Regulation of transcription of the germ-line Ig alpha constant region gene by an ATF element and by novel transforming growth factor-beta 1-responsive elements
Department of Molecular Genetics and Microbiology
Activating Transcription Factors; Animals; Base Sequence; Blood Proteins; Cell Line; Gene Expression Regulation; Genes, Immunoglobulin; Immunoglobulin A; Immunoglobulin Constant Regions; Immunoglobulin alpha-Chains; Mice; Molecular Sequence Data; Mutagenesis, Site-Directed; Neoplasm Proteins; Oligonucleotide Probes; Promoter Regions (Genetics); Restriction Mapping; Sequence Homology, Nucleic Acid; Transcription Factors; Transcription, Genetic; Transfection; Transforming Growth Factor beta
Life Sciences | Medicine and Health Sciences | Women's Studies
Inasmuch as transcription of unrearranged, or germ-line, Ig CH genes appears to direct switch recombination, understanding the regulation of this transcription is essential for understanding the regulation of class switching. Transforming growth factor-beta 1 (TGF-beta 1) induces germ-line alpha transcripts and increases class switching to IgA in the I.29 mu B lymphoma and in Peyer's patch and splenic B cells. It has been previously demonstrated that induction of germ-line alpha transcripts by TGF-beta occurs at the transcriptional level in I.29 mu cells. We now demonstrate that the DNA segment located 5' to the initiation sites of germ-line alpha RNA drives expression of a luciferase reporter gene construct in transient transfection experiments. Full constitutive expression requires no more than 106 bp of the 5' flanking segment. By creating a series of deletion and substitution mutations, we have demonstrated that an ATF/CRE site residing within this region is very important for constitutive expression of the germ-line alpha promoter, but mutation of this motif does not diminish TGF-beta induction. Inducibility by TGF-beta requires additional sequences residing between -128 to -106 relative to the first RNA initiation site. Two copies of a tandemly repeated sequence 5' CA-CAG(G)CCAGAC 3' (termed Ig alpha TGF-beta-RE) are located in the region from -127 to -105. An oligonucleotide containing multimers of these repeats confers TGF-beta inducibility to a heterologous promoter. An additional copy of the TGF-beta-RE was identified at -41/-30 and its deletion reduces the TGF-beta response. Thus, we conclude that tandem repeats of a novel TGF-beta-RE are the positive regulatory element for the TGF-beta response. Our study provides further evidence that TGF-beta directs class switching to IgA through induction of transcription of the germ-line C alpha gene and demonstrates that TGF-beta can activate the promoter for the germ-line alpha gene.
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Citation: J Immunol. 1992 Nov 1;149(9):2914-25.