Invasion is a genetic program regulated by transcription factors

Human antigen R knockdown attenuates the invasive activity of oral cancer cells through inactivation of matrix metalloproteinase-1 gene expression

Background/purpose

The RNA-binding protein human antigen R (HuR) recognizes AU-rich elements in the 3'-untranslated regions of mRNA. The expression of cytoplasmic HuR is related to the malignancy of many carcinomas. The aim of this study is investigation of effect of HuR knockdown for invasive activity of oral carcinoma.

Materials and methods

Proliferation, invasion, real-time PCR, and reporter gene assays were performed to confirm that the knockdown of HuR downregulates the invasive activity of cancer cells. Immunohistochemical staining was performed for high invasive carcinoma, squamous cell carcinoma (SCC) and low invasive carcinoma, verrucous carcinoma (VC), to determine if the localization of cytoplasmic HuR is related to matrix metalloproteinase-1 (MMP-1) expression.

Results

Invasive activity was significantly lower in HuR knockdown cancer cells than in control cells. A luciferase assay revealed that HuR knockdown inactivated the promoter activity of the MMP-1 gene. The mRNA levels of the transcription factors required for MMP-1 expression, including c-fos and c-jun, were decreased in HuR knockdown cancer cells. Immunohistochemical analysis revealed the level of cytoplasmic HuR and MMP-1 in invasive carcinoma to be higher than in low invasive cancer. HuR induced MMP-1 expression in the invasive front of most SCC cases.

Conclusion

HuR knockdown attenuated the invasive activity of cancer cells by decreasing the expression of the MMP-1, at least partially. HuR localization may help determine the invasive phenotype of cancer cells and inhibit cancer cell invasion. Furthermore, in oral SCC, HuR may be related to invasive activity through the expression of MMP-1.

Identification of a Novel ERK5 (MAPK7) Inhibitor, MHJ-627, and Verification of Its Potent Anticancer Efficacy in Cervical Cancer HeLa Cells

Extracellular signal-regulated kinase 5 (ERK5), a member of the mitogen-activated protein kinase (MAPK) family, is involved in key cellular processes. However, overexpression and upregulation of ERK5 have been reported in various cancers, and ERK5 is associated with almost every biological characteristic of cancer cells. Accordingly, ERK5 has become a novel target for the development of anticancer drugs as inhibition of ERK5 shows suppressive effects of the deleterious properties of cancer cells. Herein, we report the synthesis and identification of a novel ERK5 inhibitor, MHJ-627, and verify its potent anticancer efficacy in a yeast model and the cervical cancer HeLa cell line. MHJ-627 successfully inhibited the kinase activity of ERK5 (IC₅₀: 0.91 μM) and promoted the mRNA expression of tumor suppressors and anti-metastatic genes. Moreover, we observed significant cancer cell death, accompanied by a reduction in mRNA levels of the cell proliferation marker, proliferating cell nuclear antigen (PCNA), following ERK5 inhibition due to MHJ-627 treatment. We expect this finding to serve as a lead compound for further identification of inhibitors for ERK5-directed novel approaches for oncotherapy with increased specificity.

Nuclear-capture of endosomes depletes nuclear G-actin to promote SRF/MRTF activation and cancer cell invasion

Signals are relayed from receptor tyrosine kinases (RTKs) at the cell surface to effector systems in the cytoplasm and nucleus, and coordination of this process is important for the execution of migratory phenotypes, such as cell scattering and invasion. The endosomal system influences how RTK signalling is coded, but the ways in which it transmits these signals to the nucleus to influence gene expression are not yet clear. Here we show that hepatocyte growth factor, an activator of MET (an RTK), promotes Rab17- and clathrin-dependent endocytosis of EphA2, another RTK, followed by centripetal transport of EphA2-positive endosomes. EphA2 then mediates physical capture of endosomes on the outer surface of the nucleus; a process involving interaction between the nuclear import machinery and a nuclear localisation sequence in EphA2's cytodomain. Nuclear capture of EphA2 promotes RhoG-dependent phosphorylation of the actin-binding protein, cofilin to oppose nuclear import of G-actin. The resulting depletion of nuclear G-actin drives transcription of Myocardin-related transcription factor (MRTF)/serum-response factor (SRF)-target genes to implement cell scattering and the invasive behaviour of cancer cells.

The Role Played by SLUG, an Epithelial-Mesenchymal Transition Factor, in Invasion and Therapeutic Resistance of Malignant Glioma

In malignant gliomas, invasive phenotype and cancer stemness promoting resurgence of residual tumor cells render treatment very difficult. Hence, identification of epithelial-mesenchymal transition (EMT) factors associated with invasion and stemness of glioma cells is critical. To address the issue, we investigated several EMT factors in hypermotile U87MG and U251 cells, orthotopic mouse glioma model, and human glioma samples. Of several EMT markers, SLUG expression was notably increased at the invasive fronts of gliomas, both in mouse tumor grafts and human glioma samples. The biological role played by SLUG was investigated using a colony-forming assay after chemotherapy and irradiation, and by employing a neurosphere culture assay. The effect of SLUG on glioma progression was examined in our patient cohort and samples, and compared to large public data from the REMBRANDT and TCGA. Genetic upregulation of SLUG was associated with increased levels of stemness factors and enhanced resistance to radiation and temozolomide. In our cohort, patients exhibiting lower-level SLUG expression evidenced longer progression-free survival (P = 0.042). Also, in the REMBRANDT dataset, a group in which SLUG was downregulated exhibited a significant survival benefit (P < 0.001). Although paired glioblastoma samples from our patients did not show a significant increase of SLUG expression, increased mRNA levels of SLUG were found in recurrent glioblastoma from TCGA (P = 0.052), and in temozolomide-treated glioma cells and mouse tumor grafts. SLUG may contribute to glioma progression by controlling invasion at infiltrating margins, associated with increased stemness and therapeutic resistance.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

Gene regulation in the immediate-early response process

Immediate-early genes (IEGs) can be activated and transcribed within minutes after stimulation, without the need for de novo protein synthesis, and they are stimulated in response to both cell-extrinsic and cell-intrinsic signals. Extracellular signals are transduced from the cell surface, through receptors activating a chain of proteins in the cell, in particular extracellular-signal-regulated kinases (ERKs), mitogen-activated protein kinases (MAPKs) and members of the RhoA-actin pathway. These communicate through a signaling cascade by adding phosphate groups to neighboring proteins, and this will eventually activate and translocate TFs to the nucleus and thereby induce gene expression. The gene activation also involves proximal and distal enhancers that interact with promoters to simulate gene expression. The immediate-early genes have essential biological roles, in particular in stress response, like the immune system, and in differentiation. Therefore they also have important roles in various diseases, including cancer development. In this paper we summarize some recent advances on key aspects of the activation and regulation of immediate-early genes.

Promotion of breast cancer cells MDA-MB-231 invasion by di(2-ethylhexyl)phthalate through matrix metalloproteinase-2/-9 overexpression

Di(2-ethylhexyl)phthalate (DEHP) is an estrogenic chemical that is widely used in polyvinyl products. We aimed to determine the mechanisms behind the effects of DEHP on ERα-negative breast cancer cells MDA-MB-231 invasion and matrix metalloproteinases-2/-9 (MMP-2/-9) up-regulation in this study. Transwell assay indicated that DEHP exposure (>50 μg/ml) significantly enhanced the invasion ability of MDA-MB-231 cells. Quantitative real-time PCR (qPCR) and western blotting revealed that MMP-2/-9 is overexpressed in mRNA and protein levels after DEHP treatment. Gelatin zymography consistently demonstrated that DEHP exposure also enhances the activity of MMP-2/-9. Immunofluorescence assay showed that DEHP could accelerate NF-kappaB (NF-κB) subunits-p65 translocation into the nucleus, which is confirmed by western blotting assay, suggesting that the ratio of nuclear/cytosolic level of p65 was significantly increased. Furthermore, the invasion and MMP-2/-9 overexpression of MDA-MB-231 cells after DEHP-treated were reversed by the NF-κB chemical inhibitor JSH-23 via drug inhibition assay. This study suggested that DEHP could promote ERα-negative breast cancer cells MDA-MB-231 invasion through activating NF-κB and MMP-2/-9 overexpression.

Invasive Cell Fate Requires G1 Cell-Cycle Arrest and Histone Deacetylase-Mediated Changes in Gene Expression

Despite critical roles in development and cancer, the mechanisms that specify invasive cellular behavior are poorly understood. Through a screen of transcription factors in Caenorhabditis elegans, we identified G1 cell-cycle arrest as a precisely regulated requirement of the anchor cell (AC) invasion program. We show that the nuclear receptor nhr-67/tlx directs the AC into G1 arrest in part through regulation of the cyclin-dependent kinase inhibitor cki-1. Loss of nhr-67 resulted in non-invasive, mitotic ACs that failed to express matrix metalloproteinases or actin regulators and lack invadopodia, F-actin-rich membrane protrusions that facilitate invasion. We further show that G1 arrest is necessary for the histone deacetylase HDA-1, a key regulator of differentiation, to promote pro-invasive gene expression and invadopodia formation. Together, these results suggest that invasive cell fate requires G1 arrest and that strategies targeting both G1-arrested and actively cycling cells may be needed to halt metastatic cancer.

Immediate-early gene activation by the MAPK pathways: what do and don't we know?

The study of IE (immediate-early) gene activation mechanisms has provided numerous paradigms for how transcription is controlled in response to extracellular signalling. Many of the findings have been derived from investigating one of the IE genes, FOS, and the models extrapolated to regulatory mechanisms for other IE genes. However, whereas the overall principles of activation appear similar, recent evidence suggests that the underlying mechanistic details may differ depending on cell type, cellular stimulus and IE gene under investigation. In the present paper, we review recent advances in our understanding of IE gene transcription, chiefly focusing on FOS and its activation by ERK (extracellular-signal-regulated kinase) MAPK (mitogen-activated protein kinase) pathway signalling. We highlight important fundamental regulatory principles, but also illustrate the gaps in our current knowledge and the potential danger in making assumptions based on extrapolation from disparate studies.

Cell invasion through basement membrane: the anchor cell breaches the barrier

Cell invasion through basement membrane (BM) is a specialized cellular behavior critical to many normal developmental events, immune surveillance, and cancer metastasis. A highly dynamic process, cell invasion involves a complex interplay between cell-intrinsic elements that promote the invasive phenotype, and cell-cell and cell-BM interactions that regulate the timing and targeting of BM transmigration. The intricate nature of these interactions has made it challenging to study cell invasion in vivo and model in vitro. Anchor cell invasion in Caenorhabditis elegans is emerging as an important experimental paradigm for comprehensive analysis of BM invasion, revealing the gene networks that specify invasive behavior and the interactions that occur at the cell-BM interface.

Fra-1 controls motility of bladder cancer cells via transcriptional upregulation of the receptor tyrosine kinase AXL

Fos-related antigen 1 (Fra-1) is a Fos family member overexpressed in several types of human cancers. Here, we report that Fra-1 is highly expressed in the muscle-invasive form of the carcinoma of the bladder (80%) and to a lesser extent in superficial bladder cancer (42%). We demonstrate that in this type of cancer Fra-1 is regulated via a C-terminal instability signal and C-terminal phosphorylation. We show that manipulation of Fra-1 expression levels in bladder cancer cell lines affects cell morphology, motility and proliferation. The gene coding for AXL tyrosine kinase is directly upregulated by Fra-1 in bladder cancer and in other cell lines. Importantly, our data demonstrate that AXL mediates the effect of Fra-1 on tumour cell motility but not on cell proliferation. We suggest that AXL may represent an attractive therapeutic target in cancers expressing high Fra-1 levels.

PTHrP promotes colon cancer cell migration and invasion in an integrin α6β4-dependent manner through activation of Rac1

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Rac1 GTPase enhances colon cancer cell migration and invasion. Here we report a positive correlation between PTHrP expression and Rac1 activity in LoVo (human colon cancer) cells. The positive effects of PTHrP on Rac1 activity and on cell migration and invasion are mediated via the guanine nucleotide exchange factor Tiam1. Knockdown of integrin α6β4, which is upregulated by PTHrP, negates the PTHrP-mediated increase in Rac1 activation. Integrin α6β4 signals synergistically with growth factor receptors to activate the phosphatidylinositol 3-kinase (PI3-K) pathway. Chemical inhibition of PI3-K negates the PTHrP-mediated effects on Tiam1 and Rac1 activity. Tumors from PTHrP-overexpressing LoVo cells also show increased expression of Tiam1. Taken together, these observations provide evidence of a link between PTHrP and Rac1 activity through integrin α6β4, resulting in enhanced cell migration and invasion. Targeting PTHrP production in colon cancer may thus prove therapeutically beneficial.

SNAI2/Slug promotes growth and invasion in human gliomas

Background

Numerous factors that contribute to malignant glioma invasion have been identified, but the upstream genes coordinating this process are poorly known.

Methods

To identify genes controlling glioma invasion, we used genome-wide mRNA expression profiles of primary human glioblastomas to develop an expression-based rank ordering of 30 transcription factors that have previously been implicated in the regulation of invasion and metastasis in cancer.

Results

Using this approach, we identified the oncogenic transcriptional repressor, SNAI2/Slug, among the upper tenth percentile of invasion-related transcription factors overexpressed in glioblastomas. SNAI2 mRNA expression correlated with histologic grade and invasive phenotype in primary human glioma specimens, and was induced by EGF receptor activation in human glioblastoma cells. Overexpression of SNAI2/Slug increased glioblastoma cell proliferation and invasion in vitro and promoted angiogenesis and glioblastoma growth in vivo. Importantly, knockdown of endogenous SNAI2/Slug in glioblastoma cells decreased invasion and increased survival in a mouse intracranial human glioblastoma transplantation model.

Conclusion

This genome-scale approach has thus identified SNAI2/Slug as a regulator of growth and invasion in human gliomas.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Hyperactivated NF-{kappa}B and AP-1 transcription factors promote highly accessible chromatin and constitutive transcription across the interleukin-6 gene promoter in metastatic breast cancer cells

Interleukin-6 (IL-6), involved in cancer-related inflammation, acts as an autocrine and paracrine growth factor, which promotes angiogenesis, metastasis, and subversion of immunity, and changes the response to hormones and to chemotherapeutics. We explored transcription mechanisms involved in differential IL-6 gene expression in breast cancer cells with different metastatic properties. In weakly metastatic MCF7 cells, histone H3 K9 methylation, HP1 binding, and weak recruitment of AP-1 Fra-1/c-Jun, NF-kappaB p65 transcription factors, and coactivators is indicative of low chromatin accessibility and gene transcription at the IL-6 gene promoter. In highly metastatic MDA-MB231 cells, strong DNase, MNase, and restriction enzyme accessibility, as well potent constitutive transcription of the IL-6 gene promoter, coincide with increased H3 S10 K14 phosphoacetylation and promoter enrichment of AP-1 Fra-1/c-Jun and NF-kappaB p65 transcription factors and MSK1, CBP/p300, Brg1, and Ezh2 cofactors. Complementation, silencing, and kinase inhibitor experiments further demonstrate involvement of AP-1 Fra-1/c-Jun and NF-kappaB p65/RelB members, but not of the alpha estrogen receptor in promoting chromatin accessibility and transcription across the IL-6 gene promoter in metastatic breast cancer cells. Finally, the natural withanolide Withaferin A was found to repress IL-6 gene transcription in metastatic breast cancer cells upon dual inhibition of NF-kappaB and AP-1 Fra-1 transcription factors and silencing of IL-6 promoter chromatin accessibility.

Brain tumor hypoxia: tumorigenesis, angiogenesis, imaging, pseudoprogression, and as a therapeutic target

Hypoxia is implicated in many aspects of tumor development, angiogenesis, and growth in many different tumors. Brain tumors, particularly the highly aggressive glioblastoma multiforme (GBM) with its necrotic tissues, are likely affected similarly by hypoxia, although this involvement has not been closely studied. Invasion, apoptosis, chemoresistance, resistance to antiangiogenic therapy, and radiation resistance may all have hypoxic mechanisms. The extent of the influence of hypoxia in these processes makes it an attractive therapeutic target for GBM. Because of their relationship to glioma and meningioma growth and angiogenesis, hypoxia-regulated molecules, including hypoxia inducible factor-1, carbonic anhydrase IX, glucose transporter 1, and vascular endothelial growth factor, may be suitable subjects for therapies. Furthermore, other novel hypoxia-regulated molecules that may play a role in GBM may provide further options. Emerging imaging techniques may allow for improved determination of hypoxia in human brain tumors to better focus therapeutic treatments; however, tumor pseudoprogression, which may be prompted by hypoxia, poses further challenges. An understanding of the role of hypoxia in tumor development and growth is important for physicians involved in the care of patients with brain tumors.

TGF-beta-mediated activation of RhoA signalling is required for efficient (V12)HaRas and (V600E)BRAF transformation

Transforming growth factor beta-1 (TGF-beta) acts as both a tumour suppressor and a tumour promoter in a context-dependent manner. The tumour-promoting activities of TGF-beta are likely to result from a combination of Smad and non-Smad signalling pathways but remain poorly understood. Here we show that TGF-beta-mediated activation of RhoA is dependent on the kinase activity of ALK5 and that continuous ALK5 activity maintains basal RhoA-ROCK signalling, cell morphology and actin dynamics in serum-starved rodent fibroblasts independently of Smad2, Smad3 and Smad4. In immortalized human diploid fibroblasts, we show that oncogenic rewiring by transduction of (V12)HaRas instigates regulation of RhoA-ROCK signalling through an autocrine TGF-beta1-ALK5 pathway. Furthermore, we show that ALK5-mediated activation of RhoA is required for efficient (V12)HaRas, V-Raf and (V600E)BRAF transformation and (V12)HaRas-mediated anchorage-independent growth. These findings identify a new pro-oncogenic activity of TGF-beta and indicate that tumours harbouring (V12)HaRas and (V600E)BRAF mutations may be susceptible to TGF-beta signalling inhibitors.

Chemogenomics approaches to novel target discovery

Chemogenomics involves the combination of a compound's effect on biological targets together with modern genomics technologies. The merger of these two methodologies is creating a new way to screen for compound-target interactions, as well as map chemical and biological space in a parallel fashion. The challenge associated with mining complex databases has initiated the development of many novel in silico tools to profile and analyze data in a systematic way. The ability to analyze the combinatorial effects of chemical libraries on biological systems will aid the discovery of new therapeutic entities. Chemogenomics provides a tool for the rapid validation of novel targeted therapeutics, where a specific molecular target is modulated by a small molecule. Along with targeted therapies comes the ability to discovery pathway nodes where a single molecular target might be an essential component of more than one disease. Several disease areas will benefit directly from the chemogenomics approach, the most advanced being cancer. A genetic loss-of-function screen can be modulated in the presence of a compound to search for genes or pathways involved in the compound's activity. Several recent papers highlight how chemogenomics is changing with RNA interference-based screening and shaping the discovery of new targeted therapies. Together, chemical and RNA interference-based screens open the door for a new way to discovery disease-associated genes and novel targeted therapies.

In vivo and ex vivo comparative transcriptional profiling of invasive and non-invasive Candida albicans isolates identifies genes associated with tissue invasion

The human pathogenic fungus Candida albicans can cause a wide range of infections and invade multiple organs. To identify C. albicans genes that are expressed during invasion of the liver, we used genome-wide transcriptional profiling in vivo and ex vivo. By analysing the different phases of intraperitoneal infection from attachment to tissue penetration in a time-course experiment and by comparing the profiles of an invasive with those of a non-invasive strain, we identified genes and transcriptional pattern which are associated with the invasion process. This includes genes involved in metabolism, stress, and nutrient uptake, as well as transcriptional programmes regulating morphology and environmental sensing. One of the genes identified as associated with liver invasion was DFG16, a gene crucial for pH-dependent hyphal formation, correct pH sensing, invasion at physiological pH and systemic infection.

Increased cell survival, migration, invasion, and Akt expression in PTHrP-overexpressing LoVo colon cancer cell lines

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. We have previously shown that PTHrP increases colon cancer cell proliferation, extracellular matrix adhesion, and cell-surface integrin alpha6beta4 expression. Since cancer cell migration, invasion, and survival are crucial components of metastasis, and colon cancer has a high metastatic potential, in this study we used the human colon cancer cell line LoVo as a model system to study the effects of PTHrP on these parameters. PTHrP expression was modulated by stable transfection with a construct expressing PTHrP (-36 to +139). We report that PTHrP increases cell migration, invasion, and survival. PTHrP altered cell morphology, with PTHrP-overexpressing cells exhibiting increased spreading and several long protrusions. PTHrP also increased the steady-state mRNA levels of the integrin alpha6 and beta4 subunits, indicating a direct and/or indirect effect of PTHrP on the transcriptional and/or post-transcriptional regulation of integrin alpha6 and beta4 expression. Integrin alpha6beta4 activates the phosphoinositol 3-kinase (PI3-K)/Akt pathway, leading to glycogen synthase kinase-3 (GSK-3) deactivation. PTHrP overexpression also led to an increase in active Akt and inactive GSK-3 levels, indicating that the PTHrP-mediated upregulation of integrin alpha6beta4 expression may activate the PI3-K pathway, resulting in increased cell survival, migration and invasion.

Regulation of anchor cell invasion and uterine cell fates by the egl-43 Evi-1 proto-oncogene in Caenorhabditis elegans

Cell invasion is a tightly controlled process occurring during development and tumor progression. The nematode Caenorhabditis elegans serves as a genetic model to study cell invasion during normal development. In the third larval stage, the anchor cell in the somatic gonad first induces and then invades the adjacent epidermal vulval precursor cells. The homolog of the Evi-1 oncogene, egl-43, is necessary for basement membrane destruction and anchor cell invasion. egl-43 is part of a regulatory network mediating cell invasion downstream of the fos-1 proto-oncogene. In addition, EGL-43 is required to specify the cell fates of ventral uterus cells downstream of or in parallel with LIN-12 NOTCH. Comparison with mammalian Evi-1 suggests a conserved pathway controlling cell invasion and cell fate specification.

Identification of hypoxia-induced genes in a malignant glioma cell line (U-251) by cDNA microarray analysis

Overcoming the metabolic restrictions of hypoxia may allow the progression of lower-grade tumors to glioblastoma multiforme. Our findings of up-regulation of HIF-1alpha and its downstream targets VEGF, GLUT-1, and CAIX in higher-grade gliomas support this hypothesis. We compared the gene expression profiles of the U-251 malignant glioma cell line under normoxic and hypoxic conditions to discover future research targets. U-251 cells were grown to 75% confluence and exposed to either normoxic or hypoxic conditions for 24 h. RNA was extracted, amplified, and hybridized to a cDNA microarray chip containing ~8,800 universal cellular genes. A threefold increase in mRNA expression was used as a threshold value for differential expression. Identified genes were divided into cell cycle control, stress response, and "newly connected" genes. Hybridization identified 11 hypoxia-induced genes: 1 involved with cell cycle control (CCNG2), 6 in stress response (IGFBP3, SLC2A3, GSTT2, FOS, DDIT3, AKR1C3), and 2 newly connected genes (Depp, AKAP4). One stress-related gene (AKR1C3) encodes for an enzyme that synthesizes progesterone. Of newly connected genes, the gene decidual protein induced by progesterone (Depp) showed the highest expression (4.2-fold increase). Possible future targeting for "hypoxic" glioma cells includes the targets for the AP-1 transcription factor complex (FOS), as well as blockade of the enzyme AKR1C3 with nonsteroidal anti-inflammatory drugs. Possible functions of the highly expressed gene Depp include tumor vascularization. Future studies will focus on the hypothesis that Depp is up-regulated in an autocrine fashion by the AKR1C3 enzyme in U-251 glioma cells under hypoxic conditions.