AP-1 Factors Play an Important Role in Transformation Induced by the v-rel Oncogene

Abstract

The v-rel oncogene of the avian reticuloendotheliosis virus (REV-T) encodes a member of the Rel/NF-B family of transcription factors (reviewed in references 11, 26, and 27). REV-T induces a rapidly fatal lymphoma in young chickens and transforms both immature hematopoietic cells and fibroblasts in culture (7,9,21,32,48,52,56). The product of the v-rel oncogene, p59 v-rel (v-Rel), is a nuclear phosphoprotein that is a truncated and mutated version of the avian protooncoprotein c-Rel (69, 78). The deletion of the C terminus of c-Rel to produce v-Rel resulted in the removal of a cytoplasmic retention sequence and transactivation sequences (29,62). Like other members of the Rel/NF-B family, c-Rel and v-Rel have a conserved N terminus, the Rel homology region. This region contains sequences important for DNA binding, homoand heterodimerization, and nuclear localization (5,24,29,45). Both v-Rel and c-Rel form homodimers and heterodimers with other family members and bind to B sites located in the promoter and enhancer elements of various effector genes (42). DNA-binding complex formation and transactivation activity are necessary for the full transforming potential of v-Rel (20,32,50,58,64). Due to the deletion of sequences involved in transcriptional activation however, v-Rel exhibits a lower transcriptional activity than does c-Rel (5,40,54,62).The regulation of Rel/NF-B family members is mediated, in part, by their interaction with IB proteins. IB proteins sequester these transcription factors in the cytoplasm and inhibit their DNA binding (reviewed in references 6, 8, and 28).In response to external stimuli that result in the activation of Rel/NF-B complexes, IB-␣ is proteolytically degraded, allowing the nuclear translocation of these transcription complexes (35,44,72). The gene encoding IB-␣ is then upregulated by the nuclear Rel/NF-B factors, establishing an autoregulatory loop that results in a transient response to exogenous stimuli (17,18,41,51). We have previously shown that v-Rel activates the transcription of IB-␣ far less efficiently than c-Rel and the induction of IB-␣ occurs with delayed kinetics (38,65). Moreover, avian IB-␣ transcription is synergistically regulated by Rel and AP-1 factors (49). v-Rel, however, is less effective in the synergistic stimulation of the IB-␣ promoter than is c-Rel. Because v-Rel is impaired in the induction of IB-␣, the activity of v-Rel is less sensitive to autoregulation by IB-␣. This is likely to be an important feature in the establishment of transformation by v-Rel. The functional interaction between AP-1 factors and Rel suggested

Characterization of changes in gene expression associated with malignant transformation by the NF-κB family member, v-Rel

“…As reported earlier, overexpression of c-rel morphologically transforms CEFs (Abbadie et al, 1993;Kralova et al, 1994). Although c-rel ®broblasts do not form colonies in soft agar, they do display characteristic disruption of cellular cytoskeleton and a remarkable extension of life span.…”

Differences in κB DNA-binding properties of v-Rel and c-Rel are the result of oncogenic mutations in three distinct functional regions of the Rel protein

“…Relation between DNA-binding function and the gene induction/repression potential of the three mutation clusters present in v-Rel Several Rel/NF-kB target genes are either up or downregulated as a consequence of v-Rel's expression Carrasco et al, 1996;Hrdlickova et al, 1994bHrdlickova et al, , 1995bKralova et al, 1994;Zhang et al, 1995;Zhang and Humphries, 1996). The expression of several of these genes (MHC class I and II, IL-2R) were shown to be activated to a higher extent by v-Rel than c-Rel (Hrdlickova et al, 1994b, Nehyba et al, 1994.…”

“…Goat anti-mouse immunoglobulin antibodies conjugated with biotin were purchased from Southern Biotechnology Associates, Inc., Birmingham, Ala., and streptavidin coupled with alkaline phosphatase was obtained from Boehringer Mannheim, Corp., Indianopolis, Ind. Rabbit polyclonal antisera 1647, V1, VC and AL-1 used in electrophoretic mobility shift assays (EMSAs) were described previously (Hrdlickova et al, 1995a;Kralova et al, 1994). 1647, V1 and VC were raised against immunogens containing amino acids 2 ± 11, 115 ± 292 and 485 ± 503 of v-Rel, respectively.…”

“…Several Rel/NF-kB members and their IkB inhibitors have been implicated in the induction of various malignant processes (Fracchiolla et al, 1993;Kabrun et al, 1990;Lewis et al, 1981;Lu et al, 1991;Neri et al, 1991;Ohno et al, 1990). The cRel proto-oncoprotein itself can be transforming when overexpressed from a retroviral promoter (Abbadie et al, 1993;Diehl et al, 1993;Kralova et al, 1994;Mosialos et al, 1991;Nehyba et al, 1994). Transformation, particularly of lymphoid cells, by c-Rel is, however, very weak.…”

“…Mutants of c-Rel with deleted C-termini, apparently selected for higher tumorigenicity, have been isolated from tumors of chickens injected originally with a retrovirus expressing full length c-Rel (Hrdlickova et al, 1994a). Additionally, several mutants with increased oncogenicity have been constructed by deleting 16 to 118 amino acids from the C-terminus (Capobianco et al, 1990;Diehl et al, 1993;Kralova et al, 1994;Nehyba et al, 1994). All these truncated variants of c-Rel, however, are far less oncogenic than v-Rel which contains the Cterminal deletion of 118 amino acids as well as 19 additional mutations (Wilhelmsen et al, 1984) (Figure 1b, for de®nition of the term`mutations in v-Rel' see Materials and methods).…”