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

The human TERT (hTERT) gene encodes the telomerase catalytic subunit which plays a role in telomerase regulation. Telomerase is activated in more than 90% of all human malignancies and understanding how telomerase is regulated is necessary for implementation of successful anti-cancer therapies. microRNAs (miRNAs) are important regulators of gene expression in eukaryotic cells but evidence of their role in telomerase regulation has not been documented. To determine whether hTERT activity is regulated by multiple miRNAs, eight miRNAs which have putative binding sites in the hTERT 3′UTR together with miR-138-5p were evaluated in luciferase assays with a reporter containing the hTERT 3′UTR. Six miRNAs (let-7g*, miR-133a, miR-138-5p, miR-342-5p, miR-491-5p, and miR-541-3p) specifically inhibited the expression of the reporter luciferase-driven constructs and let-7g*, miR-133a, miR-138-5p, and miR-491-5p also downregulated endogenous telomerase activity in cells. Moreover, all six miRNAs significantly inhibited cell proliferation. miRNAs (miR-133a, miR-138-5p, 342-5p, 491-5p, 541-3p) also have predicted binding sites within the 3′UTR of three genes involved in Wnt signaling (TCF7, MSI1, and PAX5). These miRNAs inhibited the expression of the luciferase reporter constructs containing 3′UTRs of these genes and downregulated protein expression of the TCF7 transcription factor, which mediates the canonical Wnt pathway. Together, these results suggest the existence of a miRNA regulatory network involving the hTERT and Wnt pathway.

The v-rel oncogene was derived from the c-rel proto-oncogene, which encodes a transcriptional activator. Expression of v-rel transforms avian hematopoietic cells and fibroblasts. Here we report that overexpression (via a replication-competent retroviral vector) of full-length c-Rel as well as a 40-amino-acid, carboxy-terminal deletion construct of c-Rel (c-RelA) resulted in the morphological transformation of chicken embryo fibroblasts (CEFs). Subcellular localization of Rel polypeptides in these transformed cells as determined by immunofluorescence and immunoprecipitation revealed their presence in both the nucleus and the cytoplasm, with the majority of Rel polypeptides showing cytoplasmic localization. Cytoplasmic localization could be due to interaction with IKB molecules, and in fact, the overexpression of c-Rel or the C-terminal deletion construct of c-Rel resulted in an increase in the levels of mRNA encoding the avian IKB protein pp4O and the avian homolog of the NF-KB protein, p105. However, expression of v-Rel resulted in the induction of pp4O mRNA only. While c-Rel was a weak activator of KB-mediated transcription of a reporter construct in transformed CEFs, v-Rel and c-RelA were transcriptional repressors. However, in spite of these differences, all of these proteins resulted in the transformation of CEFs.

The transforming protein encoded by the v-rel oncogene of avian reticuloendotheliosis virus (REV-T) is a very low copy number molecule in the cytosol of transformed cells. Analysis of cytosolic extracts from a REV-T-transformed lymphoid cell line by gel filtration on Sephacryl S-300 indicated that most of the v-rel oncogene product, pp59v-rel, eluted These observations suggest that pp59v-rel is complexed with a 40-kDa cellular phosphoprotein to form a 400-kDa heteropolymer in the cytoplasm of transformed lymphoid cells.

The v-rel oncogene of avian reticuloendotheliosis virus type T (REV-T) encodes a 59-kilodalton (kDa) phosphoprotein located principally in the cytosol of transformed lymphoid cells. All of the detectable pp59v-rel was present in high-molecular-weight complexes containing at least five cellular proteins (p124, p115, p75c-rel p70hsC, and pp4O). Antiserum was developed against the 40-kDa protein, the most abundant cellular protein associated with the complex. The 40-kDa phosphoprotein was complexed with pp59v-rel in REV-T-transformed lymphoid cell lines arrested at different stages of B-cell development as well as in lymphoid tumor cells and in fibrosarcomas. The half-life (8 h) of pp4O in REV-T-transformed lymphoid cells was the same as that of pp59v-rel. Antiserum against pp4O permitted the identification of two pp59v-rel complexes. The most abundant cytoplasmic complex contained approximately 75% of the pp59v-rel and all of the detectable pp4O in REV-T-transformed lymphoid cells. Twenty-five percent of the pp59v-rel was present in a minor complex that contained the majority of p75crel along with p115 and p124. In nuclear extracts of REV-T-transformed lymphoid cells, pp59v-re was complexed with pp4O. The two high-molecular-weight proteins (p115 and p124) and p75c're were not detected in the nuclear complex. In the cytosolic complexes, pp4O was heavily phosphorylated, whereas the nuclear form was much less extensively phosphorylated.