Loss of prolyl hydroxylase 1 and 2 in SM22α-expressing cells prevents Hypoxia-Induced pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a disease characterized by increased vasoconstriction and vascular remodeling. Pulmonary artery smooth muscle cells (PASMCs) highly express the transcription factor hypoxia-inducible factor-1α (HIF-1α), yet the role of PASMC HIF-1α in the development of PAH remains controversial. To study the role of SMC HIF-1α in the pulmonary vascular response to acute and chronic hypoxia, we used a gain-of-function strategy to stabilize HIF-1α in PASMC by generating mice lacking prolyl hydroxylase domain (PHD) 1 and 2 in SM22α-expressing cells. This strategy increased HIF-1α expression and transcriptional activity under conditions of normoxia and hypoxia. Acute hypoxia increased right ventricular systolic pressure (RVSP) in control, but not in SM22α-PHD1/2-/- mice. Chronic hypoxia increased RVSP and vascular remodeling more in control SM22α-PHD1/2+/+ than in SM22α-PHD1/2-/- mice. In vitro studies demonstrated increased contractility and myosin light chain phosphorylation in isolated PHD1/2+/+ compared with PHD1/2-/- PASMC under both normoxic and hypoxic conditions. After chronic hypoxia, there was more p27 and less vascular remodeling in SM22α-PHD1/2-/- compared with SM22α-PHD1/2+/+ mice. Hypoxia increased p27 in PASMC isolated from control patients, but not in cells from patients with idiopathic pulmonary arterial hypertension (IPAH). These findings highlight an SM22α-expressing cell-specific role for HIF-1α in the inhibition of pulmonary vasoconstriction and vascular remodeling. Modulating HIF-1α expression in PASMC may represent a promising preventative and therapeutic strategy for patients with PAH.NEW & NOTEWORTHY In a mouse model wherein hypoxia-inducible factor 1 alpha (HIF-1α) is stabilized in vascular smooth muscle cells, we found that HIF-1α regulates vasoconstriction by limiting phosphorylation of myosin light chain and regulates vascular remodeling through p27 induction. These findings highlight a cell-specific role for HIF-1α in the inhibition of pulmonary vasoconstriction and vascular remodeling.

Pyroptosis: the dawn of a new era in endometrial cancer treatment

Endometrial cancer (EC) is a malignancy of the inner epithelial lining of the uterus. While early-stage EC is often curable through surgery, the management of advanced, recurrent and metastatic EC poses significant challenges and is associated with a poor prognosis. Pyroptosis, an emerging form of programmed cell death, is characterized by the cleavage of gasdermin proteins, inducing the formation of extensive gasdermin pores in the cell membrane and the leakage of interleukin-1β (IL-1β) and interleukin-18 (IL-18), consequently causing cell swelling, lysis and death. It has been found to be implicated in the occurrence and progression of almost all tumors. Recent studies have demonstrated that regulating tumor cells pyroptosis can exploit synergies function with traditional tumor treatments. This paper provides an overview of the research progress made in molecular mechanisms of pyroptosis. It then discusses the role of pyroptosis and its components in initiation and progression of endometrial cancer, emphasizing recent insights into the underlying mechanisms and highlighting unresolved questions. Furthermore, it explores the potential value of pyroptosis in the treatment of endometrial cancer, considering its current application in tumor radiotherapy, chemotherapy, targeted therapy and immunotherapy.

Drug Resistance in Cancers: A Free Pass for Bullying

The cancer burden continues to grow globally, and drug resistance remains a substantial challenge in cancer therapy. It is well established that cancerous cells with clonal dysplasia generate the same carcinogenic lesions. Tumor cells pass on genetic templates to subsequent generations in evolutionary terms and exhibit drug resistance simply by accumulating genetic alterations. However, recent evidence has implied that tumor cells accumulate genetic alterations by progressively adapting. As a result, intratumor heterogeneity (ITH) is generated due to genetically distinct subclonal populations of cells coexisting. The genetic adaptive mechanisms of action of ITH include activating "cellular plasticity", through which tumor cells create a tumor-supportive microenvironment in which they can proliferate and cause increased damage. These highly plastic cells are located in the tumor microenvironment (TME) and undergo extreme changes to resist therapeutic drugs. Accordingly, the underlying mechanisms involved in drug resistance have been re-evaluated. Herein, we will reveal new themes emerging from initial studies of drug resistance and outline the findings regarding drug resistance from the perspective of the TME; the themes include exosomes, metabolic reprogramming, protein glycosylation and autophagy, and the relates studies aim to provide new targets and strategies for reversing drug resistance in cancers.

The role of hypoxia in endometrial cancer

Endometrial cancer represents the most frequent neoplasia from the corpus uteri, and comprises the 14th leading cause of death in women worldwide. Risk factors that contribute to the disease include early menarche, late menopause, nulliparity, and menopausal hormone use, as well as hypertension and obesity comorbidities. The clinical effectiveness of chemotherapy is variable, suggesting that novel molecular targeted therapies against specific cellular processes associated with the maintenance of cancer cell survival and therapy resistance urged to ameliorate the rates of success in endometrial cancer treatment. In the course of tumor growth, cancer cells must adapt to decreased oxygen availability in the microenvironment by upregulation of hypoxia-inducible factors, which orchestrate the activation of a transcriptional program leading to cell survival. During this adaptative process, the hypoxic cancer cells may acquire invasive and metastatic properties as well as increased cell proliferation and resistance to chemotherapy, enhanced angiogenesis, vasculogenic mimicry, and maintenance of cancer cell stemness, which contribute to more aggressive cancer phenotypes. Several studies have shown that hypoxia-inducible factor 1 alpha (HIF-1α) protein is aberrantly overexpressed in many solid tumors from breast, prostate, ovarian, bladder, colon, brain, and pancreas. Thus, it has been considered an important therapeutic target. Here, we reviewed the current knowledge of the relevant roles of cellular hypoxia mechanisms and HIF-1α functions in diverse processes associated with endometrial cancer progression. In addition, we also summarize the role of microRNAs in the posttranscriptional regulation of protein-encoding genes involved in the hypoxia response in endometrial cancer. Finally, we pointed out the need for urgent targeted therapies to impair the cellular processes activated by hypoxia in the tumor microenvironment.

Cell cycle regulators in cancer cell metabolism

Cancer proliferation and progression involves altered metabolic pathways as a result of continuous demand for energy and nutrients. In the last years, cell cycle regulators have been involved in the control of metabolic processes, such as glucose and insulin pathways and lipid synthesis, in addition to their canonical function controlling cell cycle progression. Here we describe recent data demonstrating the role of cell cycle regulators in the metabolic control especially in studies performed in cancer models. Moreover, we discuss the importance of these findings in the context of current cancer therapies to provide an overview of the relevance of targeting metabolism using inhibitors of the cell cycle regulation.

Expression of p27Kip1 and p18Ink4c in human multiple endocrine neoplasia type 1-related pancreatic neuroendocrine tumors

PURPOSE

Pancreatic neuroendocrine tumors are a major manifestation of multiple endocrine neoplasia type 1 (MEN1). This tumor syndrome is caused by germline mutations in MEN1, encoding menin. Insight into pathogenesis of these tumors might lead to new biomarkers and therapeutic targets for these patients. Several lines of evidence point towards a role for p27^Kip1 and p18^Ink4c in MEN1-related tumor development in animal models for MEN1, but their contribution to human MEN1-related pancreatic neuroendocrine tumor development is not known.

METHODS

In this study, we characterized protein expression of p27^Kip1 and p18^Ink4c in human MEN1-related PanNETs by immunohistochemistry. From the nationwide DutchMEN1 Study Group database including > 90% of the Dutch MEN1 population, MEN1-patients, who underwent pancreatic surgery, were selected. A tissue micro-array was constructed with available paraffin tissue blocks, and PanNETs from 61 MEN1 patients were eligible for analysis.

RESULTS

Expression of p27^Kip1 was high in 57 (93%) PanNETs and 67% of the tumors showed low expression of p18^Ink4c (67.3%). No association was found between expression of either p27^Kip1 or p18^Ink4c and clinic-pathological characteristics.

CONCLUSIONS

These findings indicate that loss of p18^Ink4c, but not p27^Kip1, is a common event in the development of MEN1-related PanNETs. Restoration of p18^Ink4c function through CDK4/6 inhibitors could be a therapeutic option for MEN1-related PanNETs.

HIF-1 in cancer therapy: two decade long story of a transcription factor

BACKGROUND

Oxygen (O₂) homeostasis is an indispensable requirement of eukaryotes. O₂ concentration in cellular milieu is defined as normoxia (∼21% O₂), physoxia (∼1-13% O₂) or hypoxia (∼0.1-1% O₂). Hypoxia, a striking micro-environmental feature in tumorigenesis, is countered by tumor cells via induction of O₂ governed transcription factor, hypoxia inducible factor-1 (HIF-1). Post discovery, HIF-1 has emerged as a promising anticancer therapeutic target during the last two decades. Recent reports have highlighted that enhanced levels of HIF-1 correlate with tumor metastasis leading to poor patient prognosis.

MATERIAL AND METHODS

A systematic search in PubMed and SciFinder for the literature on HIF-1 biology and therapeutic importance in cancer was carried out.

RESULTS

This review highlights the initial description as well as the recent insights into HIF-1 biology and regulation. We have focused on emerging data regarding varied classes of HIF-1 target genes affecting various levels of crosstalk among tumorigenic pathways. We have emphasized on the fact that HIF-1 acts as a networking hub coordinating activities of multiple signaling molecules influencing tumorigenesis. Emerging evidences indicate role of many HIF-induced proteomic and genomic alterations in malignant progression by mediating a myriad of genes stimulating angiogenesis, anaerobic metabolism and survival of cancer cells in O₂-deficient microenvironment.

CONCLUSIONS

Better understanding of the crucial role of HIF-1 in carcinogenesis could offer promising new avenues to researchers and aid in elucidating various open issues regarding the use of HIF-1 as an anticancer therapeutic target. In spite of large efforts in this field, many questions still remain unanswered. Hence, future investigations are necessary to devise, assess and refine methods for translating previous research efforts into novel clinical practices in cancer treatment.

Increased iron export by ferroportin induces restriction of HIV-1 infection in sickle cell disease

The low incidence of HIV-1 infection in patients with sickle cell disease (SCD) and inhibition of HIV-1 replication in vitro under the conditions of low intracellular iron or heme treatment suggests a potential restriction of HIV-1 infection in SCD. We investigated HIV-1 ex vivo infection of SCD peripheral blood mononuclear cells (PBMCs) and found that HIV-1 replication was inhibited at the level of reverse transcription (RT) and transcription. We observed increased expression of heme and iron-regulated genes, previously shown to inhibit HIV-1, including ferroportin, IKBα, HO-1, p21, and SAM domain and HD domain-containing protein 1 (SAMHD1). HIV-1 inhibition was less pronounced in hepcidin-treated SCD PBMCs and more pronounced in the iron or iron chelators treated, suggesting a key role of iron metabolism. In SCD PBMCs, labile iron levels were reduced and protein levels of ferroportin, HIF-1α, IKBα, and HO-1 were increased. Hemin treatment induced ferroportin expression and inhibited HIV-1 in THP-1 cells, mimicking the HIV-1 inhibition in SCD PBMCs, especially as hepcidin similarly prevented HIV-1 inhibition. In THP-1 cells with knocked down ferroportin, IKBα, or HO-1 genes but not HIF-1α or p21, HIV-1 was not inhibited by hemin. Activity of SAMHD1-regulatory CDK2 was decreased, and SAMHD1 phosphorylation was reduced in SCD PBMCs and hemin-treated THP-1 cells, suggesting SAMHD1-mediated HIV-1 restriction in SCD. Our findings point to ferroportin as a trigger of HIV-1 restriction in SCD settings, linking reduced intracellular iron levels to the inhibition of CDK2 activity, reduction of SAMHD1 phosphorylation, increased IKBα expression, and inhibition of HIV-1 RT and transcription.

Expression of the RNA helicase DDX3 and the hypoxia response in breast cancer

Aims

DDX3 is an RNA helicase that has antiapoptotic properties, and promotes proliferation and transformation. In addition, DDX3 was shown to be a direct downstream target of HIF-1α (the master regulatory of the hypoxia response) in breast cancer cell lines. However, the relation between DDX3 and hypoxia has not been addressed in human tumors. In this paper, we studied the relation between DDX3 and the hypoxic responsive proteins in human breast cancer.

Methods and Results

DDX3 expression was investigated by immunohistochemistry in breast cancer in comparison with hypoxia related proteins HIF-1α, GLUT1, CAIX, EGFR, HER2, Akt1, FOXO4, p53, ERα, COMMD1, FER kinase, PIN1, E-cadherin, p21, p27, Transferrin receptor, FOXO3A, c-Met and Notch1. DDX3 was overexpressed in 127 of 366 breast cancer patients, and was correlated with overexpression of HIF-1α and its downstream genes CAIX and GLUT1. Moreover, DDX3 expression correlated with hypoxia-related proteins EGFR, HER2, FOXO4, ERα and c-Met in a HIF-1α dependent fashion, and with COMMD1, FER kinase, Akt1, E-cadherin, TfR and FOXO3A independent of HIF-1α.

Conclusions

In invasive breast cancer, expression of DDX3 was correlated with overexpression of HIF-1α and many other hypoxia related proteins, pointing to a distinct role for DDX3 under hypoxic conditions and supporting the oncogenic role of DDX3 which could have clinical implication for current development of DDX3 inhibitors.

Silica-based branched hollow microfibers as a biomimetic extracellular matrix for promoting tumor cell growth in vitro and in vivo

A novel scaffold composed of loosely branched hollow silica microfibers that has been proven to be highly biocompatible is proposed for the 3D culture of cancer cells. The MCF-7 cancer cells can grow and proliferate freely inside the scaffold in the form of multicellular spheroids. MCF-7 cancer cells cultured on the current 3D silica scaffold retained significantly more oncological characters than those cultured on the conventional 2D substrate and can serve as in vitro tumor model for studying cancer treatment.

Role of cellular iron and oxygen in the regulation of HIV-1 infection

Despite efficient antiretroviral therapy, eradication of HIV-1 infection is challenging and requires novel biological insights and therapeutic strategies. Among other physiological and environmental factors, intracellular iron greatly affects HIV-1 replication. Higher iron stores were shown to be associated with faster progression of HIV-1 infection and to inversely correlate with the survival of HIV-1 infected patients. Iron is required for several steps in the HIV-1 life cycle, including reverse transcription, HIV-1 gene expression and capsid assembly. Here, the authors present a comprehensive review of the molecular mechanisms involved in iron- and oxygen-mediated regulation of HIV-1 replication. We also propose key intracellular pathways that may be involved in regulating HIV-1 replication, via protein kinase complexes, CDK9/cyclin T1 and CDK 2/cyclin E, protein phosphatase-1 and other host factors.

Perspectives in cell cycle regulation: lessons from an anoxic vertebrate

The ability of an animal, normally dependent on aerobic respiration, to suspend breathing and enter an anoxic state for long term survival is clearly a fascinating feat, and has been the focus of numerous biochemical studies. When anoxia tolerant turtles are faced with periods of oxygen deprivation, numerous physiological and biochemical alterations take place in order to facilitate vital reductions in ATP consumption. Such strategies include reversible post-translational modifications as well as the implementation of translation and transcription controls facilitating metabolic depression. Although it is clear that anoxic survival relies on the suppression of ATP consuming processes, the state of the cell cycle in anoxia tolerant vertebrates remain elusive. Several anoxia tolerant invertebrate and embryonic vertebrate models display cell cycle arrest when presented with anoxic stress. Despite this, the cell cycle has not yet been characterized for anoxia tolerant turtles. Understanding how vertebrates respond to anoxia can have important clinical implications. Uncontrollable cellular proliferation and hypoxic tumor progression are inescapably linked in vertebrate tissues. Consequentially, the molecular mechanisms controlling these processes have profound clinical consequences. This review article will discuss the theory of cell cycle arrest in anoxic vertebrates and more specifically, the control of the retinoblastoma pathway, the molecular markers of cell cycle arrest, the activation of checkpoint kinases, and the possibility of translational controls implemented by microRNAs.

Subcellular FIH-1 expression patterns in invasive breast cancer in relation to HIF-1α expression

Background

Hypoxia Inducible Factor-1α (HIF-1α) expression in breast cancer is associated with a poor clinical outcome. HIF-1α shows two expression patterns: the canonical poor prognosis hypoxia-related perinecrotic pattern and a diffuse expression pattern that seems to have less downstream effects and is clearly associated with poor survival. Factor-inhibiting hypoxia-inducible factor 1 (FIH-1) inhibits HIF-1 activity by hydroxylating the C-terminal trans-activation domain of the HIF-1α subunit, thus preventing HIF-1 from recruiting co-activators CPB/p300, which are important for inducing the transcription of target genes. The aim of this study was to investigate the expression patterns of FIH-1 in breast cancer and evaluate the relationship between FIH-1 and HIF-1α expression in breast cancer as a possible explanation for apparently less downstream effects of diffuse HIF-1α expression.

Methods

Tissue sections from 92 consecutive invasive breast carcinomas were stained by immunohistochemistry for FIH-1, HIF-1α, glucose transporter 1 (GLUT-1) and carbonic anhydrase IX (CAIX).

Results

45 cases overexpressed HIF-1α, 5 of which in a perinecrotic fashion while FIH-1 was positive in 73 of the 92 cases studied. Contrary to our expectations, three out of five cases with perinecrotic HIF-1α expression were also positive for FIH1. Cytoplasmic FIH-1 correlated with HIF-1α expression (P = 0.03) and tumor grade (P = 0.01). HIF-1α overexpression predicted poorer prognosis as usual (P = 0.02). FIH expression had no additional prognostic value to HIF-1α.

Conclusions

FIH1 is expressed in the majority of invasive breast carcinomas and shows distinct subcellular localization patterns. FIH-1 expression does not seem to explain the proposed functional differences between diffuse and perinecrotic HIF-1α expression in breast cancer.

p38 MAPK regulates G1-S transition in hypoxic cardiac fibroblasts

Cardiac fibroblast hyperplasia associated with augmented matrix production is central to wound healing following myocardial injury. Regulation of the cardiac fibroblast cell cycle by factors in the diseased myocardium that can potentially modify the hyperplastic response of cardiac fibroblasts has, however, not been investigated. We examined the regulation of the cardiac fibroblast cell cycle by hypoxia, a major constituent of myocardial ischemia. Significant reductions in DNA synthesis and cell number, and flow cytometry indicated decreased G1/S progression in hypoxic adult rat cardiac fibroblasts. Western blot analysis showed reduced levels of cyclin D and cyclin A, induction of p27 and hypophosphorylation of Rb under hypoxia. Skp2, which targets p27 for degradation, was significantly lower and inversely related to p27 protein levels in hypoxic cells. Marked p38 MAPK activation was observed under hypoxia and its inhibition using SB203580 reversed the effects of hypoxia on DNA synthesis, cell cycle phase distribution, p27, and cyclin D1 but not cyclin A. Interestingly, a 2-fold increase in p27 mRNA in hypoxic cells, demonstrated by real-time PCR, was unaffected by SB203580, which, however, reversed the hypoxic inhibition of Skp2. In summary, p38 MAPK is an important determinant of hypoxia-induced G0/G1 block in cardiac fibroblasts. p27 induction in hypoxic cardiac fibroblasts may involve direct transcriptional regulation, independent of p38 MAPK, and post-translational regulation via p38 MAPK-dependent suppression of its degradation by Skp2. The study identifies Skp2 as a potential downstream target of p38 MAPK, suggesting a novel mechanism of G1-S regulation in cardiac fibroblasts exposed to stress conditions.

Significance of p27 as potential biomarker for intracellular oxidative status

Our previous proteomic study demonstrated that oxidative stress and antioxidant delphinidin regulated the cellular level of p27^kip1 (referred to as p27) as well as some heat shock proteins in human colon cancer HT 29 cells. Current study was conducted to validate and confirm the regulation of these proteins using both in vitro and in vivo systems. The level of p27 was decreased by hydrogen peroxide in a dose-dependent manner in human colon carcinoma HCT 116 (p53-positive) cells while it was increased upon exposure to hydrogen peroxide in HT 29 (p53-negative) cells. However, high concentration of hydrogen peroxide (100 µM) downregulated p27 in both cell lines, but delphindin, one of antioxidative anthocyanins, enhanced the level of p27 suppressed by 100 µM hydrogen peroxide. ICR mice were injected with varying concentrations of hydrogen peroxide, delphinidin and both. Western blot analysis for the mouse large intestinal tissue showed that the expression of p27 was upregulated by 25 mg/kg BW hydrogen peroxide. To investigate the association of p27 regulation with hypoxia-inducible factor 1-beta (HIF-1β), the level of p27 was analyzed in wild-type mouse hepatoma hepa1c1c7 and Aryl Hydrocarbon Nuclear Translocator (arnt, HIF-1β)-defective mutant BPRc1 cells in the absence and presence of hydrogen peroxide and delphinidin. While the level of p27 was responsive to hydrogen peroxide and delphinidin, it remained unchanged in BPRc1, suggesting that the regulation of p27 requires functional HIF-1β. We also found that hydrogen peroxide and delphinidin affected PI3K/Akt/mTOR signaling pathway which is one of upstream regulators of HIFs. In conclusion, hydrogen peroxide and antioxidant delphinidin seem to regulate intracellular level of p27 through regulating HIF-1 level which is, in turn, governed by its upstream regulators comprising of PI3K/Akt/mTOR signaling pathway. The results should also encourage further study for the potential of p27 as a biomarker for intracellular oxidative or antioxidant status.

Necrosis related HIF-1alpha expression predicts prognosis in patients with endometrioid endometrial carcinoma

BACKGROUND

Hypoxia inducible factor 1alpha (HIF-1alpha) plays an essential role in the adaptive response of cells to hypoxia and is associated with aggressive tumour behaviour. We have shown p27kip1, which is generally reduced in endometrial cancer, to be re-expressed in hypoxic regions. This possibly contributes to survival of cancer cells. The aim of this study was to evaluate the prognostic value of HIF-1alpha and p27kip expression in patients with endometrioid endometrial cancer.

METHODS

Expression levels of HIF-1alpha, CAIX, Glut-1, and p27kip1 were analyzed by immunohistochemistry. Percentage of positive cells, staining pattern (perinecrotic, diffuse, or mixed) and presence of necrosis were noted.

RESULTS

Necrosis was correlated with shortened disease free survival (DFS) (p = 0.008) and overall survival (OS) (p = 0.045). For DFS, perinecrotic HIF-1alpha expression was also prognostic (p = 0.044). Moreover, high p27kip1 expression was an additional prognostic factor for these patients with perinecrotic HIF-1alpha expression. In multivariate Cox regression, perinecrotic HIF-expression emerged as an independent prognostic factor. Perinecrotic HIF-1alpha expression was significantly associated with CAIX and Glut-1 expression, pointing towards functional HIF-1.

CONCLUSIONS

In patients with endometrioid endometrial cancer, necrosis and necrosis-related expression of HIF-1alpha are important prognostic factors. More aggressive adjuvant treatment might be necessary to improve the outcome of patients with these characteristics.

Hypoxia induced paclitaxel resistance in human ovarian cancers via hypoxia-inducible factor 1alpha

PURPOSE

Chemoresistance severely restricts the anti-cancer medicines from effectively treating human ovarian cancer, which has been shown to develop and survive in the specific hypoxic environments. To understand the relationship between hypoxia and chemoresistance, we investigated the potential role of hypoxia in the pathophysiology of chemoresistance, especially focusing on hypoxia-inducible factor 1alpha (HIF-1alpha).

METHODS

The A2780 ovarian cancer cells are cultured in gradient hypoxic conditions (5% O(2), 3% O(2), and 1% O(2)), the sensitivity of the cells to paclitaxel and the cell inhibitory rate were determined by MTT assay. The expression and the transcriptional activity of HIF-1alpha were examined by western blot, Immunocytochemical staining, reverse transcription-polymerase chain reaction (RT-PCR), and the dual luciferase reporter system, respectively. The cell cycle distribution was analyzed by flow cytometry. In addition, we silence HIF-1alpha expression by performing RNA interference.

RESULTS

MTT assay demonstrates that hypoxic challenge substantially reduces the susceptibility of cells to paclitaxel at all the tested concentrations. Coincident with this is the activation of HIF-1alpha in nuclear, which displays the increased transcriptional activity and high protein expression. Hypoxic manipulation (5% O(2), approximately 1% O(2)) significantly increased the cell population at G0/G1. Interestingly, knockdown of endogenous HIF-1alpha significantly alleviates the chemoresistance and promotes G1/S transition with the increased sensitivity of A2780 cells to paclitaxel under each hypoxic condition.

CONCLUSIONS

It suggests that HIF-1alpha, stimulated by hypoxia, exerts a pivotal role in chemoresistance by G0/G1 arrest. Eliminating hypoxic conditions or silencing HIF-1alpha by siRNA might provide a potent tool to enhance paclitaxel effectiveness in treatment of human ovarian cancer.