The many faces of S100B protein: when an extracellular factor inactivates its own receptor and activates another one

The Ca(2+)-binding protein of the EF-hand type, S100B, is an intracellular regulator and an extracellular signal. Within cells S100B interacts with several proteins thereby regulating energy metabolism, Ca2+ homeostasis, protein phosphorylation and degradation, and cell locomotion, proliferation and differentiation. Once secreted/released, S100B exerts autocrine and paracrine effects on responsive cells by engaging the receptor for advanced glycation end products. However, recent evidence suggests that S100B might also activate basic fibroblast growth factor receptor 1 via prior binding to basic fibroblast growth factor.

S100B in schizophrenia: an update

Recent research has supported a potential role of immune pathology in the etiopathogenesis of schizophrenic. In the CNS various viruses were identified in the brains of schizophrenic patients. Pro-inflammatory cytokines were found to be associated with the stage of disease. Microglial cells were reported to be activated in a subgroup of schizophrenic patients in post mortem as well as imaging studies. New research has demonstrated that astrocytes together with microglial cells are the major immunocompetent cells of the brain and play an important role in the regulation of neuronal proliferation and differentiation. S100B, a calcium binding astrocyte-specific cytokine, presents a marker of astrocytic activation. Scientific evidence for increased S100B in acute schizophrenia is very consistent. The picture is not as clear regarding schizophrenia subtypes in acute states but patients with persistent negative symptoms or deficit syndrome show constant high S100B concentrations. There is an association between high S100B and poor therapeutic response. The increased S100B concentrations appear to be functionally relevant since they are reflected by poor cognitive performance and cross validation with other methods make it unlikely that the findings are merely an epiphenomenon. These findings suggest that the activation of astrocytes might be an important pathogenic factor for the development of schizophrenia.

Low expression of S100P associated with paclitaxel resistance in ovarian cancer cell line

BACKGROUND

Recent studies indicate that S100P expression may be a biomarker that can predict the success of cancer chemotherapy. Whether it is relevant to chemotherapeutics in ovarian cancer is unknown. In this study, we investigated the association of S100P expression with paclitaxel sensitivity in ovarian cancer cell lines.

METHODS

We measured S100P expression and paclitaxel resistance profiles in parent SKOV3 and OVCAR3 cell lines. Then, the two cell lines were transiently transfected with S100P siRNA. We also constructed an OVCAR3 cell clone that stably overexpressed S100P. The effect of S100P expression level on the survival of cells exposed to paclitaxel was measured using the MTT assay. S100P expression was evaluated by semi-quantitative RT-PCR and Western blotting. Significance of differences was calculated using independent samples t-test and one way analysis of variance (ANOVA).

RESULTS

Lower S100P expression was associated with a survival advantage in OVCAR3 cells exposed to paclitaxel; the survival advantage in SKOV3 cells was smaller (P < 0.05). The survival advantage associated with decreased S100P expression was even greater for SKOV3 and OVCAR3 cells that had been transfected with S100P siRNA before being exposed to paclitaxel (P < 0.05). Consistent with this, the OVCAR3 cell clone that was transfected to overexpress S100P was more sensitive to paclitaxel (P < 0.05).

CONCLUSIONS

Low S100P expression contributes to drug resistance to paclitaxel in ovarian cancer cell lines. S100P expression thus might be a marker that can predict the effectiveness of paclitaxel based chemotherapy. Such a marker could be helpful in improving individual medication regimens for ovarian cancer patients.

S100A6 (calcyclin) enhances the sensitivity to apoptosis via the upregulation of caspase-3 activity in Hep3B cells

S100A6 (calcyclin) is a small calcium-binding protein which has been implicated in several cellular processes such as cell cycle progression, cytoskeleton rearrangement, and exocytosis. Also the upregulation of S100A6 has been reported in a variety of tumors and linked to metastasis. However, exact intracellular roles of S100A6 related with apoptosis have not been clarified yet. Here we demonstrated that the upregulation of S100A6 enhances the cell death rate compared to the control under the apoptotic conditions. In exogenously S100A6 induced Hep3B cells, cell viability was significantly decreased compared with mock and S100A6-knockdown cells under calcium ionophore A23187 treatment. The exogenously introduced S100A6 significantly affected the caspase-3-like activity in programmed cell death through the enhanced caspase-3 expression, which was verified by promoter assay in wild or mutant S100A6-transfected Hep3B cells. Next, the promoter activity of caspase-3 was increased by 2.5-folds in wild-type S100A6-transfected cells compared to mutant 2 (E67K, mutant of EF-hand motif) or control. Our results suggest that S100A6 might be involved in the processing of apoptosis by modulating the transcriptional regulation of caspase-3.

S100A1 deficiency results in prolonged ventricular repolarization in response to sympathetic activation

S100A1 is a Ca(2+)-binding protein and predominantly expressed in the heart. We have generated a mouse line of S100A1 deficiency by gene trap mutagenesis to investigate the impact of S100A1 ablation on heart function. Electrocardiogram recordings revealed that after beta-adrenergic stimulation S100A1-deficient mice had prolonged QT, QTc and ST intervals and intraventricular conduction disturbances reminiscent of 2 : 1 bundle branch block. In order to identify genes affected by the loss of S100A1, we profiled the mutant and wild type cardiac transcriptomes by gene array analysis. The expression of several genes functioning to the electrical activity of the heart were found to be significantly altered. Although the default prediction would be that mRNA and protein levels are highly correlated, comprehensive immunoblot analyses of salient up- or down-regulated candidate genes of any cellular network revealed no significant changes on protein level. Taken together, we found that S100A1 deficiency results in cardiac repolarization delay and alternating ventricular conduction defects in response to sympathetic activation accompanied by a significantly different transcriptional regulation.

Receptor for advanced glycation endproducts and atherosclerosis: From basic mechanisms to clinical implications

The receptor for advanced glycation endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules with a diverse repertoire of ligands. In the atherosclerotic milieu, three classes of RAGE ligands, i.e., products of non-enzymatic glycoxidation, S100 proteins and amphoterin, appear to drive receptor-mediated cellular activation and potentially, acceleration of vascular disease. The interaction of RAGE-ligands effectively modulates several steps of atherogenesis, triggering an inflammatory-proliferative process and furthermore, critically contributing to propagation of vascular perturbation, mainly in diabetes. RAGE has a circulating truncated variant isoform, soluble RAGE (sRAGE), corresponding to its extracellular domain only. By competing with cell-surface RAGE for ligand binding, sRAGE may contribute to the removal/neutralization of circulating ligands thus functioning as a decoy. The critical role of RAGE in the chronic vascular inflammation processes highlights this receptor-ligand axis as a possible and attractive candidate for therapeutic intervention to limit vascular damage and its associated clinical disorders.

S100B and S100A6 differentially modulate cell survival by interacting with distinct RAGE (receptor for advanced glycation end products) immunoglobulin domains

S100 proteins are EF-hand calcium-binding proteins with various intracellular functions including cell proliferation, differentiation, migration, and apoptosis. Some S100 proteins are also secreted and exert extracellular paracrine and autocrine functions. Experimental results suggest that the receptor for advanced glycation end products (RAGE) plays important roles in mediating S100 protein-induced cellular signaling. Here we compared the interaction of two S100 proteins, S100B and S100A6, with RAGE by in vitro assay and in culture of human SH-SY5Y neuroblastoma cells. Our in vitro binding data showed that S100B and S100A6, although structurally very similar, interact with different RAGE extracellular domains. Our cell assay data demonstrated that S100B and S100A6 differentially modulate cell survival. At micromolar concentration, S100B increased cellular proliferation, whereas at the same concentration, S100A6 triggered apoptosis. Although both S100 proteins induced the formation of reactive oxygen species, S100B recruited phosphatidylinositol 3-kinase/AKT and NF-kappaB, whereas S100A6 activated JNK. More importantly, we showed that S100B and S100A6 modulate cell survival in a RAGE-dependent manner; S100B specifically interacted with the RAGE V and C(1) domains and S100A6 specifically interacted with the C(1) and C(2) RAGE domains. Altogether these results highlight the complexity of S100/RAGE cellular signaling.

S100A4 contributes to the suppression of BNIP3 expression, chemoresistance, and inhibition of apoptosis in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease that is characterized by a particularly marked resistance to chemotherapy. We previously showed an association between decreased expression of BNIP3 and chemoresistance in PDAC cell lines. To further explore the molecular basis of chemoresistance in PDAC, we analyzed microarray data obtained from normal pancreas and PDAC tumor samples to identify genes exhibiting a negative correlation with the expression profile of BNIP3. This analysis identified several S100 family proteins, of which two, S100A2 and S100A4, showed in vitro the ability to repress exogenous BNIP3 promoter activity. We subsequently showed that RNA interference-mediated S100A4 knockdown resulted in an elevated expression of BNIP3 in PDAC cell lines that possess an unmethylated BNIP3 promoter, suggesting that, in addition to hypermethylation, S100A4 overexpression may represent an alternative mechanism for inhibiting BNIP3 function in PDAC. S100A4 knockdown also resulted in an increased sensitivity of PDAC cell lines to gemcitabine treatment, which was coupled with an increase in apoptosis and cell cycle arrest. To investigate the underlying mechanisms mediating these effects, we studied the effect of silencing the expression of S100A4 on the induction of apoptosis, cell cycle arrest, and the activation of apoptotic mediators. Knockdown of S100A4 clearly induced apoptosis with increased fragmentation of DNA and phosphatidyl serine externalization; activation of caspase-3, caspase-9, and poly(ADP-ribose) polymerase; and release of cytochrome c into the cytosol. These findings provide evidence that supports a novel role for S100A4 as a prosurvival factor in pancreatic cancer.

S100A1: a novel inotropic regulator of cardiac performance. Transition from molecular physiology to pathophysiological relevance

Here we review the considerable body of evidence that has accumulated to support the notion of S100A1, a cardiac-specific Ca2+-sensor protein of the EF-hand type, as a physiological regulator of excitation-contraction coupling and inotropic reserve mechanisms in the mammalian heart. In particular, molecular mechanisms will be discussed conveying the Ca2+-dependent inotropic actions of S100A1 protein in cardiomyocytes occurring independently of β-adrenergic signaling. Moreover, we will shed light on the molecular structure-function relationship of S100A1 with its cardiac target proteins at the sarcoplasmic reticulum, the sarcomere, and the mitochondria. Furthermore, pathophysiological consequences of disturbed S100A1 protein expression on altered Ca2+handling and intertwined systems in failing myocardium will be highlighted. Subsequently, therapeutic options by means of genetic manipulation of cardiac S100A1 expression will be discussed, aiming to complete our current understanding of the role of S100A1 in diseased myocardium.

Metastasis-associated protein S100A4: spotlight on its role in cell migration

S100A4 (also known as Mts1, metastasin, p9Ka, pEL98, CAPL, calvasculin, Fsp-1, placental calcium-binding protein) belongs to the family of EF-hand calcium-binding proteins, whose expression is elevated in a number of pathological conditions. Although it is well documented that S100A4 is expressed in cancer cells and contributes to tumor cell motility and metastatic progression, the exact underlying mechanisms remain elusive. An important characteristic feature of S100 proteins is their dual function, inside and outside the cell. In this review, we focus on the intracellular function of S100A4. The review contains structural analysis of S1004 in comparison with other members of S100 proteins. Possible modes of the interaction of S100 proteins with targets are described. Several examples of best-studied molecular interactions involving S100A4 with heavy chain of nonmuscle myosin IIA, LAR-interacting protein liprin beta1 and tumor suppressor protein p53 are provided. We suggest that the binding of S100A4 to these molecules is critical for the S100A4 function. Further studies of the implications of these interactions in different molecular pathways may shed additional light on the role of S100A4 protein in the control of tumor cell motility and migration. We discuss the approaches for down-regulation of S100A4 expression and their potential for application in the clinics.

Gene expression and the biological phenotype of papillary thyroid carcinomas

The purpose of this paper is to correlate the molecular phenotype of papillary thyroid carcinoma (PTC) to their biological pathology. We hybridized 26 PTC on microarrays and showed that nearly 44% of the transcriptome was regulated in these tumors. We then combined our data set with two published PTC microarray studies to produce a platform- and study-independent list of PTC-associated genes. We further confirmed the mRNA regulation of 15 genes from this list by quantitative reverse transcription-PCR. Analysis of this list with statistical tools led to several conclusions: (1) there is a change in cell population with an increased expression of genes involved in the immune response, reflecting lymphocyte infiltration in the tumor compared to the normal tissue. (2) The c-jun N-terminal kinase pathway is activated by overexpression of its components. (3) The activation of ERKK1/2 by genetic alterations is supplemented by activation of the epidermal growth factor but not of the insulin-like growth factor signaling pathway. (4) There is a downregulation of immediate early genes. (5) We observed an overexpression of many proteases in accordance with tumor remodeling, and suggested a probable role of S100 proteins and annexin A2 in this process. (6) Numerous overexpressed genes favor the hypothesis of a collective migration mode of tumor cells.

S100B in neuropathologic states: the CRP of the brain?

In recent years there has been a proliferation of interest in the brain-specific protein S100B, its many physiologic roles, and its behaviour in various neuropathologic conditions. Since the mid-1960s, its wide variety of intracellular and extracellular activities has been elucidated, and it has also been implicated in an increasing number of central nervous system (CNS) disorders. S100B is part of a superfamily of proteins, some of which (including S100B) have been implicated as calcium-dependent regulatory proteins that modulate the activity of effector proteins or cells. S100B is primarily an astrocytic protein. Within cells, it may have a role in signal transduction, and it is involved in calcium homeostasis. Information about the functional implication of S100B secretion by astrocytes into the extracellular space is scant but there is substantial evidence that secreted glial S100B exerts trophic or toxic effects depending on its concentration. This review summarises the historic development and current knowledge of S100B, including recent interesting findings relating S100B to a diversity of CNS pathologies such as traumatic brain injury, Alzheimer's disease, Down's syndrome, schizophrenia, and Tourette's syndrome. These broad implications have led some workers to describe S100B as 'the CRP (C-reactive protein) of the brain.' This review also examines S100B's potential role as a neurologic screening tool, or biomarker of CNS injury, analogous to the role of CRP as a marker of systemic inflammation.

Impact of S100B on local field potential patterns in anesthetized and kainic acid-induced seizure conditions in vivo

S100B is a calcium-binding protein predominantly expressed in astrocytes. Previous studies using gene-manipulated animals have suggested that the protein has a role in synaptic plasticity and learning. In order to assess the physiological roles of the protein in active neural circuitry, we recorded spontaneous neural activities from various layers of the neocortex and hippocampus in urethane-anesthetized S100B knockout (KO) and wildtype (WT) control mice. Typical local field oscillation patterns including the slow (0.5-2 Hz) oscillations in the neocortex, theta (3-8 Hz) and sharp wave-associated ripple (120-180 Hz) oscillations in the hippocampus were observed in both genotypes. Comparisons of the frequency, power and peak amplitude have shown that these oscillatory patterns were virtually indistinguishable between WT and KO. When seizure was induced by intraperitoneal injection of kainic acid, a difference between WT and KO appeared in the CA1 radiatum local field potential pattern, where seizure events were characterized by prominent appearance of hyper-synchronous gamma band (30-80 Hz) activity. Although both genotypes developed seizures within 40 min, the gamma amplitude was significantly smaller during the development of seizures in KO mice. Our results suggest that deficiency of S100B does not have a profound impact on spontaneous neural activity in normal conditions. However, when neural activity was sufficiently raised, activation of S100B-related pathways may take effect, resulting in modulation of neural activities.

Stable myocardial-specific AAV6-S100A1 gene therapy results in chronic functional heart failure rescue

BACKGROUND

The incidence of heart failure is ever-growing, and it is urgent to develop improved treatments. An attractive approach is gene therapy; however, the clinical barrier has yet to be broken because of several issues, including the lack of an ideal vector supporting safe and long-term myocardial transgene expression.

METHODS AND RESULTS

Here, we show that the use of a recombinant adeno-associated viral (rAAV6) vector containing a novel cardiac-selective enhancer/promoter element can direct stable cardiac expression of a therapeutic transgene, the calcium (Ca2+)-sensing S100A1, in a rat model of heart failure. The chronic heart failure-rescuing properties of myocardial S100A1 expression, the result of improved sarcoplasmic reticulum Ca2+ handling, included improved contractile function and left ventricular remodeling. Adding to the clinical relevance, long-term S100A1 therapy had unique and additive beneficial effects over beta-adrenergic receptor blockade, a current pharmacological heart failure treatment.

CONCLUSIONS

These findings demonstrate that stable increased expression of S100A1 in the failing heart can be used for long-term reversal of LV dysfunction and remodeling. Thus, long-term, cardiac-targeted rAAV6-S100A1 gene therapy may be of potential clinical utility in human heart failure.

Myosin II and mechanotransduction: a balancing act

Adherent cells respond to mechanical properties of the surrounding extracellular matrix. Mechanical forces, sensed at specialized cell-matrix adhesion sites, promote actomyosin-based contraction within the cell. By manipulating matrix rigidity and adhesion strength, new roles for actomyosin contractility in the regulation of basic cellular functions, including cell proliferation, migration and stem cell differentiation, have recently been discovered. These investigations demonstrate that a balance of forces between cell adhesion on the outside and myosin II-based contractility on the inside of the cell controls many aspects of cell behavior. Disturbing this balance contributes to the pathogenesis of various human diseases. Therefore, elaborate signaling networks have evolved that modulate myosin II activity to maintain tensional homeostasis. These include signaling pathways that regulate myosin light chain phosphorylation as well as myosin II heavy chain interactions.

Olopatadine suppresses the migration of THP-1 monocytes induced by S100A12 protein

Olopatadine hydrochloride (olopatadine) is an antiallergic drug with histamine H(1) receptor antagonistic activity. Recently, olopatadine has been shown to bind to S100A12 which is a member of the S100 family of calcium-binding proteins, and exerts multiple proinflammatory activities including chemotaxis for monocytes and neutrophils. In this study, we examined the possibility that the interaction of olopatadine with S100A12 inhibits the proinflammatory effects of S100A12. Pretreatment of olopatadine with S100A12 reduced migration of THP-1, a monocyte cell line, induced by S100A12 alone, but did not affect recombinant human regulated upon activation, normal T cell expressed and secreted (RANTES)-induced migration. Amlexanox, which also binds to S100A12, inhibited the THP-1 migration induced by S100A12. However, ketotifen, another histamine H(1) receptor antagonist, had little effect on the activity of S100A12. These results suggest that olopatadine has a new mechanism of action, that is, suppression of the function of S100A12, in addition to histamine H(1) receptor antagonistic activity.

Proteomic identification of in vivo substrates for matrix metalloproteinases 2 and 9 reveals a mechanism for resolution of inflammation

Clearance of allergic inflammatory cells from the lung through matrix metalloproteinases (MMPs) is necessary to prevent lethal asphyxiation, but mechanistic insight into this essential homeostatic process is lacking. In this study, we have used a proteomics approach to determine how MMPs promote egression of lung inflammatory cells through the airway. MMP2- and MMP9-dependent cleavage of individual Th2 chemokines modulated their chemotactic activity; however, the net effect of complementing bronchoalveolar lavage fluid of allergen-challenged MMP2(-/-)/MMP9(-/-) mice with active MMP2 and MMP9 was to markedly enhance its overall chemotactic activity. In the bronchoalveolar fluid of MMP2(-/-)/MMP9(-/-) allergic mice, we identified several chemotactic molecules that possessed putative MMP2 and MMP9 cleavage sites and were present as higher molecular mass species. In vitro cleavage assays and mass spectroscopy confirmed that three of the identified proteins, Ym1, S100A8, and S100A9, were substrates of MMP2, MMP9, or both. Function-blocking Abs to S100 proteins significantly altered allergic inflammatory cell migration into the alveolar space. Thus, an important effect of MMPs is to differentially modify chemotactic bioactivity through proteolytic processing of proteins present in the airway. These findings provide a molecular mechanism to explain the enhanced clearance of lung inflammatory cells through the airway and reveal a novel approach to target new therapies for asthma.

Expression of the calcium-binding protein S100A4 is markedly up-regulated by osmotic stress and is involved in the renal osmoadaptive response

Proteomic analysis of Inner Medullary Collecting Duct (IMCD3) cells adapted to increasing levels of tonicity (300, 600, and 900 mosmol/kg H(2)O) by two-dimensional difference gel electrophoresis and mass spectrometry revealed several proteins as yet unknown to be up-regulated in response to hypertonic stress. Of these proteins, one of the most robustly up-regulated (22-fold) was S100A4. The identity of the protein was verified by high pressure liquid chromatography-mass spectrometry. Western blot analysis confirmed increased expression with increased tonicity, both acute and chronic. S100A4 protein expression was further confirmed by immunocytochemical analysis. Cells grown in isotonic conditions showed complete absence of immunostaining, whereas chronically adapted IMCD3 cells had uniform cytoplasmic localization. The protein is also regulated in vivo as in mouse kidney tissues S100A4 expression was many -fold greater in the papilla as compared with the cortex and increased further in the papilla upon 36 h of thirsting. Increased expression of S100A4 was also observed in the medulla and papilla, but not the cortex of a human kidney. Data from Affymetrix gene chip analysis and quantitative PCR also revealed increased S100A4 message in IMCD3 cells adapted to hypertonicity. The initial expression of message increased at 8-10 h following exposure to acute sublethal hypertonic stress (550 mosmol/kg H(2)O). Protein and message half-life in IMCD3 cells were 85.5 and 6.8 h, respectively. Increasing medium tonicity with NaCl, sucrose, mannitol, and choline chloride stimulated S100A4 expression, whereas urea did not. Silencing of S100A4 expression using a stable siRNA vector (pSM2; Open Biosystems) resulted in a 48-h delay in adaptation of IMCD3 cells under sublethal osmotic stress, suggesting S100A4 is involved in the osmoadaptive response. In summary, we describe the heretofore unrecognized up-regulation of a small calcium-binding protein, both in vitro and in vivo, whose absence profoundly delays osmoadaptation and slows cellular growth under hypertonic conditions.

Pathologies involving the S100 proteins and RAGE

The S100 proteins are exclusively expressed in vertebrates and are the largest subgroup within the superfamily of EF-hand Ca2(+)-binding proteins Generally, S100 proteins are organized as tight homodimers (some as heterodimers). Each subunit is composed of a C-terminal, 'canonical' EF-hand, common to all EF-hand proteins, and a N-terminal, 'pseudo' EF-hand, characteristic of S100 proteins. Upon Ca2(+)-binding, the C-terminal EF-hand undergoes a large conformational change resulting in the exposure of a hydrophobic surface responsible for target binding A unique feature of this protein family is that some members are secreted from cells upon stimulation, exerting cytokine- and chemokine-like extracellular activities via the Receptor for Advanced Glycation Endproducts, RAGE. Recently, larger assemblies of some S100 proteins (hexamers, tetramers, octamers) have been also observed and are suggested to be the active extracellular species required for receptor binding and activation through receptor multimerization Most S100 genes are located in a gene cluster on human chromosome 1q21, a region frequently rearranged in human cancer The functional diversification of S100 proteins is achieved by their specific cell- and tissue-expression patterns, structural variations, different metal ion binding properties (Ca2+, Zn2+ and Cu2+) as well as their ability to form homo-, hetero- and oligomeric assemblies Here, we review the most recent developments focussing on the biological functions of the S100 proteins and we discuss the presently available S100-specific mouse models and their possible use as human disease models In addition, the S100-RAGE interaction and the activation of various cellular pathways will be discussed. Finally, the close association of S100 proteins with cardiomyopathy, cancer, inflammation and brain diseases is summarized as well as their use in diagnosis and their potential as drug targets to improve therapies in the future.

Up-regulation of metastasis-promoting S100A4 (Mts-1) in rheumatoid arthritis: Putative involvement in the pathogenesis of rheumatoid arthritis

OBJECTIVE

To examine the involvement of the metastasis-inducing protein S100A4 (Mts-1) in the pathogenesis of rheumatoid arthritis (RA).

METHODS

Synovial tissue, synovial fluid, and plasma were obtained from RA and osteoarthritis (OA) patients who were undergoing joint surgery. Immunohistochemical and immunofluorescence analyses and enzyme-linked immunosorbent assays were used to determine the locations and concentrations of S100A4. The conformational structure of S100A4 in plasma and synovial fluid was determined after fractionation by size-exclusion chromatography, protein separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Western blot analysis. Expression of various S100 proteins in RA synovium was determined by immunofluorescence and double-staining using specific anti-S100 antibodies.

RESULTS

We found an up-regulation of S100A4 in cells infiltrating RA synovial tissue. Most cell types identified by cell-specific markers (fibroblasts, immune cells, and vascular cells) contributed to the production of S100A4 in RA synovial tissue. The pattern of S100A4 expression differed significantly from that of the proinflammatory proteins S100A9 and S100A12, which were restricted to phagocytes and granulocytes. The up-regulation of S100A4 in RA synovial tissue was consistent with the high concentrations of the protein in RA versus OA plasma (mean 1,100 versus 211 ng/ml) and synovial fluid (mean 1,980 versus 247 ng/ml). Moreover, we found that S100A4 in RA plasma and synovial fluid was present in bioactive multimeric (M-S100A4) conformations, whereas in OA, the majority of extracellular S100A4 was detected as the less active dimeric form. Consistent with our observations in tumor models, extracellular S100A4 stabilized the p53 tumor suppressor in RA synovial fibroblast-like cells and affected the regulation of p53 target genes, including Bcl-2, p21(WAF), and Hdm-2, as well as matrix metalloproteinases.

CONCLUSION

Overexpression of S100A4 in RA synovial tissue and its release as M-S100A4 can influence p53 function and modulate the expression of several genes that are potentially implicated in the disease process. Thus, S100A4 might play an important role in the pathogenesis of RA and might represent a new target for the treatment of RA.

Osteoinductive Effect of Cerebrospinal Fluid from Brain-Injured Patients

Patients with traumatic brain injury (TBI) are predisposed to heterotopic ossification, which is believed to be due to osteoinductive factors released at the site of the brain injury. To date, little is known about the presence of such factors in human cerebrospinal fluid (CSF). This study investigated whether CSF of TBI patients is osteoinductive. In addition, known osteoinductive factors--such as bone morphogenetic protein (BMP)-2, BMP-4, and BMP-7, and S100B--were measured in CSF. Eighty-four consecutive patients were classified according to brain pathology: TBI (n = 11), non-traumatic brain pathology (NTBP) (n = 26), and no brain pathology (control group) (n = 47). The osteoinductive effect of CSF was measured repeatedly in proliferation assays using a fetal human osteoblast cell line. The mean proliferation rate (normalized to the internal negative control) of the TBI, NTBP, and control groups was 138.2% (SD 13.1), 110.0% (SD 22.1), and 118.8% (SD 16.9), respectively. The potentially confounding effect of age was investigated further by restricting the selection of patients for analysis to that of the oldest patient in the TBI group and use of multiple regression analysis. After implementation of both, it was shown that age is highly unlikely to account for the higher rates of proliferation observed among the TBI patients in this study. Of note, the TBI group had a significantly higher mean proliferation rate than the NTBP (p = 0.001) and the control group (p = 0.006). S100B and BMP-2, -4, or -7 concentrations were measured using enzyme-linked immunosorbent assay (ELISA). There was no correlation between proliferation rates and S100B (r = 0.023). Only three of 36 CSF samples had measurable levels of BMP-2 and -7, and none had detectable concentrations of BMP-4. Consequently, it is unlikely that S100B or BMP-2, -4, or -7 are the putative osteoinductive factors. The results indicate that CSF from TBI patients has an osteoinductive effect in vitro. However, the osteoinductive factor has still to be characterized.

S100A4 is expressed at site of invasion in rheumatoid arthritis synovium and modulates production of matrix metalloproteinases

The metastasis-associated protein S100A4 promotes the progression of cancer by regulating the remodelling of the extracellular matrix. The expression of S100A4 in vivo is shown and the functional role of S100A4 in the pathogenesis of osteoarthritis and rheumatoid arthritisis is explored. The expression of S100A4 in rheumatoid arthritis, osteoarthritis and normal synovial tissues was determined by immunohistochemistry. The expression of matrix metalloproteinase (MMP) mRNA was measured in rheumatoid arthritis and osteoarthritis synovial fibroblasts treated and untreated with S100A4 oligomer by real-time polymerase chain reaction. Levels of released MMPs were confirmed by ELISA in cell culture supernatants. S100A4 protein was expressed in rheumatoid arthritis and osteoarthritis synovial tissues, in contrast with normal synovium. S100A4 up regulated MMP-3 mRNA in rheumatoid arthritis synovial fluid, with a peak after 6 h. This resulted in release of MMP-3 protein. MMP-1, MMP-9 and MMP-13 mRNA were also up regulated in synovial fluid, but with different kinetics. MMP-14 mRNA showed no change. Thus, S100A4 protein is expressed in synovial tissues of patients with rheumatoid arthritis and osteoarthritis in contrast with healthy people. It induces the expression and release of MMP-3 and other MMPs from synovial fluid. The data suggest that S100A4-producing cells could be involved in the pathogenesis of osteoarthritis and rheumatoid arthritis, including pannus formation and joint destruction.