NF-Kb Activates Bcl-2 Expression in T(14;18) Lymphoma Cells

NF-kB activates Bcl-2 expression in t(14;18) lymphoma cells

Caroline A Heckman1,2, John W Mehew1,2 and Linda M Boxer*,1,2

1Center for Molecular Biology in Medicine, Veterans Aairs Palo Alto Health Care System, California, CA 94305, USA; 2Department of Medicine, Stanford University School of Medicine, Stanford, California, CA 94305, USA

The t(14;18) translocation, which is characteristic of from apoptosis (Hockenberry et al., 1990; Vaux et al., follicular lymphoma, results in the overexpression of 1988). The elevated level of Bcl-2 in t(14;18) cells the bcl-2 gene dependent upon regulatory elements within increases the survival of these cells and promotes the the bcl-2 5' flanking region and the immunoglobulin development of follicular lymphoma (Graninger et al., heavy chain gene enhancers. Con¯icting evidence 1987). Transgenic mice that constitutively overexpress exists on the eects of NF-kB expression on Bcl-2 Bcl-2 in their B cells display a polyclonal expansion of levels in dierent cell types. Lymphoma cells with the B cells with an increased survival rate but with no t(14;18) translocation show high levels of nuclear increase in cell cycling. In addition, progression to NF-kB proteins. We observed decreased levels of high-grade lymphoma is observed in these mice endogenous Bcl-2 when the IkBa-super-repressor was (McDonnell and Korsmeyer, 1991). Although the expressed in a t(14;18) cell line. Deletion analysis of the mechanism of bcl-2 deregulation in t(14;18) cells bcl-2 promoter indicated that the repressive eect of the remains unclear, elements within the IgH enhancers IkBa-super-repressor occurred through a region that and the bcl-2 regulatory region are thought to play a contained no NF-kB consensus sequences. This highly role. active region contained a c-AMP response element Two promoters mediate transcriptional control of (CRE) and several Sp1 binding sites. Chromatin the bcl-2 gene. The 5'-promoter (P1) is located 1386- immunoprecipitation assays with antibodies speci®c for 1423 base pairs upstream of the translational start site the NF-kB and CREB/ATF family members, as well as (Seto et al., 1988). This is a TATA-less, GC-rich Sp1, resulted in the isolation of this IkBa-super-repressor promoter that displays numerous start sites. The start responsive region of the bcl-2 promoter. Mutation of the sites of the 3'-promoter (P2) are located 1.3 kilobases CRE and the two Sp1 sites in dierent combinations in downstream of the P1 promoter. A major positive bcl-2 reporter constructs resulted in the loss of bcl-2 regulator of P1 activity is a c-AMP response element promoter repression by the IkBa-super-repressor. We (CRE) (Wilson et al., 1996). This element is not only therefore conclude that the activation of bcl-2 by NF-kB essential for bcl-2 deregulation in t(14;18) cells, but it is in t(14;18) lymphoma cells is mediated through the CRE also responsible for the positive regulation of bcl-2 and Sp1 binding sites. expression during the activation of mature B cells and Oncogene (2002) 21, 3898 ± 3908. DOI: 10.1038/sj/ the rescue of immature B cells from calcium-dependent onc/1205483 apoptosis (Ji et al., 1996; Wilson et al., 1996). In addition, the CRE is essential for bcl-2 expression in Keywords: bcl-2; lymphoma; transcription; NF-kB neuronal cells (Riccio et al., 1999) and for estrogen- receptor activation of bcl-2 in mammary cells (Dong et al., 1999). The P1 promoter also contains WT1 binding Introduction sites, which act as negative regulators of bcl-2 expression in t(14;18) and HeLa cells (Heckman et The majority of follicular lymphomas are characterized al., 1997; Hewitt et al., 1995) and as positive regulators by the translocation of the bcl-2 proto-oncogene from in sporadic Wilm's tumors (Mayo et al., 1999). The 18q2