Regulation of IGF-I receptor signaling in tumor cells.

Signals from the IGF-IR and other members of the IR family contribute to the growth, survival, adhesion, and motility of tumor cells. These signals are initiated through recruitment of adapter proteins including the IRS family and Shc proteins, and are mediated through the PI3-kinase, mitogen activated protein (MAP) kinase and stress-activated protein kinase (SAPK) pathways. Regulation of signaling responses from the IGF-IR involves the actions of regulatory adapter proteins including RACK1 and Grb10 that recruit or sequester cytoplasmic proteins, and the actions of phosphatases including tyrosine PTP-1B, PTEN, and PP2A. This review focuses on the signaling pathways that are activated by the IGF-IR in tumor cells, the mechanisms of regulation of these pathways by adapter proteins and phosphatases, and how modulation of IGF-IR signaling could contribute to cancer progression.     

NOX1 Supports the Metabolic Remodeling of HepG2 Cells

NADPH oxidases are important sources of reactive oxygen species (ROS) which act as signaling molecules in the regulation of protein expression, cell proliferation, differentiation, migration and cell death. The NOX1 subunit is over-expressed in several cancers and NOX1 derived ROS have been repeatedly linked with tumorigenesis and tumor progression although underlying pathways are ill defined. We engineered NOX1-depleted HepG2 hepatoblastoma cells and employed differential display 2DE experiments in order to investigate changes in NOX1-dependent protein expression profiles. A total of 17 protein functions were identified to be dysregulated in NOX1-depleted cells. The proteomic results support a connection between NOX1 and the Warburg effect and a role for NOX in the regulation of glucose and glutamine metabolism as well as of lipid, protein and nucleotide synthesis in hepatic tumor cells. Metabolic remodeling is a common feature of tumor cells and understanding the underlying mechanisms is essential for the development of new cancer treatments. Our results reveal a manifold involvement of NOX1 in the metabolic remodeling of hepatoblastoma cells towards a sustained production of building blocks required to maintain a high proliferative rate, thus rendering NOX1 a potential target for cancer therapy.     

ROS-mediated activation of AKT induces apoptosis via pVHL in prostate cancer cells

Reactive oxygen species (ROS) play a central role in oxidative stress, which leads to the onset of diseases, such as cancer. Furthermore, ROS contributes to the delicate balance between tumor cell survival and death. However, the mechanisms by which tumor cells decide to elicit survival or death signals during oxidative stress are not completely understood. We have previously reported that ROS enhanced tumorigenic functions in prostate cancer cells, such as transendothelial migration and invasion, which depended on CXCR4 and AKT signaling. Here, we report a novel mechanism by which ROS facilitated cell death through activation of AKT. We initially observed that ROS enhanced the expression of phosphorylated AKT (p-AKT) in 22Rv1 human prostate cancer cells. The tumor suppressor PTEN, a negative regulator of AKT signaling, was rendered catalytically inactive through oxidation by ROS, although the expression levels remained consistent. Despite these events, cells still underwent apoptosis. Further investigation into apoptosis revealed that expression of the tumor suppressor pVHL increased, and contains a target site for p-AKT phosphorylation. pVHL and p-AKT associated in vitro, and knockdown of pVHL rescued HIF1α expression and the cells from apoptosis. Collectively, our study suggests that in the context of oxidative stress, p-AKT facilitated apoptosis by inducing pVHL function.     

Mitophagy defects arising from BNip3 loss promote mammary tumor progression to metastasis

BNip3 is a hypoxia‐inducible protein that targets mitochondria for autophagosomal degradation. We report a novel tumor suppressor role for BNip3 in a clinically relevant mouse model of mammary tumorigenesis. BNip3 delays primary mammary tumor growth and progression by preventing the accumulation of dysfunctional mitochondria and resultant excess ROS production. In the absence of BNip3, mammary tumor cells are unable to reduce mitochondrial mass effectively and elevated mitochondrial ROS increases the expression of Hif‐1α and Hif target genes, including those involved in glycolysis and angiogenesis—two processes that are also markedly increased in BNip3‐null tumors. Glycolysis inhibition attenuates the growth of BNip3‐null tumor cells, revealing an increased dependence on autophagy for survival. We also demonstrate that BNIP3 deletion can be used as a prognostic marker of tumor progression to metastasis in human triple‐negative breast cancer (TNBC). These studies show that mitochondrial dysfunction—caused by defects in mitophagy—can promote the Warburg effect and tumor progression, and suggest better approaches to stratifying TNBC for treatment.     

Inhibition of mitogen-activated protein kinase kinase selectively inhibits cell proliferation in human breast cancer cells displaying enhanced insulin-like growth factor I-mediated mitogen-activated protein kinase activation.

Mitogen-activated protein (MAP) kinase mediates cell proliferation, cell differentiation, and cell survival by regulating signaling pathways activated by receptor protein tyrosine kinases (RPTKs), including the insulin-like growth factor 1 receptor (IGF-IR). We analyzed the upstream signaling components of the MAP kinase pathway, including RPTKs, in human breast cancer cell lines and found that some of those components were overexpressed. Importantly, signaling molecules such as IGF-IR, insulin receptor, and insulin receptor substrate 1, leading to the MAP kinase pathway, were found to be concomitantly overexpressed within certain tumor lines, i.e., MCF-7 and T-47D. When compared with the nonmalignant and other breast tumor lines examined, MCF-7 and T-47D cells displayed a more rapid, robust, and sustained MAP kinase activation in response to insulin-like growth factor I (IGF-I) stimulation. By contrast, IGF-I treatment led to a sustained down-regulation of MAP kinase in those lines overexpressing ErbB2-related RPTKs. Interestingly, blocking the MAP kinase pathway with PD098059 had the greatest antiproliferative effect on MCF-7 and T-47D among the normal and tumor lines tested. Furthermore, addition of an IGF-IR blocking antibody to growth medium attenuated the ability of PD098059 to suppress the growth of MCF-7 and T-47D cells. Thus, our study suggests that concomitant overexpression of multiple signaling components of the IGF-IR pathway leads to the amplification of IGF-I-mediated MAP kinase signaling and resultant sensitization to PD098059. The enhanced sensitivity to PD098059 implies an increased requirement for the MAP kinase pathway in those breast cancer cells, making this pathway a potential target in the treatment of selected breast malignancies.     

Pro‐inflammatory angiogenesis is mediated by p38 MAP kinase

Chronic inflammation is tightly linked to diseases associated with endothelial dysfunction including aberrant angiogenesis. To better understand the endothelial role in pro‐inflammatory angiogenesis, we analyzed signaling pathways in continuously activated endothelial cells, which were either chronically exposed to soluble TNF or the reactive oxygen species (ROS) generating H₂O₂, or express active transmembrane TNF. Testing in an in vitro capillary sprout formation assay, continuous endothelial activation increased angiogenesis dependent on activation of p38 MAP kinase, NADPH oxidase, and matrix metalloproteinases (MMP). p38 MAP kinase‐ and MMP‐9‐dependent angiogenesis in our assay system may be part of a positive feed forward autocrine loop because continuously activated endothelial cells displayed up‐regulated ROS production and subsequent endothelial TNF expression. The pro‐angiogenic role of the p38 MAP kinase in continuously activated endothelial cells was in stark contrast to the anti‐angiogenic activity of the p38 MAP kinase in unstimulated control endothelial cells. In vivo, using an experimental prostate tumor, pharmacological inhibition of p38 MAP kinase demonstrated a significant reduction in tumor growth and in vessel density, suggesting a pro‐angiogenic role of the p38 MAP kinase in pathological angiogenesis in vivo. In conclusion, our results suggest that continuous activation of endothelial cells can cause a switch of the p38 MAP kinase from anti‐angiogenic to pro‐angiogenic activities in conditions which link oxidative stress and autocrine TNF production. J. Cell. Physiol. 226: 800–808, 2011. © 2010 Wiley‐Liss, Inc.     

Insulin receptor substrate-1 prevents autophagy-dependent cell death caused by oxidative stress in mouse NIH/3T3 cells

Background

Insulin receptor substrate (IRS)-1 is associated with tumorigenesis; its levels are elevated in several human cancers. IRS-1 protein binds to several oncogene proteins. Oxidative stress and reactive oxygen species (ROS) are involved in the initiation and progression of cancers. Cancer cells produce greater levels of ROS than normal cells do because of increased metabolic stresses. However, excessive production of ROS kills cancer cells. Autophagy usually serves as a survival mechanism in response to stress conditions, but excessive induction of autophagy results in cell death. In addition to inducing necrosis and apoptosis, ROS induces autophagic cell death. ROS inactivates IRS-1 mediated signaling and reduces intracellular IRS-1 concentrations. Thus, there is a complex relationship between IRS-1, ROS, autophagy, and cancer. It is not fully understood how cancer cells grow rapidly and survive in the presence of high ROS levels.

Methods and results

In this study, we established mouse NIH/3T3 cells that overexpressed IRS-1, so mimicking cancers with increased IRS-1 expression levels; we found that the IRS-1 overexpressing cells grow more rapidly than control cells do. Treatment of cells with glucose oxidase (GO) provided a continuous source of ROS; low dosages of GO promoted cell growth, while high doses induced cell death. Evidence for GO induced autophagy includes increased levels of isoform B-II microtubule-associated protein 1 light chain 3 (LC3), aggregation of green fluorescence protein-tagged LC3, and increased numbers of autophagic vacuoles in cells. Overexpression of IRS-1 resulted in inhibition of basal autophagy, and reduced oxidative stress-induced autophagy and cell death. ROS decreased the mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase signaling, while overexpression of IRS-1 attenuated this inhibition. Knockdown of autophagy-related gene 5 inhibited basal autophagy and diminished oxidative stress-induced autophagy and cell death.

Conclusion

Our results suggest that overexpression of IRS-1 promotes cells growth, inhibits basal autophagy, reduces oxidative stress-induced autophagy, and diminishes oxidative stress-mediated autophagy-dependent cell death. ROS-mediated autophagy may occur via inhibition of IRS-1/phosphatidylinositol 3-kinase/mTOR signaling. Our data afford a plausible explanation for IRS-1 involvement in tumor initiation and progression.     

硫氧还蛋白-过氧化物氧还蛋白与过氧化氢构成环路参与肿瘤的发生与发展

组织细胞可经过多种途径产生氧自由基（ROS）,而肿瘤组织由于多种应激因素会产生大量ROS,其中最重要的是过氧化氢（H2O2).H2O2对细胞发挥着致损伤及亚毒性信使的双重作用,作为信使其不仅参与调节正常细胞信号通路,重要的是促进肿瘤的发生及进展. ROS作为一种应激刺激信号激活细胞内的AP-1（activator protein 1）、Nrf-2（NF-E2-related factor 2）等核转录因子,活化后的AP-1、Nrf-2会结合到硫氧还蛋白（sulfiredoxin, SRX）基因启动子上游的调控序列,促进SRX基因的表达.SRX的表达上调则影响其下游的抗氧化蛋白,即特定亚型的过氧化物氧还蛋白（peroxiredoxin, PRX）的活性状态,最终使细胞内H2O2浓度受到调节. 由SRX-PRX轴与H2O2形成1个环路,通过调节H2O2含量来参与细胞众多信号通路.本文对H2O2、SRX及PRX各自的功能进行综述,还进一步探讨三者构成的信号环路对肿瘤的调控机制,从而了解该环路在肿瘤发生发展中所发挥的作用.     

MAP1S Controls Breast Cancer Cell TLR5 Signaling Pathway and Promotes TLR5 Signaling-based Tumor Suppression

Targeting TLR5 signaling in breast cancer represents a novel strategy in cancer immunotherapy. However, the underlying mechanism by which TLR5 signaling inhibits cancer cell proliferation and tumor growth has not been elucidated. In this study, we found TLR5 agonist flagellin inhibited the cell state of activation and induced autophagy, and reported that autophagy protein MAP1S regulated the flagellin/TLR5 signaling pathway in breast cancer cells through enhancement of NF-κB activity and cytokine secretion. Remarkably, MAP1S played a critical role in tumor suppression induced by flagellin, and knockdown of MAP1S almost completely abrogated the suppression of tumor growth and migration by flagellin treatment. In addition, elevated expression of MAP1S in response to flagellin feed-back regulated tumor inflammatory microenvironment in the late stages of TLR5 signaling through degradation of MyD88 in autophagy process. These results indicate a mechanism of antitumor activity that involves MAP1S-controlled TLR5 signaling in breast cancer.     

Reactive oxidant and p42/44 MAP kinase signaling is necessary for mechanical strain-induced proliferation in pulmonary epithelial cells.

Mechanical strain is necessary for normal lung growth and development. Individuals with respiratory failure are supported with mechanical ventilation, leading to altered lung growth and injury. Understanding signaling pathways initiated by mechanical strain in lung epithelial cells will help guide development of strategies aimed at optimizing strain-induced lung growth while mitigating ventilator-induced lung injury. To study strain-induced proliferative signaling, focusing on the role of reactive oxidant species (ROS) and p42/44 mitogen-activated protein (MAP) kinase, human pulmonary epithelial H441 and MLE15 cells were exposed to equibiaxial cyclic mechanical strain. ROS were increased within 15 min of strain. N-acetylcysteine inactivated strain-induced ROS and inhibited p42/44 MAP kinase phosphorylation and strain-induced proliferation. PD98059 and UO126, p42/44 MAP kinase inhibitors, blocked strain-induced proliferation. To verify the specificity of p42/44 MAP kinase inhibition, cells were transfected with dominant-negative mitogen-activated protein kinase kinase-1 plasmid DNA. Transfected cells did not proliferate in response to mechanical strain. To determine whether strain-induced tyrosine kinase activity is necessary for strain-induced ROS-p42/44 MAP kinase signaling, genistein, a tyrosine kinase inhibitor, was used. Genistein did not block strain-induced ROS production or p42/44 MAP kinase phosphorylation. Gadolinium, a mechanosensitive calcium channel blocker, blocked strain-induced ROS production and p42/44 MAP kinase phosphorylation but not strain-induced tyrosine phosphorylation. These data support ROS production and p42/44 MAP kinase phosphorylation being involved in a common strain-induced signaling pathway, necessary for strain-induced proliferation in pulmonary epithelial cells, with a parallel strain-induced tyrosine kinase pathway.     

A critical role for Romo1-derived ROS in cell proliferation

Low levels of endogenous reactive oxygen species (ROS) originating from NADPH oxidase have been implicated in various signaling pathways induced by growth factors and mediated by cytokines. However, the main source of ROS is known to be the mitochondria, and increased levels of ROS from the mitochondria have been observed in many cancer cells. Thus far, the mechanism of ROS production in cancer cell proliferation in the mitochondria is not well-understood. We recently identified a novel protein, ROS modulator 1 (Romo1), and reported that increased expression of Romo1-triggered ROS production in the mitochondria. The experiments conducted in the present study showed that Romo1-derived ROS were indispensable for the proliferation of both normal and cancer cells. Furthermore, whilst cell growth was inhibited by blocking the ERK pathway in cells transfected with siRNA directed against Romo1, the cell growth was recovered by addition of exogenous hydrogen peroxide. The results of this study suggest that Romo1-induced ROS may play an important role in redox signaling in cancer cells.     

2-羟基-3-甲基蒽醌抑制结直肠癌的作用及机制研究

为观察2-羟基-3-甲基蒽醌(HMA)对结直肠癌细胞增殖的影响并探讨其作用机制,本研究采用CCK8法检测HMA对结直肠癌细胞增殖的影响;Heochst-33343/PI染色检测细胞凋亡情况;同时检测细胞内ROS及GSH含量变化并应用Western blot检测细胞凋亡相关蛋白及Keap-1/Nrf-2/ARE信号途径相关蛋白的表达。实验结果显示,HMA给予结直肠癌细胞后,细胞内ROS含量升高,GSH含量减少;HMA通过抑制Keap-1/Nrf-2/HO-1通路,诱导细胞发生凋亡。综上表明HMA具有抑制结肠癌细胞增殖的作用,其机制可能与破坏细胞内氧化还原平衡,抑制Keap-1/Nrf-2/HO-1通路有关。     

植物胁迫信号转导过程中活性氧和促细胞分裂原活化蛋白激酶的调节作用

以H2O2为代表的活性氧(reactive oxygen species,ROS)和以促细胞分裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)为代表的蛋白激酶广泛存在于植物细胞并参与各种生理反应过程.生物胁迫条件下,一些MAP激酶特异性地调节氧化猝发(oxidative burst,OXB)和过敏反应(hypersensitive response,HR),水杨酸(salicylic acid,SA)诱导的MAP激酶(SA-induced protein kinase,SIPK)和ROS共同参与系统获得性抗性(systemic acquired resistance,SAR)的建立;SIPK、P38 MAPK等分别与H2O2共同调节臭氧、受伤和渗透胁迫等多种非生物胁迫生理反应.ROS和MAP激酶共同调节植物胁迫信号转导,但其机制尚需进一步的研究.     

Reactive oxygen species in TNFα-induced signaling and cell death

TNFα is a pleotropic cytokine that initiates many downstream signaling pathways, including NF-κB activation, MAP kinase activation and the induction of both apoptosis and necrosis. TNFα has shown to lead to reactive oxygen species generation through activation of NADPH oxidase, through mitochondrial pathways, or other enzymes. As discussed, ROS play a role in potentiation or inhibition of many of these signaling pathways. We particularly discuss the role of sustained JNK activation potentiated by ROS, which generally is supportive of apoptosis and “necrotic cell death” through various mechanisms, while ROS could have inhibitory or stimulatory roles in NF-κB signaling.