Analysis of transforming growth factor-beta1-induced Ig germ-line gamma2b transcription and its implication for IgA isotype switching.
Transforming growth factor (TGF)-beta1 directs class switch recombination (CSR) to IgG2b as well as to IgA. Smad3/4, Runx3 and p300 mediate TGF-beta1-induced germ-line (GL) alpha transcription leading to IgA expression. However, the molecular mechanisms by which TGF-beta1 induces IgG2b CSR are unknown. We used luciferase reporter plasmids to investigate how TGF-beta1 regulates the activity of the promoter for GL transcripts of IgG2b constant gene (GLgamma2b promoter). Similarly to the GLalpha promoter, overexpression of Smad3/4 and Runx3 enhances TGF-beta1-induced GLgamma2b promoter activity. Mutation analysis of the promoter identified likely Smad- and Runx3-binding sites. Also similar to the GLalpha promoter, overexpression of p300 enhances Smad3/4-mediated promoter activity, whereas E1A represses promoter activity. Since these regulation mechanisms underlying both GLalpha and GLgamma2b transcription are similar, we explored the possibility that TGF-beta1 induces IgA CSR via transitional IgG2b CSR. TGF-beta1 enhances the expression of both Ialpha-Cmu and Ialpha-Cgamma2b circle transcripts, indicative of direct (Smu-->Salpha) and sequential CSR (Smu-->Sgamma2b-->Salpha).
Park
Seok-Rae
SR
Department of Microbiology, College of Natural Sciences, Kangwon National University, Chunchon, S.Korea.
Seo
Goo-Young
GY
Choi
Ae-Jin
AJ
Stavnezer
Janet
J
Kim
Pyeung-Hyeun
PH
D000818:Animals; D001483:Base Sequence; D050677:Core Binding Factor Alpha 3 Subunit; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000276:immunology; D050881:E1A-Associated p300 Protein; D024202:Electrophoretic Mobility Shift Assay; D007070:Immunoglobulin A / Q000235:genetics* / Q000276:immunology; D017578:Immunoglobulin Class Switching / Q000235:genetics* / Q000276:immunology; D007074:Immunoglobulin G / Q000235:genetics* / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000187:drug effects / Q000276:immunology; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000187:drug effects / Q000276:immunology; D014157:Transcription Factors / Q000187:drug effects / Q000276:immunology; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000276:immunology* / Q000494:pharmacology
D050677:Core Binding Factor Alpha 3 Subunit; D004268:DNA-Binding Proteins; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D009687:Nuclear Proteins; C493730:Runx3 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D050881:E1A-Associated p300 Protein; C494361:Ep300 protein, mouse