A bifunctional control element in the human IgE germline promoter involved in repression and IL-4 activation.
One of the first steps during Ig heavy chain isotype switching to IgE is the IL-4 induced synthesis of IgE germline transcripts. To further characterize the molecular mechanism of the IL-4 action, the regulatory DNA elements involved in the control of expression of these transcripts were analyzed. Transient transfection of a B cell tumor line revealed the presence of a 15 bp IL-4 responsive cis-acting element (IL-4RE) highly homologous to an IL-4 response element in the human CD23b promoter. An IL-4 induced DNA binding protein specifically interacted with this sequence. Point mutations within that sequence not only abolished IL-4 inducibility of reporter constructs but also prevented binding of the nuclear factor to the mutated sequence. A stretch of 16 nucleotides just upstream of the IL-4RE contributed to IL-4 inducibility and formed nucleoprotein complexes with constitutive factors. All reporter constructs containing the functional IL-4RE were transcriptionally very weak but could be readily activated upon IL-4 induction. Transfection of constructs containing the mutated IL-4RE or plasmids lacking that sequence displayed a high constitutive promoter activity and were IL-4 unresponsive. These data suggest that in the absence of the cytokine the activity of the IgE germline promoter is actively repressed through the action of the IL-4RE. The same sequence appears to be critically involved in the IL-4 induced activation of the promoter via the binding of a cytokine induced transcription factor.
Albrecht
B
B
Sandoz Forschungsinstitut, Vienna, Austria.
Peiritsch
S
S
Woisetschläger
M
M
D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D007073:Immunoglobulin E / Q000235:genetics*; D015847:Interleukin-4 / Q000502:physiology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
D004268:DNA-Binding Proteins; D014157:Transcription Factors; D015847:Interleukin-4; D007073:Immunoglobulin E