Mutations in the DNA-binding and dimerization domains of v-Rel are responsible for altered kappa B DNA-binding complexes in transformed cells

Abstract

The c-rel proto-oncogene encodes a member of the Rel/NF-B family of transcription factors. The oncogenic viral form, v-rel, transduced by avian reticuloendotheliosis virus T, induces lymphoid tumors. v-Rel transformation may be mediated directly by binding of v-Rel to cognate DNA sites, resulting in altered gene expression, and/or indirectly by releasing Rel/NF-B transcription factors from cytoplasmic retention molecules, resulting in their translocation to the nucleus and the inappropriate expression of genes under B control. v-Reltransformed cell lines of different phenotypes contained v-Rel as well as endogenous B DNA-binding proteins in nuclear extracts. Kinetic analysis with avian leukosis virus-transformed B-cell lines expressing v-Rel or c-Rel indicated that the presence of endogenous B DNA-binding proteins in the nucleus is temporally correlated with the relocalization of v-Rel to the cytoplasm. Supershift analysis of these DNA-binding complexes revealed that v-Rel was present in all of the nuclear DNA-binding complexes heterodimerized with c-Rel, NF-B1, and other proteins. In contrast, c-Rel-transformed cells exhibited a less-complex pattern of nuclear B DNA-binding complexes, and the nuclear appearance of these endogenous complexes was not observed. Studies with c-/v-Rel hybrids suggest that the induction of the endogenous B DNA-binding complexes is the result of the mutations in the C-terminal region of the Rel homology (RH) domain of v-Rel. Moreover, v-Rel differed from c-Rel in its DNA-binding specificity. The altered DNA-binding specificity of v-Rel was associated with mutations located in the N-terminal part of the RH domain of v-Rel. These results suggest that two different regions of v-Rel (both located in the RH domain) influence the formation of B DNA-binding complexes differently.The proto-oncogene c-rel belongs to the family of Rel/ NF-B transcription factors. This family consists of related genes which are involved in the regulation of transcription during differentiation and developmental processes. In addition to c-rel, other vertebrate members include nfkb1, nfkb2, rela, and relb. The Rel/NF-B family is regulated by a small group of inhibitors (IBs) which serve to sequester these transcription complexes in the cytoplasm. The mechanism by which this family of transcription factors is regulated suggests that it evolved to be able to respond rapidly to external signals. Rel/ NF-B transcription factors are present in inactive cytoplasmic complexes, and following the appropriate regulatory signal, they are released to the nucleus, where they participate in the transcriptional regulation of a large set of genes (reviewed in references 3 and 46).Rel/NF-B and IB proteins have two structural features that have coevolved to promote DNA-protein and proteinprotein interactions: the Rel homology (RH) domain and ankyrin repeats. The RH domain in c-Rel, NF-B1 (p105/p50), NF-B2 (p100/p52), RelA (p65), and RelB mediates DNA binding, dimerization, and interactions with IB. At the Cdistal region of the RH d...

Avian I kappa B alpha is transcriptionally induced by c-Rel and v-Rel with different kinetics

“…Both c-Rel⌬ and v-Rel were less effective in the ability to induce IB␣ expression than c-Rel, possibly because both c-Rel⌬ and v-Rel are missing the most C-terminal transactivation domain that is present in c-Rel (33). Studies using c-Relv-Rel chimeras have revealed that the low activation of IB␣ gene expression can be mapped to mutations in the C terminus of v-Rel (24). Therefore, the decreased transactivation potential of c-Rel⌬ and v-Rel could account for their lower induction of IB␣ expression.…”