Regulation of tristetraprolin expression by interleukin-1 beta and dexamethasone in human pulmonary epithelial cells: roles for nuclear factor-kappa B and p38 mitogen-activated protein kinase.
The mRNA-destabilizing protein tristetraprolin (TTP) negatively regulates adenine- and uridine-rich element (ARE)-containing mRNAs. In A549 pulmonary cells, TTP mRNA and both a approximately 40- and a approximately 45-kDa phosphorylated version of TTP protein were rapidly induced in response to interleukin (IL)-1beta. Analysis with IkappaBalphaDeltaN, a dominant version of inhibitor of kappaBalpha (IkappaBalpha), as well as dominant-negative and small-molecule IkappaB kinase (IKK) inhibitors demonstrated that IL-1beta-induced TTP is nuclear factor-kappaB (NF-kappaB)-dependent. Likewise, TTP expression and formation of the approximately 45-kDa phosphorylated form of TTP are blocked by the p38 mitogen-activated protein kinase (MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580). By contrast, and despite a 3- to 4-fold induction of TTP mRNA, the anti-inflammatory glucocorticoid dexamethasone only modestly induced expression of the approximately 40-kDa form of TTP. In the context of IL-1beta, dexamethasone exerted a marginal repressive effect on TTP mRNA expression and more considerably reduced TTP protein. Given a requirement for p38 MAPK in the induction of TTP by IL-1beta, this repressive effect may be explained by repression of the p38 MAPK pathway by dexamethasone. Knockdown of TTP protein by siRNA elevated IL-1beta-induced expression of granulocyte macrophage-colony-stimulating factor (GM-CSF) and IL-8, demonstrating a role for TTP in feedback control. Likewise, knockdown of TTP increased GM-CSF expression in the presence of IL-1beta plus dexamethasone, suggesting that feedback control by TTP also occurs in the context of IL-1beta plus dexamethasone. Taken together, our data demonstrate that NF-kappaB and p38 MAPK are critical to the induction of TTP by IL-1beta and that TTP induction provides feedback control of the ARE-containing genes GM-CSF and IL-8.
Airways Inflammation Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
Elizabeth M
EM
King
Manminder
M
Kaur
Wei
W
Gong
Christopher F
CF
Rider
Neil S
NS
Holden
Robert
R
Newton
D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D002417:Cattle; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D053583:Interleukin-1beta / Q000502:physiology*; D008175:Lung Neoplasms / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D016328:NF-kappa B / Q000502:physiology*; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism*; D051816:Tristetraprolin / Q000096:biosynthesis* / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology*
D053583:Interleukin-1beta; D016328:NF-kappa B; D051816:Tristetraprolin; C497552:ZFP36 protein, human; D003907:Dexamethasone; D048051:p38 Mitogen-Activated Protein Kinases