the intera ction of the GL epsilon and gamma 2b promoters with the HS1,2 enhancer usin g transiently transfected mouse primary B cells and cell lines. The constru cts used for the transfections contained a GL promoter upstream and HS1,2 d ownstream of a luciferase reporter gene. Both GL epsilon and gamma 2b promo ters synergized strongly with the HS1,2 enhancer in activated primary B cel ls, a mature B cell line, and a plasma cell line. We show that the major ac tivity of HS1,2 in activated primary B cells occurs within a 310-bp fragmen t that includes NF-kappaB, OCT, and NF of activated B cells (Ets/AP-1) site s. By mutating the consensus sequences for various transcription factors, w e have determined which sites in HS1,2 are important for synergy with the G L epsilon and gamma 2b promoters. Our findings indicate that different site s in HS1,2 might selectively interact with the GL epsilon and gamma 2b prom oters. We also provide evidence that B cell-specific activator protein is n ot an absolute suppressor of HS1,2 activity.