Regulation of late G1/S phase transition and APC Cdh1 by reactive oxygen species

The Role of Peroxiredoxins in the Transduction of H2O2 Signals

Hydrogen peroxide (H₂O₂) is produced on stimulation of many cell surface receptors and serves as an intracellular messenger in the regulation of diverse physiological events, mostly by oxidizing cysteine residues of effector proteins. Mammalian cells express multiple H₂O₂-eliminating enzymes, including catalase, glutathione peroxidase (GPx), and peroxiredoxin (Prx). A conserved cysteine in Prx family members is the site of oxidation by H₂O₂. Peroxiredoxins possess a high-affinity binding site for H₂O₂ that is lacking in catalase and GPx and which renders the catalytic cysteine highly susceptible to oxidation, with a rate constant several orders of magnitude greater than that for oxidation of cysteine in most H₂O₂ effector proteins. Moreover, Prxs are abundant and present in all subcellular compartments. The cysteines of most H₂O₂ effectors are therefore at a competitive disadvantage for reaction with H₂O₂. Recent Advances: Here we review intracellular sources of H₂O₂ as well as H₂O₂ target proteins classified according to biochemical and cellular function. We then highlight two strategies implemented by cells to overcome the kinetic disadvantage of most target proteins with regard to H₂O₂-mediated oxidation: transient inactivation of local Prx molecules via phosphorylation, and indirect oxidation of target cysteines via oxidized Prx. Critical Issues and Future Directions: Recent studies suggest that only a small fraction of the total pools of Prxs and H₂O₂ effector proteins localized in specific subcellular compartments participates in H₂O₂ signaling. Development of sensitive tools to selectively detect phosphorylated Prxs and oxidized effector proteins is needed to provide further insight into H₂O₂ signaling. Antioxid. Redox Signal. 28, 537-557.

Manganese oxide particles as cytoprotective, oxygen generating agents

Cell culture and cellular transplant therapies are adversely affected by oxidative species and radicals. Herein, we present the production of bioactive manganese oxide nanoparticles for the purpose of radical scavenging and cytoprotection. Manganese comprises the core active structure of somatic enzymes that perform the same function, in vivo. Formulated nanoparticles were characterized structurally and surveyed for maximal activity (superoxide scavenging, hydrogen peroxide scavenging with resultant oxygen generation) and minimal cytotoxicity (48-h direct exposure to titrated manganese oxide concentrations). Cytoprotective capacity was tested using cell exposure to hydrogen peroxide in the presence or absence of the nanoparticles. Several ideal compounds were manufactured and utilized that showed complete disproportionation of superoxide produced by the xanthine/xanthine oxidase reaction. Further, the nanoparticles showed catalase-like activity by completely converting hydrogen peroxide into the corresponding concentration of oxygen. Finally, the particles protected cells (murine β-cell insulinoma) against insult from hydrogen peroxide exposure. Based on these observed properties, these particles could be utilized to combat oxidative stress and inflammatory response in a variety of cell therapy applications.

STATEMENT OF SIGNIFICANCE

Maintaining viability once cells have been removed from their physiological niche, e.g. culture and transplant, demands proper control of critical variables such as oxygenation and removal of harmful substances e.g. reactive oxygen species. Limited catalysts can transform reactive oxygen species into molecular oxygen and, thereby, have the potential to maintain cell viability and function. Among these are manganese oxide particles which are the subject of this study.

New Challenges to Study Heterogeneity in Cancer Redox Metabolism

Reactive oxygen species (ROS) are important pathophysiological molecules involved in vital cellular processes. They are extremely harmful at high concentrations because they promote the generation of radicals and the oxidation of lipids, proteins, and nucleic acids, which can result in apoptosis. An imbalance of ROS and a disturbance of redox homeostasis are now recognized as a hallmark of complex diseases. Considering that ROS levels are significantly increased in cancer cells due to mitochondrial dysfunction, ROS metabolism has been targeted for the development of efficient treatment strategies, and antioxidants are used as potential chemotherapeutic drugs. However, initial ROS-focused clinical trials in which antioxidants were supplemented to patients provided inconsistent results, i.e., improved treatment or increased malignancy. These different outcomes may result from the highly heterogeneous redox responses of tumors in different patients. Hence, population-based treatment strategies are unsuitable and patient-tailored therapeutic approaches are required for the effective treatment of patients. Moreover, due to the crosstalk between ROS, reducing equivalents [e.g., NAD(P)H] and central metabolism, which is heterogeneous in cancer, finding the best therapeutic target requires the consideration of system-wide approaches that are capable of capturing the complex alterations observed in all of the associated pathways. Systems biology and engineering approaches may be employed to overcome these challenges, together with tools developed in personalized medicine. However, ROS- and redox-based therapies have yet to be addressed by these methodologies in the context of disease treatment. Here, we review the role of ROS and their coupled redox partners in tumorigenesis. Specifically, we highlight some of the challenges in understanding the role of hydrogen peroxide (H₂O₂), one of the most important ROS in pathophysiology in the progression of cancer. We also discuss its interplay with antioxidant defenses, such as the coupled peroxiredoxin/thioredoxin and glutathione/glutathione peroxidase systems, and its reducing equivalent metabolism. Finally, we highlight the need for system-level and patient-tailored approaches to clarify the roles of these systems and identify therapeutic targets through the use of the tools developed in personalized medicine.

APCCdh1 controls cell cycle entry during liver regeneration

Cdh1 is one of the two adaptor proteins of anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase controlling mitosis and DNA replication. To date, the in vivo functions of Cdh1 have not been fully explored. In order to characterize Cdh1 in liver regeneration, we generated a conditional knock-out mouse model. Our data showed that loss of Cdh1 leads to increased and extended S phase progression possibly due to the upregulation of cyclin D1. Moreover, the increased DNA replication resulted in activated DNA damage response. Interestingly, the final liver weight after partial hepatectomy in the Cdh1 depleted mice did not differ from that of the controls, implying that Cdh1 is not required for the competence of hepatocytes to regenerate itself.

Analysis of the mechanism of radiation-induced upregulation of mitochondrial abundance in mouse fibroblasts

Mitochondria strongly contribute to the maintenance of cellular integrity through various mechanisms, including oxidative adenosine triphosphate production and calcium homeostasis regulation. Therefore, proper regulation of the abundance, distribution and activity of mitochondria is crucial for the maintenance of cellular homeostasis. Previous studies have shown that ionizing radiation (IR) alters mitochondrial functions, suggesting that mitochondria are likely to be an important target of IR. Though IR reportedly influences cellular mitochondrial abundance, the mechanism remains largely unknown. In this study, we examined how IR influences mitochondrial abundance in mouse fibroblasts. When mouse NIH/3T3 cells were exposed to X-rays, a time-dependent increase was observed in mitochondrial DNA (mtDNA) and mitochondrial mass, indicating radiation-induced upregulation of mitochondrial abundance. Meanwhile, not only did we not observe a significant change in autophagic activity after irradiation, but in addition, IR hardly influenced the expression of two mitochondrial proteins, cytochrome c oxidase subunit IV and cytochrome c, or the mRNA expression of Polg, a component of DNA polymerase γ. We also observed that the expression of transcription factors involved in mitochondrial biogenesis was only marginally affected by IR. These data imply that radiation-induced upregulation of mitochondrial abundance is an event independent of macroautophagy and mitochondrial biogenesis. Furthermore, we found evidence that IR induced long-term cell cycle arrest and cellular senescence, indicating that these events are involved in regulating mitochondrial abundance. Considering the growing significance of mitochondria in cellular radioresponses, we believe the present study provides novel insights into understanding the effects of IR on mitochondria.

Bcl-2 delays cell cycle through mitochondrial ATP and ROS

Bcl-2 inhibits cell proliferation by delaying G₀/G₁ to S phase entry. We tested the hypothesis that Bcl-2 regulates S phase entry through mitochondrial pathways. Existing evidence indicates mitochondrial adenosine tri-phosphate (ATP) and reactive oxygen species (ROS) are important signals in cell survival and cell death, however, the molecular details of how these 2 processes are linked remain unknown. In this study, 2 cell lines stably expressing Bcl-2, 3T3Bcl-2 and C3HBcl-2, and vector-alone PB controls were arrested in G₀/G₁ phase by serum starvation and contact inhibition, and ATP and ROS were measured during re-stimulation of cell cycle entry. Both ATP and ROS levels were decreased in G₀/G₁ arrested cells compared with normal growing cells. In addition, ROS levels were significant lower in synchronized Bcl-2 cells than those in PB controls. After re-stimulation, ATP levels increased with time, reaching peak value 1-3 hours ahead of S phase entry for both Bcl-2 cells and PB controls. Consistent with 2 hours of S phase delay, Bcl-2 cells reached ATP peaks 2 hours later than PB control, which suggests a rise in ATP levels is required for S phase entry. To examine the role of ATP and ROS in cell cycle regulation, ATP and ROS level were changed. We observed that elevation of ATP accelerated cell cycle progression in both PB and Bcl-2 cells, and decrease of ATP and ROS to the level equivalent to Bcl-2 cells delayed S phase entry in PB cells. Our results support the hypothesis that Bcl-2 protein regulates mitochondrial metabolism to produce less ATP and ROS, which contributes to S phase entry delay in Bcl-2 cells. These findings reveal a novel mechanistic basis for understanding the link between mitochondrial metabolism and tumor-suppressive function of Bcl-2.

Irreversible APC(Cdh1) Inactivation Underlies the Point of No Return for Cell-Cycle Entry

Proliferating cells must cross a point of no return before they replicate their DNA and divide. This commitment decision plays a fundamental role in cancer and degenerative diseases and has been proposed to be mediated by phosphorylation of retinoblastoma (Rb) protein. Here, we show that inactivation of the anaphase-promoting complex/cyclosome (APC(Cdh1)) has the necessary characteristics to be the point of no return for cell-cycle entry. Our study shows that APC(Cdh1) inactivation is a rapid, bistable switch initiated shortly before the start of DNA replication by cyclin E/Cdk2 and made irreversible by Emi1. Exposure to stress between Rb phosphorylation and APC(Cdh1) inactivation, but not after APC(Cdh1) inactivation, reverted cells to a mitogen-sensitive quiescent state, from which they can later re-enter the cell cycle. Thus, APC(Cdh1) inactivation is the commitment point when cells lose the ability to return to quiescence and decide to progress through the cell cycle.

Sirtuin 3 Protects against Urban Particulate Matter-Induced Autophagy in Human Bronchial Epithelial Cells

Urban particulate matter (urban PM) is a heterogeneous mixture of various types of particles originating from different sources. Exposure to high concentrations of urban PM leading to adverse health effects is evaluated by using in vitro cultures of human lung epithelial cells. However, the mechanism underlying the correlation between high concentrations of urban PM exposure and adverse health effects has not been fully elucidated; urban PM-induced oxidative stress is considered as an important mechanism of urban PM-mediated cytotoxicity. Sirtuin 3 (SIRT3), a primary mitrochondrial deacetylase, controls cellular reactive oxygen species (ROS) production, and expression of antioxidant enzymes. In this study, we examined the role of SIRT3 in the regulation of urban PM-induced oxidative stress in normal primary human bronchial epithelial cells (HBEpiCs). Cell viability showed a time- and concentration-dependent decrease when exposed to urban PM, which could indicate that the amount of lactate dehydrogenase released from the cell in response to urban PM is related to cell viability in HBEpiC. The effects of urban PM on morphological and biochemical markers of autophagy in HBEpiC were analyzed by electron microscopy and Western blotting. Overexpression of SIRT3 inhibited urban PM-induced ROS generation, while concomitantly increasing the expression of antioxidant enzymes, and decreasing NF-κB activation and release of inflammation factors. Up-regulation of SIRT3 significantly inhibited the expression of autophagy markers and autophagic vacuole formation. Our findings provide a valuable insight into the potential role of the SIRT3 enzyme in regulating urban PM-induced autophagy by mediating urban PM-induced oxidative stress, which may contribute to urban PM-induced impairment of airway epithelial cell function.

Oxidative stress in psoriasis and potential therapeutic use of antioxidants

The pathophysiology of psoriasis is complex and dynamic. Recently, the involvement of oxidative stress in the pathogenesis of psoriasis has been proposed. Oxidative stress is an imbalance between oxidants and antioxidants in favor of the oxidants, leading to a disruption of redox signaling and control and/or molecular damage. In this article, the published studies on the role of oxidative stress in psoriasis pathogenesis are reviewed, focusing on the impacts of oxidative stress on dendritic cells, T lymphocytes, and keratinocytes, on angiogenesis and on inflammatory signaling (mitogen-activated protein kinase, nuclear factor-κB, and Janus kinase/signal transducer and activator of transcription). As there is compelling evidence that oxidative stress is involved in the pathogenesis of psoriasis, the possibility of using this information to develop novel strategies for treatment of patients with psoriasis is of considerable interest. In this article, we also review the published studies on treating psoriasis with antioxidants and drugs with antioxidant activity.

Mitochondrial Dysfunction in Alzheimer's Disease and the Rationale for Bioenergetics Based Therapies

Alzheimer’s disease (AD) is a debilitating neurodegenerative disorder characterized by the progressive loss of cholinergic neurons, leading to the onset of severe behavioral, motor and cognitive impairments. It is a pressing public health problem with no effective treatment. Existing therapies only provide symptomatic relief without being able to prevent, stop or reverse the pathologic process. While the molecular basis underlying this multifactorial neurodegenerative disorder remains a significant challenge, mitochondrial dysfunction appears to be a critical factor in the pathogenesis of this disease. It is therefore important to target mitochondrial dysfunction in the prodromal phase of AD to slow or prevent the neurodegenerative process and restore neuronal function. In this review, we discuss mechanisms of action and translational potential of current mitochondrial and bioenergetic therapeutics for AD including: mitochondrial enhancers to potentiate energy production; antioxidants to scavenge reactive oxygen species and reduce oxidative damage; glucose metabolism and substrate supply; and candidates that target apoptotic and mitophagy pathways to remove damaged mitochondria. While mitochondrial therapeutic strategies have shown promise at the preclinical stage, there has been little progress in clinical trials thus far.

Control of the pericentrosomal H2O2 level by peroxiredoxin I is critical for mitotic progression

Reversible oxidative inactivation of centrosome-bound protein phosphatases such as Cdc14B by H₂O₂ is likely responsible for the inhibition of Cdk1-opposing phosphatases during early mitosis, which prevents premature degradation of mitotic activators.

Proteins associated with the centrosome play key roles in mitotic progression in mammalian cells. The activity of Cdk1-opposing phosphatases at the centrosome must be inhibited during early mitosis to prevent premature dephosphorylation of Cdh1—an activator of the ubiquitin ligase anaphase-promoting complex/cyclosome—and the consequent premature degradation of mitotic activators. In this paper, we show that reversible oxidative inactivation of centrosome-bound protein phosphatases such as Cdc14B by H₂O₂ is likely responsible for this inhibition. The intracellular concentration of H₂O₂ increases as the cell cycle progresses. Whereas the centrosome is shielded from H₂O₂ through its association with the H₂O₂-eliminating enzyme peroxiredoxin I (PrxI) during interphase, the centrosome-associated PrxI is selectively inactivated through phosphorylation by Cdk1 during early mitosis, thereby exposing the centrosome to H₂O₂ and facilitating inactivation of centrosome-bound phosphatases. Dephosphorylation of PrxI by okadaic acid–sensitive phosphatases during late mitosis again shields the centrosome from H₂O₂ and thereby allows the reactivation of Cdk1-opposing phosphatases at the organelle.

Detection of reactive oxygen species during the cell cycle under normal culture conditions using a modified fixed-sample staining method

We developed an alternative method of simultaneously monitoring the generation of reactive oxygen species (ROS) and cellular oxidative responses using the oxidation-sensitive fluorescent probe dichlorofluorescein (DCF) in fixed samples. In this study, we evaluated the ability of this method to detect ROS generation during the cell cycle under normal culture conditions using flow cytometric analyses. Among the fixatives tested, only acetone and paraformaldehyde did not alter the endogenous oxidation of the responsive dye 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA), which is a chloromethyl derivative of H2DCFDA. Only acetone fixation followed by staining with propidium iodide was able to detect ROS generation during the cell cycle without altering DCF oxidation. Further thymidine treatment led to cell cycle arrest at the G1 phase followed by the downregulation of total intracellular ROS. Paraformaldehyde-based fixation enabled the evaluation of ROS generation by immunostaining at a different phase of the cell cycle, whereas MPM2 co-staining enabled identification of the specific mitotic phase. This study demonstrates a modified fixed-sample method that can be used to measure intracellular ROS production during the cell cycle using standard immunostaining techniques.

Reactive Oxygen Species Are Required for Human Mesenchymal Stem Cells to Initiate Proliferation after the Quiescence Exit

The present study focuses on the involvement of reactive oxygen species (ROS) in the process of mesenchymal stem cells “waking up” and entering the cell cycle after the quiescence. Using human endometrial mesenchymal stem cells (eMSCs), we showed that intracellular basal ROS level is positively correlated with the proliferative status of the cell cultures. Our experiments with the eMSCs synchronized in the G₀ phase of the cell cycle revealed a transient increase in the ROS level upon the quiescence exit after stimulation of the cell proliferation. This increase was registered before the eMSC entry to the S-phase of the cell cycle, and elimination of this increase by antioxidants (N-acetyl-L-cysteine, Tempol, and Resveratrol) blocked G₁–S-phase transition. Similarly, a cell cycle arrest which resulted from the antioxidant treatment was observed in the experiments with synchronized human mesenchymal stem cells derived from the adipose tissue. Thus, we showed that physiologically relevant level of ROS is required for the initiation of human mesenchymal stem cell proliferation and that low levels of ROS due to the antioxidant treatment can block the stem cell self-renewal.

Prognostic Value of FOXM1 in Patients with Malignant Solid Tumor: A Meta-Analysis and System Review

Forkhead box M1 (FOXM1), a member of the Fox transcription factors family, was closely related with cell cycle. FOXM1 played an important role in MST and prompted a poor prognosis for MST patients. However, there were also some studies revealing no significant association between the FOXM1 expression and prognosis of patients. Therefore, we conducted meta-analysis to investigate whether the expression of FOXM1 was associated with MST prognosis. We collected 36 relevant studies through PubMed database and obtained research data of 4946 patients. Stata 12.0 was used to express the results as hazard ratio (HR) for time-to-event outcomes with 95% confidence intervals (95% CI). It was shown that overexpression of FOXM1 was relevant to worse survival of MST patients (HR = 1.99, 95% CI = 1.79–2.21, P < 0.001; I² = 26.4%, P_h = 0.076). Subgroup analysis suggested that overexpression of FOXM1 in breast cancer (BC), gastric cancer (GC), hepatocellular carcinoma (HCC), pancreatic ductal adenocarcinoma (PDA), and non-small-cell lung cancer (NSCLC) all predicted a worse survival (P < 0.05), in addition to ovarian cancer (OC) (P = 0.084). In conclusion, our research indicated that overexpression of FOXM1 was to the disadvantage of the prognosis for majority of MST and therefore can be used as an evaluation index of prognosis.

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

Osteogenic differentiation of human mesenchymal stem cells in freeze-gelled chitosan/nano β-tricalcium phosphate porous scaffolds crosslinked with genipin

The objective of this work was to investigate material properties and osteogenic differentiation of human mesenchymal stem cells (hMSCs) in genipin (GN) crosslinked chitosan/nano β-tricalcium phosphate (CS/nano β-TCP) scaffolds, and compare the results with tripolyphosphate (TPP) crosslinked scaffolds. Porous crosslinked CS/nano β-TCP scaffolds were produced by freeze-gelation using GN (CBG scaffold) and TPP (CBT scaffold) as crosslinkers. The prepared CBT and CBG scaffolds were characterized with respect to porosity, pore size, water content, wettability, compressive strength, mass loss, and osteogenic differentiation of hMSCs. All scaffolds displayed interconnected honeycomb-like microstructures. There was a significant difference between the average pore size, porosity, contact angle, and percent swelling of CBT and CBG scaffolds. The average pore size of CBG scaffolds was higher than CBT, the porosity of CBG was lower than CBT, the water contact angle of CBG was higher than CBT, and the percent swelling of CBG was lower than CBT. At a given crosslinker concentration, there was not a significant difference in compressive modulus and mass loss of CBG and CBT scaffolds. Metabolic activity of hMSCs seeded in CBG scaffolds was slightly higher than CBT. Furthermore, CBG scaffolds displayed slightly higher extent of mineralization after 21 days of incubation in osteogenic medium compared to CBT.

PSMB4 promotes multiple myeloma cell growth by activating NF-κB-miR-21 signaling

Proteasomal subunit PSMB4, was recently identified as potential cancer driver genes in several tumors. However, the regulatory mechanism of PSMB4 on carcinogenesis process remains unclear. In this study, we investigated the expression and roles of PSMB4 in multiple myeloma (MM). We found a significant up-regulation of PSMB4 in MM plasma and cell lines. Ectopic overexpression of PSMB4 promoted cell growth and colony forming ability of MM cells, whereas inhibition of PSMB4 led to a decrease of such events. Furthermore, our results demonstrated the up-regulation of miR-21 and a positive correlation between the levels of miR-21 and PSMB4 in MM. Re-expression of miR-21 markedly rescued PSMB4 knockdown-mediated suppression of cell proliferation and clone-formation. Additionally, while enforced expression of PSMB4 profoundly increased NF-κB activity and the level of miR-21, PSMB4 knockdown or NF-κB inhibition suppressed miR-21 expression in MM cells. Taken together, our results demonstrated that PSMB4 regulated MM cell growth in part by activating NF-κB-miR-21 signaling, which may represent promising targets for novel specific therapies.

Chloride channels in cancer: Focus on chloride intracellular channel 1 and 4 (CLIC1 AND CLIC4) proteins in tumor development and as novel therapeutic targets

In recent decades, growing scientific evidence supports the role of ion channels in the development of different cancers. Both potassium selective pores and chloride permeabilities are considered the most active channels during tumorigenesis. High rate of proliferation, active migration, and invasiveness into non-neoplastic tissues are specific properties of neoplastic transformation. All these actions require partial or total involvement of chloride channel activity. In this context, this class of membrane proteins could represent valuable therapeutic targets for the treatment of resistant tumors. However, this encouraging premise has not so far produced any valid new channel-targeted antitumoral molecule for cancer treatment. Problematic for drug design targeting ion channels is their vital role in normal cells for essential physiological functions. By targeting these membrane proteins involved in pathological conditions, it is inevitable to cause relevant side effects in healthy organs. In light of this, a new protein family, the chloride intracellular channels (CLICs), could be a promising class of therapeutic targets for its intrinsic individualities: CLIC1 and CLIC4, in particular, not only are overexpressed in specific tumor types or their corresponding stroma but also change localization and function from hydrophilic cytosolic to integral transmembrane proteins as active ionic channels or signal transducers during cell cycle progression in certain cases. These changes in intracellular localization, tissue compartments, and channel function, uniquely associated with malignant transformation, may offer a unique target for cancer therapy, likely able to spare normal cells. This article is part of a special issue itled "Membrane Channels and Transporters in Cancers."

Thymosin beta-4 knockdown in IEC-6 normal intestinal epithelial cells induces DNA re-replication via downregulating Emi1

Thymosin β4 (Tβ4 ) is a multifunctional protein already used clinically to treat various diseases; however, the promoting effect of this protein on tumor malignancy should not be neglected. Here, we assessed whether Tβ4 alteration influences normal intestinal epithelial cells because Tβ4 is deemed a novel target for treating colorectal cancer (CRC). For this purpose, we examined the consequences of shRNA-mediated knockdown of Tβ4 in IEC-6 normal rat small intestinal cells and found that inhibiting Tβ4 expression significantly suppressed their growth and induced apoptosis in some cells. Flow cytometric analysis further revealed a marked decrease of G0/G1 population but a drastic increase of polyploid ones in these cells. The increase of polyploidy likely resulted from DNA re-replication because not only the de novo DNA synthesis was greatly increased but also the expression levels of Cdc6 (a replication-licensing factor), cyclin A, and phosphorylated-checkpoint kinase 1 were all dramatically elevated. Moreover, marked reductions in both RNA and protein levels of Emi1 (early mitotic inhibitor 1) were also detected in Tβ4 -downregulated IEC-6 cells which might be accounted by the downregulation of E2F1, a transcription factor capable of inducing Emi1 expression, mediated by glycogen synthase-3β (GSK-3β). To our best knowledge, this is the first report showing that inhibiting Tβ4 expression triggers DNA re-replication in normal intestinal epithelial cells, suggesting that this G-actin sequester may play a crucial role in maintaining genome stability in these cells. More importantly, clinical oncologists should take this novel activity into consideration when design CRC therapy based on targeting Tβ4 .

p53 as a retrovirus-induced oxidative stress modulator

Infection of astrocytes by the neuropathogenic mutant of Moloney murine leukemia virus, ts1, exhibits increased levels of reactive oxygen species (ROS) and signs of oxidative stress compared with uninfected astrocytes. Previously, we have demonstrated that ts1 infection caused two separate events of ROS upregulation. The first upregulation occurs during early viral establishment in host cells and the second during the virus-mediated apoptotic process. In this study, we show that virus-mediated ROS upregulation activates the protein kinase, ataxia telangiectasia mutated, which in turn phosphorylates serine 15 on p53. This activation of p53 however, is unlikely associated with ts1-induced cell death. Rather p53 appears to be involved in suppressing intracellular ROS levels in astrocytes under oxidative stress. The activated p53 appears to delay retroviral gene expression by suppressing NADPH oxidase, a superoxide-producing enzyme. These results suggest that p53 plays a role as a retrovirus-mediated oxidative stress modulator.

STRESS-responsive deacetylase SIRT3 is up-regulated by areca nut extract-induced oxidative stress in human oral keratinocytes

Areca chewing is an important environmental risk factor for development of oral premalignant lesions and cancer. Epidemiological evidence indicates that areca chewing is tightly linked to oral carcinogenesis. However, the pathogenetic impacts of areca nut extract (ANE) on normal human oral keratinocytes (HOKs) are unclear and possibly involve oxidative stress via redox imbalance. Sirtuin 3 (SIRT3) is a member of the sirtuin family of proteins that play an important role in regulating cellular reactive oxygen species (ROS) production. Recent studies have confirmed that ANE and other areca ingredients can induce ROS. In this study, we examined the role of SIRT3 in the regulation of ANE-induced ROS in HOK cells. We examined HOK cell viability following treatment with various ANE concentrations. ANE-induced cytotoxicity increased in a dose-dependent manner and was approximately 48% at a concentration of 50 μg/ml after 24 h. SIRT3 expression and enzyme activity were up-regulated in HOK cells by ANE-induced oxidative stress. Additionally, we identified that SIRT3 controls the enzymatic activity of mitochondrial proteins, such as forkhead box O3a (Foxo3a) transcription factor and antioxidant-encoding gene superoxide dismutase 2 (SOD2), by deacetylation in HOK cells. Moreover, SIRT3-mediated deacetylation and activation of Foxo3a promotes nuclear localization in vivo. These findings suggest that SIRT3 is an endogenous negative regulator in response to ANE-induced oxidative stress and demonstrate an essential role for redox balance in HOK cells.

Resveratrol inhibits estrogen-induced breast carcinogenesis through induction of NRF2-mediated protective pathways

The importance of estrogens in the etiology of breast cancer is widely recognized. Estrogen-induced oxidative stress has been implicated in this carcinogenic process. Resveratrol (Res), a natural antioxidant phytoestrogen has chemopreventive effects against a variety of illnesses including cancer. The objective of the present study was to characterize the mechanism(s) of Res-mediated protection against estrogen-induced breast carcinogenesis. Female August Copenhagen Irish rats were treated with 17β-estradiol (E2), Res and Res + E2 for 8 months. Cotreatment of rats with Res and E2 inhibited E2-mediated proliferative changes in mammary tissues and significantly increased tumor latency and reduced E2-induced breast tumor development. Resveratrol treatment alone or in combination with E2 significantly upregulated expression of nuclear factor erythroid 2-related factor 2 (NRF2) in mammary tissues. Expression of NRF2-regulated antioxidant genes NQO1, SOD3 and OGG1 that are involved in protection against oxidative DNA damage was increased in Res- and Res + E2-treated mammary tissues. Resveratrol also prevented E2-mediated inhibition of detoxification genes AOX1 and FMO1. Inhibition of E2-mediated alterations in NRF2 promoter methylation and expression of NRF2 targeting miR-93 after Res treatment indicated Res-mediated epigenetic regulation of NRF2 during E2-induced breast carcinogenesis. Resveratrol treatment also induced apoptosis and inhibited E2-mediated increase in DNA damage in mammary tissues. Increased apoptosis and decreased DNA damage, cell migration, colony and mammosphere formation in Res- and Res + E2-treated MCF-10A cells suggested a protective role of Res against E2-induced mammary carcinogenesis. Small-interfering RNA-mediated silencing of NRF2 inhibited Res-mediated preventive effects on the colony and mammosphere formation. Taken together, these results suggest that Res inhibits E2-induced breast carcinogenesis via induction of NRF2-mediated protective pathways.

Mitochondrial dysfunction in cancer

A mechanistic understanding of how mitochondrial dysfunction contributes to cell growth and tumorigenesis is emerging beyond Warburg as an area of research that is under-explored in terms of its significance for clinical management of cancer. Work discussed in this review focuses less on the Warburg effect and more on mitochondria and how dysfunctional mitochondria modulate cell cycle, gene expression, metabolism, cell viability, and other established aspects of cell growth and stress responses. There is increasing evidence that key oncogenes and tumor suppressors modulate mitochondrial dynamics through important signaling pathways and that mitochondrial mass and function vary between tumors and individuals but the significance of these events for cancer are not fully appreciated. We explore the interplay between key molecules involved in mitochondrial fission and fusion and in apoptosis, as well as in mitophagy, biogenesis, and spatial dynamics of mitochondria and consider how these distinct mechanisms are coordinated in response to physiological stresses such as hypoxia and nutrient deprivation. Importantly, we examine how deregulation of these processes in cancer has knock on effects for cell proliferation and growth. We define major forms of mitochondrial dysfunction and address the extent to which the functional consequences of such dysfunction can be determined and exploited for cancer diagnosis and treatment.

Lysine metabolism in mammalian brain: an update on the importance of recent discoveries

The lysine catabolism pathway differs in adult mammalian brain from that in extracerebral tissues. The saccharopine pathway is the predominant lysine degradative pathway in extracerebral tissues, whereas the pipecolate pathway predominates in adult brain. The two pathways converge at the level of ∆(1)-piperideine-6-carboxylate (P6C), which is in equilibrium with its open-chain aldehyde form, namely, α-aminoadipate δ-semialdehyde (AAS). A unique feature of the pipecolate pathway is the formation of the cyclic ketimine intermediate ∆(1)-piperideine-2-carboxylate (P2C) and its reduced metabolite L-pipecolate. A cerebral ketimine reductase (KR) has recently been identified that catalyzes the reduction of P2C to L-pipecolate. The discovery that this KR, which is capable of reducing not only P2C but also other cyclic imines, is identical to a previously well-described thyroid hormone-binding protein [μ-crystallin (CRYM)], may hold the key to understanding the biological relevance of the pipecolate pathway and its importance in the brain. The finding that the KR activity of CRYM is strongly inhibited by the thyroid hormone 3,5,3'-triiodothyronine (T3) has far-reaching biomedical and clinical implications. The inter-relationship between tryptophan and lysine catabolic pathways is discussed in the context of shared degradative enzymes and also potential regulation by thyroid hormones. This review traces the discoveries of enzymes involved in lysine metabolism in mammalian brain. However, there still remain unanswered questions as regards the importance of the pipecolate pathway in normal or diseased brain, including the nature of the first step in the pathway and the relationship of the pipecolate pathway to the tryptophan degradation pathway.

ALDH7A1 expression is associated with recurrence in patients with surgically resected non-small-cell lung carcinoma

AIM

The purpose of this study was to describe the prognostic significance of ALDH7A1 in surgically treated non-small-cell lung carcinoma. (NSCLC).

MATERIALS & METHODS

We immunohistochemically analyzed ALDH7A1 expression in surgically resected NSCLC from 89 patients using a tissue microarray.

RESULTS

ALDH7A1 staining was positive in 43 patients and negative in 44 patients, with two tumor sections missing. For stage I NSCLC patients, ALDH7A1 positivity was associated with decreased recurrence-free and overall survival. Multivariate analysis demonstrated that ALDH7A1-expressing NSCLC tumors had a significantly higher incidence of lung cancer recurrence compared with patients with ALDH7A1-negative tumors, although there was no association with overall survival.

CONCLUSION

For patients with NSCLC, low ALDH7A1 expression was associated with a decreased incidence of cancer recurrence. Specifically in stage I patients, negative staining for ALDH7A1 was associated with improved recurrence-free and overall survival, suggesting a predictive role in surgically treated patients.

Interferon regulatory factor-1 together with reactive oxygen species promotes the acceleration of cell cycle progression by up-regulating the cyclin E and CDK2 genes during high glucose-induced proliferation of vascular smooth muscle cells

Background

The high glucose-induced proliferation of vascular smooth muscle cells (VSMCs) plays an important role in the development of diabetic vascular diseases. In a previous study, we confirmed that Interferon regulatory factor-1 (Irf-1) is a positive regulator of the high glucose-induced proliferation of VSMCs. However, the mechanisms remain to be determined.

Methods

The levels of cyclin/CDK expression in two cell models involving Irf-1 knockdown and overexpression were quantified to explore the relationship between Irf-1 and its downstream effectors under normal or high glucose conditions. Subsequently, cells were treated with high glucose/NAC, normal glucose/H₂O₂, high glucose/U0126 or normal glucose/H₂O₂/U0126 during an incubation period. Then proliferation, cyclin/CDK expression and cell cycle distribution assays were performed to determine whether ROS/Erk1/2 signaling pathway was involved in the Irf-1-induced regulation of VSMC growth under high glucose conditions.

Results

We found that Irf-1 overexpression led to down-regulation of cyclin D1/CDK4 and inhibited cell cycle progression in VSMCs under normal glucose conditions. In high glucose conditions, Irf-1 overexpression led to an up-regulation of cyclin E/CDK2 and an acceleration of cell cycle progression, whereas silencing of Irf-1 suppressed the expression of both proteins and inhibited the cell cycle during the high glucose-induced proliferation of VSMCs. Treatment of VSMCs with antioxidants prevented the Irf-1 overexpression-induced proliferation of VSMCs, the up-regulation of cyclin E/CDK2 and the acceleration of cell cycle progression in high glucose conditions. In contrast, under normal glucose conditions, H₂O₂ stimulation and Irf-1 overexpression induced cell proliferation, up-regulated cyclin E/CDK2 expression and promoted cell cycle acceleration. In addition, overexpression of Irf-1 promoted the activation of Erk1/2 and when VSMCs overexpressing Irf-1 were treated with U0126, the specific Erk1/2 inhibitor abolished the proliferation of VSMCs, the up-regulation of cyclin E/CDK2 and the acceleration of cell cycle progression under high glucose or normal glucose/H₂O₂ conditions.

Conclusions

These results demonstrate that the downstream effectors of Irf-1 are cyclin E/CDK2 during the high glucose-induced proliferation of VSMCs, whereas they are cyclin D1/CDK4 in normal glucose conditions. The Irf-1 overexpression-induced proliferation of VSMCs, the up-regulation of cyclin E/CDK2 and the acceleration of cell cycle progression are associated with ROS/Erk1/2 signaling pathway under high glucose conditions.

Lipid-induced toxicity stimulates hepatocytes to release angiogenic microparticles that require Vanin-1 for uptake by endothelial cells

Angiogenesis is a key pathological feature of experimental and human steatohepatitis, a common chronic liver disease that is associated with obesity. We demonstrated that hepatocytes generated a type of membrane-bound vesicle, microparticles, in response to conditions that mimicked the lipid accumulation that occurs in the liver in some forms of steatohepatitis and that these microparticles promoted angiogenesis. When applied to an endothelial cell line, medium conditioned by murine hepatocytes or a human hepatocyte cell line exposed to saturated free fatty acids induced migration and tube formation, two processes required for angiogenesis. Medium from hepatocytes in which caspase 3 was inhibited or medium in which the microparticles were removed by ultracentrifugation lacked proangiogenic activity. Isolated hepatocyte-derived microparticles induced migration and tube formation of an endothelial cell line in vitro and angiogenesis in mice, processes that depended on internalization of microparticles. Microparticle internalization required the interaction of the ectoenzyme Vanin-1 (VNN1), an abundant surface protein on the microparticles, with lipid raft domains of endothelial cells. Large quantities of hepatocyte-derived microparticles were detected in the blood of mice with diet-induced steatohepatitis, and microparticle quantity correlated with disease severity. Genetic ablation of caspase 3 or RNA interference directed against VNN1 protected mice from steatohepatitis-induced pathological angiogenesis in the liver and resulted in a loss of the proangiogenic effects of microparticles. Our data identify hepatocyte-derived microparticles as critical signals that contribute to angiogenesis and liver damage in steatohepatitis and suggest a therapeutic target for this condition.

Lysine metabolism in mammalian brain: an update on the importance of recent discoveries

The lysine catabolism pathway differs in adult mammalian brain from that in extracerebral tissues. The saccharopine pathway is the predominant lysine degradative pathway in extracerebral tissues, whereas the pipecolate pathway predominates in adult brain. The two pathways converge at the level of ∆(1)-piperideine-6-carboxylate (P6C), which is in equilibrium with its open-chain aldehyde form, namely, α-aminoadipate δ-semialdehyde (AAS). A unique feature of the pipecolate pathway is the formation of the cyclic ketimine intermediate ∆(1)-piperideine-2-carboxylate (P2C) and its reduced metabolite L-pipecolate. A cerebral ketimine reductase (KR) has recently been identified that catalyzes the reduction of P2C to L-pipecolate. The discovery that this KR, which is capable of reducing not only P2C but also other cyclic imines, is identical to a previously well-described thyroid hormone-binding protein [μ-crystallin (CRYM)], may hold the key to understanding the biological relevance of the pipecolate pathway and its importance in the brain. The finding that the KR activity of CRYM is strongly inhibited by the thyroid hormone 3,5,3'-triiodothyronine (T3) has far-reaching biomedical and clinical implications. The inter-relationship between tryptophan and lysine catabolic pathways is discussed in the context of shared degradative enzymes and also potential regulation by thyroid hormones. This review traces the discoveries of enzymes involved in lysine metabolism in mammalian brain. However, there still remain unanswered questions as regards the importance of the pipecolate pathway in normal or diseased brain, including the nature of the first step in the pathway and the relationship of the pipecolate pathway to the tryptophan degradation pathway.

Mitochondrial fission-fusion as an emerging key regulator of cell proliferation and differentiation

Mitochondrial shape change, brought about by molecules that promote either fission or fusion between individual mitochondria, has been documented in several model systems. However, the deeper significance of mitochondrial shape change has only recently begun to emerge: among others, it appears to play a role in the regulation of cell proliferation. Here, I review the emerging interplay between mitochondrial fission-fusion components with cell cycle regulatory machineries and how that may impact cell differentiation. Regulation of mitochondrial shape may modulate mitochondrial metabolism and/or energetics to promote crosstalk between signaling components and the cell cycle machinery. Focused research in this area will reveal the exact role of mitochondria in development and disease, specifically in stem cell regulation and tumorigenesis. Such research may also reveal whether and how the endosymbiotic event that gave rise to the mitochondrion was crucial for the evolution of cell cycle regulatory mechanisms in eukaryotes that are absent in prokaryotes.

Induction of a tumor-associated activating mutation in protein tyrosine phosphatase Ptpn11 (Shp2) enhances mitochondrial metabolism, leading to oxidative stress and senescence

Activating mutations in Ptpn11 (Shp2), a protein tyrosine phosphatase involved in diverse cell signaling pathways, are associated with pediatric leukemias and solid tumors. However, the pathogenic effects of these mutations have not been fully characterized. Here, we report that induction of the Ptpn11(E76K/+) mutation, the most common and active Ptpn11 mutation found in leukemias and solid tumors, in primary mouse embryonic fibroblasts resulted in proliferative arrest and premature senescence. As a result, apoptosis was markedly increased. These cellular responses were accompanied and mediated by up-regulation of p53 and p21. Moreover, intracellular levels of reactive oxygen species (ROS), byproducts of mitochondrial oxidative phosphorylation, were elevated in Ptpn11(E76K/+) cells. Since Shp2 is also distributed to the mitochondria (in addition to the cytosol), the impact of the Ptpn11(E76K/+) mutation on mitochondrial function was analyzed. These analyses revealed that oxygen consumption of Ptpn11(E76K/+) cells and the respiratory function of Ptpn11(E76K/+) mitochondria were significantly increased. Furthermore, we found that phosphorylation of mitochondrial Stat3, one of the substrates of Shp2 phosphatase, was greatly decreased in the mutant cells with the activating mutation Ptpn11(E76K/+). This study provides novel insights into the initial effects of tumor-associated Ptpn11 mutations.

ROS-mediated platelet generation: a microenvironment-dependent manner for megakaryocyte proliferation, differentiation, and maturation

Platelets have an important role in the body because of their manifold functions in haemostasis, thrombosis, and inflammation. Platelets are produced by megakaryocytes (MKs) that are differentiated from haematopoietic stem cells via several consecutive stages, including MK lineage commitment, MK progenitor proliferation, MK differentiation and maturation, cell apoptosis, and platelet release. During differentiation, the cells migrate from the osteoblastic niche to the vascular niche in the bone marrow, which is accompanied by reactive oxygen species (ROS)-dependent oxidation state changes in the microenvironment, suggesting that ROS can distinctly influence platelet generation and function in a microenvironment-dependent manner. The objective of this review is to reveal the role of ROS in regulating MK proliferation, differentiation, maturation, and platelet activation, thereby providing new insight into the mechanism of platelet generation, which may lead to the development of new therapeutic agents for thrombocytopenia and/or thrombosis.

Effects of iodonium-class flavin dehydrogenase inhibitors on growth, reactive oxygen production, cell cycle progression, NADPH oxidase 1 levels, and gene expression in human colon cancer cells and xenografts

Iodonium-class flavoprotein dehydrogenase inhibitors have been demonstrated to possess antiproliferative potential and to inhibit reactive oxygen production in human tumor cells, although the mechanism(s) that explains the relationship between altered cell growth and the generation of reactive oxygen species (ROS) remains an area of active investigation. Because of the ability of these compounds to inhibit the activity of flavoprotein-containing epithelial NADPH oxidases, we chose to examine the effects of several iodonium-class flavoprotein inhibitors on human colon cancer cell lines that express high, functional levels of a single such oxidase (NADPH oxidase 1, or Nox1). We found that diphenyleneiodonium (DPI), di-2-thienyliodonium (DTI), and iodonium diphenyl inhibited the growth of Caco2, HT-29, and LS-174T colon cancer cells at concentrations (10-250nM for DPI, 0.5-2.5μM for DTI, and 155nM to 10μM for iodonium diphenyl) substantially lower than needed for DU145 human prostate cancer cells, which do not possess functional NADPH oxidase activity. Drug treatment was associated with decreased H2O2 production and diminished intracellular ROS levels, lasting up to 24h, after short-term (1-h) exposure to the iodonium analogs. Decreased tumor cell proliferation was caused, in part, by a profound block in cell cycle progression at the G1/S interface in both LS-174T and HT-29 cells exposed to either DPI or DTI; and the G1 block was produced, for LS-174T cells, by upregulation of p27 and a drug concentration-related decrease in the expression of cyclins D1, A, and E that was partially prevented by exogenous H2O2. Not only did DPI and DTI decrease intracellular ROS, they both also significantly decreased the mRNA expression levels of Nox1, potentially contributing to the prolonged reduction in tumor cell reactive oxygen levels. We also found that DPI and DTI significantly decreased the growth of both HT-29 and LS-174T human tumor xenografts, at dose levels that produced peak plasma concentrations similar to those utilized for our in vitro experiments. These findings suggest that iodonium analogs have therapeutic potential for NADPH oxidase-containing human colon cancers in vivo and that at least part of their antineoplastic mechanism of action may be related to targeting Nox1.

Oxidative DNA damage and inflammatory responses in cultured human cells and in humans exposed to traffic-related particles

Particulate pollution is a major public health concern because epidemiological studies have demonstrated that exposure to particles is associated with respiratory diseases and lung cancer. Diesel exhaust particles (DEP), which is classified as a human carcinogen (IARC, 2012), are considered a major contributor to traffic-related particulate matter (PM) in urban areas. DEP consists of various compounds, including PAHs and metals which are the principal components that contribute to the toxicity of PM. The present study aimed to investigate effects of PM on induction of oxidative DNA damage and inflammation by using lymphocytes in vitro and in human exposed to PM in the environment. Human lymphoblasts (RPMI 1788) were treated with DEP (SRM 2975) at various concentrations (25-100 μg/ml) to compare the extent of responses with alveolar epithelial cells (A549). ROS generation was determined in each cell cycle phase of DEP-treated cells in order to investigate the influence of the cell cycle stage on induction of oxidative stress. The oxidative DNA damage was determined by measurement of 8-hydroxy-deoxyguanosine (8-OHdG) whereas the inflammatory responses were determined by mRNA expression of interleukin-6 and -8 (IL-6 and IL-8), Clara cell protein (CC16), and lung surfactant protein-A (SP-A). The results showed that RPMI 1788 and A549 cells had a similar pattern of dose-dependent responses to DEP in terms of particle uptake, ROS generation with highest level found in G2/M phase, 8-OHdG formation, and induction of IL-6 and IL-8 expression. The human study was conducted in 51 healthy subjects residing in traffic-congested areas. The effects of exposure to PM2.5 and particle-bound PAHs and toxic metals on the levels of 8-OHdG in lymphocyte DNA, IL-8 expression in lymphocytes, and serum CC16 were evaluated. 8-OHdG levels correlated with the exposure levels of PM2.5 (P<0.01) and PAHs (P<0.05), but this was not the case with IL-8. Serum CC16 showed significantly negative correlations with B[a]P equivalent (P<0.05) levels, but positive correlation with Pb (P<0.05). In conclusion, a similar pattern of the dose-dependent responses to DEP in the lymphoblasts and lung cells suggests that circulating lymphocytes could be used as a surrogate for assessing PM-induced oxidative DNA damage and inflammatory responses in the lung. Human exposure to PM leads to oxidative DNA damage whereas PM-induced inflammation was not conclusive and should be further investigated.

MicroRNA-93 regulates NRF2 expression and is associated with breast carcinogenesis

MicroRNAs (miRNA) are small non-coding RNAs that regulate the expression of approximately 60% of all human genes and play important roles in disease processes. Recent studies have demonstrated a link between dysregulated expression of miRNAs and breast carcinogenesis. Long-term estrogen exposure is implicated in development of human breast cancers, yet underlying mechanisms remain elusive. We have recently demonstrated that antioxidant vitamin C (vit C) prevents estrogen-induced breast tumor development. In this study, we investigated the role of vit C in the regulation of microRNA-93 (miR-93) and its target gene(s) in a rat model of mammary carcinogenesis. Female August Copenhagen Irish (ACI) rats were treated with vit C in the presence or absence of 17β-estradiol (E2) for 8 months. We demonstrate an increased expression of the miR-93 in E2-treated mammary tissues and in human breast cell lines and vit C treatment reverted E2-mediated increase in miR-93 levels. MiRNA target prediction programs suggest one of the target genes of miR-93 to be nuclear factor erythroid 2-related factor 2 (NRF2). In contrast with miR-93 expression, NRF2 protein expression was significantly decreased in E2-treated mammary tissues, mammary tumors, and in breast cancer cell lines, and its expression was significantly increased after vit C treatment. Ectopic expression of miR-93 decreased protein expression of NRF2 and NRF2-regulated genes. Furthermore, miR-93 decreased apoptosis, increased colony formation, mammosphere formation, cell migration and DNA damage in breast epithelial cells, whereas silencing of miR-93 in these cells inhibited these carcinogenic processes. Taken together, our findings suggest an oncogenic potential of miR-93 during E2-induced breast carcinogenesis.

Integrated metabolomics and genomics analysis provides new insights into the fiber elongation process in Ligon lintless-2 mutant cotton (Gossypium hirsutum L.)

BACKGROUND

The length of cotton fiber is an important agronomic trait characteristic that directly affects the quality of yarn and fabric. The cotton (Gossypium hirsutum L.) fiber mutation, Ligon lintless-2, is controlled by a single dominant gene (Li(2)) and results in extremely shortened lint fibers on mature seeds with no visible pleiotropic effects on vegetative growth and development. The Li(2) mutant phenotype provides an ideal model system to study fiber elongation. To understand metabolic processes involved in cotton fiber elongation, changes in metabolites and transcripts in the Li(2) mutant fibers were compared to wild-type fibers during development.

RESULTS

Principal component analysis of metabolites from GC-MS data separated Li(2) mutant fiber samples from WT fiber samples at the WT elongation stage, indicating that the Li(2) mutation altered the metabolome of the mutant fibers. The observed alterations in the Li(2) metabolome included significant reductions in the levels of detected free sugars, sugar alcohols, sugar acids, and sugar phosphates. Biological processes associated with carbohydrate biosynthesis, cell wall loosening, and cytoskeleton were also down-regulated in Li(2) fibers. Gamma-aminobutyric acid, known as a signaling factor in many organisms, was significantly elevated in mutant fibers. Higher accumulation of 2-ketoglutarate, succinate, and malate suggested higher nitrate assimilation in the Li(2) line. Transcriptional activation of genes involved in nitrogen compound metabolism along with changes in the levels of nitrogen transport amino acids suggested re-direction of carbon flow into nitrogen metabolism in Li(2) mutant fibers.

CONCLUSIONS

This report provides the first comprehensive analysis of metabolite and transcript changes in response to the Li(2) mutation in elongating fibers. A number of factors associated with cell elongation found in this study will facilitate further research in understanding metabolic processes of cotton fiber elongation.

Targeting cell cycle regulation in cancer therapy

Cell proliferation is an essential mechanism for growth, development and regeneration of eukaryotic organisms; however, it is also the cause of one of the most devastating diseases of our era: cancer. Given the relevance of the processes in which cell proliferation is involved, its regulation is of paramount importance for multicellular organisms. Cell division is orchestrated by a complex network of interactions between proteins, metabolism and microenvironment including several signaling pathways and mechanisms of control aiming to enable cell proliferation only in response to specific stimuli and under adequate conditions. Three main players have been identified in the coordinated variation of the many molecules that play a role in cell cycle: i) The cell cycle protein machinery including cyclin-dependent kinases (CDK)-cyclin complexes and related kinases, ii) The metabolic enzymes and related metabolites and iii) The reactive-oxygen species (ROS) and cellular redox status. The role of these key players and the interaction between oscillatory and non-oscillatory species have proved essential for driving the cell cycle. Moreover, cancer development has been associated to defects in all of them. Here, we provide an overview on the role of CDK-cyclin complexes, metabolic adaptations and oxidative stress in regulating progression through each cell cycle phase and transitions between them. Thus, new approaches for the design of innovative cancer therapies targeting crosstalk between cell cycle simultaneous events are proposed.

Increased proliferative cells in the medullary thick ascending limb of the loop of Henle in the Dahl salt-sensitive rat

Studies of transcriptome profiles have provided new insights into mechanisms underlying the development of hypertension. Cell type heterogeneity in tissue samples, however, has been a significant hindrance in these studies. We performed a transcriptome analysis in medullary thick ascending limbs of the loop of Henle isolated from Dahl salt-sensitive rats. Genes differentially expressed between Dahl salt-sensitive rats and salt-insensitive consomic SS.13(BN) rats on either 0.4% or 7 days of 8.0% NaCl diet (n=4) were highly enriched for genes located on chromosome 13, the chromosome substituted in the SS.13(BN) rat. A pathway involving cell proliferation and cell cycle regulation was identified as one of the most highly ranked pathways based on differentially expressed genes and by a Bayesian model analysis. Immunofluorescent analysis indicated that just 1 week of a high-salt diet resulted in a severalfold increase in proliferative medullary thick ascending limb cells in both rat strains, and that Dahl salt-sensitive rats exhibited a significantly greater proportion of medullary thick ascending limb cells in a proliferative state than in SS.13(BN) rats (15.0±1.4% versus 10.1±0.6%; n=7-9; P<0.05). The total number of cells per medullary thick ascending limb section analyzed was not different between the 2 strains. The study revealed alterations in regulatory pathways in Dahl salt-sensitive rats in tissues highly enriched for a single cell type, leading to the unexpected finding of a greater increase in the number of proliferative medullary thick ascending limb cells in Dahl salt-sensitive rats on a high-salt diet.

Oxidases and reactive oxygen species during hematopoiesis: a focus on megakaryocytes

Reactive oxygen species (ROS), generated as a result of various reactions, control an array of cellular processes. The role of ROS during megakaryocyte (MK) development has been a subject of interest and research. The bone marrow niche is a site of MK differentiation and maturation. In this environment, a gradient of oxygen tension, from normoxia to hypoxia results in different levels of ROS, impacting cellular physiology. This article provides an overview of major sources of ROS, their implication in different signaling pathways, and their effect on cellular physiology, with a focus on megakaryopoiesis. The importance of ROS-generating oxidases in MK biology and pathology, including myelofibrosis, is also described.

The influence of reactive oxygen species on cell cycle progression in mammalian cells

Cell cycle regulation is performed by cyclins and cyclin dependent kinases (CDKs). Recently, it has become clear that reactive oxygen species (ROS) influence the presence and activity of these enzymes and thereby control cell cycle progression. In this review, we first describe the discovery of enzymes specialized in ROS production: the NADPH oxidase (NOX) complexes. This discovery led to the recognition of ROS as essential players in many cellular processes, including cell cycle progression. ROS influence cell cycle progression in a context-dependent manner via phosphorylation and ubiquitination of CDKs and cell cycle regulatory molecules. We show that ROS often regulate ubiquitination via intermediate phosphorylation and that phosphorylation is thus the major regulatory mechanism influenced by ROS. In addition, ROS have recently been shown to be able to activate growth factor receptors. We will illustrate the diverse roles of ROS as mediators in cell cycle regulation by incorporating phosphorylation, ubiquitination and receptor activation in a model of cell cycle regulation involving EGF-receptor activation. We conclude that ROS can no longer be ignored when studying cell cycle progression.

Ionizing radiation induces mitochondrial reactive oxygen species production accompanied by upregulation of mitochondrial electron transport chain function and mitochondrial content under control of the cell cycle checkpoint

Whereas ionizing radiation (Ir) instantaneously causes the formation of water radiolysis products that contain some reactive oxygen species (ROS), ROS are also suggested to be released from biological sources in irradiated cells. It is now becoming clear that these ROS generated secondarily after Ir have a variety of biological roles. Although mitochondria are assumed to be responsible for this Ir-induced ROS production, it remains to be elucidated how Ir triggers it. Therefore, we conducted this study to decipher the mechanism of Ir-induced mitochondrial ROS production. In human lung carcinoma A549 cells, Ir (10 Gy of X-rays) induced a time-dependent increase in the mitochondrial ROS level. Ir also increased mitochondrial membrane potential, mitochondrial respiration, and mitochondrial ATP production, suggesting upregulation of the mitochondrial electron transport chain (ETC) function after Ir. Although we found that Ir slightly enhanced mitochondrial ETC complex II activity, the complex II inhibitor 3-nitropropionic acid failed to reduce Ir-induced mitochondrial ROS production. Meanwhile, we observed that the mitochondrial mass and mitochondrial DNA level were upregulated after Ir, indicating that Ir increased the mitochondrial content of the cell. Because irradiated cells are known to undergo cell cycle arrest under control of the checkpoint mechanisms, we examined the relationships between cell cycle and mitochondrial content and cellular oxidative stress level. We found that the cells in the G2/M phase had a higher mitochondrial content and cellular oxidative stress level than cells in the G1 or S phase, regardless of whether the cells were irradiated. We also found that Ir-induced accumulation of the cells in the G2/M phase led to an increase in cells with a high mitochondrial content and cellular oxidative stress level. This suggested that Ir upregulated mitochondrial ETC function and mitochondrial content, resulting in mitochondrial ROS production, and that Ir-induced G2/M arrest contributed to the increase in the mitochondrial ROS level by accumulating cells in the G2/M phase.

Polyphenols sensitization potentiates susceptibility of MCF-7 and MDA MB-231 cells to Centchroman

Polyphenols as “sensitizers” together with cytotoxic drugs as “inducers” cooperate to trigger apoptosis in various cancer cells. Hence, their combination having similar mode of mechanism may be a novel approach to enhance the efficacy of inducers. Additionally, this will also enable to achieve the physiological concentrations facilitating significant increase in the activity at concentrations which the compound can individually provide. Here we propose that polyphenols (Resveratrol (RES) and Curcumin (CUR)) pre-treatment may sensitize MCF-7/MDA MB-231 (Human Breast Cancer Cells, HBCCs) to Centchroman (CC, antineoplastic agent). 6 h pre-treated cells with 10 µM RES/CUR and 100 µM RES/30 µM CUR doses, followed by 10 µM CC for 18 h were investigated for Ser-167 ER-phosphorylation, cell cycle arrest, redox homeostasis, stress activated protein kinase (SAPKs: JNK and p38 MAPK) pathways and downstream apoptosis effectors. Low dose RES/CUR enhances the CC action through ROS mediated JNK/p38 as well as mitochondrial pathway in MCF-7 cells. However, RES/CUR sensitization enhanced apoptosis in p53 mutant MDA MB-231 cells without/with involvement of ROS mediated JNK/p38 adjunct to Caspase-9. Contrarily, through high dose sensitization in CC treated cells, the parameters remained unaltered as in polyphenols alone. We conclude that differential sensitization of HBCCs with low dose polyphenol augments apoptotic efficacy of CC. This may offer a novel approach to achieve enhanced action of CC with concomitant reduction of side effects enabling improved management of hormone-dependent breast cancer.

Oxidative stress adaptation in aggressive prostate cancer may be counteracted by the reduction of glutathione reductase

Oxidative stress has been associated with prostate cancer development and progression due to an increase of reactive oxygen species (ROS). However, the mechanisms whereby ROS and the antioxidant system participate in cancer progression remain unclear.

In order to clarify the influence of oxidative stress in prostate cancer progression, we performed this study in two human prostate cancer cell lines, PC3 and HPV10 (from metastasis and from localized cancer, respectively) and RWPE1 cells derived from normal prostate epithelium. Cells were treated with hydrogen peroxide (H₂O₂) and PC3 cells were also treated with diethyl maleate (DEM). The effect on cell growth, viability, mitochondria membrane potential and oxidative stress was analysed. Oxidative stress was evaluated based on ROS production, oxidative lesion of lipids (MDA) and on determination of antioxidants, including enzyme activity of glutathione peroxidase (Gl-Px), glutathione reductase (Gl-Red) and on the quantification of glutathione (GSH), glutathione-s-transferase (GST) and total antioxidant status (TAS).

PC3 shows higher ROS production but also the highest GSH levels and Gl-Red activity, possibly contributing to oxidative stress resistance. This is also associated with higher mitochondrial membrane potential, TAS and lower lipid peroxidation. On the other hand, we identified Gl-Red activity reduction as a new strategy in overcoming oxidative stress resistance, by inducing H₂O₂ cytotoxicity. Therefore these results suggest Gl-Red activity reduction as a new potential therapeutic approach, in prostate cancer.

MetaMapp: mapping and visualizing metabolomic data by integrating information from biochemical pathways and chemical and mass spectral similarity

BACKGROUND

Exposure to environmental tobacco smoke (ETS) leads to higher rates of pulmonary diseases and infections in children. To study the biochemical changes that may precede lung diseases, metabolomic effects on fetal and maternal lungs and plasma from rats exposed to ETS were compared to filtered air control animals. Genome- reconstructed metabolic pathways may be used to map and interpret dysregulation in metabolic networks. However, mass spectrometry-based non-targeted metabolomics datasets often comprise many metabolites for which links to enzymatic reactions have not yet been reported. Hence, network visualizations that rely on current biochemical databases are incomplete and also fail to visualize novel, structurally unidentified metabolites.

RESULTS

We present a novel approach to integrate biochemical pathway and chemical relationships to map all detected metabolites in network graphs (MetaMapp) using KEGG reactant pair database, Tanimoto chemical and NIST mass spectral similarity scores. In fetal and maternal lungs, and in maternal blood plasma from pregnant rats exposed to environmental tobacco smoke (ETS), 459 unique metabolites comprising 179 structurally identified compounds were detected by gas chromatography time of flight mass spectrometry (GC-TOF MS) and BinBase data processing. MetaMapp graphs in Cytoscape showed much clearer metabolic modularity and complete content visualization compared to conventional biochemical mapping approaches. Cytoscape visualization of differential statistics results using these graphs showed that overall, fetal lung metabolism was more impaired than lungs and blood metabolism in dams. Fetuses from ETS-exposed dams expressed lower lipid and nucleotide levels and higher amounts of energy metabolism intermediates than control animals, indicating lower biosynthetic rates of metabolites for cell division, structural proteins and lipids that are critical for in lung development.

CONCLUSIONS

MetaMapp graphs efficiently visualizes mass spectrometry based metabolomics datasets as network graphs in Cytoscape, and highlights metabolic alterations that can be associated with higher rate of pulmonary diseases and infections in children prenatally exposed to ETS. The MetaMapp scripts can be accessed at http://metamapp.fiehnlab.ucdavis.edu.