title: Transcriptional down-regulation of the rearranged C-myc expression in murine cell hybrids between a plasmacytoma and a T-cell lymphoma.
abstract: Regulation of the rearranged and non-rearranged c-myc expression was studied in murine cell hybrids (SBWI and SBWII) between plasmacytoma (S194) and T-cell lymphoma (BW5147) cells. Expression of the rearranged c-myc of heterogeneous mRNA sizes (1.8 approximately 2.4 kb) was markedly down-regulated in these hybrids regardless of retention of the gene. On the other hand, expression of the non-rearranged c-myc (2.4 kb) was not significantly affected in these hybrids. Treatment of SBWI hybrid cells with cycloheximide enhanced the non-rearranged c-myc 2- to 4-fold but did not release the down-regulation of the rearranged c-myc at all, suggesting that the down-regulation of the rearranged c-myc in the hybrid cells was mainly at a transcriptional rather than a post-transcriptional level. This was supported by the results of nuclear run-on assay: the high level of run-on transcripts in S194 cells declined in SBWI hybrid cells comparable to the level in BW5147 cells. The rearranged c-myc was hemi-methylated in S194 cells and the pattern was the same in SBWI hybrid cells. Furthermore, down-regulation of the rearranged c-myc in the hybrid was also not restored by treatment with 5-azacytidine (5-AzaC), 12-O-tetradecanoylphorbol-13-acetate (TPA) or forskolin, suggesting no causative involvement of DNA methylation or protein phosphorylation in down-regulation. Higher DNase I sensitivity of the rearranged c-myc in S194 cells decreased to a similar extent to that of the non-rearranged c-myc after cell fusion with BW5147 cells. These results suggest that expression of the rearranged c-myc is down-regulated at the level of transcription in murine cell hybrids between a plasmacytoma and a T-cell lymphoma, probably by changing chromatin configuration around the gene from the open to the closed state.
authors.affiliation: Laboratory of Molecular Genetics, Cancer Institute, Sapporo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Oikawa
authors.forename: N
authors.initials: N
authors.lastname: Kondoh
authors.forename: H
authors.initials: H
authors.lastname: Fujita
authors.forename: C
authors.initials: C
authors.lastname: Satoh
authors.forename: S Z
authors.initials: SZ
authors.lastname: Li
authors.forename: M C
authors.initials: MC
authors.lastname: Yoshida
authors.forename: M
authors.initials: M
authors.lastname: Imamura
authors.forename: K
authors.initials: K
authors.lastname: Onoé
authors.forename: N
authors.initials: N
authors.lastname: Kuzumaki
mesh_terms: D000818:Animals; D004273:DNA, Neoplasm / Q000032:analysis / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics*; D015321:Gene Rearrangement; D006825:Hybridomas / Q000032:analysis* / Q000378:metabolism / Q000473:pathology; D008223:Lymphoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008745:Methylation; D051379:Mice; D008807:Mice, Inbred BALB C; D009857:Oncogenes; D010766:Phosphorylation; D010954:Plasmacytoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D013601:T-Lymphocytes; D014158:Transcription, Genetic
chemical_list: D004273:DNA, Neoplasm