title: Glucocorticoids induce a G1/G0 cell cycle arrest of Con8 rat mammary tumor cells that is synchronously reversed by steroid withdrawal or addition of transforming growth factor-alpha.
abstract: Con8 mammary tumor cells are an epithelial cell line derived from the 7,12-dimethylbenz(alpha)anthracene-induced 13762NF rat mammary adenocarcinoma. The synthetic glucocorticoid dexamethasone suppresses the growth of Con8 cells, and after 5 days of treatment with this steroid, Con8 cells undergo less than 0.5 population doublings. This growth arrest is accompanied by a 30-fold elevation in c-jun transcript levels, no change in c-fos expression, and a moderate increase in total AP-1 transcriptional activity. Dexamethasone inhibited DNA synthesis within one cell cycle, and flow cytometry of propidium iodide-stained nuclei demonstrated that dexamethasone growth-suppressed cells had a DNA content indicative of a specific cell cycle block in either G1 or G0. Consistent with a G1/G0 arrest of the cell cycle, dexamethasone did not prevent Con8 cells from entering the S phase after release from synchronization at the G1/S boundary by a double thymidine block. Analysis of [3H]thymidine incorporation and autoradiography of [3H]thymidine-labeled nuclei revealed that after either dexamethasone withdrawal or the addition of transforming growth factor-alpha (TGF alpha), Con8 cells synchronously reinitiate cell cycle progression. Northern blot analysis demonstrated that an induction of transcripts for the G1 marker genes c-myc and cyclin D1 occurs before cells enter the S-phase. After dexamethasone withdrawal, c-myc and cyclin D1 expression transiently peak at 2 and 4 h, respectively. In contrast, c-myc expression peaked at 0.5-1 h, whereas cyclin D1 expression was induced at 2 h and maintained at a high level after the addition of TGF alpha. Our results demonstrate that glucocorticoids induce a specific block of the cell cycle progression of a rat mammary tumor cell, and that after synchronous progression through the cell cycle, the temporal expression pattern for c-myc and cyclin D1 is distinct for dexamethasone release vs. the addition of TGF alpha to glucocorticoid-suppressed cells.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors.forename: L
authors.initials: L
authors.lastname: Goya
authors.forename: A C
authors.initials: AC
authors.lastname: Maiyar
authors.forename: Y
authors.initials: Y
authors.lastname: Ge
authors.forename: G L
authors.initials: GL
authors.lastname: Firestone
mesh_terms: D000230:Adenocarcinoma; D000818:Animals; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000378:metabolism; D002999:Clone Cells; D016213:Cyclins / Q000096:biosynthesis; D004273:DNA, Neoplasm / Q000032:analysis / Q000096:biosynthesis* / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D016193:G1 Phase / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D016259:Genes, myc / Q000187:drug effects; D007700:Kinetics; D008325:Mammary Neoplasms, Experimental; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D051381:Rats; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D016213:Cyclins; D004273:DNA, Neoplasm; D016271:Proto-Oncogene Proteins c-myc; D016211:Transforming Growth Factor alpha; D003907:Dexamethasone; D015500:Chloramphenicol O-Acetyltransferase; D013936:Thymidine