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NF-kappaB activates Bcl-2 expression in t(14;18) lymphoma cells
Caroline A Heckman1, John W Mehew, Linda M Boxer
1Center for Molecular Biology in Medicine, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94305, USA.
Oncogene
|May 29, 2002
Summary
The t(14;18) translocation in follicular lymphoma activates the bcl-2 gene. NF-kappaB activation of bcl-2 in these lymphoma cells is mediated by CRE and Sp1 binding sites.
Area of Science:
- Molecular Biology
- Oncology
- Gene Regulation
Background:
- The t(14;18) translocation characterizes follicular lymphoma, leading to bcl-2 gene overexpression.
- The role of NF-kappaB in regulating Bcl-2 levels is complex and cell-type dependent.
- Follicular lymphoma cells with t(14;18) exhibit elevated nuclear NF-kappaB levels.
Purpose of the Study:
- To investigate the mechanism by which NF-kappaB influences Bcl-2 expression in t(14;18) follicular lymphoma cells.
- To identify the specific regulatory elements within the bcl-2 promoter involved in NF-kappaB-mediated activation.
Main Methods:
- Utilized IkappaBalpha-super-repressor expression to modulate NF-kappaB activity in a t(14;18) cell line.
- Performed deletion analysis of the bcl-2 promoter region.
- Conducted chromatin immunoprecipitation assays targeting NF-kappaB, CREB/ATF, and Sp1.
- Introduced mutations in the CRE and Sp1 binding sites within bcl-2 reporter constructs.
Main Results:
- Expression of IkappaBalpha-super-repressor decreased endogenous Bcl-2 levels.
- Deletion analysis identified a critical regulatory region containing a cAMP response element (CRE) and Sp1 sites.
- Chromatin immunoprecipitation confirmed the binding of NF-kappaB, CREB/ATF, and Sp1 to this region.
- Mutating the CRE and Sp1 sites abolished the repressive effect of IkappaBalpha-super-repressor on bcl-2 promoter activity.
Conclusions:
- NF-kappaB activation of the bcl-2 gene in t(14;18) follicular lymphoma is not directly mediated by NF-kappaB binding sites.
- The activation is indirectly achieved through the interaction of NF-kappaB pathway components with the CRE and Sp1 binding sites on the bcl-2 promoter.