Snail1 mediates hypoxia-induced melanoma progression

Determinants of resistance and response to melanoma therapy

Metastatic melanoma is among the most enigmatic advanced cancers to clinically manage despite immense progress in the way of available therapeutic options and historic decreases in the melanoma mortality rate. Most patients with metastatic melanoma treated with modern targeted therapies (for example, BRAFV600E/K inhibitors) and/or immune checkpoint blockade (for example, anti-programmed death 1 therapy) will progress, owing to profound tumor cell plasticity fueled by genetic and nongenetic mechanisms and dichotomous host microenvironmental influences. Here we discuss the determinants of tumor heterogeneity, mechanisms of therapy resistance and effective therapy regimens that hold curative promise.

HIF2α-dependent Dock4/Rac1-signaling regulates formation of adherens junctions and cell polarity in normoxia

Hypoxia-inducible factors (HIF) 1 and 2 regulate similar but distinct sets of target genes. Although HIFs are best known for their roles in mediating the hypoxia response accumulating evidence suggests that under certain conditions HIFs, particularly HIF2, may function also under normoxic conditions. Here we report that HIF2α functions under normoxic conditions in kidney epithelial cells to regulate formation of adherens junctions. HIF2α expression was required to induce Dock4/Rac1/Pak1-signaling mediating stability and compaction of E-cadherin at nascent adherens junctions. Impaired adherens junction formation in HIF2α- or Dock4-deficient cells led to aberrant cyst morphogenesis in 3D kidney epithelial cell cultures. Taken together, we show that HIF2α functions in normoxia to regulate epithelial morphogenesis.

Endothelial Function in Pulmonary Arterial Hypertension: From Bench to Bedside

Pulmonary arterial hypertension is a complex pathology whose etiology is still not completely well clarified. The pathogenesis of pulmonary arterial hypertension involves different molecular mechanisms, with endothelial dysfunction playing a central role in disease progression. Both individual genetic predispositions and environmental factors seem to contribute to its onset. To further understand the complex relationship between endothelial and pulmonary hypertension and try to contribute to the development of future therapies, we report a comprehensive and updated review on endothelial function in pulmonary arterial hypertension.

OTUD4 regulates metastasis and chemoresistance in melanoma by stabilizing Snail1

Melanoma is the most aggressive form of skin cancer with rapidly increased incidence worldwide especially in the Caucasian population. Surgical excision represents the curative treatment choice in patients with early-stage disease. However, the therapeutic outcomes in patients with metastatic melanoma remains unsatisfactory. Thus, understanding molecular mechanisms contributing to metastasis and chemoresistance is critical for new improved therapies of melanoma. Snail1, an important epithelial-mesenchymal transition transcription factors (EMT-TFs), is critical to induce the EMT process, thereby contributing to cancer metastasis. However, the involvement of Snail1 in melanoma metastasis remains elusive and the underlying mechanism to regulate Snail1 in melanoma needs to be further investigated. Here, we identified OTUD4 as a novel deubiquitinase of Snail1 in melanoma. Moreover, the depletion of OTUD4 in melanoma cells markedly inhibited Snail1 stability and Snail1-driven malignant phenotypes both in vitro and in vivo. Overall, our study establishes OTUD4 as a novel therapeutic target in metastasis and chemoresistance of melanoma by stabilizing Snail1 and provides a rationale for potential therapeutic strategies of melanoma.

Regulation and signaling pathways in cancer stem cells: implications for targeted therapy for cancer

Cancer stem cells (CSCs), initially identified in leukemia in 1994, constitute a distinct subset of tumor cells characterized by surface markers such as CD133, CD44, and ALDH. Their behavior is regulated through a complex interplay of networks, including transcriptional, post-transcriptional, epigenetic, tumor microenvironment (TME), and epithelial-mesenchymal transition (EMT) factors. Numerous signaling pathways were found to be involved in the regulatory network of CSCs. The maintenance of CSC characteristics plays a pivotal role in driving CSC-associated tumor metastasis and conferring resistance to therapy. Consequently, CSCs have emerged as promising targets in cancer treatment. To date, researchers have developed several anticancer agents tailored to specifically target CSCs, with some of these treatment strategies currently undergoing preclinical or clinical trials. In this review, we outline the origin and biological characteristics of CSCs, explore the regulatory networks governing CSCs, discuss the signaling pathways implicated in these networks, and investigate the influential factors contributing to therapy resistance in CSCs. Finally, we offer insights into preclinical and clinical agents designed to eliminate CSCs.

Transcription factors and potential therapeutic targets for pulmonary hypertension

Pulmonary hypertension (PH) is a refractory and fatal disease characterized by excessive pulmonary arterial cell remodeling. Uncontrolled proliferation and hypertrophy of pulmonary arterial smooth muscle cells (PASMCs), dysfunction of pulmonary arterial endothelial cells (PAECs), and abnormal perivascular infiltration of immune cells result in pulmonary arterial remodeling, followed by increased pulmonary vascular resistance and pulmonary pressure. Although various drugs targeting nitric oxide, endothelin-1 and prostacyclin pathways have been used in clinical settings, the mortality of pulmonary hypertension remains high. Multiple molecular abnormalities have been implicated in pulmonary hypertension, changes in numerous transcription factors have been identified as key regulators in pulmonary hypertension, and a role for pulmonary vascular remodeling has been highlighted. This review consolidates evidence linking transcription factors and their molecular mechanisms, from pulmonary vascular intima PAECs, vascular media PASMCs, and pulmonary arterial adventitia fibroblasts to pulmonary inflammatory cells. These findings will improve the understanding of particularly interactions between transcription factor-mediated cellular signaling pathways and identify novel therapies for pulmonary hypertension.

The epigenome and the many facets of cancer drug tolerance

The use of chemotherapeutic agents and the development of new cancer therapies over the past few decades has consequently led to the emergence of myriad therapeutic resistance mechanisms. Once thought to be explicitly driven by genetics, the coupling of reversible sensitivity and absence of pre-existing mutations in some tumors opened the way for discovery of drug-tolerant persisters (DTPs): slow-cycling subpopulations of tumor cells that exhibit reversible sensitivity to therapy. These cells confer multi-drug tolerance, to targeted and chemotherapies alike, until the residual disease can establish a stable, drug-resistant state. The DTP state can exploit a multitude of distinct, yet interlaced, mechanisms to survive otherwise lethal drug exposures. Here, we categorize these multi-faceted defense mechanisms into unique Hallmarks of Cancer Drug Tolerance. At the highest level, these are comprised of heterogeneity, signaling plasticity, differentiation, proliferation/metabolism, stress management, genomic integrity, crosstalk with the tumor microenvironment, immune escape, and epigenetic regulatory mechanisms. Of these, epigenetics was both one of the first proposed means of non-genetic resistance and one of the first discovered. As we describe in this review, epigenetic regulatory factors are involved in most facets of DTP biology, positioning this hallmark as an overarching mediator of drug tolerance and a potential avenue to novel therapies.

Therapeutic Targeting Hypoxia-Inducible Factor (HIF-1) in Cancer: Cutting Gordian Knot of Cancer Cell Metabolism

Metabolic alterations are one of the hallmarks of cancer, which has recently gained great attention. Increased glucose absorption and lactate secretion in cancer cells are characterized by the Warburg effect, which is caused by the metabolic changes in the tumor tissue. Cancer cells switch from oxidative phosphorylation (OXPHOS) to aerobic glycolysis due to changes in glucose degradation mechanisms, a process known as “metabolic reprogramming”. As a result, proteins involved in mediating the altered metabolic pathways identified in cancer cells pose novel therapeutic targets. Hypoxic tumor microenvironment (HTM) is anticipated to trigger and promote metabolic alterations, oncogene activation, epithelial-mesenchymal transition, and drug resistance, all of which are hallmarks of aggressive cancer behaviour. Angiogenesis, erythropoiesis, glycolysis regulation, glucose transport, acidosis regulators have all been orchestrated through the activation and stability of a transcription factor termed hypoxia-inducible factor-1 (HIF-1), hence altering crucial Warburg effect activities. Therefore, targeting HIF-1 as a cancer therapy seems like an extremely rational approach as it is directly involved in the shift of cancer tissue. In this mini-review, we present a brief overview of the function of HIF-1 in hypoxic glycolysis with a particular focus on novel therapeutic strategies currently available.

Hypoxia-dependent drivers of melanoma progression

Hypoxia, a condition of low oxygen availability, is a hallmark of tumour microenvironment and promotes cancer progression and resistance to therapy. Many studies reported the essential role of hypoxia in regulating invasiveness, angiogenesis, vasculogenic mimicry and response to therapy in melanoma. Melanoma is an aggressive cancer originating from melanocytes located in the skin (cutaneous melanoma), in the uveal tract of the eye (uveal melanoma) or in mucosal membranes (mucosal melanoma). These three subtypes of melanoma represent distinct neoplasms in terms of biology, epidemiology, aetiology, molecular profile and clinical features.In this review, the latest progress in hypoxia-regulated pathways involved in the development and progression of all melanoma subtypes were discussed. We also summarized current knowledge on preclinical studies with drugs targeting Hypoxia-Inducible Factor-1, angiogenesis or vasculogenic mimicry. Finally, we described available evidence on clinical studies investigating the use of Hypoxia-Inducible Factor-1 inhibitors or antiangiogenic drugs, alone or in combination with other strategies, in metastatic and adjuvant settings of cutaneous, uveal and mucosal melanoma.Hypoxia-Inducible Factor-independent pathways have been also reported to regulate melanoma progression, but this issue is beyond the scope of this review.As evident from the numerous studies discussed in this review, the increasing knowledge of hypoxia-regulated pathways in melanoma progression and the promising results obtained from novel antiangiogenic therapies, could offer new perspectives in clinical practice in order to improve survival outcomes of melanoma patients.

Hypoxia and Extracellular Acidification as Drivers of Melanoma Progression and Drug Resistance

Hypoxia and elevated extracellular acidification are prevalent features of solid tumors and they are often shown to facilitate cancer progression and drug resistance. In this review, we have compiled recent and most relevant research pertaining to the role of hypoxia and acidification in melanoma growth, invasiveness, and response to therapy. Melanoma represents a highly aggressive and heterogeneous type of skin cancer. Currently employed treatments, including BRAF V600E inhibitors and immune therapy, often are not effective due to a rapidly developing drug resistance. A variety of intracellular mechanisms impeding the treatment were discovered. However, the tumor microenvironment encompassing stromal and immune cells, extracellular matrix, and physicochemical conditions such as oxygen level or acidity, may also influence the therapy effectiveness. Hypoxia and acidification are able to reprogram the metabolism of melanoma cells, enhance their survival and invasiveness, as well as promote the immunosuppressive environment. For this reason, these physicochemical features of the melanoma niche and signaling pathways related to them emerge as potential therapeutic targets.

The great escape: tumour cell plasticity in resistance to targeted therapy

The success of targeted therapies in cancer treatment has been impeded by various mechanisms of resistance. Besides the acquisition of resistance-conferring genetic mutations, reversible mechanisms that lead to drug tolerance have emerged. Plasticity in tumour cells drives their transformation towards a phenotypic state that no longer depends on the drug-targeted pathway. These drug-refractory cells constitute a pool of slow-cycling cells that can either regain drug sensitivity upon treatment discontinuation or acquire permanent resistance to therapy and drive relapse. In the past few years, cell plasticity has emerged as a mode of targeted therapy evasion in various cancers, ranging from prostate and lung adenocarcinoma to melanoma and basal cell carcinoma. Our understanding of the mechanisms that control this phenotypic switch has also expanded, revealing the crucial role of reprogramming factors and chromatin remodelling. Further deciphering the molecular basis of tumour cell plasticity has the potential to contribute to new therapeutic strategies which, combined with existing anticancer treatments, could lead to deeper and longer-lasting clinical responses.

Loss of Phd2 cooperates with BRAFV600E to drive melanomagenesis

Prolyl hydroxylase domain protein 2 (PHD2) is a well-known master oxygen sensor. However, the role of PHD2 in tumor initiation remains controversial. We find that during the transition of human nevi to melanoma, the expression of PHD2 protein is significantly decreased and lower expression PHD2 in melanoma is associated with worse clinical outcome. Knockdown of PHD2 leads to elevated Akt phosphorylation in human melanocytes. Mice with conditional melanocyte-specific expression of Phd2^lox/lox (Tyr::CreER;Phd2^lox/lox) fail to develop pigmented lesions. However, deletion of Phd2 in combination with expression of BRaf^V600E in melanocytes (Tyr::CreER;Phd2^lox/lox;BRaf^CA) leads to the development of melanoma with 100% penetrance and frequent lymph node metastasis. Analysis of tumor tissues using reverse phase protein arrays demonstrates that Phd2 deletion activates the AKT-mTOR-S6 signaling axis in the recovered tumors. These data indicate that PHD2 is capable of suppressing tumor initiation largely mediated through inhibiting of the Akt-mTOR signaling pathway in the melanocyte lineage.

Prolyl hydroxylase domain protein 2 (PHD2) regulates cellular response to hypoxia. Here the authors show that PHD2 is downregulated in melanoma and that PHD2 depletion, in a mouse model, promotes the progression of benign melanocytic lesions into melanoma, via activation of the Akt/mTOR signaling cascade.

The impact of chemotherapy-associated hemoglobin on prognosis of colorectal cancer patients receiving adjuvant chemotherapy

BACKGROUND AND OBJECTIVE

The association of chemotherapy-associated hemoglobin and survival of colorectal cancer (CRC) receiving adjuvant chemotherapy is uncertain. We sought to explore the prognostic value of chemotherapy-associated hemoglobin in CRC receiving adjuvant chemotherapy and the best cut point affecting prognosis.

METHODS

Three hundred and twenty stage II and III CRC patients receiving adjuvant FOLFOX chemotherapy from March 2003 to March 2012 were enrolled. The associations between chemotherapy-associated hemoglobin (the absolute levels of post-chemotherapy) or chemotherapy-associated hemoglobin change (change between the pre- and post-chemotherapy hemoglobins) and disease free survival (DFS) or overall survival (OS) of CRC, and the best cut point were investigated.

RESULTS

Log rank test showed the best cut points for chemotherapy-associated hemoglobin and chemotherapy-associated hemoglobin change were respectively 90 g/L, 30 g/L. Cox regression model showed chemotherapy-associated hemoglobin < 90 g/L was the independent prognostic factor for DFS (HR, 2.221; 95% CI = 1.157-4.262), OS (HR, 2.058; 95% CI = 1.009-4.197), respectively, but no association of chemotherapy-associated hemoglobin change ⩾ 30g/L and DFS (HR, 2.063; 95% CI = 0.929-4.583), OS (HR, 1.386; 95% CI = 0.553-3.471) was found.

CONCLUSIONS

Chemotherapy-associated hemoglobin < 90 g/L has a significant prognostic value in CRC receiving adjuvant chemotherapy, which is a significant biomarker in the individualized management and may suggest the simple indication for the treatment of anemia in adjuvant chemotherapy in CRC.

Microenvironment-Driven Dynamic Heterogeneity and Phenotypic Plasticity as a Mechanism of Melanoma Therapy Resistance

Drug resistance constitutes a major challenge in designing melanoma therapies. Microenvironment-driven tumor heterogeneity and plasticity play a key role in this phenomenon. Melanoma is highly heterogeneous with diverse genomic alterations and expression of different biological markers. In addition, melanoma cells are highly plastic and capable of adapting quickly to changing microenvironmental conditions. These contribute to variations in therapy response and durability between individual melanoma patients. In response to changing microenvironmental conditions, like hypoxia and nutrient starvation, proliferative melanoma cells can switch to an invasive slow-cycling state. Cells in this state are more aggressive and metastatic, and show increased intrinsic drug resistance. During continuous treatment, slow-cycling cells are enriched within the tumor and give rise to a new proliferative subpopulation with increased drug resistance, by exerting their stem cell-like behavior and phenotypic plasticity. In melanoma, the proliferative and invasive states are defined by high and low microphthalmia-associated transcription factor (MITF) expression, respectively. It has been observed that in MITFhigh melanomas, inhibition of MITF increases the efficacy of targeted therapies and delays the acquisition of drug resistance. Contrarily, MITF is downregulated in melanomas with acquired drug resistance. According to the phenotype switching theory, the gene expression profile of the MITFlow state is predominantly regulated by WNT5A, AXL, and NF-κB signaling. Thus, different combinations of therapies should be effective in treating different phases of melanoma, such as the combination of targeted therapies with inhibitors of MITF expression during the initial treatment phase, but with inhibitors of WNT5A/AXL/NF-κB signaling during relapse.

Priming of the Cells: Hypoxic Preconditioning for Stem Cell Therapy

Objective:

Stem cell-based therapies are promising in regenerative medicine for protecting and repairing damaged brain tissues after injury or in the context of chronic diseases. Hypoxia can induce physiological and pathological responses. A hypoxic insult might act as a double-edged sword, it induces cell death and brain damage, but on the other hand, sublethal hypoxia can trigger an adaptation response called hypoxic preconditioning or hypoxic tolerance that is of immense importance for the survival of cells and tissues.

Data Sources:

This review was based on articles published in PubMed databases up to August 16, 2017, with the following keywords: “stem cells,” “hypoxic preconditioning,” “ischemic preconditioning,” and “cell transplantation.”

Study Selection:

Original articles and critical reviews on the topics were selected.

Results:

Hypoxic preconditioning has been investigated as a primary endogenous protective mechanism and possible treatment against ischemic injuries. Many cellular and molecular mechanisms underlying the protective effects of hypoxic preconditioning have been identified.

Conclusions:

In cell transplantation therapy, hypoxic pretreatment of stem cells and neural progenitors markedly increases the survival and regenerative capabilities of these cells in the host environment, leading to enhanced therapeutic effects in various disease models. Regenerative treatments can mobilize endogenous stem cells for neurogenesis and angiogenesis in the adult brain. Furthermore, transplantation of stem cells/neural progenitors achieves therapeutic benefits via cell replacement and/or increased trophic support. Combinatorial approaches of cell-based therapy with additional strategies such as neuroprotective protocols, anti-inflammatory treatment, and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the recent progress regarding cell types and applications in regenerative medicine as well as future applications.

HIF-2α dictates the susceptibility of pancreatic cancer cells to TRAIL by regulating survivin expression

Cancer cells develop resistance to therapy by adapting to hypoxic microenvironments, and hypoxia-inducible factors (HIFs) play crucial roles in this process. We investigated the roles of HIF-1α and HIF-2α in cancer cell death induced by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) using human pancreatic cancer cell lines. siRNA-mediated knockdown of HIF-2α, but not HIF-1α, increased susceptibility of two pancreatic cancer cell lines, Panc-1 and AsPC-1, to TRAIL in vitro under normoxic and hypoxic conditions. The enhanced sensitivity to TRAIL was also observed in vivo. This in vitro increased TRAIL sensitivity was observed in other three pancreatic cancer cell lines. An array assay of apoptosis-related proteins showed that knockdown of HIF-2α decreased survivin expression. Additionally, survivin promoter activity was decreased in HIF-2α knockdown Panc-1 cells and HIF-2α bound to the hypoxia-responsive element in the survivin promoter region. Conversely, forced expression of the survivin gene in HIF-2α shRNA-expressing Panc-1 cells increased resistance to TRAIL. In a xenograft mouse model, the survivin suppressant YM155 sensitized Panc-1 cells to TRAIL. Collectively, our results indicate that HIF-2α dictates the susceptibility of human pancreatic cancer cell lines, Panc-1 and AsPC-1, to TRAIL by regulating survivin expression transcriptionally, and that survivin could be a promising target to augment the therapeutic efficacy of death receptor-targeting anti-cancer therapy.

Endothelial HIF-2α contributes to severe pulmonary hypertension due to endothelial-to-mesenchymal transition

Pulmonary vascular remodeling characterized by concentric wall thickening and intraluminal obliteration is a major contributor to the elevated pulmonary vascular resistance in patients with idiopathic pulmonary arterial hypertension (IPAH). Here we report that increased hypoxia-inducible factor 2α (HIF-2α) in lung vascular endothelial cells (LVECs) under normoxic conditions is involved in the development of pulmonary hypertension (PH) by inducing endothelial-to-mesenchymal transition (EndMT), which subsequently results in vascular remodeling and occlusive lesions. We observed significant EndMT and markedly increased expression of SNAI, an inducer of EndMT, in LVECs from patients with IPAH and animals with experimental PH compared with normal controls. LVECs isolated from IPAH patients had a higher level of HIF-2α than that from normal subjects, whereas HIF-1α was upregulated in pulmonary arterial smooth muscle cells (PASMCs) from IPAH patients. The increased HIF-2α level, due to downregulated prolyl hydroxylase domain protein 2 (PHD2), a prolyl hydroxylase that promotes HIF-2α degradation, was involved in enhanced EndMT and upregulated SNAI1/2 in LVECs from patients with IPAH. Moreover, knockdown of HIF-2α (but not HIF-1α) with siRNA decreases both SNAI1 and SNAI2 expression in IPAH-LVECs. Mice with endothelial cell (EC)-specific knockout (KO) of the PHD2 gene, egln1 (egln1EC-/-), developed severe PH under normoxic conditions, whereas Snai1/2 and EndMT were increased in LVECs of egln1EC-/- mice. EC-specific KO of the HIF-2α gene, hif2a, prevented mice from developing hypoxia-induced PH, whereas EC-specific deletion of the HIF-1α gene, hif1a, or smooth muscle cell (SMC)-specific deletion of hif2a, negligibly affected the development of PH. Also, exposure to hypoxia for 48-72 h increased protein level of HIF-1α in normal human PASMCs and HIF-2α in normal human LVECs. These data indicate that increased HIF-2α in LVECs plays a pathogenic role in the development of severe PH by upregulating SNAI1/2, inducing EndMT, and causing obliterative pulmonary vascular lesions and vascular remodeling.

Targeting hypoxic response for cancer therapy

Hypoxic tumor microenvironment (HTM) is considered to promote metabolic changes, oncogene activation and epithelial mesenchymal transition, and resistance to chemo- and radio-therapy, all of which are hallmarks of aggressive tumor behavior. Cancer cells within the HTM acquire phenotypic properties that allow them to overcome the lack of energy and nutrients supply within this niche. These phenotypic properties include activation of genes regulating glycolysis, glucose transport, acidosis regulators, angiogenesis, all of which are orchestrated through the activation of the transcription factor, HIF1A, which is an independent marker of poor prognosis. Moreover, during the adaptation to a HTM cancer cells undergo deep changes in mitochondrial functions such as “Warburg effect” and the “reverse Warburg effect”.

This review aims to provide an overview of the characteristics of the HTM, with particular focus on novel therapeutic strategies currently in clinical trials, targeting the adaptive response to hypoxia of cancer cells.

Hypoxia-activated prodrug enhances therapeutic effect of sunitinib in melanoma

Angiogenesis is a critical step during tumor progression. Anti-angiogenic therapy has only provided modest benefits in delaying tumor progression despite its early promise in cancer treatment. It has been postulated that anti-angiogenic therapy may promote the emergence of a more aggressive cancer cell phenotype by generating increased tumor hypoxia—a well-recognized promoter of tumor progression. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug (HAP) which has been shown to selectively target the hypoxic tumor compartment and reduce tumor volume. Here, we show that melanoma cells grown under hypoxic conditions exhibit increased resistance to a wide variety of therapeutic agents in vitro and generate larger and more aggressive tumors in vivo than melanoma cells grown under normoxic conditions. However, hypoxic melanoma cells exhibit a pronounced sensitivity to TH-302 which is further enhanced by the addition of sunitinib. Short term sunitinib treatment fails to prolong the survival of melanoma bearing genetically engineered mice (Tyr::CreER; BRaf^CA;Pten^lox/lox) but increases tumor hypoxia. Long term TH-302 alone modestly prolongs the overall survival of melanoma bearing mice. Combination therapy of TH-302 with sunitinib further increases the survival of treated mice. These studies provide a translational rationale for combining hypoxic tumor cell targeted therapies with anti-angiogenics for treatment of melanoma.

Silencing Snail suppresses tumor cell proliferation and invasion by reversing epithelial-to-mesenchymal transition and arresting G2/M phase in non-small cell lung cancer

Epithelial-to-mesenchymal transition (EMT) is essential for tumor invasion and metastasis. Snail has been proven to be a key regulator of EMT. Several studies have shown compelling evidence that Snail is also an important regulator of tumor growth and aggression; however, the role of Snail in the cell cycle has not been clarified. We decreased Snail expression by siRNA transfection and lentiviral‑mediated RNAi, to explore the effect of silencing Snail on the tumorigenicity and migration of lung carcinoma (lung cancer) cells. The results showed that silencing Snail conferred significant anti-proliferative activity and inhibited cell migration, tumor growth and metastasis both in vitro and in vivo. To understand the mechanism of these effects, we further investigated correlations among Snail expression, EMT and cell cycle. Significantly, Snail knockdown reversed EMT processes in lung cancer cells. Furthermore, the cyclin-dependent kinase inhibitor P21 was upregulated after silencing Snail. P21 upregulation manifested its tumor suppressor effects and arrested cells in the G2/M phase, not the G1/S phase following Snail depletion in lung cancer cells. These data suggest that silencing Snail decreases the malignant behaviors of lung cancer cells by reversing EMT processes and causing cell cycle defects.

Therapeutic implications of cellular and molecular biology of cancer stem cells in melanoma

Melanoma is a form of cancer that initiates in melanocytes. Melanoma has multiple phenotypically distinct subpopulation of cells, some of them have embryonic like plasticity which are involved in self-renewal, tumor initiation, metastasis and progression and provide reservoir of therapeutically resistant cells. Cancer stem cells (CSCs) can be identified and characterized based on various unique cell surface and intracellular markers. CSCs exhibit different molecular pattern with respect to non-CSCs. They maintain their stemness and chemoresistant features through specific signaling cascades. CSCs are weak in immunogenicity and act as immunosupressor in the host system. Melanoma treatment becomes difficult and survival is greatly reduced when the patient develop metastasis. Standard conventional oncology treatments such as chemotherapy, radiotherapy and surgical resection are only responsible for shrinking the bulk of the tumor mass and tumor tends to relapse. Thus, targeting CSCs and their microenvironment niche addresses the alternative of traditional cancer therapy. Combined use of CSCs targeted and traditional therapies may kill the bulk tumor and CSCs and offer a promising therapeutic strategy for the management of melanoma.

Reprogramming Factors Remodel Melanoma Cell Phenotype by Changing Stat3 Expression

The limited availability of melanoma stem cells is a major challenge for therapeutic reagent screening and study of molecular mechanisms. It has been shown that induced expression of four stem cell factors (Oct4, Sox2, Klf4, and c-Myc) changes the phenotype of osteosarcoma and breast cancer cells to osteosarcoma stem cells and breast cancer stem cells, respectively. The present study aimed to explore whether these four factors might change the phenotype of melanoma cells to melanoma stem cells and, if so, to examine the possible molecular signal involved. Melanoma B16-F10 cells were transfected with the plasmid TetO-FUW-OSKM which contains cDNA expressing four factors, driven by the Tet-On element. We found that expression of the four transcription factors was highly induced by DOX in the stable melanoma cell clones. Further studies confirmed that induced expression of these factors remodeled the phenotype of the melanoma cells to melanoma stem cells (MSCs). This conclusion was supported by the evidence that induced expression of these factors increased the numbers of tumor-initiating cells, (namely MSCs), both in an in vitro cell culture system and in a mouse in vivo model. The conclusion was further supported by the observation that the induction of these factors exclusively increased the mRNA of signal transducer and activator of transcription 3 which has been reported to play a crucial role in stem cell maintenance. Thus, phenotypic remodeling of melanoma cells following the induction of these four factors provided a simple and optimal means to constantly obtain MSCs for screening new therapeutic reagents. The result also reveals that Stat3 may be a crucial link between the induction of the four factors and the cell remodeling, suggesting its potential role as a target to fight melanoma.

Overexpression of angiopoietin 2 promotes the formation of oral squamous cell carcinoma by increasing epithelial-mesenchymal transition-induced angiogenesis

Oral squamous cell carcinoma (OSCC) is the most common cancer of the head and neck and is associated with a high rate of lymph node metastasis. The initial step in the metastasis and transition of tumors is epithelial-mesenchymal transition (EMT)-induced angiogenesis, which can be mediated by angiopoietin 2 (ANG2), a key regulatory factor in angiogenesis. In the present study, immunohistochemistry and real-time quantitative reverse transcriptase (qRT-PCR) were used to measure the expression of ANG2 in OSCC tissues. Plasmids encoding ANG2 mRNA were used for increased ANG2 expression in the OSCC cell line TCA8113. The short interfering RNA (siRNA)-targeting ANG2 mRNA sequences were used to inhibit ANG2 expression in TCA8113 cells. Subsequently, transwell assays were performed to examine the effects of ANG2 on TCA8113 cell migration and invasion. Furthermore, in vivo assays were performed to assess the effect of ANG2 on tumor growth. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays and immunohistochemistry were used to examine cell apoptosis and angiogenesis in tumor tissues, respectively. Finally, western blot analysis was performed to evaluate tumor formation-related proteins in OSCC tissues. We found that protein expression of ANG2 was remarkably upregulated in OSCC tissues. Overexpression of ANG2 increased the migration and invasion of TCA8113 cells by regulating EMT. Further investigations showed that overexpression of ANG2 increased tumor growth in nude mice, and angiogenesis of OSCC tissues increased in the presence of ANG2 overexpression. Overexpression of ANG2 also reduced cell apoptosis in tumor tissue cells. Finally, we found that overexpression of ANG2 resulted in changes in the expression of tumor formation-related proteins including vimentin, E-cadherin, Bim, PUMA, Bcl-2, Bax, Cyclin D1, PCNA and CD31. Our findings show that ANG2 has an important role in the migration and invasion of OSCC. More importantly, further investigations suggested that overexpression of ANG2 might increase OSCC metastasis by promoting angiogenesis in nude mice. This stimulatory effect could be achieved by inducing abnormal EMT and by reducing apoptosis and increasing proliferation of cells.

Hypoxia promotes colon cancer dissemination through up-regulation of cell migration-inducing protein (CEMIP)

Hypoxic stress drives cancer progression by causing a transcriptional reprogramming. Recently, KIAA1199 was discovered to be a cell-migration inducing protein (renamed CEMIP) that is upregulated in human cancers. However, the mechanism of induction of CEMIP in cancer was hitherto unknown. Here we demonstrate that hypoxia induces CEMIP expression leading to enhanced cell migration. Immunohistochemistry of human colon cancer tissues revealed that CEMIP is upregulated in cancer cells located at the invasive front or in the submucosa. CEMIP localization inversely correlated with E-cadherin expression, which is characteristic of the epithelial-to-mesenchymal transition. Mechanistically, hypoxia-inducible-factor-2α (HIF-2α), but not HIF-1α binds directly to the hypoxia response element within the CEMIP promoter region resulting in increased CEMIP expression. Functional characterization reveals that CEMIP is a downstream effector of HIF-2α-mediated cell migration. Expression of CEMIP was demonstrated to negatively correlate with the expression of Jarid1A, a histone demethylase that removes methyl groups from H3K4me3 (an activation marker for transcription), resulting in altered gene repression. Low oxygen tension inhibits the function of Jarid1A, leading to increased presence of H3K4me3 within the CEMIP promoter. These results provide insight into the upregulation of CEMIP within cancer and can lead to novel treatment strategies targeting this cancer cell migration-promoting gene.

Cancer Stem Cell Quiescence and Plasticity as Major Challenges in Cancer Therapy

Cells with stem-like properties, tumorigenic potential, and treatment-resistant phenotypes have been identified in many human malignancies. Based on the properties they share with nonneoplastic stem cells or their ability to initiate and propagate tumors in vivo, such cells were designated as cancer stem (stem-like) or tumor initiating/propagating cells. Owing to their implication in treatment resistance, cancer stem cells (CSCs) have been the subject of intense investigation in past years. Comprehension of CSCs' intrinsic properties and mechanisms they develop to survive and even enhance their aggressive phenotype within the hostile conditions of the tumor microenvironment has reoriented therapeutic strategies to fight cancer. This report provides selected examples of malignancies in which the presence of CSCs has been evidenced and briefly discusses methods to identify, isolate, and functionally characterize the CSC subpopulation of cancer cells. Relevant biological targets in CSCs, their link to treatment resistance, proposed targeting strategies, and limitations of these approaches are presented. Two major aspects of CSC physiopathology, namely, relative in vivo quiescence and plasticity in response to microenvironmental cues or treatment, are highlighted. Implications of these findings in the context of the development of new therapies are discussed.

Regulation of COX-2 expression and epithelial-to-mesenchymal transition by hypoxia-inducible factor-1α is associated with poor prognosis in hepatocellular carcinoma patients post TACE surgery

Currently, it is not entirely clear whether hypoxia-inducible factor-1α (HIF-1α) is involved in the regulation of COX-2 expression and epithelial-to-mesenchymal transition (EMT), and whether these events affect the prognosis of hepatocellular carcinoma (HCC) patients treated with transcatheter arterial chemoembolization (TACE). In this report the relationship between HIF-1α and COX-2 protein expression, EMT in tumor specimens from HCC patients after TACE surgery and the clinical significance of HIF-1α and COX-2 expression were analyzed using statistical approaches. HepG2 cells treated with CoCl₂ was employed as a hypoxia cell model in vitro to study hypoxia-induced HIF-1α, COX-2 expression, and EMT alteration. The results showed that HIF-1α and COX-2 protein expression increased in HCC tissues after TACE surgery. Moreover, there was positive correlation between upregulation of HIF-1α and COX-2. Elevated expression of HIF-1α increased both Snail and Vimentin protein expression, while it reduced E-cadherin protein expression. It was further verified that hypoxia enhanced protein expression of HIF-1α and COX-2 in HepG2 cells treated with CoCl₂. Upregulation of HIF-1α and COX-2, together with EMT alteration resulted in increased migration and invasion of HepG2 cells under hypoxia. In conclusion, TACE surgery results in aggravated hypoxia status, leading to increased HIF-1α protein expression in HCC tissue. To adapt to hypoxic environment, HIF-1α stimulates COX-2 protein expression and promotes EMT process in hepatocellular cancer cells, which enhances HCC invasion and metastasis, and might contribute to poor prognosis in HCC patients post TACE treatment.

Hypoxia suppresses cylindromatosis (CYLD) expression to promote inflammation in glioblastoma: possible link to acquired resistance to anti-VEGF therapy

Cylindromatosis (CYLD) is a tumor suppressor that regulates signaling pathways by acting as a deubiquitinating enzyme. CYLDdown-regulation occurred in several malignancies, with tumor-promoting effects. Although we found loss of CYLD expression in hypoxic regions of human glioblastoma multiforme (GBM), the most aggressive brain tumor, biological roles of CYLD in GBM remain unknown. This study aimed to determine the biological significance of CYLD down-regulation to GBM progression and therapy. CYLD mRNA transcription was dramatically down-regulated in hypoxic GBM cells, consistent with our clinical observations of human GBM tissues. Hypoxia enhanced both basal and tumor necrosis factor-α-induced expression of various proinflammatory cytokines, whereas CYLD overexpression strongly counteracted these responses. In addition, chronic anti-angiogenic therapy with bevacizumab, an anti-vascular endothelial growth factor (VEGF) antibody, with enhanced hypoxia produced responses similar to these CYLD-regulated proinflammatory responses in a xenograft mouse model. Histologically, CYLD clearly prevented massive immune cell infiltration surrounding necrotic regions, and pseudopalisades appeared in bevacizumab-treated control tumors. Furthermore, CYLD overexpression, which had no impact on survival by itself, significantly improved the prosurvival effect of bevacizumab. These data suggest that CYLD down-regulation is crucial for hypoxia-mediated inflammation in GBM, which may affect the long-term efficacy of anti-VEGF therapy.

Snail Is a Critical Mediator of Invadosome Formation and Joint Degradation in Arthritis

Progressive cartilage destruction, mediated by invasive fibroblast-like synoviocytes, is a central feature in the pathogenesis of rheumatoid arthritis (RA). Members of the Snail family of transcription factors are required for cell migration and invasion, but their role in joint destruction remains unknown. Herein, we demonstrate that Snail is essential for the formation of extracellular matrix-degrading invadosomal structures by synovial cells from collagen-induced arthritis (CIA) rats and RA patients. Mechanistically, Snail induces extracellular matrix degradation in synovial cells by repressing PTEN, resulting in increased phosphorylation of platelet-derived growth factor receptor and activation of the phosphatidylinositol 3-kinase/AKT pathway. Of significance, Snail is overexpressed in synovial cells and tissues of CIA rats and RA patients, whereas knockdown of Snail in CIA joints prevents cartilage invasion and joint damage. Furthermore, Snail expression is associated with an epithelial-mesenchymal transition gene signature characteristic of transglutaminase 2/transforming growth factor-β activation. Transforming growth factor-β and transglutaminase 2 stimulate Snail-dependent invadosome formation in rat and human synoviocytes. Our results identify the Snail-PTEN platelet-derived growth factor receptor/phosphatidylinositol 3-kinase axis as a novel regulator of the prodestructive invadosome-forming phenotype of synovial cells. New therapies for RA target inflammation, and are only partly effective in preventing joint damage. Blocking Snail and/or its associated gene expression program may provide an additional tool to improve the efficacy of treatments to prevent joint destruction.

Thrombospondin 1 promotes an aggressive phenotype through epithelial-to-mesenchymal transition in human melanoma

Epithelial-to-mesenchymal transition (EMT), in which epithelial cells loose their polarity and become motile mesenchymal cells, is a determinant of melanoma metastasis. We compared gene expression signatures of mesenchymal-like melanoma cells with those of epithelial-like melanoma cells, and identified Thrombospondin 1 (THBS1) as highly up-regulated in the mesenchymal phenotype. This study investigated whether THBS1, a major physiological activator of transforming growth factor (TGF)-beta, is involved in melanoma EMT-like process. We sought to examine expression patterns in distinct melanoma phenotypes including invasive, de-differentiated, label-retaining and drug resistant populations that are putatively associated with an EMT-like process.

Here we show that THBS1 expression and secretion was elevated in melanoma cells exhibiting invasive, drug resistant, label retaining and mesenchymal phenotypes and correlated with reduced expression of genes involved in pigmentation. Elevated THBS1 levels were detected in Vemurafenib resistant melanoma cells and inhibition of THBS1 led to significantly reduced chemoresistance in melanoma cells. Notably, siRNA-mediated silencing of THBS1 and neutralizing antibody to THBS1 reduced invasion in mesenchymal-like melanoma cells, while ectopic THBS1 expression in epithelial-like melanoma cells enhanced invasion. Furthermore, the loss of THBS1 inhibited in vivo motility of melanoma cells within the embryonic chicken neural tube. In addition, we found aberrant THBS1 protein expression in metastatic melanoma tumor biopsies. These results implicate a role for THBS1 in EMT, and hence THBS1 may serve as a novel target for strategies aimed at the treatment of melanoma invasion and drug resistance.

miR-200c/Bmi1 axis and epithelial-mesenchymal transition contribute to acquired resistance to BRAF inhibitor treatment

Resistance to BRAF inhibitors (BRAFi) is one of the major challenges for targeted therapies for BRAF-mutant melanomas. However, little is known about the role of microRNAs in conferring BRAFi resistance. Herein, we demonstrate that miR-200c expression is significantly reduced whereas miR-200c target genes including Bmi1, Zeb2, Tubb3, ABCG5, and MDR1 are significantly increased in melanomas that acquired BRAFi resistance compared to pretreatment tumor biopsies. Similar changes were observed in BRAFi-resistant melanoma cell lines. Overexpression of miR-200c or knock-down of Bmi1 in resistant melanoma cells restores their sensitivities to BRAFi, leading to deactivation of the PI3K/AKT and MAPK signaling cascades, and acquisition of epithelial-mesenchymal transition-like phenotypes, including upregulation of E-cadherin, downregulation of N-cadherin, and ABCG5 and MDR1 expression. Conversely, knock-down of miR-200c or overexpression of Bmi1 in BRAFi-sensitive melanoma cells activates the PI3K/AKT and MAPK pathways, upregulates N-cadherin, ABCG5, and MDR1 expression, and downregulates E-cadherin expression, leading to BRAFi resistance. Together, our data identify miR-200c as a critical signaling node in BRAFi-resistant melanomas impacting the MAPK and PI3K/AKT pathways, suggesting miR-200c as a potential therapeutic target for overcoming acquired BRAFi resistance.

The emerging role of hypoxia-inducible factor-2 involved in chemo/radioresistance in solid tumors

The hypoxic condition is a common feature that negatively impacts the efficacy of radio- and chemotherapy in solid tumors. Hypoxia-inducible factors (HIF-1, 2, 3) predominantly regulate the adaptation to hypoxia at the cellular or organismal level. HIF-2 is one of the three known alpha subunits of HIF transcription factors. Previous studies have shown that HIF-1 is associated with chemotherapy failure. Accumulating evidence in recent years suggests that HIF-2 also contributes to chemo/radioresistance in solid tumors. Despite sharing similar structures, HIF-1α and HIF-2α had highly divergent and even opposing roles in solid tumors under hypoxic conditions. Recent studies have also implied that HIF-2α had a role in chemo/radioresistance through different mechanisms, at least partly, compared to HIF-1α. The present paper summarizes the function of HIF-2 in chemo/radioresistance in solid tumors as well as some of its novel mechanisms that contributed to this pathological process.

Systems biology of cancer: entropy, disorder, and selection-driven evolution to independence, invasion and "swarm intelligence"

Our knowledge of the biology of solid cancer has greatly progressed during the last few years, and many excellent reviews dealing with the various aspects of this biology have appeared. In the present review, we attempt to bring together these subjects in a general systems biology narrative. It starts from the roles of what we term entropy of signaling and noise in the initial oncogenic events, to the first major transition of tumorigenesis: the independence of the tumor cell and the switch in its physiology, i.e., from subservience to the organism to its own independent Darwinian evolution. The development after independence involves a constant dynamic reprogramming of the cells and the emergence of a sort of collective intelligence leading to invasion and metastasis and seldom to the ultimate acquisition of immortality through inter-individual infection. At each step, the probability of success is minimal to infinitesimal, but the number of cells possibly involved and the time scale account for the relatively high occurrence of tumorigenesis and metastasis in multicellular organisms.

A novel hypoxia-associated subset of FN1 high MITF low melanoma cells: identification, characterization, and prognostic value

In many human cancers, the epithelial-to-mesenchymal transition has an important role in the induction of cancer stem-like cells, and hence, in the causation of intratumoral heterogeneity. This process, also referred to as mesenchymal mimicry, is, however, only poorly understood in melanoma and histological correlation is still lacking. In an immunohistochemical analysis of a large prospective series of 220 primary and metastatic melanomas for the well-known epithelial-to-mesenchymal transition marker FN1, we observed melanoma cells with high FN1 expression in metastases with ischemic necrosis, but rarely or not at all in samples lacking evidence of hypoxia. In a blinded, retrospective series of 82 melanoma metastases with 10-year follow-up, the presence of clusters of these FN1(high) melanoma cells correlated significantly with shortened melanoma-specific survival, highlighting the prognostic value of their presence. We describe in detail the unique light- and electron-microscopic features of these FN1(high) melanoma cells, enabling their identification in routinely hematoxylin-and-eosin-stained sections. In addition, by laser microdissection and subsequent gene expression analysis and immunohistochemistry, we highlight their distinctive, molecular phenotype that includes expression of various markers of the epithelial-to-mesenchymal transition (eg, ZEB1) and of melanoma stem-like cells (eg, NGFR), and lack of immunoreactivity for the melanocytic marker MITF. This phenotype could be reproduced in vitro by culturing melanoma cells under hypoxic conditions. Functionally, the hypoxic microenvironment was shown to induce a more migratory and invasive cell type. In conclusion, we identified a novel clinically relevant FN1(high)MITF(low) cell type in melanoma associated with ischemic necrosis, and propose that these cells reside at the crossroad of the epithelial-to-mesenchymal transition and stem-like cell induction, plausibly triggered by the hypoxic environment.

Snail plays an oncogenic role in glioblastoma by promoting epithelial mesenchymal transition

BACKGROUND

The factors affecting glioblastoma progression are of great clinical importance since dismal outcomes have been observed for glioblastoma patients. The Snail gene is known to coordinate the regulation of tumor progression in diverse tumors through induction of epithelial mesenchymal transition (EMT); however, its role in glioblastoma is still uncertain. Therefore, we aimed to further define its role in vitro.

METHODS AND RESULTS

The small interfering RNA (siRNA) technique was employed to knock down Snail expression in three glioblastoma cell lines (KNS42, U87, and U373). Specific inhibition of Snail expression increased E-cadherin expression but decreased vimentin expression in all cell lines. In addition, inhibition of the expression of Snail significantly reduced the proliferation, viability, invasion, and migration of glioblastoma cells as well as increased the number of cells in the G1 phase.

CONCLUSIONS

Knockdown of Snail suppresses the proliferation, viability, migration, and invasion of cells as well as inhibits cell cycle progression by promoting EMT induction. The findings suggest that expression of this gene facilitates glioblastoma progression. Therefore, these results indicate the clinical significance of Snail for use as a potential therapeutic target for glioblastoma.

Hypoxia induces epithelial-mesenchymal transition via activation of SNAI1 by hypoxia-inducible factor -1α in hepatocellular carcinoma

Background

High invasion and metastasis are the primary factors causing poor prognosis of patients with hepatocellular carcinoma (HCC). However, the molecular mechanisms underlying these biological behaviors have not been completely elucidated. In this study, we investigate the molecular mechanism by which hypoxia promotes HCC invasion and metastasis through inducing epithelial-mesenchymal transition (EMT).

Methods

The expression of EMT markers was analyzed by immunohistochemistry. Effect of hypoxia on induction of EMT and ability of cell migration and invasion were performed. Luciferase reporter system was used for evaluation of Snail regulation by hypoxia-inducible factor -1α (HIF-1α).

Results

We found that overexpression of HIF-1α was observed in HCC liver tissues and was related to poor prognosis of HCC patients. HIF-1α expression profile was correlated with the expression levels of SNAI1, E-cadherin, N-cadherin and Vimentin. Hypoxia was able to induce EMT and enhance ability of invasion and migration in HCC cells. The same phenomena were also observed in CoCl2-treated cells. The shRNA-mediated HIF-1α suppression abrogated CoCl2-induced EMT and reduced ability of migration and invasion in HCC cells. Luciferase assay showed that HIF-1α transcriptional regulated the expression of SNAI1 based on two hypoxia response elements (HREs) in SNAI1 promoter.

Conclusions

We demonstrated that hypoxia-stabilized HIF1α promoted EMT through increasing SNAI1 transcription in HCC cells. This data provided a potential therapeutic target for HCC treatment.