title: Cell-cycle associated transcriptional regulation of ribonucleotide reductase in L1210 leukemia cells and drug-resistant variants.
abstract: Previous studies from this laboratory have shown that the steady-state levels of the mRNA for the non-heme iron (NHI) subunit of ribonucleotide reductase were markedly elevated in hydroxyurea-resistant L1210 cell lines with minimal changes in the mRNA levels for the effector-binding (EB) subunit. In the present study, wild-type L1210 cells and their drug-resistant variants [hydroxyurea-resistant (HU-7); deoxyadenosine-resistant (Y-8); and deoxyadenosine/pyrazoloimidazole-resistant (ED2)] were synchronized by EGTA treatment in the G0/G1-phase of the cell cycle. Upon the addition of CaCl2, the cells reentered the cell cycle. The steady-state levels and the transcriptional rates of the mRNAs for the EB subunit and glyceraldehyde-3-phosphate dehydrogenase were measured and found to be similar in the drug-resistant variants compared to the wild-type cells. While the steady-state level of the mRNA for the NHI subunit was increased 35-fold in the HU-7 cell line, the transcription rate was increased only 7-fold. The increase in the transcription rate did not account for the large increase in the steady-state level. These data indicate that the increased steady-state level of the mRNA for the NHI subunit in the HU-7 L1210 cell line was not due to cell-cycle differences and that post-transcriptional processing and/or stability may play a role as well.
authors.affiliation: Department of Internal Medicine, University of South Florida College of Medicine, Tampa.
authors.forename: C E
authors.initials: CE
authors.lastname: Johnson
authors.forename: K
authors.initials: K
authors.lastname: Hughes
authors.forename: J G
authors.initials: JG
authors.lastname: Cory
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D002118:Calcium / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D003839:Deoxyadenosines / Q000494:pharmacology*; D004351:Drug Resistance / Q000235:genetics; D004533:Egtazic Acid / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D014644:Genetic Variation; D006918:Hydroxyurea / Q000494:pharmacology*; D007700:Kinetics; D007939:Leukemia L1210 / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D051379:Mice; D012264:Ribonucleotide Reductases / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D003839:Deoxyadenosines; D004533:Egtazic Acid; D012264:Ribonucleotide Reductases; D002118:Calcium; D006918:Hydroxyurea