A biochemical characterization of the binding of osteopontin to integrins alpha v beta 1 and alpha v beta 5

Osteopontin expression by CD103- dendritic cells drives intestinal inflammation

Intestinal CD103(-) dendritic cells (DCs) are pathogenic for colitis. Unveiling molecular mechanisms that render these cells proinflammatory is important for the design of specific immunotherapies. In this report, we demonstrated that mesenteric lymph node CD103(-) DCs express, among other proinflammatory cytokines, high levels of osteopontin (Opn) during experimental colitis. Opn expression by CD103(-) DCs was crucial for their immune profile and pathogenicity, including induction of T helper (Th) 1 and Th17 cell responses. Adoptive transfer of Opn-deficient CD103(-) DCs resulted in attenuated colitis in comparison to transfer of WT CD103(-) DCs, whereas transgenic CD103(-) DCs that overexpress Opn were highly pathogenic in vivo. Neutralization of secreted Opn expressed exclusively by CD103(-) DCs restrained disease severity. Also, Opn deficiency resulted in milder disease, whereas systemic neutralization of secreted Opn was therapeutic. We determined a specific domain of the Opn protein responsible for its CD103(-) DC-mediated proinflammatory effect. We demonstrated that disrupting the interaction of this Opn domain with integrin α9, overexpressed on colitic CD103(-) DCs, suppressed the inflammatory potential of these cells in vitro and in vivo. These results add unique insight into the biology of CD103(-) DCs and their function during inflammatory bowel disease.

An osteopontin-integrin interaction plays a critical role in directing adipogenesis and osteogenesis by mesenchymal stem cells

An imbalance between normal adipogenesis and osteogenesis by mesenchymal stem cells (MSCs) has been shown to be related to various human metabolic diseases, such as obesity and osteoporosis; however, the underlying mechanisms remain elusive. We found that the interaction between osteopontin (OPN), an arginine-glycine-aspartate-containing glycoprotein, and integrin αv/β1 plays a critical role in the lineage determination of MSCs. Although OPN is a well-established marker during osteogenesis, its role in MSC differentiation is still unknown. Our study reveals that blockade of OPN function promoted robust adipogenic differentiation, while inhibiting osteogenic differentiation. Re-expression of OPN restored a normal balance between adipogenesis and osteogenesis in OPN(-/-) MSCs. Retarded bone formation by OPN(-/-) MSCs was also verified by in vivo implantation with hydroxyapatite-tricalcium phosphate, a bone-forming matrix. The role of extracellular OPN in MSC differentiation was further demonstrated by supplementation and neutralization of OPN. Blocking well-known OPN receptors integrin αv/β1 but not CD44 also affected MSC differentiation. Further studies revealed that OPN inhibits the C/EBPs signaling pathway through integrin αv/β1. Consistent with these in vitro results, OPN(-/-) mice had a higher fat to total body weight ratio than did wild-type mice. Therefore, our study demonstrates a novel role for OPN-integrin αv/β1 in regulating MSC differentiation.

Osteopontin mediates macrophage chemotaxis via α4 and α9 integrins and survival via the α4 integrin

Osteopontin (OPN) is highly expressed by macrophages and plays a key role in the pathology of several chronic inflammatory diseases including atherosclerosis and the foreign body reaction. However, the molecular mechanism behind OPN regulation of macrophage functions is not well understood. OPN is a secreted molecule and interacts with several integrins via two domains: the RGD sequence binding to α(v) -containing integrins, and the SLAYGLR sequence binding to α(4) β(1), α(4) β(7), and α(9) β(1) integrins. Here we determined the role of OPN in macrophage survival, chemotaxis, and activation state. For survival studies, OPN treated-bone marrow derived macrophages (BMDMs) were challenged with growth factor withdrawal and neutralizing integrin antibodies. We found that survival in BMDMs is mediated primarily through the α(4) integrin. In chemotaxis studies, we observed that migration to OPN was blocked by neutralizing α(4) and α(9) integrin antibodies. Further, OPN did not affect macrophage activation as measured by IL-12 production. Finally, the relative contributions of the RGD and the SLAYGLR functional domains of OPN to leukocyte recruitment were evaluated in an in vivo model. We generated chimeric mice expressing mutated forms of OPN in myeloid-derived leukocytes, and found that the SLAYGLR functional domain of OPN, but not the RGD, mediates macrophage accumulation in response to thioglycollate-elicited peritonitis. Collectively, these data indicate that α(4) and α(9) integrins interacting with OPN via the SLAYGLR domain play a key role in macrophage biology by regulating migration, survival, and accumulation.

Binding of αvβ1 and αvβ6 integrins to tenascin-C induces epithelial-mesenchymal transition-like change of breast cancer cells

Tenascin-C (TNC), a large hexameric extracellular glycoprotein, is a pleiotropic molecule with multiple domains binding to a variety of receptors mediating a wide range of cellular functions. We earlier reported that TNC induces epithelial–mesenchymal transition (EMT)-like change in breast cancer cells. In the present study, we clarified TNC receptor involvement in this process. Among integrins previously reported as TNC receptors, substantial expression of αv, α2, β1 and β6 subunits was detected by quantitative PCR and immunoblotting in MCF-7 cells. Integrin β6 mRNA was remarkably upregulated by transforming growth factor (TGF)-β1 treatment, and protein expression was prominently increased by additional exposure to TNC. Immunofluorescent labeling demonstrated integrin αvβ6 accumulation in focal adhesions after TNC treatment, especially in combination with TGF-β1. The α2 and β1 subunits were mainly localized at cell–cell contacts, αv being found near cell cluster surfaces. Immunoprecipitation showed increase in αvβ1 heterodimers, but not α2β1, after TNC treatment. Activated β1 subunits detected by an antibody against the Ca²⁺-dependent epitope colocalized with αv in focal adhesion complexes, associated with FAK phosphorylation at tyrosine 925. Neutralizing antibodies against αv and β1 blocked EMT-like change caused by TNC alone. In addition, anti-αv and combined treatment with anti-β1 and anti-αvβ6 inhibited TGF-β1/TNC-induced EMT, whereas either of these alone did not. Integrin subunits αv, β1 and β6, but not α2, bound to TNC immobilized on agarose beads in a divalent cation-dependent manner. Treatments with neutralizing antibodies against β1 and αvβ6 reduced αv subunit bound to the beads. Immunohistochemistry of these receptors in human breast cancer tissues demonstrated frequent expression of β6 subunits in cancer cells forming scattered nests localized in TNC-rich stroma. These findings provide direct evidence that binding of αvβ6 and αvβ1 integrins to TNC as their essential ligand induces EMT-like change in breast cancer cells.

Mechanistic mammalian target of rapamycin (MTOR) cell signaling: effects of select nutrients and secreted phosphoprotein 1 on development of mammalian conceptuses

Morphological differentiation of uterine glands in mammals is a postnatal event vulnerable to adverse effects of endocrine disruptors. Exposure of ewe lambs to a progestin from birth to postnatal day 56 prevents development of uterine glands and, as adults, the ewes are unable to exhibit estrous cycles or maintain pregnancy. Uterine epithelia secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling and implantation, including arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate MTOR cell signaling to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds αvβ3 and α5β1 integrins and induces focal adhesion assembly, adhesion and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation.

Prognostic significance of bone markers in patients with lung cancer metastatic to the skeleton: a review of published data

The presence of bone metastases significantly affects clinical outcome and quality of life parameters in patients with lung cancer. In this review, we aimed to evaluate the predictive value of markers of bone turnover in skeletal morbidity and clinical parameters, including disease-free survival (DFS) and overall survival (OS), in patients with lung cancer metastatic to the skeleton who were receiving bisphosphonate treatment. A comprehensive overview of all articles published from 1995 to date in 3 medical databases (PubMed, Scopus, and Cochrane) was performed using the keywords bone markers and lung cancer. Most bone formation markers (including bone alkaline phosphatase [bALP], osteocalcin [OC], and osteoprotegerin [OPG]), most bone absorption markers (including urinary calcium, osteopontin [OPN], receptor activator of nuclear factor κ-B ligand [RANKL], tartrate-resistant acid phosphatase isoform-5b [TRACP 5b]), and the metabolites of type I collagen had elevated concentrations in patients with lung cancer and bone metastases compared with patients without skeletal involvement. Two large studies showed that urinary N-terminal telopeptide (NTX) levels are a valid diagnostic method for early detection of bone metastases and a more consistent prognosticator than bALP. Treatment with zoledronic acid reduces NTX, TRACP-5b, RANKL, and OPG levels. Furthermore posttherapeutic reduction of urinary NTX levels seems to correlate with lower risk of skeletal-related events (SREs). Levels of markers of bone remodeling reflect the presence of bone metastases and may contribute to early detection of occult skeletal disease or monitor the effect of bisphosphonate treatment. However their ability to predict SREs, as well as DFS and OS, remains debatable.

Osteopontin in macrophage function

The secreted phosphorylated protein osteopontin (OPN) is expressed in a variety of tissues and bodily fluids, and is associated with pathologies including tissue injury, infection, autoimmune disease and cancer. Macrophages are ubiquitous, heterogeneous cells that mediate aspects of cell and tissue damage in all these pathologies. Here, the role of OPN in macrophage function is reviewed. OPN is expressed in macrophage cells in multiple pathologies, and the regulation of its expression in these cells has been described in vitro. The protein has been implicated in multiple functions of macrophages, including cytokine expression, expression of inducible nitric oxide synthase, phagocytosis and migration. Indeed, the role of OPN in cells of the macrophage lineage might underlie its physiological role in many pathologies. However, there are numerous instances where the published literature is inconsistent, especially in terms of OPN function in vitro. Although the heterogeneity of OPN and its receptors, or of macrophages themselves, might underlie some of these inconsistencies, it is important to understand the role of OPN in macrophage biology in order to exploit its function therapeutically.

The extracellular matrix dimension of skeletal muscle development

Cells anchor to substrates by binding to extracellular matrix (ECM). In addition to this anchoring function however, cell-ECM binding is a mechanism for cells to sense their surroundings and to communicate and coordinate behaviour amongst themselves. Several ECM molecules and their receptors play essential roles in muscle development and maintenance. Defects in these proteins are responsible for some of the most severe muscle dystrophies at every stage of life from neonates to adults. However, recent studies have also revealed a role of cell-ECM interactions at much earlier stages of development as skeletal muscle forms. Here we review which ECM molecules are present during the early phases of myogenesis, how myogenic cells interact with the ECM that surrounds them and the potential consequences of those interactions. We conclude that cell-ECM interactions play significant roles during all stages of skeletal muscle development in the embryo and suggest that this "extracellular matrix dimension" should be added to our conceptual network of factors contributing to skeletal myogenesis.

Osteopontin, intrinsic tissue regulator of intractable inflammatory diseases

Within classical extracellular matrix (ECM) proteins, there are a unique group of proteins that should be regarded as a distinct functional group of molecules. Matricellular proteins including osteopontin (OPN) and tenascin-c (TN-C) are highly expressed at the pathological foci of various inflammatory diseases. Unlike classical ECM proteins, these are soluble proteins and induce cell motility and persistent inflammation rather than providing a scaffold for stable cell adhesion. Osteopontin is a pleiotropic cytokine expressed by various cells. Two forms of OPN are present. A secreted form of OPN (sOPN) is involved in generation of T helper type 1 (Th1) and Th17 cells that are pathogenic T cells for various autoimmune diseases. An intracellular form of OPN (iOPN) is a critical regulator for Toll like receptor-9 (TLR-9) and/or TLR-7-dependent interferon-α (IFN-α) expression by plasmacytoid dendritic cells (DCs) and Th17 development. Indeed, both OPN and TN-C deficient mice are resistant to various Th1- and/or Th17-related autoimmune diseases. Interestingly, thrombin-cleaved forms of sOPN and TN-C share a common integrin receptor, α9β1, and α9β1 integrin-mediated signaling is involved in the pathogenesis of various autoimmune diseases. Thus, OPN, TN-C and its common receptor, α9β1 integrin may serve as potential therapeutic targets for various intractable inflammatory diseases.

AlphaV-integrins mediate the mechanoprotective action of osteopontin in podocytes

Increased mechanical load in podocytes due to glomerular hypertension is one of the important factors leading to podocyte damage and chronic kidney disease. In previous studies, we have shown that mechanical stretch increases osteopontin (OPN) expression in podocytes and that exogenous OPN is mechanoprotective via facilitating cytoskeletal reorganization of podocytes. In the present study, we asked whether the mechanoprotective effect of OPN in podocytes is mediated through specific integrins and whether endogenous OPN of podocytes is required for mechanoprotection. Conditionally immortalized mouse podocytes and primary podocytes (PP) from OPN-/- and OPN+/+ mice were used. Cyclic biaxial mechanical stretch (0.5 Hz, 7% linear strain) was applied for up to 3 days. Stretch-induced cell loss was ∼30% higher in OPN-/- PP compared with OPN+/+ PP. Increased cell loss of OPN-/- PP was rescued by OPN coating. Analysis of integrin expression by RT-PCR, application of RGD and SLAYGLR peptides and anti-integrin antibodies, small-interfering RNA knockdown of integrins, and application of kinase inhibitors identified αV-integrins (αVβ1, αVβ3, and αVβ5) to mediate the mechano-protective effect of OPN in podocytes involving focal adhesion kinase, Src, phosphatidylinositol 3-kinase, and mitogen-activated protein kinase. Our results demonstrate that endogenous OPN of podocytes plays a nonredundant role in podocyte adaptation to mechanical stretch, and that OPN signaling via α(V)-integrins may represent a relevant therapeutical target in podocytes.

Osteopontin is a new target molecule for ovarian clear cell carcinoma therapy

Recent studies have demonstrated overexpression of osteopontin (OPN) in ovarian clear cell carcinoma. Here, we revealed the role of OPN in invasiveness in ovarian clear cell carcinoma. We used immunofluorescence analysis to detect OPN in a total of 160 patient-derived specimens. Ovarian clear cell carcinoma cell lines, RMG-1 and TOV-21G, were used to monitor changes in OPN and integrin levels, and cell invasiveness following treatment with OPN, simvastatin, and transfection with siRNA. Immunofluorescence analysis revealed statistically significant differences among the histological groups, and ovarian clear cell carcinoma expressed a strong OPN signal. The OPN receptors, alpha v and 5, and beta 1 and 3 integrins, were increased after treatment with OPN. Invasion assays indicated that OPN enhanced in vitro extracellular matrix invasion dose-dependently in ovarian clear cell carcinoma. Simvastatin significantly reduced expression of OPN and the integrins, and decreased ECM invasion. RNA interference also suppressed ECM invasion. These results suggest that down- or up-regulation of OPN is involved in carcinoma cell invasion. We thus conclude that OPN regulation could have a crucial role in ovarian clear cell carcinoma therapy.

Osteopontin promotes gastric cancer metastasis by augmenting cell survival and invasion through Akt-mediated HIF-1alpha up-regulation and MMP9 activation

Osteopontin (OPN) is a secreted, integrin-binding matrix phosphorylated glycoprotein. OPN has been shown to facilitate the progression and metastasis of malignancies and has prognostic value in several types of cancer, including gastric cancer. However, the functional mechanism of OPN mediated metastatic growth in gastric cancer remains unclear. Here, using multiple in vitro and in vivo models, we report that OPN strongly promoted the progression and metastasis of gastric cancer. Immunohistochemical staining revealed that OPN, matrix metalloproteinase (MMP)9 and hypoxia-inducible factor (HIF)-1alpha have statistically significant different expression patterns between well- and poorly differentiated tissue samples (P < 0.05). Correlations existed between OPN and MMP9, and between OPN and HIF-1 (r(1) = 0.872, p(1) < 0.01 and r(2) = 0.878, p(2) < 0.01). Furthermore, OPN dramatically increased colony formation and invasion of gastric cancer cells in vitro and promoted tumour growth and metastasis in vivo. In addition, OPN potently protected gastric cancer cells from serum depletion-induced apoptosis. Further study shows that OPN activated phosphoinositide 3-kinase/Akt survival pathway and up-regulated HIF-1alpha via binding to v3 integrins in gastric cancer cells. Moreover, we found that OPN could activate MMP9 and upregulate MMP2. Taken together, our results suggest that the survival-promoting function is crucial for OPN to promote the development of gastric cancer, and HIF-1 and MMP9 may play key roles during this process. Thus, targeting OPN and its related signalling network may develop an effective therapeutic approach for the management of gastric cancer.

Osteopontin: an effector and an effect of tumor metastasis

Osteopontin (OPN) is a matricellular protein that is produced by multiple tissues in our body and is most abundant in bone. It is also produced by cancer cells and plays a determinative role in the growth, progression and metastasis of cancer. Clinically, OPN has been reported to be upregulated in tumor cells per se; this is also reflected by increased levels of OPN in the circulation. Thus, increased OPN levels the plasma are an effect of tumor growth and progression. Functionally, high OPN levels are determinative of higher incidence of bone metastases in mouse models and are clinically correlated with metastatic bone disease and bone resorption in advanced breast cancer patients. Several research efforts have been made to therapeutically target and inhibit the activities of OPN. In this article we have reviewed OPN in its role as an effector of critical steps in tumor progression and metastasis, with a particular emphasis on its role in facilitating bone metastasis of breast cancer. We have also addressed the role of the host-derived OPN in influencing the malignant behavior of the tumor cells.

Elevated myocardial Na+/H+ exchanger isoform 1 activity elicits gene expression that leads to cardiac hypertrophy

In myocardial disease, elevated expression and activity of Na(+)/H(+) exchanger isoform 1 (NHE1) are detrimental. To better understand the involvement of NHE1, transgenic mice with elevated heart-specific NHE1 expression were studied. N-line mice expressed wild-type NHE1, and K-line mice expressed activated NHE1. Cardiac morphology, interstitial fibrosis, and cardiac function were examined by histological staining and echocardiography. Differences in gene expression between the N-line or K-line and nontransgenic littermates were probed with genechip analysis. We found that NHE1 K-line (but not N-line) hearts developed hypertrophy, including elevated heart weight-to-body weight ratio and increased cross-sectional area of the cardiomyocytes, interstitial fibrosis, as well as depressed cardiac function. N-line hearts had modest changes in gene expression (50 upregulations and 99 downregulations, P < 0.05), whereas K-line hearts had a very strong transcriptional response (640 upregulations and 677 downregulations, P < 0.05). In addition, the magnitude of expression alterations was much higher in K-line than N-line mice. The most significant changes in gene expression were involved in cardiac hypertrophy, cardiac necrosis/cell death, and cardiac infarction. Secreted phosphoprotein 1 and its signaling pathways were upregulated while peroxisome proliferator-activated receptor gamma signaling was downregulated in K-line mice. Our study shows that expression of activated NHE1 elicits specific pathways of gene activation in the myocardium that lead to cardiac hypertrophy, cell death, and infarction.

Gene delivery mediated by recombinant silk proteins containing cationic and cell binding motifs

Silk proteins are biodegradable and biocompatible, and can also be tailored to contain additional features via genetic engineering, suggesting utility for gene delivery. In the present study, novel silk-based block copolymers were bioengineered both with poly(L-lysine) domains to interact with plasmid DNA (pDNA) and RGD, to enhance cell-binding and transfection efficiency. Ionic complexes of these silk-polylysine-RGD block copolymers with pDNA were prepared, characterized and utilized for gene delivery to HeLa cells and human embryonic kidney (HEK) cells. The material systems were characterized by agarose gel electrophoresis, zeta-potentialmeter, atomic force microscopy, and dynamic light scattering. Sizes and charges of the pDNA complexes were regulated by the polymer/nucleotide molar ratio. Samples with 30-lysine residues and 11 RGD sequences, prepared at the ratio of number of amines/phosphates from pDNA (N/P) of 2, had an average solution diameter of 186 nm and showed the highest transfection efficiency. The intracellular distribution of complexes of Cy5-labeled pDNA was investigated by confocal laser scanning microscopy. The Cy5-labeled pDNA was distributed near the cell membrane and around the nuclei, indicating that the pDNA was transferred near the nucleus. The results demonstrated the potential of bioengineered silk proteins with additional functional features as a new family of highly tailored gene delivery systems.

The RGD domain of human osteopontin promotes tumor growth and metastasis through activation of survival pathways

BACKGROUND

Human osteopontin (OPN), a known tumor associated protein, exists in different isoforms, whose function is unclear. It also possesses a RGD domain, which has been implicated in diverse function. Here, we use genetic approaches to systematically investigate the function of the RGD domain in different OPN isoforms on tumor progression and metastasis for 2 different solid tumor models.

METHODOLOGY/PRINCIPAL FINDINGS

Using isoform-specific qRT-PCR, we found that OPN-A and B were the main isoforms overexpressed in evaluated human tumors, which included 4 soft tissue sarcomas, 24 lung and 30 head and neck carcinomas. Overexpression of either OPN-A or B in two different cell types promoted local tumor growth and lung metastasis in SCID mouse xenografts. However, expression of either isoform with the RGD domain either mutated or deleted decreased tumor growth and metastasis, and resulted in increased apoptosis by TUNEL staining. In vitro, whereas mutation of the RGD domain did not affect cell-cell adhesion, soft agar growth or cell migration, it increased apoptosis under hypoxia and serum starvation. This effect could be mitigated when the RGD mutant cells were treated with condition media containing WT OPN. Mechanistically, the RGD region of OPN inhibited apoptosis by inducing NF-kappaB activation and FAK phosphorylation. Inhibition of NF-kappaB (by siRNA to the p65 subunit) or FAK activation (by a inhibitor) significantly increased apoptosis under hypoxia in WT OPN cells, but not in RGD mutant cells.

CONCLUSION/SIGNIFICANCE

Unlike prior reports, our data suggest that the RGD domain of both OPN-A and B promote tumor growth and metastasis mainly by protecting cells against apoptosis under stressed conditions and not via migration or invasion. Future inhibitors directed against OPN should target multiple isoforms and should inhibit cell survival mechanisms that involve the RGD domain, FAK phosphorylation and NF-kappaB activation.

A modifier locus on chromosome 5 contributes to L1 cell adhesion molecule X-linked hydrocephalus in mice

Humans with L1 cell adhesion molecule (L1CAM) mutations exhibit X-linked hydrocephalus, as well as other severe neurological disorders. L1-6D mutant mice, which are homozygous for a deletion that removes the sixth immunoglobulin-like domain of L1cam, seldom display hydrocephalus on the 129/Sv background. However, the same L1-6D mutation produces severe hydrocephalus on the C57BL/6J background. To begin to understand how L1cam deficiencies result in hydrocephalus and to identify modifier loci that contribute to X-linked hydrocephalus by genetically interacting with L1cam, we conducted a genome-wide scan on F2 L1-6D mice, bred from L1-6D 129S2/SvPasCrlf and C57BL/6J mice. Linkage studies, utilizing chi-square tests and quantitative trait loci mapping techniques, were performed. Candidate modifier loci were further investigated in an extension study. Linkage was confirmed for a locus on chromosome 5, which we named L1cam hydrocephalus modifier 1 (L1hydro1), p = 4.04 X 10(-11).

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.

Endometrial osteopontin mRNA expression and plasma osteopontin levels are increased in patients with endometriosis

PROBLEM

The aim of this study was to evaluate osteopontin (OPN) mRNA expression in eutopic endometrium and plasma OPN levels in patients with endometriosis.

METHOD OF STUDY

A total of 79 patients with histologically confirmed endometriosis and 43 patients without endometriosis participated in this study. OPN mRNA expression in endometrial tissues was measured by real-time quantitative polymerase chain reaction (PCR) and plasma concentrations of OPN were quantified using a specific commercial sandwich enzyme-linked immunosorbent assays (ELISA).

RESULTS

Osteopontin mRNA expression in endometrial tissue was significantly higher in women with endometriosis than in controls (P = 0.010). The mean plasma levels of OPN (mean +/- S.E.M.) in patients with endometriosis and controls were 407.31 +/- 37.80 ng/mL and 165.84 +/- 19.29 ng/mL, respectively (P < 0.001). Receiver operating characteristic (ROC) analysis for plasma OPN revealed an area under the curve (AUC) of 0.894, with a sensitivity of 93.0%, specificity of 72.4%, positive likelihood ratio of 3.37, and negative likelihood ratio of 0.1 using a cut-off value of 167.68 ng/mL.

CONCLUSION

Osteopontin may be involved in the pathogenesis of endometriosis and plasma OPN may be a useful non-invasive marker for the diagnosis of endometriosis.

Secreted phosphoprotein 1 (SPP1, osteopontin) binds to integrin alpha v beta 6 on porcine trophectoderm cells and integrin alpha v beta 3 on uterine luminal epithelial cells, and promotes trophectoderm cell adhesion and migration

Conceptus implantation involves pregnancy-specific alterations in extracellular matrix at the conceptus-maternal interface. Secreted phosphoprotein 1 (SPP1, osteopontin) is induced just before implantation and is present at the conceptus-maternal interface in mammals. In the present study, we investigated mechanisms by which SPP1 facilitates porcine conceptus and uterine luminal epithelial cell attachment. Native bovine milk and wild-type rat recombinant SPP1 stimulated trophectoderm cell migration. Bovine milk SPP1, ovine uterine SPP1, and recombinant wild-type, but not mutated, rat SPP1 promoted dose- and cation-dependent attachment of porcine trophectoderm and uterine luminal epithelial cells, which was markedly reduced in the presence of a linear Arg-Gly-Asp integrin-blocking peptide. Affinity chromatography and immunoprecipitation experiments revealed direct binding of alpha v beta 6 trophectoderm and alpha v beta 3 uterine epithelial cell integrins to SPP1. Immunofluorescence microscopy using SPP1-coated microspheres revealed colocalization of the alpha v integrin subunit and talin at focal adhesions as well as at the apical domain of trophectoderm cells. Similarly, immunofluorescence staining of implantation sites in frozen gravid uterine cross sections localized SPP1 and alpha v integrin to the apical surfaces of trophectoderm and luminal epithelium and beta 3 integrin to the apical surface of luminal epithelium. To our knowledge, the present study is the first to demonstrate functionally that SPP1 directly binds specific integrins to promote trophectoderm cell migration and attachment to luminal epithelium that may be critical to conceptus elongation and implantation.

The hedgehog pathway transcription factor GLI1 promotes malignant behavior of cancer cells by up-regulating osteopontin

The role of Hedgehog (Hh) signaling as a developmental pathway is well established. Several recent studies have implicated a role for this pathway in multiple cancers. In this study we report that expression of GLI1 and osteopontin (OPN) increase progressively with the progression of melanoma from primary cutaneous cancer to metastatic melanoma in clinically derived specimens. We have further determined that OPN is a direct transcriptional target of GLI1. We have observed that OPN expression is stimulated in the presence of Hh ligands and inhibited in the presence of the Smoothened (SMO) inhibitor, cyclopamine. Transcriptional silencing of GLI1 negatively impacts OPN expression and compromises the ability of cancer cells to proliferate, migrate, and invade in vitro and interferes with their ability to grow as xenografts and spontaneously metastasize in nude mice. These altered attributes could be rescued by re-expressing OPN in the GLI1-silenced cells, suggesting that OPN is a critical downstream effector of active GLI1 signaling. Our observations lead us to conclude that the GLI1-mediated up-regulation of OPN promotes malignant behavior of cancer cells.

Established and newly proposed mechanisms of chronic cyclosporine nephropathy

Cyclosporine (CsA) has improved patient and graft survival rates following solid-organ transplantation and has shown significant clinical benefits in the management of autoimmune diseases. However, the clinical use of CsA is often limited by acute or chronic nephropathy, which remains a major problem. Acute nephropathy depends on the dosage of CsA and appears to be caused by a reduction in renal blood flow related to afferent arteriolar vasoconstriction. However, the mechanisms underlying chronic CsA nephropathy are not completely understood. Activation of the intrarenal renin-angiotensin system (RAS), increased release of endothelin-1, dysregulation of nitric oxide (NO) and NO synthase, up-regulation of transforming growth factor-beta1 (TGF-beta1), inappropriate apoptosis, stimulation of inflammatory mediators, enhanced innate immunity, endoplasmic reticulum stress, and autophagy have all been implicated in the pathogenesis of chronic CsA nephropathy. Reducing the CsA dosage or using other renoprotective drugs (angiotensin II receptor antagonist, mycophenolate mofetil, and statins, etc.) may ameliorate chronic CsA-induced renal injury. This review discusses old and new concepts in CsA nephropathy and preventive strategies for this clinical dilemma.

Dentin matrix protein-1 isoforms promote differential cell attachment and migration

Dentin matrix protein-1 (DMP1), bone sialoprotein (BSP), and osteopontin (OPN) are three SIBLINGs (small integrin-binding ligand, N-linked glycoproteins) co-expressed/secreted by skeletal and active ductal epithelial cells. Although etiological mechanisms remain unclear, DMP1 is the only one of these three genes currently known to have mutations resulting in human disease, and yet it remains the least studied. All three contain the highly conserved integrin-binding tripeptide, RGD, and experiments comparing the cell attachment and haptotactic migration-enhancing properties of DMP1 to BSP and OPN were performed using human skeletal (MG63 and primary dental pulp cells) and salivary gland (HSG) cells. Mutation of any SIBLING's RGD destroyed all attachment and migration activity. Using its alphaVbeta5 integrin, HSG cells attached to BSP but not to DMP1 or OPN. However, HSG cells could not migrate onto BSP in a modified Boyden chamber assay. Expression of alphaVbeta3 integrin enhanced HSG attachment to DMP1 and OPN and promoted haptotactic migration onto all three proteins. Interchanging the first four coding exons or the conserved amino acids adjacent to the RGD of DMP1 with corresponding sequences of BSP did not enhance the ability of DMP1 to bind alphaVbeta5. For alphaVbeta3-expressing cells, intact DMP1, its BMP1-cleaved C-terminal fragment, and exon six lacking all post-translational modifications worked equally well but the proteoglycan isoform of DMP1 had greatly reduced ability for cell attachment and migration. The sequence specificity of the proposed BMP1-cleavage site of DMP1 was verified by mutation analysis. Direct comparison of the three proteins showed that cells discriminate among these SIBLINGs and among DMP1 isoforms.

Spironolactone suppresses inflammation and prevents L-NAME-induced renal injury in rats

Chronic inhibition of nitric oxide synthase by N(omega)-nitro- L-arginine methyl ester (L-NAME) causes progressive renal injury with systemic hypertension and interstitial macrophage infiltration. We have previously shown that there is local activation of the renin-angiotensin-aldosterone system in the renal cortex as a major pathogenic feature of macrophage infiltration. In this study, we measured the effects of the aldosterone antagonist, spironolactone, on renal injury in L-NAME-treated male Wistar rats. After 12 weeks of L-NAME-treatment, rats had increased systolic blood pressure, urinary protein excretion, and serum creatinine and histological analysis showed glomerulosclerosis, interstitial fibrosis, and macrophage infiltration. Treatment with spironolactone significantly prevented these renal changes, whereas treatment with hydralazine had no effect. The cortical expression of osteopontin was significantly elevated in L-NAME-treated rats, and expression of its mRNA significantly correlated with the number of infiltrating macrophages and degree of interstitial fibrosis. Spironolactone treatment markedly suppressed osteopontin expression. Our results suggest that reduced nitric oxide bioavailability caused renal inflammation and fibrosis through an aldosterone receptor-dependent mechanism associated with osteopontin expression independent of its systemic hemodynamic effects.

Osteopontin prevents curcumin-induced apoptosis and promotes survival through Akt activation via alpha v beta 3 integrins in human gastric cancer cells

Osteopontin (OPN) is a secreted, integrin-binding matrix phosphorylated glycoprotein that is overexpressed in many advanced cancers. However, the functional mechanisms by which OPN contributes to gastric cancer development are poorly understood. Here, we report that curcumin inhibited the growth of SGC7901 cell and induced apoptosis in a concentration- and time-dependent manner, while the acquired expression of OPN in SGC7901 cells dramatically promoted cell survival under serum depletion and prevented curcumin-induced apoptosis. Furthermore, PI3-K inhibitor LY294002 attenuated OPN-mediated Akt activation. Moreover, inhibiting the binding of OPN to alpha(v)beta(3) integrins reduced activation of Akt. Taken together, these results demonstrate that the pro-survival and anti-apoptosis activities of OPN in gastric cancer cells are mediated in part through PI3-K/Akt pathway via alpha(v)beta(3) integrins.

Lower osteopontin plasma levels are associated with superior outcomes in advanced non-small-cell lung cancer patients receiving platinum-based chemotherapy: SWOG Study S0003

PURPOSE

S0003 was a phase III trial of carboplatin/paclitaxel with or without the hypoxic cytotoxin tirapazamine in patients with advanced or metastatic non-small-cell lung cancer (NSCLC). We investigated the relationship between clinical outcomes and plasma levels of the hypoxia-associated protein osteopontin (OPN) in patients on this protocol.

PATIENTS AND METHODS

Baseline plasma was obtained from 172 patients. In 56 patients, sequential plasma was obtained after one or two cycles. Concentrations of OPN, as well as plasminogen activator inhibitor-1 (PAI-1) and vascular endothelial growth factor (VEGF), were measured using enzyme-linked immunosorbent assay. Tumor expression of OPN was assessed by immunohistochemistry in 61 matched archival specimens.

RESULTS

Patients with lower OPN levels (below the median) had a significantly superior overall survival compared with patients with higher levels, regardless of treatment arm (hazard ratio [HR] = 0.60, P = .002). A similar correlation was observed for progression-free survival (HR = 0.69, P = .02). When examined as a continuous variable, OPN maintained its significant association with both progression-free (HR = 1.05, P = .01) and overall survival (HR = 1.09, P < .0001). Patients with lower plasma OPN levels were significantly more likely to have tumor response (P = .03). No differences were observed between treatment arms. Tumor OPN levels did not correlate with patient outcomes or with plasma levels. No associations were observed between patient outcomes and VEGF or PAI-1 levels; however, plasma concentrations of these markers were significantly interrelated (P < .0001) and significantly decreased after treatment (P = .0002 and P = .03, respectively).

CONCLUSION

Pretreatment plasma levels of OPN are significantly associated with patient response, progression-free survival, and overall survival in chemotherapy-treated patients with advanced NSCLC.

In vivo osteopontin-induced macrophage accumulation is dependent on CD44 expression

In order to assess the role of osteopontin (OPN) in leukocyte accumulation in inflammatory conditions, native OPN and its thrombin cleaved form (OPN+Thr) were studied in vivo using a rodent subcutaneous air pouch model (AP). Both forms of OPN-induced macrophage infiltration into the AP in wild-type mice. In animals lacking CD44, macrophage numbers were significantly reduced within the cavity, but cells still accumulated along the subcutaneous lining. In animals lacking endogenous OPN, no differences were found in exogenous OPN-induced macrophage accumulation, although macrophage exhibited increased alpha4 integrin expression. These studies reveal that both OPN and OPN+Thr attract macrophages in vivo through CD44.

Molecular basis of recognition of human osteopontin by 23C3, a potential therapeutic antibody for treatment of rheumatoid arthritis

Osteopontin plays an important role in the development and perpetuation of rheumatoid arthritis (RA). Antibodies targeting osteopontin have shown promising therapeutic benefits against this disease. We have previously reported a novel anti-RA monoclonal antibody, namely, 23C3, and shown it capable of alleviating the symptoms of RA in a murine collagen-induced arthritis model, restoring the cytokine production profile in joint tissues, and reducing T-cell recall responses to collagen type II. We describe here the crystal structure of 23C3 in complex with its epitope peptide. Analyses of the complex structure reveal the molecular mechanism of osteopontin recognition by 23C3. The peptide folds into two tandem β-turns, and two key residues of the peptide are identified to be critical for the recognition by 23C3: TrpP43 is deeply embedded into a hydrophobic pocket formed by AlaL34, TyrL36, LeuL46, TyrL49, PheL91, and MetH102 and therefore has extensive hydrophobic interactions with 23C3, while AspP47 has a network of hydrophilic interactions with residues ArgH50, ArgH52, SerH53, and AsnH56 of the antibody. Besides the complementarity-determining region loops, the framework region L2 of 23C3 is also shown to interact with the epitope peptide, which is not common in the antibody–antigen interactions and thus could be exploited in the engineering of 23C3. These results not only provide valuable information for further improvement of 23C3 such as chimerization or humanization for its therapeutic application, but also reveal the features of this specific epitope of osteopontin that may be useful for the development of new antibody drugs against RA.

Role of hyaluronan in glioma invasion

Gliomas are the most common primary intracranial tumors. Their distinct ability to infiltrate into the extracellular matrix (ECM) of the brain makes it impossible to treat these tumors using surgery and radiation therapy. A number of different studies have suggested that hyaluronan (HA), the principal glycosaminoglycan (GAG) in the ECM of the brain, is the critical factor for glioma invasion. HA-induced glioma invasion was driven by two important molecular events: matrix metalloproteinase (MMP) secretion and up-regulation of cell migration. MMP secretion was triggered by HA-induced focal adhesion kinase (FAK) activation, which transmits its signal through ERK activation and nuclear factor kappa B (NF-kappaB) translocation. Another important molecular event is osteopontin (OPN) expression. OPN expression by AKT activation triggers cell migration. These results suggest that HA-induced glioma invasion is tightly regulated by signaling mechanisms, and a detailed understanding of this molecular mechanism will provide important clues for glioma treatment.

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 expression in the liver with severe perisinusoidal fibrosis: autopsy case of Down syndrome with transient myeloproliferative disorder

Down syndrome with transient myeloproliferative disorder (TMD) is often associated with perinatal liver fibrosis. The authors recently encountered an autopsy case of this disease with a characteristic severe perisinusoidal liver fibrosis. Osteopontin (OPN) is a molecule that plays an important role in diverse fibro-inflammatory diseases. The purpose of the present report was to examine the involvement of OPN in development of the Down syndrome-associated liver fibrosis. Histology indicated severe perisinusoidal fibrosis and ductular arrangements of hepatocytes in the liver. Appearance of atypical megakaryocytes in the liver, a feature of TMD associated with Down syndrome, was not evident. On immunohistochemistry expression of OPN was observed in hepatocytes often having ductular arrangements and infiltrating macrophages. In contrast, a small number of transforming growth factor-beta1 (TGF-beta1)-positive mononuclear cells were present in the liver. Numerous activated hepatic stellate cells (HSC) expressing alpha-smooth muscle actin (alpha-SMA) were seen in the perisinusoidal area. A recent report indicated that OPN could directly activate the HSC. Thus, it is suggested that OPN produced by hepatocytes and macrophages induces activation of the HSC, and leads to the development of perisinusoidal liver fibrosis.

Molecular mapping of human hepatocellular carcinoma provides deeper biological insight from genomic data

DNA microarray analysis of human cancer has resulted in considerable accumulation of global gene profiles. However, extraction and understanding the underlying biology of cancer progression remains a significant challenge. This study applied a novel integrative computational and analytical approach to this challenge in human hepatocellular carcinoma (HCC) with the aim of identifying potential molecular markers or novel therapeutic targets. We analysed 100 HCC tissue samples by human 30K DNA microarray. The gene expression data were uploaded into the network analysis tool, and the biological networks were displayed graphically. We identified several activated 'hotspot' regions harbouring a concentration of upregulated genes. Several 'hotspot' regions revealed integrin and Akt/NF-kappaB signalling. We identified key members linked to these signalling pathways including osteopontin (SPP1), glypican-3 (GPC3), annexin 2 (ANXA2), S100A10 and vimentin (VIM). Our integrative approach should significantly enhance the power of microarray data in identifying novel potential targets in human cancer.

Control of osteopontin signaling and function by post-translational phosphorylation and protein folding

Osteopontin (OPN) plays roles in a variety of cellular processes from bone resorption and extracellular matrix (ECM) remodeling to immune cell activation and inhibition of apoptosis. Because it binds receptors (integrins, CD44 variants) typically engaged by ECM molecules, OPN acts as a "soluble" ECM molecule. A persistent theme throughout the characterization of how OPN functions has been the importance of phosphorylation. The source of the OPN used in specific experiments and the location of modified sites is an increasingly important consideration for OPN research. We review briefly some of the ways OPN impacts on the biology of mammalian systems with an emphasis on the importance of serine phosphorylation in modulating its signaling ability. We describe experiments that support the hypothesis that differences in the post-translational phosphorylation of OPN expressed by different cell types regulate how it impacts on target cells. Analyses of OPN's potential secondary structure reveal a possible beta-sheet conformation that offers an interpretation of certain experimental observations, specifically the effect of thrombin cleavage; it is consistent with an interaction between the C-terminal region of the protein and the central integrin-binding RGD sequence.

Undifferentiated human mesenchymal stem cells (hMSCs) are highly sensitive to mechanical strain: transcriptionally controlled early osteo-chondrogenic response in vitro

OBJECTIVE

Physical cues play a crucial role in skeletogenesis and osteochondral regeneration. Although human mesenchymal stem cells (hMSCs) offer considerable therapeutic potential, little is known about the molecular mechanisms that control their differentiation. We hypothesized that mechanical strain might be an inherent stimulus for chondrogenic and/or osteogenic differentiation in undifferentiated hMSCs, where c-Fos (FOS) might play a major role in mechanotransduction.

METHOD

hMSCs from 10 donors were intermittently stimulated by cyclic tensile strain (CTS) at 3000 mustrain for a period of 3 days. Differential gene expression of strained and unstrained hMSCs was analysed by real-time RT-PCR for several marker genes, including the transcription factors FOS, RUNX2, SOX9, and others. Additionally, alkaline phosphatase activity (ALP) was determined kinetically.

RESULTS

The application of CTS significantly stimulated the expression levels of the early chondrogenic and osteogenic marker genes (SOX9, LUM, DCN; RUNX2, SPARC, SPP1, ALPL); this was accompanied by stimulation of ALP activity (+38%+/-12 standard error of mean, P<0.05). Matrix analysis revealed that the osteo-chondrogenic response followed a coordinated expression pattern, in which FOS was attributed to early osteogenic but not chondrogenic differentiation.

CONCLUSION

Undifferentiated hMSCs are highly sensitive to mechanical strain with a transcriptionally controlled osteo-chondrogenic differentiation response in vitro.

Immunohistochemical study of osteopontin and l-selectin in a rat endometriosis model and in human endometriosis

OBJECTIVE

To investigate the localization of the proteins osteopontin (OPN) and L-selectin (SELL).

DESIGN

Retrospective nonrandomized immunohistochemical study in a surgically induced rat model of peritoneal endometriosis and in samples of human endometriotic lesions of ovaries.

SETTING

Department of gynecology in a university hospital.

PATIENT(S)

A rat endometriosis model was induced in 10 8-week-old SLC-Sprague-Dawley rats by surgical autotransplantation of uterus. Fourteen premenopausal women with histologically diagnosed endometriosis were selected (mean age, 39 y; range, 25-53 y). Twenty endometriotic specimens were obtained from 14 patients who underwent laparoscopic surgery for enlarged endometriotic cysts.

INTERVENTION(S)

Histopathological examination of endometriotic ovarian specimens for OPN and SELL expression by immunohistochemistry.

MAIN OUTCOME MEASURE(S)

Demonstration of the immunoreactive staining of OPN and SELL expressions in tissues of a rat endometriosis model and of human endometriosis.

RESULT(S)

In both tissues from a rat endometriosis model and from human endometriosis, OPN was stained more prominently in glandular epithelium than in interstitial space, whereas SELL stained more prominently in interstitial space (macrophages and lymphocytes) than in epithelium. The staining pattern of OPN in ectopic endometriotic lesions was very similar to that in eutopic normal human endometrium in the secretory phase.

CONCLUSION(S)

These results suggested important roles for OPN and SELL in the pathogenesis of endometriosis.

Secreted phosphoprotein 1 (osteopontin) is expressed by stromal macrophages in cyclic and pregnant endometrium of mice, but is induced by estrogen in luminal epithelium during conceptus attachment for implantation

Secreted phosphoprotein 1 (SPP1, osteopontin) is the most highly upregulated extracellular matrix/adhesion molecule/cytokine in the receptive phase human uterus, and Spp1 null mice manifest decreased pregnancy rates during mid-gestation as compared with wild-type counterparts. We hypothesize that Spp1 is required for proliferation, migration, survival, adhesion, and remodeling of cells at the conceptus-maternal interface. Our objective was to define the temporal/spatial distribution and steroid regulation of Spp1 in mouse uterus during estrous cycle and early gestation. In situ hybridization localized Spp1 to luminal epithelium (LE) and immune cells. LE expression was prominent at proestrus, decreased by estrus, and was nearly undetectable at diestrus. During pregnancy, Spp1 mRNA was not detected in LE until day 4.5 (day 1 = vaginal plug). Spp1-expressing immune cells were scattered within the endometrial stroma throughout the estrous cycle and early pregnancy. Immunoreactive Spp1 was prominent at the apical LE surface by day 4.5 of pregnancy and Spp1 protein was also co-localized with subsets of CD45-positive (leukocytes) and F4/80-positive (macrophages) cells. In ovariectomized mice, estrogen, but not progesterone, induced Spp1 mRNA, whereas estrogen plus progesterone did not induce Spp1 in LE. These results establish that estrogen regulates Spp1 in mouse LE and are the first to identify macrophages that produce Spp1 within the peri-implantation endometrium of any species. We suggest that Spp1 at the apical surface of LE provides a mechanism to bridge conceptus to LE during implantation, and that Spp1-positive macrophages within the stroma may be involved in uterine remodeling for conceptus invasion.

Patched haploinsufficient mouse rhabdomyosarcoma overexpress secreted phosphoprotein 1 and matrix metalloproteinases

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood. Improving the management of rhabdomyosarcoma requires a better understanding of growth regulation. Patched haploinsufficient (Ptch+/-) mice spontaneously develop soft tissue sarcomas that resemble human rhabdomyosarcomas. Using microarray profiling and quantitative real-time reverse transcriptase polymerase chain reaction, we identified candidate genes differentially expressed in Ptch+/- mouse rhabdomyosarcoma relative to mature muscle. Overexpressed genes include Secreted Phosphoprotein 1 (Spp1, Osteopontin), and Matrix Metalloproteinases-2 and -14 (Mmp2 and Mmp14). Spp1 is an integrin-binding phosphoglycoprotein upregulated in carcinomas, and Mmps regulate tumour invasion. Immunochemical analyses of murine and human rhabdomyosarcoma specimens confirmed increased expression of Spp1, Mmp2, Mmp14, nuclear factor-kappa B (NF-kappaB) p65 and its phosphorylated active isoform. Neutralising Spp1 antibody decreased Mmp14 RNA in murine rhabdomyosarcoma cultures, indicating a positive regulatory role for extracellular Spp1. Plasma from rhabdomyosarcoma patients display elevated levels of SPP1. These results implicate Spp1, NF-kappaB, and Mmp activation as a putative signalling pathway involved in rhabdomyosarcoma growth.

Chemotherapy resistance of mouse WAP-SVT/t breast cancer cells is mediated by osteopontin, inhibiting apoptosis downstream of caspase-3

Impairment of the complex regulatory network of cell death and survival is frequently the reason for therapy resistance of breast cancer cells and a major cause of tumor progression. We established two independent cell lines from a fast growing mouse breast tumor (WAP-SVT/t transgenic animal). Cells from one line (ME-A cells) are sensitive to apoptotic stimuli such as growth factor depletion or treatment with antitumor agents (e.g. doxorubicin). Cells from the second line (ME-C cells), which carry a missense mutation at the p53 codon 242, are very insensitive to apoptotic stimuli. Co-cultivation experiments revealed that the ME-C cells mediate cell death resistance to the ME-A cells. Microarray and Western blot analysis showed that osteopontin (OPN) is selectively overexpressed by the ME-C cells. This glycoprotein is the most abundant protein secreted by the ME-C cells and we obtained strong indications that OPN is the main antiapoptotic factor. However, the OPN containing ME-C cell medium does not alter the expression level of pro- or antiapoptotic genes or known inhibitors of apoptosis (IAPs). Its signaling involves mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)1/2 as the kinase inhibitor PD98059 restores apoptosis but not the Akt inhibitor. In the ME-A cells, mitochondrial cytochrome c release occurs with and without external apoptotic stimuli. OPN containing ME-C cell medium does not prevent the mitochondrial cytochrome c release and caspase-9 processing. In serum starved ME-A cells, the OPN containing ME-C cell medium prevents caspase-3 activation. However, in doxorubicin-treated cells, although apoptosis is blocked, it does not inhibit caspase-3. This indicates that the ME-A cells distinguish between the initial apoptotic stimuli and that the cells possess a further uncharacterized control element acting downstream from caspase-3.

Osteopontin expression in salivary gland tumours

Osteopontin (OPN) is expressed in numerous carcinomas and plays a role in tumour development, invasion and metastasis. This study examines by immunohistochemistry the expression of OPN in normal salivary gland tissue and three types of salivary gland tumour: pleomorphic adenoma (PA), adenoid cystic carcinoma (ACC) and polymorphous low grade adenocarcinoma (PLGA). PAs and PLGAs demonstrated higher levels of OPN than normal salivary gland tissue, while ACC, although showing a trend towards increased OPN, was not significantly different. The results of this study indicate that OPN expression is present in normal salivary gland tissue, and is increased in certain salivary gland tumours, but further investigation is necessary to clarify its role.

Osteopontin: a bridge between bone and blood

The production of mature blood cells within the bone marrow (BM) is attributed to a pool of haemopoietic stem cells (HSC). It is now evident that HSC reside preferentially at the endosteal region within the BM where bone-lining osteoblasts are a key cellular component of the HSC niche that directly regulates HSC fate. Osteoblasts synthesise proteins that stimulate and inhibit HSC proliferation. In addition to angiopoietin 1 (Ang-1), osteoblasts synthesise and express the highly acidic glycoprotein, osteopontin (Opn), which, like Ang-1, acts as a potent constraining factor on HSC proliferation. Overexpression of Opn is a feature of haemopoietic malignancies, such as multiple myeloma and chronic myeloid leukaemia, although its exact role in the aetiology and progression of these diseases remains unclear. Through osteoblasts and their cell surface and expressed proteins including Opn, bone is able to regulate the tissue that resides within it. In doing so, Opn can be considered a bridge between bone and blood.