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Regulation of IkappaB beta in WEHI 231 mature B cells
1Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Insights
Constitutive activation of Nuclear Factor-kappa B (NF-kappaB) in WEHI 231 cells involves hypophosphorylated IkappaB beta. This protein shields NF-kappaB from IkappaB alpha, enabling continuous nuclear import.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Constitutive Nuclear Factor-kappa B (NF-kappaB) activation in WEHI 231 B cells mirrors prolonged NF-kappaB activation seen in other stimulated cells.
- In both scenarios, NF-kappaB DNA binding complexes persist in the nucleus despite high levels of cytosolic Inhibitor of kappa B alpha (IkappaB alpha).
Purpose of the Study:
- To investigate the role of IkappaB beta in the constitutive activation of NF-kappaB in WEHI 231 B cells.
- To elucidate the mechanism by which NF-kappaB remains active in the nucleus.
Main Methods:
- Analysis of IkappaB beta phosphorylation status in WEHI 231 cells.
- Detection of NF-kappaB and IkappaB beta complexes in both cytosol and nucleus.
- Assessment of NF-kappaB DNA binding activity.
Main Results:
- The predominant form of IkappaB beta in WEHI 231 cells is hypophosphorylated.
- Hypophosphorylated IkappaB beta forms a stable complex with NF-kappaB in the cytosol.
- This complex, containing NF-kappaB, is also found in nuclear DNA binding complexes.
Conclusions:
- Hypophosphorylated IkappaB beta in WEHI 231 cells likely protects NF-kappaB from cytosolic IkappaB alpha.
- This protection mechanism facilitates the continuous nuclear import of NF-kappaB, leading to its constitutive activation.
Abstract:
Constitutive activation of NF-kappaB in WEHI 231 early mature B cells resembles the persistent activation of NF-kappaB that is observed upon prolonged stimulation of other cells. In both cases, NF-kappaB DNA binding complexes are found in the nucleus, despite the abundance of cytosolic IkappaB alpha. Recently, we have shown that prolonged activation of 70Z/3 cells with lipopolysaccharide results in the degradation of IkappaB beta, followed by its subsequent resynthesis as a hypophosphorylated protein. This protein was shown to facilitate transport of a portion of NF-kappaB to the nucleus in a manner that protects it from cytosolic IkappaB alpha. We now demonstrate that the most abundant form of IkappaB beta in WEHI 231 cells is a hypophosphorylated protein. This hypophosphorylated IkappaB beta is found in a stable complex with NF-kappaB in the cytosol and is also detected in NF-kappaB DNA binding complexes in the nucleus. It is likely that hypophosphorylated IkappaB beta in WEHI 231 cells also protects NF-kappaB from IkappaB alpha, thus leading to the continuous nuclear import of this transcription factor.
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