Hypoxia-induced modulation of apoptosis and BCL-2 family proteins in different cancer cell types

Natural killer cells in cancer immunotherapy

Natural killer (NK) cells, as innate lymphocytes, possess cytotoxic capabilities and engage target cells through a repertoire of activating and inhibitory receptors. Particularly, natural killer group 2, member D (NKG2D) receptor on NK cells recognizes stress-induced ligands-the MHC class I chain-related molecules A and B (MICA/B) presented on tumor cells and is key to trigger the cytolytic response of NK cells. However, tumors have developed sophisticated strategies to evade NK cell surveillance, which lead to failure of tumor immunotherapy. In this paper, we summarized these immune escaping strategies, including the downregulation of ligands for activating receptors, upregulation of ligands for inhibitory receptors, secretion of immunosuppressive compounds, and the development of apoptosis resistance. Then, we focus on recent advancements in NK cell immune therapies, which include engaging activating NK cell receptors, upregulating NKG2D ligand MICA/B expression, blocking inhibitory NK cell receptors, adoptive NK cell therapy, chimeric antigen receptor (CAR)-engineered NK cells (CAR-NK), and NKG2D CAR-T cells, especially several vaccines targeting MICA/B. This review will inspire the research in NK cell biology in tumor and provide significant hope for improving cancer treatment outcomes by harnessing the potent cytotoxic activity of NK cells.

Deciphering the Molecular Mechanisms behind Drug Resistance in Ovarian Cancer to Unlock Efficient Treatment Options

Ovarian cancer is a highly lethal form of gynecological cancer. This disease often goes undetected until advanced stages, resulting in high morbidity and mortality rates. Unfortunately, many patients experience relapse and succumb to the disease due to the emergence of drug resistance that significantly limits the effectiveness of currently available oncological treatments. Here, we discuss the molecular mechanisms responsible for resistance to carboplatin, paclitaxel, polyadenosine diphosphate ribose polymerase inhibitors, and bevacizumab in ovarian cancer. We present a detailed analysis of the most extensively investigated resistance mechanisms, including drug inactivation, drug target alterations, enhanced drug efflux pumps, increased DNA damage repair capacity, and reduced drug absorption/accumulation. The in-depth understanding of the molecular mechanisms associated with drug resistance is crucial to unveil new biomarkers capable of predicting and monitoring the kinetics during disease progression and discovering new therapeutic targets.

Signaling controversy and future therapeutical perspectives of targeting sphingolipid network in cancer immune editing and resistance to tumor necrosis factor-α immunotherapy

Anticancer immune surveillance and immunotherapies trigger activation of cytotoxic cytokine signaling, including tumor necrosis factor-α (TNF-α) and TNF-related apoptosis-inducing ligand (TRAIL) pathways. The pro-inflammatory cytokine TNF-α may be secreted by stromal cells, tumor-associated macrophages, and by cancer cells, indicating a prominent role in the tumor microenvironment (TME). However, tumors manage to adapt, escape immune surveillance, and ultimately develop resistance to the cytotoxic effects of TNF-α. The mechanisms by which cancer cells evade host immunity is a central topic of current cancer research. Resistance to TNF-α is mediated by diverse molecular mechanisms, such as mutation or downregulation of TNF/TRAIL receptors, as well as activation of anti-apoptotic enzymes and transcription factors. TNF-α signaling is also mediated by sphingosine kinases (SphK1 and SphK2), which are responsible for synthesis of the growth-stimulating phospholipid, sphingosine-1-phosphate (S1P). Multiple studies have demonstrated the crucial role of S1P and its transmembrane receptors (S1PR) in both the regulation of inflammatory responses and progression of cancer. Considering that the SphK/S1P/S1PR axis mediates cancer resistance, this sphingolipid signaling pathway is of mechanistic significance when considering immunotherapy-resistant malignancies. However, the exact mechanism by which sphingolipids contribute to the evasion of immune surveillance and abrogation of TNF-α-induced apoptosis remains largely unclear. This study reviews mechanisms of TNF-α-resistance in cancer cells, with emphasis on the pro-survival and immunomodulatory effects of sphingolipids. Inhibition of SphK/S1P-linked pro-survival branch may facilitate reactivation of the pro-apoptotic TNF superfamily effects, although the role of SphK/S1P inhibitors in the regulation of the TME and lymphocyte trafficking should be thoroughly assessed in future studies.

Molecular mechanisms of TACE refractoriness: Directions for improvement of the TACE procedure

Transcatheter arterial chemoembolisation (TACE) is the standard of care for intermediate-stage hepatocellular carcinoma and selected patients with advanced hepatocellular carcinoma. However, TACE does not achieve a satisfactory objective response rate, and the concept of TACE refractoriness has been proposed to identify patients who do not fully benefit from TACE. Moreover, repeated TACE is necessary to obtain an optimal and sustained anti-tumour response, which may damage the patient's liver function. Therefore, studies have recently been performed to improve the effectiveness of TACE. In this review, we summarise the detailed molecular mechanisms associated with TACE responsiveness and relapse after this treatment to provide more effective targets for adjuvant therapy while helping to improve TACE regimens.

Tumour response to hypoxia: understanding the hypoxic tumour microenvironment to improve treatment outcome in solid tumours

Hypoxia is a common feature of solid tumours affecting their biology and response to therapy. One of the main transcription factors activated by hypoxia is hypoxia-inducible factor (HIF), which regulates the expression of genes involved in various aspects of tumourigenesis including proliferative capacity, angiogenesis, immune evasion, metabolic reprogramming, extracellular matrix (ECM) remodelling, and cell migration. This can negatively impact patient outcomes by inducing therapeutic resistance. The importance of hypoxia is clearly demonstrated by continued research into finding clinically relevant hypoxia biomarkers, and hypoxia-targeting therapies. One of the problems is the lack of clinically applicable methods of hypoxia detection, and lack of standardisation. Additionally, a lot of the methods of detecting hypoxia do not take into consideration the complexity of the hypoxic tumour microenvironment (TME). Therefore, this needs further elucidation as approximately 50% of solid tumours are hypoxic. The ECM is important component of the hypoxic TME, and is developed by both cancer associated fibroblasts (CAFs) and tumour cells. However, it is important to distinguish the different roles to develop both biomarkers and novel compounds. Fibronectin (FN), collagen (COL) and hyaluronic acid (HA) are important components of the ECM that create ECM fibres. These fibres are crosslinked by specific enzymes including lysyl oxidase (LOX) which regulates the stiffness of tumours and induces fibrosis. This is partially regulated by HIFs. The review highlights the importance of understanding the role of matrix stiffness in different solid tumours as current data shows contradictory results on the impact on therapeutic resistance. The review also indicates that further research is needed into identifying different CAF subtypes and their exact roles; with some showing pro-tumorigenic capacity and others having anti-tumorigenic roles. This has made it difficult to fully elucidate the role of CAFs within the TME. However, it is clear that this is an important area of research that requires unravelling as current strategies to target CAFs have resulted in worsened prognosis. The role of immune cells within the tumour microenvironment is also discussed as hypoxia has been associated with modulating immune cells to create an anti-tumorigenic environment. Which has led to the development of immunotherapies including PD-L1. These hypoxia-induced changes can confer resistance to conventional therapies, such as chemotherapy, radiotherapy, and immunotherapy. This review summarizes the current knowledge on the impact of hypoxia on the TME and its implications for therapy resistance. It also discusses the potential of hypoxia biomarkers as prognostic and predictive indictors of treatment response, as well as the challenges and opportunities of targeting hypoxia in clinical trials.

The Prognosis of Cancer Depends on the Interplay of Autophagy, Apoptosis, and Anoikis within the Tumor Microenvironment

Within the tumor microenvironment, the fight between the immune system and cancer influences tumor transformation. Metastasis formation is an important stage in the progression of cancer. This process is aided by cellular detachment and resistance to anoikis, which are achieved by altering intercellular signaling. Autophagy, specifically pro-survival autophagy, aids cancer cells in developing treatment resistance. Numerous studies have shown that autophagy promotes tumor growth and resistance to anoikis. To regulate protective autophagy, cancer-related genes phosphorylate both pro- and anti-apoptotic proteins. Apoptosis, a type of controlled cell death, eliminates damaged or unwanted cells. Anoikis is a type of programmed cell death in which cells lose contact with the extracellular matrix. The dysregulation of these cellular pathways promotes tumor growth and spread. Apoptosis, anoikis, and autophagy interact meticulously and differently depending on the cellular circumstances. For instance, autophagy can protect cancer cells from apoptosis by removing cellular components that are damaged and might otherwise trigger apoptotic pathways. Similarly, anoikis dysregulation can trigger autophagy by causing cellular harm and metabolic stress. In order to prevent or treat metastatic disease, specifically, targeting these cellular mechanisms may present a promising prospect for cancer therapy. This review discourses the state of our understanding of the molecular and cellular mechanisms underlying tumor transformation and the establishment of metastatic tumors. To enhance the prognosis for cancer, we highlight and discuss potential therapeutic approaches that target these processes and genes involved in them.

Melatonin induces cell cycle arrest and suppresses tumor invasion in urinary bladder urothelial carcinoma

Urinary bladder urothelial carcinoma (UBUC) encompasses about 90% of all bladder cancer cases, and the mainstream treatment is the transurethral resection of the bladder tumor followed by intravesical instillation. High rates of mortality, recurrence, and progression in bladder cancer have stimulated the search for alternative adjuvant therapies. The aim of this study was to investigate the potential of melatonin as adjuvant therapy in bladder cancer. Cell viability and clonogenic ability were assessed by an MTT assay and colony formation. Cell cycle and apoptosis analysis were performed by flow cytometry and Hoechst 33342 staining, while cell metastasis capacity was measured by wound healing and transwell assays. Potential mechanisms were investigated by an oncology array and verified via western blotting. The melatonin treatment significantly reduced T24 and UMUC3 bladder cancer cell proliferation and clonogenic ability. G1 arrest and sub-G1 accumulation in the T24 and UMUC3 cells led to cell proliferation suppression and cell death, and Hoechst 33342 staining further verified the apoptosis induction directly by melatonin. Moreover, melatonin weakened cell motility and invasiveness. Based on the oncology array results, we demonstrated that melatonin exerts its anti-cancer effect by down-regulating the HIF-1α and NF-κB pathways and downstream pathways, including Bcl-2, leading to cell cycle arrest and apoptosis induction in the UBUC cells. Overall, these findings support the potential of melatonin as adjuvant therapy in bladder cancer.

Nrf2 and Parkin-Hsc70 regulate the expression and protein stability of p62/SQSTM1 under hypoxia

Solid tumors often contain regions with very low oxygen concentrations or hypoxia resulting from altered metabolism, uncontrolled proliferation, and abnormal tumor blood vessels. Hypoxia leads to resistance to both radio- and chemotherapy and a predisposition to tumor metastases. Under hypoxia, sequestosome 1 (SQSTM1/p62), a multifunctional stress-inducible protein involved in various cellular processes, such as autophagy, is down-regulated. The hypoxic depletion of p62 is mediated by autophagic degradation. We herein demonstrated that hypoxia down-regulated p62 in the hepatoma cell line Hep3B at the transcriptional and post-translational levels. At the transcriptional level, hypoxia down-regulated p62 mRNA by inhibiting nuclear factor erythroid 2-related factor 2 (Nrf2). The overexpression of Nrf2 and knockdown of Siah2, a negative regulator of Nrf2 under hypoxia, diminished the effects of hypoxia on p62 mRNA. At the post-translational level, the proteasome inhibitor MG132, but not the lysosomal inhibitors ammonium chloride and bafilomycin, prevented the hypoxic depletion of p62, suggesting the involvement of the proteasome pathway. Under hypoxia, the expression of the E3 ubiquitin ligase Parkin was up-regulated in a hypoxia-inducible factor 1α-dependent manner. Parkin ubiquitinated p62 and led to its proteasomal degradation, ensuring low levels of p62 under hypoxia. We demonstrated that the effects of Parkin on p62 required heat shock cognate 71 kDa protein (Hsc70). We also showed that the overexpression of Nrf2 and knockdown of Parkin or Hsc70 induced the accumulation of p62 and reduced the viability of cells under hypoxia. We concluded that a decrease in p62, which involves regulation at the transcriptional and post-translational levels, is critical for cell survival under hypoxia. The present results show the potential of targeting Nrf2/Parkin-Hsc70-p62 as a novel strategy to eradicate hypoxic solid tumors.

BNIP3 and Nix: Atypical regulators of cell fate

Since their discovery nearly 25 years ago, the BCL-2 family members BNIP3 and BNIP3L (aka Nix) have been labelled 'atypical'. Originally, this was because BNIP3 and Nix have divergent BH3 domains compared to other BCL-2 proteins. In addition, this atypical BH3 domain is dispensable for inducing cell death, which is also unusual for a 'death gene'. Instead, BNIP3 and Nix utilize a transmembrane domain, which allows for dimerization and insertion into and through organelle membranes to elicit cell death. Much has been learned regarding the biological function of these two atypical death genes, including their role in metabolic stress, where BNIP3 is responsive to hypoxia, while Nix responds variably to hypoxia and is also down-stream of PKC signaling and lipotoxic stress. Interestingly, both BNIP3 and Nix respond to signals related to cell atrophy. In addition, our current view of regulated cell death has expanded to include forms of necrosis such as necroptosis, pyroptosis, ferroptosis, and permeability transition-mediated cell death where BNIP3 and Nix have been shown to play context- and cell-type specific roles. Perhaps the most intriguing discoveries in recent years are the results demonstrating roles for BNIP3 and Nix outside of the purview of death genes, such as regulation of proliferation, differentiation/maturation, mitochondrial dynamics, macro- and selective-autophagy. We provide a historical and unbiased overview of these 'death genes', including new information related to alternative splicing and post-translational modification. In addition, we propose to redefine these two atypical members of the BCL-2 family as versatile regulators of cell fate.

Repositioning of Old Drugs for Novel Cancer Therapies: Continuous Therapeutic Perfusion of Aspirin and Oseltamivir Phosphate with Gemcitabine Treatment Disables Tumor Progression, Chemoresistance, and Metastases

Simple Summary

Repositioning old drugs in combination with clinical standard chemotherapeutics opens a promising clinical treatment approach for patients with pancreatic cancer. This report presents a therapeutic repositioning of continuous perfusion of aspirin and oseltamivir phosphate in combination with gemcitabine treatment as an effective treatment option for pancreatic cancer. The data suggest that repositioning these drugs with continuous perfusion with gemcitabine disables chemoresistance, tumor progression, EMT program, cancer stem cells, and metastases in a preclinical mouse model of human pancreatic cancer. These promising results warrant additional investigation to assess the potential of translating into the clinical setting to improve the cancer patient prognosis for an otherwise fatal disease.

Abstract

Metastatic pancreatic cancer has an invariably fatal outcome, with an estimated median progression-free survival of approximately six months employing our best combination chemotherapeutic regimens. Once drug resistance develops, manifested by increased primary tumor size and new and growing metastases, patients often die rapidly from their disease. Emerging evidence indicates that chemotherapy may contribute to the development of drug resistance through the upregulation of epithelial–mesenchymal transition (EMT) pathways and subsequent cancer stem cell (CSC) enrichment. Neuraminidase-1 (Neu-1) regulates the activation of several receptor tyrosine kinases implicated in EMT induction, angiogenesis, and cellular proliferation. Here, continuous therapeutic targeting of Neu-1 using parenteral perfusion of oseltamivir phosphate (OP) and aspirin (ASA) with gemcitabine (GEM) treatment significantly disrupts tumor progression, critical compensatory signaling mechanisms, EMT program, CSC, and metastases in a preclinical mouse model of human pancreatic cancer. ASA- and OP-treated xenotumors significantly inhibited the metastatic potential when transferred into animals.

TGF-β1 induced autophagy in cancer associated fibroblasts during hypoxia contributes EMT and glycolysis via MCT4 upregulation

The Transforming growth factor-β1(TGF- β1) in the tumor microenvironment(TME) is the major cytokine that acts as a mediator of tumor-stroma crosstalk, which in fact has a dual role in either promoting or suppressing tumor development. The cancer-associated fibroblasts (CAFs) are the major cell types in the TME, and the interaction with most of the epithelial cancers is the prime reason for cancer survival. However, the molecular mechanisms, associated with the TGF- β1 induced tumor promotion through tumor-CAF crosstalk are not well understood. In the Reverse Warburg effect, CAFs feed the adjacent cancer cells by lactate produced during the aerobic glycolysis. We hypothesized that the monocarboxylate transporter, MCT4 which is implicated in lactate efflux from the CAFs, must be overexpressed in the CAFs. Contextually, to explore the role of TGF- β1 in the hypoxia-induced autophagy in CAFs, we treated CoCl₂ and external TGF- β1 to the human dermal fibroblasts and L929 murine fibroblasts. We demonstrated that hypoxia accelerated the TGF- β1 signaling and subsequent transformation of normal fibroblasts to CAFs. Moreover, we elucidated that synergistic induction of autophagy by hypoxia and TGF- β1 upregulate the aerobic glycolysis and MCT4 expression in CAFs. Furthermore, we showed a positive correlation between glucose consumption and MCT4 expression in the CAFs. Autophagy was also found to be involved in the EMT in hypoxic CAFs. Collectively, these findings reveal the unappreciated role of autophagy in TME, which enhances the CAF transformation and that promotes tumor migration and metastasis via the reverse Warburg effect.

Culture of cancer spheroids and evaluation of anti-cancer drugs in 3D-printed miniaturized continuous stirred tank reactors (mCSTR)

Cancer continues to be a leading cause of mortality in modern societies; therefore, improved and more reliable in vitro cancer models are needed to expedite fundamental research and anti-cancer drug development. Here, we describe the use of a miniaturized continuous stirred tank reactor (mCSTR) to first fabricate and mature cancer spheroids (i.e, derived from MCF7 cells, DU145 cells, and a mix of MCF7 cells and fibroblasts), and then to conduct anti-cancer drug assays under continuous perfusion. This 3 mL mCSTR features an off-center agitation system that enables homogeneous chaotic laminar mixing at low speeds to support cell aggregation. We incubated cell suspensions for 3 days in ultra-low-adherence (ULA) plates to allow formation of discoid cell aggregates (~600 µm in diameter). These cell aggregates were then transferred into mCSTRs and continuously fed with culture medium. We characterized the spheroid morphology and the expression of relevant tumor biomarkers at different maturation times for up to 4 weeks. The spheroids progressively increased in size during the first 5 to 6 days of culture to reach a steady diameter between 600 and 800 µm. In proof-of-principle experiments, we demonstrated the use of this mCSTR in anti-cancer drug testing. Three drugs commonly used in breast cancer treatment (doxorubicin, docetaxel, and paclitaxel) were probed at different concentrations in MCF7 derived spheroids. In these experiments, we evaluated cell viability, glucose consumption, spheroid morphology, lactate dehydrogenase activity, and the expression of genes associated with drug resistance (ABCB1 and ABCC1) and anti-apoptosis (Bcl2). We envision the use of this agitated system as a tumor-on-a-chip platform to expedite efficacy and safety testing of novel anti-cancer drugs and possibly in personalized medicine applications.

Oxygen-Generating Cryogels Restore T Cell Mediated Cytotoxicity in Hypoxic Tumors

Solid tumors are protected from antitumor immune responses due to their hypoxic microenvironments. Weakening hypoxia-driven immunosuppression by hyperoxic breathing of 60% oxygen has shown to be effective in unleashing antitumor immune cells against solid tumors. However, efficacy of systemic oxygenation is limited against solid tumors outside of lungs and has been associated with unwanted side effects. As a result, it is essential to develop targeted oxygenation alternatives to weaken tumor hypoxia as novel approaches to restore immune responses against cancer. Herein, we report on injectable oxygen-generating cryogels (O2-cryogels) to reverse tumor-induced hypoxia. These macroporous biomaterials were designed to locally deliver oxygen, inhibit the expression of hypoxia-inducible genes in hypoxic melanoma cells, and reduce the accumulation of immunosuppressive extracellular adenosine. Our data show that O2-cryogels enhance T cell-mediated secretion of cytotoxic proteins, restoring the killing ability of tumor-specific CTLs, both in vitro and in vivo. In summary, O2-cryogels provide a unique and safe platform to supply oxygen as a co-adjuvant in hypoxic tumors and have the potential to improve cancer immunotherapies.

Bcl-2/Bcl-xL inhibitor ABT-263 overcomes hypoxia-driven radioresistence and improves radiotherapy

Hypoxia, a characteristic of most human solid tumors, is a major obstacle to successful radiotherapy. While moderate acute hypoxia increases cell survival, chronic cycling hypoxia triggers adaptation processes, leading to the clonal selection of hypoxia-tolerant, apoptosis-resistant cancer cells. Our results demonstrate that exposure to acute and adaptation to chronic cycling hypoxia alters the balance of Bcl-2 family proteins in favor of anti-apoptotic family members, thereby elevating the apoptotic threshold and attenuating the success of radiotherapy. Of note, inhibition of Bcl-2 and Bcl-xL by BH3-mimetic ABT-263 enhanced the sensitivity of HCT116 colon cancer and NCI-H460 lung cancer cells to the cytotoxic action of ionizing radiation. Importantly, we observed this effect not only in normoxia, but also in severe hypoxia to a similar or even higher extent. ABT-263 furthermore enhanced the response of xenograft tumors of control and hypoxia-selected NCI-H460 cells to radiotherapy, thereby confirming the beneficial effect of combined treatment in vivo. Targeting the Bcl-2 rheostat with ABT-263, therefore, is a particularly promising approach to overcome radioresistance of cancer cells exposed to acute or chronic hypoxia with intermittent reoxygenation. Moreover, we found intrinsic as well as ABT-263- and irradiation-induced regulation of Bcl-2 family members to determine therapy sensitivity. In this context, we identified Mcl-1 as a resistance factor that interfered with apoptosis induction by ABT-263, ionizing radiation, and combinatorial treatment. Collectively, our findings provide novel insights into the molecular determinants of hypoxia-mediated resistance to apoptosis and radiotherapy and a rationale for future therapies of hypoxic and hypoxia-selected tumor cell fractions.

Links between the unfolded protein response and the DNA damage response in hypoxia: a systematic review

Hypoxia is a feature of most solid tumours and predicts for poor prognosis. In radiobiological hypoxia (<0.1% O₂) cells become up to three times more resistant to radiation. The biological response to radiobiological hypoxia is one of few physiologically relevant stresses that activates both the unfolded protein and DNA damage responses (UPR and DDR). Links between these pathways have been identified in studies carried out in normoxia. Based in part on these previous studies and recent work from our laboratory, we hypothesised that the biological response to hypoxia likely includes overlap between the DDR and UPR. While inhibition of the DDR is a recognised strategy for improving radiation response, the possibility of achieving this through targeting the UPR has not been realised. We carried out a systematic review to identify links between the DDR and UPR, in human cell lines exposed to <2% O₂. Following PRISMA guidance, literature from January 2010 to October 2020 were retrieved via Ovid MEDLINE and evaluated. A total of 202 studies were included. LAMP3, ULK1, TRIB3, CHOP, NOXA, NORAD, SIAH1/2, DYRK2, HIPK2, CREB, NUPR1, JMJD2B, NRF2, GSK-3B, GADD45a, GADD45b, STAU1, C-SRC, HK2, CAV1, CypB, CLU, IGFBP-3 and SP1 were highlighted as potential links between the hypoxic DDR and UPR. Overall, we identified very few studies which demonstrate a molecular link between the DDR and UPR in hypoxia, however, it is clear that many of the molecules highlighted warrant further investigation under radiobiological hypoxia as these may include novel therapeutic targets to improve radiotherapy response.

Quantitative Proteomic Approach Reveals Altered Metabolic Pathways in Response to the Inhibition of Lysine Deacetylases in A549 Cells under Normoxia and Hypoxia

Growing evidence is showing that acetylation plays an essential role in cancer, but studies on the impact of KDAC inhibition (KDACi) on the metabolic profile are still in their infancy. Here, we analyzed, by using an iTRAQ-based quantitative proteomics approach, the changes in the proteome of KRAS-mutated non-small cell lung cancer (NSCLC) A549 cells in response to trichostatin-A (TSA) and nicotinamide (NAM) under normoxia and hypoxia. Part of this response was further validated by molecular and biochemical analyses and correlated with the proliferation rates, apoptotic cell death, and activation of ROS scavenging mechanisms in opposition to the ROS production. Despite the differences among the KDAC inhibitors, up-regulation of glycolysis, TCA cycle, oxidative phosphorylation and fatty acid synthesis emerged as a common metabolic response underlying KDACi. We also observed that some of the KDACi effects at metabolic levels are enhanced under hypoxia. Furthermore, we used a drug repositioning machine learning approach to list candidate metabolic therapeutic agents for KRAS mutated NSCLC. Together, these results allow us to better understand the metabolic regulations underlying KDACi in NSCLC, taking into account the microenvironment of tumors related to hypoxia, and bring new insights for the future rational design of new therapies.

Hypoxia-induced alternative splicing in human diseases: the pledge, the turn, and the prestige

Maintenance of oxygen homeostasis is an indispensable criterion for the existence of multicellular life-forms. Disruption of this homeostasis due to inadequate oxygenation of the respiring tissues leads to pathological hypoxia, which acts as a significant stressor in several pathophysiological conditions including cancer, cardiovascular defects, bacterial infections, and neurological disorders. Consequently, the hypoxic tissues develop necessary adaptations both at the tissue and cellular level. The cellular adaptations involve a dramatic alteration in gene expression, post-transcriptional and post-translational modification of gene products, bioenergetics, and metabolism. Among the key responses to oxygen-deprivation is the skewing of cellular alternative splicing program. Herein, we discuss the current concepts of oxygen tension-dependent alternative splicing relevant to various pathophysiological conditions. Following a brief description of cellular response to hypoxia and the pre-mRNA splicing mechanism, we outline the impressive number of hypoxia-elicited alternative splicing events associated with maladies like cancer, cardiovascular diseases, and neurological disorders. Furthermore, we discuss how manipulation of hypoxia-induced alternative splicing may pose promising strategies for novel translational diagnosis and therapeutic interventions.

Hypoxia-mediated drug resistance in breast cancers

Tissue hypoxia in solid tumors is caused by several pathological changes associated with tumor growth, including altered microvasculature structure, increased diffusional distances, and tumor-associated anemia. As the oxygen tension decreases, tumor cells adapt to the limited oxygen supply. Previous studies have shown that such adaptation leads to an aggressive phenotype that is resistant to many anti-cancer therapies. Induction of hypoxia inducible factors (HIFs) mediates many proteomic and genomic changes associated with tumor hypoxia. In breast cancers, HIFs not only predict poor prognosis, but also promote metastasis and drug resistance. Several studies have proposed HIF-1α as a druggable target in drug-resistant breast cancers, leading to the synthesis and development of small molecule inhibitors. Disappointingly, however, none of these small molecule inhibitors have progressed to clinical use. In this review, we briefly discuss the role of HIF-1α in breast cancer drug resistance and summarize the current and future approaches to targeting this transcription factor in breast cancer treatment.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

Hypoxia-inducible factors not only regulate but also are myeloid-cell treatment targets

Hypoxia describes limited oxygen availability at the cellular level. Myeloid cells are exposed to hypoxia at various bodily sites and even contribute to hypoxia by consuming large amounts of oxygen during respiratory burst. Hypoxia-inducible factors (HIFs) are ubiquitously expressed heterodimeric transcription factors, composed of an oxygen-dependent α and a constitutive β subunit. The stability of HIF-1α and HIF-2α is regulated by oxygen-sensing prolyl-hydroxylases (PHD). HIF-1α and HIF-2α modify the innate immune response and are context dependent. We provide a historic perspective of HIF discovery, discuss the molecular components of the HIF pathway, and how HIF-dependent mechanisms modify myeloid cell functions. HIFs enable myeloid-cell adaptation to hypoxia by up-regulating anaerobic glycolysis. In addition to effects on metabolism, HIFs control chemotaxis, phagocytosis, degranulation, oxidative burst, and apoptosis. HIF-1α enables efficient infection defense by myeloid cells. HIF-2α delays inflammation resolution and decreases antitumor effects by promoting tumor-associated myeloid-cell hibernation. PHDs not only control HIF degradation, but also regulate the crosstalk between innate and adaptive immune cells thereby suppressing autoimmunity. HIF-modifying pharmacologic compounds are entering clinical practice. Current indications include renal anemia and certain cancers. Beneficial and adverse effects on myeloid cells should be considered and could possibly lead to drug repurposing for inflammatory disorders.

miR-20b-5p attenuates hypoxia-induced apoptosis in cardiomyocytes via the HIF-1α/NF-κB pathway

Chronic hypoxia is a common inducer of end-stage cardiovascular disease. In cells under hypoxia, the hypoxia-inducible factor-1 (HIF-1) plays a vital role in regulating downstream target genes. However, the mechanism of hypoxia in cardiomyocytes is still unclear. In this study, we aimed to identify novel downstream epigenetic targets of HIF-1α in cardiomyocytes under hypoxia. H9c2 cells were exposed to hypoxia condition, and quantitative real-time PCR analysis was performed to evaluate the expression of miR-20b-5p. The results indicated that the expression of miR-20b-5p was down-regulated in H9c2 cells under low oxygen condition. Meanwhile, HIF-1α overexpression further down-regulated the miR-20b-5p expression in H9c2 cells transfected with HIF-1α plasmids. In addition, Annexin-V-FITC/PI flow cytometry analysis suggested that overexpression of miR-20b-5p attenuated cell apoptosis under hypoxia condition in H9c2 cells. Western blot analysis showed that the hypoxia apparently increased Bax and cleaved-caspase-3, but decreased Bcl-2 expression in H9c2 cells, indicating that hypoxia-induced NF-κB signaling pathway activation is mediated by miR-20b-5p. Hypoxia-induced H9c2 cell apoptosis was reduced after HIF-1α knockdown as shown by the flow cytometry analysis. In conclusion, we identified that miR-20b-5p plays an important role in mediating cardiomyocytes apoptosis under hypoxia, which is mediated by the HIF-1/NF-κB signaling pathway.

Bcl-2 Overexpression and Hypoxia Synergistically Enhance Angiogenic Properties of Dental Pulp Stem Cells

Post-implantation cell survival and angio-/vasculogenesis are critical for the success of cell-based regenerative strategies. The current study aimed to overexpress B-cell lymphoma 2 (Bcl-2) gene in dental pulp stem cells (DPSCs) and examine the anti-apoptotic and angio-/vasculogenic effects both in-vitro and in-vivo. DPSCs were transduced with Bcl-2-green fluorescent protein (GFP) lentiviral particles and examined for cell proliferation and apoptosis. The cells were cultured under normoxic or hypoxic (0.5 mM CoCl₂) conditions and examined for the expression of angiogenic factors and effects on endothelial cell proliferation, migration and vessel morphogenesis. Cells with or without hypoxic preconditioning were used in in-vivo Matrigel plug assay to study the post-implantation cell survival and angio-/vasculogenesis. Bcl-2-overexpressing-DPSCs showed significantly lower apoptosis than that of null-GFP-DPSCs under serum-free conditions. Under hypoxia, Bcl-2-overexpressing-DPSCs expressed significantly higher levels of vascular endothelial growth factor compared to that under normoxia and null-GFP-DPSCs. Consequently, Bcl-2-overexpressing-DPSCs significantly enhanced endothelial cell proliferation, migration and vascular tube formation on Matrigel. Immunohistological assessment of in-vivo transplanted Matrigel plugs showed significantly higher cell survival and vasculature in hypoxic preconditioned Bcl-2-overexpressing-DPSC group compared to null-GFP-DPSC group. In conclusion, Bcl-2 overexpression and hypoxic-preconditioning could be synergistically used to enhance post-implantation cell survival and angio-/vasculogenic properties of DPSCs.

Tumor microenvironment in chemoresistance, metastasis and immunotherapy of pancreatic cancer

Pancreatic cancer (PC) is a fatal disease with high malignancy and difficult for early diagnosis. PC causes more than 400,000 patient deaths world widely and becomes the severe health problems. The tumor microenvironment (TME) is comprised of acellular stroma, pancreatic stellate cells, immune cells, and soluble factors. TME is maintained by continuous cell-matrix and cell-cell interactions. TME induced by the interaction among pancreatic cancer cells, epithelial cells and stromal cells is essential for the progression of PC and leads to resistance to chemotherapy. Components in the microenvironment can also promote the formation of connective tissue in the primary or metastatic site, or promote the metastatic ability of PC by enhancing angiogenesis, epithelial-mesenchymal transformation, and lymph angiogenesis. In addition, the TME also leaves pancreatic cancer unsusceptible to different immunotherapeutic strategies. In this review, we summarized the current knowledge about TME in PC. And the focus was placed on the role of TME in chemotherapeutic resistance and metastasis in the field of PC. And we also paid attention to the immunological therapy targeting the TME, aiming to provide the novel therapy for pancreatic cancer.

β-Escin alleviates cobalt chloride-induced hypoxia-mediated apoptotic resistance and invasion via ROS-dependent HIF-1α/TGF-β/MMPs in A549 cells

Hypoxia is contributed in various pathophysiological conditions including obesity, cardiovascular diseases, and cancer. In cancer, hypoxia is a salient phenomenon and has been correlated with tumor progression, metastasis, and provoke resistance to therapies in cancer patients, which exert with stabilization of main effector, hypoxia inducible factor-1 alpha (HIF-1α). Therefore, therapeutic targeting of hypoxic responses in cancer is the potential approach to improve the better treatment efficacy. In the present study, we evaluated the effect of β-Escin (β-Es) on hypoxia-induced resistance to apoptosis and metastasis in human non-small-cell lung cancer cells. The MTT assay revealed that β-Es treatment decreased the A549 cells viability under cobalt chloride-induced hypoxia. Apoptotic proteins were analyzed by western blot that showed cancer cells treated with β-Es induced cell death in hypoxia condition as proteins compared with normoxia. Moreover, we observed that cobalt chloride induced hypoxia through the generation of intracellular reactive oxygen species and stabilized the transcriptional factor HIF-1α, which leads to cancer metastasis. This notion was supported by the migration, invasion, and adhesion assays. Furthermore, hypoxia increased the expression of transforming growth factor-β, and the activation of matrix metalloproteinases were suppressed by the treatment of β-Es as well as pretreatment with N-acetylcysteine (NAC). Therefore, we demonstrate that a concurrent activation of HIF-1α, transforming growth factor-β, and matrix metalloproteinases participate in hypoxia-induced metastasis and that β-Es prevent A549 cells metastasis by inhibition of reactive oxygen species.

Mechanisms of Apoptosis Resistance to NK Cell-Mediated Cytotoxicity in Cancer

Natural killer (NK) cells are major contributors to immunosurveillance and control of tumor development by inducing apoptosis of malignant cells. Among the main mechanisms involved in NK cell-mediated cytotoxicity, the death receptor pathway and the release of granules containing perforin/granzymes stand out due to their efficacy in eliminating tumor cells. However, accumulated evidence suggest a profound immune suppression in the context of tumor progression affecting effector cells, such as NK cells, leading to decreased cytotoxicity. This diminished capability, together with the development of resistance to apoptosis by cancer cells, favor the loss of immunogenicity and promote immunosuppression, thus partially inducing NK cell-mediated killing resistance. Altered expression patterns of pro- and anti-apoptotic proteins along with genetic background comprise the main mechanisms of resistance to NK cell-related apoptosis. Herein, we summarize the main effector cytotoxic mechanisms against tumor cells, as well as the major resistance strategies acquired by tumor cells that hamper the extrinsic and intrinsic apoptotic pathways related to NK cell-mediated killing.

Pathophysiological implications of hypoxia in human diseases

Oxygen is essentially required by most eukaryotic organisms as a scavenger to remove harmful electron and hydrogen ions or as a critical substrate to ensure the proper execution of enzymatic reactions. All nucleated cells can sense oxygen concentration and respond to reduced oxygen availability (hypoxia). When oxygen delivery is disrupted or reduced, the organisms will develop numerous adaptive mechanisms to facilitate cells survived in the hypoxic condition. Normally, such hypoxic response will cease when oxygen level is restored. However, the situation becomes complicated if hypoxic stress persists (chronic hypoxia) or cyclic normoxia-hypoxia phenomenon occurs (intermittent hypoxia). A series of chain reaction-like gene expression cascade, termed hypoxia-mediated gene regulatory network, will be initiated under such prolonged or intermittent hypoxic conditions and subsequently leads to alteration of cellular function and/or behaviors. As a result, irreversible processes occur that may cause physiological disorder or even pathological consequences. A growing body of evidence implicates that hypoxia plays critical roles in the pathogenesis of major causes of mortality including cancer, myocardial ischemia, metabolic diseases, and chronic heart and kidney diseases, and in reproductive diseases such as preeclampsia and endometriosis. This review article will summarize current understandings regarding the molecular mechanism of hypoxia in these common and important diseases.

Thyroid Hormone Protects Primary Cortical Neurons Exposed to Hypoxia by Reducing DNA Methylation and Apoptosis

Traumatic brain injury (TBI) is associated with disruption of cerebral blood flow leading to localized brain hypoxia. Thyroid hormone (TH) treatment, administered shortly after injury, has been shown to promote neural protection in rodent TBI models. The mechanism of TH protection, however, is not established. We used mouse primary cortical neurons to investigate the effectiveness and possible pathways of T3-promoted cell survival after exposure to hypoxic injury. Cultured primary cortical neurons were exposed to hypoxia (0.2% oxygen) for 7 hours with or without T3 (5 nM). T3 treatment enhanced DNA 5-hydroxymethylcytosine levels and attenuated the hypoxia-induced increase in DNA 5-methylcytosine (5-mc). In the presence of T3, mRNA expression of Tet family genes was increased and DNA methyltransferase (Dnmt) 3a and Dnmt3b were downregulated, compared with conditions in the absence of T3. These T3-induced changes decreased hypoxia-induced DNA de novo methylation, which reduced hypoxia-induced neuronal damage and apoptosis. We used RNA sequencing to characterize T3-regulated genes in cortical neurons under hypoxic conditions and identified 22 genes that were upregulated and 15 genes that were downregulated. Krüppel-like factor 9 (KLF9), a multifunctional transcription factor that plays a key role in central nervous system development, was highly upregulated by T3 treatment in hypoxic conditions. Knockdown of the KLF9 gene resulted in early apoptosis and abolished the beneficial role of T3 in neuronal survival. KLF9 mediates, in part, the neuronal protective role of T3. T3 treatment reduces hypoxic damage, although pathways that reduce DNA methylation and apoptosis remain to be elucidated.

Hypoxia inducible factor-1α/B-cell lymphoma 2 signaling impacts radiosensitivity of H1299 non-small cell lung cancer cells in a normoxic environment

Hypoxia inducible factor-1α (HIF-1α) is a critical transcriptional factor for the response of cells to hypoxic microenvironment and its expression induces resistance of hypoxic non-small-cell lung cancer (NSCLC) cells to radiotherapy. This study investigated how the activation of HIF-1α/B-cell lymphoma 2 (BCL-2) signaling under normoxic conditions impacted radiosensitivity of NSCLC cells. The recombinant pcDNA3.0-EGFP plasmids with wild-type or mutant HIF-1α complementary DNA (cDNA) were transfected into H1299 cells, an NSCLC cell line, establishing two H1299 sublines with high expression of HIF-1α. Compared with the levels of HIF-1α and BCL-2 proteins in non-transfected cells, increased levels of both proteins were found in transfected cells. Moreover, the expression of HIF-1α in non-transfected cells induced by chloride cobalt (CoCl₂), a commonly used mimetic hypoxia reagent, was concomitant with the enhancement of BCL-2 expression. Conversely, reduction of HIF-1α expression by an inhibitor decreased the levels of BCL-2 proteins. The results revealed that the stabilization and expression of HIF-1α promoted the accumulation of BCL-2 proteins in H1299 cells. Subsequent experiments showed that intracellular HIF-1α/BCL-2 signaling was triggered in a normoxic environment after H1299 cells were exposed to irradiation, causing an elevated radioresistance. In contrast, blockage of HIF-1α/BCL-2 signaling leads to an elevated radiosensitivity. Proliferation of cells assay showed that, under normoxic conditions, population doubling times (PDTs) of irradiated cells were prolonged by suppression of HIF-1α/BCL-2 signaling. It is, therefore, indicated that HIF-1α/BCL-2 signaling activated by ionizing radiation reduces the radiosensitivity of H1299 cells independent of the hypoxic environment.

The biochemical and molecular mechanisms involved in the role of tumor micro-environment stress in development of drug resistance

BACKGROUND

Multi-drug resistance (MDR) is a leading cause of morbidity and mortality in cancer and it continues to be a challenge in cancer treatment. Moreover, the tumor micro-environment is essential to the formation of drug resistant cancers. Recent evidence indicates that the tumor micro-environment is a critical regulator of cancer progression, distant metastasis and acquired resistance of tumors to various therapies. Despite significant advances in chemotherapy and radiotherapy, the development of therapeutic resistance leads to reduced drug efficacy.

SCOPE OF REVIEW

This review highlights mechanistic aspects of the biochemistry of the tumor micro-enviroment, such as the hypoglycaemia, reactive oxygen species (ROS), hypoxia and their effects in propagating MDR. This is achieved through: (A) increased survival via autophagy and failure of apoptosis; (B) altered metabolic processing; and (C) reduction in drug delivery and uptake or increased drug efflux.

MAJOR CONCLUSIONS

The development of MDR in cancer has been demonstrated to be majorly influenced by naturally occurring stressors within the tumor micro-environment, as well as chemotherapeutics. Thus, the tumor micro-environment is currently emerging as a major focus of research which needs to be carefully addressed before cancer can be successfully treated.

GENERAL SIGNIFICANCE

Elucidating the biochemical mechanisms which promote MDR is essential in development of effective therapeutics that can overcome these acquired defences in cancer cells.

The dual inhibitor of the phosphoinositol-3 and PIM kinases, IBL-202, is effective against chronic lymphocytic leukaemia cells under conditions that mimic the hypoxic tumour microenvironment

Despite significant advances in treatment, chronic lymphocytic leukaemia (CLL) remains an incurable disease. Ibrutinib and idelalisib, which inhibit Bruton Tyrosine kinase (BTK) and phosphoinositol-3 (PI3) kinase-δ respectively, have become important treatment options for the disease and demonstrate the potential of targeting components of the B-cell receptor-signalling pathway. IBL-202 is a dual inhibitor of the PIM and PI3 kinases. Synergy between the pan-PIM inhibitor, pPIMi, and idelalisib against a range of haematological cell lines and primary CLL cells supports the rationale for preclinical studies of IBL-202 in CLL. Importantly, IBL-202, but not idelalisib, was cytotoxic against CLL cells under in vitro conditions that mimic the hypoxic tumour microenvironment. The significant effects of IBL-202 on CD49d and CXCR4 expression and migration, cycle and proliferation of CLL cells suggest the drug may also interfere with the migratory and proliferative capacity of the leukaemic cells. Collectively, these data demonstrate that dual inhibition of the PIM and PI3 kinases by IBL-202 may be an effective strategy for targeting CLL cells, particularly within the environmental niches known to confer drug-resistance.

Tumor control by hypoxia-specific chemotargeting of iron-oxide nanoparticle - Berberine complexes in a mouse model

AIM

To evaluate the therapeutic efficacy of hypoxic cell-sensitizer Sanazole (SAN) -directed targeting of cytotoxic drug Berberine (BBN) and Iron-oxide nanoparticle (NP) complexes, to solid tumor in Swiss albino mice.

MAIN METHODS

NP-BBN-SAN complexes were characterized by FTIR, XRD, TEM and Nano-size analyzer. This complex was orally administered to mice-bearing solid tumor in hind limb. Tumor regression was analysed by measuring tumor volume. Cellular DNA damages were assessed by comet assay. Transcriptional expression of genes related to tumor hypoxia and apoptosis was evaluated by quantitative real-time PCR and morphological changes in tissues were analysed by histopathology. Also levels of antioxidants and tumor markers in tissues and serum biochemical parameters were analysed.

KEY FINDINGS

Administration of NP-BBN-SAN complexes reduced tumor volume and studies were focussed on the underlying mechanisms. Extensive damage to cellular-DNA; down-regulated transcription of hif-1α, vegf, akt and bcl2; and up-regulated expression of bax and caspases, were observed in tumor. Results on tumor markers, antioxidant-status and serum parameters corroborated the molecular findings. Histopathology of tumor, liver and kidney revealed the therapeutic specificity of NP-BBN-SAN.

SIGNIFICANCE

Thus SAN and NP can be used for specific targeting of drugs, to hypoxic solid tumor, to improve therapeutic efficacy.

Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1α and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/knock-down upon CIRBP in the process of HIF-1α mediated neuron apoptosis. Results: HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1α and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.

Detection of p53 and Bcl-2 expression in cutaneous hemangioma through the quantum dot technique

Hemangioma is one of the most common types of infantile vascular benign tumor. The aim of the present study was to investigate the role of B-cell lymphoma 2 (Bcl-2) and tumor protein p53 (p53) in the proliferation and apoptosis of hemangioma cells. A total of 38 paraffin-embedded hemangioma specimens (16 males and 22 females) and another 5 paraffin-embedded healthy surrounding tissue samples, collected between January 2007 and December 2010, were obtained from the Department of Pathology at Renmin Hospital of Wuhan University (Wuhan, China). Immunohistochemistry, hematoxylin and eosin staining, and quantum dot double staining were used to detect the expression of proliferating cell nuclear antigen (PCNA), Bcl-2 and p53 in hemangioma and healthy surrounding skin tissue samples. All hemangioma specimens were classified into proliferative or the involuting stage hemangioma according to Mulliken's criteria and their expression of PCNA. The results of the quantum dot double staining were analyzed using a multi-spectral imaging system. One-way analysis of the variance and the Student-Newman-Keuls q test were performed to statistically analyze the data. There were 24 cases of proliferative stage and 14 cases of involuting stage hemangioma among the specimens. Immunohistochemical analysis results indicated a high expression of Bcl-2 and p53 in proliferative stage hemangioma tissue samples, and low expression in involuting stage hemangioma and healthy tissue samples. Statistical analysis of the results from quantum dot double staining demonstrated that the expression of Bcl-2 and p53 in proliferative hemangioma was significantly increased compared with that in involuting stage specimens (P<0.05) and healthy tissue samples (P<0.05). No significant difference in Bcl-2 and p53 expression was identified between the involuting hemangioma and healthy surrounding tissue samples. The higher expression of Bcl-2 and p53 in proliferative hemangioma suggests that Bcl-2 may cause an imbalance between endothelial cell proliferation and apoptosis through the inhibition of endothelial cell apoptosis. Furthermore, p53 may promote the proliferation of endothelial cells in proliferative hemangioma.

Cancer stem cell niche models and contribution by mesenchymal stroma/stem cells

Background

The initiation and progression of malignant tumors is driven by distinct subsets of tumor-initiating or cancer stem-like cells (CSCs) which develop therapy/apoptosis resistance and self-renewal capacity. In order to be able to eradicate these CSCs with novel classes of anti-cancer therapeutics, a better understanding of their biology and clinically-relevant traits is mandatory.

Main body

Several requirements and functions of a CSC niche physiology are combined with current concepts for CSC generation such as development in a hierarchical tumor model, by stochastic processes, or via a retrodifferentiation program. Moreover, progressive adaptation of endothelial cells and recruited immune and stromal cells to the tumor site substantially contribute to generate a tumor growth-permissive environment resembling a CSC niche. Particular emphasis is put on the pivotal role of multipotent mesenchymal stroma/stem cells (MSCs) in supporting CSC development by various kinds of interaction and cell fusion to form hybrid tumor cells.

Conclusion

A better knowledge of CSC niche physiology may increase the chances that cancer stemness-depleting interventions ultimately result in arrest of tumor growth and metastasis.

Low hypoxia inducible factor-1α (HIF-1α) expression in testicular germ cell tumors - a major reason for enhanced chemosensitivity?

The molecular basis for enhanced chemosensitivity of testicular germ cell tumors (GCT) has been an area of great interest, as it could potentially give us therapeutic leads in other resistant malignancies. Thus far, however, the increased sensitivity of GCT has been variously attributed to multiple factors — an inability to detoxify cisplatin, a lack of export pumps, an inability to repair the DNA damage, an intact apoptotic cascade and lack of p53 mutation; but a unifying underlying etiology leading to the aforementioned processes and having a translational implication has so far been elusive. Herein, we offer evidence to support a potential significant role for the previously demonstrated low hypoxia inducible factor-1α (HIF-1α) expression in mediating the general exquisite chemosensitivity of testicular GCT, through the aforementioned processes. This molecular mechanism based hypothesis could have a significant translational implication in platinum refractory GCT as well as other platinum resistant malignancies.

Polysialic acid sustains cancer cell survival and migratory capacity in a hypoxic environment

Polysialic acid (polySia) is a unique carbohydrate polymer expressed on the surface of NCAM (neuronal cell adhesion molecule) in a number of cancers where it modulates cell-cell and cell-matrix adhesion, migration, invasion and metastasis and is strongly associated with poor clinical prognosis. We have carried out the first investigation into the effect of polySia expression on the behaviour of cancer cells in hypoxia, a key source of chemoresistance in tumours. The role of polysialylation and associated tumour cell migration and cell adhesion were studied in hypoxia, along with effects on cell survival and the potential role of HIF-1. Our findings provide the first evidence that polySia expression sustains migratory capacity and is associated with tumour cell survival in hypoxia. Initial mechanistic studies indicate a potential role for HIF-1 in sustaining polySia-mediated migratory capacity, but not cell survival. These data add to the growing body of evidence pointing to a crucial role for the polysialyltransferases (polySTs) in neuroendocrine tumour progression and provide the first evidence to suggest that polySia is associated with an aggressive phenotype in tumour hypoxia. These results have significant potential implications for polyST inhibition as an anti-metastatic therapeutic strategy and for targeting hypoxic cancer cells.

Cell Death Conversion under Hypoxic Condition in Tumor Development and Therapy

Hypoxia, which is common during tumor progression, plays important roles in tumor biology. Failure in cell death in response to hypoxia contributes to progression and metastasis of tumors. On the one hand, the metabolic and oxidative stress following hypoxia could lead to cell death by triggering signal cascades, like LKB1/AMPK, PI3K/AKT/mTOR, and altering the levels of effective components, such as the Bcl-2 family, Atg and p62. On the other hand, hypoxia-induced autophagy can serve as a mechanism to turn over nutrients, so as to mitigate the adverse condition and then avoid cell death potentially. Due to the effective role of hypoxia, this review focuses on the crosstalk in cell death under hypoxia in tumor progression. Additionally, the illumination of cell death in hypoxia could shed light on the clinical applications of cell death targeted therapy.

Cycling hypoxia induces a specific amplified inflammatory phenotype in endothelial cells and enhances tumor-promoting inflammation in vivo

Abnormal architecture of the tumor blood network, as well as heterogeneous erythrocyte flow, leads to temporal fluctuations in tissue oxygen tension exposing tumor and stromal cells to cycling hypoxia. Inflammation is another feature of tumor microenvironment and is considered as a new enabling characteristic of tumor progression. As cycling hypoxia is known to participate in tumor aggressiveness, the purpose of this study was to evaluate its role in tumor-promoting inflammation. Firstly, we assessed the impact of cycling hypoxia in vitro on endothelial inflammatory response induced by tumor necrosis factor α. Results showed that endothelial cells exposed to cycling hypoxia displayed an amplified proinflammatory phenotype, characterized by an increased expression of inflammatory cytokines, namely, interleukin (IL)-6 and IL-8; by an increased expression of adhesion molecules, in particular intercellular adhesion molecule-1 (ICAM-1); and consequently by an increase in THP-1 monocyte adhesion. This exacerbation of endothelial inflammatory phenotype occurs through nuclear factor-κB overactivation. Secondly, the role of cycling hypoxia was studied on overall tumor inflammation in vivo in tumor-bearing mice. Results showed that cycling hypoxia led to an enhanced inflammation in tumors as prostaglandin-endoperoxide synthase 2 (PTGS2), IL-6, CXCL1 (C-X-C motif ligand 1), and macrophage inflammatory protein 2 (murine IL-8 functional homologs) mRNA expression was increased and as a higher leukocyte infiltration was evidenced. Furthermore, cycling hypoxia-specific inflammatory phenotype, characterized by a simultaneous (baculoviral inhibitor of apoptosis repeat-containing 5)(low)/PTGS2(high)/ICAM-1(high)/IL-6(high)/IL-8(high) expression, is associated with a poor prognosis in human colon cancer. This new phenotype could thus be used in clinic to more precisely define prognosis for colon cancer patients. In conclusion, our findings evidenced for the first time the involvement of cycling hypoxia in tumor-promoting inflammation amplification.

HIF-1α Induces Multidrug Resistance in Gastric Cancer Cells by Inducing MiR-27a

This study aimed to determine the correlation between HIF-1α and miR-27a expression and to evaluate the effect of inhibition of HIF-1α expression on miR-27a expression and drug resistance in gastric cancer (GC). In the present study, real time-PCR and Western blot were performed to detect the expression of HIF-1α in GC tissues and cell lines. Then, OCUM-2MD3/L-OHP cells were transfected with HIF-1α-siRNA, a miR-27a mimic or pcDNA-HIF-1α, and cell survival was determined via the MTT assay. The expression of HIF-1α, miR-27a, and MDR-related genes was measured via real time-PCR and Western blot. ChIP and dual luciferase activity assays were performed to assess the transcriptional regulation of HIF-1α and miR-27a. The results revealed that transfection with HIF-1α-siRNA markedly decreased the levels of miR-27a, resulting in dramatically enhanced inhibition of the proliferation rate of OCUM-2MD3/L-OHP cells. Compared to non-transfected cells, the survival rate was significantly reduced in the cells transfected with HIF-1α-siRNA after treatment with L-OHP. The cell survival rate was significantly increased in OCUM-2MD3/L-OHP cells transfected with the miR-27a mimic, whereas HIF-1α overexpression did not result in any clear change in cell survival. The results of the dual luciferase activity assay demonstrated that HIF-1α enhances the transcriptional activity of the miR27a promoter in cells transfected with a reporter plasmid containing the upstream promoter region of miR27a together with pcDNA-HIF-1α. ChIP analysis suggested that HIF-1α directly binds to the promoter region of miR27a. Inhibition of HIF-1α or miR27a expression decreased MDR1/P-gp, LRP, and Bcl-2 expression in OCUM-2MD3/L-OHP cells. Thus, we found that HIF-1α is closely associated with MDR in GC and that HIF-1α may suppress MDR1/P-gp, LRP and Bcl-2 expression by inhibiting miR-27a expression.

Organelle-specific initiation of cell death

In a majority of pathophysiological settings, cell death is not accidental - it is controlled by a complex molecular apparatus. Such a system operates like a computer: it receives several inputs that inform on the current state of the cell and the extracellular microenvironment, integrates them and generates an output. Thus, depending on a network of signals generated at specific subcellular sites, cells can respond to stress by attemptinwg to recover homeostasis or by activating molecular cascades that lead to cell death by apoptosis or necrosis. Here, we discuss the mechanisms whereby cellular compartments - including the nucleus, mitochondria, plasma membrane, endoplasmic reticulum, Golgi apparatus, lysosomes, cytoskeleton and cytosol - sense homeostatic perturbations and translate them into a cell-death-initiating signal.

LGL1 modulates proliferation, apoptosis, and migration of human fetal lung fibroblasts

Rapid growth and formation of new gas exchange units (alveogenesis) are hallmarks of the perinatal lung. Bronchopulmonary dysplasia (BPD), common in very premature infants, is characterized by premature arrest of alveogenesis. Mesenchymal cells (fibroblasts) regulate both lung branching and alveogenesis through mesenchymal-epithelial interactions. Temporal or spatial deficiency of late-gestation lung 1/cysteine-rich secretory protein LD2 (LGL1/CRISPLD2), expressed in and secreted by lung fibroblasts, can impair both lung branching and alveogenesis (LGL1 denotes late gestation lung 1 protein; LGL1 denotes the human gene; Lgl1 denotes the mouse/rat gene). Absence of Lgl1 is embryonic lethal. Lgl1 levels are dramatically reduced in oxygen toxicity rat models of BPD, and heterozygous Lgl1(+/-) mice exhibit features resembling human BPD. To explore the role of LGL1 in mesenchymal-epithelial interactions in developing lung, we developed a doxycycline (DOX)-inducible RNA-mediated LGL1 knockdown cellular model in human fetal lung fibroblasts (MRC5(LGL1KD)). We assessed the impact of LGL1 on cell proliferation, cell migration, apoptosis, and wound healing. DOX-induced MRC5(LGL1KD) suppressed cell growth and increased apoptosis of annexin V(+) staining cells and caspase 3/7 activity. LGL1-conditioned medium increased migration of fetal rat primary lung epithelial cells and human airway epithelial cells. Impaired healing by MRC5(LGL1KD) cells of a wound model was attenuated by addition of LGL1-conditioned medium. Suppression of LGL1 was associated with dysregulation of extracellular matrix genes (downregulated MMP1, ColXVα1, and ELASTIN) and proapoptosis genes (upregulated BAD, BAK, CASP2, and TNFRSF1B) and inhibition of 44/42MAPK phosphorylation. Our findings define a role for LGL1 in fibroblast expansion and migration, epithelial cell migration, and mesenchymal-epithelial signaling, key processes in fetal lung development.

Effects of copper sulfate-oxidized or myeloperoxidase-modified LDL on lipid loading and programmed cell death in macrophages under hypoxia

Atheromatous plaques contain heavily lipid-loaded macrophages that die, hence generating the necrotic core of these plaques. Since plaque instability and rupture is often correlated with a large necrotic core, it is important to understand the mechanisms underlying foam cell death. Furthermore, macrophages within the plaque are associated with hypoxic areas but little is known about the effect of low oxygen partial pressure on macrophage death. The aim of this work was to unravel macrophage death mechanisms induced by oxidized low-density lipoproteins (LDL) both under normoxia and hypoxia. Differentiated macrophages were incubated in the presence of native, copper sulfate-oxidized, or myeloperoxidase-modified LDL. The unfolded protein response, apoptosis, and autophagy were then investigated. The unfolded protein response and autophagy were triggered by myeloperoxidase-modified LDL and, to a larger extent, by copper sulfate-oxidized LDL. Electron microscopy observations showed that oxidized LDL induced excessive autophagy and apoptosis under normoxia, which were less marked under hypoxia. Myeloperoxidase-modified LDL were more toxic and induced a higher level of apoptosis. Hypoxia markedly decreased apoptosis and cell death, as marked by caspase activation. In conclusion, the cell death pathways induced by copper sulfate-oxidized and myeloperoxidase-modified LDL are different and are differentially modulated by hypoxia.

Insulin induces C2C12 cell proliferation and apoptosis through regulation of cyclin D1 and BAD expression

Insulin is a secreted peptide hormone identified in human pancreas to promote glucose utilization. Insulin has been observed to induce cell proliferation and myogenesis in C2C12 cells. The precise mechanisms underlying the proliferation of C2C12 cells induced by insulin remain unclear. In this study, we observed for the first time that 10 nM insulin treatment promotes C2C12 cell proliferation. Additionally, 50 and 100 nM insulin treatment induces C2C12 cell apoptosis. By utilizing real-time PCR and Western blotting analysis, we found that the mRNA levels of cyclinD1 and BAD are induced upon 10 and 50 nM/100 nM insulin treatment, respectively. The similar results were observed in C2C12 cells expressing GATA-6 or PPARα. Our results identify for the first time the downstream targets of insulin, cyclin D1, and BAD, elucidate a new molecular mechanism of insulin in promoting cell proliferation and apoptosis.

The potential role of HIF on tumour progression and dissemination

Cancer is the second cause of mortality worldwide, primarily owing to failure to cure metastatic disease. The need to target the metastatic process to reduce mortality is clear and research over the past decade has shown hypoxia-inducible factor-1 (HIF-1) to be one of the promising targets. In order for metastatic disease to be established, multiple steps need to be taken whereby the tumour cells escape into the bloodstream and survive, disseminate and then establish at a premetastatic niche. HIF-1 mediates hypoxia-induced proangiogenic factors such as vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), which promote extravasation and chemotaxis. The migration of tumour cells is mediated by loss of E-cadherin, which results in a more invasive phenotype; dissemination of the tumour cells by increased vascular permeability and survival in the bloodstream through resistance to apoptosis as well as adhesion at the premetastatic niche are all controlled by factors under the influence of HIF-1. The overexpression of HIF in many aggressive cancer types as well as its role in the establishment of metastatic disease and treatment resistance demonstrate its potential target in therapeutics. Taken together, the role of HIF-1 in cancer and metastatic disease is clear and the need for better treatment targeting metastases is paramount; more aggressive phenotypes with less response to treatment are associated with HIF-1 expression. Our research has shown promise but many questions still remain to be answered.

Insulin induces proliferation and cardiac differentiation of P19CL6 cells in a dose-dependent manner

Insulin is a peptide hormone produced by beta cells of the pancreas. The roles of insulin in energy metabolism have been well studied, with most of the attention focused on glucose utilization, but the roles of insulin in cell proliferation and differentiation remain unclear. In this study, we observed for the first time that 10 nmol/L insulin treatment induces cell proliferation and cardiac differentiation of P19CL6 cells, whereas 50 and 100 nmol/L insulin treatment induces P19CL6 cell apoptosis and blocks cardiac differentiation of P19CL6 cells. By using real-time polymerase chain reaction (PCR) and Western blotting analysis, we found that the mRNA levels of cyclin D1 and α myosin heavy chain (α-MHC) are induced upon 10 nmol/L insulin stimulation and inhibited upon 50/100 nmol/L insulin treatment, whereas the mRNA levels of BCL-2-antagonist of cell death (BAD) exists a reverse trend. The similar results were observed in P19CL6 cells expressing GATA-6 or peroxisome proliferator-activated receptor α (PPARα). Our results identified the downstream targets of insulin, cyclin D1, BAD, α-MHC, and GATA-4, elucidate a novel molecular mechanism of insulin in promoting cell proliferation and differentiation.

Expression of apoptosis-associated microRNAs in ethanol-induced acute gastric mucosal injury via JNK pathway

MicroRNAs (miRNAs) have been shown to be closely associated with cellular apoptosis, but their involvement in response to ethanol-induced gastric mucosal epithelial cell apoptosis remains largely unknown. The purpose of this study was to investigate the expression profile of apoptosis-associated miRNAs in ethanol-induced acute gastric mucosal injury and the mechanisms underlying injury. Gastric mucosal injury was induced in rats by oral administration of ethanol, and gastric tissues were collected for analysis of gastric ulcer index, apoptosis ratio, caspase-3 activity, and miRNAs expression. Cell cultures of human gastric mucosal epithelial cells (GES-1) were incubated with ethanol to induce apoptosis. Mimics or inhibitors of miRNAs or c-Jun N-terminal kinase (JNK) inhibitor were added to the cell culture medium. GES-1 cells were collected for analysis of apoptosis ratio, caspase-3 activity, miRNAs expression, and protein phosphorylation levels of JNK, p38 mitogen-activated protein kinase (p38MAPK), or extracellular signal-regulated kinase (ERK). In the animal experiments, gastric ulcer index, cellular apoptosis, and caspase-3 activity were significantly increased, accompanied by up-regulation of miR-145 and down-regulation of the microRNAs miR-17, miR-19a, miR-21, miR-181a, and miR-200c. In the human cell culture experiments, the anti-apoptotic effects of miR-19a and miR-21 or pro-apoptotic effect of miR-145 were confirmed by their corresponding mimics or inhibitor; the ethanol-induced GES-1 apoptosis as well as the changes in miRNAs expression were significantly attenuated in the presence of JNK inhibitor. These results demonstrated that miR-145, miR-19a, and miR-21 were the apoptosis-associated miRNAs in gastric mucosal epithelial cells. The regulation of expression of these 3 miRNAs in ethanol-induced GES-1 apoptosis involved the JNK pathway.

Anoikis molecular pathways and its role in cancer progression

Anoikis is a programmed cell death induced upon cell detachment from extracellular matrix, behaving as a critical mechanism in preventing adherent-independent cell growth and attachment to an inappropriate matrix, thus avoiding colonizing of distant organs. As anchorage-independent growth and epithelial-mesenchymal transition, two features associated with anoikis resistance, are vital steps during cancer progression and metastatic colonization, the ability of cancer cells to resist anoikis has now attracted main attention from the scientific community. Cancer cells develop anoikis resistance due to several mechanisms, including change in integrins' repertoire allowing them to grow in different niches, activation of a plethora of inside-out pro-survival signals as over-activation of receptors due to sustained autocrine loops, oncogene activation, growth factor receptor overexpression, or mutation/upregulation of key enzymes involved in integrin or growth factor receptor signaling. In addition, tumor microenvironment has also been acknowledged to contribute to anoikis resistance of bystander cancer cells, by modulating matrix stiffness, enhancing oxidative stress, producing pro-survival soluble factors, triggering epithelial-mesenchymal transition and self-renewal ability, as well as leading to metabolic deregulations of cancer cells. All these events help cancer cells to inhibit the apoptosis machinery and sustain pro-survival signals after detachment, counteracting anoikis and constituting promising targets for anti-metastatic pharmacological therapy. This article is part of a Special Section entitled: Cell Death Pathways.