Regulation of Bcl-2 expression by C/EBP in t(14;18) lymphoma cells

Heckman CA, Wheeler MA and Boxer LM
Source: Oncogene
Publication Date: (2003)
Issue: 22(39): 5947-5955
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Species: human
Tissue Origin: blood
In follicular lymphomas, Bcl-2 is expressed at elevated levels increasing cell survival and protection from apoptosis. The mechanisms involved in the deregulated expression of the bcl-2 gene are not entirely clear, but several transcription factors that play a role have been identified. The authors studied the role of C/EBP family of transcription factors in the regulation of Bcl-2 expression. To further confirm the relation between C/EBP and Bcl-2 expression the human B cell line DHL-4, was nucleofected with siRNA targeting C/EBPalpha and C/EBPbeta. Compared to non-specific siRNA, siRNA molecules targeting C/EBP decreased C/EBP and Bcl-2 expression. Together with other findings the results reveal that the C/EBP family members play a role in the regulation of Bcl-2 expression.
In follicular lymphomas with the t(14;18) translocation, there is increased expression of the bcl-2 gene, which is dependent upon regulatory elements within the bcl-2 5' flanking region and the immunoglobulin heavy-chain gene enhancers. We found that t(14;18) lymphomas expressed C/EBPalpha, which is not normally expressed in B lymphocytes. Expression of C/EBPalpha increased bcl-2 expression, and two regions of the bcl-2 P2 promoter that mediated this effect were identified. C/EBPbeta was also able to increase bcl-2 promoter activity through these sites. The 5' site was GC-rich and did not contain a C/EBP consensus sequence; however, C/EBP was observed to interact with this site both in vitro by EMSA and in vivo by chromatin immunoprecipitation assay. The 3' region contained the Cdx site, which mediates the effect of A-Myb on the bcl-2 promoter. In vivo binding studies revealed that C/EBP interacted with this region of the bcl-2 promoter as well. Decreased expression of C/EBP factors due to targeting of their transcripts by siRNA molecules resulted in downregulation of Bcl-2 protein. We conclude that C/EBPalpha and C/EBPbeta contribute to the deregulated expression of Bcl-2 in t(14;18) lymphoma cells.