Long-acting beta2-adrenoceptor agonists synergistically enhance glucocorticoid-dependent transcription in human airway epithelial and smooth muscle cells

Addition of an inhaled long-acting beta(2)-adrenoceptor agonist (LABA) to an inhaled corticosteroid (ICS) is more effective at improving asthma control and reducing exacerbations than increasing the dose of ICS. Given that LABA monotherapy is not anti-inflammatory, pathways may exist by which LABAs enhance ICS actions. In the current study, the glucocorticoid dexamethasone had no effect on beta(2)-adrenoceptor agonist-induced cAMP-response element-dependent transcription in the human bronchial epithelial cell line BEAS-2B. In contrast, simple glucocorticoid response element (GRE)-dependent transcription induced by dexamethasone, budesonide, and fluticasone was synergistically enhanced by beta(2)-adrenoceptor agonists, including salmeterol and formoterol, to a level that could not be achieved by glucocorticoid alone. This enhancement was mimicked by other cAMP-elevating agents, and a cAMP mimetic, and was blocked by an inhibitor of cAMP-dependent protein kinase (PKA). Thus, beta(2)-adrenoceptor agonists synergistically enhance simple GRE-dependent transcription via the classical cAMP-PKA pathway. Consistent with the clinical situation, the addition of a beta(2)-adrenoceptor agonist to a glucocorticoid is steroid-sparing in that maximal GRE-dependent responses, evoked by glucocorticoid, are achieved at approximately 10-fold lower concentrations in the presence of beta(2)-adrenoceptor agonist. Finally, analysis of dexamethasone-inducible genes, including glucocorticoid-inducible leucine zipper (GILZ), aminopeptidase N, FKBP51, PAI-1, tristetraprolin, DNB5, p57KIP2, metallothionein 1X, and MKP-1, revealed enhanced inducibility of some genes by glucocorticoid/beta(2)-adrenoceptor agonist combinations in a manner that was consistent with the GRE-reporter. Because such effects also occur in primary human airway smooth muscle cells, we propose that enhancement of glucocorticoid-inducible gene expression may contribute to the superior efficacy of LABA/ICS combination therapies, over ICS alone, in asthma treatment.

Analysis of the dissociated steroid RU24858 does not exclude a role for inducible genes in the anti-inflammatory actions of glucocorticoids

Although repression of inflammatory gene expression makes glucocorticoids powerful anti-inflammatory agents, side effects limit usage and drive the search for improved glucocorticoid receptor (GR) ligands. In A549 pulmonary cells, dexamethasone and the prototypical dissociated ligand RU24858 (Mol Endocrinol 11:1245-1255, 1997) repress interleukin (IL)-1beta-induced expression of cyclooxygenase (COX)-2 and IL-8. Although RU24858 is a weaker GR ligand, both glucocorticoids showed similar efficacies on transrepression of nuclear factor kappaB (NF-kappaB)-dependent transcription, whereas RU24858 yielded less than 12% of the response to dexamethasone on a classic glucocorticoid response element (GRE) reporter (transactivation). Modest NF-kappaB-dependent transrepression ( approximately 40%), along with analysis of IL-8 transcription rate and the accumulation of unspliced nuclear RNA, indicates that transrepression does not fully account for the repression of genes such as IL-8. This was confirmed by the finding that mRNA degradation is increased by both dexamethasone and RU24858. Analysis of IL-1beta-induced steady-state mRNA levels for IL-8 and COX-2 show that dexamethasone- and RU24858-dependent repression of these genes is attenuated by inhibitors of transcription and protein synthesis. Because similar effects were observed with respect to COX-2 and IL-8 protein expression, we conclude that glucocorticoid-dependent gene expression is necessary for repression by both glucocorticoids. Despite RU24858 being defective at classic GRE-dependent transactivation, both dexamethasone and RU24858 induced the expression of potentially anti-inflammatory genes and metabolic genes, suggesting the importance of nontraditional glucocorticoid-dependent gene expression. Thus, classic transactivation- and transrepressionbased screens for anti-inflammatory "dissociated" GR ligands may be flawed because they may not reflect the effects on real glucocorticoid-inducible genes.

Critical role for peptide YY in protein-mediated satiation and body-weight regulation

Dietary protein enhances satiety and promotes weight loss, but the mechanisms by which appetite is affected remain unclear. We investigated the role of gut hormones, key regulators of ingestive behavior, in mediating the satiating effects of different macronutrients. In normal-weight and obese human subjects, high-protein intake induced the greatest release of the anorectic hormone peptide YY (PYY) and the most pronounced satiety. Long-term augmentation of dietary protein in mice increased plasma PYY levels, decreased food intake, and reduced adiposity. To directly determine the role of PYY in mediating the satiating effects of protein, we generated Pyy null mice, which were selectively resistant to the satiating and weight-reducing effects of protein and developed marked obesity that was reversed by exogenous PYY treatment. Our findings suggest that modulating the release of endogenous satiety factors, such as PYY, through alteration of specific diet constituents could provide a rational therapy for obesity.

Anti-inflammatory and relaxatory effects of prostaglandin E2 in myometrial smooth muscle

The onset of human labour is complex and involves multiple mediators, prostaglandins, cytokines and chemokines. However, whilst prostaglandins are routinely used for labour induction and inhibitors of prostaglandin synthesis are used to prevent pre-term labour, these practices are not invariably successful, and the rationale for their use is equivocal. As COX-2 and prostaglandin E(2) (PGE(2)) production is increased towards term, we have investigated the effect of PGE(2) and other cAMP-elevating agents on events associated with labour induction. Time-dependent increases in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-8 (IL-8) release were observed following treatment of primary human myometrial smooth muscle (HMSM) cells with IL-1beta, via mechanisms that required de novo transcription and translation. Prior treatment with PGE(2) (1 microM) produced 86 and 80% decreases in GM-CSF and IL-8 release, respectively. Similarly, the cAMP analogue, 8-bromo-cAMP (8Br-cAMP) and the phosphodiesterase-4 (PDE(4)) inhibitor, rolipram, also repressed GM-CSF and IL-8 release. In addition, PGE(2), 8Br-cAMP, rolipram and salbutamol all had a dose-dependent inhibitory effect on spontaneous myometrial contractions in vitro. In this study, PGE(2) reduced the release of factors associated with cervical ripening and attenuated force development in myometrial smooth muscle, raising the possibility that in myometrium, PGE(2) may act to down-regulate some of the processes that contribute to the onset of human labour and may be beneficial in helping to maintain pregnancy towards term.

Validation of IKK beta as therapeutic target in airway inflammatory disease by adenoviral-mediated delivery of dominant-negative IKK beta to pulmonary epithelial cells

Asthma is an inflammatory disease of the lungs and the transcription factor NF-kappa B regulates the production of numerous inflammatory mediators that may have a role in the pathogenesis of asthma. Hence, the signalling pathways leading to NF-kappa B activation are considered prime targets for novel anti-inflammatory therapies. The prevention of NF-kappa B activity in mice, through the knockout of IKK beta or p65, causes fatal liver degeneration in utero making it difficult to determine the full implications of inhibiting NF-kappaB activity in tissues physiologically relevant to human diseases. This study used adenovirus delivery of a dominant inhibitor of NF-kappaB (I kappa B alpha delta N) and dominant-negative IKK alpha (IKK alpha(KM)) and IKK beta (IKK beta(KA)) to investigate the role of the individual IKKs in NF-kappa B activation and inflammatory gene transcription by human pulmonary A549 cells. Overexpression of IKK beta(KA) or I kappa B alpha delta N prevented NF-kappa B-dependent transcription and DNA binding. IKK beta(KA) also prevented I kappa B alpha kinase activity. Similarly, IKK beta(KA) and I kappa B alpha delta N overexpression also inhibited IL-1beta- and TNF alpha-dependent increases in ICAM-1, IL-8 and GM-CSF in addition to IL-1beta-mediated increases in cyclooxygenase-2 expression, whereas IKK alpha(KM) overexpression had little effect on these outputs. IKK beta(KA) also reduced cell viability and induced caspase-3 and PARP cleavage regardless of the stimuli, indicating the induction of apoptosis. This effect seemed to be directly related to IKK beta kinase activity since I kappa B alpha delta N only induced PARP cleavage in TNF alpha-treated cells. These results demonstrate that inhibition of IKK beta and NF-kappa B suppresses inflammatory mediator production and reduces A549 cell viability. Thus, novel therapies that target IKK beta could have potent anti-inflammatory effects and may be beneficial in the treatment of certain cancers.

Differential effects of RU486 reveal distinct mechanisms for glucocorticoid repression of prostaglandin E2 release

In A549 pulmonary cells, the dexamethasone- and budesonide-dependent repression of interleukin-1beta-induced prostaglandin E2 release was mimicked by the steroid antagonist, RU486. Conversely, whereas dexamethasone and budesonide were highly effective inhibitors of interleukin-1beta-induced cyclooxygenase (COX)/prostaglandin E synthase (PGES) activity and COX-2 expression, RU486 (<1 microm) was a poor inhibitor, but was able to efficiently antagonize the effects of dexamethasone and budesonide. In addition, both dexamethasone and RU486 repressed [3H]arachidonate release, which is consistent with an effect at the level of phospholipase A2 activity. By contrast, glucocorticoid response element-dependent transcription was unaffected by RU486 but induced by dexamethasone and budesonide, whilst dexamethasone- and budesonide-dependent repression of nuclear factor-kappaB-dependent transcription was maximally 30-40% and RU486 (<1 microm) was without significant effect. Thus, two pharmacologically distinct mechanisms of glucocorticoid-dependent repression of prostaglandin E2 release are revealed. First, glucocorticoid-dependent repression of arachidonic acid is mimicked by RU486 and, second, repression of COX/PGES is antagonized by RU486. Finally, whilst all compounds induced glucocorticoid receptor translocation, no role for glucocorticoid response element-dependent transcription is supported in these inhibitory processes and only a limited role for glucocorticoid-dependent inhibition of nuclear factor-kappaB in the repression of COX-2 is indicated.

Inhibitors of protein kinase C (PKC) prevent activated transcription: role of events downstream of NF-kappaB DNA binding

In pulmonary A549 cells, the protein kinase C (PKC) inhibitor, Ro 31-8220, and the phosphotidylcholine-specific phospholipase C inhibitor, D609, prevent NF-kappaB-dependent transcription, yet NF-kappaB DNA binding is unaffected (Bergmann, M., Hart, L., Lindsay, M., Barnes, P. J., and Newton, R. (1998) J. Biol. Chem. 273, 6607-6610). We now show that this effect also occurs in BEAS-2B bronchial epithelial cells as well as with other PKC inhibitors (Gö 6976, GF109203X, and calphostin C) in A549 cells. Similarly, phorbol ester, a diacylglycerol mimetic, activates NF-kappaB-dependent transcription and potentiates tumor necrosis factor alpha (TNFalpha)-induced NF-kappaB-dependent transcription, yet unlike TNFalpha, poorly activates IkappaB kinase (IKK) activity, IkappaBalpha degradation, or NF-kappaB DNA binding in both A549 and BEAS-2B cells. As phorbol ester-induced NF-kappaB-dependent transcription was relatively insensitive to the proteasome inhibitor, MG-132, PKC may affect NF-kappaB-dependent transcription via mechanisms other than the core IKK-IkappaB pathway. This is supported by Gal4 one hybrid analysis of p65/RelA transactivation, which was potentiated by TNFalpha and phorbol ester and was inhibited by Ro 31-8220 and D609. Additionally, a number of PKC isoforms, particularly the novel isoform PKCepsilon, induced p65/RelA transactivation. Phosphorylation of p65/RelA and cAMP-responsive element-binding protein (CREB)-binding protein (CBP) was increased by TNFalpha treatment and, in the case of CBP, was prevented by Ro 31-8220 or D609. However, p65/RelA-CBP interactions were unaffected by either compound. As this effect was not limited to NF-kappaB, but was a more general feature of inducible gene transcription, we suggest PKC isoforms may provide a point of intervention in diseases such as inflammation, or cancer, where activated gene expression is prominent.

IL-1beta-dependent activation of NF-kappaB mediates PGE2 release via the expression of cyclooxygenase-2 and microsomal prostaglandin E synthase

Prostaglandin (PG) E2 release is induced in pulmonary A549 cells by the NF-kappaB-activating stimuli interleukin-1beta (IL-1beta) and phorbol 12-myristate 13-acetate (PMA). Adenoviral over-expression of IkappaBalphaDeltaN, a dominant NF-kappaB inhibitor, prevents NF-kappaB-dependent transcription and was used to qualify the role of NF-kappaB in the release of PGE2. IkappaBalphaDeltaN repressed IL-1beta-induced, but not PMA-induced, cycloxygenase-2 (COX-2) and microsomal prostaglandin E synthase (mPGES) expression. These data conclusively demonstrate a substantial role for NF-kappaB in the co-ordinate induction of COX-2, mPGES and in the corresponding release of PGE2 by IL-1beta. However, other pathways are primarily responsible for PGE2 release induced by PMA.