Cloning and characterization of the human osteopontin gene and its promoter

Osteopontin as a Regulator of Colorectal Cancer Progression and Its Clinical Applications

Simple Summary

The mortality of colorectal cancer is principally related to metastatic disease at the time of diagnosis or to the growth of initially undetectable micro-metastasis. Current therapeutic strategies are efficient in patients with locally advanced cancer, but are rarely able to cure patients with metastatic disease. Therapeutic failure is mainly associated with drug resistance and an aggressive phenotype. The identification of new biomarkers for micro-metastasis and tumor progression remains an unmet clinical need that should allow for improved patient stratification for optimal treatment and may lead to the identification of novel therapeutic targets. Osteopontin (OPN), a multifunctional protein, has emerged as a potentially valuable biomarker in several cancer types. This review principally describes the molecular mechanisms of OPN that are associated with colorectal cancer (CRC) progression and metastasis, as well as the use of OPN as a clinical biomarker. This review identifies a role for OPN as a biomarker ready for extended clinical application and discusses its use as a therapeutic target.

Abstract

A high expression of the phosphoprotein osteopontin (OPN) has been associated with cancer progression in several tumor types, including breast cancer, hepatocarcinoma, ovarian cancer, and colorectal cancer (CRC). Interestingly, OPN is overexpressed in CRC and is associated with a poor prognosis linked to invasion and metastasis. Here, we review the regulation and functions of OPN with an emphasis on CRC. We examine how epigenetic and genetic regulators interact with the key signaling pathways involved in this disease. Then, we describe the role of OPN in cancer progression, including proliferation, survival, migration, invasion, and angiogenesis. Furthermore, we outline the interest of using OPN as a clinical biomarker, and discuss if and how osteopontin can be implemented as a routine assay in clinical laboratories for monitoring CRC patients. Finally, we discuss the use of OPN an attractive, but challenging, therapeutic target.

Immunohistochemical evaluation of osteopontin expression in triple-negative breast cancer

Introduction

Triple-negative breast cancer (TNBC) is associated with lack of expression of estrogen and progesterone receptors and HER2 and is the subgroup of breast cancers with the worst prognosis. Osteopontin is a phosphorylated glycoprotein whose overexpression may occur in pathological states such as cancers. The main purpose of our study was to evaluate the immunohistochemical expression of osteopontin in connection with the analysis of recognized clinical and pathological prognostic factors in primary sites of TNBC with and without lymph node metastases.

Material and methods

The immunohistochemical evaluation of osteopontin expression in 35 women with TNBC, chosen from a group of 726 patients, was performed. The material came from the excisional biopsies of primary breast cancers and total mastectomies.

Results

All patients showed expression of osteopontin, in most cases the expression of osteopontin rated at [+] (57.1%) and [++] (42.9%). Our study analyzed the relationship between the expression of osteopontin and traditional prognostic markers, such as the tumor grade, size, and lymph node involvement. We found a strong relationship only between the expression of osteopontin and the presence of lymph node metastases (p ≤ 0.0001). 93% of patients for whom the expression of osteopontin was determined at [++] had metastasis to lymph nodes and, for comparison, only 15% of women for whom the expression of osteopontin was rated at [+] showed the presence of metastases in the lymphatic nodes.

Conclusions

There is a correlation between osteopontin expression and the presence of lymph node metastases in TNBC, suggesting that osteopontin plays an important role in the invasiveness of TNBC.

Molecular Characterization and Expression of SPP1, LAP3 and LCORL and Their Association with Growth Traits in Sheep

The SPP1, LAP3, and LCORL are located on chromosome 6 of sheep and a domain of 36.15-38.56 Mb, which plays an essential role in tissue and embryonic growth. In this study, we cloned the complete coding sequences of SPP1 and partial coding regions of LAP3 and LCORL from Hu sheep (Gansu Province, China) and analyzed their genomic structures. The RT-qPCR showed that the three genes were expressed widely in the different tissues of Hu sheep. The SPP1 expression was significantly higher in the kidney (p < 0.01) and LAP3 expression was significantly higher in the spleen, lung, kidney, and duodenum than in the other tissues (heart, liver, rumen, muscle, fat, and ovary; p < 0.05). The LCORL was preferentially expressed in the spleen, duodenum, and lung (p < 0.05). In addition, the nucleotide substitution NM_001009224.1:c.132A>C was found in SPP1; an association analysis showed that it was associated with birth weight and yearling weight (p < 0.05), and NM_001009224.1:c.132C was the dominant allele. Two mutations XM_012179698.3:c.232C>G and XM_012179698.3:c.1154C>T were identified in LAP3. The nucleotide substitution XM_012179698.3:c.232C>G was confirmed to be associated with birth weight, 1-month weight, 3-month weight (p < 0.05), and 2-month weight (p < 0.01). The nucleotide substitution XM_012179698.3:c.1154C>T was associated with birth weight (p < 0.01), 1-month weight, and 2-month weight (p < 0.05). The LAP3 gene XM_012179698.3:c.232C>G mutation with the C allele has higher body weight than other sheep, and CC genotype individuals show higher birth weight, 1-month weight, and weaning weight than the GG genotype individuals (p < 0.05). Our results support the conclusion that the mutations on ovine SPP1 and LAP3 successfully track functional alleles that affect growth in sheep, and these genes could be used as candidate genes for improving the growth traits of sheep during breeding.

Osteopontin as a Link between Inflammation and Cancer: The Thorax in the Spotlight

The glycoprotein osteopontin (OPN) possesses multiple functions in health and disease. To this end, osteopontin has beneficial roles in wound healing, bone homeostasis, and extracellular matrix (ECM) function. On the contrary, osteopontin can be deleterious for the human body during disease. Indeed, osteopontin is a cardinal mediator of tumor-associated inflammation and facilitates metastasis. The purpose of this review is to highlight the importance of osteopontin in malignant processes, focusing on lung and pleural tumors as examples.

Osteopontin and interleukin-17A genes polymorphisms in Egyptian systemic lupus erythematosus patients: A relation to disease activity and severity

Osteopontin (OPN) is involved in the regulation of the immune response and is accused in the pathogenesis of several autoimmune diseases including systemic lupus erythematosus (SLE). An obvious link between OPN and T cells, particularly T helper 17 cells is reported, where OPN produced by dendritic cells supports interleukin-17 (IL-17) expression, contributing to pathology of autoimmune disorders. The aim of the study was to investigate the association of genotypes and alleles frequencies of OPN 9250 (rs1126616) and IL-17A 197 (rs2275913) genes polymorphisms with their serum levels, susceptibility, disease activity and severity in Egyptian SLE patients. A total of 80 SLE patients and 80 healthy subjects were enrolled. The PCR-RFLP technique was used to detect OPN 9250 C/T and IL-17A 197 G/A genes polymorphisms. Serum OPN and IL- 17 levels were measured by the enzyme-linked immunosorbent assay. OPN TT genotype and T allele were significantly detected in SLE patients more than controls (P = 0.003, P < 0.001 respectively). IL-17A AA genotype showed non-significant higher frequency in SLE patients than in their controls (P = 0.07). While only the A allele of IL-17A polymorphism was significantly elevated in patients (P = 0.048). There was statistical significant association between OPN CT and TT genotypes and both renal and mucocutaneous manifestations. Also IL-17A AG and AA genotypes was significantly associated with renal, mucocutaneous in addition to the hematological manifestations. Serum OPN levels were significantly increased with TT genotype while serum IL-17 levels were significantly increased with AA genotype. Disease activity and severity scores were significantly elevated with both OPN TT and IL-17A AA genotypes. In conclusion, OPN 9250 C/T and IL-17A 197 G/A genes polymorphisms and their serum levels seemed to have a role in pathogenesis of SLE.

Osteopontin in hepatocellular carcinoma: A possible biomarker for diagnosis and follow-up

Recently osteopontin (OPN), a protein of the extracellular matrix, has generated in hepatocellular carcinoma (HCC) a significant interest as a prognostic factor. Aim of this study was to confirm, in liver tissues of subjects with HCV-positive HCC undergoing liver transplantation (RL, n=10) and of donors (DL, n=14), the increase of OPN plasma and tissue concentration, the OPN splicing isoforms expression profiling together with those of thrombin, and to evaluate a possible association between OPN measurements. Their association with Notch-1, IV-Collagen-7s domain, IL-6 and TNF-α were also evaluated. Real-Time PCR experiments and immunometric assay were performed. mRNA expression resulted higher in RL than in DL for all analyzed genes and several correlations were found between them. The more relevant association were between OPN-a and OPN-b (p<0.0001), between thrombin and OPN-a (p=0.007), between 7s-collagen and OPN isoforms (p<0.05) and between Notch-1 with OPN-c (p=0.004). Both OPN plasma and liver tissue extract concentrations were assessed confirming the trend observed at the mRNA level. An important association was found between OPN plasma and protein (p<0.0001, r=0.96) even splitting patients in DL (p<0.0001, r=0.93) and RL (p<0.0001, r=0.96). A reduction of OPN plasma levels was found at 6months after transplantation. Considering MELD score as liver disease severity, the mRNA expression of our markers as well as of OPN plasma and tissue concentrations resulted increased as a function of clinical severity. Our results might be considered a useful starting point to validate OPN as a prognostic and diagnostic marker of HCC.

Induction of Osteopontin by Dengue Virus-3 Infection in THP-1 Cells: Inhibition of the Synthesis by Brefelamide and Its Derivative

Osteopontin (OPN) is a multifunctional matricellular protein produced by a broad range of cells including osteoclasts, macrophages, T cells, endothelial cells, and vascular smooth muscle cells. OPN modulates various physiological and pathological events such as inflammation, wound healing, and bone formation and remodeling. Dengue virus (DENV) infection causes an increase in plasma OPN levels, which is correlated with the severity of symptoms and coagulation abnormalities. DENV infection also induces OPN gene expression in human macrophages. This study investigated the inhibitory effects of brefelamide and its methyl ether derivative on DENV-3 by measuring changes in OPN levels in human THP-1 and 293T cell lines infected at different multiplicities of infection and post-infection time points. OPN mRNA expression and viral RNA were detected by reverse transcriptase quantitative real-time PCR, whereas protein level was determined by enzyme-linked immunosorbent assay. We found that viral copy number was higher in 293T than in THP-1 cells. However, THP-1 constitutively expressed higher levels of OPN mRNA and protein, which were enhanced by DENV-3 infection. Brefelamide and its derivative suppressed OPN production in DENV-3 infected THP-1 cells; the effective doses of these compounds had no effect on uninfected cells, indicating low cytotoxicity. These results suggest that brefelamide and its methyl ether derivative have therapeutic effects in preventing inflammation, coagulopathy, and fibrinolysis caused by OPN upregulation induced by DENV-3 infection.

Osteopontin splice variants and polymorphisms in cancer progression and prognosis

Osteopontin (OPN) is an extracellular matrix protein that is overexpressed in various cancers and promotes oncogenic features including cell proliferation, survival, migration, and angiogenesis, among others. OPN can participate in the regulation of the tumor microenvironment, affecting both cancer and neighboring cells. Here, we review the roles of OPN splice variants (a, b, c) in cancer development, progression, and prognosis, and also discuss the identities of isoforms 4 and 5. We also discussed how single-nucleotide polymorphisms (SNPs) of the OPN gene are an additional factor influencing the level of OPN in individuals, modulating the risks of cancer development and outcome.

Targeting of the leukemia microenvironment by c(RGDfV) overcomes the resistance to chemotherapy in acute myeloid leukemia in biomimetic polystyrene scaffolds

The bone marrow microenvironment provides a relative sanctuary from cytotoxic drugs for leukemia cells. The present niche models concentrate on a two-dimensional (2D) co-culture system in vitro, which does not imitate the in vivo environment, while the 3D scaffolds are more reflective of this. Osteopontin (Opn) secreted by bone marrow osteoblasts, may participate in protecting leukemia cells from apoptosis by binding to its receptor αvβ3, which can be expressed on the surface of the leukemia MV4-11 cell line. However, the association between the Opn/αvβ3 axis and leukemia cells is unknown. In the present study, experiments were conducted on 3D polystyrene scaffolds coated with osteoblasts and leukemia cells. The cells were exposed to cyclo(Arg-Gly-Asp-d-Phe-Val) [c(RGDfV)] (35 nmol/ml), which blocks αvβ3, for a period of 24 h. Cytarabine was applied 24 h later. The adhesion, migration and apoptosis rates, and the cell cycle of the leukemia cells were analyzed after incubation for 24 and 48 h. In contrast to the 2D culture system, the stromal cells in the scaffolds secreted significantly more alkaline phosphatase and Opn (P<0.05). c(RGDfV) disrupted the adhesion and migration between the tumor cells and the matrix, induced the leukemia cells to leave the protective microenvironment and increased their sensitivity to cell cycle-dependent agents (P<0.05). In summary, the data certified that the 3D scaffolds are suitable for the growth of cells, and that c(RGDfV) inhibits the adhesion and migration abilities of leukemia cells in the endosteal niche. Therefore, blocking the function of Opn may be beneficial in the treatment of acute myeloid leukemia.

Myocardial Expression Analysis of Osteopontin and Its Splice Variants in Patients Affected by End-Stage Idiopathic or Ischemic Dilated Cardiomyopathy

Osteopontin (OPN) is a phosphoglycoprotein of cardiac extracellular matrix and it is still poorly defined whether its expression changes in failing heart of different origin. The full-length OPN-a and its isoforms (OPN-b, OPN-c) transcriptomic profile were evaluated in myocardium of patients with dilated or ischemic cardiomyopathy (DCM n = 8; LVEF% = 17.5±3; ICM n = 8; LVEF% = 19.5±5.2) and in auricle of valvular patients (VLP n = 5; LVEF%≥50), by Real-time PCR analysis. OPN-a and thrombin mRNA levels resulted significantly higher in DCM compared to ICM patients (DCM:31.3±7.4, ICM:2.7±1.1, p = 0.0002; DCM:19.1±4.9, ICM:5.4±2.2, p = 0.007, respectively). Although both genes’ mRNA levels increased in patients with LVEF<50% (DCM+ICM) with respect to VLP with LVEF>50%, a significant increase in OPN (p = 0.0004) and thrombin (p = 0.001) expression was observed only in DCM. In addition, a correlation between OPN-a and thrombin was found in patients with LVEF<50% (r = 0.6; p = 0.003). The mRNA pattern was confirmed by OPN-a cardiac protein concentration (VLP:1.127±0.26; DCM:1.29±0.22; ICM:1.00±0.077 ng/ml). The OPN splice variants expression were detectable only in ICM (OPN-b: 0.357±0.273; OPN-c: 0.091±0.033) and not in DCM patients. A significant correlation was observed between collagen type I, evaluated by immunohistochemistry analysis, and both OPN-a mRNA expression (r = 0.87, p = 0.002) and OPN protein concentrations (r = 0.77, p = 0.016). Concluding, OPN-a and thrombin mRNA resulted dependent on the origin of heart failure while OPN-b and OPN-c highlighted a different expression for DCM and ICM patients, suggesting their correlation with different clinical-pathophysiological setting.

Prognostic Value of Osteopontin Splice Variant-c Expression in Breast Cancers: A Meta-Analysis

Objectives. Osteopontin (OPN) is overexpressed in breast cancers, while its clinical and prognostic significance remained unclear. This study aimed to assess the prognostic value of OPN, especially its splice variants, in breast cancers. Methods. Data were extracted from eligible studies concerning the OPN and OPN-c expression in breast cancer patients and were used to calculate the association between OPN/OPN-c and survival. Two reviewer teams independently screened the literatures according to the inclusion and exclusion criteria based on quality evaluation. Following the processes of data extraction, assessment, and transformation, meta-analysis was carried out via RevMan 5.3 software. Results. A total of ten studies involving 1,567 patients were included. The results demonstrated that high level OPN indicated a poor outcome in the OS (HR = 2.22, 95% CI: 1.23–4.00, and P = 0.008; random-effects model) with heterogeneity (I² = 62%) of breast cancer patients. High level OPN-c appeared to be more significantly associated with poor survival (HR = 2.14, 95% CI: 1.51–3.04, and P < 0.0001; fixed-effects model) with undetected heterogeneity (I² = 0%). Conclusions. Our analyses indicated that both OPN and OPN-c could be considered as prognostic markers for breast cancers. The high level of OPN-c was suggested to be more reliably associated with poor survival in breast cancer patients.

Associations between the Genetic Polymorphisms of Osteopontin Promoter and Susceptibility to Cancer in Chinese Population: A Meta-Analysis

Background and Aim

Several studies have been conducted to examine the associations between osteopontin (OPN) promoter gene SPP1 polymorphisms with human cancers in Chinese population, but the results remain inconsistent. The aim of this meta-analysis is to clarify the associations between SPP1 polymorphisms and cancer susceptibility.

Methods

All eligible case-control studies published up to March 2015 were identified by searching PubMed, Web of Science, Embase, and Cochrane Library without language restrictions. Pooled odds ratio (OR) and 95% confidence interval (95% CI) were calculated using fixed- or random-effect model.

Results

A total of 11 case-control studies were included; of those, there were eleven studies (3130 cases and 3828 controls) for -443T>C polymorphism, ten studies (3019 cases and 3615 controls) for -156G>GG polymorphism, eight studies (2258 cases and 2846 controls) for -66T>G polymorphism. Overall, no evidence indicated that the -443 T>C polymorphism was associated with cancer risk (OR = 0.93, 95%CI 0.62–1.38 for dominant model, OR = 1.06, 95%CI 0.73–1.55 for recessive model, OR = 0.88, 95%CI 0.62–1.26 for CT vs TT model, OR = 1.03, 95%CI 0.61–1.73 for CC vs TT model). While, a significantly increase risk was found for -156 G>GG polymorphism (OR = 1.22, 95%CI 1.10–1.35 for dominant model, OR = 1.25, 95%CI 1.10–1.41 for recessive model, OR = 1.18, 95%CI 1.06–1.32 for GGG vs GG model, OR = 1.35, 95%CI 1.09–1.68 for GGGG vs GG model). For -66T>G polymorphism, we found a decrease risk of cancer (OR = 0.84, 95% CI 0.71–0.98 for dominant model), but this result changed (OR = 0.93, 95% CI 0.77–1.12 for dominant model) when we excluded a study.

Conclusion

This meta-analysis suggests that in Chinese population the -156G>GG polymorphism of SPP1 might be a risk factor for human cancers, while -443T>C mutation is not associated with cancer risk. For -66T>G polymorphism, it may be a protective factor for human cancers.

Osteopontin expression in healing wounds of horses and in human keloids

REASONS FOR PERFORMING STUDY

Convincing evidence shows that persistent or excessive expression of osteopontin (OPN) is linked to fibroproliferation of various organs in laboratory animals and in man, such that its downregulation is a logical therapeutic objective.

OBJECTIVES

To investigate OPN expression in an equine model of wound healing and in clinical specimens of equine exuberant granulation tissue and human keloids in an effort to better understand the contribution of this protein to inflammation-associated skin fibrosis.

STUDY DESIGN

Description of gene and protein expression in an experimental equine model of wound healing and clinical specimens in horse and man.

METHODS

Osteopontin gene expression was evaluated by quantitative PCR, while protein expression was investigated by means of immunohistochemical staining.

RESULTS

Quantitative PCR showed that the OPN gene is expressed in normal intact skin of horses and continues to be expressed during the wound-healing process. An increase in gene expression was observed throughout the phases of wound healing, with a final decrease at wound closure. The protein was not detected in normal skin. Keratinocytes in wound-edge samples did not express the protein, whereas dermal immunoreactivity was confined to inflammatory cells. Healed wounds were devoid of staining. Equine exuberant granulation tissue showed immunoreactivity of the surrounding epidermis, infiltrating neutrophils, mononuclear cells, endothelial cells and fibroblasts. Human keloids showed OPN immunoreactivity throughout the epidermis as well as in mononuclear cells and scattered fibroblasts.

CONCLUSIONS

Immunohistochemical data show a different pattern of expression between normally healing and fibrotic wounds (exuberant granulation tissue and keloids), thus suggesting a role in fibroproliferation in horses and man.

Osteopontin: A novel regulator at the cross roads of inflammation, obesity and diabetes

Since its first description more than 20 years ago osteopontin has emerged as an active player in many physiological and pathological processes, including biomineralization, tissue remodeling and inflammation. As an extracellular matrix protein and proinflammatory cytokine osteopontin is thought to facilitate the recruitment of monocytes/macrophages and to mediate cytokine secretion in leukocytes. Modulation of immune cell response by osteopontin has been associated with various inflammatory diseases and may play a pivotal role in the development of adipose tissue inflammation and insulin resistance. Here we summarize recent findings on the role of osteopontin in metabolic disorders, particularly focusing on diabetes and obesity.

Mechanism of hepatitis C virus (HCV)-induced osteopontin and its role in epithelial to mesenchymal transition of hepatocytes

Osteopontin (OPN) is a secreted phosphoprotein, originally characterized in malignant-transformed epithelial cells. OPN is associated with tumor metastasis of several tumors and is overexpressed in hepatocellular carcinoma (HCC) tissue involving HCC invasion and metastasis. Importantly, OPN is significantly up-regulated in liver injury, inflammation, and hepatitis C virus (HCV)-associated HCC. However, the underlying mechanisms of OPN activation and its role in HCV-mediated liver disease pathogenesis are not known. In this study, we investigated the mechanism of OPN activation in HCV-infected cells. We demonstrate that HCV-mediated Ca(2+) signaling, elevation of reactive oxygen species, and activation of cellular kinases such as p38 MAPK, JNK, PI3K, and MEK1/2 are involved in OPN activation. Incubation of HCV-infected cells with the inhibitors of AP-1 and Sp1 and site-directed mutagenesis of AP-1- and Sp1-binding sites on the OPN promoter suggest the critical role of AP-1 and Sp1 in OPN promoter activation. In addition, we show the in vivo interactions of AP-1 and Sp1 with the OPN promoter using chromatin immunoprecipitation assay. We also show the calpain-mediated processing of precursor OPN (∼75 kDa) into ∼55-, ∼42-, and ∼36-kDa forms of OPN in HCV-infected cells. Furthermore, we demonstrate the critical role of HCV-induced OPN in increased phosphorylation of Akt and GSK-3β followed by the activation of β-catenin, which can lead to EMT of hepatocytes. Taken together, these studies provide an insight into the mechanisms of OPN activation that is relevant to the metastasis of HCV-associated HCC.

New insights into the pathogenesis of pseudoxanthoma elasticum and related soft tissue calcification disorders by identifying genetic interactions and modifiers

Screening of the adenosine triphosphate binding cassette transporter protein subfamily C member 6 gene (ABCC6) in pseudoxanthoma elasticum (PXE) revealed a mutation detection rate of approximately 87%. Although 25% of the unidentified disease alleles underlie deletions/insertions, there remain several PXE patients with no clear genotype. The recent identification of PXE-related diseases and the high intra-familiar and inter-individual clinical variability of PXE led to the assumption that secondary genetic co-factors exist. Here, we summarize current knowledge of the genetics underlying PXE and PXE-related disorders based on human and animal studies. Furthermore, we discuss the role of genetic interactions and modifier genes in PXE and PXE-related diseases characterized by soft tissue calcification.

Loss of RUNX3 increases osteopontin expression and promotes cell migration in gastric cancer

Loss of RUNX3 expression is frequently observed in gastric cancer and is highly associated with lymph node metastasis and poor prognosis. However, the underlying molecular mechanisms of gastric cancer remain unknown. In this study, we found that the protein levels of RUNX3 and osteopontin (OPN) are inversely correlated in gastric cancer clinical specimens and cell lines. Furthermore, similar inverse trends between RUNX3 and OPN messenger RNA (mRNA) expression were demonstrated in six out of seven normal-tumor-paired gastric cancer clinical specimens. In addition, low RUNX3 and high OPN expression were associated with poor prognosis in gastric cancer patients. Ectopic expression of green fluorescent protein-RUNX3 reduced OPN protein and mRNA expression in the AGS and SCM-1 gastric cancer cell lines. In contrast, knockdown of RUNX3 in GES-1, a normal gastric epithelial cell line, increased OPN expression. Although three RUNX3-binding sequences have been identified in the OPN promoter region, direct binding of RUNX3 to the specific binding site, -142 to -137bp, was demonstrated by chromatin immunoprecipitation assay. The binding of RUNX3 to the OPN promoter significantly decreased OPN promoter activity. The knockdown of OPN or overexpression of RUNX3 inhibited cell migration in AGS and SCM-1 cells; however, the coexpression of RUNX3 and OPN reversed the RUNX3-reduced migration ability in AGS and SCM-1 cells. In contrast, the knockdown of both RUNX3 and OPN inhibited RUNX3-knockdown-induced migration of GES-1 cells. Together, our data demonstrated that RUNX3 is a transcriptional repressor of OPN and that loss of RUNX3 upregulates OPN, which promotes migration in gastric cancer cells.

Deciphering the calcitriol-induced transcriptomic response in keratinocytes: presentation of novel target genes

Numerous studies to date have been aimed at unraveling the large suite of calcitriol (1α,25-dihydroxyvitamin D(3)) response genes in diverse tissues including skin, where this hormone is involved in regulating keratinocyte proliferation, differentiation, permeability barrier formation, innate immunity promotion, antimicrobial peptide production, and wound healing. However, the various approaches differ considerably in probed cell types, scale, throughput, and statistical reliability and do, of note, not reveal much overlap. To further expand our knowledge on presently elusive targets and characterize the extent of fragmentation of existing datasets, we have performed whole-transcriptome microarray examinations of calcitriol-treated human primary keratinocytes. Out of 28,869 genes investigated, we uncovered 86 differentially expressed (67 upregulated and 19 downregulated) candidates that were functionally clustered into five annotation categories: response to wounding, protease inhibition, secondary metabolite biosynthesis, cellular migration, and amine biosynthetic processes. A complementary RTq-PCR study of 78 nominees selected thereof demonstrated significant differential expression of 55 genes (48 upregulated and seven downregulated) within biological replicates. Our hit list contains nine previously authenticated targets (16.36%, proof of concept) and 46 novel genes (83.6%) that have not yet been explicitly described as being differentially regulated within human primary keratinocytes. Direct vitamin D receptor response element predictions within the regulatory promoter regions of 50 of the RTq-PCR-validated targets agreed with known biological functionality and corroborated our stringent data validation pipeline. Altogether, our results indicate the value of continuing these kinds of gene expression studies, which contribute to an enhanced comprehension of calcitriol-mediated processes that may be dysregulated in human skin pathophysiology.

Regulatory role of osteopontin in malignant transformation of endometrial cancer

Osteopontin (OPN) involves in the tumor-promoting or metastasis in human endometrial cancer. Depletion of OPN gene expression in endometrial cancer cells was significantly decreased in cell viability and the cells undergo apoptotic cell death. The status of OPN in THESC, RL95, Hec1A and Ishikawa cell lines were analyzed by RT-PCR and western blot. After OPN-siRNA transfection, mRNA and protein expression levels of OPN were determined in Hec1A and Ishikawa cells. Cell proliferation and cell cycle distribution were observed by MTT and flow cytometry analysis. DNA fragmentation assay was used to measure cell apoptosis. Cell migration was assessed by wound healing assay. Depletion of OPN gene expression in endometrial cancer cell lines (Hec1A and Ishikawa cells) reproducibly changed their ability of proliferation. Concomitant changes were seen in the expression of OPN binding cell surface receptors, cell cycle-regulatory genes, cell invasion and colony formation nature of the tumor cells. Decreased colonizing potential in the absence of OPN was reversed in the presence of recombinant OPN. Inhibition of anchorage-independent growth was observed in the presence of metabolic inhibitors of the PI3K, Src and integrin signaling cascades, which was ameliorated in the presence of exogenously added OPN. Our result showed the role of OPN in endometrial cancer, in particular on the malignancy-promoting aspects of OPN that may pave way for new approaches to the clinical management of endometrial cancer.

Osteopontin splice variants differentially exert clinicopathological features and biological functions in gastric cancer

Purpose: Gastric cancer (GC) remains a leading cause of death worldwide, and an elevated expression of osteopontin (OPN) may correlate with its poor survival. Alternative splicing of OPN can result in three isoforms, OPN-a, OPN-b and OPN-c. The aim of our current study is to examine the expression pattern and biological functions of OPN splice variants in GC.

Methods: Firstly, we evaluated the expression of OPN splice variants in 7 gastric cell lines, 101 pairs of GC tissues and their adjacent non-tumor tissues by Quantative real-time PCR (QT-PCR). Gain-of-function experiments were subsequently performed to determine their diverse roles in malignant behaviors of GC. Besides, their differential effects on the regulation of crucial downstream molecules were further explored in the anti-apoptotic and pro-metastatic process.

Results: We found that OPN-b is the dominant kind of OPN isoform in GC cell lines. Although the expression levels of three variants were all elevated in GC tissues, increased OPN-b or OPN-c expression could correlate with clinicopathological features. Functional analyses further showed that OPN-b most strongly promoted GC cell survival possibly by regulation of Bcl-2 family proteins and CD44v expressions. Moreover, OPN-c most effectively stimulated GC metastatic activity by increasing secretion of MMP-2, uPa, and IL-8.

Conclusions: Our results suggest that OPN splice variants differentially exert clinicopathological features and biological functions in GC. Therefore, focusing on specific OPN isoform could be a novel direction for developing diagnostic and therapeutic approaches in GC.

Osteopontin is overexpressed in colorectal carcinoma and is correlated with P53 by immunohistochemistry

Osteopontin (OPN), a secreted phosphorylated glycoprotein, has been found to be involved in carcinogenesis, progression and metastasis of several types of cancers. The aim of the present study was to investigate the immunohistochemical expression of OPN in colorectal carcinoma (CRC) and its relationship with clinicopathological parameters and P53. Expression of OPN, Ki-67 and TP53 was detected in 77 cases of CRC by immunohistochemistry and the correlation of the expression of OPN with clinicopathological features, Ki-67 and P53 staining was investigated. Thirty-eight cases (49.4%) of CRC demonstrated OPN overexpression. Overexpression of OPN was associated with lymph node metastasis (P=0.025) and Dukes' stages (P=0.031), but not with gender, histological differentiation, depth of tumor invasion, TNM stages or Ki-67 index. The correlation between expression of OPN and TP53 was statistically significant (P=0.030). In conclusion, OPN is overexpressed in CRC, and plays a role in tumor progression and metastasis, which is possibly regulated by P53.

Abnormal expression of the ERG transcription factor in prostate cancer cells activates osteopontin

Osteopontin (OPN) is an extracellular matrix glycophosphoprotein that plays a key role in the metastasis of a wide variety of cancers. The high level of OPN expression in prostate cells is associated with malignancy and reduced survival of the patient. Recent studies on prostate cancer (PCa) tissue have revealed recurrent genomic rearrangements involving the fusion of the 5' untranslated region of a prostate-specific androgen-responsive gene with a gene coding for transcription factors from the ETS family. The most frequently identified fusion gene is TMPRSS2:ERG, which causes ERG protein overexpression in PCa cells. ERG is a transcription factor linked to skeletogenesis. This study was designed to test whether ERG and the product of the TMPRSS2:ERG fusion gene modulate OPN gene expression in PCa cells. To characterize ERG and TMPRSS2:ERG transcriptional activity of OPN, we focused on ETS binding sites (EBS) localized in conserved regions of the promoter. Using in vitro and in vivo molecular assays, we showed that ERG increases OPN expression and binds to an EBS (nt -115 to -118) in the OPN promoter. Moreover, stable transfection of prostate tumor cell lines by TMPRSS2:ERG upregulates endogenous OPN expression. Finally, in human prostate tumor samples, detection of the TMPRSS2:ERG fusion gene was significantly associated with OPN overexpression. Taken together, these data suggest that OPN is an ERG-target gene in PCa where the abnormal expression of the transcription factor ERG, due to the TMPRSS2:ERG fusion, disturbs the expression of genes that play an important role in PCa cells and associated metastases.

Pre- and post-translational regulation of osteopontin in cancer

Osteopontin (OPN) is a matricellular protein that binds to a number of cell surface receptors including integrins and CD44. It is expressed in many tissues and secreted into body fluids including blood, milk and urine. OPN plays important physiological roles in bone remodeling, immune response and inflammation. It is also a tumour-associated protein, and elevated OPN levels are associated with tumour formation, progression and metastasis. Research has revealed a promising role for OPN as a cancer biomarker. OPN is subject to alternative splicing, as well as post-translational modifications such as phosphorylation, glycosylation and proteolytic cleavage. Functional differences have been revealed for different isoforms and post-translational modifications. The pattern of isoform expression and post-translational modification is cell-type specific and may influence the potential role of OPN in malignancy and as a cancer biomarker.

Osteopontin and allergic disease: pathophysiology and implications for diagnostics and therapy

Osteopontin (OPN) is a phosphoglycoprotein that is expressed by various immune cells in a secreted and intracellular form. It has cytokine, chemotactic and cell signaling functions enhancing Th1 and Th17 immunity and protects against apoptosis. Recent studies found OPN to be modulatory in cell-mediated and immediate-type allergic diseases. In allergic asthma, OPN enhances sensitization but downmodulates Th2-driven IL-4-dominated inflammation. The finding that OPN expression is augmented during specific immunotherapy supports a Th2 suppressive effect of OPN. In Th1-driven delayed-type allergy, such as allergic contact dermatitis, OPN supports dendritic cell migration and IL-12 expression and is secreted by T effector cells and keratinocytes, augmenting Th1-mediated allergy and supporting disease chronification. There are numerous missing links as to how OPN variants modulate allergic inflammation through different OPN receptors. OPN research in allergy is an interesting, rapidly expanding field that has high potential for translational research.

Transcription factor c-Myb promotes the invasion of hepatocellular carcinoma cells via increasing osteopontin expression

Background

Specific gene expression is tightly regulated by various transcription factors. Osteopontin (OPN) is a phosphoprotein that mediates hepatocellular carcinoma (HCC) progression and metastasis. However, the mechanism of OPN up-regulation in HCC metastasis remains to be clarified.

Methods

Oligonucleotide array-based transcription factor assays were applied to compare different activities of transcription factors in two human HCC cell lines with different OPN expression levels. The effects of one selected transcription factor on OPN expression were further evaluated.

Results

Eleven transcription factors were over-expressed in metastatic HCC cell line HCCLM6 cells whereas twelve transcription factors were down-regulated. Electrophoretic mobility shift assays (EMSA) and reporter gene assays showed that one of up-regulated transcription factors c-Myb could bind the OPN promoter and increase its transcription activity. In addition, small interfering RNA targeting c-Myb could inhibit OPN expression and significantly decrease migration and invasion of HCCLM6 cells in vitro.

Conclusion

Our data first demonstrate that c-Myb has a functionally important role in the regulation of OPN expression in HCC cells, suggesting that c-Myb might be a new target to control HCC metastasis.

Hydroxyapatite growth inhibition by osteopontin hexapeptide sequences

The effects of three acidic hexapeptides on in vitro hydroxyapatite growth were characterized by pH-stat kinetic studies, adsorption isotherms, and molecular modeling. The three peptides, pSDEpSDE, SDESDE, and DDDDDD, are equal-length model compounds for the acidic sequences in osteopontin, a protein that inhibits mineral formation in both calcified and noncalcified tissues. Growth rates from 1.67 mM calcium and 1.00 mM phosphate solution were measured at pH 7.4 and 37 degrees C in 150 mM NaCl. pSDEpSDE was a strong growth inhibitor when preadsorbed onto hydroxyapatite (HA) seeds from > or = 0.67 mM solutions, concentrations where adsorption isotherms showed relatively complete surface coverage. The nonphosphorylated SDESDE control showed no growth inhibition. Although it adsorbed to almost the same extent as pSDEpSDE, it rapidly desorbed under the pH-stat growth conditions while pSDEpSDE did not. DDDDDD exhibited weak inhibition as its concentration was increased and similar adsorption/desorption behavior to pSDEpSDE. Molecular modeling yielded binding energy trends based on simple adsorption of peptides on the [100] surface that were consistent with observed inhibition, but not for the [001] surface. The relatively unfavorable binding energies for peptides on the [001] surface suggest that their absorption will be primarily on the [100] face. The kinetic and adsorption data are consistent with phosphorylation of osteopontin acting to control mineral formation.

SPP1 promoter polymorphisms and glioma risk in a Chinese Han population

SPP1 was found to be significantly upregulated in many kinds of malignant tumors, including gliomas. Considering that gene polymorphisms have been implicated in the development of gliomas, we performed an association study between SPP1 functional promoter region polymorphisms and glioma risk in a Chinese population. We found significant evidence of an association between SPP1 promoter polymorphisms and glioma risk. For the -155_156insG variant, the -155_156GG allele was found to be significantly associated with an increased risk of glioma (P=0.020, odds ratio (OR)=1.202, 95% confidence interval (CI): 1.028-1.408). Individuals with the genotype containing the GG allele had a 1.372-fold increased risk (P=0.006, OR=1.372, 95% CI: 1.095-1.719). Further stratified analyses suggested that a significant association existed in adult glioma patients, male subjects and in cases without a family history of cancer. Alternatively, the study of single-nucleotide polymorphism -443C/T in a recessive model revealed that the genotype CC+CT significantly decreased the risk of glioma when compared with TT (P=0.023, OR=0.774, 95% CI: 0.621-0.966). After the analysis of haplotypes, the haplotype -155_156GG/-443T was represented at a significantly higher frequency in cases (P=0.029, OR=1.192, 95% CI: 1.018-1.395). Cellular assay indicated that the transcriptional activity of the SPP1 promoter containing the -155_156GG allele significantly increased in glioma cells. Thus, variants of the SPP1 promoter might influence the risk of glioma by regulating promoter activity. Further analyses are necessary to validate our observation in larger samples or in other ethnic groups.

A humanized anti-osteopontin antibody inhibits breast cancer growth and metastasis in vivo

Osteopontin (OPN) has been implicated as an important mediator of breast cancer progression and metastasis and has been investigated for use as a potential therapeutic target in the treatment of breast cancer. However, the in vivo antitumor effect of anti-OPN antibodies on breast cancer has not been reported. In this study, a mouse anti-human OPN antibody (1A12) was humanized by complementarity-determining region grafting method based on computer-assisted molecular modeling. A humanized version of 1A12, denoted as hu1A12, was shown to possess affinity comparable to that of its parental antibody. The ability of hu1A12 to inhibit cell migration, adhesion, invasion and colony formation was assessed in a highly metastatic human breast cancer cell line MDA-MB-435S. The results indicated that hu1A12 was effective in inhibiting the cell adhesion, migration, invasion and colony formation of MDA-MB-435S cells in vitro. hu1A12 also showed significant efficacy in suppressing primary tumor growth and spontaneous metastasis in a mouse lung metastasis model of human breast cancer. The specific epitope recognized by hu1A12 was identified to be (212)NAPSD(216), adjacent to the calcium binding domain of OPN. Our data strongly support that OPN is a potential target for the antibody-based therapies of breast cancer. The humanized anti-OPN antibody hu1A12 may be a promising therapeutic agent for the treatment of human breast cancer.

Transactivation of human osteopontin promoter by human T-cell leukemia virus type 1-encoded Tax protein

Osteopontin (OPN) is a cytokine that contributes substantially to the growth and metastasis in a wide spectrum of malignancies. We report here that OPN gene is transactivated by Tax protein of human T-cell leukemia virus type 1 (HTLV-1). Northern blot showed enhanced OPN gene expression in cells stably expressing Tax. Co-expression of Tax increased the reporter gene expression directed by OPN promoter. Tax-induced OPN activation was abrogated by treatment with LY294002 (PI3K inhibitor) or co-transfection with AKT siRNA, suggesting PI3K/AKT pathway is involved in Tax-mediated transactivation. Reporter assay with deletion mutants showed that the 5'-partial sequence between -765 and -660 of the OPN promoter is the region responsive to Tax, and further, disrupting the AP-1 site within this region abolished the OPN induction by Tax, indicating that Tax activation of OPN promoter is likely mediated by AP-1 site. This study suggests that OPN is one of the downstream mediators of aberrantly activated PI3K/AKT signaling by Tax, which may partially contribute to HTLV-1-associated leukemogenesis.

Identification of osteopontin-dependent signaling pathways in a mouse model of human breast cancer

Background

Osteopontin (OPN) is a secreted phosphoprotein which functions as a cell attachment protein and cytokine that signals through two cell adhesion molecules, α_vβ₃-integrin and CD44, to regulate cancer growth and metastasis. However, the signaling pathways associated with OPN have not been extensively characterized. In an in vivo xenograft model of MDA-MB-231 human breast cancer, we have previously demonstrated that ablation of circulating OPN with an RNA aptamer blocks interaction with its cell surface receptors to significantly inhibit adhesion, migration and invasion in vitro and local progression and distant metastases.

Findings

In this study, we performed microarray analysis to compare the transcriptomes of primary tumor in the presence and absence of aptamer ablation of OPN. The results were corroborated with RT-PCR and Western blot analysis. Our results demonstrate that ablation of OPN cell surface receptor binding is associated with significant alteration in gene and protein expression critical in apoptosis, vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), interleukin-10 (IL-10), granulocyte-macrophage colony stimulating factor (GM-CSF) and proliferation signaling pathways. Many of these proteins have not been previously associated with OPN.

Conclusion

We conclude that secreted OPN regulates multiple signaling pathways critical for local tumor progression.

EF1A1-actin interactions alter mRNA stability to determine differential osteopontin expression in HepG2 and Hep3B cells

Cancer progression depends on an accumulation of metastasis-supporting physiological changes which are regulated by cell signaling molecules. One such molecule, osteopontin (OPN), is a secreted phosphoprotein which mediates increased cellular migratory and invasive behavior, increased metastasis, protection from apoptosis, promotion of colony formation and 3D growth ability, induction of tumor-associated inflammatory cells, and induction of expression of angiogenic factors. Studies show that OPN expression is controlled by complex regulatory pathways at the transcriptional level in several cancers, but the molecular mechanisms which determine expression of OPN in HCC are largely unknown. In HepG2 and Hep3B tumor cell lines that differentially express OPN mRNA and protein, we identify elongation translation factor-1A1 (EF1A1) to be the trans-acting factor regulating differential OPN mRNA stability between HepG2 and Hep3B cell lines and characterize its interactions with G- and F-actin. EF1A1 binds to the OPN 5'-UTR to regulate OPN mRNA half-life. EF1A1 binds to actin in Hep3B cells. Pharmacologic manipulation to increase the G:F actin ratio in Hep3B increases OPN mRNA half-life and protein expression with simultaneous decrease in EF1A1 binding to OPN 5'-UTR. The converse findings were noted in HepG2 cells. Overall, our results suggest that EF1A1 regulation of OPN mRNA stability is actin dependent. EF1A1 has not been previously identified as a regulatory factor in OPN expression in cancer.

Clinical significance of osteopontin expression in T1 and T2 tongue cancers

BACKGROUND

Osteopontin (OPN) is considered to be a tumor-related protein associated with tumor aggressiveness and metastasis.

METHODS

Immunohistochemistry was used to study the clinical significance of OPN expression in T1 and T2 tongue cancers.

RESULTS

Positive OPN expression significantly correlated with higher tumor classification (T) (p = .004), positive nodal classification (N) (p < .001), greater tumor thickness (p < .001), and presence of tumor necrosis (p = .016), respectively. The unfavorable cumulative 5-year disease-free survival rate significantly correlated with positive OPN expression (p < .001), T2 (p = .024), positive N (p < .001), greater tumor thickness (p = .023), and positive tumor necrosis (p = .003). However, taking CD105 into consideration, only CD105 expression was the independent prognostic factor for survival by Cox's regression analysis.

CONCLUSION

Overexpression of OPN in the tumors implicated a more aggressive tumor behavior and was an important factor for survival. In addition, there might be relationship between OPN and CD105 expressions in angiogenesis.

Osteopontin: regulation in tumor metastasis

Osteopontin is a secreted phosphoprotein that has been implicated as an important mediator of tumor metastasis and has been investigated for use as a biomarker for advanced disease and as a potential therapeutic target in the regulation of cancer metastasis. The OPN DNA sequence is highly conserved and the protein contains several important functional domains including alpha(v)beta integrin and CD44 binding sites. High levels of OPN expression correlate with tumor invasion, progression or metastasis in multiple cancer. Studies demonstrate that osteopontin mediates the molecular mechanisms which determine metastatic spread, such as prevention of apoptosis, extracellular matrix proteolysis and remodeling, cell migration, evasion of host-immune cells and neovascularization. Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-B/BMPs/Smad/Hox, and Wnt/ss-catenin/APC/GSK-3ss/Tcf-4. The current state of knowledge of OPN biology suggests that it is an attractive target for therapeutic modulation of metastatic disease.

Osteopontin regulates ubiquitin-dependent degradation of Stat1 in murine mammary epithelial tumor cells

BACKGROUND

Osteopontin (OPN) is a secreted glycoprotein that mediates cell-matrix interactions and cellular signaling by binding with integrin (primarily alpha(v)beta(3)) and CD44 receptors. OPN regulates cell adhesion, chemotaxis, macrophage-directed IL-10 suppression, stress-dependent angiogenesis, apoptosis prevention, and anchorage-independent growth of tumor cells. However, the molecular mechanisms that define the role of OPN in tumor progression and metastasis are incompletely understood.

METHODS

In this study, we use a system of 4T1 and 4T07 murine mammary epithelial tumor cell lines that are divergent in both metastatic phenotype and OPN expression. 4T1 expresses OPN and hematogeneously metastasizes, whereas 4T07 does not express OPN and is highly tumorigenic but fails to metastasize.

RESULTS

Our results demonstrate that OPN regulates Stat1 protein degradation through the ubiquitin-proteasome pathway to alter interferon-gamma-dependent growth inhibition and p21 expression. We identify Stat-interacting LIM protein as the critical Stat ubiquitin E3 ligase in this setting.

CONCLUSIONS

OPN regulates Stat1-dependent functions, such as growth inhibition and p21 expression, in the murine mammary epithelial cells lines 4T1 and 4T07. This relationship between OPN and Stat1 in the context of tumor biology has not been previously examined.

Elevation of osteopontin levels in brain tumor cells reduces burden and promotes survival through the inhibition of cell dispersal

Osteopontin (OPN) is a pleotrophic molecule that has been associated with multiple disorders of the central nervous system (CNS). Its roles in CNS malignancy are unclear but suggest that higher levels of OPN expression correlate with increased tumor grade and increased migratory capacity of tumor cells. In this study OPN cDNA was cloned into a retroviral vector and used to infect F98 Fischer rat-derived glioma cells and U87 human-derived glioblastoma multiforme (GBM) cells in vitro. Cells expressing high levels of OPN migrated less distance than control cells in vitro. This effect was not RGD mediated, but was reversed in the presence of c-Jun N-terminal kinase (JNK) inhibitor suggesting that JNK1 is an essential component of a negative feedback loop affecting OPN activated signaling cascades. Implantation of tumor cells expressing high levels of OPN into adult Fischer rats and nude rats resulted in morphologically distinct tumors and prolonged host survival relative to controls. We propose that local produced, high level OPN expression limits the malignant character of glioma cells and that the downstream mechanisms involved represent pathways that may have therapeutic value in the treatment of human CNS malignancy.

The role of osteopontin in tumor progression and metastasis in breast cancer

The use of cancer biomarkers to anticipate the outlines of disease has been an emerging issue, especially as cancer treatment has made such positive steps in the last few years. Progress in the development of consistent malignancy markers is imminent because advances in genomics and bioinformatics have allowed the examination of immense amounts of data. Osteopontin is a phosphorylated glycoprotein secreted by activated macrophages, leukocytes, and activated T lymphocytes, and is present in extracellular fluids, at sites of inflammation, and in the extracellular matrix of mineralized tissues. Several physiologic roles have been attributed to osteopontin, i.e., in inflammation and immune function, in mineralized tissues, in vascular tissue, and in kidney. Osteopontin interacts with a variety of cell surface receptors, including several integrins and CD44. Binding of osteopontin to these cell surface receptors stimulates cell adhesion, migration, and specific signaling functions. Overexpression of osteopontin has been found in a variety of cancers, including breast cancer, lung cancer, colorectal cancer, stomach cancer, ovarian cancer, and melanoma. Moreover, osteopontin is present in elevated levels in the blood and plasma of some patients with metastatic cancers. Therefore, suppression of the action of osteopontin may confer significant therapeutic activity, and several strategies for bringing about this suppression have been identified. This review looks at the recent advances in understanding the possible mechanisms by which osteopontin may contribute functionally to malignancy, particularly in breast cancer. Furthermore, the measurement of osteopontin in the blood or tumors of patients with cancer, as a way of providing valuable prognostic information, will be discussed based on emerging clinical data.

Sp1 regulates osteopontin expression in SW480 human colon adenocarcinoma cells

BACKGROUND

Osteopontin (OPN) mediates cancer metastasis. Mechanisms regulating OPN expression in human colorectal cancer are unknown. Using SW480 colon adenocarcinoma cells, we hypothesized that transcription determines OPN expression.

METHODS

SW480 constitutively express OPN. Transient transfection and deletion analysis of human OPN promoter (full-length 2.1 kb)-luciferase constructs identified cis-regulatory regions. Gelshift and chromatin immunoprecipitation (ChIP) assays identified the trans-regulatory nuclear protein. Using in vitro adhesion, migration, and invasion studies, siRNA was used to determine the functional effect of decreased nuclear protein expression.

RESULTS

A cis-regulatory promoter region, nt-80 to nt-108, upregulated OPN transcription. Gelshift assays demonstrated specific binding of nuclear proteins. Competition with unlabeled mutant oligonucleotides indicated that the region, nt-94 to nt-104 (TGGGCTGGGC), was essential for protein binding in gelshift assays. Confirmatory ChIP assays showed the corresponding nuclear protein to be Sp1. Sp1 expression was ablated with siRNA (si-Sp1), resulting in decreased OPN-dependent adhesion, migration, and invasion by 50%, 70%, and 65%, respectively. Exogenous addition of OPN to si-Sp1 cells restored adhesion, migration, and invasion indices.

CONCLUSIONS

In SW480 human colon cancer cells, we conclude that Sp1 mediated expression of the tumor metastasis protein, OPN, regulates in vitro functional correlates of tumor metastasis.

Association of osteopontin gene haplotypes with nephrolithiasis

Osteopontin (OPN) is one of the glycosylated phosphoproteins produced in the kidney that can modulate nephrolithiasis. We had previously found a modest association between OPN gene polymorphisms and the risk for urinary stone formation. In order to determine if sequence variants within the OPN gene could be linked to the risk of nephrolithiasis; we sequenced the entire OPN gene of 45 stone forming patients and 54 control patients of Japanese ancestry. We identified 61 polymorphisms and of these evaluated four haplotype-tagging single nucleotide polymorphisms in a total of 126 kidney stone cases and 214 healthy individuals; all of Japanese ancestry. There was a significant association of two of these haplotypes located in the OPN promoter with the relative probability of nephrolithiasis; one of increased and one of reduced risk. Our findings provide potential support for significant increased and decreased associations between OPN gene haplotypes and the relative potential of stone formation in the Japanese population. We suggest that such genetic findings may help to clarify the function of OPN in nephrolithiasis.

Thrombin-cleaved COOH(-) terminal osteopontin peptide binds with cyclophilin C to CD147 in murine breast cancer cells

Osteopontin is a glycoprotein that has been linked to metastatic function in breast, lung, and prostate cancers. However, the mechanism by which osteopontin acts to induce metastatic properties is largely unknown. One intriguing feature of osteopontin is the presence of a conserved thrombin cleavage site that is COOH-terminal from a well-characterized RGD domain. Although the COOH-terminal fragment may bind to cell surface CD44 receptors, little is known about the COOH-terminal osteopontin fragment. In the current study, we use the murine mammary epithelial tumor cell lines 4T1 and 4T07; these cells are thioguanine-resistant sublines derived from the parental population of 410.4 cells from Balb/cfC3H mice. Using flow cytometry and Forster resonance energy transfer, we show that the COOH-terminal fragment of osteopontin binds with another marker of metastatic function (cyclophilin C or rotamase) to the CD147 cell surface glycoprotein (also known as extracellular matrix metalloproteinase inducer), to activate Akt1/2 and matrix metalloproteinase-2. In in vitro assays, thrombin cleavage of osteopontin to generate short COOH-terminal osteopontin in the presence of cyclophilin C increases migration and invasion of both 4T07 and 4T1 cells. This interaction between osteopontin peptide and cyclophilin C has not been previously described but assigns a heretofore unknown function for the thrombin-cleaved osteopontin COOH-terminal fragment.

SPP1 Promoter Polymorphisms: Identification of the First Modifier Gene for Pseudoxanthoma Elasticum

Background: Progressive calcification and fragmentation of elastic fibers are characteristic hallmarks of pseudoxanthoma elasticum (PXE), which is caused by mutations in ABCC6 encoding multidrug resistance–associated protein 6 (MRP6). Because of the great clinical variability of PXE, secondary genetic risk factors are suspected to exist. We investigated whether SPP1 (secreted phosphoprotein 1; previously OPN, osteopontin) promoter polymorphisms are associated with PXE.

Methods: We screened an ∼2-kb region spanning the theoretical promoter of the SPP1 gene for sequence variations by denaturing HPLC and direct sequencing in 93 PXE patients. Sequence variations with a prevalence &gt;5% were genotyped in 93 age- and sex-matched healthy controls. Statistical and haplotype association analyses were performed using Fisher exact test, PHASE v2.1.1, and Haploview 3.2.

Results: Mutational screening revealed 9 different sequence variations. Three SPP1 promoter polymorphisms (c.−1748A&gt;G, c.−155_156insG, and c.244_245insTG) were significantly more frequent in PXE patients than in 93 age- and sex-matched healthy controls (Pcorrected &lt; 0.05 each). The odds ratios (95% CI) for PXE among carriers of the 3 alleles were, respectively, 2.16 (1.34–3.48), 2.41 (1.51–3.82), and 1.97 (1.23–3.15). Haplotype analysis of 6 SPP1 promoter polymorphisms revealed 1 haplotype to be significantly reduced among PXE patients (Pcorrected = 0.035, odds ratio 1.80, 95% CI 1.19–2.71).

Conclusions: Polymorphisms in the SPP1 promoter are secondary genetic risk factors contributing to PXE susceptibility.

Osteopontin induces ubiquitin-dependent degradation of STAT1 in RAW264.7 murine macrophages

In systemic inflammation induced by endotoxin (LPS), the macrophage produces the majority of the circulating NO metabolites. However, while the molecular pathways which up-regulate iNOS expression have been extensively studied in the macrophage, little is known of the parallel counterregulatory pathways which repress or inhibit macrophage iNOS expression. Using both in vivo and in vitro murine models of endotoxin (LPS) stimulation, we have previously demonstrated that NO feedback inhibits its own synthesis by increasing transcription of osteopontin (OPN), a potent transrepressor of inducible NO synthase expression. In this current study, using a system of LPS-treated RAW264.7 macrophages, we go on to demonstrate that OPN increases STAT1 ubiquitination and subsequent 26s proteasome-mediated degradation to inhibit STAT1 dependent iNOS promoter activity, transcription, and protein expression. In addition, we identify STAT-interacting LIM protein as the critical STAT ubiquitin E3 ligase critical for STAT1 degradation in this setting. OPN has not been linked previously to STAT1 degradation. This regulation of STAT1 degradation underlies OPN's effect as an inhibitor of iNOS gene transcription. These are novel findings and define OPN as a unique and as yet, poorly characterized, transactivator of STAT1 degradation by the ubiquitin-proteasome system.

Osteopontin in metastatic lesions as a prognostic marker in ovarian cancers

Osteopontin (OPN) is expressed in various human cancers and associated with tumor progression, invasion and metastasis in many manners. The purpose of this study is to investigate the clinical significance of OPN expression in metastatic lesions of ovarian cancers, since the prognosis of the patients with peritoneal dissemination is extremely poor. In primary tumors and peritoneal metastatic lesions from 40 patients with stage III ovarian cancers, the protein levels of OPN and histoscores were determined by enzyme immunoassay and immunohistochemistry, respectively. Immunohistochemical staining revealed OPN was distributed in the cytoplasm and nuclear compartments of the cancer and stromal cells within and around the tumor. The OPN level was significantly (p < 0.05) increased in 32 of 40 metastatic lesions of ovarian cancers. The OPN increased cases identified by immunohistochemical staining were consistent with those identified by the sandwich immunoassay. The prognosis of the 32 patients with significant increase of OPN in ovarian cancers was extremely poor, whereas the 36-month survival rate of the 8 patients with no increase of OPN was 75%. Multivariate analysis revealed that the levels of OPN were independent predictors of prognosis from clinical characteristics (age, lesion size, histological types). OPN might be associated with peritoneal metastasis and its advancement, and that the OPN level in metastatic lesion may be a prognostic indicator in ovarian cancers.

Interleukin-10 and Th2 cytokines differentially regulate osteopontin expression in human monocytes and dendritic cells

Osteopontin (OPN) is a pleiotrophic phosphoprotein involved in homeostatic and pathophysiologic responses. It is known to be a chemotactic cytokine for dendritic cells (DCs), a critical cell type in both innate and adaptive immune responses. We report herein a contrasting role of interleukin-10 (IL-10) and Th2 cytokines in the regulation of OPN expression in human monocytes and monocyte-derived DCs (Mo-DCs). Our results showed first that the expression of OPN in monocytes and Mo-DCs was induced in a time-dependent and dose-dependent manner by IL-10 but was inhibited by IL-4 or IL-13. Further, the basal level of OPN expression was also inhibited by IL-4. This inhibitory effect of IL-4 was associated with a faster decay of OPN transcripts and a decreased proximal promoter activity of OPN in IL-4-treated cells. These results demonstrate a novel role of IL-10 and Th2 cytokines in the regulation of DC function through their contrasting regulatory activities on the expression of OPN.

Clinical implications of osteopontin in metastatic lesions of uterine cervical cancers

Osteopontin (OPN) is a glycophosphoprotein that has variety of physiological functions. OPN is expressed in various human cancers and associated with tumor progression, invasion and metastasis in many manners. The purpose of this study is to investigate the clinical significance of OPN expression in metastatic lymph node of uterine cervical cancers, since the prognosis of the patients with lymph node metastasis is extremely poor. Immunohistochemical staining revealed OPN was distributed in the cytoplasm and nuclear compartments of the cancer and stromal cells within and around the tumor. In 25 of the 40 cases, stronger staining for OPN was found in the cancer cells or stromal cells of the metastatic lymph node lesion than in those of the primary tumor. The OPN level was significantly (P<0.05) increased in 25 of 40 metastatic lymph node lesions of uterine cervical cancers. The OPN increased cases identified by immunohistochemical staining were consistent with those identified by the sandwich immunoassay. The prognosis of the 25 patients with significant increase of OPN in uterine cervical cancers was extremely poor, whereas the 24-month survival rate of the 15 patients with no increase of OPN was 67%. This indicates that OPN may contribute to lymph node metastasis and its advancement, and that the OPN level in metastatic lesion may be a prognostic indicator in uterine cervical cancers.

Ets-1 and runx2 regulate transcription of a metastatic gene, osteopontin, in murine colorectal cancer cells

Osteopontin (OPN) is a sialic acid-rich phosphoprotein secreted by a wide variety of cancers. We have shown previously that OPN is necessary for mediating hepatic metastasis in CT26 colorectal cancer cells. Although a variety of stimuli can induce OPN, the molecular mechanisms that regulate OPN gene transcription in colorectal cancer are unknown. We hypothesized that cis- and trans-regulatory elements determine OPN transcription in CT26 cells. OPN transcription was analyzed in CT26 cancer cells and compared with YAMC (young adult mouse colon) epithelial cells. Clonal deletion analysis of OPN promoter-luciferase constructs identified cis-regulatory regions. A specific promoter region, nucleotide (nt) -107 to -174, demonstrated a >8.0-fold increase in luciferase activity in CT26 compared with YAMC. Gel-shift assays sublocalized two cis-regulatory regions, nt -101 to -123 and nt -121 to -145, which specifically bind CT26 nuclear proteins. Competition with unlabeled mutant oligonucleotides revealed that the regions nt -115 to -118 and nt -129 to -134 were essential for protein binding. Subsequent supershift and chromatin immunoprecipitation assays confirmed the corresponding nuclear proteins to be Ets-1 and Runx2. Functional relevance was demonstrated through mutations in the Ets-1 and Runx2 consensus binding sites resulting in >60% decrease in OPN transcription. Ets-1 and Runx2 protein expression in CT26 was ablated using antisense oligonucleotides and resulted in a >7-fold decrease in OPN protein expression. Ets-1 and Runx2 are critical transcriptional regulators of OPN expression in CT26 colorectal cancer cells. Suppression of these transcription factors results in significant down-regulation of the OPN metastasis protein.