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NF-kappaB is required for CD38-mediated induction of C(gamma)1 germline transcripts in murine B lymphocytes
Hiroaki Kaku1, Keisuke Horikawa, Yuichi Obata
1Division of Immunology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Japan.
Insights
CD38 ligation on B cells triggers NF-kappaB signaling, crucial for germline gamma1 transcript expression and IgG1 production. This pathway involves Bruton
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- CD38 ligation on murine B cells induces proliferation, germline gamma1 transcript expression, and enhanced IL-5 receptor expression.
- This process leads to immunoglobulin (Ig) class switch recombination and significant IgM and IgG1 production, especially with co-stimulation.
- Signaling pathways mediating CD38-induced germline gamma1 transcript expression in B cells remain poorly understood.
Purpose of the Study:
- To elucidate the signaling pathways involved in CD38-mediated germline gamma1 transcript expression in murine B cells.
- To investigate the role of NF-kappaB/Rel family proteins in CD38-induced B cell activation and Ig class switching.
Main Methods:
- Activation of NF-kappaB/Rel family proteins (c-Rel, p65, p50) in murine splenic B cells following CD38 ligation.
- Analysis of NF-kappaB activation in B cells deficient in Bruton's tyrosine kinase (Btk(-/-)).
- Assessment of NF-kappaB activation using inhibitors of protein kinase C (PKC) and phosphatidylinositol (PI)-3 kinase.
- Evaluation of germline gamma1 transcript expression in B cells from p50(-/-) and c-Rel(-/-) mice following CD38 or CD40 ligation.
Main Results:
- CD38 ligation activates NF-kappaB/Rel proteins (c-Rel, p65, p50) in murine splenic B cells, with distinct kinetics compared to CD40 stimulation.
- NF-kappaB activation by CD38 requires Bruton's tyrosine kinase (Btk), protein kinase C (PKC), and PI-3 kinase.
- p50(-/-) B cells exhibit impaired germline gamma1 transcript expression upon CD38 ligation, while c-Rel(-/-) B cells show severe impairment in response to both CD38 and CD40 ligation.
- CD38-mediated germline gamma1 transcript induction is dependent on NF-kappaB/Rel signaling.
Conclusions:
- NF-kappaB/Rel proteins, particularly c-Rel and p50, play an essential role in CD38-induced germline gamma1 transcript expression in murine B cells.
- The signaling cascade involves Btk, PI-3 kinase, and PKC, leading to NF-kappaB activation and subsequent IgG1 production.
- These findings clarify key molecular mechanisms underlying CD38-mediated B cell responses and Ig class switching.
Abstract:
Ligation of CD38 on murine B cells with agonistic anti-CD38 mAb induces B cell proliferation, expression of germline gamma1 transcripts and enhances IL-5 receptor expression. This leads to Ig class switch recombination from the micro to gamma1 heavy chain gene, and high levels of IgM and lgG1 production, particularly in response to anti-CD38 and IL-5 co-stimulation. Although some of the post-receptor signaling events initiated by CD38 ligation have been characterized, signaling pathways involved in CD38-mediated germline gamma1 transcript expression in B cells are poorly understood. Here we show that CD38 ligation of murine splenic B cells activates members of the NF-kappaB/Rel family of proteins including c-Rel, p65 and p50. The activation patterns and kinetics of NF-kappaB-like proteins in CD38-stimulated B cells differ somewhat from those seen in CD40-stimulated B cells. Activation of NF-kappaB-like proteins by CD38 ligation is not observed in splenic B cells from Bruton's tyrosine kinase (Btk)-deficient (Btk(-/-)) mice, with inhibitors of protein kinase C (PKC) and phosphatidylinositol (PI)-3 kinase also suppressing NF-kappaB activation in CD38-activated B cells. We infer from these results that activation of Btk, PI-3 kinase and PKC play, at least in part, important roles in the induction of NF-kappaB in CD38-stimulated murine B cells. Consistent with a role for NF-kappaB/Rel signaling in CD38-mediated germline gamma1 transcript expression, p50(-/-) B cells show significant impairment of germline gamma1 transcript expression in response to CD38 ligation, whereas the CD40-induced response was not altered. In contrast, c-Rel(-/-) B cells show a severe impairment of germline gamma1 transcript expression in response to CD38 or CD40 ligation. These results indicate an essential role for NF-kappaB proteins in the induction of germline gamma1 transcripts by CD38-ligated murine B cells giving rise to IL-5-induced IgG1 production.