Hypoxia-inducible factor-1-mediated activation of stanniocalcin-1 in human cancer cells

Stanniocalcin supports the functional adaptation of adult-sized kidneys transplanted into the pediatric recipients

BACKGROUND

The functional adaptation of adult-sized kidney (ASK) grafts to the recipient's size is not completely reversible and is associated with irreversible histologic damage in the smallest recipients. The aim of the study was to unveil the molecular mechanisms underlying the functional adaptation of ASK transplants to small pediatric recipients.

METHODS

Because physiologic and functional adaption of ASK in infants is seen maximally at 3 months after transplantation, we selected 21 pediatric recipients of an ASK with protocol biopsies at engraftment and 3 and 6 months, without delayed graft function or interval rejection, and we conducted whole-genome expression profiles of the renal allograft biopsies at 3 months and correlated results with subsequent absolute glomerular filtration rate (aGFR).

RESULTS

Seven hundred twenty-four unique genes correlated significantly with aGFR (q value <5%). Canonical pathway analysis identified overrepresentation of relevant pathways involved in regulation of tubular salt reabsorption and enzymatic pathways for organ development and hypertrophy. The single gene that correlated best with aGFR was stanniocalcin 1 (STC1). STC1 expression also correlated with the recipient's size at the time of transplantation and the chronic allograft damage index at 6 months.

CONCLUSIONS

Functional adaptation of adult-sized grafts to the pediatric recipient is associated with molecular adaptation for normal-volume homeostasis of the recipient. Our finding also suggests that stanniocalcin (STC1) plays an important role on functional adaption in pediatric kidney transplantation.

Synergistic effect of p53 on TSA-induced stanniocalcin 1 expression in human nasopharyngeal carcinoma cells, CNE2

Human stanniocalcin 1 (STC1) has recently been identified as a putative protein factor involved in cellular apoptosis. The use of histone deacetylase inhibitor (i.e. trichostatin A (TSA)) and doxorubicin (Dox) is one of the common treatment methods to induce apoptosis in human cancer cells. A study on TSA and Dox-mediated apoptosis may shed light on the regulation and function of STC1 in cancer treatment. In this study, TSA and Dox cotreatment in human nasopharyngeal carcinoma cells (CNE2) elicited synergistic effects on STC1 gene expression and cellular apoptosis. An activation of p53 (TP53) transcriptional activity in Dox- or Dox+TSA-treated cells was revealed by the increased expression levels of p53 mRNA/protein as well as p53-driven luciferase activities. To elucidate the possible involvement of p53 in STC1 gene transcription, a vector expressing wild-type or dominant negative (DN) p53 was transiently transfected into the cells. Both STC1 promoter luciferase constructs and chromatin immunoprecipitation assays did not support the direct role of p53 in STC1 gene transactivation. However, the synergistic effects of p53 on the induction of NF-κB phosphorylation and the recruitment of acetylated histone H3 in STC1 promoter were observed in TSA-cotreated cells. The overexpression of exogenous STC1 sensitized apoptosis in Dox-treated cells. Taken together, this study provides data to show the cross talk of NF-κB, p53, and histone protein in the regulation of STC1 expression and function.

Evolution and roles of stanniocalcin

In fish, stanniocalcin-1 (STC1) is a key endocrine factor that acts on gill, intestine and kidney to regulate serum calcium and phosphate homeostasis. The recent identification and study of mammalian STCs (STC1 and STC2) revealed that the hormones are made in virtually all tissues and they act primarily as paracrine/autocrine factors to regulate various biological functions. Based on their ubiquitous expression patterns and generally undetectable levels in blood serum, it is unlikely that the mammalian STCs play important roles in serum Ca(2+)/P(i) homeostasis. However current evidences still support the local action of STCs in Ca(2+) and P(i) transport, probably via their action on Ca(2+)-channels and Na(+)/P(i) co-transporter. At present, information about the sequence, expression and distribution of the STC receptor(s) is lacking. However, recent emerging evidence hints the involvement of STC1 and STC2 in the sub-cellular functions of mitochondria and endoplasmic reticulum respectively, particularly responding to oxidative stress and unfolded protein response. With increasing evidence that demonstrates the local actions of STCs, the focus of the research has been moved to cellular inflammation and carcinogenesis. This review integrates the information available on STCs in fish and mammals, focusing mainly on their embryonic origin, tissue distribution, their potential regulatory mechanisms and the modes of action, and their physiological and pathophysiological functions, particularly in cancer biology.

Assessment of stanniocalcin-1 as a prognostic marker in human esophageal squamous cell carcinoma

Stanniocalcin-1 (STC1) is a secreted glycoprotein hormone and highly expressed in various types of human malignancies. Although evidence points to the role of STC1 in human cancers, the clinical significance of STC1 expression in esophageal cancer has not been well established. Quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry were performed to assess the expression of STC1 in the cancer cell line TE8 and esophageal cancer tissues from 229 esophageal squamous cell carcinomas (ESCC). Surgically-resected tissue sections were immunostained for potential regulators of STC1 expression, hypoxia-inducible factor-1α (HIF-1α) and p53. Marked increase in STC1 mRNA and protein expression was noted in TE8 cells cultured under hypoxic conditions. Overexpression of STC1 mRNA was noted in ESCC tumors compared to normal counterparts. Positive immunohistochemical staining for STC1 protein was observed in 38.9% of patients, and correlated significantly with advanced pT status (P=0.019), poor prognosis [overall survival (P<0.0006) and disease-free survival (P<0.0002) of ESCC patients who had undergone curative surgery]. Positive staining for HIF-1α and p53 proteins in ESCC did not correlate with STC1 expression. The results showed marked induction of STC1 expression under hypoxia in cultured cells and in esophageal cancer cells and that overexpression of STC1 was an independent prognostic factor in patients with esophageal cancer who had undergone curative surgery. STC1 is a potentially useful biomarker for ESCC treatment.

Sp1 is a transcription repressor to stanniocalcin-1 expression in TSA-treated human colon cancer cells, HT29

Our previous study demonstrated that, stanniocalcin-1 (STC1) was a target of histone deacetylase (HDAC) inhibitors and was involved in trichostatin A (TSA) induced apoptosis in the human colon cancer cells, HT29. In this study, we reported that the transcriptional factor, specificity protein 1 (Sp1) in association with retinoblastoma (Rb) repressed STC1 gene transcription in TSA-treated HT29 cells. Our data demonstrated that, a co-treatment of the cells with TSA and Sp1 inhibitor, mithramycin A (MTM) led to a marked synergistic induction of STC1 transcript levels, STC1 promoter (1 kb)-driven luciferase activity and an increase of apoptotic cell population. The knockdown of Sp1 gene expression in TSA treated cells, revealed the repressor role of Sp1 in STC1 transcription. Using a protein phosphatase inhibitor okadaic acid (OKA), an increase of Sp1 hyperphosphorylation and so a reduction of its transcriptional activity, led to a significant induction of STC1 gene expression. Chromatin immunoprecipitation (ChIP) assay revealed that Sp1 binding on STC1 proximal promoter in TSA treated cells. The binding of Sp1 to STC1 promoter was abolished by the co-treatment of MTM or OKA in TSA-treated cells. Re-ChIP assay illustrated that Sp1-mediated inhibition of STC1 transcription was associated with the recruitment of another repressor molecule, Rb. Collectively our findings identify STC1 is a downstream target of Sp1.

Stanniocalcin-1 regulates re-epithelialization in human keratinocytes

Stanniocalcin-1 (STC1), a glycoprotein hormone, is believed to be involved in various biological processes such as inflammation, oxidative responses and cell migration. Riding on these emerging evidences, we hypothesized that STC1 may participate in the re-epithelialization during wound healing. Re-epithelialization is a critical step that involves keratinocyte lamellipodia (e-lam) formation, followed by cell migration. In this study, staurosporine (STS) treatment induced human keratinocyte (HaCaT) e-lam formation on fibronectin matrix and migration via the activation of focal adhesion kinase (FAK), the surge of intracellular calcium level [Ca²⁺]i and the inactivation of Akt. In accompanied with these migratory features, a time- and dose-dependent increase in STC1 expression was detected. STC1 gene expression was found not the downstream target of FAK-signaling as illustrated by FAK inhibition using PF573228. The reduction of [Ca²⁺]i by BAPTA/AM blocked the STS-mediated keratinocyte migration and STC1 gene expression. Alternatively the increase of [Ca²⁺]i by ionomycin exerted promotional effect on STS-induced STC1 gene expression. The inhibition of Akt by SH6 and GSK3β by lithium chloride (LiCl) could respectively induce and inhibit the STS-mediated e-lam formation, cell migration and STC1 gene expression. The STS-mediated e-lam formation and cell migration were notably hindered or induced respectively by STC1 knockdown or overexpression. This notion was further supported by the scratched wound assay. Collectively the findings provide the first evidence that STC1 promotes re-epithelialization in wound healing.

Protein kinase Cα suppresses the expression of STC1 in MDA-MB-231 breast cancer cells

Several protein kinase C (PKC) isoforms have been shown to influence different cellular processes that may contribute to the malignancy of breast cancer cells. To obtain insight into mechanisms mediating the PKC effects, global gene expression was analyzed in MDA-MB-231 breast cancer cells in which PKCα, PKCδ or PKCε had been down-regulated with siRNA. Gene set enrichment analyses revealed that hypoxia-induced genes were enriched among genes that increased in PKCα-down-regulated cells. The STC1 mRNA, encoding stanniocalcin 1, was particularly up-regulated following depletion of PKCα and was also induced by hypoxia. Both hypoxia and PKCα down-regulation also led to increased STC1 protein levels. The results demonstrate that PKCα suppresses the expression of STC1 in breast cancer cells.

Increased methylation variation in epigenetic domains across cancer types

Tumor heterogeneity is a major barrier to effective cancer diagnosis and treatment. We recently identified cancer-specific differentially DNA-methylated regions (cDMRs) in colon cancer, which also distinguish normal tissue types from each other, suggesting that these cDMRs might be generalized across cancer types. Here we show stochastic methylation variation of the same cDMRs, distinguishing cancer from normal tissue, in colon, lung, breast, thyroid and Wilms' tumors, with intermediate variation in adenomas. Whole-genome bisulfite sequencing shows these variable cDMRs are related to loss of sharply delimited methylation boundaries at CpG islands. Furthermore, we find hypomethylation of discrete blocks encompassing half the genome, with extreme gene expression variability. Genes associated with the cDMRs and large blocks are involved in mitosis and matrix remodeling, respectively. We suggest a model for cancer involving loss of epigenetic stability of well-defined genomic domains that underlies increased methylation variability in cancer that may contribute to tumor heterogeneity.

Stanniocalcin-1 promotes tumor angiogenesis through up-regulation of VEGF in gastric cancer cells

BACKGROUND

Stanniocalcin-1(STC-1) is up-regulated in several cancers including gastric cancer. Evidences suggest that STC-1 is associated with carcinogenesis and angiogenic process. However, it is unclear on the exact role for STC-1 in inducing angiogenesis and tumorigeneisis.

METHOD

BGC/STC cells (high-expression of STC-1) and BGC/shSTC cells (low- expression of STC-1) were constructed to investigate the effect of STC-1 on the xenograft tumor growth and angiogenesis in vitro and in vivo. ELISA assay was used to detect the expression of vascular endothelial growth factor (VEGF) in the supernatants. Neutralizing antibody was used to inhibit VEGF expression in supernatants. The expression of phosphorylated -PKCβII, phosphorylated -ERK1/2 and phosphorylated -P38 in the BGC treated with STC-1protein was detected by western blot.

RESULTS

STC-1 could promote angiogenesis in vitro and in vivo, and the angiogenesis was consistent with VEGF expression in vitro. Inhibition of VEGF expression in supernatants with neutralizing antibody markedly abolished angiogenesis induced by STC-1 in vitro. The process of STC-1-regulated VEGF expression was mediated via PKCβII and ERK1/2.

CONCLUSIONS

STC-1 promotes the expression of VEGF depended on the activation of PKCβII and ERK1/2 pathways. VEGF subsequently enhances tumor angiogenesis which in turn promotes the gastric tumor growth.

The diagnostic value of circulating stanniocalcin-1 mRNA in non-small cell lung cancer

BACKGROUND AND OBJECTIVES

Previous studies have suggested that the aberrant expression of Stanniocalcin-1 (STC1) occurs in tumor cells. In this study, we explored whether the circulating STC1 mRNA is a promising biomarker in the peripheral blood in patients with non-small cell lung cancer (NSCLC).

METHODS

The level of circulating STC1 mRNA was determined with a sensitive quantitative real-time reverse transcription PCR assay. and the data were analyzed by the statistical methods of one-way ANOVA, Mann-Whitney-Wilcoxon U-Test, and Receiver operating characteristic (ROC) curve analysis.

RESULTS

The level of circulating STC1 mRNA in patients with NSCLC was significantly higher than in patients with benign pulmonary disease (P < 0.001) or healthy volunteers (P < 0.001). Higher levels of circulating STC1 mRNA were associated with more advanced tumor stages and histological subtypes. Using a cutoff of 0.055, the sensitivity and specificity of STC1 mRNA levels to differentiate between patients with NSCLC and patients with benign pulmonary diseases was 66.7 and 90.9%, and it was 63.7 and 99.8% for patients with NSCLC and healthy volunteers, respectively.

CONCLUSIONS

These findings support our hypothesis that circulating STC1 mRNA is a promising biomarker in the peripheral blood.

Cyclin A2 confers cisplatin resistance to endometrial carcinoma cells via up-regulation of an Akt-binding protein, periplakin

Although overexpression of cyclin A2 is reportedly an indicator of a poor prognosis of various malignancies including endometrial carcinoma, its molecular mechanism remains undetermined. To address this issue, we examined the effect of cyclin A2 on the development of resistance to chemotherapeutic drugs. The expression of cyclin A2 protein was increased in advanced-stage and chemotherapy-refractory stage endometrial carcinomas compared with that in early-stage tumours. The expression levels of cyclin A2 in endometrial carcinoma cell lines correlated positively with the IC₅₀ for cisplatin. Endometrial carcinoma HHUA cells that overexpressed cyclin A2 showed increased resistance to cisplatin in vitro and in vivo, via the activation of a survival pathway, the inositol-3 phosphate kinase (PI3K) cascade. The use of a cDNA microarray identified an Akt-binding protein, periplakin, as a novel target of cyclin A2. The cyclin A2-induced up-regulation of periplakin was mediated via direct binding of Sp1 to the promoter that was activated by cyclin A2 along with chromatin remodelling involving CBP/p300, and the siRNA-mediated silencing of periplakin suppressed the PI3K pathway. These results indicate cyclin A2 to be involved in the acquisition of aggressive behaviour of tumour cells through the activation of PI3K by cyclin A2-induced periplakin, and to be a promising therapeutic target.

Modulation of gene expression by α-tocopherol and α-tocopheryl phosphate in THP-1 monocytes

The natural vitamin E analog α-tocopheryl phosphate (αTP) modulates atherosclerotic and inflammatory events more efficiently than the unphosphorylated α-tocopherol (αT). To investigate the molecular mechanisms involved, we have measured plasma levels of αTP and compared the cellular effects of αT and αTP in THP-1 monocytes. THP-1 cell proliferation is slightly increased by αT, whereas it is inhibited by αTP. CD36 surface expression is inhibited by αTP within hours without requiring transport of αTP into cells, suggesting that αTP may bind to CD36 and/or trigger its internalization. As assessed by gene expression microarrays, more genes are regulated by αTP than by αT. Among a set of confirmed genes, the expression of vascular endothelial growth factor is induced by αTP as a result of activating protein kinase B (PKB/Akt) and is associated with increased levels of reactive oxygen species (ROS). Increased Akt(Ser473) phosphorylation and induction of ROS by αTP occur in a wortmannin-sensitive manner, indicating the involvement of phosphatidylinositol kinases. The induction of Akt(Ser473) phosphorylation and ROS production by αTP can be attenuated by αT. It is concluded that αTP and αT influence cell proliferation, ROS production, and Akt(Ser473) phosphorylation in an antagonistic manner, most probably by modulating phosphatidylinositol kinases.

Production of calcium maintenance factor Stanniocalcin-1 (STC1) by the equine endometrium during the early pregnant period

A factor responsible for progression to pregnancy establishment in the mare has not been definitively characterized. To identify factors possibly involved in the establishment of equine pregnancy, the endometrium was collected from day 13 (day 0=day of ovulation) cyclic and day 13, 19 and 25 pregnant animals. From initial subtractive hybridization studies, a calcium regulating factor, Stanniocalcin-1 (STC1) mRNA, was found as a candidate molecule expressed uniquely in the pregnant endometrium. Endometrial expression of STC1 mRNA was noted on day 19 and was markedly increased in the day 25 gravid endometrium. STC1 protein was found in the extracts of day 25 gravid endometrium and immunochemically localized in the uterine glands. In addition, STC1 protein was detected in uterine flushing media collected from day 25 pregnant mares. High concentrations of estradiol-17 β (E(2)) were detected in day 25 conceptuses. E(2) levels were much higher in the gravid endometrium than in other regions, whereas progesterone levels did not differ among the samples from different endometrial regions. Expression of STC1 mRNA, however, was not significantly upregulated in cultured endometrial explants treated with various concentrations of E(2) (0.01-100 ng/ml) with or without 10 ng/ml progesterone. These results indicate that an increase in STC1 expression appears to coincide with capsule disappearance in the conceptus, and suggest that STC1 from the uterine glands likely plays a role in conceptus development during the pregnancy establishment period in the mare.

Human stanniocalcin-1 interacts with nuclear and cytoplasmic proteins and acts as a SUMO E3 ligase

Human stanniocalcin-1 (STC1) is a glycoprotein that has been implicated in different physiological process, including angiogenesis, apoptosis and carcinogenesis. Here we identified STC1 as a putative molecular marker for the leukemic bone marrow microenvironment and identified new interacting protein partners for STC1. Seven selected interactions retrieved from yeast two-hybrid screens were confirmed by GST-pull down assays in vitro. The N-terminal region was mapped to be the region that mediates the interaction with cytoplasmic, mitochondrial and nuclear proteins. STC1 interacts with SUMO-1 and several proteins that have been shown to be SUMOylated and localized to SUMOylation related nuclear bodies. Although STC1 interacts with SUMO-1 and has a high theoretical prediction score for a SUMOylation site, endogenous co-immunoprecipitation and in vitro SUMOylation assays with the purified recombinant protein could not detect STC1 SUMOylation. However, when we tested STC1 for SUMO E3 ligase activity, we found in an in vitro assay, that it significantly increases the SUMOylation of two other proteins. Confocal microscopic subcellular localization studies using both transfected cells and specific antibodies for endogenous STC1 revealed a cytoplasmic and nuclear deposition, the latter in the form of some specific dot-like substructure resembling SUMOylation related nuclear bodies. Together, these findings suggest a new role for STC1 in SUMOylation pathways, in nuclear bodies.

Induction of the renal stanniocalcin-1 gene in rodents by water deprivation

Stanniocalcin-1 (STC-1) is made by kidney collecting duct cells for targeting of nephron mitochondria to promote respiratory uncoupling and calcium uniport activity. However, the purpose of these actions and how the renal gene is regulated are poorly understood. This study has addressed the latter issue by monitoring renal STC-1 gene expression in different models of kidney function. Unilateral nephrectomy and over-hydration had no bearing on renal gene activity in adult Wistar rats. Dehydration, on the other hand, had time-dependent stimulatory effects in male and female kidney cortex, where STC-1 mRNA levels increased 8-fold by 72h. Medullary gene activity was significantly increased as well, but muted in comparison ( approximately 2-fold). Gene induction was accompanied by an increase in mitochondrial sequestration of STC-1 protein. Aldosterone and angiotensin II had no bearing on STC-1 gene induction, although there was evidence of a role for arginine vasopressin. Gene induction was unaltered in integrin alpha1 knockout mice, which have an impaired tonicity enhancer binding protein (TonEBP) response to dehydration. The STC-1 gene response could be cytoprotective in intent, as dehydration entails a fall in renal blood flow and a rise in medullary interstitial osmolality. Alternatively, STC-1 could have a role in salt and water balance as dehydration necessitates water conservation as well as controlled natriuresis and kaliuresis.

Stanniocalcin 1 induction by thyroid hormone depends on thyroid hormone receptor β and phosphatidylinositol 3-kinase activation

CONTEXT

Thyroid hormone (TH) mediated changes in gene expression were thought to be primarily initiated by the nuclear TH receptor (TR) binding to a thyroid hormone response element in the promoter of target genes. A recently described extranuclear mechanism of TH action consists of the association of TH-liganded TRβ with phosphatidylinositol 3-kinase (PI3K) in the cytosol and subsequent activation of the PI3K pathway.

OBJECTIVE

The aim of this study was to examine the effect of TH, TRβ and PI3K on stanniocalcin 1 (STC1) expression in human cells.

DESIGN

We treated human skin fibroblasts with triiodothyronine (T3) in the absence or presence of the PI3K inhibitor LY294002, a dominant negative PI3K subunit, Δp85α, and the protein synthesis inhibitor cycloheximide (CHX). The role of the TRβ was studied in cells from patients with resistance to thyroid hormone (RTH). STC-1 mRNA expression was measured by real-time PCR.

RESULTS

We found an induction of STC1 by T3 in normal cells, but less in cells from subjects with RTH (2.7 ± 0.2 vs. 1.6 ± 0.04, P < 0.01). The effect of T3 was completely abrogated by blocking PI3K with LY294002 (3.9 ± 0.5 vs. 0.85 ± 0.5; P < 0.05) and greatly reduced after transfection of a dominant negative PI3K subunit, demonstrating dependency on the PI3K pathway.

CONCLUSION

These results establish STC1 as a TH target gene in humans. Furthermore, we show that STC1 induction by TH depends on both TRβ and PI3K activation.

Clinical significance of detection of stanniocalcin 1 expression in peripheral blood of patients with gastrointestinal cancer

AIM: To detect the expression of stanniocalcin 1 mRNA (STC1) in peripheral blood of patients with gastrointestinal cancer and to analyze its relationship with tumor micrometastasis.

METHODS: RT-PCR was performed to detect the expression of STC1 mRNA in peripheral blood samples obtained from 40 patients with gastrointestinal cancer, 10 patients with gastrointestinal inflammatory disease and 10 healthy blood donors, and in tumor tissue and tumor-adjacent normal intestinal tissue samples taken from 2 patients with gastric cancer and 6 patients with colorectal cancer.

RESULTS: The positive rate of STC1 mRNA expression was 60% (24/40) in peripheral blood from patients with gastrointestinal cancer, 100% (6/6) in tumor tissue and 16.7% (1/6) in tumor-adjacent normal intestinal tissue from patients with gastric cancer or colorectal cancer. STC1 mRNA expression was undetectable in peripheral blood from patients with gastrointestinal inflammatory disease or healthy blood donors.

CONCLUSION: Detection of STC1 mRNA expression in peripheral blood can be used to predict early micrometastasis and therefore represents an objective indicator for evaluation of tumor metastasis and recurrence and therapeutic efficacy in patients with gastrointestinal cancer.

Expression and localization of stanniocalcin 1 in swine ovary

Stanniocalcin 1 (STC 1) is a glycoprotein involved in mineral homeostasis and was first identified in fish. Its mammalian homologue has been implicated in the regulation of various biological processes, including angiogenesis and steroidogenesis both of which are fundamental events in ovarian function. Interestingly, the highest level of STC 1 expression in mammals occurs in ovarian tissue but no information is available on swine species. Therefore, the present study was undertaken to investigate the expression and the immunolocalization of STC 1 in swine ovary. In addition, we evaluated whether swine granulosa cells synthesize STC 1 and its possible modulation by hypoxia, a physiological condition in ovarian follicle growth. Our data show STC 1 for the first time in swine ovary; moreover, we demonstrate STC 1 production by granulosa cells, both in basal condition and in response to oxygen deprivation. The latter is suggestive of a potential modulatory role for STC 1 in hypoxia-driven angiogenesis.

Stanniocalcin-2 is a HIF-1 target gene that promotes cell proliferation in hypoxia

Stanniocalcin-2 (STC2), the paralog of STC1, has been suggested as a novel target of oxidative stress response to protect cells from apoptosis. The expression of STC2 has been reported to be highly correlated with human cancer development. In this study, we reported that STC2 is a HIF-1 target gene and is involved in the regulation of cell proliferation. STC2 was shown to be up-regulated in different breast and ovarian cancer cells, following exposure to hypoxia. Using ovarian cancer cells (SKOV3), the underlying mechanism of HIF-1 mediated STC2 gene transactivation was characterized. Hypoxia-induced STC2 expression was found to be HIF-1alpha dependent and required the recruitment of p300 and HDAC7. Using STC2 promoter deletion constructs and site-directed mutagenesis, two authentic consensus HIF-1 binding sites were identified. Under hypoxic condition, the silencing of STC2 reduced while the overexpression of STC2 increased the levels of phosphorylated retinoblastoma and cyclin D in both SKOV3 and MCF7 cells. The change in cell cycle proteins correlated with the data of the serial cell counts. The results indicated that cell proliferation was reduced in STC2-silenced cells but was increased in STC2-overexpressing hypoxic cells. Solid tumor progression is usually associated with hypoxia. The identification and functional analysis of STC2 up-regulation by hypoxia, a feature of the tumor microenvironment, sheds light on a possible role for STC2 in tumors.

Stanniocalcin, a potential ovarian angiogenesis regulator, does not affect endothelial cell apoptosis

The ovarian follicle represents an outstanding model for the investigation of the angiogenic process. In fact, follicular development is associated with an extensive neovascularization, and physiological angiogenesis is necessary for folliculogenesis. However, although the major factors triggering the angiogenic events have been thoroughly investigated and are now relatively well defined, information about the molecular events involved in the modulation and/or arrest of neovascularization is still scarce. Therefore, this research focused on the potential involvement of stanniocalcin (STC), a protein whose biological function is still unclear, in the control mechanisms of follicular angiogenesis. We evaluated the effect of 5 and 50 ng/mL STC on the production of the main proangiogenic factor, vascular endothelial growth factor (VEGF), by swine granulosa cells. Moreover, STC's effect on cell viability and the modulation of caspase-3 and -7 activities in swine aortic endothelial cells were also examined. Granulosa cell VEGF production was significantly (P < 0.001) inhibited by STC. Endothelial cell viability was significantly (P < 0.001) increased, whereas caspase activities were reduced (P < 0.01) by STC. These data indicate that STC is not angiosuppressive for endothelial cells, although it could potentially modulate local angiogenesis acting at the granulosa cell level.

Multipotent stromal cells are activated to reduce apoptosis in part by upregulation and secretion of stanniocalcin-1

Multipotent stromal cells (MSCs) have been shown to reduce apoptosis in injured cells by secretion of paracrine factors, but these factors were not fully defined. We observed that coculture of MSCs with previously UV-irradiated fibroblasts reduced apoptosis of the irradiated cells, but fresh MSC conditioned medium was unable reproduce the effect. Comparative microarray analysis of MSCs grown in the presence or absence of UV-irradiated fibroblasts demonstrated that the MSCs were activated by the apoptotic cells to increase synthesis and secretion of stanniocalcin-1 (STC-1), a peptide hormone that modulates mineral metabolism and has pleiotrophic effects that have not been fully characterized. We showed that STC-1 was required but not sufficient for reduction of apoptosis of UV-irradiated fibroblasts. In contrast, we demonstrated that MSC-derived STC-1 was both required and sufficient for reduction of apoptosis of lung cancer epithelial cells made apoptotic by incubation at low pH in hypoxia. Our data demonstrate that STC-1 mediates the antiapoptotic effects of MSCs in two distinct models of apoptosis in vitro.

Mammalian stanniocalcin-1 activates mitochondrial antioxidant pathways: new paradigms for regulation of macrophages and endothelium

The mammalian homolog of the fish calcium regulatory hormone stanniocalcin-1 (STC1) is ubiquitously expressed and likely functions in an autocrine/paracrine fashion. Mammalian STC1 does not appear to exert significant effects on serum calcium, and its physiological role remains to be determined. In macrophages, STC1 decreases intracellular calcium and cell mobility; attenuates the response to chemoattractants; and diminishes superoxide generation through induction of uncoupling protein-2 (UCP2). In cytokine-treated endothelial cells, STC1 attenuates superoxide generation and the activation of inflammatory pathways [c-Jun NH(2)-terminal kinase (JNK) and NF-kappaB]; maintains the expression of tight junction proteins, preserving the endothelial monolayer seal; and decreases transendothelial migration of leukocytes. Combined, the effects of STC1 on endothelial cells and macrophages predict potent anti-inflammatory action. Indeed, application of the anti-glomerular basement membrane (GBM) glomerulonephritis model to STC1 transgenic mice that display increased expression of STC1 transgene in endothelial cells and macrophages yields renal protection. Our data suggest that STC1 activates antioxidant pathways in endothelial cells and macrophages and displays cytoprotective and anti-inflammatory actions.

Wnt2 acts as an angiogenic growth factor for non-sinusoidal endothelial cells and inhibits expression of stanniocalcin-1

Recently, we have shown that Wnt2 is an autocrine growth and differentiation factor for hepatic sinusoidal endothelial cells. As Wnt signaling has become increasingly important in vascular development and cancer, we analyzed Wnt signaling in non-sinusoidal endothelial cells of different vascular origin (HUVEC, HUAEC, HMVEC-LLy). Upon screening the multiple components of the Wnt pathway, we demonstrated lack of Wnt2 expression, but presence of Frizzled-4, one of its receptors, in cultured non-sinusoidal endothelial cells. Treatment of these cells by exogenous Wnt2 induced endothelial proliferation and sprouting angiogenesis in vitro. Upon analysis of Wnt2 tissue expression as a basis for paracrine Wnt2 effects on non-sinusoidal endothelial cells in vivo, Wnt2 was found to be expressed in densely vascularized murine malignant tumors and in wound healing tissues in close proximity to CD31+ endothelial cells. By gene profiling, stanniocalcin-1 (STC1), a known regulator of angiogenesis, was identified as a target gene of Wnt2 signaling in HUVEC down-regulated by Wnt2 treatment. Tumor-conditioned media counter-acted Wnt2 and up-regulated STC1 expression in HUVEC. In conclusion, we provide evidence that Wnt2 acts as an angiogenic factor for non-sinusoidal endothelium in vitro and in vivo whose target genes undergo complex regulation by the tissue microenvironment.

Stanniocalcin-1 acts in a negative feedback loop in the prosurvival ERK1/2 signaling pathway during oxidative stress

Mammalian Stanniocalcin-1 (STC1) is a glycoprotein that has been implicated in various biological processes including angiogenesis. Aberrant STC1 expression has been reported in breast, ovarian and prostate cancers, but the significance of this is not well understood. Here, we report that oxidative stress caused a 40-fold increase in STC1 levels in mouse embryo fibroblasts (MEFs). STC1-/- MEFs were resistant to growth inhibition and cell death induced by H(2)O(2) or by 20% O(2) (which is hyperoxic for most mammalian cells); this is the first phenotype reported for STC1-null cells. STC1-/- cells had higher levels of activated MEK and ERK1/2 than their wild-type (WT) counterparts, and these levels were all reduced by stable expression of exogenous STC1 in STC1-/- cells. Furthermore, pharmacological inhibition by PD98059 or UO126 of MEK and therefore of ERK1/2 activation restored sensitivity of STC1-/- cells to oxidative stress. We also found that H(2)O(2)-induced STC1 expression in WT cells was abolished by inhibition of ERK1/2 activation. Thus, the ERK1/2 signaling pathway upregulates STC1 expression, which in turn downregulates the level of activated MEK and consequently ERK1/2 in a novel negative feedback loop. Therefore, STC1 expression downregulates prosurvival ERK1/2 signaling and reduces survival under conditions of oxidative stress.

Regulation of microRNA expression by HMGA1 proteins

The High Mobility Group proteins HMGA1 are nuclear architectural factors that play a critical role in a wide range of biological processes. Since recent studies have identified the microRNAs (miRNAs) as important regulators of gene expression, modulating critical cellular functions such as proliferation, apoptosis and differentiation, the aim of our work was to identify the miRNAs that are physiologically regulated by HMGA1 proteins. To this purpose, we have analysed the miRNA expression profile of mouse embryonic fibroblasts (MEFs) carrying two, one or no Hmga1 functional alleles using a microarray (miRNA microarray). By this approach, we found a miRNA expression profile that differentiates Hmga1-null MEFs from the wild-type ones. In particular, a significant decrease in miR-196a-2, miR-101b, miR-331 and miR-29a was detected in homozygous Hmga1-knockout MEFs in comparison with wild-type cells. Consistently, these miRNAs are downregulated in most of the analysed tissues of Hmga1-null mice in comparison with the wild-type mice. ChIP assay shows that HMGA1 is able to bind regions upstream of these miRNAs. Moreover, we identified the HMGA2 gene product as a putative target of miR-196a-2, suggesting that HMGA1 proteins are able to downregulate the expression of the other member of the HMGA family through the regulation of the miR-196a-2 expression. Finally, ATXN1 and STC1 gene products have been identified as targets of miR-101b. Therefore, it is reasonable to hypothesize that HMGA1 proteins are involved in several functions by regulating miRNA expression.

Silencing of HIF-1alpha by RNA interference in human glioma cells in vitro and in vivo

Higher-grade gliomas are distinguished by increased vascular endothelial cell proliferation and peritumoral edema. These are thought to be instigated by vascular endothelial growth factor, which in turn is regulated by cellular oxygen tension. Hypoxia inducible factor-1alpha (HIF-1alpha) is a main responder to intracellular hypoxia and is overexpressed in many human cancers, including gliomas. Here we present methods for investigating the role of HIF-1alpha in glioma growth in vivo and in vitro using RNA interference in U251, U87, and U373 glioma cells.

Biological and functional analysis of statistically significant pathways deregulated in colon cancer by using gene expression profiles

Gene expression profiling offers a great opportunity for studying multi-factor diseases and for understanding the key role of genes in mechanisms which drive a normal cell to a cancer state. Single gene analysis is insufficient to describe the complex perturbations responsible for cancer onset, progression and invasion. A deeper understanding of the mechanisms of tumorigenesis can be reached focusing on deregulation of gene sets or pathways rather than on individual genes. We apply two known and statistically well founded methods for finding pathways and biological processes deregulated in pathological conditions by analyzing gene expression profiles. In particular, we measure the amount of deregulation and assess the statistical significance of predefined pathways belonging to a curated collection (Molecular Signature Database) in a colon cancer data set. We find that pathways strongly involved in different tumors are strictly connected with colon cancer. Moreover, our experimental results show that the study of complex diseases through pathway analysis is able to highlight genes weakly connected to the phenotype which may be difficult to detect by using classical univariate statistics. Our study shows the importance of using gene sets rather than single genes for understanding the main biological processes and pathways involved in colorectal cancer. Our analysis evidences that many of the genes involved in these pathways are strongly associated to colorectal tumorigenesis. In this new perspective, the focus shifts from finding differentially expressed genes to identifying biological processes, cellular functions and pathways perturbed in the phenotypic conditions by analyzing genes co-expressed in a given pathway as a whole, taking into account the possible interactions among them and, more importantly, the correlation of their expression with the phenotypical conditions.

Histone deacetylase inhibitor-induced cellular apoptosis involves stanniocalcin-1 activation

Our previous studies have demonstrated the involvement of HIF-1 and p53 in the regulation of stanniocalcin-1 (STC1) gene transcription in human cancer cells. In this study, we reported that the treatment of human colon adenoma HT29 cells with a histone deacetylase (HDAC) inhibitor (i.e. trichostatin A, TSA) induced both cellular apoptosis and STC1 expression. The activation of STC1 expression was also observed in other TSA-treated human cancer cells (i.e. SKOV3, CaCo-2, Jurkat and CNE-2 cells). STC1 mRNA was rapidly induced within 4 h in TSA-treated HT29 cells, and was found to be transcriptionally regulated and was independent of new protein synthesis as revealed by ActD and CHX treatment respectively. The induction was correlated with increased cellular levels of acetyl histone H3 and H4 and acetyl NFkappaB. Chromatin immunoprecipitation (ChIP) assay showed the increased binding of acetyl histone H3 and H4 to STC1 promoter in the TSA-treated cells. A cotreatment of HT29 cells with a NFkappaB inhibitor (parthenolide) significantly inhibited the TSA-induced cellular levels of acetyl NFkappaB p65 and abolished the stimulation of STC1 gene expression. ChIP assay also demonstrated that TSA treatment increased while TSA/parthenolide cotreatment decreased NFkappaB p65 binding to STC1 gene promoter. In the STC1-luciferase promoter construct (1 kb) study, the data implied that the promoter can be activated by TSA treatment. Interestingly, the promoter region contains 2 putative NFkappaB binding sites. Consistent with the STC1mRNA expression data, TSA/parthenolide cotreatment also significantly inhibited the TSA-induced STC1 promoter-driven luciferase activity. Importantly, TSA-induced apoptotic process was found to be significantly reduced by the silencing of STC1 expression. This is the first study to show that histone hyper-acetylation and the recruitment of activated NFkappaB stimulated STC1 gene expression. In addition, our results support the notion that STC1 is a pro-apoptotic factor.

The murine stanniocalcin 2 gene is a negative regulator of postnatal growth

Stanniocalcin (STC), a secreted glycoprotein, was first studied in fish as a classical hormone with a role in regulating serum calcium levels. There are two closely related proteins in mammals, STC1 and STC2, with functions that are currently unclear. Both proteins are expressed in numerous mammalian tissues rather than being secreted from a specific endocrine gland. No phenotype has been detected yet in Stc1-null mice, and to investigate whether Stc2 could have compensated for the loss of Stc1, we have now generated Stc2(-/-) and Stc1(-/-) Stc2(-/-) mice. Although Stc1 is expressed in the ovary and lactating mouse mammary glands, like the Stc1(-/-) mice, the Stc1(-/-) Stc2(-/-) mice had no detected decrease in fertility, fecundity, or weight gain up until weaning. Serum calcium and phosphate levels were normal in Stc1(-/-) Stc2(-/-) mice, indicating it is unlikely that the mammalian stanniocalcins have a major physiological role in mineral homeostasis. Mice with Stc2 deleted were 10-15% larger and grew at a faster rate than wild-type mice from 4 wk onward, and the Stc1(-/-) Stc2(-/-) mice had a similar growth phenotype. This effect was not mediated through the GH/IGF-I axis. The results are consistent with STC2 being a negative regulator of postnatal growth.

Epigenetic and HIF-1 regulation of stanniocalcin-2 expression in human cancer cells

Mammalian stanniocalcin-2 (STC2) is a secreted glycoprotein hormone with a putative role in unfolded protein response and apoptosis. Here we reported that STC2 expression was sporadically abrogated in human cancer cells by transcriptional silencing associated with CpG island promoter hypermethylation. Direct sequencing of bisulfite-modified DNA from a panel of seven human cancer cell lines revealed that CpG dinucleotides in STC2 promoter was methylated in human ovarian epithelial cancer (SKOV3, OVCAR3 and CaOV3), pancreatic cancer (BxP3), colon adenoma (HT29), and leukemia (Jurkat cells). STC2 CpG island hypermethylation was accompanied with a low basal STC2 expression level. Treatment of these cancer cells with 5-aza-2'-deoxycytidine (5-aza-CdR), an inhibitor of DNA methylation significantly induced STC2 expression. Using SKOV3 cells as a model, the link between DNA demethylation and STC2 expression was consistently demonstrated with hydralazine treatment, which was shown to reduce the protein level of DNA methyltransferase 1 (DNMT1) but stimulated STC2 expression. Two human normal surface ovarian cell-lines (i.e. IOSE 29 and 398) showed no methylation at CpG dinucleotides in the examined promoter region and were accompanied with high basal STC2 levels. Hypoxia stimulated STC2 expression in SKOV3 cells was markedly increased in 5-aza-CdR pretreated cells, showing that DNA methylation may hinder the HIF-1 mediated activation. To elucidate this possibility, RNA interference studies confirmed that endogenous HIF-1 alpha was a key factor for STC2 gene activation as well as in the synergistic induction of STC2 expression in 5-aza-CdR pretreated cells. Chromatin immunoprecipitation (ChIP) assay demonstrated the binding of HIF-1 alpha to STC2 promoter. The binding was increased in 5-aza-CdR pretreated cells. Collectively, this is the first report to show that STC2 was aberrantly hypermethylated in human cancer cells. The findings demonstrated that STC2 epigenetic inactivation may interfere with HIF-1 mediated activation of STC2 expression.

Vascular endothelial growth factor regulates stanniocalcin-1 expression via neuropilin-1-dependent regulation of KDR and synergism with fibroblast growth factor-2

Stanniocalcin-1 (STC-1) is a glycoprotein hormone originally identified as a regulator of calcium and phosphate homeostasis in bony fish. Up-regulation of the mammalian homolog in numerous gene profiling studies of angiogenesis and vascular endothelial growth factor-A (VEGF-A(165))-regulated gene expression, suggests that regulation of this factor may be a key feature of the angiogenic response. Here we investigated the mechanisms mediating VEGF-A(165)-induced STC-1 gene expression in human endothelial cells. VEGF-A(165), acting via VEGFR2/KDR, induced STC-1 through de novo transcription, mediated primarily via intracellular protein kinase C (PKC)- and extracellular signal-regulated protein kinase (ERK)-dependent pathways. VEGF-A(165)-induced STC-1 mRNA expression was synergistically enhanced up to 2-fold by co-treatment with FGF-2, in a mechanism dependent on VEGFR2/KDR and FGFR1. Production of STC-1 protein by endothelial cells was also induced by VEGF-A(165) and synergistically enhanced by co-treatment with FGF-2. Synergism between VEGF-A(165) and FGF-2 was mediated via a novel neuropilin-1 (NP-1)-dependent mechanism, as indicated by the complete inhibition of synergism with either EG3287, a specific neuropilin antagonist, or siRNA-mediated NP-1 knockdown, and by the inability of the VEGF-A(121) isoform to synergise with FGF-2. Surprisingly, we found that NP-1 knockdown also markedly reduced KDR expression in HUVECs, and enhanced the VEGF-A(165)-induced reduction in KDR expression resulting from receptor-mediated endocytosis. These findings support a role for NP-1 in mediating synergistic effects between VEGF-A(165) and FGF-2, which may occur in part through a contribution of NP-1 to KDR stability.

Mechanisms operative in the antitumor activity of temozolomide in glioblastoma multiforme

PURPOSE

Glioblastoma multiforme (GBM) is the most frequent and incurable brain tumor in adults. Although temozolomide (TMZ) does not cure GBM, it has demonstrated anti-GBM activity and has improved survival (8-14 months) and quality of life. We studied the mechanisms by which TMZ affects 2 human GBM cell lines; U251-MG and U87-MG, aiming to unravel the drug-activated cascades to enable the development of combination therapies that will improve the efficacy of TMZ.

MATERIALS AND METHODS

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assay was used to assess cell viability. Modulation of gene expression by TMZ therapy was assayed by gene profiling and verified by quantitative real-time polymerase chain reaction. Protein levels influenced by the treatment were studied by Western blots and immunocytochemistry.

RESULTS

Increasing concentrations of TMZ decreased cell viability in a concentration-dependent manner. The expression of 1,886 genes was altered >2-fold after TMZ treatment. We focused on the 81 genes similarly altered by TMZ treatment in both cell lines to neutralize tissue-specific characteristics. Fourteen target genes of hypoxia-inducible factor (HIF-1), were found to be up-regulated after TMZ treatment including vascular endothelial growth factor (VEGF). HIF-1alpha expression was constant at the mRNA level; however, its post-treatment protein levels increased compared with those of untreated control cells.

DISCUSSION

The genetic analyses suggest that treatment with TMZ activates stress mechanisms in GBM cells that include the angiogenesis-inducing proteins HIF-1alpha and VEGF. We propose that treatment with TMZ be supplemented with either an antibody to VEGF or down-regulators of HIF-1alpha to improve clinical results of TMZ in the treatment of GBM.

Silencing of hypoxia inducible factor-1alpha by RNA interference attenuates human glioma cell growth in vivo

PURPOSE

Higher-grade gliomas are distinguished by increased vascular endothelial cell proliferation and peritumoral edema. These are thought to be instigated by vascular endothelial growth factor, which, in turn, is regulated by cellular oxygen tension. Hypoxia inducible factor-1alpha (HIF-1alpha) is a main responder to intracellular hypoxia and is overexpressed in many human cancers, including gliomas.

EXPERIMENTAL DESIGN

We investigated the role of HIF-1alpha in glioma growth in vivo using RNA interference (RNAi) in U251, U87, and U373 glioma cells.

RESULTS

We found that RNAi can be used to significantly attenuate glioma growth by reducing HIF-1alpha levels constitutively using short hairpin RNAs and transiently using small interfering RNAs (siRNA). HIF-1alpha levels on average were reduced 55% in normoxia and 71% in hypoxia. Vascular endothelial growth factor and GLUT-1 levels were reduced 81% and 71%, respectively, in the stable HIF-1alpha-reduced clones. These clones showed significant growth attenuation (up to 73%) compared with negative controls when grown in vivo in mouse flanks. Cellular proliferation was also reduced significantly, as determined by MIB-1 staining. Treating gliomas grown in mouse flank transiently with siRNA against HIF-1alpha by intratumoral injection resulted in a significant reduction of HIF-1alpha activity. This activity was followed using a hypoxia-responsive luciferase construct that enabled hypoxia imaging in vivo. Tumor volume in these siRNA injection experiments was reduced by 50% over the negative controls.

CONCLUSIONS

These results indicate that transient RNAi directed against HIF-1alpha can effectively curb glioma growth in vivo.

Hypoxic preconditioning induces elevated expression of stanniocalcin-1 in the heart

Animals exposed for a few hours to low oxygen content (8%) develop resistance against further ischemic myocardial damage. The molecular mechanism(s) behind this phenomenon, known as hypoxic preconditioning (HOPC), is still incompletely understood. Stanniocalcin-1 (STC-1) is an evolutionarily conserved glycoprotein originally discovered in fish, in which it regulates calcium/phosphate homeostasis and protects against toxic hypercalcemia. Our group originally reported expression of mammalian STC-1 in brain neurons and showed that STC-1 is a prosurvival factor that guards neurons against hypercalcemic and hypoxic damage. This study investigates the involvement of STC-1 in HOPC-induced cardioprotection. Wild-type mice and IL-6-deficient ( Il-6−/−) mice were kept in hypoxic conditions (8% O2) for 6 h. Myocardial Stc-1 mRNA expression was quantified during hypoxia and after recovery. HOPC triggered a biphasic upregulation of Stc-1 expression in hearts of wild-type mice but not in those of Il-6−/−mice. Treatment of cardiomyocyte cells in culture with hypoxia or IL-6 elicited an Stc-1 response, and ectopically expressed STC-1 in HL-1 cells localized to the mitochondria. Our findings indicate that IL-6-induced expression of STC-1 is one molecular mechanism behind the ischemic tolerance generated by HOPC in the heart.

The role of ascorbate in the modulation of HIF-1alpha protein and HIF-dependent transcription by chromium(VI) and nickel(II)

Molecular oxygen is involved in hydroxylation and subsequent degradation of HIF-1alpha, a subunit of HIF-1 transcription factor; therefore oxygen shortage (hypoxia) stabilizes this protein. However, HIF-1alpha can also be stabilized by transition metal ions in the presence of oxygen, suggesting that a different mechanism is involved in metal-induced hypoxic stress. Recently, we showed that the depletion of intracellular ascorbate by metals may lead to the inhibition of hydroxylases. Because nickel(II) has similarity to iron(II), an alternative hypothesis suggests that iron substitution for nickel in the enzyme inhibits hydroxylase activity. Here we investigated the induction of HIF-1 by another metal, chromium, which cannot replace iron in the enzyme. We show that chromium(VI), but not chromium(III), can oxidize ascorbate both in cells and in a cell-free system. In agreement with these data chromium(VI) stabilizes HIF-1alpha protein in cells only until it is reduced to chromium(III). In contrast, nickel(II) was found to be a catalyst, which facilitated continuous oxidation of ascorbate by ambient oxygen. These data correlate with extended stabilization of HIF-1alpha after acute exposure to nickel(II). The HIF-1-dependent reporter assays revealed that 20-24 h was required to fully develop the HIF-1 transcriptional response, and the acute exposure to nickel(II), but not chromium(VI), meets this requirement. However, repeated (chronic) exposure to chromium(VI) can also lead to extended stabilization of HIF-1alpha. Thus, the obtained data emphasize the important role of ascorbate in regulation of HIF-1 transcriptional activity in metal-exposed human lung cells.

Induction of stanniocalcin-1 expression in apoptotic human nasopharyngeal cancer cells by p53

There is growing evidence to suggest that altered patterns of STC1 gene expression relate to the process of human cancer development. Our previous study has demonstrated the involvement of HIF-1 in the regulation of STC1 expression in human cancer cells. Recently, STC1 has been implicated as a putative pro-apoptotic factor in regulating the cell-death mechanism. Thus it would be of interest to know if STC1 is regulated by a tumor suppressor protein, p53. In this study, we provide evidence to demonstrate that the induction of STC1 expression in apoptotic human nasopharyngeal cancer cells (CNE2) is mediated by the activation of p53. Our study indicated that the activation of STC1 and heat-shock protein (hsp70) accompanied iodoacetamide (IDAM)-induced apoptosis in CNE-2. In addition, cellular events such as GSH depletion, mitochondrial membrane depolarization, reduction of pAkt and procaspase-3, and the induction of total p53 protein, acetylated p53, and annexin V positive cells were observed. The activation of STC1 was found to be at the transcriptional level and was independent of prior protein synthesis. Co-treatment of IDAM exposed cells with N-acetyl cysteine (NAC) prevented cell death by restoring mitochondrial membrane potential and cellular levels of GSH. NAC co-treatment also suppressed STC1 expression but had no effect on IDAM-induced hsp70 expression. RNA interference studies demonstrated that endogenous p53 was involved in activating STC1 gene expression. Collectively, the present findings provide the first evidence of p53 regulation of STC1 expression in human cancer cells.

Hypoxic preconditioning induces neuroprotective stanniocalcin-1 in brain via IL-6 signaling

BACKGROUND AND PURPOSE

Exposure of animals for a few hours to moderate hypoxia confers relative protection against subsequent ischemic brain damage. This phenomenon, known as hypoxic preconditioning, depends on new RNA and protein synthesis, but its molecular mechanisms are poorly understood. Increased expression of IL-6 is evident, particularly in the lungs of animals subjected to hypoxic preconditioning. Stanniocalcin-1 (STC-1) is a 56-kDa homodimeric glycoprotein originally discovered in bony fish, where it regulates calcium/phosphate homeostasis and protects against toxic hypercalcemia. We originally reported expression of mammalian STC-1 in brain neurons and showed that STC-1 guards neurons against hypercalcemic and hypoxic damage.

METHODS

We treated neural Paju cells with IL-6 and measured the induction of STC-1 mRNA. In addition, we quantified the effect of hypoxic preconditioning on Stc-1 mRNA levels in brains of wild-type and IL-6 deficient mice. Furthermore, we monitored the Stc-1 response in brains of wild-type and transgenic mice, overexpressing IL-6 in the astroglia, before and after induced brain injury.

RESULTS

Hypoxic preconditioning induced an upregulated expression of Stc-1 in brains of wild-type but not of IL-6-deficient mice. Induced brain injury elicited a stronger STC-1 response in brains of transgenic mice, with targeted astroglial IL-6 expression, than in brains of wild-type mice. Moreover, IL-6 induced STC-1 expression via MAPK signaling in neural Paju cells.

CONCLUSIONS

These findings indicate that IL-6-mediated expression of STC-1 is one molecular mechanism of hypoxic preconditioning-induced tolerance to brain ischemia.

Recruitment of HIF-1alpha and HIF-2alpha to common target genes is differentially regulated in neuroblastoma: HIF-2alpha promotes an aggressive phenotype

In neuroblastoma specimens, HIF-2alpha but not HIF-1alpha is strongly expressed in well-vascularized areas. In vitro, HIF-2alpha protein was stabilized at 5% O2 (resembling end capillary oxygen conditions) and, in contrast to the low HIF-1alpha activity at this oxygen level, actively transcribed genes like VEGF. Under hypoxia (1% O2), HIF-1alpha was transiently stabilized and primarily mediated acute responses, whereas HIF-2alpha protein gradually accumulated and governed prolonged hypoxic gene activation. Knockdown of HIF-2alpha reduced growth of neuroblastoma tumors in athymic mice. Furthermore, high HIF-2alpha protein levels were correlated with advanced clinical stage and high VEGF expression and predicted poor prognosis in a clinical neuroblastoma material. Our results demonstrate the relevance of HIF-2alpha in neuroblastoma progression and have general tumor biological implications.

Involvement of HIF-1 in invasion of Mum2B uveal melanoma cells

The propensity of uveal melanoma cells for invasion and metastasis is critical factor for the clinical outcome of this form of cancer, and the essential biology of its aggressiveness is not completely understood. In the present study we investigated the involvement of hypoxia-inducible factor 1 (HIF-1) in uveal melanoma migration, invasion and adhesion, the hallmarks of aggressive behavior of cancer cells. We demonstrate that exposure to hypoxia increased migration, invasion and adhesion of uveal melanoma cells in in vitro assays. The "silencing" of HIF-1alpha, the oxygen-regulated subunit of HIF-1, using RNA interference technology resulted in a marked decrease of the uveal melanoma cell migration, invasion and adhesion. GeneChip microarray analysis revealed that a number of genes which regulate cancer invasion and metabolism such as CXCR4, angiopoietin-related protein, pyruvate dehydrogenase kinase 1 (PDK1) are also activated by hypoxia in a HIF-1-dependent manner in Mum2B uveal melanoma cells. We further demonstrate that serum deprivation resulted in HIF-1 and CXCR4 activation, suggesting specific metabolic regulation of HIF-1 in these cells. Microarray analysis of serum-deprived cells identified among the upregulated genes a number of cancer invasion-related genes, some of them being known HIF-1-regulated targets. Taken together, these results suggest that the involvement of HIF-1 in uveal melanoma tumorigenesis is significant and complex, and that metabolic regulation of HIF-1 activation in Mum2B uveal melanoma cells has its specificities.