K-Ras-mediated increase in cyclooxygenase 2 mRNA stability involves activation of the protein kinase B1.
Cyclooxygenase (COX) 2 expression is regulated via the Ras signaling pathway, and induction of mutated Ras rapidly increases COX-2 levels in intestinal epithelial cells. Protein kinase B (Akt/PKB) is an important effector of Ras signaling and a critical component of Ras-mediated transformation. Here we investigate the role of Akt/PKB in K-Ras-mediated induction of COX-2. Rat intestinal epithelial cells (IEC-6) were transfected with an inducible K-RasVal12 cDNA (IEC-iK-Ras cells). Addition of 5 mM isopropyl-1-thio-beta-D-galactopyranoside induced the expression of K-RasVal12, followed by increased activity of extracellular signal-regulated kinase and Akt/PKB. COX-2 levels were dramatically increased after induction of K-RasVal12. Inhibition of MAPK/ERK kinase activity by PD 98059 completely blocked the K-Ras-mediated induction of COX-2, whereas inhibition of PI3K/Akt/PKB activity with LY 294002 or by expressing a dominant negative Akt (Akt-K179M) partially blocked the induction of COX-2 by K-Ras. Transient transfection of cells with phosphatidylinositol 3-kinase and Akt expression vectors revealed that PI3/Akt/PKB activity predominantly regulates the stability of COX-2 mRNA. Thus, Akt/PKB activity is involved in K-Ras-induced expression of COX-2 and stabilization of COX-2 mRNA largely depends on the activation of Akt/PKB.
Sheng
H
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Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232, USA.
Shao
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Dubois
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D000818:Animals; D002460:Cell Line; D051546:Cyclooxygenase 2; D004789:Enzyme Activation; D004790:Enzyme Induction; D004847:Epithelial Cells / Q000201:enzymology / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D011905:Genes, ras; D007413:Intestinal Mucosa / Q000166:cytology / Q000201:enzymology / Q000502:physiology; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D014162:Transfection; D018631:ras Proteins / Q000235:genetics / Q000502:physiology*
D007527:Isoenzymes; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins