[Na]i -induced c-Fos expression is not mediated by activation of the 5' -promoter containing known transcriptional elements.
In vascular smooth muscle cells and several other cell types, inhibition of Na(+)/K(+)-ATPase leads to the expression of early response genes, including c-Fos. We designed this study to examine whether or not a putative Na(+) (i)/K(+) (i)-sensitive element is located within the c-Fos 5'-UTR from - 650 to + 103 containing all known response elements activated by 'classic' stimuli, such as growth factors and Ca(2+) (i)-raising compounds. In HeLa cells, the highest increment of c-Fos mRNA content was noted after 6 h of Na(+)/K(+)-ATPase inhibition with ouabain that was abolished by actinomycin D, an inhibitor of RNA synthesis. c-Fos protein accumulation in ouabain-treated cells correlated with a gain of Na(+) (i) and loss of K(+) (i). Augmented c-Fos expression was also observed under inhibition of Na(+)/K(+)-ATPase in K(+)-free medium and in the presence of the Na(+) ionophore monensin. The effect of ouabain on c-Fos expression was sharply attenuated under dissipation of the transmembrane Na(+) gradient, but was preserved in the presence of Ca(2+) chelators and the extracellular regulated kinase inhibitor PD98059, thus indicating an Na(+) (i)-mediated, Ca(2+) (i)- and extracellular regulated kinase-independent mechanism of gene expression. In contrast to massive c-Fos expression, we failed to detect any effect of ouabain on accumulation of luciferase driven by the c-Fos 5'-UTR. Negative results were also obtained in ouabain-treated vascular smooth muscle cells and C11 Madin-Darby canine kidney cells possessing augmented c-Fos expression. Our results reveal that Na(+) (i)-induced c-Fos expression is not mediated by the 5'-UTR containing transcriptional elements activated by growth factors and other 'classic stimuli'.
Haloui
Mounsif
M
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Taurin
Sebastien
S
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Akimova
Olga A
OA
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Guo
Deng-Fu
DF
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Tremblay
Johanne
J
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Dulin
Nickolai O
NO
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Hamet
Pavel
P
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
Orlov
Sergei N
SN
 Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM) - Technopôle ANGUS, Montreal, PQ, Canada Department of Medicine, University of Chicago, Chicago, IL, USA.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics* / Q000378:metabolism*; D012313:RNA / Q000096:biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D012680:Sensitivity and Specificity; D027602:Serum Response Element; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics*
D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D010042:Ouabain; D012313:RNA; D012964:Sodium; D048049:Extracellular Signal-Regulated MAP Kinases; D002118:Calcium