Aa-Z2 triggers ROS-induced apoptosis of osteosarcoma by targeting PDK-1

BACKGROUND

Osteosarcoma (OS) is the most frequent cancer derived from bone, and the prognosis of OS is poor. Metabolic alterations have been previously reported to contribute to the development of OS, and arsenic compounds have been suggested to exhibit strong anti-OS effects. However, few studies have described the therapeutic efficiency of arsenic compounds by targeting metabolism in OS.

METHODS

Here, we presented a novel organo-arsenic compound, Aa-Z2, and its antitumour efficacy against OS both in vitro and in vivo.

RESULTS

Aa-Z2 induced OS cell apoptosis, G2/M phase arrest, and autophagy through the accumulation of reactive oxygen species (ROS). Elevated ROS functioned by promoting the mitochondrial-dependent caspase cascade and attenuating the PI3K/Akt/mTOR signalling pathway. N-acetylcysteine (NAC), a kind of ROS scavenger, could reverse the effects of Aa-Z2 treatment on 143B and HOS cells. Specifically, by targeting pyruvate dehydrogenase kinase 1 (PDK-1), Aa-Z2 induced changes in mitochondrial membrane potential and alterations in glucose metabolism to accumulate ROS. Overexpression of PDK-1 could partially desensitize OS cells to Aa-Z2 treatment. Importantly, Aa-Z2 suppressed tumour growth in our xenograft osteosarcoma model.

CONCLUSION

The study provides new insights into the mechanism of Aa-Z2-related metabolic alterations in OS inhibition, as well as pharmacologic evidence supporting the development of metabolism-targeting therapeutics.

Pentacyclic triterpenoid ursolic acid induces apoptosis with mitochondrial dysfunction in adult T-cell leukemia MT-4 cells to promote surrounding cell growth

We investigated the antitumor effects of oleanolic acid (OA) and ursolic acid (UA) on adult T-cell leukemia cells. OA and UA dose-dependently inhibited the proliferation of adult T-cell leukemia cells. UA-treated cells showed caspase 3/7 and caspase 9 activation. PARP cleavage was detected in UA-treated MT-4 cells. Activation of mTOR and PDK-1 was inhibited by UA. Autophagosomes were detected in MT-4 cells after UA treatment using electron microscopy. Consistently, mitophagy was observed in OA- and UA-treated MT-4 cells by confocal microscopy. The mitochondrial membrane potential in MT-4 cells considerably decreased, and mitochondrial respiration and aerobic glycolysis were significantly reduced following UA treatment. Furthermore, MT-1 and MT-4 cells were sorted into two regions based on their mitochondrial membrane potential. UA-treated MT-4 cells from both regions showed high activation of caspase 3/7, which were inhibited by Z-vad. Interestingly, MT-4 cells cocultured with sorted UA-treated cells showed enhanced proliferation. Finally, UA induced cell death and ex vivo PARP cleavage in peripheral blood mononuclear cells from patients with adult T-cell leukemia. Therefore, UA-treated MT-4 cells show caspase activation following mitochondrial dysfunction and may produce survival signals to the surrounding cells.

MeCP2 Increases Cisplatin Resistance in Human Gastric Cancer through the Activation of the AKT Pathway by Facilitating PDK-1 Transcription

BACKGROUND

Increasing evidence indicates that an imbalance of oncogenes is implicated in chemotherapy resistance in cancers. Methyl-CpG binding protein 2 (MeCP2), which acts as a master epigenetic regulator of various gene expressions, is involved in the carcinogenesis and progression of gastric cancer. However, whether this vital role may participates in acquired cisplatin resistance in GC remains unknown.

OBJECTIVE

This study aimed to determine whether inhibition of MeCP2 expression could sensitize DDP-resistant GC cells to DDP and to elucidate its underlying molecular mechanism.

METHODS

qRT-PCR and western blotting were used to evaluate MeCP2 expression in GC DDP-resistant GC cells. Subsequently, cell viability, colony formation, cell cycle, cell apoptosis and tumorigenicity assays were performed to explore the role of MeCP2 in vitro and in vivo. Chromatin immunoprecipitation-qPCR and luciferase reporter assays were used to identify whether 3-phosphoinositide-dependent protein kinase 1 (PDK-1) is a direct target gene of MeCP2.

RESULTS

MeCP2 was upregulated in malignant DDP-resistant cells compared to that in non-DDP-resistant GC cells or normal gastric epithelial cells. MeCP2 knockdown increased the sensitivity of DDP-resistant GC cells to DDP, resulting in reduced cell growth, G0/G1 phase arrest and increased apoptosis, wheras MeCP2 overexpression attenuated DDP sensitivity of DDP-resistant GC cells. In addition, MeCP2 knockdown enhanced DDP sensitivity in tumors in vivo. MeCP2 elevated PDK-1 expression by binding to its CpG sites in promoter regions, and inhibition of PDK-1 reversed the inductive effect of MeCP2 overexpression on DDP resistance in GC cells.

CONCLUSION

These findings indicate that silencing MeCP2 may potentiate DDP induced cell death, providing a promising therapeutic strategy for GC.

mTORC and PKCε in Regulation of Alcohol Use Disorder

Alcohol use disorder (AUD) is characterized by compulsive binge alcohol intake, leading to various health and social harms. Protein Kinase C epsilon (PKCε), a specific family of PKC isoenzyme, regulates binge alcohol intake, and potentiates alcohol-related cues. Alcohol via upstream kinases like the mammalian target to rapamycin complex 1 (mTORC1) or 2 (mTORC2), may affect the activities of PKCε or vice versa in AUD. mTORC2 phosphorylates PKCε at hydrophobic and turn motif, and was recently reported to be associated with alcohol-seeking behavior, suggesting the potential role of mTORC2-PKCε interactions in the pathophysiology of AUD. mTORC1 regulates translation of synaptic proteins involved in alcohol-induced plasticity. Hence, in this article, we aimed to review the molecular composition of mTORC1 and mTORC2, drugs targeting PKCε, mTORC1, and mTORC2 in AUD, upstream regulation of mTORC1 and mTORC2 in AUD and downstream cellular mechanisms of mTORCs in the pathogenesis of AUD.

Vitamin C activates pyruvate dehydrogenase (PDH) targeting the mitochondrial tricarboxylic acid (TCA) cycle in hypoxic KRAS mutant colon cancer

Background: In hypoxic tumors, positive feedback between oncogenic KRAS and HIF-1α involves impressive metabolic changes correlating with drug resistance and poor prognosis in colorectal cancer. Up to date, designed KRAS-targeting molecules do not show clear benefits in patient overall survival (POS) so pharmacological modulation of aberrant tricarboxylic acid (TCA) cycle in hypoxic cancer has been proposed as a metabolic vulnerability of KRAS-driven tumors. Methods: Annexin V-FITC and cell viability assays were carried out in order to verify vitamin C citotoxicity in KRAS mutant SW480 and DLD1 as well as in Immortalized Human Colonic Epithelial Cells (HCEC). HIF1a expression and activity were determined by western blot and functional analysis assays. HIF1a direct targets GLUT1 and PDK1 expression was checked using western blot and qRT-PCR. Inmunohistochemical assays were perfomed in tumors derived from murine xenografts in order to validate previous observations in vivo. Vitamin C dependent PDH expression and activity modulation were detected by western blot and colorimetric activity assays. Acetyl-Coa levels and citrate synthase activity were assessed using colorimetric/fluorometric activity assays. Mitochondrial membrane potential (Δψ) and cell ATP levels were assayed using fluorometric and luminescent test. Results: PDK-1 in KRAS mutant CRC cells and murine xenografts was downregulated using pharmacological doses of vitamin C through the proline hydroxylation (Pro402) of the Hypoxia inducible factor-1(HIF-1)α, correlating with decreased expression of the glucose transporter 1 (GLUT-1) in both models. Vitamin C induced remarkable ATP depletion, rapid mitochondrial Δψ dissipation and diminished pyruvate dehydrogenase E1-α phosphorylation at Serine 293, then boosting PDH and citrate synthase activity. Conclusion: We report a striking and previously non reported role of vitamin C in the regulation of the pyruvate dehydrogenase (PDH) activity, then modulating the TCA cycle and mitochondrial metabolism in KRAS mutant colon cancer. Potential impact of vitamin C in the clinical management of anti-EGFR chemoresistant colorectal neoplasias should be further considered.

Conditional knockout of the PDK-1 gene in osteoblasts affects osteoblast differentiation and bone formation

Osteoblasts are the main functional cells of bone formation, and they are responsible for the synthesis, secretion, and mineralization of the bone matrix. Phosphatidylinositol-3-kinase/Akt is an important signaling pathway involved in the regulation of cell proliferation, death, and survival. Some studies have shown that 3-phosphoinositide-dependent protein kinase-1 (PDK-1) plays an important role in the phosphorylation of Akt. In the present study, an osteocalcin (OCN) promoter-driven Cre-LoxP system was established to specifically delete the PDK-1 gene in osteoblasts. It was found that the size and weight of PDK-1 conditional gene knockout (cKO) mice were significantly reduced. von Kossa staining and microcomputed tomography showed that the trabecular thickness, trabecular number, and bone volume were significantly decreased, whereas trabecular separation was increased, as compared with wide-type littermates, which were characterized by a decreased bone mass. A model of distal femoral defect was established, and it was found that cKO mice delayed bone defect repair. In osteoblasts derived from PDK-1 cKO mice, the alkaline phosphatase (ALP) secretion and ability of calcium mineralization were significantly decreased, and the expressions of osteoblast-related proteins, runt-related transcription factor 2, OCN, and ALP were also clearly decreased. Moreover, the phosphorylation level of Akt and downstream factor GSK3β and their response to insulin-like growth factor-1 (IGF-1) decreased clearly. Therefore, we believe that PDK-1 plays a very important role in osteoblast differentiation and bone formation by regulating the PDK-1/Akt/GSK3β signaling pathway.

PD-L1, PDK-1 and p-Akt are correlated in patients with papillary thyroid carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC) is the most common type of thyroid carcinoma.

OBJECTIVES

To investigate the clinical significance of programmed death ligand 1 (PD-L1) and phosphoinositide-dependent protein kinase 1 (PDK1) in PTC.

MATERIAL AND METHODS

A total of 194 PTC patients were recruited. Contralateral normal thyroid tissues were obtained and used as controls (n = 80). The expression levels of PD-L1, PDK1 and p-Akt were determined using immunohistochemistry.

RESULTS

The PD-L1, PDK1 and p-Akt were upregulated in cancer tissues compared to the normal tissues. The mean optical density (MOD) values of PD-L1, PDK1 and p-Akt were significantly higher in the PTC tissues. The expression of PD-L1 positively correlated with the levels of PDK1 and p-Akt. In addition, the expression of PD-L1, PDK1 and p-Akt in PTC patients without chronic lymphocytic thyroiditis (CLT) was significantly higher than the expression of those proteins in the CLT patients. The patients with higher expression levels of PD-L1, PDK1 or p-Akt had remarkably larger tumors and higher rates of TNM III-IV, capsular infiltration, lymph node metastasis, and of recurrence. The Kaplan-Meier curve showed that patients with lower expression of PD-L1, PDK1 or p-Akt had significantly longer recurrence-free time. The logistic regression analysis revealed that only CLT, PD-L and capsular infiltration were risk factors for patients' five-year recurrence.

CONCLUSIONS

The PD-L1, PDK1 and p-Akt were found to be positively correlated with a poor prognosis in PTC.

Ku80 promotes melanoma growth and regulates antitumor effect of melatonin by targeting HIF1-α dependent PDK-1 signaling pathway

Melanoma is one of the most malignant and aggressive cancers with high cancer-related deaths. However, it is unclear whether Ku80 regulates tumor growth in human melanoma. In this study, we screened a siRNA library targeting 6024 human genes and identified Ku80 as a potential therapeutic target in melanoma cells. Knockdown of Ku80 significantly suppressed melanoma cell proliferation and induced apoptosis, as well as enhanced the antitumor effect of melatonin in melanoma in vitro and in vivo. Overexpression of Ku80, however, promoted melanoma growth and increased the insensitivity of melanoma cells to melatonin. Mechanistically, we found that Ku80 bound to the PDK1 promoter and activated the transcription of PDK1. Moreover, we showed that the binding of Ku80 at the PDK-1 promoter was HIF1-α dependent, and melatonin degraded HIF1-α in melanoma cells. Furthermore, clinical data revealed that the expression of Ku80 and PDK-1 proteins were positively correlated and elevated in the tumor tissues of melanoma patients, and high expression of Ku80 predicted a poor prognosis in melanoma. Collectively, our study demonstrated that Ku80 promoted melanoma growth and regulated antitumor activity of melatonin by targeting HIF1-α dependent PDK-1 signaling pathway, suggesting that Ku80 may be a potential molecular target for melanoma treatment.

PDK-1 mediated Hippo-YAP-IRS2 signaling pathway and involved in the apoptosis of non-small cell lung cancer cells

Pyruvate dehydrogenase kinase-1 (PDK-1), a gatekeeper enzyme, was involved in cancer progression, such as tumor angiogenesis, cell survival, and growth. Recent evidence indicated that PDK-1 may be involved in lung cancer, however, the function and underlying mechanism of PDK-1 is remaining unclear. In the present study, our aim was to investigate the role and mechanisms of PDK-1 in human non-small cell lung cancer (NSCLC) cells. We first observed that PDK-1 was highly expressed in NSCLC cell lines. PDK-1 silence resulted in the inhibition of NSCLC cell survival. Also, cell apoptosis and caspase-3 activity were increased by PDK-1 knockdown in H1299 and A549 cells. Attenuation of PDK-1 expression blocked YAP and insulin receptor substrate 2 (IRS2) expression, and PDK-1 silence suppressed IRS2 expression dependent on Hippo-YAP signaling pathway. Moreover, further studies confirmed that YAP or IRS2 overexpression reversed the action of PDK-1 in NSCLC cells. In conclusion, our findings indicate that PDK1/Hippo-YAP/IRS2 signaling pathway plays a critical role in NSCLC cell survival and apoptosis.

Time-dependent PPARγ Modulation of HIF-1α Signaling in Hypoxic Pulmonary Artery Smooth Muscle Cells

BACKGROUND

Pathogenesis of pulmonary hypertension is complex and involves activation of the transcription factor, hypoxia-inducible factor-1 (HIF-1) that shifts cellular metabolism from aerobic respiration to glycolysis, in part, by increasing the expression of its downstream target pyruvate dehydrogenase kinase-1 (PDK-1), thereby promoting a proliferative, apoptosis-resistant phenotype in pulmonary vascular cells. Activation of the nuclear hormone transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ), attenuates pulmonary hypertension and pulmonary artery smooth muscle cell (PASMC) proliferation. In the current study, we determined whether PPARγ inhibits HIF-1α and PDK-1 expression in human PASMCs.

METHODS

HPASMCs were exposed to normoxia (21% O2) or hypoxia (1% O2) for 2-72 hours ± treatment with the PPARγ-ligand, rosiglitazone (RSG, 10μM).

RESULTS

Compared to normoxia, HIF-1α mRNA levels were elevated in HPASMC at 2 hours hypoxia and reduced to baseline levels by 24-72 hours. HIF-1α protein levels increased following 4 and 8 hours of hypoxia and returned to baseline levels by 24 and 72 hours. PDK-1 protein levels increased following 24 hours hypoxia and remained elevated by 72 hours. RSG treatment at the onset of hypoxia attenuated HIF-1α protein and PDK-1 mRNA and protein levels at 4, 8 and 24 hours of hypoxia, respectively. However, RSG treatment during final 24 hours of 72-hour hypoxia, an intervention that inhibits HPASMC proliferation, failed to prevent hypoxia-induced PDK-1 expression.

CONCLUSION

Hypoxia causes transient activation of HPASMC HIF-1α that is attenuated by RSG treatment initiated at hypoxia onset. These findings provide novel evidence that PPARγ modulates fundamental and acute cellular responses to hypoxia through both HIF-1-dependent and HIF-1-independent mechanisms.

Regulators of Glucose Metabolism in CD4+ and CD8+ T Cells

Much like cancer cells, activated T cells undergo various metabolic changes that allow them to grow and proliferate rapidly. By adopting aerobic glycolysis upon activation, T cells effectively prioritize efficiency in biosynthesis over energy generation. There are distinct differences in the way CD4⁺ and CD8⁺ T cells process activation signals. CD8⁺ effector T cells are less dependent on Glut1 and oxygen levels compared to their CD4⁺ counterparts. Similarly the downstream signaling by TCR also differs in both effector T cell types. Recent studies have explored PI3K/Akt, mTORC, HIF1α, p70S6K and Bcl-6 signaling in depth providing definition of the crucial roles of these regulators in glucose metabolism. These new insights may allow improved therapeutic manipulation against inflammatory conditions that are associated with dysfunctional T-cell metabolism such as autoimmune disorders, metabolic syndrome, HIV, and cancers.

A DAF-16/FoxO3a-dependent longevity signal is initiated by antioxidants

The precise mechanisms of antioxidant-mediated longevity are poorly understood. We show that an antioxidant treatment can extend the lifespan of Caenorhabditis elegans (C. elegans) through the nuclear translocation of the forkhead box O transcription factor (FoxO) homolog DAF-16. This pathway was found to involve 3-phosphoinositide-dependent kinase-1 (PDK-1) and serum- and glucocorticoid-regulated kinase-1 (SGK-1), distinct from the known oxidative stress-mediated mechanism in which FoxO3a translocation is regulated by c-Jun N-terminal kinase (JNK) and mammalian sterile 20-like kinase-1 (MST-1). The differences in the mechanisms of FoxO activation by antioxidants and oxidants result in differences in FoxO phosphorylation and target gene expression. Based on these results, we found that a combination of early antioxidant treatment and late oxidant treatment is most effective for lifespan extension in C. elegans.

Akt signaling and freezing survival in the wood frog, Rana sylvatica

BACKGROUND

The wood frog (Rana sylvatica) exhibits well-developed natural freeze tolerance supported by multiple mechanisms of biochemical adaptation. The present study investigated the role and regulation of the Akt signaling pathway in wood frog tissues (with a focus on liver) responding to freezing stress.

METHODS

Immunoblotting was used to assess total and phospho-Akt levels, total and phospho-PDK1, PTEN protein level, as well as total and phospho-FOXO1 levels. RT-PCR was used to investigate transcript levels of PTEN and microRNAs.

RESULTS

Akt was inhibited in skeletal muscle, kidney and heart after 24h freezing exposure with a reversal after thawing. The responses of the main kinase (PDK-1) and phosphatase (PTEN) that regulate Akt were consistent with freeze activation of Akt in liver; freezing exposure activated PDK-1 via enhanced Ser-241 phosphorylation whereas PTEN protein levels were reduced. Levels of three microRNAs (miR-26a, miR-126 and miR-217) that regulate pten expression were elevated in liver during freezing. One well-known role of Akt is in anti-apoptosis, mediated in part by Akt phosphorylation of Ser-256 on FOXO1. Freezing triggered an increase in liver phospho-FOXO1 Ser-256 content, suggesting that an important action of Akt may be apoptosis inhibition.

CONCLUSIONS

Akt activation in wood frog is stress and tissue specific, with multi-facet regulations (posttranslational and posttranscriptional) involved in supporting this specific signal transduction response.

GENERAL SIGNIFICANCE

This study implicates the Akt pathway in the metabolic reorganization of cellular metabolism in support of freezing survival.

Endogenous RNAi and adaptation to environment in C. elegans

The contributions of short RNAs to the control of repetitive elements are well documented in animals and plants. Here, the role of endogenous RNAi and AF10 homolog ZFP-1 in the adaptation of C. elegans to the environment is discussed. First, modulation of insulin signaling through regulation of transcription of the PDK-1 kinase (Mansisidor et al., PLoS Genetics, 2011) is reviewed. Second, an siRNA-based natural selection model is proposed in which variation in endogenous siRNA pools between individuals is subject to natural selection similarly to DNA-based genetic variation. The value of C. elegans for the research of siRNA-based epigenetic variation and adaptation is highlighted.