Expression of c-fos in quiescent Swiss 3T3 cells exposed to aqueous cigarette smoke fractions.
The exposure of quiescent Swiss 3T3 cells to mainstream cigarette smoke (CS) trapped in PBS solution (smoke-bubbled PBS) resulted in the dose-dependent expression of c-fos mRNA and protein. Kinetic investigations revealed that in contrast to mitogens, which strongly but transiently induce the c-fos promoter within minutes, c-fos transcripts in cells exposed to 0.03 puffs (approximately 1 cm3) of CS/ml of medium accumulated slowly but were still seen after 8 h; the maximum expression rates were between 2 and 6 h of exposure. This specific expression pattern appears to be the result of altered posttranscriptional as well as transcriptional regulation, since a strikingly increased stability of the c-fos message (t1/2, > or = 2 h versus < 20 min in serum-stimulated cells) in smoke-treated cells was observed in addition to slight transcriptional activation of the c-fos promoter. CS-dependent DNA damage can be excluded as the only source for this altered expression pattern, since inhibition of DNA strand break formation by either catalase or o-phenanthroline had no detectable effect on the CS-induced c-fos expression. The results described here, and other CS-dependent cellular and biochemical effects, are similar to those induced in vitro by okadaic acid, a specific inhibitor of cell growth-regulatory protein phosphatases 1/2A (PP-1/2A). Hence, the effects of smoke treatment on these key enzymes were compared to those of okadaic acid based on the ability of cell-free extracts to release radiolabeled phosphate from glycogen phosphorylase a, a substrate of PP-1/2A. Results from these experiments indicate that both treatments inhibited PP-1/2A in a concentration- and analogous time-dependent manner. The data presented suggest that PP-1/2A may, at least in vitro, be targeted by water-soluble active compounds present in cigarette smoke.
Müller
T
T
INBIFO Institut für Biologische Forschung, Köln, Germany.
D016475:3T3 Cells / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015152:Blotting, Northern; D004249:DNA Damage; D004988:Ethers, Cyclic / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D016762:Genes, fos / Q000187:drug effects*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010947:Plants, Toxic; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D012906:Smoke / Q000009:adverse effects*; D012996:Solutions; D014026:Nicotiana; D014158:Transcription, Genetic / Q000187:drug effects
D004988:Ethers, Cyclic; D007527:Isoenzymes; D012333:RNA, Messenger; D012906:Smoke; D012996:Solutions; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases