H2O2 scavenging inhibits G1/S transition by increasing nuclear levels of p27KIP1

Association of Gpx1 fluctuation in cell cycle progression

This research demonstrates fluctuation of glutathione peroxidase1 (Gpx1) throughout cell cycle progression with significant decreased expression at mitosis of HeLa cell. This was achieved with western blot (WB) analysis of target proteins from each phase of synchronized cells. The synchronizations were performed with double thymidine (T/T) for G1/S arrest and thymidine followed by nocodazole (T/N) for G2/M arrest. The G1/S arrested cells were released in fresh medium for 3, 6, 9, 10, and 15h to obtain cell at each phase such as gap1 (G1), synthesis (S), gap2 (G2), mitosis (M), and gap1 (G1) phase, respectively, for investigating Gpx1 expression throughout a complete cycle. The synchronizations were confirmed using fluorescence activated cell sorting (FACS) and WB analysis of phase-specific markers. The fluctuations of Gpx1 expression were verified with universal protein actin and peroxiredoxin1 (Prx1) which are stable throughout the cell cycle. Intriguingly, immunoblots showed the level of Gpx1 decreases at mitosis phase and increased during mitotic exit to G1 phase in HeLa cells, while Prx1 protein level remained constant. The fractionation experiments reveal that only the cytosolic Gpx1 was decreased while their levels at mitochondria remain constant. The highest levels of mitochondrial ROS were measured in mitosis phase with FACS analysis using Mito sox indicating that antioxidant activity of Gpx1 for detoxifying excessive induced endogenous reactive oxygen species (ROS) in the mitosis phase could be the reason for such decreasing level. For unfolding the molecular mechanism of such decreased expression, the Gpx1 was investigated at transcriptional, translational, and proteosomal level. The results revealed that translational mechanism is involve in the decreased expression rather than transcriptional or proteosomal degradation at mitosis phase. This finding supports that Gpx1 is involved in the cell cycle progression through regulation of endogenous ROS. Based on this observation, further research could uncover their possible association with the infinitive division of a cancer cell.

Reprogramming human A375 amelanotic melanoma cells by catalase overexpression: Reversion or promotion of malignancy by inducing melanogenesis or metastasis

Advanced melanoma is the most aggressive form of skin cancer. It is highly metastatic and dysfunctional in melanogenesis; two processes that are induced by H₂O₂. This work presents a melanoma cell model with low levels of H₂O₂ induced by catalase overexpression to study differentiation/dedifferentiation processes. Three clones (A7, C10 and G10) of human A375 amelanotic melanoma cells with quite distinct phenotypes were obtained. These clones faced H₂O₂ scavenging by two main strategies. One developed by clone G10 where ROS increased. This resulted in G10 migration and metastasis associated with the increased of cofilin-1 and CAP1. The other strategy was observed in clone A7 and C10, where ROS levels were maintained reversing malignant features. Particularly, C10 was not tumorigenic, while A7 reversed the amelanotic phenotype by increasing melanin content and melanocytic differentiation markers. These clones allowed the study of potential differentiation and migration markers and its association with ROS levels in vitro and in vivo, providing a new melanoma model with different degree of malignancy.

Reprogramming human A375 amelanotic melanoma cells by catalase overexpression: Upregulation of antioxidant genes correlates with regression of melanoma malignancy and with malignant progression when downregulated

Reactive oxygen species (ROS) are implicated in tumor transformation. The antioxidant system (AOS) protects cells from ROS damage. However, it is also hijacked by cancers cells to proliferate within the tumor. Thus, identifying proteins altered by redox imbalance in cancer cells is an attractive prognostic and therapeutic tool. Gene expression microarrays in A375 melanoma cells with different ROS levels after overexpressing catalase were performed. Dissimilar phenotypes by differential compensation to hydrogen peroxide scavenging were generated. The melanotic A375-A7 (A7) upregulated TYRP1, CNTN1 and UCHL1 promoting melanogenesis. The metastatic A375-G10 (G10) downregulated MTSS1 and TIAM1, proteins absent in metastasis. Moreover, differential coexpression of AOS genes (EPHX2, GSTM3, MGST1, MSRA, TXNRD3, MGST3 and GSR) was found in A7 and G10. Their increase in A7 improved its AOS ability and therefore, oxidative stress response, resembling less aggressive tumor cells. Meanwhile, their decrease in G10 revealed a disruption in the AOS and therefore, enhanced its metastatic capacity.

These gene signatures, not only bring new insights into the physiopathology of melanoma, but also could be relevant in clinical prognostic to classify between non aggressive and metastatic melanomas.

NADPH oxidase 5 (NOX5)-induced reactive oxygen signaling modulates normoxic HIF-1α and p27Kip1 expression in malignant melanoma and other human tumors

NADPH oxidase 5 (NOX5) generated reactive oxygen species (ROS) have been implicated in signaling cascades that regulate cancer cell proliferation. To evaluate and validate NOX5 expression in human tumors, we screened a broad range of tissue microarrays (TMAs), and report substantial overexpression of NOX5 in malignant melanoma and cancers of the prostate, breast, and ovary. In human UACC-257 melanoma cells that possesses high levels of functional endogenous NOX5, overexpression of NOX5 resulted in enhanced cell growth, increased numbers of BrdU positive cells, and increased γ-H2AX levels. Additionally, NOX5-overexpressing (stable and inducible) UACC-257 cells demonstrated increased normoxic HIF-1α expression and decreased p27Kip1 expression. Similarly, increased normoxic HIF-1α expression and decreased p27Kip1 expression were observed in stable NOX5-overexpressing clones of KARPAS 299 human lymphoma cells and in the human prostate cancer cell line, PC-3. Conversely, knockdown of endogenous NOX5 in UACC-257 cells resulted in decreased cell growth, decreased HIF-1α expression, and increased p27Kip1 expression. Likewise, in an additional human melanoma cell line, WM852, and in PC-3 cells, transient knockdown of endogenous NOX5 resulted in increased p27Kip1 and decreased HIF-1α expression. Knockdown of endogenous NOX5 in UACC-257 cells resulted in decreased Akt and GSK3β phosphorylation, signaling pathways known to modulate p27Kip1 levels. In summary, our findings suggest that NOX5 expression in human UACC-257 melanoma cells could contribute to cell proliferation due, in part, to the generation of high local concentrations of extracellular ROS that modulate multiple pathways that regulate HIF-1α and networks that signal through Akt/GSK3β/p27Kip1 .

Thioredoxin reductase 1 suppresses adipocyte differentiation and insulin responsiveness

Recently thioredoxin reductase 1 (TrxR1), encoded by Txnrd1, was suggested to modulate glucose and lipid metabolism in mice. Here we discovered that TrxR1 suppresses insulin responsiveness, anabolic metabolism and adipocyte differentiation. Immortalized mouse embryonic fibroblasts (MEFs) lacking Txnrd1 (Txnrd1^−/−) displayed increased metabolic flux, glycogen storage, lipogenesis and adipogenesis. This phenotype coincided with upregulated PPARγ expression, promotion of mitotic clonal expansion and downregulation of p27 and p53. Enhanced Akt activation also contributed to augmented adipogenesis and insulin sensitivity. Knockdown of TXNRD1 transcripts accelerated adipocyte differentiation also in human primary preadipocytes. Furthermore, TXNRD1 transcript levels in subcutaneous adipose tissue from 56 women were inversely associated with insulin sensitivity in vivo and lipogenesis in their isolated adipocytes. These results suggest that TrxR1 suppresses anabolic metabolism and adipogenesis by inhibition of intracellular signaling pathways downstream of insulin stimulation.

In vitro evaluation of antitumoral efficacy of catalase in combination with traditional chemotherapeutic drugs against human lung adenocarcinoma cells

Lung cancer is the most lethal cancer-related disease worldwide. Since survival rates remain poor, there is an urgent need for more effective therapies that could increase the overall survival of lung cancer patients. Lung tumors exhibit increased levels of oxidative markers with altered levels of antioxidant defenses, and previous studies demonstrated that the overexpression of the antioxidant enzyme catalase (CAT) might control tumor proliferation and aggressiveness. Herein, we evaluated the effect of CAT treatment on the sensitivity of A549 human lung adenocarcinoma cells toward various anticancer treatments, aiming to establish the best drug combination for further therapeutic management of this disease. Exponentially growing A549 cells were treated with CAT alone or in combination with chemotherapeutic drugs (cisplatin, 5-fluorouracil, paclitaxel, daunorubicin, and hydroxyurea). CalcuSyn(®) software was used to assess CAT/drug interactions (synergism or antagonism). Growth inhibition, NFκB activation status, and redox parameters were also evaluated in CAT-treated A549 cells. CAT treatment caused a cytostatic effect, decreased NFκB activation, and modulated the redox parameters evaluated. CAT treatment exhibited a synergistic effect among most of the anticancer drugs tested, which is significantly correlated with an increased H2O2 production. Moreover, CAT combination caused an antagonism in paclitaxel anticancer effect. These data suggest that combining CAT (or CAT analogs) with traditional chemotherapeutic drugs, especially cisplatin, is a promising therapeutic strategy for the treatment of lung cancer.

Radiation resistance: Cancer stem cells (CSCs) and their enigmatic pro-survival signaling

Despite the fact that radiation therapy is a highly effective therapeutic approach, a small intratumoral cell subpopulation known as "cancer stem cells" (CSCs) is radiation-resistant and possesses specific molecular properties protecting it against radiation-induced damage. The exact mechanisms of this radioresistance are still not fully elucidated, but they relate to these cells' enhanced DNA repair capacities and their low intracellular ROS concentrations, resulting from their up-regulation of ROS scavengers. The low ROS content is accompanied by disturbances in cell cycle regulation, so it can be assumed that either CSCs are quiescent or dormant themselves, or that this cell population consists of at least two cell subpopulations: the normally and the slowly proliferating cells (quiescent or dormant cells). Slowly dividing CSCs show concomitant dysregulation of the signaling molecules mediating both cell cycle progression and maintenance of cell stemness. Despite a massive accumulation of data concerning the mechanisms underlying DNA damage response in CSCs, it represents a challenge to researchers in the era of personalized medicine to elucidate the role of intracellular ROS and of signaling pathways associated with the radiation resistance of these cells; there is a clear need to understand the molecular mechanisms helping CSCs to survive radiation exposure.

Oxidative stress associates with aggressiveness in lung large-cell carcinoma

Oxidative stress is involved in many cancer-related processes; however, current therapeutics are unable to benefit from this approach. The lungs have a very exquisite redox environment that may contribute to the frequent and deadly nature of lung cancer. Very few studies specifically address lung large-cell carcinoma (LCC), even though this is one of the major subtypes. Using bioinformatic (in silico) tools, we demonstrated that a more aggressive lung LCC cell line (HOP-92) has an overall increase activity of the human antioxidant gene (HAG) network (P = 0.0046) when compared to the less aggressive cell line H-460. Gene set enrichment analysis (GSEA) showed that the expression of metallothioneins (MT), glutathione peroxidase 1 (GPx-1), and catalase (CAT) are responsible for this difference in gene signature. This was validated in vitro, where HOP-92 showed a pro-oxidative imbalance, presenting higher antioxidant enzymes (superoxide dismutase (SOD), CAT, and GPx) activities, lower reduced sulfhydryl groups and antioxidant potential, and higher lipoperoxidation and reactive species production. Also, HAG network is upregulated in lung LCC patients with worst outcome. Finally, the prognostic value of genes enriched in the most aggressive cell line was assessed in this cohort. Isoforms of metallothioneins are associated with bad prognosis, while the thioredoxin-interacting protein (TXNIP) is associated with good prognosis. Thus, redox metabolism can be an important aspect in lung LCC aggressiveness and a possible therapeutic target.

A catalase-magnetic switch for cell proliferation

The combination of enzymes to tackle cell messengers with magnetite nanoparticles was exploited to control cell behavior by means of magnetic fields.

The tumor microenvironment: characterization, redox considerations, and novel approaches for reactive oxygen species-targeted gene therapy

The tumor microenvironment is a complex system that involves the interaction between malignant and neighbor stromal cells embedded in a mesh of extracellular matrix (ECM) components. Stromal cells (fibroblasts, endothelial, and inflammatory cells) are co-opted at different stages to help malignant cells invade the surrounding ECM and disseminate. Malignant cells have developed adaptive mechanisms to survive under the extreme conditions of the tumor microenvironment such as restricted oxygen supply (hypoxia), nutrient deprivation, and a prooxidant state among others. These conditions could be eventually used to target drugs that will be activated specifically in this microenvironment. Preclinical studies have shown that modulating cellular/tissue redox state by different gene therapy (GT) approaches was able to control tumor growth. In this review, we describe the most relevant features of the tumor microenvironment, addressing reactive oxygen species-generating sources that promote a prooxidative microenvironment inside the tumor mass. We describe different GT approaches that promote either a decreased or exacerbated prooxidative microenvironment, and those that make use of the differential levels of ROS between cancer and normal cells to achieve tumor growth inhibition.

Phosphorylation and subcellular localization of p27Kip1 regulated by hydrogen peroxide modulation in cancer cells

The Cyclin-dependent kinase inhibitor 1B (p27Kip1) is a key protein in the decision between proliferation and cell cycle exit. Quiescent cells show nuclear p27Kip1, but this protein is exported to the cytoplasm in response to proliferating signals. We recently reported that catalase treatment increases the levels of p27Kip1 in vitro and in vivo in a murine model. In order to characterize and broaden these findings, we evaluated the regulation of p27Kip1 by hydrogen peroxide (H(2)O(2)) in human melanoma cells and melanocytes. We observed a high percentage of p27Kip1 positive nuclei in melanoma cells overexpressing or treated with exogenous catalase, while non-treated controls showed a cytoplasmic localization of p27Kip1. Then we studied the levels of p27Kip1 phosphorylated (p27p) at serine 10 (S10) and at threonine 198 (T198) because phosphorylation at these sites enables nuclear exportation of this protein, leading to accumulation and stabilization of p27pT198 in the cytoplasm. We demonstrated by western blot a decrease in p27pS10 and p27pT198 levels in response to H(2)O(2) removal in melanoma cells, associated with nuclear p27Kip1. Melanocytes also exhibited nuclear p27Kip1 and lower levels of p27pS10 and p27pT198 than melanoma cells, which showed cytoplasmic p27Kip1. We also showed that the addition of H(2)O(2) (0.1 µM) to melanoma cells arrested in G1 by serum starvation induces proliferation and increases the levels of p27pS10 and p27pT198 leading to cytoplasmic localization of p27Kip1. Nuclear localization and post-translational modifications of p27Kip1 were also demonstrated by catalase treatment of colorectal carcinoma and neuroblastoma cells, extending our findings to these other human cancer types. In conclusion, we showed in the present work that H(2)O(2) scavenging prevents nuclear exportation of p27Kip1, allowing cell cycle arrest, suggesting that cancer cells take advantage of their intrinsic pro-oxidant state to favor cytoplasmic localization of p27Kip1.