Mutations in the v-Rel Transactivation Domain Indicate Altered Phosphorylation and Identify a Subset of NF-κB-Regulated Cell Death Inhibitors Important for v-Rel Transforming Activity

Abstract

Consistent with the constitutive activation of Rel/NF-B in human hematopoietic tumors, the v-Rel oncoprotein induces aggressive leukemia/lymphomas in animal models. v-Rel is thus a valuable tool to characterize the role of Rel/NF-B in cancer and the mechanisms involved. Prior studies by our group identified a serine-rich domain in v-Rel that was required for biological activity. Here, we investigated the molecular basis for the transformation defect of specific serine mutants. We show that the transforming efficiency of these mutants in primary lymphoid cells is correlated with their ability to mediate B site-dependent transactivation and with specific changes in phosphorylation profiles. Interestingly, coexpression of the death antagonists Bcl-xL and Bcl-2 significantly increased their oncogenicity, whereas other NF-B-regulated death inhibitors showed little or no effect. The fact that a subset of apoptosis inhibitors could rescue v-Rel transactivation mutants suggests that their reduced transcriptional activity may critically affect expression of defined death antagonists essential for oncogenesis. Consistent with this hypothesis, we observed selection for high endogenous expression of Bcl-2-related death antagonists in cells transformed by weakly transforming v-Rel mutants. These results emphasize the need for Rel/NF-B to efficiently activate expression of a subset of antiapoptotic genes from the Bcl-2 family to manifest its oncogenic phenotype.The Rel/NF-B family of transcription factors plays a key role in regulating immune and inflammatory responses and also participates in the control of cell proliferation and apoptosis, two functions that are critical in cancer. The implication of Rel/NF-B factors in malignancy was initially suggested by the acute oncogenicity of their viral derivative, the v-Rel oncoprotein. v-Rel induces aggressive and fatal lymphomas in chickens and transgenic mice. This phenotype can be accurately reproduced in vitro through malignant transformation of primary splenic lymphoid cells. Consistent with the oncogenic phenotype of v-Rel, cellular rel and nf-b genes are amplified, rearranged, overexpressed, and/or constitutively activated in human lymphoma, leukemia, myeloma, and Hodgkin's disease (reviewed in reference 49). Aberrant rel/nf-b genes and/or activity are also observed in solid tumors, including lung, breast, and colon carcinomas. Moreover, rel/nf-b genes serve as essential mediators for transformation by oncogenes such as bcr-abl, and RET (20,37,41,50). These observations highlight the importance of elucidating how Rel/NF-B functions in oncogenesis.

To be, or not to be: NF-κB is the answer – role of Rel/NF-κB in the regulation of apoptosis

“…Recent work suggests that the oncogenic potential of Rel proteins arises at least in part from their ability to upregulate antiapoptotic proteins. Both v-Rel mutants with impaired transforming activity due to transactivation domain mutations or weakly transforming Rel proteins could be rescued by coexpression of death suppressors Bcl-xL or Bcl-2 (White and Gilmore, 1996;Gilmore et al, 2001;Rayet et al, 2003). In support of this idea, v-Rel upregulates expression of c-IAP1 in transformed cells and does so at higher levels than its cellular homologue c-Rel (Kralova et al, 2002).…”

The c-Rel transcription factor and B-cell proliferation: a deal with the devil

“…First, BCL2 is rearranged in a high percentage of GCB-like DLBCLs, which constitute the same subclass of DLBCLs in which REL gene amplifications are exclusively found . Second, coexpression of Bcl-2 can enhance the transforming activity of weakly transforming mutants of v-Rel and of human REL in chicken lymphoid cells (White and Gilmore, 1996;Gilmore et al, 2001;Rayet et al, 2003). A second candidate gene for cooperating with REL is the BCL11a (aka Evi9) gene, which is located quite near to REL at chromosome 2p13 and is frequently coamplified with REL in B-cell lymphomas (Satterwhite et al, 2001).…”

NF-κB/Rel-mediated regulation of apoptosis in hematologic malignancies and normal hematopoietic progenitors

“…It is then necessary to analyze whether the hyperexpression of single genes can substitute for NF-kB/Rel activity in NF-kB/Rel-cells: this can allow to verify the relevance of specific genes in the NF-kB/Rel-mediated pathway of apoptosis regulation. 11,66,[75][76][77] Based on similar approaches, classes of apoptosis-modulating genes, whose expression is regulated by NF-kB/Rel, have been identified: some examples are reported in Table 1. Table 1 NF-kB/Rel target genes in apoptosis modulation Among these genes, iaps (inhibitor of apoptosis protein) encode intracellular proteins that can bind and inhibit various caspases through their baculoviral IAP repeat (BIR) domains.…”

“…Antiapoptotic genes regulated by NF-kB/Rel include, among others, bcl2 family members, 77,[86][87] genes for enzymes, such as SOD-2, which control the redox state of the cell, 66,88 and genes encoding proteins that can modulate NF-kB/Rel activation, by serving as transducer or regulatory proteins in the NF-kB/Rel-activating signaling machinery. 66,[89][90] Furthermore, NF-kB/Rel activation results, either directly or indirectly, in repressing the expression of proapoptotic genes.…”