AMPK regulates metabolic actions of glucocorticoids by phosphorylating the glucocorticoid receptor through p38 MAPK

Metformin-mediated downregulation of p38 mitogen-activated protein kinase-dependent excision repair cross-complementing 1 decreases DNA repair capacity and sensitizes human lung cancer cells to paclitaxel

Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (Taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation.

Glucose can promote a glucocorticoid resistance state

It has been shown that ingestion of glucose, amino acids, protein or mixed meals tends to increase serum and salivary cortisol concentrations in healthy adults. Recently, it has been demonstrated that morning glucose ingestion stimulates pulsatile cortisol and adrenocorticotropic hormone (ACTH) secretion, thus elevating their mean concentrations. In light of the above, a question arises: could the frequent food – and specifically glucose – consumption lead to hypercortisolism with possible clinical implications? And can the human body, under normal conditions raise defence mechanisms against the transient hypercortisolism caused by the frequent glucose consumption? Studies have revealed novel mechanisms, which are implicated in the glucocorticoid receptor (GR)-mediated action, providing a kind of glucocorticoid resistance. This glucocorticoid resistance could be mediated through both enhancing acetylation (via, among others, regulation of essential clock genes such as Per) and inhibiting deacetylation of GR (via possible regulation of sirtuin activity). Interestingly, the acetylation/deacetylation processes seem to be regulated by glucose. Thus, glucose apart from causing increased cortisol secretion can, simultaneously, counter-regulate this hypercortisolism, by promoting directly and/or indirectly a glucocorticoid resistance state. Undoubtedly, before extracting conclusions regarding the clinical significance of the increased cortisol secretion following glucose ingestion, we should first thoroughly investigate the ‘defence’ mechanisms provided by ‘nature’ to handle this hypercortisolism.

Effects of fatty acid treatments on the dexamethasone-induced intramuscular lipid accumulation in chickens

BACKGROUND

Glucocorticoid has an important effect on lipid metabolism in muscles, and the type of fatty acid likely affects mitochondrial utilization. Therefore, we hypothesize that the different fatty acid types treatment may affect the glucocorticoid induction of intramuscular lipid accumulation.

METHODOLOGY/PRINCIPAL FINDINGS

The effect of dexamethasone (DEX) on fatty acid metabolism and storage in skeletal muscle of broiler chickens (Gallus gallus domesticus) was investigated with and without fatty acid treatments. Male Arbor Acres chickens (31 d old) were treated with either palmitic acid (PA) or oleic acid (OA) for 7 days, followed by DEX administration for 3 days (35-37 d old). The DEX-induced lipid uptake and oxidation imbalance, which was estimated by increased fatty acid transport protein 1 (FATP1) expression and decreased carnitine palmitoyl transferase 1 activity, contributed to skeletal muscle lipid accumulation. More sensitive than glycolytic muscle, the oxidative muscle in DEX-treated chickens showed a decrease in the AMP to ATP ratio, a decrease in AMP-activated protein kinase (AMPK) alpha phosphorylation and its activity, as well as an increase in the phosphorylation of mammalian target of rapamycin (mTOR) and ribosomal p70S6 kinase, without Akt activation. DEX-stimulated lipid deposition was augmented by PA, but alleviated by OA, in response to pathways that were regulated differently, including AMPK, mTOR and FATP1.

CONCLUSIONS

DEX-induced intramuscular lipid accumulation was aggravated by SFA but alleviated by unsaturated fatty acid. The suppressed AMPK and augmented mTOR signaling pathways were involved in glucocortcoid-mediated enhanced intramuscular fat accumulation.

Daytime restricted feeding modifies 24 h rhythmicity and subcellular distribution of liver glucocorticoid receptor and the urea cycle in rat liver

The timing system in mammals is formed by a set of peripheral biological clocks coordinated by a light-entrainable pacemaker located in the suprachiasmatic nucleus. Daytime restricted feeding (DRF) modifies the circadian control and uncouples the light-dependent physiological rhythmicity, food access becoming the principal external time cue. In these conditions, an alternative biological clock is expressed, the food-entrainable oscillator (FEO). Glucocorticoid hormones are an important part of the humoral mechanisms in the daily synchronisation of the metabolic response of peripheral oscillators by the timing system. A peak of circulating corticosterone has been reported before food access in DRF protocols. In the present study we explored in the liver the 24 h variations of: (1) the subcellular distribution of glucocorticoid receptor (GCR), (2) the activities of the corticosterone-forming and NADPH-generating enzymes (11β-hydroxysteroid dehydrogenase type 1 (11β-HSD-1) and hexose-6-phosphate dehydrogenase (H6PDH)), and, (3) parameters related with the urea cycle (circulating urea and activities of carbamoyl phosphate synthetase and ornithine transcarbamylase) elicited by DRF. The results showed that DRF promoted an increase of more than two times of the hepatic GCR, but exclusively in the cytosolic compartment, since the GCR in the nuclear fraction showed a reduction. No changes were observed in the activities of 11β-HSD-1 and H6PDH, but the rhythmicity of all of the urea cycle-related parameters was modified. It is concluded that liver glucocorticoid signalling and the urea cycle are responsive to feeding-restricted schedules and could be part of the FEO.

Strategies for improving the efficacy and therapeutic ratio of glucocorticoids

Although glucocorticoids are very effective in suppressing inflammation there is a clear clinical unmet need for new or improved glucocorticoids in patients with severe asthma and COPD. Recent developments include the targeted deposition of ultrafine glucocorticoid particles to treat small airways and the potential of novel agents that have a reduced side effect profile. Understanding the drivers of relative glucocorticoid resistance in these patients may lead to the development of newer drugs aimed at subsets of patients, for example asthmatics with high periostin levels. Alternatively, inhibitors of kinase pathways that are associated with inflammatory responses may be able to modulate glucocorticoid function and combinations of these inhibitors along with novel glucocorticoids may provide the combination therapy of the future.

AMPKα modulation in cancer progression: multilayer integrative analysis of the whole transcriptome in Asian gastric cancer

Gastric cancer is the most common cancer in Asia and most developing countries. Despite the use of multimodality therapeutics, it remains the second leading cause of cancer death in the world. To identify the molecular underpinnings of gastric cancer in the Asian population, we applied an RNA-sequencing approach to gastric tumor and noncancerous specimens, generating 680 million informative short reads to quantitatively characterize the entire transcriptome of gastric cancer (including mRNAs and miRNAs). A multilayer analysis was then developed to identify multiple types of transcriptional aberrations associated with different stages of gastric cancer, including differentially expressed mRNAs, recurrent somatic mutations, and key differentially expressed miRNAs. Through this approach, we identified the central metabolic regulator AMP-activated protein kinase (AMPK)α as a potential functional target in Asian gastric cancer. Furthermore, we experimentally showed the translational relevance of this gene as a potential therapeutic target for early-stage gastric cancer in Asian patients. Together, our findings not only provide a valuable information resource for identifying and elucidating the molecular mechanisms of Asian gastric cancer, but also represent a general integrative framework to develop more effective therapeutic targets.

Nuclear receptors and AMPK: resetting metabolism

Obesity, and in particular central adiposity, is a key feature of metabolic syndrome, which includes trends toward increased triglycerides, insulin resistance, high blood pressure, hypercholesterolemia, and heart disease. It has a prevalence of 25% or more and is a dominant component of the health care budgets in Western societies. In addition to genetic causes, high-fat diets and disrupted sleep patterns have major influences on the development of metabolic syndrome. Recent studies have demonstrated active roles for the nuclear receptor superfamily and the energy-sensing kinase adenosine monophosphate (AMP)-activated protein kinase (AMPK) in regulating metabolism and circadian rhythm. In this chapter, we review these findings and attempt to develop a better understanding of the interplay between metabolism and circadian rhythm and their coordinated regulation by nuclear receptors and AMPK. This supraregulatory network may be considered a target for novel therapeutic applications against metabolic syndrome.

Glucocorticoids reduce inflammation in cystic fibrosis bronchial epithelial cells

Reduction of lung inflammation is one of the goals of cystic fibrosis (CF) therapy. Among anti-inflammatory molecules, glucocorticoids (GC) are one of the most prescribed. However, CF patients seem to be resistant to glucocorticoid treatment. Several molecular mechanisms that contribute to decrease anti-inflammatory effects of glucocorticoids have been identified in pulmonary diseases, but the molecular actions of glucocorticoids have never been studied in CF. In the cytoplasm, glucocorticoids bind to glucocorticoid receptor (GR) and then, control NF-κB and MAPK pathways through direct interaction with AP-1 and NF-κB in the nucleus. Conversely, MAPK can regulate glucocorticoid activation by targeting GR phosphorylation. Together these pathways regulate IL-8 release in the lung. Using bronchial epithelial cell lines derived from non CF and CF patients, we analyzed GR-based effects of glucocorticoids on NF-κB and MAPK pathways, after stimulation with TNF-α. We demonstrate that the synthetic glucocorticoid dexamethasone (Dex) significantly decreases IL-8 secretion, AP-1 and NF-κB activity in CF cells in a pro-inflammatory context. Moreover, we show that p38 MAPK controls IL-8 release by determining GR activation through specific phosphorylation on serine 211. Finally, we demonstrate a synergistic effect of dexamethasone treatment and inhibition of p38 MAPK inducing more than 90% inhibition of IL-8 production in CF cells. All together, these results demonstrate the good responsiveness to glucocorticoids of CF bronchial epithelial cells and the reciprocal link between glucocorticoids and p38 MAPK in the control of CF lung inflammation.

Glucocorticoid receptor mutants: man-made tools for functional research

The glucocorticoid receptor (GR) is a ligand-dependent transcription factor that can bind to glucocorticoids (GCs). Upon ligand binding, GR sheds its cytoplasmic chaperoning complex and translocates to the nucleus, where it can act as a ligand-dependent transcription factor, transactivating or transrepressing specific gene promoters. Often, GR interacts with specific cofactors to implement a variety of gene promoter effects. GR activity and function is further modulated by post-translational modifications. To assess the diverse aspects of GR mechanisms of activation and gene regulation, researchers continue to use a range of artificial GR mutants. In this review we analyze the characteristics of GR mutants with the aim of assisting the design and interpretation of GR mutant-based experiments.

Prednisolone-induced beta cell dysfunction is associated with impaired endoplasmic reticulum homeostasis in INS-1E cells

Glucocorticoids (GCs), such as prednisolone (PRED), are widely prescribed anti-inflammatory drugs, but their use may induce glucose intolerance and diabetes. GC-induced beta cell dysfunction contributes to these diabetogenic effects through mechanisms that remain to be elucidated. In this study, we hypothesized that activation of the unfolded protein response (UPR) following endoplasmic reticulum (ER) stress could be one of the underlying mechanisms involved in GC-induced beta cell dysfunction. We report here that PRED did not affect basal insulin release but time-dependently inhibited glucose-stimulated insulin secretion in INS-1E cells. PRED treatment also decreased both PDX1 and insulin expression, leading to a marked reduction in cellular insulin content. These PRED-induced detrimental effects were found to be prevented by prior treatment with the glucocorticoid receptor (GR) antagonist RU486 and associated with activation of two of the three branches of the UPR. Indeed, PRED induced a GR-mediated activation of both ATF6 and IRE1/XBP1 pathways but was found to reduce the phosphorylation of PERK and its downstream substrate eIF2α. These modulations of ER stress pathways were accompanied by upregulation of calpain 10 and increased cleaved caspase 3, indicating that long term exposure to PRED ultimately promotes apoptosis. Taken together, our data suggest that the inhibition of insulin biosynthesis by PRED in the insulin-secreting INS-1E cells results, at least in part, from a GR-mediated impairment in ER homeostasis which may lead to apoptotic cell death.

Acetylation-mediated epigenetic regulation of glucocorticoid receptor activity: circadian rhythm-associated alterations of glucocorticoid actions in target tissues

Glucocorticoids influence organ functions through the glucocorticoid receptor, a protein acetylated and deacetylated by several histone acetyltransferases and deacetylases. We reported that the circadian rhythm-related transcription factor "Clock", a key component of the biological CLOCK with inherent histone acetyltransferase activity, acetylates glucocorticoid receptor lysines within its hinge region--a "lysine cluster" containing a KXKK motif--and represses its transcriptional activity. This Clock-induced repression of the glucocorticoid receptor activity is inversely phased to the diurnally circulating glucocorticoids and may act as a local counter regulatory mechanism to the actions of these hormones. Importantly, uncoupling of the central CLOCK-regulated hypothalamic-pituitary-adrenal axis and peripheral CLOCK-mediated alterations of glucocorticoid action, such as chronic stress and frequent trans-time zone travel or night-shift work, may cause functional hypercortisolism and contribute to various pathologies. Thus, acetylation-mediated epigenetic regulation of the glucocorticoid receptor may be essential for the maintenance of proper time-integrated glucocorticoid action, significantly influencing human well-being and longevity.

Circadian CLOCK-mediated regulation of target-tissue sensitivity to glucocorticoids: implications for cardiometabolic diseases

Glucocorticoids, the end-products of the hypothalamic-pituitary- adrenal (HPA) axis, influence the functions of virtually all organs and tissues through the nuclear glucocorticoid receptor (GR). Circulating levels of glucocorticoids fluctuate naturally in a circadian fashion under the strong influence of the hypothalamic suprachiasmatic nucleus (SCN) circadian CLOCK system, and regulate the transcriptional activity of the GR in the brain and peripheral target tissues. We recently reported that the basic helix-loop- helix transcription factor Clock, which is a histone acetyltransferase and a central component of the self-oscillating transcription factor loop that generates circadian rhythms, represses GR transcriptional activity by acetylating lysine residues within the 'lysine cluster' located in the hinge region of the receptor. This Clock-mediated repression of GR transcriptional activity oscillates in inverse phase to the HPA axis, acting as a target tissue counter-regulatory mechanism to the diurnally fluctuating circulating glucocorticoids. Interestingly, mild evening elevations of corti-sol, as occurs in chronic stress situations, and frequent uncoupling of the SCN CLOCK-directed HPA axis from the daily oscillation of target tissue sensitivity to glucocorticoids, as happens in trans-time zone travel and night shift work, produce functional hypercortisolism and, hence, multiple components of the metabolic syndrome with resultant cardiovascular complications.