Critical Role of cAMP Response Element Binding Protein Expression in Hypoxia-elicited Induction of Epithelial Tumor Necrosis Factor-α

Abstract

Tissue hypoxia is intimately associated with a number of chronic inflammatory conditions of the intestine. In this study, we investigated the impact of hypoxia on the expression of a panel of inflammatory mediators by intestinal epithelia. Initial experiments revealed that epithelial (T84 cell) exposure to ambient hypoxia evoked a time-dependent induction of the proinflammatory markers tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and major histocompatibility complex (MHC) class II (37 ± 6.1-, 7 ± 0.8-, and 9 ± 0.9-fold increase over normoxia, respectively, each p < 0.01). Since the gene regulatory elements for each of these molecules contains an NF-κB binding domain, we investigated the influence of hypoxia on NF-κB activation. Cellular hypoxia induced a time-dependent increase in nuclear p65, suggesting a dominant role for NF-κB in hypoxia-elicited induction of proinflammatory gene products. Further work, however, revealed that hypoxia does not influence epithelial intercellular adhesion molecule 1 (ICAM-1) or MHC class I, the promoters of which also contain NF-κB binding domains, suggesting differential responses to hypoxia. Importantly, the genes for TNF-α, IL-8, and MHC class II, but not ICAM-1 or MHC class I, contain cyclic AMP response element (CRE) consensus motifs. Thus, we examined the role of cAMP in the hypoxia-elicited phenotype. Hypoxia diminished CRE binding protein (CREB) expression. In parallel, T84 cell cAMP was diminished by hypoxia (83 ± 13.2% decrease, p < 0.001), and pharmacologic inhibition of protein kinase A induced TNF-α and protein release (9 ± 3.9-fold increase). Addback of cAMP resulted in reversal of hypoxia-elicited TNF-α release (86 ± 3.2% inhibition with 3 mm 8-bromo-cAMP). Furthermore, overexpression of CREB but not mutated CREB by retroviral-mediated gene transfer reversed hypoxia-elicited induction of TNF-α defining a causal relationship between hypoxia-elicited CREB reduction and TNF-α induction. Such data indicate a prominent role for CREB in the hypoxia-elicited epithelial phenotype and implicate intracellular cAMP as an important second messenger in differential induction of proinflammatory mediators. Tissue hypoxia is intimately associated with a number of chronic inflammatory conditions of the intestine. In this study, we investigated the impact of hypoxia on the expression of a panel of inflammatory mediators by intestinal epithelia. Initial experiments revealed that epithelial (T84 cell) exposure to ambient hypoxia evoked a time-dependent induction of the proinflammatory markers tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and major histocompatibility complex (MHC) class II (37 ± 6.1-, 7 ± 0.8-, and 9 ± 0.9-fold increase over normoxia, respectively, each p < 0.01). Since the gene regulatory elements for each of these molecules contains an NF-κB binding domain, we investigated the influence of hypoxia on NF-κB activation. Cellular hypoxia induced a time-dependent increase in nuclear p65, suggesting a dominant role for NF-κB in hypoxia-elicited induction of proinflammatory gene products. Further work, however, revealed that hypoxia does not influence epithelial intercellular adhesion molecule 1 (ICAM-1) or MHC class I, the promoters of which also contain NF-κB binding domains, suggesting differential responses to hypoxia. Importantly, the genes for TNF-α, IL-8, and MHC class II, but not ICAM-1 or MHC class I, contain cyclic AMP response element (CRE) consensus motifs. Thus, we examined the role of cAMP in the hypoxia-elicited phenotype. Hypoxia diminished CRE binding protein (CREB) expression. In parallel, T84 cell cAMP was diminished by hypoxia (83 ± 13.2% decrease, p < 0.001), and pharmacologic inhibition of protein kinase A induced TNF-α and protein release (9 ± 3.9-fold increase). Addback of cAMP resulted in reversal of hypoxia-elicited TNF-α release (86 ± 3.2% inhibition with 3 mm 8-bromo-cAMP). Furthermore, overexpression of CREB but not mutated CREB by retroviral-mediated gene transfer reversed hypoxia-elicited induction of TNF-α defining a causal relationship between hypoxia-elicited CREB reduction and TNF-α induction. Such data indicate a prominent role for CREB in the hypoxia-elicited epithelial phenotype and implicate intracellular cAMP as an important second messenger in differential induction of proinflammatory mediators. interferon-γ tumor necrosis factor-α Hanks' balanced salt solution cyclic AMP response element cyclic AMP response element binding protein electrophoretic mobility shift assay major histocompatibility complex intercellular adhesion molecule 1 protein kinase A interleukin enzyme-linked immunosorbent assays polymerase chain reaction phorbol 12-myristate 13-acetate polyacrylamide gel electrophoresis protein kinase A inhibitor The human intestine is lined with a single layer of protective epithelial cells that possess properties such as barrier and ion (and subsequent fluid) transport functions (1Powell D. Am. J. Physiol. 1981; 241: G275-G288PubMed Google Scholar, 2Powell D.W. Johnson L.R. Physiology of the Gastrointestinal Tract. Raven Press, Ltd., New York.1987: 1267-1291Google Scholar, 3Madara J.L. Am. J. Pathol. 1990; 137: 1273-1278PubMed Google Scholar). Such epithelial functions are tightly controlled by an array of immune-derived factors within the intestinal microenvironment, and regulation of such conditions can vary greatly during active episodes of inflammation. A number of previous studies have revealed specificity with regard to regulation of epithelial end point function, including tight junction permeability, electrogenic chloride secretion, and neutrophil transmigration (4Colgan S.P. Resnick M.B. Parkos C.A. Delp-Archer C. Bacarra A.E. Weller P.E. Madara J.L. J. Immunol. 1994; 153: 2122-2129PubMed Google Scholar, 5Colgan S.P. Parkos C.A. Matthews J.B. D'Andrea L. Awtrey C.S. Lichtman A. Delp C. Madara J.L. Am. J. Physiol. 1994; 267: C402-C410Crossref PubMed Google Scholar, 6Colgan S.P. Parkos C.A. Delp C. Arnaout M.A. Madara J.L. J. Cell Biol. 1993; 120: 785-795Crossref PubMed Scopus (146) Google Scholar, 7Sanders S.E. Madara J.L. McGuirk D.K. Gelman D.S. Colgan S.P. Epithelial Cell Biol. 1995; 4: 25-34PubMed Google Scholar, 8Zünd G. Madara J.L. Dzus A.L. Awtrey C.S. Colgan S.P. J. Biol. Chem. 1996; 271: 7460-7464Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). This work utilizing intestinal epithelial cells in vitro has revealed that ligation of receptors for IFN-γ,1 interleukin-4, or interleukin-13 results in increased macromolecular permeability (4Colgan S.P. Resnick M.B. Parkos C.A. Delp-Archer C. Bacarra A.E. Weller P.E. Madara J.L. J. Immunol. 1994; 153: 2122-2129PubMed Google Scholar,7Sanders S.E. Madara J.L. McGuirk D.K. Gelman D.S. Colgan S.P. Epithelial Cell Biol. 1995; 4: 25-34PubMed Google Scholar, 8Zünd G. Madara J.L. Dzus A.L. Awtrey C.S. Colgan S.P. J. Biol. Chem. 1996; 271: 7460-7464Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar, 9Madara J.L. Stafford J. J. Clin. Invest. 1989; 83: 724-727Crossref PubMed Scopus (652) Google Scholar). On the whole, other cytokine responses (i.e.regulation of Cl− secretion, fluid transport, MHC, and MHC-like molecule expression, polymorphonuclear leukocyte transmigration, etc.) appear to reveal a unique “functional fingerprint” with respect to individual cytokines. Others have demonstrated the presence of functional receptors for IL-2 (10Ciacci C. Mahida Y.R. Dignass A. Koizumi M. Podolsky D.K. J. Clin. Invest. 1993; 92: 527-532Crossref PubMed Scopus (96) Google Scholar, 11Reinecker H.C. Podolsky D.K. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 8353-8357Crossref PubMed Scopus (145) Google Scholar), transforming growth factor-β (12Kurokawa M. Lynch K. Podolsky D.K. Biochem. Biophys. Res. Commun. 1987; 142: 775-782Crossref PubMed Scopus (262) Google Scholar), and hepatocyte growth factor (13Nusrat A. Parkos C.A. Bacarra A.E. Godowski P.J. Delp-Archer C. Rosen E.M. Madara J.L. J. Clin. Invest. 1994; 93: 2056-2065Crossref PubMed Scopus (200) Google Scholar) on intestinal epithelial cells. Based on this previous work, we have proposed that epithelial cells have the unique ability to “phenotype-switch,” whereby epithelia lose classic qualities of epithelia (i.e. barrier function, ion transport properties, etc.) and assume features resembling immune-type cells (i.e.surface expression of MHC class I and II, antigen presentation properties, regulated polymorphonuclear leukocyte trafficking, etc.) (5Colgan S.P. Parkos C.A. Matthews J.B. D'Andrea L. Awtrey C.S. Lichtman A. Delp C. Madara J.L. Am. J. Physiol. 1994; 267: C402-C410Crossref PubMed Google Scholar). Tissue ischemia/hypoxia often occurs concomitantly with other inflammatory processes, and thus, appropriate models to study mechanisms of inflammation should also account for conditions of cellular hypoxia. Surprisingly little is known about the mechanisms of hypoxic signal transduction. Several reports indicate that hypoxia down-regulates activity of cellular cAMP-generating machinery and that such diminished cAMP signaling can influence gene expression and end point cellular functions (14Taylor C.T. Lisco S.J. Awtrey C.S. Colgan S.P. J. Pharmacol. Exp. Ther. 1998; 284: 568-575PubMed Google Scholar, 15Ogawa S. Koga S. Kuwabara K. Brett J. Morrow B. Morris S.A. Bilezikian J.P. Silverstein S.C. Stern D. Am. J. Physiol. 1992; 262: C546-C554Crossref PubMed Google Scholar, 16Ogawa S. Shreeniwas R. Butura C. Brett J. Stern D. Adv. Exp. Med. Biol. 1990; 281: 303-312Crossref PubMed Google Scholar, 17Stevens T. Rodman D.M. Endothelium. 1995; 3: 1-11Crossref Scopus (12) Google Scholar, 18Zünd G. Nelson D.P. Neufeld E.J. Dzus A.L. Bischoff J. Mayer J.E. Colgan S.P. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 7075-7080Crossref PubMed Scopus (51) Google Scholar). At the transcriptional level, a primary target for cAMP-mediated signaling is cAMP response element binding proteins, a family of 43-kDa leucine zipper transcription factors that share certain structural motifs, bind DNA as dimers, and regulate transcription of target genes (19Meyer T.E. Habener J.F. Endocr. Rev. 1993; 14: 269-290PubMed Google Scholar). At present, it is not known whether hypoxia-mediated gene expression is directly related to CREB activity or CREB expression. Recently, we have studied the role of epithelia in intestinal ischemia using a model epithelium, T84 cells. In response to conditions of ambient hypoxia, epithelia express a more classical immune-like phenotype, including release of proinflammatory cytokines and chemokines (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar, 21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar), regulated neutrophil transmigration (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar), diminished ion transport (14Taylor C.T. Lisco S.J. Awtrey C.S. Colgan S.P. J. Pharmacol. Exp. Ther. 1998; 284: 568-575PubMed Google Scholar), and induction of major histocompatibility complex class II expression (21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar). The basis for these changes in epithelial function are not well understood, and thus, in the studies defined here, we hypothesized a basic mechanism of hypoxia-induced phenotype switch. These studies revealed that hypoxia specifically induces a panel of epithelial proteins that bear cyclic AMP response elements (CRE) within the important for regulation of gene expression. Further was defined with gene TNF-α, and revealed a role for CRE and proteins (CREB) in induction of Such results a primary role for CRE in the hypoxia-elicited epithelial phenotype and implicate CREB as a mechanism of differential induction of proinflammatory mediators by cellular hypoxia. The T84 cell is a human cell K. J. Am. J. Physiol. PubMed Google Scholar) on of epithelial cells. T84 cells are well with regard to electrogenic Cl− and ion transport and as models of epithelial cells K. J. Am. J. Physiol. PubMed Google Scholar, K. Madara J.L. 1990; PubMed Scopus Google Scholar). T84 cells as in a of and with mm and by and mm in and Epithelial exposure to hypoxia was as (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar). T84 cell growth with hypoxic and cells in a within the hypoxia and hypoxic on previous work (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar), with the of and cells to the conditions of and within a Epithelial expression of proteins was using a as (5Colgan S.P. Parkos C.A. Matthews J.B. D'Andrea L. Awtrey C.S. Lichtman A. Delp C. Madara J.L. Am. J. Physiol. 1994; 267: C402-C410Crossref PubMed Google Scholar). Epithelial cells and for binding exposure to or hypoxia for the with with for J.B. 1993; PubMed Google Scholar) the as cell class I G. G. C. A. 14: Full Text PDF PubMed Scopus Google Scholar) the as or class II the as cell to protein expression by with a was was in by of 1 mm and on a of and are as the ± S.E. as a for induction of these as (5Colgan S.P. Parkos C.A. Matthews J.B. D'Andrea L. Awtrey C.S. Lichtman A. Delp C. Madara J.L. Am. J. Physiol. 1994; 267: C402-C410Crossref PubMed Google Scholar). and by as (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar, 21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar). as a for induction of (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar) and TNF-α (21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar). of epithelial cell of CREB and as D. M.A. T. T. Biol. 1994; 14: PubMed Scopus Google Scholar). of nuclear of T84 cells on in and by in of A mm mm mm mm mm mm 1 of and for The by by in A and in of mm mm mm mm 1 of and on a for and by for protein as of T84 cell by to and in mm and for of or for 3 and was as G. S. Dzus A.L. Colgan S.P. Am. J. Physiol. PubMed Google Scholar). by using of cells to conditions as The The and as in the to the transcription in the TNF-α for to with nuclear for and by electrophoresis on a polyacrylamide to with and by of and with for 1 to T84 on to and cAMP was as (14Taylor C.T. Lisco S.J. Awtrey C.S. Colgan S.P. J. Pharmacol. Exp. Ther. 1998; 284: 568-575PubMed Google Scholar). cells to cAMP was with the inhibitor and by for and to in assay and cAMP was using to to using a and as cAMP of Epithelial cells on to protein kinase A inhibitor or for to of cells for CREB or for TNF-α assay as was to the and hypoxic or T84 cells using of each was with I and protein a and in The reaction was to 1 of was to the reaction of of of of of each of in inhibitor of and of in a of The was using for for and for by a for The DNA was in the The reaction for human TNF-α 1 of the and the of of of of and of in a of The reaction a and a by of for and for with a for The on a gel A to TNF-α was In to that an of was in each of reaction was as with 1 of human and in a with was in gene transfer of T84 cells with CREB and CREB to mutated the was using a P.E. S. J. J. Clin. Invest. PubMed Scopus Google Scholar). CREB or CREB was the of the and the for the dominant was of the epithelial cells to and of with to the cells. of was and the cells for and data by of and by with p < are as ± S.E. for Recently, we demonstrated that hypoxia epithelial responses to the cytokine and such responses to induction of epithelial TNF-α release the (21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar). These however, not reveal mechanisms that induction of TNF-α, and we to such the an a panel of epithelial proinflammatory markers examined to whether such signaling by hypoxia was for TNF-α or is to other in responses to hypoxia epithelial exposure to hypoxia induced TNF-α release ± p < release ± < and induced expression of MHC class II ± 0.9-fold p < 0.01). Hypoxia however, influence epithelial ICAM-1 expression not with or MHC class I not with a of specificity for signaling by hypoxia. In an to such we by induction of these The regulatory of each of these genes contain a binding for a transcription factor important in induction of a number of proinflammatory genes T. M.A. D. T. J. 1995; PubMed Scopus Google Scholar). in of nuclear epithelia to hypoxia for revealed of the a of NF-κB G. S. Dzus A.L. Colgan S.P. Am. J. Physiol. PubMed Google Scholar). of hypoxia as as revealed a of the of Such responses to hypoxia by of of and to on of epithelial gene induction by hypoxia, specifically using TNF-α to these TNF-α gene induction and protein release can regulated in a number of including transcriptional and we examined whether hypoxia induces transcription of the epithelial TNF-α in revealed a time-dependent induction of Such induction was and that of for These data reveal that hypoxia transcriptional In to a binding for the transcription factor the TNF-α, IL-8, and MHC class II genes bear a cAMP consensus binding a cAMP response element (CRE) D. M.A. T. T. Biol. 1994; 14: PubMed Scopus Google Scholar, G. S. Dzus A.L. Colgan S.P. Am. J. Physiol. PubMed Google Scholar). Importantly, the regulatory of molecules not induced by hypoxia class I and not contain a These CRE DNA consensus to regulate transcription of genes protein kinase A and In in intracellular cAMP are associated with TNF-α release C.S. J. Immunol. 1989; 142: Google Scholar). of nuclear proteins, cAMP response element binding proteins or regulate the of genes cAMP can increase or on the gene M. Rev. Biochem. PubMed Scopus Google Scholar). Since a number of consensus as functional we examined the of the CRE within the TNF-α we an using the TNF-α CRE G. J. Biol. 1994; PubMed Scopus Google Scholar). in proteins nuclear of T84 cells bind to the CRE of the TNF-α Furthermore, of to the of CREB that the protein is This reaction that the TNF-α gene a CRE which CREB of epithelial whether hypoxia cellular CREB in revealed that conditions which epithelial TNF-α, IL-8, and MHC class II resulted in of CREB and by and hypoxia, respectively, with of the the of CREB expression by hypoxia, the point of as in of nuclear also by hypoxia and by and hypoxia, respectively, with and of reversed this the role of CREB in induction of epithelial TNF-α, we the impact of intracellular have demonstrated that conditions that TNF-α (i.e. cellular in in intracellular cAMP (14Taylor C.T. Lisco S.J. Awtrey C.S. Colgan S.P. J. Pharmacol. Exp. Ther. 1998; 284: 568-575PubMed Google Scholar). Thus, we TNF-α induction is regulated by of intracellular cAMP the should TNF-α The results in that cAMP increased epithelial TNF-α Furthermore, the of diminished TNF-α release in a of p < of cAMP to cells not of and not influence NF-κB by or by cellular hypoxia by of p65, data not of to hypoxic cells reversed the in CREB with of hypoxia J.B. 1993; PubMed Google Scholar, and not CREB not suggesting that the hypoxic (i.e. within the signaling for induction of such data indicate the that the is to induction of epithelial directly the role of in induction of epithelial TNF-α a inhibitor was to cAMP signaling in cells. TNF-α release and CREB expression as for this in induced a increase in epithelial TNF-α release ± 3.9-fold increase over to a epithelial exposure to hypoxia 1 also induced in cellular CREB expression 7 also induced TNF-α release ± increase over a for these we examined the influence of on epithelial ICAM-1 expression. to increase ± over p not with or ± over p not with expression of Such data indicate a role for in induction of genes and that hypoxia-elicited in intracellular cAMP induction of epithelial The results a prominent role for of CREB and expression in induction of TNF-α by hypoxia. Thus, we that overexpression of CREB in hypoxia-elicited induction of T84 cells CREB or CREB by gene transfer by with epithelia ± of of cells CREB ± < with but not CREB ± p not with to hypoxia. These data for CREB in hypoxia-elicited induction of a role for ischemia and hypoxia in and of chronic and inflammatory this a of the responses to hypoxia is for the of In the studies in this we to in the induction of proinflammatory gene by cellular hypoxia, with an on the role of epithelia in a well defined intestinal epithelial model (T84 was to these primary are of these data indicate that cellular hypoxia results in transcriptional induction of genes that bear a CRE within the for the regulation of gene expression. of protein kinase A cellular hypoxia, results in of CREB expression, and overexpression of CREB in epithelial cells to hypoxia the cells to the hypoxic phenotype. these data reveal that of intracellular cAMP of epithelial hypoxia. Recently, we a of studies factors that permeability These studies revealed a factor the epithelial in a to (20Colgan S.P. Dzus A.L. Parkos C.A. J. Exp. Med. 1996; 184: 1003-1015Crossref PubMed Scopus (78) Google Scholar) and to functional epithelial receptors to and G. Madara J.L. Dzus A.L. Awtrey C.S. Colgan S.P. J. Biol. Chem. 1996; 271: 7460-7464Abstract Full Text Full Text PDF PubMed Scopus (115) Google Scholar). This factor was defined as TNF-α (21Taylor C.T. Dzus A.L. Colgan S.P. Gastroenterology. 1998; 114: 657-668Abstract Full Text Full Text PDF PubMed Scopus (175) Google Scholar). of this work revealed induction of a number of epithelial proinflammatory markers IL-8, MHC class and of specificity in this regard (i.e. of induced MHC class I or of the of each these molecules revealed a binding for a transcription factor important in a number of T. M.A. D. T. J. 1995; PubMed Scopus Google Scholar). Hypoxia induced NF-κB however, it was that factors ICAM-1 and MHC class I contain NF-κB but are not induced by hypoxia. have not the mechanism of epithelial NF-κB by cellular hypoxia. we demonstrated a role for in and subsequent NF-κB in cells G. S. Dzus A.L. Colgan S.P. Am. J. Physiol. PubMed Google Scholar). mechanisms a role are not known the of hypoxia-elicited gene TNF-α, and MHC class revealed the presence of CRE binding motifs, and thus, we the role of CRE and intracellular cAMP in induction of A number of previous studies have that proinflammatory gene are to in intracellular and in TNF-α gene expression, is specifically by that cAMP and C.S. J. Immunol. 1989; 142: Google Scholar, J.F. S.A. Immunol. 1989; 120: PubMed Scopus Google Scholar, 1989; PubMed Google Scholar, 1995; Google Scholar, M. E.J. M. D. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). a gene Johnson T. J. Biol. Chem. 1994; Google Scholar), is related to intracellular cAMP G. Nelson D.P. Neufeld E.J. Dzus A.L. Bischoff J. Mayer J.E. Colgan S.P. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 7075-7080Crossref PubMed Scopus (51) Google Scholar). with previous we that responses to cellular hypoxia are diminished intracellular cAMP and a in protein kinase A activity (14Taylor C.T. Lisco S.J. Awtrey C.S. Colgan S.P. J. Pharmacol. Exp. Ther. 1998; 284: 568-575PubMed Google Scholar, 15Ogawa S. Koga S. Kuwabara K. Brett J. Morrow B. Morris S.A. Bilezikian J.P. Silverstein S.C. Stern D. Am. J. Physiol. 1992; 262: C546-C554Crossref PubMed Google Scholar). the mechanisms cAMP and activity to the of hypoxia with induction of genes as a basic mechanism in proinflammatory gene expression these the role of CRE in induction of epithelial TNF-α, we defined the impact of intracellular Addback of intracellular cAMP the diminished hypoxia-induced TNF-α and of activity and induced TNF-α, to a hypoxia. Importantly, epithelial exposure to not influence NF-κB not a it is important to that CRE can also regulated or directly by in intracellular as the with exposure M. Rev. Biochem. PubMed Scopus Google Scholar). such data indicate the that the is to induction of epithelial the causal relationship between hypoxia-elicited in CREB expression and TNF-α we T84 cells. of such cells to hypoxia resulted in release of TNF-α, a relationship between hypoxia-elicited CREB and TNF-α These studies also reveal a for in the hypoxia CREB and diminished by overexpression of CREB hypoxia-elicited TNF-α mutated CREB a functional the to responses to hypoxia. results indicate that chronic cellular results in diminished nuclear of it is known that gene induction is tightly a of CREB and transcriptional M. A. R. J. R. Biol. 1993; PubMed Scopus Google Scholar), little is known about of diminished CREB expression by hypoxia a in which diminished activity expression of for such a is epithelial by hypoxia, and CREB to These results a primary role for regulation of CREB expression during hypoxia. little is known about regulated CREB expression, a role for differential CREB in gene CREB protein expression can induced or a number of including intracellular cAMP C.A. 1993; Full Text PDF PubMed Scopus Google Scholar, Habener J.F. E.J. J. 1996; PubMed Scopus Google Scholar, L. Habener J.F. 1995; PubMed Google Scholar, Biochem. Biophys. Res. Commun. 1996; PubMed Scopus Google Scholar). and cell specificity with regard to this of cell cAMP CREB expression L. Habener J.F. 1995; PubMed Google Scholar, T.E. G. J. Habener J.F. 1993; PubMed Scopus Google Scholar), and conditions in in D.S. E.J. Proc. Acad. Sci. U. S. A. 1994; PubMed Scopus Google Scholar). in cells it was demonstrated that hypoxia of CREB an D. J. Biol. Chem. Full Text Full Text PDF Scopus Google Scholar). data with epithelia that diminished activity hypoxia results in CREB expression and subsequent of TNF-α a second of for this in a as hypoxia, inhibition of in cells resulted in a of and of hypoxic conditions the of Thus, the inhibition of to the hypoxia-elicited phenotype by overexpression of CREB for a causal relationship between hypoxia-elicited in CREB and the induction of TNF-α release by intestinal epithelial cells. In these results indicate that hypoxia-elicited of CREB expression diminished activity as a basic mechanism of genes in epithelia. Such have in the of a number of and a target for the of The for the of the CREB cells a of