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Identification of a novel NF-kappaB p50-related protein in B lymphocytes
R J Phillips1, S Gustafson, S Ghosh
1Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Insights
Researchers discovered a novel NF-kappaB p50-related protein (p55) in plasma cells that binds to kappaB sites and activates transcription. This finding suggests a distinct gene product regulating NF-kappaB signaling in these cells.
Area of Science:
- Molecular Biology
- Immunology
- Cell Biology
Background:
- Nuclear Factor-kappaB (NF-kappaB) is typically inactive in most cells, bound by inhibitory IkappaB proteins.
- Constitutive NF-kappaB activity is characteristic of mature B lymphocytes and macrophages.
Purpose of the Study:
- To investigate the regulation of constitutively active NF-kappaB in B lymphocytes.
- To characterize the composition of Rel protein complexes in different mouse B-cell lines, particularly plasmacytomas.
Main Methods:
- Analysis of Rel protein complexes in various mouse B-cell lines.
- Western blot analysis using p50 antisera.
- Reporter construct transfections in plasma cells.
Main Results:
- Mature B cells primarily contain a p50:c-Rel complex.
- Plasmacytomas exhibit a kappaB binding complex lacking c-Rel, containing a p50-related protein (p55).
- The p55 protein is transcriptionally active and appears to be encoded by a distinct gene.
Conclusions:
- A novel NF-kappaB p50-related protein (p55) exists in plasma cells.
- This p55 protein binds to kappaB sites and activates transcription, suggesting a unique regulatory mechanism in plasma cells.
- The discovery has implications for understanding NF-kappaB signaling pathways in B cell differentiation and function.
Abstract:
In most cell types other than mature B lymphocytes and macrophages, the transcription factor NF-kappaB remains in an inactive form in the cytosol by being bound to the inhibitory proteins IkappaBalpha and IkappaBbeta. To investigate the regulation of constitutively active NF-kappaB in B lymphocytes, we have examined the composition of Rel protein complexes in different mouse B-cell lines. As reported previously, the constitutively active complex in mature B cells was predominantly p50:c-Rel. However, the kappaB binding complex in the plasmacytomas that were examined lacked c-Rel and instead contained only a p50-related protein. This p50-related protein (p55) cross-reacts with three different p50 antisera, exists in both the cytosol and the nucleus, and is the protein that binds to kappaB sites in plasma cells. Transfection of reporter constructs into plasma cells indicates that the p55 complex is also transcriptionally active. The p55 protein can be detected in splenocytes from mice lacking the p105/p50 gene, and therefore it appears to be the product of a distinct gene. The implications of the existence of a NF-kappaB p50-related protein in plasma cells that is capable of binding to kappaB sites and activating transcription are discussed.