Characterization of CD40 signaling determinants regulating nuclear factor-kappa B activation in B lymphocytes.
CD40 signaling to B cells is important for generating an effective humoral immune response. CD40 ligation leads to B cell activation events such as proliferation, Ig secretion, isotype switching, and up-regulation of cell surface molecules, as well as the generation of memory B cells. Many of these events are dependent upon the ability of CD40 to activate the transcription factor NF-kappa B (NF-kappa B). To define the CD40 signaling components upstream of NF-kappa B activation and the functional consequences downstream of NF-kappa B activation, we examined mouse B cell transfectants expressing wild-type or mutant human CD40. Analysis of CD40 cytoplasmic domain truncation and point mutants defined a 10-amino acid CD40 cytoplasmic signaling determinant required for NF-kappa B activation. A threonine residue at position 234, previously shown to be important for CD40 association with TNF receptor-associated factor 2 (TRAF2), TRAF3, and TRAF5, was not required for NF-kappa B activation. This suggests that in B cells, CD40-induced NF-kappa B activation can occur independently of TRAF2 and TRAF5 association. NF-kappa B activation was independent of the transmembrane domain of CD40, suggesting that it is independent of p23, a molecule that associates with CD40 in a region other than the cytoplasmic domain. Proteasome-dependent inhibitory kappa B alpha (I kappa B alpha) and I kappa B beta degradation occurred downstream of CD40 ligation and preceded CD40-mediated NF-kappa B nuclear translocation. CD40- or pervanadate-mediated I kappa B tyrosine phosphorylation was not detected. NF-kappa B activation correlated with the ability of CD40 to induce Ab secretion and the up-regulation of ICAM-1 and LFA-1. However, NF-kappa B activation was insufficient for CD40-mediated up-regulation of B7-1, Fas, and CD23.
Hsing
Y
Y
The Immunology Graduate Program, University of Iowa, Iowa City 52242, USA.
Hostager
B S
BS
Bishop
G A
GA
D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D019013:CD40 Antigens / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D003593:Cytoplasm / Q000737:chemistry / Q000276:immunology / Q000502:physiology; D018985:Epitopes, B-Lymphocyte / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D016393:Lymphoma, B-Cell; D051379:Mice; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism* / Q000502:physiology; D052002:NF-kappa B p50 Subunit; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D020569:Proto-Oncogene Proteins c-rel; D015398:Signal Transduction / Q000276:immunology*; D013329:Structure-Activity Relationship; D051841:Transcription Factor RelB; D014157:Transcription Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
D019013:CD40 Antigens; D018985:Epitopes, B-Lymphocyte; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D011518:Proto-Oncogene Proteins; D020569:Proto-Oncogene Proteins c-rel; C497593:RELB protein, human; C497594:Relb protein, mouse; D014157:Transcription Factors; D051841:Transcription Factor RelB