NDRG1 and CRK-I/II are regulators of endothelial cell migration under intermittent hypoxia

Obstructive sleep apnea hypopnea syndrome and vascular lesions: An update on what we currently know

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is the most prevalent sleep and respiratory disorder. This syndrome can induce severe cardiovascular and cerebrovascular complications, and intermittent hypoxia is a pivotal contributor to this damage. Vascular pathology is closely associated with the impairment of target organs, marking a focal point in current research. Vascular lesions are the fundamental pathophysiological basis of multiorgan ailments and indicate a shared pathogenic mechanism among common cardiovascular and cerebrovascular conditions, suggesting their importance as a public health concern. Increasing evidence shows a strong correlation between OSAHS and vascular lesions. Previous studies predominantly focused on the pathophysiological alterations in OSAHS itself, such as intermittent hypoxia and fragmented sleep, leading to vascular disruptions. This review aims to delve deeper into the vascular lesions affected by OSAHS by examining the microscopic pathophysiological mechanisms involved. Emphasis has been placed on examining how OSAHS induces vascular lesions through disruptions in the endothelial barrier, metabolic dysregulation, cellular phenotype alterations, neuroendocrine irregularities, programmed cell death, vascular inflammation, oxidative stress and epigenetic modifications. This review examines the epidemiology and associated risk factors for OSAHS and vascular diseases and subsequently describes the existing evidence on vascular lesions induced by OSAHS in the cardiovascular, cerebrovascular, retinal, renal and reproductive systems. A detailed account of the current research on the pathophysiological mechanisms mediating vascular lesions caused by OSAHS is provided, culminating in a discussion of research advancements in therapeutic modalities to mitigate OSAHS-related vascular lesions and the implications of these treatment strategies.

NDRG1 promotes endothelial dysfunction and hypoxia-induced pulmonary hypertension by targeting TAF15

Background

Pulmonary hypertension (PH) represents a threatening pathophysiologic state that can be induced by chronic hypoxia and is characterized by extensive vascular remodeling. However, the mechanism underlying hypoxia-induced vascular remodeling is not fully elucidated.

Methods and Results

By using quantitative polymerase chain reactions, western blotting, and immunohistochemistry, we demonstrate that the expression of N-myc downstream regulated gene-1 (NDRG1) is markedly increased in hypoxia-stimulated endothelial cells in a time-dependent manner as well as in human and rat endothelium lesions. To determine the role of NDRG1 in endothelial dysfunction, we performed loss-of-function studies using NDRG1 short hairpin RNAs and NDRG1 over-expression plasmids. In vitro, silencing NDRG1 attenuated proliferation, migration, and tube formation of human pulmonary artery endothelial cells (HPAECs) under hypoxia, while NDRG1 over-expression promoted these behaviors of HPAECs. Mechanistically, NDRG1 can directly interact with TATA-box binding protein associated factor 15 (TAF15) and promote its nuclear localization. Knockdown of TAF15 abrogated the effect of NDRG1 on the proliferation, migration and tube formation capacity of HPAECs. Bioinformatics studies found that TAF15 was involved in regulating PI3K-Akt, p53, and hypoxia-inducible factor 1 (HIF-1) signaling pathways, which have been proved to be PH-related pathways. In addition, vascular remodeling and right ventricular hypertrophy induced by hypoxia were markedly alleviated in NDRG1 knock-down rats compared with their wild-type littermates.

Conclusions

Taken together, our results indicate that hypoxia-induced upregulation of NDRG1 contributes to endothelial dysfunction through targeting TAF15, which ultimately contributes to the development of hypoxia-induced PH.

Long-Term Characteristics of Human-Derived Biliary Organoids under a Single Continuous Culture Condition

Organoids have been used to investigate the three-dimensional (3D) organization and function of their respective organs. These self-organizing 3D structures offer a distinct advantage over traditional two-dimensional (2D) culture techniques by creating a more physiologically relevant milieu to study complex biological systems. The goal of this study was to determine the feasibility of establishing organoids from various pediatric liver diseases and characterize the long-term evolution of cholangiocyte organoids (chol-orgs) under a single continuous culture condition. We established chol-orgs from 10 different liver conditions and characterized their multicellular organization into complex epithelial structures through budding, merging, and lumen formation. Immunofluorescent staining, electron microscopy, and single-nucleus RNA (snRNA-seq) sequencing confirmed the cholangiocytic nature of the chol-orgs. There were significant cell population differences in the transcript profiles of two-dimensional and organoid cultures based on snRNA-seq. Our study provides an approach for the generation and long-term maintenance of chol-orgs from various pediatric liver diseases under a single continuous culture condition.

A Tumor Suppressor Gene, N-myc Downstream-Regulated Gene 1 (NDRG1), in Gliomas and Glioblastomas

The development of potent and selective therapeutic approaches to glioblastoma (GBM) requires the identification of molecular pathways that critically regulate the survival and proliferation of GBM. Glioblastoma stem-like cells (GSCs) possess stem-cell-like properties, self-renewal, and differentiation into multiple neural cell lineages. From a clinical point of view, GSCs have been reported to resist radiation and chemotherapy. GSCs are influenced by the microenvironment, especially the hypoxic condition. N-myc downstream-regulated gene 1 (NDRG1) is a tumor suppressor with the potential to suppress the proliferation, invasion, and migration of cancer cells. Previous studies have reported that deregulated expression of NDRG1 affects tumor growth and clinical outcomes of patients with GBM. This literature review aimed to clarify the critical role of NDRG1 in tumorigenesis and acquirement of resistance for anti-GBM therapies, further to discussing the possibility and efficacy of NDRG1 as a novel target of treatment for GBM. The present review was conducted by searching the PubMed and Scopus databases. The search was conducted in February 2022. We review current knowledge on the regulation and signaling of NDRG1 in neuro-oncology. Finally, the role of NDRG1 in GBM and potential clinical applications are discussed.

NDRG1 is expressed in human granulosa cells: An implicative role of NDRG1 in the ovary

Purpose

N-myc downstream-regulated gene 1 (NDRG1) is expressed in various human tissues and plays a role in regulating cellular proliferation, angiogenesis, and hypoxia sensing. However, the role of NDRG1 in the ovary remains poorly understood. Therefore, we investigated NDRG1 expression and the role of NDRG1 in the human ovary.

Methods

Follicular fluid (FF) and luteinized granulosa cells were collected from follicles during oocyte retrieval. KGN cells were cultured with cobalt chloride (CoCl2, a hypoxia-mimicking agent) and/or echinomycin. mRNA, protein levels and secretion, and localization were assessed by real-time PCR, Western blotting, ELISA, and immunohistochemical analysis, respectively. KGN cells were also transfected with NDRG1 siRNA for 72 h.

Results

NDRG1 protein was expressed in luteinized granulosa cells. NDRG1 concentration was positively correlated with vascular endothelial growth factor (VEGF) and progesterone concentrations in FF. CoCl2-induced hypoxic stress significantly increased NDRG1 and VEGF mRNA and protein and hypoxia-inducible factor-1α expression compared with those in the controls. The CoCl2-induced overexpression of NDRG1 and VEGF was suppressed by echinomycin. Transfection with NDRG1 siRNA significantly suppressed the release of progesterone in the culture medium.

Conclusions

These results indicate that ovarian NDRG1 may play important roles in follicular development, especially in the early luteinization of pre-ovulatory follicles.

Differential expression and hypoxia-mediated regulation of the N-myc downstream regulated gene family

Many organisms rely on oxygen to generate cellular energy (adenosine triphosphate or ATP). During severe hypoxia, the production of ATP decreases, leading to cell damage or death. Conversely, excessive oxygen causes oxidative stress that is equally damaging to cells. To mitigate pathological outcomes, organisms have evolved mechanisms to adapt to fluctuations in oxygen levels. Zebrafish embryos are remarkably hypoxia-tolerant, surviving anoxia (zero oxygen) for hours in a hypometabolic, energy-conserving state. To begin to unravel underlying mechanisms, we analyze here the distribution of the N-myc Downstream Regulated Gene (ndrg) family, ndrg1-4, and their transcriptional response to hypoxia. These genes have been primarily studied in cancer cells and hence little is understood about their normal function and regulation. We show here using in situ hybridization that ndrgs are expressed in metabolically demanding organs of the zebrafish embryo, such as the brain, kidney, and heart. To investigate whether ndrgs are hypoxia-responsive, we exposed embryos to different durations and severity of hypoxia and analyzed transcript levels. We observed that ndrgs are differentially regulated by hypoxia and that ndrg1a has the most robust response, with a ninefold increase following prolonged anoxia. We further show that this treatment resulted in de novo expression of ndrg1a in tissues where the transcript is not observed under normoxic conditions and changes in Ndrg1a protein expression post-reoxygenation. These findings provide an entry point into understanding the role of this conserved gene family in the adaptation of normal cells to hypoxia and reoxygenation.

Crk and CrkL as Therapeutic Targets for Cancer Treatment

Crk and CrkL are cellular counterparts of the viral oncoprotein v-Crk. Crk and CrkL are overexpressed in many types of human cancer, correlating with poor prognosis. Furthermore, gene knockdown and knockout of Crk and CrkL in tumor cell lines suppress tumor cell functions, including cell proliferation, transformation, migration, invasion, epithelial-mesenchymal transition, resistance to chemotherapy drugs, and in vivo tumor growth and metastasis. Conversely, overexpression of tumor cells with Crk or CrkL enhances tumor cell functions. Therefore, Crk and CrkL have been proposed as therapeutic targets for cancer treatment. However, it is unclear whether Crk and CrkL make distinct or overlapping contributions to tumor cell functions in various cancer types because Crk or CrkL have been examined independently in most studies. Two recent studies using colorectal cancer and glioblastoma cells clearly demonstrated that Crk and CrkL need to be ablated individually and combined to understand distinct and overlapping roles of the two proteins in cancer. A comprehensive understanding of individual and overlapping roles of Crk and CrkL in tumor cell functions is necessary to develop effective therapeutic strategies. This review systematically discusses crucial functions of Crk and CrkL in tumor cell functions and provides new perspectives on targeting Crk and CrkL in cancer therapy.

Technical Feasibility and Physiological Relevance of Hypoxic Cell Culture Models

Hypoxia is characterized as insufficient oxygen delivery to tissues and cells in the body and is prevalent in many human physiology processes and diseases. Thus, it is an attractive state to experimentally study to understand its inner mechanisms as well as to develop and test therapies against pathological conditions related to hypoxia. Animal models in vivo fail to recapitulate some of the key hallmarks of human physiology, which leads to human cell cultures; however, they are prone to bias, namely when pericellular oxygen concentration (partial pressure) does not respect oxygen dynamics in vivo. A search of the current literature on the topic revealed this was the case for many original studies pertaining to experimental models of hypoxia in vitro. Therefore, in this review, we present evidence mandating for the close control of oxygen levels in cell culture models of hypoxia. First, we discuss the basic physical laws required for understanding the oxygen dynamics in vitro, most notably the limited diffusion through a liquid medium that hampers the oxygenation of cells in conventional cultures. We then summarize up-to-date knowledge of techniques that help standardize the culture environment in a replicable fashion by increasing oxygen delivery to the cells and measuring pericellular levels. We also discuss how these tools may be applied to model both constant and intermittent hypoxia in a physiologically relevant manner, considering known values of partial pressure of tissue normoxia and hypoxia in vivo, compared to conventional cultures incubated at rigid oxygen pressure. Attention is given to the potential influence of three-dimensional tissue cultures and hypercapnia management on these models. Finally, we discuss the implications of these concepts for cell cultures, which try to emulate tissue normoxia, and conclude that the maintenance of precise oxygen levels is important in any cell culture setting.

Microfluidic device to attain high spatial and temporal control of oxygen

Microfluidic devices have been successfully used to recreate in vitro biological microenvironments, including disease states. However, one constant issue for replicating microenvironments is that atmospheric oxygen concentration (21% O2) does not mimic physiological values (often around 5% O2). We have created a microfluidic device that can control both the spatial and temporal variations in oxygen tensions that are characteristic of in vivo biology. Additionally, since the microcirculation is responsive to hypoxia, we used a 3D sprouting angiogenesis assay to confirm the biological relevance of the microfluidic platform. Our device consists of three parallel connected tissue chambers and an oxygen scavenger channel placed adjacent to these tissue chambers. Experimentally measured oxygen maps were constructed using phosphorescent lifetime imaging microscopy and compared with values from a computational model. The central chamber was loaded with endothelial and fibroblast cells to form a 3D vascular network. Four to six days later, fibroblasts were loaded into the side chambers, and a day later the oxygen scavenger (sodium sulfite) was flowed through the adjacent channel to induce a spatial and temporal oxygen gradient. Our results demonstrate that both constant chronic and intermittent hypoxia can bias vessel growth, with constant chronic hypoxia showing higher degrees of biased angiogenesis. Our simple design provides consistent control of spatial and temporal oxygen gradients in the tissue microenvironment and can be used to investigate important oxygen-dependent biological processes in conditions such as cancer and ischemic heart disease.

An innovative intermittent hypoxia model for cell cultures allowing fast Po2 oscillations with minimal gas consumption

Performing hypoxia-reoxygenation cycles in cell culture with a cycle duration accurately reflecting what occurs in obstructive sleep apnea (OSA) patients is a difficult but crucial technical challenge. Our goal was to develop a novel device to expose multiple cell culture dishes to intermittent hypoxia (IH) cycles relevant to OSA with limited gas consumption. With gas flows as low as 200 ml/min, our combination of plate holders with gas-permeable cultureware generates rapid normoxia-hypoxia cycles. Cycles alternating 1 min at 20% O2 followed by 1 min at 2% O2 resulted in Po2 values ranging from 124 to 44 mmHg. Extending hypoxic and normoxic phases to 10 min allowed Po2 variations from 120 to 25 mmHg. The volume of culture medium or the presence of cells only modestly affected the Po2 variations. In contrast, the nadir of the hypoxia phase increased when measured at different heights above the membrane. We validated the physiological relevance of this model by showing that hypoxia inducible factor-1α expression was significantly increased by IH exposure in human aortic endothelial cells, murine breast carcinoma (4T1) cells as well as in a blood-brain barrier model (2.5-, 1.5-, and 6-fold increases, respectively). In conclusion, we have established a new device to perform rapid intermittent hypoxia cycles in cell cultures, with minimal gas consumption and the possibility to expose several culture dishes simultaneously. This device will allow functional studies of the consequences of IH and deciphering of the molecular biology of IH at the cellular level using oxygen cycles that are clinically relevant to OSA.

Frequency and magnitude of intermittent hypoxia modulate endothelial wound healing in a cell culture model of sleep apnea

Intermittent hypoxia (IH) has been implicated in the cardiovascular consequences of obstructive sleep apnea (OSA). However, the lack of suitable experimental systems has precluded assessment as to whether IH is detrimental, protective, or both for the endothelium. The aim of the work was to determine the effects of frequency and amplitude of IH oxygenation swings on aortic endothelial wound healing. Monolayers of human primary endothelial cells were wounded and subjected to constant oxygenation (1%, 4%, 13%, or 20% O₂) or IH at different frequencies (0.6, 6, or 60 cycles/h) and magnitude ranges (13-4% O₂ or 20-1% O₂), using a novel well-controlled system, with wound healing being measured after 24 h. Cell monolayer repair was similar at 20% O₂ and 13% O₂, but was considerably increased (approximately twofold) in constant hypoxia at 4% O₂ The magnitude and frequency of IH considerably modulated wound healing. Cycles ranging 13-4% O₂ at the lowest frequency (0.6 cycles/h) accelerated endothelial wound healing by 102%. However, for IH exposures consisting of 20% to 1% O₂ oscillations, wound closure was reduced compared with oscillation in the 13-4% range (by 74% and 44% at 6 cycles/h and 0.6 cycles/h, respectively). High-frequency IH patterns simulating severe OSA (60 cycles/h) did not significantly modify endothelial wound closure, regardless of the oxygenation cycle amplitude. In conclusion, the frequency and magnitude of hypoxia cycling in IH markedly alter wound healing responses and emerge as key factors determining how cells will respond in OSA.NEW & NOTEWORTHY Intermittent hypoxia (IH) induces cardiovascular consequences in obstructive sleep apnea (OSA) patients. However, the vast array of frequencies and severities of IH previously employed in OSA-related experimental studies has led to controversial results on the effects of IH. By employing an optimized IH experimental system here, we provide evidence that the frequency and magnitude of IH markedly alter human aortic endothelial wound healing, emerging as key factors determining how cells respond in OSA.

Dynamic regulation of VEGF-inducible genes by an ERK/ERG/p300 transcriptional network

The transcriptional pathways activated downstream of vascular endothelial growth factor (VEGF) signaling during angiogenesis remain incompletely characterized. By assessing the signals responsible for induction of the Notch ligand delta-like 4 (DLL4) in endothelial cells, we find that activation of the MAPK/ERK pathway mirrors the rapid and dynamic induction of DLL4 transcription and that this pathway is required for DLL4 expression. Furthermore, VEGF/ERK signaling induces phosphorylation and activation of the ETS transcription factor ERG, a prerequisite for DLL4 induction. Transcription of DLL4 coincides with dynamic ERG-dependent recruitment of the transcriptional co-activator p300. Genome-wide gene expression profiling identified a network of VEGF-responsive and ERG-dependent genes, and ERG chromatin immunoprecipitation (ChIP)-seq revealed the presence of conserved ERG-bound putative enhancer elements near these target genes. Functional experiments performed in vitro and in vivo confirm that this network of genes requires ERK, ERG and p300 activity. Finally, genome-editing and transgenic approaches demonstrate that a highly conserved ERG-bound enhancer located upstream of HLX (which encodes a transcription factor implicated in sprouting angiogenesis) is required for its VEGF-mediated induction. Collectively, these findings elucidate a novel transcriptional pathway contributing to VEGF-dependent angiogenesis.

Role of mitochondrial hydrogen peroxide induced by intermittent hypoxia in airway epithelial wound repair in vitro

The airway epithelium acts as a frontline barrier against various environmental insults and its repair process after airway injury is critical for the lung homeostasis restoration. Recently, the role of intracellular reactive oxygen species (ROS) as transcription-independent damage signaling has been highlighted in the wound repair process. Both conditions of continuous hypoxia and intermittent hypoxia (IH) induce ROS. Although IH is important in clinical settings, the roles of IH-induced ROS in the airway repair process have not been investigated. In this study, we firstly showed that IH induced mitochondrial hydrogen peroxide (H2O2) production and significantly decreased bronchial epithelial cell migration, prevented by catalase treatment in a wound scratch assay. RhoA activity was higher during repair process in the IH condition compared to in the normoxic condition, resulting in the cellular morphological changes shown by immunofluorescence staining: round cells, reduced central stress fiber numbers, pronounced cortical actin filament distributions, and punctate focal adhesions. These phenotypes were replicated by exogenous H2O2 treatment under the normoxic condition. Our findings confirmed the transcription-independent role of IH-induced intracellular ROS in the bronchial epithelial cell repair process and might have significant implications for impaired bronchial epithelial cell regeneration.

Aryl Hydrocarbon Receptor Activates NDRG1 Transcription under Hypoxia in Breast Cancer Cells

Hypoxia has been intensively investigated over the past several decades based on the observations that hypoxic tumors are more resistant to therapy and have a worse prognosis. Previously, we reported that N-myc downstream-regulated gene 1 (NDRG1) is strongly up-regulated under hypoxia and may play an important role in tumor adaptation to fluctuating oxygen concentrations. However, the regulatory mechanism of NDRG1 under hypoxia remains elusive. Therefore, the purpose of this study was to identify the transcription factors that regulate NDRG1 and to investigate the functional roles of NDRG1 in hypoxia. We showed that binding sites of aryl hydrocarbon receptor (AHR) were predicted in the NDRG1 promoter. Nuclear AHR was up-regulated in the presence of cobalt and hypoxia. AHR translocated to nuclei and bound between base pairs -412 and -388 of the NDRG1 promoter in hypoxia. Moreover, hypoxia-mimetic induction of NDRG1 was attenuated by knockdown of AHR expression. Also, overexpression of AHR facilitated cell proliferation and migration via up-regulation of NDRG1. These results showed for the first time that AHR positively regulates NDRG1 transcription through an AHR binding site by way of hypoxia-mimetic signaling, which may lead to development of a specific therapeutic regimen to prevent tumor malignancy under hypoxia.

Obstructive sleep apnea and cancer: effects of intermittent hypoxia?

Obstructive sleep apnea (OSA) is a common disorder characterized by pauses in regular breathing. Apneic episodes lead to recurrent hypoxemia-reoxygenation cycles with concomitant cellular intermittent hypoxia. Studies suggest that intermittent hypoxia in OSA may influence tumorigenesis. This review presents recent articles on the potential role of OSA in cancer development. Relevant research has focused on: molecular pathways mediating the influence of intermittent hypoxia on tumor physiology, animal and epidemiological human studies linking OSA and cancer. Current data relating OSA to risk of neoplastic disease remain scarce, but recent studies reveal the potential for a strong relation. More work is, therefore, needed on the impact of OSA on many cancer-related aspects. Results may offer enlightenment for improved cancer diagnosis and treatment.

MicroRNA-769-3p down-regulates NDRG1 and enhances apoptosis in MCF-7 cells during reoxygenation

Hypoxia and reoxygenation are common characteristics of solid tumors, which lead to oxidative stress and activation of stress-response genes. Previously, we observed that N-myc downstream-regulated gene 1 (NDRG1) was strongly down-regulated after shifting to reoxygenation, but the regulatory mechanism of NDRG1 remained elusive. Here we focused on the regulation of NDRG1 by microRNAs (miRNAs). Breast cancer MCF-7 cells were cultured under hypoxia for 24 h followed by 24 h of reoxygenation. The miRNA profiles were examined by Nanostring nCounter assays. Forty-three miRNAs had significant changes upon reoxygenation. In silico analysis identified four oxygen-sensitive miRNAs whose seed regions perfectly matched the 3′-UTR of NDRG1. In particular, miR-769-3p was able to inhibit the expression of NDRG1, which caused a significant reduction of NDRG1 protein upon reoxygenation. Furthermore, overexpression of miR-769-3p significantly inhibited cell proliferation and enhanced apoptosis. Our results revealed that miR-769-3p can functionally regulate NDRG1 during changes in oxygen concentration.

The role of NDRG1 in the pathology and potential treatment of human cancers

N-myc downstream regulated gene 1 (NDRG1) has been well characterised to act as a metastatic suppressor in a number of human cancers. It has also been implicated to have a significant function in a number of physiological processes such as cellular differentiation and cell cycle. In this review, we discuss the role of NDRG1 in cancer pathology. NDRG1 was observed to be downregulated in the majority of cancers. Moreover, the expression of NDRG1 was found to be significantly lower in neoplastic tissues as compared with normal tissues. The most important function of NDRG1 in inhibiting tumour progression is associated with its ability to suppress metastasis. However, it has also been shown to have important effects on other stages of cancer progression (primary tumour growth and angiogenesis). Recently, novel iron chelators with selective antitumour activity (ie, Dp44mT, DpC) were shown to upregulate NDRG1 in cancer cells. Moreover, Dp44mT showed its antimetastatic potential only in cells expressing NDRG1, making this protein an important therapeutic target for cancer chemotherapy. This observation has led to increased interest in the examination of these novel anticancer agents.

Metastasis suppressor, NDRG1, mediates its activity through signaling pathways and molecular motors

The metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), is negatively correlated with tumor progression in multiple neoplasms, being a promising new target for cancer treatment. However, the precise molecular effects of NDRG1 remain unclear. Herein, we summarize recent advances in understanding the impact of NDRG1 on cancer metastasis with emphasis on its interactions with the key oncogenic nuclear factor-kappaB, phosphatidylinositol-3 kinase/phosphorylated AKT/mammalian target of rapamycin and Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase signaling pathways. Recent studies demonstrating the inhibitory effects of NDRG1 on the epithelial-mesenchymal transition, a key initial step in metastasis, TGF-β pathway and the Wnt/β-catenin pathway are also described. Furthermore, NDRG1 was also demonstrated to regulate molecular motors in cancer cells, leading to inhibition of F-actin polymerization, stress fiber formation and subsequent reduction of cancer cell migration. Collectively, this review summarizes the underlying molecular mechanisms of the antimetastatic effects of NDRG1 in cancer cells.

Roles for crk in cancer metastasis and invasion

The Crk family of adaptors is implicated in regulating various biological and pathological processes such as cell proliferation, adhesion, migration, invasion, phagocytosis, and survival. A large number of studies have shown that Crk plays an important role in aggressive and malignant behaviors of human cancers. In immunohistochemical analyses and gene-expression profiles, enhanced expression of Crk has been identified in adenocarcinomas of lung, breast, and stomach and in sarcomas and glioma. Overexpression of Crk in tumor cells induces the prominent tyrosine phosphorylations of scaffolding molecules such as p130(Cas) and paxillin through Src family tyrosine kinases and stimulates the activation loop of intracellular signalling, ultimately contributing to the increased motility and aggressive potential of cancer cells. Crk proteins thus are not simply conduits for intracellular signal transduction but also can control the amplitude of signalling. This review summarizes the significance of Crk and its mediated signaling assemblies, particularly in regulating tumor metastasis and invasion, and discusses the possibilities that they are potential cancer therapeutic targets.

An enteral leucine supply modulates human duodenal mucosal proteome and decreases the expression of enzymes involved in fatty acid beta-oxidation

Leucine is well known to regulate protein metabolism in muscle. We recently reported that enteral leucine infusion decreased proteasome activity in human duodenal mucosa and enhanced intestinal cell proliferation, but its effects on gut proteome remain unknown. Therefore, we aimed to assess the effects of an enteral leucine infusion on the whole proteome of duodenal mucosa. In this work, 5 healthy volunteers received for 5h, on 2 occasions and in random order, an enteral supply of maltodextrins (0.25 g kg(-1) h(-1)) or maltodextrins supplemented with leucine (0.035 g kg(-1) h(-1)). At the end of infusion, endoscopic duodenal biopsy samples were collected and analyzed by 2D-PAGE. Eleven protein spots were differentially and significantly (P<0.05) expressed in response to the leucine-supplemented maltodextrins compared with maltodextrins alone. Forty percent of identified proteins by mass spectrometry were located in mitochondria. Four proteins were involved in lipid metabolism: HADHA, ACADVL and CPT2 expressions were reduced, whereas FABP1 expression was increased. In addition, the expression of DHA kinase involved in glycerol metabolism was also downregulated. Finally, leucine supplementation altered the duodenal mucosal proteome by regulating the expression of several enzymes mainly involved in lipid metabolism. These results suggest that leucine supplementation may slowdown fatty acid beta-oxidation in human duodenal mucosa.

NDRG1/Cap43 overexpression in tumor tissues and serum from lung cancer patients

PURPOSE

The N-myc downstream regulated gene 1 (NDRG1)/Cap43 is overexpressed in multiple cancer types, including lung cancer. In this study, we investigated the expression of NDRG1/Cap43 in lung cancer tissues and in serum from 90 lung cancer patients and 60 healthy controls.

MATERIALS AND METHODS

Ninety patients with pathologically confirmed primary lung cancer who underwent surgical resections were recruited for the study. From resected sections, we dissected lung tumor tissues and adjacent noncancerous tissues that were used as controls and collected patient sera for NDRG1/Cap43 expression levels. Immunohistochemical staining was applied to detect NDRG1/Cap43-positive tumor cells, and real-time quantitative-PCR (RT-PCR) was used to determine mRNA transcript levels of NDRG1/Cap43 in lung cancer tissues. Serum levels of NDRG1/Cap43 were measured by Enzyme-linked immunosorbent assays (ELISA). Data comparison between two groups was performed by independent two sample test, and comparison between more than two groups was applied by the analysis of variance (ANOVA) test.

RESULTS

Compared with adjacent normal tissues, lung cancer tissues had significantly increased expression of NDRG1/Cap43 (P < 0.05). Lung adenocarcinomas also had significantly higher NDRG1/Cap43 levels than lung squamous carcinomas (P < 0.01). RT-PCR analysis showed significantly higher levels of NDRG1/Cap43 mRNA transcripts in lung cancer tissues compared with matched adjacent noncancerous tissues (P < 0.05). mRNA expression of NDRG1/Cap43 was associated with the histological pattern of lung cancer. ELISA analysis for serum NDRG1/Cap43 levels revealed significantly higher levels in lung cancer patients (358.56 ± 233.82 ng/mL) compared with healthy controls (28.83 ± 10.51 ng/mL, P < 0.001).

CONCLUSIONS

NDRG1/Cap43 overexpression may be of predictive value in determining the prognosis of lung cancer patients.

Down-regulation of NDRG1 promotes migration of cancer cells during reoxygenation

One characteristic of tumor microenvironment is oxygen fluctuation, which results from hyper-proliferation and abnormal metabolism of tumor cells as well as disorganized neo-vasculature. Reoxygenation of tumors can induce oxidative stress, which leads to DNA damage and genomic instability. Although the cellular responses to hypoxia are well known, little is known about the dynamic response upon reoxygenation. In order to investigate the transcriptional responses of tumor adaptation to reoxygenation, breast cancer MCF-7 cells were cultured under 0.5% oxygen for 24 h followed by 24 h of reoxygenation in normoxia. Cells were harvested at 0, 1, 4, 8, 12, and 24 h during reoxygenation. The transcriptional profile of MCF-7 cells upon reoxygenation was examined using Illumina Human-6 v3 BeadChips. We identified 127 differentially expressed genes, of which 53.1% were up-regulated and 46.9% were down-regulated upon reoxygenation. Pathway analysis revealed that the HIF-1-alpha transcription factor network and validated targets of C-MYC transcriptional activation were significantly enriched in these differentially expressed genes. Among these genes, a subset of interest genes was further validated by quantitative reverse-transcription PCR. In particular, human N-MYC down-regulated gene 1 (NDRG1) was highly suppressed upon reoxygenation. NDRG1 is associated with a variety of stress and cell growth-regulatory conditions. To determine whether NDRG1 plays a role in reoxygenation, NDRG1 protein was overexpressed in MCF-7 cells. Upon reoxygenation, overexpression of NDRG1 significantly inhibited cell migration. Our results revealed the dynamic nature of gene expression in MCF-7 cells upon reoxygenation and demonstrated that NDRG1 is involved in tumor adaptation to reoxygenation.

NDRG1 as a biomarker for metastasis, recurrence and of poor prognosis in hepatocellular carcinoma

N-myc downstream-regulated gene 1 (NDRG1) has been reported to be a multifunctional protein associated with carcinogenesis, however, the cellular function of NDRG1 remains elusive in human cancers. Here, our proteomics profile analysis of HCC tissues with different metastatic capabilities revealed that NDRG1 was correlated with metastasis and recurrence in HCC patients after liver transplantation (LT). Immunohistochemical staining of 143 HCC patients after LT showed that NDRG1-positive expression had poor prognosis, either for shorter disease-free survival or overall survival (P < 0.001), compared with NDRG1-negative expression. Multivariate analysis confirmed NDRG1 as an independent prognostic value (P < 0.001). In addition, in vitro experiments HCC cells with small interfering RNA against NDRG1 significantly suppressed its proliferation, colony formation, invasion and migration ability. Microarray analysis revealed that NDRG1 modulated the expression of genes associated with transmembrane transporter activity, chemoattractant activity, immune response, cell adhesion and cell proliferation process. Taken together, these results suggested that NDRG1 was an important molecule in controlling HCC metastasis and thus suggested as a novel biomarker for predicting HCC recurrence after LT.