Avian Leukosis Virus-induced Lymphomas Research Articles

Avian bic , a Gene Isolated from a Common Retroviral Site in Avian Leukosis Virus-Induced Lymphomas That Encodes a Noncoding RNA, Cooperates with c- myc in Lymphomagenesis and Erythroleukemogenesis

bic is a novel gene identified at a common retroviral integration site in avian leukosis virus-induced lymphomas and has been implicated as a collaborator with c-myc in B lymphomagenesis. It lacks an extensive open reading frame and is believed to function as an untranslated RNA (W. Tam, Gene 274:157-167, 2001; W. Tam, D. Ben-Yehuda, and W. S. Hayward, Mol. Cell. Biol. 17:1490-1502, 1997). The oncogenic potential of bic, particularly its ability to cooperate with c-myc in oncogenesis, was tested directly by expressing c-myc and bic, either singly or in pairwise combination, in cultured chicken embryo fibroblasts (CEFs) and in chickens using replication-competent retrovirus vectors. Coexpression of c-myc and bic in CEFs caused growth enhancement of cells. Most importantly, chick oncogenicity assays demonstrated that bic can cooperate with c-myc in lymphomagenesis and erythroleukemogenesis. The present study provides direct evidence for the involvement of untranslated RNAs in oncogenesis and provides further support for the role of noncoding RNAs as riboregulators.

Bic, a novel gene activated by proviral insertions in avian leukosis virus-induced lymphomas, is likely to function through its noncoding RNA.

The bic locus is a common retroviral integration site in avian leukosis virus (ALV)-induced B-cell lymphomas originally identified by infection of chickens with ALVs of two different subgroups (Clurman and Hayward, Mol. Cell. Biol. 9:2657-2664, 1989). Based on its frequent association with c-myc activation and its preferential activation in metastatic tumors, the bic locus is thought to harbor a gene that can collaborate with c-myc in lymphomagenesis and presumably plays a role in late stages of tumor progression. In the present study, we have cloned and characterized two novel genes, bdw and bic, at the bic locus. bdw encoded a putative novel protein of 345 amino acids. However, its expression did not appear to be altered in tumor tissues, suggesting that it is not involved in oncogenesis. The bic gene consisted of two exons and was expressed as two spliced and alternatively polyadenylated transcripts at low levels in lymphoid/hematopoietic tissues. In tumors harboring bic integrations, proviruses drove bic gene expression by promoter insertion, resulting in high levels of expression of a chimeric RNA containing bic exon 2. Interestingly, bic lacked an extensive open reading frame, implying that it may function through its RNA. Computer analysis of RNA from small exon 2 of bic predicted extensive double-stranded structures, including a highly ordered RNA duplex between nucleotides 316 and 461. The possible role of bic in cell growth and differentiation is discussed in view of the emerging evidence that untranslated RNAs play a role in growth control.

Multiple proto-oncogene activations in avian leukosis virus-induced lymphomas: evidence for stage-specific events.

We have examined avian leukosis virus-induced B-cell lymphomas for multiple, stage-specific oncogene activations. Three targets for viral integration were identified: c-myb, c-myc, and a newly identified locus termed c-bic. The c-myb and c-myc genes were associated with different lymphoma phenotypes. The c-bic locus was a target for integration in one class of lymphomas, usually in conjunction with c-myc activation. The data indicate that c-myc and c-bic may act synergistically during lymphomagenesis and that c-bic is involved in late stages of tumor progression.

Penetrance and low concordance in monozygotic twins in disease: are they the results of alterations in somatic genomes?

Penetrance and low concordance in monozygotic twins in disease: are they the results of alterations in somatic genomes?

Patterns of proviral insertion and deletion in avian leukosis virus-induced lymphomas.

Sixty-eight lymphomas induced by eight different avian leukosis viruses have been analyzed on Southern blots for virus-induced mutations in the chicken c-myc gene. Sixty-six of the lymphomas exhibited a proviral insertion in c-myc, whereas one exhibited a new transduction of c-myc. Sixty-four of the proviral insertions were in the same transcriptional orientation as c-myc. Two were in the opposite transcriptional orientation. All of the insertions were upstream of the protein-coding sequences of c-myc, with most residing in the first exon or the first intron of c-myc. All of the lymphoma-inducing proviruses had deletions that included either sequences near the 5' long terminal repeat (LTR) or an LTR. The most frequent lymphoma-inducing provirus appeared to have retained both of its LTRs, but had lost sequences near its 5' LTR. The second and third most frequent lymphoma-inducing proviruses consisted of solo LTRs or of proviruses that had lost the 5' LTR as well as some internal sequences. Twenty-four insertions were mapped in c-myc. Each of these mapped to within 150 base pairs of one of the five DNase I-hypersensitive sites that occur in a 3-kilobase region immediately 5' to the protein-coding sequences of c-myc. One lymphoma contained a new c-myc transducing virus. This virus, MYC-3475, caused rapid-onset myelocytomatosis.

Nucleotide sequence 5′ of the chicken c- myc coding region: Localization of a noncoding exon that is absent from myc transcripts in most avian leukosis virus-induced lymphomas

Nucleotide sequence 5′ of the chicken c- <i>myc</i> coding region: Localization of a noncoding exon that is absent from <i>myc</i> transcripts in most avian leukosis virus-induced lymphomas

Nucleotide sequence 5' of the chicken c-myc coding region: localization of a noncoding exon that is absent from myc transcripts in most avian leukosis virus-induced lymphomas.

We have determined the nucleotide sequence of the 2.2-kilobase-pair region upstream of the chicken c-myc coding exons. Using RNA blot analysis, we have localized a noncoding exon to a region that is separated from the c-myc coding sequences by an intron of 700-800 base pairs. In most avian leukosis virus-induced lymphomas proviral integration has occurred within, or downstream of, the first exon, thus presumably displacing the regulatory sequences that normally control c-myc expression. More than 70% of the integration sites were clustered in a 250-base-pair region in the first intron, immediately preceding the coding sequences. Sequences from the upstream noncoding exon were absent from the myc transcripts in these lymphomas; RNA transcripts from the normal c-myc allele were not expressed at detectable levels.

Molecular analysis of the c-myc locus in normal tissue and in avian leukosis virus-induced lymphomas.

We isolated molecular clones of the provirus-host cell junctions (tumor junction fragments) from two avian leukosis virus-induced lymphomas and compared the structures of these clones with a clone of the normal c-myc gene. Restriction mapping and DNA sequencing demonstrated that normal proviral integration events occurred adjacent to c-myc in both tumors, without gross structural alteration of c-myc. The right long terminal repeat of an avian leukosis virus provirus is integrated upstream from the bulk of the c-myc coding sequences and oriented such that transcription can initiate within the long terminal repeat and proceed downstream into c-myc. A comparison of a tumor junction fragment with the v-myc gene showed that there are two regions of v-myc-related sequences (which are probably exons) separated by 1 kilobase of sequences unrelated to v-myc (probably an intron). A DNA sequence analysis of the tumor junction fragments suggested that integration had occurred in exons adjacent to splice donor sites. This suggests that there are additional exons and introns in c-myc. Based on these findings, a model is proposed for the genesis of the tumor-specific RNAs containing viral-5' and c-myc information in avian leukosis virus-induced lymphomas.