Roles of Ets proteins, NF-kappa B and nocodazole in regulating induction of transcription of mouse germline Ig alpha RNA by transforming growth factor-beta 1

Antibody class switch recombination (CSR) occurs after antigen activation o f B cells, CSR is directed to specific heavy chain isotypes by cytokines an d B cell activators that induce transcription from the unrearranged, or ger mline (GL), C-H region genes, Transforming growth factor (TGF)-beta1 is ess ential for switch recombination to IgA due to its ability to induce transcr iption from GL Ig alpha genes, It has been shown that the promoters which r egulate transcription of mouse and human GL alpha RNAs contain a TGF-beta1- responsive element that binds Smad and core binding factor (CBF alpha)/AML/ PEBP alpha /Runx. They also contain other elements which bind the transcrip tion factors CREB, BSAP and Ets family proteins, In this manuscript we demo nstrate that two tandem Ets sites in the mouse GL alpha promoter bind the t ranscription factors Elf-1 and PU.1, and that the 3' site is essential for expression of a luciferase reporter gene driven by the GL alpha promoter. B inding of Elf-1 to the GL alpha promoter is inducible by lipopolysaccharide in nuclear extracts from splenic B cells, An NF-kappaB site is identified, although it does not contribute to expression of the promoter in reporter gene essays. Since CSR to IgA is greatly reduced in NF-kappaB/p50-deficient mice, these data support the hypothesis that NF-kappaB has roles in switch ing in addition to regulation of GL transcription. Finally, we demonstrate that nocodazole, which disrupts microtubules that sequester Smad proteins i n the cytoplasm, stimulates transcription from the GL alpha promoter.