Characterization of the enhancer region for germline transcription of the gamma 3 constant region gene of human immunoglobulin

Abstract

A constant region gene (C) of the immunoglobulin heavy chain can be transcribed as germline transcripts from a promoter located upstream of a switch region. We have studied the structure and function of the human C_γ3 promoter region. When the human IgM-producing cell line SSK41 is stimulated with interleukin 4 (IL-4) in the presence of phorbol myristate acetate (PMA) or Staphylococcus aureus Cowan I, expression of germline C_γ3transcripts was specifically augmented within 4 h. Upstream DNA fragments flanking the I_γ3 exon were fused with a reporter gene and tested for IL-4-induced promoter/enhancer activity by transfection of SSK41 cells. The DNA fragment between 450 and 250 bp upstream of the transcription initiation site of the Cγ3 gene was shown to be required for transcriptlonal up-regulation by PMA and IL-4. The upstream 514 bp fragment of the I_γ3 flanking region was shown to contain an enhancer activity In response to PMA and IL-4.