Analysis of transforming growth factor-beta1-induced Ig germ-line gamma2b transcription and its implication for IgA isotype switching

Eur J Immunol. 2005 Mar;35(3):946-56. doi: 10.1002/eji.200425848.


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).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Core Binding Factor Alpha 3 Subunit
  • DNA-Binding Proteins / drug effects
  • DNA-Binding Proteins / immunology
  • E1A-Associated p300 Protein
  • Electrophoretic Mobility Shift Assay
  • Immunoglobulin A / genetics*
  • Immunoglobulin A / immunology
  • Immunoglobulin Class Switching / genetics*
  • Immunoglobulin Class Switching / immunology
  • Immunoglobulin G / genetics*
  • Immunoglobulin G / immunology
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Nuclear Proteins / drug effects
  • Nuclear Proteins / immunology
  • Promoter Regions, Genetic
  • Reverse Transcriptase Polymerase Chain Reaction
  • Smad3 Protein
  • Smad4 Protein
  • Trans-Activators / drug effects
  • Trans-Activators / immunology
  • Transcription Factors / drug effects
  • Transcription Factors / immunology
  • Transcription, Genetic*
  • Transfection
  • Transforming Growth Factor beta / immunology*
  • Transforming Growth Factor beta / pharmacology


  • Core Binding Factor Alpha 3 Subunit
  • DNA-Binding Proteins
  • Immunoglobulin A
  • Immunoglobulin G
  • Nuclear Proteins
  • Runx3 protein, mouse
  • Smad3 Protein
  • Smad3 protein, mouse
  • Smad4 Protein
  • Smad4 protein, mouse
  • Trans-Activators
  • Transcription Factors
  • Transforming Growth Factor beta
  • E1A-Associated p300 Protein
  • Ep300 protein, mouse