title: Antagonistic actions of phorbol ester in mammalian G0-->G1-->S cell cycle transition.
abstract: We have developed a protocol that reveals two antagonistic effects of phorbol-12-myristate-12-acetate (PMA) on the G0-->G1-->S transition of mammalian cell cycle. Balb-3T3 (Clone A31) cells arrested in G0 by serum starvation can be stimulated to traverse the G1 phase and initiate DNA synthesis 12 h later by a 2-h pulse with PMA. In contrast with this early stimulatory effect, PMA has an inhibitory effect when presented to the cells during the last 6 h of G1. PMA is able to inhibit DNA synthesis initiation irrespective of the triggering agent, i.e., serum, fibroblast growth factor, epidermal growth factor, platelet-derived growth factor, or PMA itself (presented as an early pulse). We have established that the critical period for the PMA inhibitory effect is between 6 and 8 h after cell stimulation. This dual effect of PMA is not a peculiarity of Balb-3T3 (clone A31) cells because it is also observed with other fibroblastic cell lines, namely, SWISS 3T3, NIL 8, and RAT 1, and also with the epithelial Y-1 adrenocortical cell line. Treatment with PMA for 0.5 or 2 h activates protein kinase C (PKC) in Balb-3T3-A31 cells, but is not sufficient to down-regulate the enzyme because a second 30-min PMA pulse applied between 6 and 6.5 h activates PKC again. On the other hand, a continuous 6.5-h PMA treatment causes PKC down-regulation; therefore, the inhibitory effect of PMA could be mediated by PKC. Growth factor early response proto-oncogenes c-myc, c-fos, and c-jun are induced transiently by both early and late PMA pulses, suggesting that these genes are not involved in the PMA inhibitory effect.
authors.affiliation: Departamento de Bioquímica, Universidade de São Paulo, SP, Brazil.
authors.forename: M
authors.initials: M
authors.lastname: Faria
authors.forename: H A
authors.initials: HA
authors.lastname: Armelin
mesh_terms: D016475:3T3 Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D000818:Animals; D015152:Blotting, Northern; D002453:Cell Cycle / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D016193:G1 Phase / Q000187:drug effects; D016762:Genes, fos / Q000187:drug effects; D016758:Genes, jun / Q000187:drug effects; D016259:Genes, myc / Q000187:drug effects; D008322:Mammals; D051379:Mice; D008807:Mice, Inbred BALB C; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D016196:S Phase / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D012333:RNA, Messenger; D004247:DNA; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate