TR3 is involved in hypoxia-induced apoptosis resistance in lung cancer cells downstream of HIF-1α.

OBJECTIVES: Lung cancer is the leading cause of cancer death worldwide. Like in all solid tumors, hypoxia is common in lung cancer and contributes to apoptosis, and thus chemotherapy resistance. However, the underlying mechanisms are not entirely clear. TR3 (NR4A1, Nur77) is an orphan nuclear receptor that induces apoptosis and may mediate chemotherapy-induced apoptosis in cancer cells. MATERIALS AND METHODS: We used A549, H23 and H1299 cell lines to investigate how TR3-mediated apoptosis is affected by hypoxia in non-small cell lung cancer (NSCLC) cells. Cell culture, western blot analysis, apoptosis assay, and siRNA-mediated gene silencing were performed in this study. RESULTS AND CONCLUSION: The TR3 activator cytosporone B was used to investigate TR3-mediated apoptosis in NSCLC cells under normoxic and hypoxic conditions. Cytosporone B induced apoptosis in a concentration-dependent manner. Chronic moderate hypoxia induced a significant down-regulation of TR3. Accordingly, the cytosporone B effect was reduced under these conditions. Hypoxia-induced down-regulation of TR3 was mediated by hypoxia-inducible factor 1α. Our immunoblotting analysis and expression data from a public dataset suggest that TR3 is downregulated in NSCLC. In conclusion, our findings suggest that hypoxia-induced down-regulation of TR3 might play an important role for hypoxia-induced apoptosis resistance in NSCLC.

Positional therapy in sleep apnoea - one fits all? What determines success in positional therapy in sleep apnoea syndrome.

INTRODUCTION: Positional therapy is a simple means of therapy in sleep apnoea syndrome, but due to controversial or lacking evidence, it is not widely accepted as appropriate treatment. In this study, we analysed data to positional therapy with regard to successful reduction of AHI and predictors of success. METHODS: All consecutive patients undergoing polysomnography between 2007 and 2011 were analysed. We used a strict definition of positional sleep apnoea syndrome (supine-exclusive sleep apnoea syndrome) and of therapy used. Patients underwent polysomnography initially and during follow-up. RESULTS: 1275 patients were evaluated, 112 of which had supine-exclusive sleep apnoea syndrome (AHI 5-66/h, median 13/h), 105 received positional therapy. With this treatment alone 75% (70/105) reached an AHI <5/h, in the follow-up 1 year later 37% (37/105) of these still had AHI<5/h, 46% (43/105) yielded an AHI between 5 and 10/h. Nine patient switched to APAP due to deterioration, 3 wanted to try APAP due to comfort reasons. At the last follow-up, 32% patients (34/105) were still on positional therapy with AHI <5/h. BMI was a predictor for successful reduction of AHI, but success was independent of sex, the presence of obstructive versus central sleep apnoea, severity of sleep apnoea syndrome or co-morbidities. CONCLUSION: Positional therapy may be a promising therapy option for patients with positional sleep apnoea. With appropriate adherence it yields a reasonable success rate in the clinical routine.

Panobinostat reduces hypoxia-induced cisplatin resistance of non-small cell lung carcinoma cells via HIF-1α destabilization.

BACKGROUND: Lung cancer is one of the most frequent cancer types and the leading cause of cancer death worldwide. Cisplatin is a widely used chemotherapeutic for non-small cell lung carcinoma (NSCLC), however, its positive effects are diminished under hypoxia. We wanted to determine if co-treatment with cisplatin and histone deacetalyse (HDAC) inhibitor panobinostat can reduce hypoxia-induced cisplatin resistance in NSCLC cells, and to elucidate mechanism involved. METHODS: Expression status of different HDACS was determined in two cell lines and in tumor tissue from 20 patients. Cells were treated with cisplatin, panobinostat, or with combination of both under normoxic and hypoxic (1% O(2)) conditions. Cell cycle, viability, acetylation of histones, and activation of apoptosis were determined. HIF-1α stability and its interaction with HDAC4 were analyzed. RESULTS: Most class I and II HDACs were expressed in NSCLC cells and tumor samples. Co-treatment of tumor cells with cisplatin and panobinostat decreased cell viability and increased apoptosis more efficiently than in primary, non-malignant bronchial epithelial cells. Co-treatment induced apoptosis by causing chromatin fragmentation, activation of caspases-3 and 7 and PARP cleavage. Toxic effects were more pronounced under hypoxic conditions. Co-treatment resulted in destabilization and degradation of HIF-1α and HDAC4, a protein responsible for acetylation and de/stabilization of HIF-1α. Direct interaction between HDAC4 and HIF-1α proteins in H23 cells was detected. CONCLUSIONS: Here we show that hypoxia-induced cisplatin resistance can be overcome by combining cisplatin with panobinostat, a potent HDAC inhibitor. These findings may contribute to the development of a new therapeutic strategy for NSCLC.

Hypoxia increases membrane metallo-endopeptidase expression in a novel lung cancer ex vivo model - role of tumor stroma cells.

BACKGROUND: Hypoxia-induced genes are potential targets in cancer therapy. Responses to hypoxia have been extensively studied in vitro, however, they may differ in vivo due to the specific tumor microenvironment. In this study gene expression profiles were obtained from fresh human lung cancer tissue fragments cultured ex vivo under different oxygen concentrations in order to study responses to hypoxia in a model that mimics human lung cancer in vivo. METHODS: Non-small cell lung cancer (NSCLC) fragments from altogether 70 patients were maintained ex vivo in normoxia or hypoxia in short-term culture. Viability, apoptosis rates and tissue hypoxia were assessed. Gene expression profiles were studied using Affymetrix GeneChip 1.0 ST microarrays. RESULTS: Apoptosis rates were comparable in normoxia and hypoxia despite different oxygenation levels, suggesting adaptation of tumor cells to hypoxia. Gene expression profiles in hypoxic compared to normoxic fragments largely overlapped with published hypoxia-signatures. While most of these genes were up-regulated by hypoxia also in NSCLC cell lines, membrane metallo-endopeptidase (MME, neprilysin, CD10) expression was not increased in hypoxia in NSCLC cell lines, but in carcinoma-associated fibroblasts isolated from non-small cell lung cancers. High MME expression was significantly associated with poor overall survival in 342 NSCLC patients in a meta-analysis of published microarray datasets. CONCLUSIONS: The novel ex vivo model allowed for the first time to analyze hypoxia-regulated gene expression in preserved human lung cancer tissue. Gene expression profiles in human hypoxic lung cancer tissue overlapped with hypoxia-signatures from cancer cell lines, however, the elastase MME was identified as a novel hypoxia-induced gene in lung cancer. Due to the lack of hypoxia effects on MME expression in NSCLC cell lines in contrast to carcinoma-associated fibroblasts, a direct up-regulation of stroma fibroblast MME expression under hypoxia might contribute to enhanced aggressiveness of hypoxic cancers.

Peroxisome proliferator-activated receptor-ß/δ, the acute signaling factor in prostacyclin-induced pulmonary vasodilation.

As powerful vasodilators, prostacyclin analogues are presently the mainstay in the treatment of severe pulmonary arterial hypertension. Although the hemodynamic effects of prostacyclin analogues are well known, the molecular mechanism of their acute effects on pulmonary vascular tone and systemic vascular tone remains poorly understood. Peroxisome proliferator-activated receptor-ß/δ (PPARß/δ) was previously identified as a putative receptor responsible for the modulation of target gene expression in response to prostacyclin analogues. The present study investigated the signaling pathway of prostacyclin in human pulmonary arterial smooth muscle cells (PASMCs), and sought to define the role of PPARß/δ in the acute vasodilating effect. In human PASMCs, prostacyclin rapidly activated TWIK-related acid-sensitive K channel 1 (TASK-1) and calcium-dependent potassium channels (K(Ca)). This pathway was mediated via the prostanoid I receptor-protein kinase A pathway. The silencing of PPARß/δ demonstrated that the downstream K(Ca) activation was exclusively dependent on PPARß/δ signaling, whereas the activation of TASK-1 was not. In addition, the PPARß/δ-induced activation of K(Ca) was independent of NO. The acute prostacyclin-induced K(Ca) activation is critically dependent on PPARß/δ as a rapid signaling factor. This accounts in part for the vasodilating effect of prostacyclin in pulmonary arteries, and provides insights into a new molecular explanation for the effects of prostanoids.

Hypoxia-induced cisplatin resistance is reversible and growth rate independent in lung cancer cells.

Hypoxia frequently occurs in solid tumors and is known to contribute to chemotherapy resistance. However, the mechanisms leading to chemotherapy resistance are not entirely known. We investigated hypoxia-induced resistance to cisplatin in NSCLC cell lines. We show that chronic moderate hypoxia induced resistance to cisplatin in NSCLC cells without involvement of selection pressure. Our data suggest that stabilization of the hypoxia-inducible factor 1 alpha and down-regulation of the pro-apoptotic protein BAX play a role in this process. Furthermore, we provide evidence that hypoxia-induced resistance to cisplatin is not due to the reduced growth rate of cancer cells under hypoxic conditions.

Nuclear and cytoplasmic death receptor 5 as prognostic factors in patients with non-small cell lung cancer treated with chemotherapy.

BACKGROUND: Death receptor 4 (DR4) and death receptor 5 (DR5) are tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) receptors that activate apoptosis via the extrinsic apoptosis pathway. DcR1 and DcR2 are decoy receptors for TRAIL that act antagonistically. Intracellular trafficking of TRAIL receptors has been described, but the role of the subcellular localization of TRAIL receptors in non-small cell lung cancer (NSCLC) progression is unclear. METHODS: Expression and intracellular localization of pro-apoptotic and decoy TRAIL receptors were analyzed by immunohistochemistry in 50 samples of advanced or recurrent NSCLC. Using confocal microscopy, localization of TRAIL receptors was studied in NSCLC cell lines. RESULTS: Cytoplasmic staining for all four TRAIL receptors was observed in the majority of samples. Nuclear staining was infrequent in the case of DR4 (12%) and DcR2 (8%), while DR5 and DcR1 were localized in the nucleus in 27% and 60% of samples. When overall survival was analyzed, cytoplasmic staining for DR5 in tumor cells (P=0.025) and nuclear staining for DR5 in tumor cells (P=0.007) were significant prognostic factors in univariate, as well as in multivariate analysis including clinicopathologic factors (P=0.026 and 0.021, respectively). In A549, NCI-H358, and A427 NSCLC cells all four TRAIL receptors were found to be mainly located perinuclearly, but also in the nucleus. CONCLUSION: The study for the first time shows that TRAIL receptors are found in different intracellular compartments including the nucleus in NSCLC cells and that both nuclear and cytoplasmic DR5 might predict improved survival in patients with advanced NSCLC.