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.
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.
Lin
Y C
YC
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Stavnezer
J
J
D051696:Activating Transcription Factors; D000818:Animals; D001483:Base Sequence; D001798:Blood Proteins / Q000502:physiology*; D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology*; D005803:Genes, Immunoglobulin / Q000502:physiology*; D007070:Immunoglobulin A / Q000096:biosynthesis; D007127:Immunoglobulin Constant Regions / Q000096:biosynthesis*; D007137:Immunoglobulin alpha-Chains / Q000096:biosynthesis*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000502:physiology*; D015345:Oligonucleotide Probes; D011401:Promoter Regions, Genetic / Q000502:physiology; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology*
D051696:Activating Transcription Factors; D001798:Blood Proteins; D007070:Immunoglobulin A; D007127:Immunoglobulin Constant Regions; D007137:Immunoglobulin alpha-Chains; D009363:Neoplasm Proteins; D015345:Oligonucleotide Probes; D014157:Transcription Factors; D016212:Transforming Growth Factor beta