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CD40-mediated tumor necrosis factor receptor-associated factor 3 signaling upregulates IL-4-induced germline Cepsilon

Yuji Basaki1, Koichi Ikizawa, Keiichi Kajiwara

  • 1Clinical Research Center, National Sagamihara Hospital, 18-1 Sakuradai, Sagamihara 228-8522, Japan.

Archives of Biochemistry and Biophysics
|September 11, 2002
PubMed

Insights

CD40 engagement enhances B cell germline C epsilon transcription, a key step for IgE class switching. This study reveals TRAF3 (tumor necrosis factor receptor-associated factor 3) protein activates MEK1, upregulating this transcription.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Signaling

Background:

  • Interleukin-4 (IL-4) induces germline C epsilon transcription in B cells, initiating IgE class switching.
  • CD40 engagement enhances this IL-4-driven transcription.
  • The role of tumor necrosis factor receptor-associated factor (TRAF) proteins in CD40-mediated enhancement of germline C epsilon transcription is unclear.

Purpose of the Study:

  • To investigate the involvement of TRAF proteins in CD40-mediated enhancement of IL-4-driven germline C epsilon transcription.
  • To elucidate the signaling pathway, specifically the mitogen-activated protein kinase (MAPK) pathway, involved in this process.

Main Methods:

  • Utilized a human Burkitt's lymphoma B cell line (DG75).
  • Employed antisense oligodeoxynucleotides (ODNs) targeting specific TRAF proteins (TRAF2, 3, 5, 6).
  • Assessed activation of the MEK1-ERK pathway and measured germline C epsilon transcription; used a MEK1 inhibitor (PD98059).

Main Results:

  • TRAF2, 3, 5, and 6 associated with CD40, with levels unaffected by anti-CD40 stimulation.
  • Antisense ODN for TRAF3, but not TRAF2, 5, or 6, inhibited CD40-induced MEK1-ERK activation.
  • Inhibition of TRAF3 or MEK1 significantly reduced CD40-mediated enhancement of IL-4-driven germline C epsilon transcription.

Conclusions:

  • TRAF3-dependent activation of the MEK1-ERK pathway is crucial for CD40-mediated upregulation of germline C epsilon transcription in DG75 cells.
  • These findings identify TRAF3 as a key mediator in the signaling cascade initiated by CD40 engagement that enhances IgE class switching.

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