Correction: PPARγ sumoylation-mediated lipid accumulation in lung cancer.

[This corrects the article DOI: 10.18632/oncotarget.19700.].

PPARgamma-mediated ALDH1A3 suppression exerts anti-proliferative effects in lung cancer by inducing lipid peroxidation.

CONTEXT: The metabolic function of peroxisome proliferator-activated receptor gamma (PPARγ) in lung cancer remains unclear. OBJECTIVES: To determine the relationship of PPARγ on ALDH1A3-induced lipid peroxidation to inhibit lung cancer cell growth. MATERIALS AND METHODS: In silico analysis using microarray dataset was performed to screen the positive correlation between PPARγ and all ALDH isoforms. NUBIscan software and ChIP assay were used to identify the binding sites (BSs) of PPARγ on ALDH1A3 promoter. The expression of ALDH1A3 under thiazolidinedione (TZD) treatment was evaluated by QPCR and Western Blot in HBEC and H1993 cell lines. Upon treatment of TZD, colony formation assay was used to check cell growth inhibition and 4-hydroxy-2-nonenal (4HNE) production as lipid peroxidation marker was determined by Western Blot in PPARγ positive cell H1993 and PPARγ negative cell H1299. RESULTS: Compared to other ALDH isoforms, ALDH1A3 showed the highest positive correlation to PPARγ expression. ALDH1A3 upregulated PPARγ expression while PPARγ activation suppressed ALDH1A3. Among 2 potential screened PPARγ response elements, BS 1 and 2 in the promoter of ALDH1A3 gene, PPARγ bound directly to BS2. Ligand activation of PPARγ suppressed mRNA and protein expression of ALDH1A3. Growth inhibition was observed in H1993 (PPARγ positive cell) treated with PPARγ activator and ALDH inhibitor compared to H1299 (PPARγ negative cell). PPARγ activation increased 4HNE which is known to be suppressed by ALDH1A3. CONCLUSIONS: ALDH1A3 suppression could be one of PPARγ tumor suppressive function. This study provides a better understanding of the role of PPARγ in lung cancer.

TRAP1 Inhibition Increases Glutamine Synthetase Activity in Glutamine Auxotrophic Non-small Cell Lung Cancer Cells.

BACKGROUND/AIM: Cancer cells are distinct in terms of glutamine dependence. Here we investigated the different susceptibility of glutamine-independent and glutamine-dependent non-small cell lung cancer (NSCLC) to treatment with tumor necrosis factor receptor-associated protein 1 (TRAP1) inhibitor gamitrinib-triphenylphosphonium (G-TPP). MATERIALS AND METHODS: Cell viability and proliferation under glutamine deprivation and G-TPP treatment were determined by the MTT and colony-formation assays. Protein and mRNA expression were determined by western blot and quantitative polymerase chain reaction. Colorimetric-based assay was performed to check for glutamine synthetase (GS) activity. RESULTS: NSCLC cells showed diverse adaptation under glutamine-depleted condition and were categorized into glutamine-independent and glutamine-dependent cells. Treatment with G-TPP particularly increased GS activity and induced cell death due to energy shortage indicated by phosphorylated AMP-activated protein kinase (AMPK) in glutamine-dependent cells. CONCLUSION: This finding provides better understanding of TRAP1-mediated glutamine metabolism through GS activity, and evidence that TRAP1 could be a promising therapeutic target for glutamine-addicted cancer.

Anti-cancer Effects of Polyphenolic Compounds in Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor-resistant Non-small Cell Lung Cancer.

BACKGROUND: Polyphenolic phytochemicals are natural compounds, easily found in fruits and vegetables. Importantly, polyphenols have been intensively studied as excellent antioxidant activity which contributes to anticancer function of the natural compounds. Lung cancer has been reported to mainly account for cancer-related deaths in the world. Moreover, epidermal growth factor receptor tyrosine kinase inhibitor (TKI) resistance is one of the biggest issues in cancer treatment, especially in nonsmall cell lung cancer (NSCLC). Even though several studies both in preclinical and clinical trials have showed promising therapeutic effects of polyphenolic compounds in anticancer therapy, the function of the natural compounds in TKI-resistant (TKIR) lung cancer remains poorly studied. OBJECTIVE: The aim of this study is to screen polyphenolic compounds as potential anticancer adjuvants which suppress TKIR lung cancer. MATERIALS AND METHODS: Colony formation and thiazolyl blue tetrazolium blue assay were performed in the pair-matched TKI-sensitive (TKIS) versus TKIR tumor cell lines to investigate the therapeutic effect of polyphenolic compounds in TKIR NSCLC. RESULTS: Our data show that equol, kaempferol, resveratrol, and ellagic acid exhibit strong anticancer effect in HCC827 panel. Moreover, the inhibitory effect of most of tested polyphenolic compounds was highly selective for TKIR lung cancer cell line H1993 while sparing the TKIS one H2073. CONCLUSION: This study provides an important screening of potential polyphenolic compounds for drug development to overcome TKI resistance in advanced lung cancer. SUMMARY: The study provides an important screening of potential polyphenolic compounds for drug development to overcome tyrosine kinase inhibitor (TKI) resistance in advance lung cancerEquol, kaempferol, resveratrol, and ellagic acid show strong anticancer effect in HCC827 panel, including TKI-sensitive (TKIS) and TKI-resistant clonesThe inhibitory effect of polyphenolic compounds such as equol, kaempferol, resveratrol, ellagic acid, gallic acid, p-Coumaric, and hesperidin is highly selective for TKI-resistant lung cancer cell line H1993 while sparing the TKIS one H2073. Abbreviations used: EGFR: Epidermal growth factor receptor, EMT: Epithelial-to-mesenchymal transition, GTP: Green tea polyphenols, IGF1R: Insulin-like growth factor 1 receptor, MET: Met proto-oncogene, MTT: Thiazolyl blue tetrazolium blue, NSCLC: Non-small cell lung cancer, ROS: Reactive oxygen species, RTK: Receptor tyrosine kinase, STAT3: Signal transducer and activator of transcription 3, TKIR: TKI-resistant, TKIs: Tyrosine kinase inhibitors, TKIS: TKI-sensitive.

PPARγ sumoylation-mediated lipid accumulation in lung cancer.

Metabolic reprogramming as a crucial emerging hallmark of cancer is critical for tumor cells to maintain cellular bioenergetics, biosynthesis and reduction/oxidation (REDOX) balance. Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear hormone receptor regulating transcription of diverse gene sets involved in inflammation, metabolism, and suppressing tumor growth. Thiazolidinediones (TZDs), as selective PPARγ ligands, are insulin-sensitizing drugs widely prescribed for type 2 diabetic patients in the clinic. Here, we report that sumoylation of PPARγ couples lipid metabolism to tumor suppressive function of the receptor in lung cancer. We found that ligand activation of PPARγ dramatically induced de novo lipid synthesis as well as fatty acid beta (ß)-oxidation in lung cancer both in vitro and in vivo. More importantly, it turns out that PPARγ regulation of lipid metabolism was dependent on sumoylation of PPARγ. Further biochemical analysis revealed that PPARγ-mediated lipid synthesis depletes nicotinamide adenine dinucleotide phosphate (NADPH), consequently resulting in increased mitochondrial reactive oxygen species (ROS) level that subsequently disrupted REDOX balance in lung cancer. Therefore, liganded PPARγ sumoylation is not only critical for cellular lipid metabolism but also induces oxidative stress that contributes to tumor suppressive function of PPARγ. This study provides an important insight of future translational and clinical research into targeting PPARγ regulation of lipid metabolism in lung cancer patients accompanying type 2 diabetes.

Gallic acid inhibition of Src-Stat3 signaling overcomes acquired resistance to EGF receptor tyrosine kinase inhibitors in advanced non-small cell lung cancer.

Tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) have clinically benefited to lung cancer patients harboring a subset of activating EGFR mutations. However, even with the remarkable therapeutic response at the initial TKI treatment, most lung cancer patients eventually have relapsed aggressive tumors due to acquired resistance to the TKIs. Here, we report that 3, 4, 5-trihydroxybenzoic acid or gallic acid (GA), a natural polyphenolic compound, shows anti-tumorigenic effects in TKI-resistant non-small cell lung cancer (NSCLC). Using both in vitro growth assay and in vivo xenograft animal model, we demonstrated tumor suppressive effect of GA was more selective for the TKI-resistant cancer compared to the TKI-sensitive one. Mechanistically, GA treatment inhibited Src-Stat3-mediated signaling and decreased the expression of Stat3-regulated tumor promoting genes, subsequently inducing apoptosis and cell cycle arrest in the TKI-resistant lung cancer but not in the TKI-sensitive one. Consistent with the in vitro results, in vivo xenograft experiments showed the TKI-resistant tumor-selective growth inhibition and suppression of Src-Stat3-dependent signaling in the GA-treated tumors isolated from the xenograft model. This finding identified an importance of Src-Stat3 signaling cascade in GA-mediated tumor-suppression activity and, more importantly, provides a novel therapeutic insight of GA for advanced TKI-resistant lung cancer.

Insulin priming effect on estradiol-induced breast cancer metabolism and growth.

Diabetes is a risk factor for breast cancer development and is associated with poor prognosis for breast cancer patients. However, the molecular and biochemical mechanisms underlying the association between diabetes and breast cancer have not been fully elucidated. Here, we investigated estradiol response in MCF-7 breast cancer cells with or without chronic exposure to insulin. We found that insulin priming is necessary and specific for estradiol-induced cancer cell growth, and induces anaplerotic shunting of glucose into macromolecule biosynthesis in the estradiol treated cells. Treatment with ERK or Akt specific inhibitors, U0126 or LY294002, respectively, suppressed estradiol-induced growth. Interestingly, molecular analysis revealed that estradiol treatment markedly increases expression of cyclin A and B, and decreases p21 and p27 in the insulin-primed cells. In addition, estradiol treatment activated metabolic genes in pentose phosphate (PPP) and serine biosynthesis pathways in the insulin-primed cells while insulin priming decreased metabolic gene expression associated with glucose catabolism in the breast cancer cells. Finally, we found that anti-diabetic drug metformin and AMPK ligand AICAR, but not thiazolidinediones (TZDs), specifically suppress the estradiol-induced cellular growth in the insulin-primed cells. These findings suggest that estrogen receptor (ER) activation under chronic hyperinsulinemic condition increases breast cancer growth through the modulation of cell cycle and apoptotic factors and nutrient metabolism, and further provide a mechanistic evidence for the clinical benefit of metformin use for ER-positive breast cancer patients with diabetes.

Nuclear receptor gene alteration in human induced pluripotent stem cells with hepatic differentiation propensity.

AIM: Human induced pluripotent stem (hiPS) cells are an alternative cell source of regenerative medicine for liver disease. Because variations in hepatic differentiation efficacy among hiPS cells exist, it is important to select a hiPS cell line with hepatic differentiation propensity. In addition, nuclear receptors (NR) regulate essential biological processes including differentiation and development. In this study, we identified the hiPS cell line with hepatic differentiation propensity and examined expression levels of 48 NR during this process. METHODS: We screened 28 hiPS cell lines, which are established from various tissues of healthy persons with various reprogramming methods, using a three-step differentiation method, and examined expression levels of 48 NR by quantitative real-time polymerase chain reaction during the differentiation process in the selected cells. RESULTS: hiPS-RIKEN-2B and hiPS-RIKEN-2F cells have hepatic differentiation propensity. Differentiation propensity towards endoderm was affected by donor origin but not by reprogramming methods or cell type of origins. Expression levels of NR were closely associated with those of hepatic differentiation markers. Furthermore, expression patterns of NR were categorized as five patterns. In particular, seven NR such as chicken ovalbumin upstream promoter transcription factor 1, retinoic acid receptor α, peroxisome proliferator-activated receptor-γ, progesterone receptor, photoreceptor cell-specific nuclear receptor, tailless homolog orphan receptor and glucocorticoid receptor were identified as the genes of which expression gradually goes up with differentiation. CONCLUSION: These findings will be useful for not only elucidating mechanisms of hepatic differentiation of hiPS cells but also cell-based therapy for liver diseases.