An osteopontin fragment is essential for tumor cell invasion in hepatocellular carcinoma

Recurrence and poor prognosis following resection of small hepatitis B-related hepatocellular carcinoma lesions are associated with aberrant tumor expression profiles of glypican 3 and osteopontin

BACKGROUND

Early detection and following appropriate treatments of hepatocellular carcinoma (HCC) is still the gold standard for favored outcome of HCC patients; nevertheless, a small portion of hepatitis B virus (HBV)-related small HCC (<5 cm) patients got poor prognosis. Furthermore, the study for small HBV-HCC was limited. Therefore, the aim of this study was to explore the potential genetic signature for HBV-related small HCC as novel prognostic factors.

METHODS

We examined expression profiles of HBV-related small HCC using an Affymetrix U133A GeneChip, evaluated differential gene expression by quantitative real-time polymerase chain reaction (qRT-PCR), and finally validated these expression patterns by immunohistochemistry (IHC).

RESULTS

A total of 57 genes were differentially expressed between tumor and normal parts (n = 20 pairs) using Affymetrix U133A chip, and 16 genes were further evaluated by qRT-PCR. The result was compatible with the finding of oligonucleotide microarray (Pearson's correlation, r = 0.87). Furthermore, the expression pattern in HCC tissue by IHC in another group of small HBV-HCC (n = 100) showed overexpression of either osteopontin (OPN) or glypican 3 (GPC3) is an independent prognostic factor for disease-free survival (DFS) in HBV-positive small HCC (P < 0.01 and 0.03, respectively). Long-term DFS and overall survival (OS) for small HBV-HCC patients with high risk (both elevated GPC3(+)/OPN(+)) were DFS 0%, OS 0%, respectively; on the other hand, DFS and OS in patients with moderate (only 1 gene elevated) or low (OPN(-)/GPC3(-)) risk were 35.0 and 46.5%, respectively.

CONCLUSIONS

Elevation of both OPN and GPC3 may act as an adverse indicator for HBV-related small HCC patients after curative resection.

Osteopontin-stimulated expression of matrix metalloproteinase-9 causes cardiomyopathy in the mdx model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is a common and lethal form of muscular dystrophy. With progressive disease, most patients succumb to death from respiratory or heart failure, or both. However, the mechanisms, especially those governing cardiac inflammation and fibrosis in DMD, remain less understood. Matrix metalloproteinase (MMPs) are a group of extracellular matrix proteases involved in tissue remodeling in both physiologic and pathophysiologic conditions. Previous studies have shown that MMP-9 exacerbates myopathy in dystrophin-deficient mdx mice. However, the role and the mechanisms of action of MMP-9 in cardiac tissue and the biochemical mechanisms leading to increased levels of MMP-9 in mdx mice remain unknown. Our results demonstrate that the levels of MMP-9 are increased in the heart of mdx mice. Genetic ablation of MMP-9 attenuated cardiac injury, left ventricle dilation, and fibrosis in 1-y-old mdx mice. Echocardiography measurements showed improved heart function in Mmp9-deficient mdx mice. Deletion of the Mmp9 gene diminished the activation of ERK1/2 and Akt kinase in the heart of mdx mice. Ablation of MMP-9 also suppressed the expression of MMP-3 and MMP-12 in the heart of mdx mice. Finally, our experiments have revealed that osteopontin, an important immunomodulator, contributes to the increased amounts of MMP-9 in cardiac and skeletal muscle of mdx mice. This study provides a novel mechanism for development of cardiac dysfunction and suggests that MMP-9 and OPN are important therapeutic targets to mitigating cardiac abnormalities in patients with DMD.

Osteopontin: a potentially important therapeutic target in cancer

INTRODUCTION

Cancer is an extremely complex disease and most cancer treatments are limited to chemotherapy, radiation and surgery. The progression of tumours towards malignancy requires the interaction of various cytokines, growth factors, transcription factors and effector molecules. Osteopontin is a cytokine-like, calcium-binding, extracelular-matrix- associated member of the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family of proteins. It plays an important role in determining the oncogenic potential of various cancers. The role of osteopontin in various pathophysiological conditions suggests that the alteration in post-translational modification result in different functional forms that might change its normal physiological functions.

AREAS COVERED

Osteopontin -based anticancer therapy, which may provide a new insight for the effective management of cancer.

EXPERT OPINION

A better understanding of the signalling mechanism by which osteopontin promotes tumourigenesis may be useful in crafting novel osteopontin -based anticancer therapy. The role of osteopontin in promoting cancer progression is the subject of in depth investigation and thus targeting osteopontin might be a suitable therapeutic approach for the treatment of cancer.

Pathogenesis of alcohol-induced liver disease: classical concepts and recent advances

Alcoholic liver disease (ALD) is a primary consequence of heavy and prolonged drinking. ALD contributes to the bulk of liver disease burden worldwide. Progression of ALD is a multifactorial and multistep process that includes many genetic and environmental risk factors. The molecular pathogenesis of ALD involves alcohol metabolism and secondary mechanisms such as oxidative stress, endotoxin, cytokines and immune regulators. The histopathological manifestation of ALD occurs as an outcome of complex but controlled interactions between hepatic cell types. Hepatic stellate cells (HSCs) are the key drivers of fibrogenesis, but transformation of hepatocytes to myofibroblastoids also implicate parenchymal cells as playing an active role in hepatic fibrogenesis. Recent discoveries indicate that lipogenesis during the early stages of ALD is a risk for advancement to cirrhosis. Other recently identified novel molecules and physiological/cell signaling pathways include fibrinolysis, osteopontin, transforming growth factor-β-SMAD and hedgehog signaling, and involvement of novel cytokines in hepatic fibrogenesis. The observation that ALD and non-alcoholic steatohepatitis share common pathways and genetic polymorphisms suggests operation of parallel pathogenic mechanisms. Future research involving genomics, epigenomics, deep sequencing and non-coding regulatory elements holds promise to identify novel diagnostic and therapeutic targets for ALD. There is also a need for adequate animal models to study pathogenic mechanisms at the molecular level and targeted therapy.

The significance of MMP-9 over MMP-2 in HCC invasiveness and recurrence of hepatocellular carcinoma after curative resection

BACKGROUND

The extracellular matrix metalloproteases MMP-9 and MMP-2 are critical for the invasive potential of tumors. However, it is not clear which of the two plays the predominant role in tumor invasion and progression. In the present study, we compared the clinical efficacy of MMP-9 and MMP-2 overexpression for predicting tumor recurrence and survival after surgical resection in HCC patients.

MATERIALS AND METHODS

MMP-9 and MMP-2 expression in HCC cell lines and in vitro HCC invasion model were detected by quantitative RT-PCR and immunofluorescence. The expression levels of MMP-9 and MMP-2 were assessed by immunohistochemistry in HCC tissue microarrays from HCC patients (study set) who underwent curative resection. The clinicopathological data were retrospectively analyzed. The results were further verified in an independent cohort of 92 HCC patients (validation set).

RESULTS

Univariate analysis demonstrated that high expression of MMP-9 was associated with both time to recurrence (TTR, P = .015) and overall survival (OS, P = .024), whereas high expression of MMP-2 was only correlated with TTR (P = .041). Multivariate analysis confirmed that MMP-9 expression was an independent predictor of TTR and OS. The coindex of MMP-9 and preoperative serum AFP levels was significantly correlated with TTR and OS (P = .036 and P = .040), but the coindex of MMP-2 and AFP did not show prognostic significance for either TTR or OS (P = .067 and P = .053). The prognostic value of MMP-9 overexpression was validated in the independent data set.

CONCLUSION

MMP-9 is superior to MMP-2 for the prediction of tumor recurrence and survival in HCC patients after surgical resection.

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: an important molecule in liver diseases

Osteopontin (OPN) is a multi-functional glycoprotein that has been implicated in a number of physiological and pathological events in vivo. Recent studies have shown that abnormal changes in OPN expression occur in many liver diseases and animal models of liver diseases and may play an important role in the pathogenesis of these diseases. Elucidation of mechanisms underlying the role of OPN in the pathogenesis of different liver diseases will help identify new therapeutic targets and develop new drugs for these diseases.

A unique metastasis gene signature enables prediction of tumor relapse in early-stage hepatocellular carcinoma patients

Metastasis-related recurrence often occurs in hepatocellular carcinoma (HCC) patients who receive curative therapies. At present, it is challenging to identify patients with high risk of recurrence, which would warrant additional therapies. In this study, we sought to analyze a recently developed metastasis-related gene signature for its utility in predicting HCC survival, using 2 independent cohorts consisting of a total of 386 patients who received radical resection. Cohort 1 contained 247 predominantly HBV-positive cases analyzed with an Affymetrix platform, whereas cohort 2 contained 139 cases with mixed etiology analyzed with the NCI Oligo Set microarray platform. We employed a survival risk prediction algorithm with training, test, and independent cross-validation strategies and found that the gene signature is predictive of overall and disease-free survival. Importantly, risk was significantly predicted independently of clinical characteristics and microarray platform. In addition, survival prediction was successful in patients with early disease, such as small (<5 cm in diameter) and solitary tumors, and the signature predicted particularly well for early recurrence risk (<2 years), especially when combined with serum alpha fetoprotein or tumor staging. In conclusion, we have shown in 2 independent cohorts with mixed etiologies and ethnicity that the metastasis gene signature is a useful tool to predict HCC outcome, suggesting the general utility of this classifier. We recommend the use of this classifier as a molecular diagnostic test to assess the risk that an HCC patient will develop tumor relapse within 2 years after surgical resection, particularly for those with early-stage tumors and solitary presentation.

Osteopontin as a potential biomarker of proliferation and invasiveness for lung cancer

PURPOSE

Lung cancer is one of the most malignant tumors and poses a significant threat to human health. Osteopontin (OPN) is a variably expressed, secreted glycophosphoprotein that mediates the growth and metastases of several carcinoma types. In this study, we aimed to understand the role of OPN in lung cancer cell proliferation and invasiveness.

METHODS

Expression of OPN was examined using an immunohistochemical method in paraffin-embedded sections collected from 49 patients with lung cancer. We silenced OPN expression by lentivirus-mediated OPN-specific small interfering RNA (siRNA) and examined the proliferation and invasiveness of OPN-silenced lung cancer cell (A549) through MTT, BrdU, flow cytometry, and Matrigel assay. In addition, we tested the role of individual OPN splice variants in A549 cell growth and invasion by constructing OPN overexpression lentiviruses.

RESULT

Downregulation of OPN inhibited A549 cell proliferation and in vivo tumor growth, abrogated augmentation of invasion, induced G1-phase cell cycle arrest, and induced cell late apoptosis and necrosis. Moreover, the proliferation and invasiveness was linked to different OPN splice variants, of which OPN-b affected the cell proliferation and OPN-c showed significant correlation with invasion behavior.

CONCLUSIONS

Our data suggested that OPN served as a potential biomarker for invasive lung cancer and provided new molecular-targeted therapy for lung cancer based on lentivirus-mediated RNA interference.

Osteopontin expression predicts overall survival after liver transplantation for hepatocellular carcinoma in patients beyond the Milan criteria

BACKGROUND & AIMS

Microarray data showed that osteopontin overexpression predicts early HCC-recurrence after liver resection. Osteopontin (OPN) expression could serve as a predictor of HCC-recurrence after OLT.

METHODS

Osteopontin expression was investigated immunohistochemically in a unique population of 125 HCC-patients undergoing OLT between 1982 and 2002, including 81 patients (65%) outside the Milan criteria. Multivariate analysis of factors associated with median overall survival (OS) and time to recurrence (TTR) was performed.

RESULTS

Osteopontin was expressed in 40/125 (32%) of the HCCs. Overall survival post-OLT at 1, 2, 3, 5 years was 77%, 62%, 52%, and 43% (median survival 37 months). Overall survival was significantly longer without expression of OPN (p < 0.05; (median OS: 56 vs. 23 months). The same was true for median TTR (p = 0.008). Outside Milan criteria, patients without OPN-expression had better prognosis (median OS: 37.8 vs. 19.2 months, p = 0.003). Tumor recurrence in patients transplanted outside Milan criteria occurred in 43% (23 of 54) of patients without and 70% (19 of 27, p = 0.018) of patients with OPN-expression after a median TTR of 83.5 vs. 13.9 months. On multivariate analysis, vascular invasion and OPN-expression were independently associated with OS and TTR in HCC-patients after OLT.

CONCLUSIONS

Immunohistochemically detectable Osteopontin in HCC is an independent predictor of tumor recurrence and survival in patients beyond Milan criteria undergoing OLT.

Role of osteopontin in synovial Th17 differentiation in rheumatoid arthritis

OBJECTIVE

Osteopontin (OPN) that is aberrantly produced in rheumatoid synovium is thought to play an important role in rheumatoid arthritis (RA). This study was undertaken to investigate the role of OPN in the differentiation and accumulation of Th17 cells in rheumatoid synovium.

METHODS

Peripheral blood mononuclear cells and purified CD4+ T cells derived from patients with RA or healthy controls were used to test the effect of OPN in vitro. Cytokine expression was determined by enzyme-linked immunosorbent assay and quantitative polymerase chain reaction. Intracellular staining and flow cytometry were used to detect the percentages of Th17 cells and OPN receptors. Signaling and molecular events were analyzed by immunoblotting and chromatin immunoprecipitation.

RESULTS

The levels of OPN correlated significantly with interleukin-17 (IL-17) production and the frequency of Th17 cells in the synovial fluid (SF) of RA patients. Endogenous OPN produced in RA SF was responsible for markedly increased production of IL-17 in T cells, which was blocked by OPN antibody. The effect of OPN in Th17 differentiation was mediated through a mechanism independent of the IL-6/STAT-3 pathway or other cytokines and specifically involved the OPN receptors CD44 and CD29 and the transcription factor retinoic acid-related orphan receptor (ROR). Furthermore, OPN was found to induce H3 acetylation of the IL17A gene promoter, mainly through the CD44 binding domain in CD4+ T cells, allowing the interaction of the IL17A gene locus with ROR.

CONCLUSION

This study reveals new evidence of the critical role of OPN in Th17 differentiation in rheumatoid synovitis.

Osteopontin promotes hepatocellular carcinoma invasion by up-regulating MMP-2 and uPA expression

Osteopontin (OPN) is over-expressed in a variety of cancers, but its role in hepatocellular carcinoma (HCC) progression has not been clarified. In this study, weakly tumorigenic, non-metastastic human HCC cell line SMMC-7721 cells were forced to over-express OPN via stable transfection. A series of functional assays were performed to assess the effects of OPN on tumor cell behaviors and cDNA microarray was used to identify the genes regulated by OPN. The results showed that OPN significantly enhanced the migration and invasion of SMMC-7721 cells in vitro. In addition, CD44v6 antibody could significantly inhibit the invasion of OPN over-expressing SMMC-7721 cells. Moreover, MMP-2 and uPA expressions were significantly up-regulated in OPN over-expressing SMMC-7721 cells. Together, these findings indicate that OPN enhanced HCC cells invasion through interaction with its receptor CD44v6 and increased MMP-2 and uPA expressions, providing at least one mechanism for OPN-mediated HCC progression and metastasis.

Osteopontin predicts long-term functional outcome among ischemic stroke patients

Osteopontin (OPN) is a multifunctional protein which has shown neuroprotective properties in animal models of cerebral ischemia. Nevertheless, its role in acute human stroke has not yet been established. Therefore, we aimed to determine human serum OPN level during acute ischemic stroke and its relationship with patient outcome. We measured OPN levels in 178 consecutive patients with a middle cerebral artery (MCA) occlusion who received fibrinolytic therapy and in 40 control subjects. OPN level was determined by an enzyme-linked immunosorbent assay (ELISA). Bad functional outcome was defined by modified Rankin Scale (mRS) score >2 at 3 months after stroke onset. A logistic regression analysis was performed to determine factors that could be independently associated with poor prognosis. OPN levels among stroke patients did not differ from the controls' OPN levels (16.65 vs. 17.83 ng/mL, p = 0.404). Interestingly, OPN level was increased among those patients who showed worse prognosis at 3 months (19.96 vs. 15.48 ng/mL, p = 0.040). In a logistic regression model, an OPN level >27.22 ng/mL was found to be an independent factor for a bad outcome (OR 5.01, 95% CI 1.60-15.72, p = 0.006) after adjusting for potential confounders. Those patients showing higher OPN levels before tPA administration displayed a worse prognosis compared to those with lower OPN levels. Further research is necessary to elucidate the role of OPN in ischemic stroke pathophysiology and validate OPN as a useful tool to predict long-term stroke outcome.

The tumor microenvironment in hepatocellular carcinoma: current status and therapeutic targets

A growing body of literature highlights the cross-talk between tumor cells and the surrounding peri-tumoral stroma as a key modulator of the processes of hepatocarcinogenesis, epithelial mesenchymal transition (EMT), tumor invasion and metastasis. The tumor microenvironment can be broadly classified into cellular and non-cellular components. The major cellular components include hepatic stellate cells, fibroblasts, immune, and endothelial cells. These cell types produce the non-cellular components of the tumor stroma, including extracellular matrix (ECM) proteins, proteolytic enzymes, growth factors and inflammatory cytokines. The non-cellular component of the tumor stroma modulates hepatocellular carcinoma (HCC) biology by effects on cancer signaling pathways in tumor cells and on tumor invasion and metastasis. Global gene expression profiling of HCC has revealed that the tumor microenvironment is an important component in the biologic and prognostic classification of HCC. There are substantial efforts underway to develop novel drugs targeting tumor-stromal interactions. In this review, we discuss the current knowledge about the role of the tumor microenvironment in pathogenesis of HCC, the role of the tumor microenvironment in the classification of HCC and efforts to develop treatments targeting the tumor microenvironment.

Involvement of osteopontin in the matrix-degrading and proangiogenic changes mediated by nicotine in pancreatic cancer cells

BACKGROUND

Substantial evidence indicates that exposure to cigarette smoke is associated with an elevated risk of pancreatic ductal adenocarcinoma (PDA). However, the mechanisms underlying the effects of nicotine on the development or progression of PDA remain to be investigated. Previously, we showed that nicotine promotes the expression of osteopontin c (OPNc), an isoform of OPN protein that confers on cancer cells a migratory phenotype. In this study, we explored the potential prometastatic role of nicotine in PDA through studying its effect on the expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF) and evaluated the role of OPN in mediating these effects.

MATERIALS AND METHODS

MMP-9 and VEGF mRNA and protein were analyzed in PDA cells treated with or without nicotine (3-300 nM). Transient transfection and luciferase-labeled promoter studies evaluated the effects of OPNc and OPN protein on the transcription and translation of MMP-9 and VEGF. Real-time PCR and immunohistochemistry were used to analyze the mRNA expression levels and localization of OPN, MMP-9, and VEGF proteins in matched invasive human PDA and surrounding nonmalignant tissues.

RESULTS AND DISCUSSION

Nicotine significantly enhanced the expression of MMP-9 and VEGF mRNA and protein in PDA cells. Blocking OPN with siRNA or OPN antibody prevented the nicotine-mediated increase of both MMP-9 and VEGF. Transient transfection of OPNc gene in PDA cells or their treatment with recombinant OPN protein significantly (p < 0.05) increased MMP-9 and VEGF mRNA expression levels and induced their promoter activities. In invasive PDA lesions, MMP-9 mRNA levels were significantly (p < 0.005) higher in smokers vs. nonsmokers. VEGF protein co-localized with MMP-9 and OPN in the malignant ducts and correlated well with their higher levels in invasive PDA lesions.

CONCLUSIONS

Our data show for the first time that cigarette smoking and nicotine may contribute to PDA metastasis through inducing MMP-9 and VEGF and suggest that OPN plays a central role in mediating these effects. The presence of OPN as a downstream effector of nicotine that is capable of mediating its prometastatic effects in PDA cells is novel and could provide a unique therapeutic target to control pancreatic cancer aggressiveness, especially in the cigarette-smoking population.

Extracellular matrix roles during cardiac repair

The cardiac extracellular matrix (ECM) provides a platform for cells to maintain structure and function, which in turn maintains tissue function. In response to injury, the ECM undergoes remodeling that involves synthesis, incorporation, and degradation of matrix proteins, with the net outcome determined by the balance of these processes. The major goals of this review are a) to serve as an initial resource for students and investigators new to the cardiac ECM remodeling field, and b) to highlight a few of the key exciting avenues and methodologies that have recently been explored. While we focus on cardiac injury and responses of the left ventricle (LV), the mechanisms reviewed here have pathways in common with other wound healing models.

Role of the metastasis-promoting protein osteopontin in the tumour microenvironment

Osteopontin (OPN) is a secreted protein present in bodily fluids and tissues. It is subject to multiple post-translational modifications, including phosphorylation, glycosylation, proteolytic cleavage and crosslinking by transglutamination. Binding of OPN to integrin and CD44 receptors regulates signalling cascades that affect processes such as adhesion, migration, invasion, chemotaxis and cell survival. A variety of cells and tissues express OPN, including bone, vasculature, kidney, inflammatory cells and numerous secretory epithelia. Normal physiological roles include regulation of immune functions, vascular remodelling, wound repair and developmental processes. OPN also is expressed in many cancers, and elevated levels in patients’ tumour tissue and blood are associated with poor prognosis. Tumour growth is regulated by interactions between tumour cells and their tissue microenvironment. Within a tumour mass, OPN can be expressed by both tumour cells and cellular components of the tumour microenvironment, and both tumour and normal cells may have receptors able to bind to OPN. OPN can also be found as a component of the extracellular matrix. The functional roles of OPN in a tumour are thus complex, with OPN secreted by both tumour cells and cells in the tumour microenvironment, both of which can in turn respond to OPN. Much remains to be learned about the cross-talk between normal and tumour cells within a tumour, and the role of multiple forms of OPN in these interactions. Understanding OPN-mediated interactions within a tumour will be important for the development of therapeutic strategies to target OPN.

Induction of monocyte chemoattractant protein-1 by nicotine in pancreatic ductal adenocarcinoma cells: role of osteopontin

BACKGROUND

Cigarette smoke and nicotine are among the leading environmental risk factors for developing pancreatic ductal adenocarcinoma (PDA). We showed recently that nicotine induces osteopontin (OPN), a protein that plays critical roles in inflammation and tumor metastasis. We identified an OPN isoform, OPNc, that is selectively inducible by nicotine and highly expressed in PDA tissue from smokers. In this study, we explored the potential proinflammatory role of nicotine in PDA through studying its effect on the expression of monocyte chemoattractant protein (MCP)-1 and evaluated the role of OPN in mediating these effects.

METHODS

MCP-1 mRNA and protein in PDA cells treated with or without nicotine (3-300 nmol/L) or OPN (0.15-15 nmol/L) were analyzed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Luciferase-labeled promoter studies evaluated the effects of nicotine and OPN on MCP-1 transcription. Intracellular and tissue colocalization of OPN and MCP-1 were examined by immunofluorescence and immunohistochemistry.

RESULTS

Nicotine treatment significantly increased MCP-1 expression in PDA cells. Interestingly, blocking OPN with siRNA or OPN antibody abolished these effects. Transient transfection of the OPNc gene in PDA cells or their treatment with recombinant OPN protein significantly (P < .05) increased MCP-1 mRNA and protein and induced its promoter activity. MCP-1 was found in 60% of invasive PDA lesions, of whom 66% were smokers. MCP-1 colocalized with OPN in PDA cells and in the malignant ducts, and correlated well with higher expression levels of OPN in the tissue from patients with invasive PDA.

CONCLUSION

Our data suggest that cigarette smoking and nicotine may contribute to PDA inflammation by inducing MCP-1 and provide a novel insight into a unique role for OPN in mediating these effects.

Osteopontin expression is an independent adverse prognostic factor in resectable gastrointestinal stromal tumor and its interaction with CD44 promotes tumor proliferation

BACKGROUND

Osteopontin (OPN) is a multifunctional secreted glycophosphoprotein involved in miscellaneous physiologic and pathologic processes and is functionally related to the transmembrane receptor CD44. Although OPN expression has been identified to be associated with poor prognosis in several gastrointestinal malignancies, its expression in gastrointestinal stromal tumor (GIST) has not been thoroughly investigated. This study was designed to evaluate the clinicopathologic significance of OPN expression in patients with resectable GIST.

METHODS

OPN expression was analyzed for its clinicopathologic significance in surgical specimens from 99 patients with resectable GIST by immunohistochemistry. In situ Proximity Ligation Assay was used for examining OPN and CD44 interaction in tumor tissues and GIST cell lines. The in vitro effects of OPN and its interaction with CD44 also were assessed.

RESULTS

Increased OPN expression was a significant poor prognostic factor that independently predicted recurrence and poor disease-free survival in patients with resectable GIST. The interaction of OPN and CD44 was confirmed by their significant correlation in both GIST tumor tissues and cell lines by in situ Proximity Ligation Assay analysis. OPN and its interaction with CD44 were related to increased mitosis and significantly enhanced GIST tumor cell proliferation in vitro.

CONCLUSIONS

Our study identified the clinicopathologic significance and biologic effects of OPN expression in resectable GIST. Increased OPN expression was an independent poor prognostic factor and its interaction with CD44 significantly correlated with increased mitosis as well as in vitro proliferation-promoting effects.

Biomarkers for prediction of metastasis and recurrence of hepatocellular carcinoma

The metastasis of hepatocellular carcinoma (HCC) has long been recognized as a multi-step process that involves multiple factors. Instead of diagnostic models based on single-molecule detection, the combination of multiple molecules will be the trend for early tumor diagnosis or prediction of tumor metastasis and recurrence. Many differentially expressed metastasis-associated genes and proteins have been reported in HCC. This article gives an overview of protein biomarkers for prediction of HCC metastasis and recurrence.

RhoGTPases and Rho-effectors in hepatocellular carcinoma metastasis: ROCK N'Rho move it

Hepatocellular carcinoma (HCC) is an intractable disease with an extremely high mortality rate. Metastasis is the major factor of liver failure, tumour recurrence and death in HCC patients. Unfortunately, no promising curative therapy for HCC metastasis is available as yet; therefore, treatment for advanced HCC still remains a formidable challenge. A large body of evidence has demonstrated that the RhoGTPases/Rho-effector pathway plays important roles in mediating HCC metastasis based on their foremost functions in orchestrating the cell cytoskeletal reorganization. This review will first discuss the general principles of cancer metastasis and cancer cell movement with a particular focus on HCC.We will then summarize the implications of various members in the RhoGTPases/Rho-effectors signalling cascade including the upstream RhoGTPase regulators RhoGTPases and Rho-effectors and their downstream targets in HCC metastasis. Finally, we will discuss the therapeutic insight of targeting the RhoGTPases/Rho-effector pathway in HCC. Taken together, the literature demonstrates the importance of the RhoGTPases/Rho-effector signalling pathway in HCC metastasis and marks the necessity to have a more thorough knowledge of this complicated signalling network in order to develop novel therapeutic strategies for HCC patients.

Elevated tumor and serum levels of the hypoxia-associated protein osteopontin are associated with prognosis for soft tissue sarcoma patients

BACKGROUND

Osteopontin (OPN) overexpression is correlated with a poor prognosis for tumor patients. However, only a few studies investigated the prognostic impact of expression of OPN in soft tissue sarcomas (STS) yet.

METHODS

This study is based on tumor and serum samples from 93 adult STS patients. We investigated OPN protein levels in serum (n = 86) and tumor tissue (n = 80) by ELISA and OPN mRNA levels in tumor tissue (n = 68) by quantitative real-time PCR.

RESULTS

No correlation was found between OPN levels in serum and tumor tissue. Moreover, an elevated OPN protein level in the serum was significantly associated with clinical parameters such as higher stage (p = 0.004), higher grade (p = 0.003), subtype (p = 0.002) and larger tumor size (p = 0.03). OPN protein levels in the tumor tissue were associated with higher stage (p = 0.06), higher grade (p = 0.003), subtype (p = 0.07) and an increased rate of relapse (p = 0.02). In addition, using a Cox's proportional hazards regression model, we found that an elevated OPN protein level in the serum and tumor tissue extracts is a significant negative prognostic factor for patients with STS. The relative risks of tumor-related death were 2.2 (p < 0.05) and 3.7 (p = 0.01), respectively.

CONCLUSION

Our data suggest OPN protein in serum as well as in tumor tissue extracts is an important prognostic factor for soft tissue sarcoma patients.

CD44, a therapeutic target for metastasising tumours

Members of the CD44 family of transmembrane glycoproteins, in particular CD44v6 isoforms, were shown to be metastatic determinants of rat pancreatic tumour cells back in the early 1990s. Furthermore, the expression of several CD44 proteins correlates with aggressive stages of various human cancers. Because of the frequent and homogeneous expression of CD44v6 isoforms in squamous cell carcinoma, antibodies recognising these proteins were used in clinical trials for patients suffering from head and neck squamous cell carcinoma (HNSCC). Although the phase I clinical trials looked promising, the studies were abruptly ended after the death of a patient. Despite the termination of the trials, CD44 certainly remains a valid target for anti-cancer therapy. In this review, alternative strategies targeting CD44 functions are presented. These functions include the binding to hyaluronan (HA), the collaboration with osteopontin and the contribution of CD44 isoforms to receptor tyrosine kinase (RTKs) activation. These new attempts led to the development of peptides that interfere for example with HA binding and that might be used to induce apoptosis in mammary carcinoma or to prevent homing of leukaemia stem cells. Other peptides block RTK activation and thereby inhibit tumour angiogenesis and metastatic spread.

Clinical implication and mitotic effect of CD44 cleavage in relation to osteopontin/CD44 interaction and dysregulated cell cycle protein in gastrointestinal stromal tumor

BACKGROUND

CD44 and osteopontin (OPN) are functionally related molecules that, alone or in combination, play miscellaneous biological and pathophysiologic roles. CD44 cleavage, one unique feature of CD44, occurs in human cancers, but its function remains unclear. This study aimed to assess the clinicopathologic significance and mechanism of CD44 cleavage in gastrointestinal stromal tumor (GIST) with respect to OPN and OPN/CD44 interaction.

MATERIALS AND METHODS

CD44 cleavage was evaluated by immunoblotting in 31 primary GIST tumor specimens with paired normal tissues. OPN/CD44 interaction was examined by in situ proximity ligation assay. The associations of CD44 cleavage activity with clinicopathologic parameters, cyclin D1 expression, beta-catenin expression, OPN expression, and OPN/CD44 interaction were analyzed.

RESULTS

CD44 cleavage activity was demonstrated in 87.1% of GIST, in contrast to its absence in normal tissues. Increased CD44 cleavage activity was significantly associated with enhanced mitosis by multivariate analysis, in addition to being related to tumor size, recurrence, high-risk status, and poor survival by univariate analysis. Mitosis was significantly higher in GIST with increased CD44 cleavage activity, which also positively correlated with tumor-specific beta-catenin and cyclin D1 overexpression, indicating a mitotic effect through aberrant cell cycle. Both OPN and OPN/CD44 interactions were significantly associated with CD44 cleavage.

CONCLUSION

Our study demonstrates the clinicopathological significance of CD44 cleavage in GIST. There is a significantly increased mitosis associated with CD44 cleavage in relation to OPN/CD44 interaction and dysregulated cell cycle in GIST.

Expression pattern of osteopontin splice variants and its functions on cell apoptosis and invasion in glioma cells

Osteopontin (OPN) is widely overexpressed in various cancers, including gliomas, and plays an important role in tumorigenesis. However, the expression pattern and functions of OPN splice variants expressed in gliomas remain unclear. The aims of our current study were to examine the expression pattern and functions of OPN splice variants in gliomas. In present study, the mRNA levels of OPN splice variants are markedly increased in gliomas tissues, and all OPN splice variants were also found in U251 and U87 cells. Furthermore, knock-down and regain of function experiments were designed to explore the functions of OPN splice variants in U251 and U87 cells. Lentiviral vectors of OPN small interference RNA (siRNA) targeting all three endogenous mRNAs of OPN and OPN splice variants synonymous mutant that were not silenced by OPN siRNA were constructed. Our results showed that all OPN splice variants synonymous mutant-protected glioma cells from apoptosis induced by OPN siRNA through alteration of the levels of Bcl-2 family proteins and OPN-b Mu elicted a significant effect. Both OPN-a Mu and -c Mu promoted glioma cell invasion through alteration of the levels of uPA, MMP-2, and MMP-9 expressions and the activities of MMP-2 and MMP-9 via activation PI-3K/AKT/NF-kappaB signaling pathway. Moreover, OPN-c Mu showed the strongest effect on glioma cell invasion, while OPN-b Mu showed no effect on the invasion of U251 and U87 cells. Thus, different splice variants of OPN have divergent functions in regulating apoptosis and invasion of glioma cells, which broadens their importance in glioma biotherapy.

Osteopontin is cleaved at multiple sites close to its integrin-binding motifs in milk and is a novel substrate for plasmin and cathepsin D

Osteopontin (OPN) is a highly modified integrin-binding protein present in most tissues and body fluids where it has been implicated in numerous biological processes. A significant regulation of OPN function is mediated through phosphorylation and proteolytic processing. Proteolytic cleavage by thrombin and matrix metalloproteinases close to the integrin-binding Arg-Gly-Asp sequence modulates the function of OPN and its integrin binding properties. In this study, seven N-terminal OPN fragments originating from proteolytic cleavage have been characterized from human milk. Identification of the cleavage sites revealed that all fragments contained the Arg-Gly-Asp(145) sequence and were generated by cleavage of the Leu(151)-Arg(152), Arg(152)-Ser(153), Ser(153)-Lys(154), Lys(154)-Ser(155), Ser(155)-Lys(156), Lys(156)-Lys(157), or Phe(158)-Arg(159) peptide bonds. Six cleavages cannot be ascribed to thrombin or matrix metalloproteinase activity, whereas the cleavage at Arg(152)-Ser(153) matches thrombin specificity for OPN. The principal protease in milk, plasmin, hydrolyzed the same peptide bond as thrombin, but its main cleavage site was identified to be Lys(154)-Ser(155). Another endogenous milk protease, cathepsin D, cleaved the Leu(151)-Arg(152) bond. OPN fragments corresponding to plasmin activity were also identified in urine showing that plasmin cleavage of OPN is not restricted to milk. Plasmin, but not cathepsin D, cleavage of OPN increased cell adhesion mediated by the alpha(V)beta(3)- or alpha(5)beta(1)-integrins. Similar cellular adhesion was mediated by plasmin and thrombin-cleaved OPN showing that plasmin can be a potent regulator of OPN activity. These data show that OPN is highly susceptible to cleavage near its integrin-binding motifs, and the protein is a novel substrate for plasmin and cathepsin D.

Identification of tyrosine-phosphorylated proteins associated with metastasis and functional analysis of FER in human hepatocellular carcinoma cells

BACKGROUND

Aberrant activity of tyrosine-phosphorylated proteins is commonly associated with HCC metastasis. Cell signaling events driven by these proteins are implicated in numerous processes that alter cancer cell behavior. Exploring the activities and signaling pathways of these proteins in HCC metastasis may help in identifying new candidate molecules for HCC-targeted therapy.

METHODS

Hep3B (a nonmetastatic HCC cell line) and MHCC97H (a highly metastatic HCC cell line) were used in this study, and the tyrosine-phosphorylated proteins expressed in these cell lines were profiled by a phosphoproteomics technique based on LC-MS/MS. Protein-protein interaction and functional clustering analyses were performed to determine the activities of the identified proteins and the signaling pathways closely related to HCC metastasis.

RESULTS

In both cell lines, a total of 247 phosphotyrosine (pTyr) proteins containing 281 pTyr sites were identified without any stimulation. The involvement of almost 30% of these in liver or liver cancer has not been reported previously. Biological process clustering analysis indicated that pTyr proteins involved in cell motility, migration, protein autophosphorylation, cell-cell communication, and antiapoptosis functions were overexpressed during metastasis. Pathway clustering analysis revealed that signaling pathways such as those involved in EGFR signaling, cytokine- and chemokine-mediated signal transduction, and the PI3K and JAK-STAT cascades were significantly activated during HCC metastasis. Moreover, noncanonical regulation of the JNK cascade might also provide new targets for HCC metastasis. After comparing the pTyr proteins that were differentially expressed during HCC cell metastasis, we selected FER, a nonreceptor tyrosine kinase, and validated its role in terms of both expression and function. The data confirmed that FER might play a critical role in the invasion and metastasis of HCC.

CONCLUSION

The identification of pTyr proteins and signaling pathways associated with HCC metastasis could provide useful information for selecting new molecular intervention targets. Moreover, FER might serve as a novel drug target in future HCC therapy.

The role of osteopontin in inflammatory processes

Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions. OPN is involved in normal physiological processes and is implicated in the pathogenesis of a variety of disease states, including atherosclerosis, glomerulonephritis, cancer, and several chronic inflammatory diseases. Through interactions with several integrins, OPN mediates cell migration, adhesion, and survival in many cell types. OPN also functions as a Th1 cytokine, promotes cell-mediated immune responses, and plays a role in chronic inflammatory and autoimmune diseases. Besides its function in inflammation, OPN is also a regulator of biomineralization and a potent inhibitor of vascular calcification.

Expression of a prometastatic splice variant of osteopontin, OPNC, in human pancreatic ductal adenocarcinoma

BACKGROUND

Osteopontin (OPN) is a secreted phosphoprotein that confers on cancer cells a migratory phenotype. We demonstrated recently that nicotine, a major risk factor in pancreatic ductal adenocarcinoma (PDA), increases OPN expression in PDA cells. An OPN splice variant, OPNc, supports anchorage independence and maybe the most potent OPN isoform to convey metastatic behavior. In this study, we tested the effect of nicotine on OPNc expression and analyzed the correlation between total OPN/OPNc levels and patients' smoking history.

METHODS

Real-time polymerase chain reaction and ultraviolet light illumination of ethidium-bromide staining were used to examine the mRNA expression in tissue and in PDA cells treated with or without nicotine (3-300 nmol/L). OPN and OPNc were localized by immunohistochemistry, and an enzyme-linked immunosorbent assay was used to analyze OPN serum levels.

RESULTS

Nicotine treatment of PDA cells selectively induced de novo expression of OPNc. OPNc was found in 87% of invasive PDA lesions, of which 73% were found in smokers. The levels of OPNc correlated well with higher expression levels of total OPN in the tissue and serum from patients with invasive PDA.

CONCLUSION

Our data suggest that smoking and nicotine may contribute to PDA metastatic potential through promoting OPNc expression. Although the direct role of OPNc in PDA progression is not defined, OPNc may have value as a diagnostic and prognostic marker, especially in invasive PDA.

Role of osteopontin and CD44s expression for patients with hepatocellular carcinoma undergoing liver transplantation or resection

BACKGROUND

Detection of new biomarkers for hepatocellular carcinoma (HCC) is needed to estimate prognosis after liver transplantation (OLT) or hepatic resection. Osteopontin (OPN) is a secreted, calcium-binding, phosphorylated, acidic glycoprotein that is overexpressed in various cancers. Cluster differentiation 44 standard isoform (CD44s) is one of the primary receptors of OPN; it may contribute to metastatic tumor spread.

MATERIALS AND METHODS

Tumor tissue and surrounding hepatic parenchyma were obtained from 53 HCC patients who underwent liver resection. Their RNA was extracted from nitrogen-frozen tissues, and OPN mRNA levels were estimated by quantitative reverse transcription-polymerase chain reactions. Formalin-fixed, paraffin-embedded tissues were obtained from the same patients, and additionally from 60 OLT HCC patients to perform expression analysis for OPN and CD44s by standard avidin-biotin immunostaining methods.

RESULTS

Expression of OPN and CD44s was significantly higher among HCC compared with adjacent nontumor tissue. The OPN mRNA expression and protein abundance correlated positively; OPN overexpression was associated with high tumor grade. A positive correlation existed between OPN and CD44s expression; both proteins were significantly overexpressed in HCC lesions with positive lymph nodes. No significant correlation existed between patient survival and OPN and CD44s expression.

CONCLUSION

Expression of both OPN and CD44s in HCC is associated with advanced tumor stage, thus possibly contributing prognostic information when evaluated together with classical clinicopathological parameters.

MicroRNAs: target recognition and regulatory functions

MicroRNAs (miRNAs) are endogenous approximately 23 nt RNAs that play important gene-regulatory roles in animals and plants by pairing to the mRNAs of protein-coding genes to direct their posttranscriptional repression. This review outlines the current understanding of miRNA target recognition in animals and discusses the widespread impact of miRNAs on both the expression and evolution of protein-coding genes.

Activation of the osteopontin/matrix metalloproteinase-9 pathway correlates with prostate cancer progression

PURPOSE

Prostate cancer remains the second most frequent cause of tumor-related deaths in the Western world. Additional markers for the identification of prostate cancer development and progression are needed. Osteopontin (OPN), which activates matrix metalloproteinases (MMP), is considered a prognostic biomarker in several cancers. "In silico" and experimental approaches were used to determine whether OPN-mediated MMP activation may be a signal of prostate cancer progression.

EXPERIMENTAL DESIGN

Pearson correlation coefficients were computed for each OPN/MMP pair across seven publicly available prostate cancer gene expression data sets. Using Gene Set Enrichment Analysis, 101 cancer-related gene sets were analyzed for association with OPN and MMP-9 expression. OPN, MMP-9, MMP-2 tissue inhibitor of metalloproteinase-1 plasma levels, and MMP gelatinase activity were measured by ELISA and zymography in 96 and 92 patients with prostate cancer and benign prostatic hyperplasia, respectively, and 125 age-matched healthy men.

RESULTS

Computational analyses identified a significant correlation only between MMP-9 and OPN, and showed significant enrichment scores in "cell proliferation", "genes constituting the phosphoinositide-3-kinase predictor", "proliferation signature", and "tumor metastasis" gene sets in association with both OPN and MMP-9. Plasma analyses revealed a significant increase in OPN and MMP-9 levels and activity in patients with prostate cancer in association with clinical variables (prostate-specific antigen > 4 ng/mL and Gleason score > 7). Significant correlation between OPN and MMP-9 levels were also observed. Mean plasma levels of OPN and MMP-9 decreased in patients with prostate cancer within 6 months after prostatectomy.

CONCLUSIONS

The concordant computational and experimental data indicate that the extent of OPN pathway activation correlates with prostate cancer progression.

Overexpression of osteopontin independently correlates with vascular invasion and poor prognosis in patients with hepatocellular carcinoma

This study retrospectively evaluated the immunohistochemical expression of 3 cell adhesion molecules (CAMs), E-cadherin, beta-catenin, and osteopontin, according to tumor grade in 125 surgically resected specimens of hepatocellular carcinoma (HCC). The aims of this study were to identify factors associated with vascular invasion and to elucidate the prognostic value of CAMs. The median follow-up time was 110 months. The levels of E-cadherin, beta-catenin, and osteopontin immunoreactivity were significantly associated with Edmondson-Steiner grade but not with tumor size. There was increased loss of E-cadherin, nonnuclear overexpression of beta-catenin, and overexpression of osteopontin in tumors of higher histologic grade. Vascular invasion was found in 44 (35%) of 125 resected specimens. Logistic regression analysis identified 3 tumor-related factors that were independently associated with vascular invasion-tumor size more than 3 cm, Edmondson-Steiner grades III to IV, and overexpression of osteopontin. Among the tested CAMs, osteopontin (P = .0110) and E-cadherin (P = .0287) were significant prognostic factors by univariate analysis. The Cox proportional hazard regression analysis revealed that Edmondson-Steiner grades III to IV (relative risk [RR], 3.028; P < .001), the presence of vascular invasion (RR, 1.964; P = .011), overexpression of osteopontin (RR, 1.755; P = .034), serum alpha-fetoprotein level more than 20 ng/mL (RR, 1.834; P = .037), and Child-Pugh classification B to C (RR, 1.880; P = .040) were found to be independently significant factors associated with survival after hepatectomy. These results suggest that overexpression of osteopontin independently correlates with vascular invasion and thus predicts poor survival for patients with HCC, whereas aberrant expression of E-cadherin or beta-catenin does not.

DLC1 suppresses distant dissemination of human hepatocellular carcinoma cells in nude mice through reduction of RhoA GTPase activity, actin cytoskeletal disruption and down-regulation of genes involved in metastasis

The process of cell dissemination from the primary tumors to distant sites is the most harmful event during cancer progression, and the leading cause of cancer death. We have previously demonstrated that restoration of DLC1 tumor suppressor gene expression in the DLC1-negative Focus and 7703K human hepatocellular carcinoma (HCC) cell lines induced caspase-3 mediated apoptosis, reduced cell growth in vitro and tumorigenicity in vivo and diminished the ability to migrate through Matrigel, a property suggestive of metastatic potential in vivo. We now show that subcutaneous tumors developing after inoculation of Focus and 7703K cells into nude mice disseminate cells to liver and lung, and this process is markedly suppressed by restoration of DLC1 expression. Inhibition of tumor cell dissemination was associated with lower levels of RhoA activity, an increase in rounded cells and a reduction in actin stress fibers and focal adhesion molecules that are of critical importance in cancer cell invasion and metastasis. In addition, DLC1 down-regulated the expression of osteopontin and matrix metalloproteinase-9, which are highly up-regulated in most primary HCC with associated metastases. These observations implicate the DLC1 gene in suppression of HCC cell dissemination and identify novel cellular and genetic alterations that contribute to prevention of metastasis, a life-threatening event in cancer progression.

Bone marrow microenvironment and tumor progression

The bone marrow constitutes an unique microenvironment for cancer cells in three specific aspects. First, the bone marrow actively recruits circulating tumor cells where they find a sanctuary rich in growth factors and cytokines that promote their proliferation and survival. When in the bone marrow, tumor cells profoundly affect the homeostasis of the bone and the balance between osteogenesis and osteolysis. As a consequence, growth and survival factors normally sequestered into the bone matrix are released, further fueling cancer progression. Second, tumor cells actively recruit bone marrow-derived precursor cells into their own microenvironment. When in the tumors, these bone marrow-derived cells contribute to an inflammatory reaction and to the formation of the tumor vasculature. Third, bone marrow-derived cells can home in distant organs, where they form niches that attract circulating tumor cells. Our understanding of the contribution of the bone marrow microenvironment to cancer progression has therefore dramatically improved over the last few years. The importance of this new knowledge cannot be underestimated considering that the vast majority of cancer treatments such as cytotoxic and myeloablative chemotherapy, bone marrow transplantation and radiation therapy inflict a trauma to the bone marrow microenvironment. How such trauma affects the influence that the bone marrow microenvironment exerts on cancer is still poorly understood. In this article, the reciprocal relationship between the bone marrow microenvironment and tumor cells is reviewed, and its potential impact on cancer therapy is discussed.

Identification of metastasis-related microRNAs in hepatocellular carcinoma

MicroRNAs (miRNAs) have been used as cancer-related biomarkers. Hepatocellular carcinoma (HCC) is an aggressive cancer with a dismal outcome largely due to metastasis and postsurgical recurrence. We investigated whether the expression of certain miRNAs are associated with HCC metastasis. We examined the miRNA expression profiles of 482 cancerous and noncancerous specimens from radical resection of 241 patients with HCC. Using a supervised algorithm and a clinically well-defined cohort of 131 cases, we built a unique 20-miRNA metastasis signature that could significantly predict (P < 0.001) primary HCC tissues with venous metastases from metastasis-free solitary tumors with 10-fold cross-validation. However, significant miRNAs could not be identified from the corresponding noncancerous hepatic tissues. A survival risk prediction analysis revealed that a majority of the metastasis-related miRNAs were associated with survival. Furthermore, the 20-miRNA tumor signature was validated in 110 additional cases as a significant independent predictor of survival (P = 0.009) and was significantly associated with both survival and relapse in 89 cases of early stage HCC (P = 0.022 and 0.002, respectively). These 20 miRNAs may provide a simple profiling method to assist in identifying patients with HCC who are likely to develop metastases/recurrence. In addition, functional analysis of these miRNAs may enhance our biological understanding of HCC metastasis.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Development of fragment-specific osteopontin antibodies and ELISA for quantification in human metastatic breast cancer

Background

Osteopontin (OPN) is associated with human cancers, and circulating blood OPN may have diagnostic or prognostic value in clinical oncology.

Methods

To evaluate OPN as a cancer biomarker, we generated and characterized five novel mouse monoclonal antibodies against the human full-length OPN (fl-OPN). Epitopes recognized by four antibodies (2C5, 2F10, 2H9, and 2E11) map to N-terminal OPN (aa1-166); one (1F11) maps to C-terminal OPN (aa167-314). These antibodies recognize recombinant and native OPN by ELISA and immunoblot, cross reacting with human and mouse OPN. Two of these novel antibodies (2F10 and 1F11) were used to develop a quantitative enzyme linked immunosorbent assay (ELISA) for fl-OPN.

Results

In comparison with commercially available ELISAs, our assay had high accuracy in measuring fl-OPN standards, and high sensitivity. Specifically, our ELISA has a linear dose response between 0.078 ng/ml-10 ng/ml, with a sensitivity of 13.9 pg/ml. We utilized this assay to quantify fl-OPN in the plasma of healthy volunteers in comparison with patients with metastatic breast cancer. The average circulating plasma fl-OPN in healthy volunteers was 1.2 ng/ml, compared to 4.76 ng/ml in patients with metastatic breast cancer (p = 0.0042). Although the increase in fl-OPN in cancer patients is consistent with previous studies, the measured quantity varied greatly between all existing fl-OPN ELISAs.

Conclusion

Because OPN is a complex molecule with diversity from alternative splicing, post-translational modification, extracellular proteolytic modification, and participation in protein complexes, we suggest that further understanding of specific isoform recognition of multiple OPN species is essential for future studies of OPN biomarker utility.