Oligomeric forms of the metastasis-related Mts1 (S100A4) protein stimulate neuronal differentiation in cultures of rat hippocampal neurons

Mechanism of the Ca²+-dependent interaction between S100A4 and tail fragments of nonmuscle myosin heavy chain IIA

The interaction between the calcium-binding protein S100A4 and the C-terminal fragments of nonmuscle myosin heavy chain IIA has been studied by equilibrium and kinetic methods. Using site-directed mutants, we conclude that Ca(2+) binds to the EF2 domain of S100A4 with micromolar affinity and that the K(d) value for Ca(2+) is reduced by several orders of magnitude in the presence of myosin target fragments. The reduction in K(d) results from a reduced dissociation rate constant (from 16 s(-1) to 0.3 s(-1) in the presence of coiled-coil fragments) and an increased association rate constant. Using peptide competition assays and NMR spectroscopy, we conclude that the minimal binding site on myosin heavy chain IIA corresponds to A1907-G1938; therefore, the site extends beyond the end of the coiled-coil region of myosin. Electron microscopy and turbidity assays were used to assess myosin fragment filament disassembly by S100A4. The latter assay demonstrated that S100A4 binds to the filaments and actively promotes disassembly rather than just binding to the myosin monomer and displacing the equilibrium. Quantitative modelling of these in vitro data suggests that S100A4 concentrations in the micromolar region could disassemble myosin filaments even at resting levels of cytoplasmic [Ca(2+)]. However, for Ca(2+) transients to be effective in further promoting dissociation, the elevated Ca(2+) signal must persist for tens of seconds. Fluorescence recovery after photobleaching of A431/SIP1 cells expressing green fluorescent protein-myosin IIA, immobilised on fibronectin micropatterns to control stress fibre location, yielded a recovery time constant of around 20 s, consistent with in vitro data.

Natural and amyloid self-assembly of S100 proteins: structural basis of functional diversity

The S100 proteins are 10-12 kDa EF-hand proteins that act as central regulators in a multitude of cellular processes including cell survival, proliferation, differentiation and motility. Consequently, many S100 proteins are implicated and display marked changes in their expression levels in many types of cancer, neurodegenerative disorders, inflammatory and autoimmune diseases. The structure and function of S100 proteins are modulated by metal ions via Ca(2+) binding through EF-hand motifs and binding of Zn(2+) and Cu(2+) at additional sites, usually at the homodimer interfaces. Ca(2+) binding modulates S100 conformational opening and thus promotes and affects the interaction with p53, the receptor for advanced glycation endproducts and Toll-like receptor 4, among many others. Structural plasticity also occurs at the quaternary level, where several S100 proteins self-assemble into multiple oligomeric states, many being functionally relevant. Recently, we have found that the S100A8/A9 proteins are involved in amyloidogenic processes in corpora amylacea of prostate cancer patients, and undergo metal-mediated amyloid oligomerization and fibrillation in vitro. Here we review the unique chemical and structural properties of S100 proteins that underlie the conformational changes resulting in their oligomerization upon metal ion binding and ultimately in functional control. The possibility that S100 proteins have intrinsic amyloid-forming capacity is also addressed, as well as the hypothesis that amyloid self-assemblies may, under particular physiological conditions, affect the S100 functions within the cellular milieu.

Sumoylation and nuclear translocation of S100A4 regulate IL-1beta-mediated production of matrix metalloproteinase-13

S100A4, a member of the S100 family of proteins, plays an important role in matrix remodeling by up-regulating the expression of matrix metalloproteinases (MMPs). We have previously shown that S100A4 is overexpressed in diseased cartilage and that extracellular S100A4 stimulates MMP-13 production, a major type II collagen-degrading enzyme, via activation of receptor for advanced glycation end product signaling. In the present study, using human articular chondrocytes, we show that intracellular S100A4 translocated into the nucleus upon interleukin-1β (IL-1β) stimulation and translocation required post-translational modification of S100A4 by the sumo-1 protein. Two sumoylation sites were identified on the S100A4 molecule, Lys(22) and Lys(96). Mutation of these lysine residues abolished the ability of S100A4 to be sumoylated and to translocate into the nucleus. Blocking of sumoylation and nuclear transport of S100A4 inhibited the IL-1β-induced production of MMP-13. Nuclear S100A4 was bound to the promoter region of MMP-13 in IL-1β-treated cells. Thus, we demonstrate a novel mechanism for sumoylated S100A4 as a regulator of expression of the MMP-13 gene.

Signal transduction mechanisms involved in S100A4-induced activation of the transcription factor NF-kappaB

BACKGROUND

The metastasis-promoting protein S100A4 activates the transcription factor NF-kappaB through the classical NF-kappaB activation pathway. The upstream signal transduction mechanisms leading to increased NF-kappaB activity are, however, incompletely characterized.

METHODS

The human osteosarcoma cell line II-11b was stimulated with recombinant S100A4 in the presence or absence of inhibitors of common signal transduction pathways, and NF-kappaB activity was examined using a luciferase-based reporter assay and phosphorylation of IkappaBalpha. mRNA expression was analyzed by real-time RT-PCR, protein expression was examined by Western blotting and IKK activity was measured using an in vitro kinase assay. The role of upstream kinases and the cell surface receptor RAGE was investigated by overexpression of dominant negative proteins and by siRNA transfection.

RESULTS

The Ser/Thr kinase inhibitors H-7 and staurosporine inhibited S100A4-induced IkappaBalpha phosphorylation and subsequent NF-kappaB activation. The protein tyrosine kinase inhibitor genistein and the phospholipase C inhibitor compound 48/80 had a partial inhibitory effect on IkappaBalpha phosphorylation, whereas inhibitors of protein kinase C, G-protein coupled receptors and PI 3-kinases had no effect on the level of phosphorylation. Interestingly, S100A4 treatment induced activating phosphorylations of IKKalpha/beta, but neither H-7 nor staurosporine was able to significantly inhibit IKK activation. Dominant negative MEKK1 or NIK did not inhibit S100A4-induced NF-kappaB activity, and S100A4 stimulation did not influence AKT phosphorylation. Furthermore, diminished expression of the putative S100 protein receptor RAGE did not affect the observed phosphorylation of IkappaBalpha.

CONCLUSIONS

S100A4 activates NF-kappaB by inducing phosphorylation of IKKalpha/beta, leading to increased IkappaBalpha phosphorylation. The Ser/Thr kinase inhibitors H-7 and staurosporine attenuated S100A4-induced NF-kappaB activation and inhibited IKK-mediated phosphorylation of IkappaBalpha. S100A4-induced NF-kappaB activation was independent of the putative S100 protein receptor RAGE and the Ser/Thr kinases MEKK1, NIK and AKT. These findings lead to increased understanding of S100A4 signaling, which may contribute to the identification of novel targets for anti-metastatic therapy.

Effects of Reg-2 on survival of spinal cord neurons in vitro

Regeneration gene protein 2 (Reg-2) is a small secreted protein expressed in motor and sensory neurons of spinal cord during developmental stages and following injury of peripheral nerves. Reg-2 appears to act as a neurotrophic factor and protects injured neurons from death during regeneration. To illustrate these potential protective effects in vitro, we investigated the blocking effects of Reg-2 antibodies on the survival of primary cultured spinal cord neurons and astrocytes, as well as on neurite outgrowth. In addition, the effects of Reg-2 in neuron injury models induced by peroxide and mitochondrial poisoning were assessed. Our results showed that Reg-2 antibody markedly reduced survival and neurite outgrowth from neurons, whereas astrocyte survival was unaffected. Addition of Reg-2 into the culture medium had no effect on neuron survival or neurite outgrowth. However, the addition of the Reg-2 into culture media after peroxide treatment or cellular hypoxia insult induced by mitochondrial poisoning can reduce lactate dehydrogenase release levels and cell death. Thus, the data suggests that Reg-2 is essential for the survival and neurite outgrowth of developing spinal cord neurons but not the survival of glial cells, and that Reg-2 plays protective effects on spinal cord neurons against injury in vitro.

Subcellular distribution of S100A4 and its transcriptional regulation under hypoxic conditions in gastric cancer cell line BGC823

It is well known that S100A4 is overexpressed in many tumors and involved in tumor invasion and metastasis. But the regulation of it is ill understood. We previously found that hypoxia mimicking cobalt chloride (CoCl(2)) enhanced the mRNA and protein expressions of the S100A4 gene in the gastric cancer cell line BGC823. In this study we found that S100A4 also displayed increased expression in BGC823 cells after exposure to real hypoxia (2.5% O(2)) as that by CoCl(2) treatment. Moreover, S100A4 protein showed different subcellular distribution under real hypoxia compared with that by CoCl(2) treatment or in normoxic conditions. To investigate the underlying molecular mechanism by which hypoxia regulates the expression of S100A4, we analyzed the regulatory sequences of the genes by bioinformatics and found a putative hypoxia responsive element (HRE) motif in the first intron of S1004. Furthermore, luciferase reporter assay showed that it is responsive to hypoxia. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays demonstrated that hypoxia-inducible factor 1 (HIF-1) binds to the functional HRE in vitro and in vivo. The results provide evidence that S100A4 is a hypoxia-inducible gene, whose transcription is stimulated at least partly through the interaction of HIF-1 and HRE located at +329 to +334 of S100A4.

Metastasis-inducing S100A4 and RANTES cooperate in promoting tumor progression in mice

BACKGROUND

The tumor microenvironment has been described as a critical milieu determining tumor growth and metastases. A pivotal role of metastasis-inducing S100A4 in the development of tumor stroma has been proven in animal models and verified in human breast cancer biopsies. Expression and release of S100A4 has been shown in various types of stroma composing cells, including fibroblasts and immune cells. However, the events implicated in upstream and downstream pathways regulating the activity of the extracellular S100A4 protein in the tumor milieu remain unsolved.

METHODOLOGY/PRINCIPAL FINDINGS

We studied the interplay between the tumor cell-derived cytokine regulated-upon-activation, normal T-cell expressed and secreted (RANTES; CCL5) and S100A4 which were shown to be critical factors in tumor progression. We found that RANTES stimulates the externalization of S100A4 via microparticle shedding from the plasma membrane of tumor and stroma cells. Conversely, the released S100A4 protein induces the upregulation of fibronectin (FN) in fibroblasts and a number of cytokines, including RANTES in tumor cells as well as stimulates cell motility in a wound healing assay. Importantly, using wild type and S100A4-deficient mouse models, we demonstrated a substantial influence of tumor cell-derived RANTES on S100A4 release into blood circulation which ultimately increases the metastatic burden in mice.

CONCLUSIONS/SIGNIFICANCE

Altogether, the data presented strongly validate the pro-metastatic function of S100A4 in the tumor microenvironment and define how the tumor cell-derived cytokine RANTES acts as a critical regulator of S100A4-dependent tumor cell dissemination. Additionally, for the first time we demonstrated the mechanism of S100A4 release associated with plasma membrane microparticle shedding from various cells types.

Lung metastasis fails in MMTV-PyMT oncomice lacking S100A4 due to a T-cell deficiency in primary tumors

Interactions between tumor and stroma cells are essential for the progression of cancer from its initial growth at a primary site to its metastasis to distant organs. The metastasis-stimulating protein S100A4 exerts its function as a stroma cell-derived factor. Genetic depletion of S100A4 significantly reduced the metastatic burden in lungs of PyMT-induced mammary tumors. In S100A4(+/+) PyMT mice, massive leukocyte infiltration at the site of the growing tumor at the stage of malignant transition was associated with increased concentration of extracellular S100A4 in the tumor microenvironment. In contrast, in S100A4(-/-) PyMT tumors, a significant suppression of T-cell infiltration was documented at the transition period. In vitro, the S100A4 protein mediated the attraction of T cells. Moreover, S100A4(+/+), but not S100A4(-/-), fibroblasts stimulated the invasion of T lymphocytes into fibroblast monolayers. In vivo, the presence of S100A4(+/+), but not S100A4(-/-), fibroblasts significantly stimulated the attraction of T lymphocytes to the site of the growing tumor. Increased levels of T cells were also observed in the premetastatic lungs of tumor-bearing mice primed to metastasize by S100A4(+/+) fibroblasts. Treatment of T cells with the S100A4 protein stimulated production of cytokines, particularly granulocyte colony-stimulating factor and eotaxin-2. The same cytokines were detected in the fluid of S100A4(+/+) PyMT tumors at the transition period. We suggest that release of S100A4 in the primary tumor stimulates infiltration of T cells and activates secretion of cytokines, thus triggering sequential events that fuel tumor cells to metastasize. Similar processes could occur in the premetastatic lungs, facilitating generation of inflammatory milieu favorable for metastasis formation.

S100A4 and metastasis: a small actor playing many roles

The calcium-binding protein S100A4 promotes metastasis in several experimental animal models, and S100A4 protein expression is associated with patient outcome in a number of tumor types. S100A4 is localized in the nucleus, cytoplasm, and extracellular space and possesses a wide range of biological functions, such as regulation of angiogenesis, cell survival, motility, and invasion. In this review, we summarize the evidence connecting S100A4 and cancer metastasis and discuss the mechanisms by which S100A4 promotes tumor progression.

Metastasis-inducing S100A4 protein is associated with the disease activity of rheumatoid arthritis

OBJECTIVES

To evaluate the association between metastasis-inducing protein S100A4 and disease activity in patients with RA, and to demonstrate the effect of TNF-alpha blocking therapy on plasma levels of S100A4 in these patients.

METHODS

Plasma levels of the S100A4 protein were analysed in 40 anti-TNF-alpha naive patients with active RA. Of the 40 patients, 25 were treated with adalimumab and monitored over time. The conformational form of S100A4 was analysed using size-exclusion gel chromatography. TNF-alpha mRNA expression and protein synthesis were analysed by RT-PCR and ELISA, respectively.

RESULTS

Baseline levels of S100A4 were significantly correlated with disease activity in RA patients (r = 0.41; P < 0.01). After 12 weeks of treatment with adalimumab, there was an obvious shift in the conformations of S100A4 from the multimeric to the dimeric forms, whereas the total levels of the S100A4 protein remained unchanged. This suggests that the bioactive (multimer) S100A4 may decline in response to successful treatment with adalimumab. In addition, we showed significant up-regulation of TNF-alpha mRNA (P < 0.01), and protein release to the cell culture medium of monocytes stimulated with the S100A4 multimer compared with those treated with the dimer and to the unstimulated monocytes (P < 0.001).

CONCLUSIONS

This is the first study to show that the levels of the S100A4 protein are correlated with RA disease activity. Furthermore, only the bioactive form, but not the total amount of S100A4, decreases after successful TNF-alpha blocking therapy in patients with RA. These data support an important role for the S100A4 multimer in the pathogenesis of RA.

The crystal structures of human S100A12 in apo form and in complex with zinc: new insights into S100A12 oligomerisation

The functions of the members of the S100 family of EF-hand proteins are modulated by calcium and, in a number of cases, by zinc or copper. One such protein is S100A12, which is implicated in inflammation and host-parasite responses. Previously, we reported the structures of human S100A12 in both low (dimeric) and high (hexameric) calcium forms and, in addition, that of a complex with copper and calcium. Here we report the crystal structures of the metal-free apo form of human S100A12 at 1.77 A resolution and of the zinc complex in two crystal forms (P2(1)2(1)2(1) and F222) to 1.88 A and 1.73 A resolution, respectively. These are the first structures of a zinc-only complex of an S100 protein to be determined. The zinc complex structure shows significant differences from those of both calcium-loaded and apo-S100A12 structures, and comparisons suggest an explanation for the zinc-induced 1500-fold increase in calcium affinity. In addition, the new structures provide insight into the role of zinc-calcium interplay in the transition of S100A12 from a dimer through a tetramer to a hexamer. The role of both zinc and calcium in target binding by S100A12 during host-parasite responses is confirmed by experiments with paramyosin from the tropical parasites Onchocerca volvulus and Brugia malayi.

Induction of S100A4, S100A6, and galectin-1 during the lineage commitment of CD4+CD8+ thymocyte cell line is suppressed by 2,3,7,8-tetrachlorodibenzo-p-dioxin

To study the mechanisms underlying the linage commitment of CD4+CD8+ thymocytes and the skewed differentiation of CD4+CD8+ into CD4-CD8+ thymocytes induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we stimulated with antigen DPK cells, a CD4+CD8+ thymic lymphoma cell line which can differentiate into CD4+CD8- thymocytes and performed a comparative proteomic analysis of DPK cells stimulated with antigen or not. Among the 10 up-regulated or induced proteins upon antigenic stimulation, S100A4, S100A6, and galectin-1 were highly up-regulated. Kinetic studies revealed that expression of S100A4, S100A6, and galectin-1 was dramatically increased as early as 10min after antigen stimulation, similar to that of cKrox and Runx3, transcription factors intimately associated with the lineage commitment. Among four thymocyte subpopulations of the thymus examined, S100A4, S1006, and galectin-1 were most prominently expressed in CD4+CD8+ thymocytes, but not at all in CD4-CD8+ and CD4-CD8- thymocytes. In the spleen, expression of S100A4, S1006, and galectin-1 was greater in CD4 than in CD8 splenocytes. When TCDD was added to antigen-stimulated DPK cells, antigen-induced up-regulation of S100A4, S1006, and galectin-1 were remarkably inhibited, probably partly accounting for the skewed differentiation of CD4+CD8+ into CD4-CD8+ thymocytes induced by TCDD.

Interleukin-7 stimulates secretion of S100A4 by activating the JAK/STAT signaling pathway in human articular chondrocytes

OBJECTIVE

S100A4 has been shown to be increased in osteoarthritic (OA) cartilage and to stimulate chondrocytes to produce matrix metalloproteinase 13 (MMP-13) through activation of the receptor for advanced glycation end products (RAGE). The aim of this study was to examine the mechanism of S100A4 secretion by chondrocytes.

METHODS

Human articular chondrocytes isolated from ankle cartilage were stimulated with 10 ng/ml of interleukin-1beta (IL-1beta), IL-6, IL-7, or IL-8. Cells were pretreated with either a JAK-3 inhibitor, brefeldin A, or cycloheximide. Immunoblotting with phospho-specific antibodies was used to determine the activation of signaling proteins. Secretion of S100A4 was measured in conditioned media by immunoblotting, and MMP-13 was measured by enzyme-linked immunosorbent assay.

RESULTS

Chondrocyte secretion of S100A4 was observed after treatment with IL-6 or IL-8 but was much greater in cultures treated with equal amounts of IL-7 and was not observed after treatment with IL-1beta. IL-7 activated the JAK/STAT pathway, with increased phosphorylation of JAK-3 and STAT-3, leading to increased production of S100A4 and MMP-13. Overexpression of a dominant-negative RAGE construct inhibited the IL-7-mediated production of MMP-13. Pretreatment of chondrocytes with a JAK-3 inhibitor or with cycloheximide blocked the IL-7-mediated secretion of S100A4, but pretreatment with brefeldin A did not.

CONCLUSION

IL-7 stimulates chondrocyte secretion of S100A4 via activation of JAK/STAT signaling, and then S100A4 acts in an autocrine manner to stimulate MMP-13 production via RAGE. Since both IL-7 and S100A4 are up-regulated in OA cartilage and can stimulate MMP-13 production by chondrocytes, this signaling pathway could contribute to cartilage destruction during the development of OA.

The metastasis associated protein S100A4: a potential novel link to inflammation and consequent aggressive behaviour of rheumatoid arthritis synovial fibroblasts

The metastasis-associated protein S100A4 belongs to the large family of S100 calcium-binding proteins that appear to play regulatory roles in diverse biological activities. Moreover, a prognostic role of S100A4 has been suggested for patients with several types of cancer. Cancer promoting properties for S100A4 have been demonstrated, particularly through its regulation of cell motility, proliferation and apoptosis, as well as by stimulation of angiogenesis and remodelling of the extracellular matrix. Increased expression of S100A4 mRNA has been detected in proliferating synovial fibroblasts in rheumatoid arthritis. Furthermore, strong upregulation of the S100A4 protein in rheumatoid arthritis synovial tissue compared with osteoarthritis and control tissues has been demonstrated recently, especially at sites of joint invasion. Several immune and vascular cells were also identified to be producing S100A4 within the synovium. The local upregulation of S100A4 was accompanied by high plasma and synovial fluid concentrations of the S100A4 protein existing in the bioactive oligomeric form in patients with rheumatoid arthritis. Consistent with data from cancer studies, the extracellular S100A4 oligomer appears to be involved in regulation of several matrix-degrading enzymes and modulation of the transcriptional activation function of the tumour suppressor protein p53 in rheumatoid arthritis synovial fibroblasts. Taken together, one can speculate that increased S100A4 protein in circulation and locally at sites of inflammation, particularly at sites of joint destruction, might be linked to the process of aggressive fibroblast behaviour contributing to the pathogenesis of chronic autoinflammatory diseases such as rheumatoid arthritis.

S100A4 overexpression proves to be independent marker for breast cancer progression

BACKGROUND

Breast cancer is the most common cancer and cause of deaths in women around the world. Oncogene amplification usually occurs late in tumor progression and correlates well with aggressiveness of tumor. In fact the function of the S100A4 protein and its role in metastasis is unclear at present. The purpose of the study was to determine the expression of S100A4 protein in the invasion status and metastatic potential of breast cancer by using tissue microarray and to determine its role in breast cancer based on the expression of S100A4 gene product.

METHODS

S100A4 protein expression was examined by immunohistochemistry (IHC) using commercially available tissue microarray containing malignant and normal breast tissue cores from 216 patients.

RESULTS

S100A4 was absent in normal breast tissues while positive in 45.1% of infiltrating ductal carcinoma (IDC) node negative and 48.8% of infiltrating lobular carcinoma node negative. In paired samples, S100A4 protein was expressed in 13.5% of IDC node positive cases and 35.1% of matched lymph node metastasis.

CONCLUSION

S100A4 protein expression appears widely expressed in early and advanced breast cancer stages compared with normal breast. Our study suggests S100A4 may play a role in breast cancer progression and may prove to be an independent marker of breast cancer which appears to be down regulated in more advanced stages of breast cancer.

15N relaxation studies of Apo-Mts1: a dynamic S100 protein

Mts1 is a member of the S100 family of EF-hand calcium-binding proteins. Like most S100 proteins, Mts1 exists as a dimer in solution and contains one canonical and one pseudo-EF-hand motif per monomer, each of which consists of two alpha helices connected by a loop capable of coordinating a calcium ion. The backbone dynamics of murine apo-Mts1 homodimer have been examined by nuclear magnetic resonance spectroscopy. Longitudinal and transverse relaxation data and steady-state (1)H- (15)N nuclear Overhauser effects were analyzed using model-free formalism. The extracted global correlation time is 9.94 ns. Results indicate that the protein backbone is most rigid at the dimer interface, made up of helices 1 and 4 from each monomer with mean S (2) ( S avg (2)) values approximately 0.9, flanked by helices 2 and 3 with lower S avg (2) values of 0.84 and 0.77, respectively. Each calcium-binding site along with the hinge joining the two EF-hands and the N- and C-termini are considerably more flexible than the dimer interface on a range of time scales and more flexible than the corresponding regions of other S100 proteins studied to date. As the hinge and the C-terminal tail are believed to interact with target proteins, these dynamic characteristics may have implications for Mts1 activity.

Activation of NF-kappaB by extracellular S100A4: analysis of signal transduction mechanisms and identification of target genes

The metastasis-promoting protein S100A4 stimulates metastatic progression through both intracellular and extracellular functions. Extracellular activities of S100A4 include stimulation of angiogenesis, regulation of cell death and increased cell motility and invasion, but the exact molecular mechanisms by which extracellular S100A4 exerts these effects are incompletely elucidated. The aim of the present study was to characterize S100A4-induced signal transduction mechanisms and to identify S100A4 target genes. We demonstrate that extracellular S100A4 activates the transcription factor NF-kappaB in a subset of human cancer cell lines through induction of phosphorylation and subsequent degradation of the NF-kappaB inhibitor IkappaBalpha. Concomitantly, S100A4 induced a sustained activation of the MAP kinase JNK, whereas no increased activity of the MAP kinases p38 or ERK was observed. Microarray analyses identified 136 genes as being significantly regulated by S100A4 treatment, and potentially interesting S100A4-induced gene products include IkappaBalpha, p53, ephrin-A1 and optineurin. Increased expression of ephrin-A1 and optineurin was validated using RT-PCR, Western blotting and functional assays. Furthermore, S100A4-stimulated transcription of these target genes was dependent on activation of the NF-kappaB pathway. In conclusion, these findings contribute to the understanding of the complex molecular mechanisms responsible for the diverse biological functions of extracellular S100A4, and provide further evidence of how S100A4 may stimulate metastatic progression.

Transamidation by transglutaminase 2 transforms S100A11 calgranulin into a procatabolic cytokine for chondrocytes

In osteoarthritis (OA), low-grade joint inflammation promotes altered chondrocyte differentiation and cartilage catabolism. S100/calgranulins share conserved calcium-binding EF-hand domains, associate noncovalently as homodimers and heterodimers, and are secreted and bind receptor for advanced glycation end products (RAGE). Chondrocyte RAGE expression and S100A11 release are stimulated by IL-1beta in vitro and increase in OA cartilage in situ. Exogenous S100A11 stimulates chondrocyte hypertrophic differentiation. Moreover, S100A11 is covalently cross-linked by transamidation catalyzed by transglutaminase 2 (TG2), itself an inflammation-regulated and redox stress-inducible mediator of chondrocyte hypertrophic differentiation. In this study, we researched mouse femoral head articular cartilage explants and knee chondrocytes, and a soluble recombinant double point mutant (K3R/Q102N) of S100A11 TG2 transamidation substrate sites. Both TG2 and RAGE knockout cartilage explants retained IL-1beta responsiveness. The K3R/Q102N mutant of S100A11 retained the capacity to bind to RAGE and chondrocytes but lost the capacity to signal via the p38 MAPK pathway or induce chondrocyte hypertrophy and glycosaminoglycans release. S100A11 failed to induce hypertrophy, glycosaminoglycan release, and appearance of the aggrecanase neoepitope NITEGE in both RAGE and TG2 knockout cartilages. We conclude that transamidation by TG2 transforms S100A11 into a covalently bonded homodimer that acquires the capacity to signal through the p38 MAPK pathway, accelerate chondrocyte hypertrophy and matrix catabolism, and thereby couple inflammation with chondrocyte activation to potentially promote OA progression.

S100A4: a common mediator of epithelial-mesenchymal transition, fibrosis and regeneration in diseases?

Multiple reports have focused on S100A4's role in cancer progression, specifically its ability to enhance metastasis. However, recent studies have linked S100A4 to several diseases besides cancer, including kidney fibrosis, cirrhosis, pulmonary disease, cardiac hypertrophy and fibrosis, arthritis and neuronal injuries. Common to all these diseases is the involvement of fibrotic and inflammatory processes, i.e. processes greatly dependent on tissue remodelling, cell motility and epithelial-mesenchymal transition. Therefore, the basic biological mechanisms behind S100A4's effects are emerging. S100A4 belongs to the S100 family of proteins that contain two Ca2+-binding sites including a canonical EF-hand motif. S100A4 is involved in the regulation of a wide range of biological effects including cell motility, survival, differentiation and contractility. S100A4 has both intracellular and extracellular effects. Hence, S100A4 interacts with cytoskeletal proteins and enhances metastasis of several types of cancer cells. In addition, S100A4 is secreted by unknown mechanisms, thus, paracrinely stimulating a variety of cellular responses, including angiogenesis and neuronal growth. Although many cellular effects of S100A4 are well described, the molecular mechanisms whereby S100A4 elicits these responses remain largely unknown. However, it is likely that the intracellular and the extracellular effects involve distinct mechanisms. In this review, we explore the possible roles of S100A4 in non-cancer diseases and employ this knowledge to describe underlying biological mechanisms including a change in cellular phenotype towards less tightly adherent cells and activation of fibrotic processes that may explain this protein's involvement in multiple pathologies.

Expression of S100A4 by a variety of cell types present in the tumor microenvironment of human breast cancer

The S100A4 protein, which is involved in the metastasis process, is a member of the S100 superfamily of Ca-binding proteins. Members of this family are multifunctional signaling proteins with dual extra and intracellular functions involved in the regulation of diverse cellular processes. Several studies have established a correlation between S100A4 protein expression and worse prognosis for patients with various malignancies including breast cancer. In this article, we have used specific antibodies in combination with immunohistochemistry (IHC) to identify the cell types that express S100A4 in human breast cancer biopsies obtained from high-risk patients. IHC analysis of 68 tumor biopsies showed that the protein is expressed preferentially by various cell types present in the tumor microenvironment (macrophages, fibroblasts, activated lymphocytes), rather than by the tumor cells themselves. Moreover, we show that the protein is externalized by the stroma cells to the fluid that bathes the tumor microenvironment, where it is found in several forms that most likely correspond to charge variants. Using a specific ELISA test, we detected a significant higher concentration of S100A4 in the tumor interstitial fluid (TIF) as compared to their corresponding normal counterparts (NIF).

Modified expression of Mts1/S100A4 protein in C6 glioma cells or surrounding astrocytes affects migration of tumor cells in vitro and in vivo

The calcium-binding Mts1/S100A4 protein plays an important role in motility and metastatic activity of tumor cells. Recently we showed that Mts1/S100A4 is expressed in white matter astrocytes and influences their migration in vitro and in vivo. Here, we have investigated the role of Mts1/S100A4 expression in C6 glioma cells or surrounding astrocytes for migration of C6 cells on astrocytes, using short interference (si) RNA to silence Mts1/S100A4 expression. We find that in vitro, the migration of Mts1/S100A4 expressing and silenced C6 cells on astrocytes is predominantly dependent on the expression of Mts1/S100A4 in astrocytes, i.e. C6 cells preferably migrate on Mts1/S100A4-silenced astrocytes. In vivo, Mts1/S100A4-positive C6 cells preferably migrate in white matter. In contrast Mts1/S100A4-silenced C6 cells avoid white matter and migrate in gray matter and meninges. Thus, the migration pattern of C6 cells is affected by their intrinsic Mts1/S100A4 expression as well as Mts1/S100A4 expression in astrocytes. To investigate if Mts1/S100A4 has a significant role on brain tumor progression, we made quantitative RT-PCR analysis for the expression of S100A4/Mts1 in various grades of astrocytic tumors. Our data showed that high-grade glioblastomas express higher amount of S100A4/Mts1 than low-grade astrocytic tumors.

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.

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.

Increase in production of matrix metalloproteinase 13 by human articular chondrocytes due to stimulation with S100A4: Role of the receptor for advanced glycation end products

OBJECTIVE

S100 proteins have been implicated in various inflammatory conditions, including arthritis. The aims of this study were to determine whether chondrocytes produce S100A4 and whether S100A4 can stimulate the production of matrix metalloproteinase 13 (MMP-13) by articular chondrocytes via receptor for advanced glycation end products (RAGE)-mediated signaling.

METHODS

The expression of chondrocyte S100A4 was analyzed by immunohistochemistry using normal and osteoarthritic (OA) cartilage and by immunoblotting of chondrocyte cell lysates. RAGE signaling was examined by stimulating chondrocytes with S100A4 and monitoring for the activation of MAP kinases and NF-kappaB. Production of MMP-13 was determined in the conditioned medium. A pulldown assay using biotin-labeled S100A4 was used to demonstrate binding to RAGE.

RESULTS

S100A4 expression was detected in human articular chondrocytes by immunoblotting and appeared to increase in the cell lysates from OA tissue. Marked positive immunostaining for S100A4 was also noted in sections of human cartilage with changes due to OA. Stimulation of chondrocytes with S100A4 increased the phosphorylation of Pyk-2, MAP kinases, and activated NF-kappaB, followed by increased production of MMP-13 in the conditioned medium. This signaling was inhibited in cells pretreated with soluble RAGE, advanced glycation end product-bovine serum albumin, or the antioxidant Mn(III)tetrakis (4-benzoic acid) porphyrin, or by overexpression of a dominant-negative RAGE construct. A pulldown assay showed that S100A4 binds to RAGE in chondrocytes.

CONCLUSION

This is the first study to demonstrate that S100A4 binds to RAGE and stimulates a RAGE-mediated signaling cascade, leading to increased production of MMP-13. Since both S100A4 and RAGE are up-regulated in OA cartilage, this signaling pathway could contribute to cartilage degradation in OA.

S100A16, a novel calcium-binding protein of the EF-hand superfamily

S100A16 protein is a new and unique member of the EF-hand Ca(2+)-binding proteins. S100 proteins are cell- and tissue-specific and are involved in many intra- and extracellular processes through interacting with specific target proteins. In the central nervous system S100 proteins are implicated in cell proliferation, differentiation, migration, and apoptosis as well as in cognition. S100 proteins became of major interest because of their close association with brain pathologies, for example depression or Alzheimer's disease. Here we report for the first time the purification and biochemical characterization of human and mouse recombinant S100A16 proteins. Flow dialysis revealed that both homodimeric S100A16 proteins bind two Ca(2+) ions with the C-terminal EF-hand of each subunit, the human protein exhibiting a 2-fold higher affinity. Trp fluorescence variations indicate conformational changes in the orthologous proteins upon Ca(2+) binding, whereas formation of a hydrophobic patch, implicated in target protein recognition, only occurs in the human S100A16 protein. In situ hybridization analysis and immunohistochemistry revealed a widespread distribution in the mouse brain. Furthermore, S100A16 expression was found to be astrocyte-specific. Finally, we investigated S100A16 intracellular localization in human glioblastoma cells. The protein was found to accumulate within nucleoli and to translocate to the cytoplasm in response to Ca(2+) stimulation.

Nuclear expression of S100A4 is associated with aggressive behavior of epithelial ovarian carcinoma: an important autocrine/paracrine factor in tumor progression

Although S100A4 expression has reportedly been associated with metastasis of various malignancies, little is known about its biological significance in ovarian carcinomas. In this study, we investigated expression and secretion of S100A4 and its extracellular function in ovarian carcinoma cells. We first used immunohistochemistry to examine the expression and localization of S100A4 in 113 epithelial ovarian neoplasms (24 benign, 20 borderline, and 69 malignant tumors) and analyzed its prognostic significance in patients with ovarian carcinoma. Then we investigated the expression, subcellular localization, and secretion of S100A4 in four ovarian carcinoma cell lines. Finally, we examined the effect of S100A4 treatment on the cell proliferation and invasiveness of ovarian carcinoma cells, along with activation of small GTPase, RhoA. Both cytoplasmic and nuclear expressions of S100A4 were significantly stronger in carcinomas than those in benign and borderline tumors. Ovarian carcinoma patients with strong nuclear S100A4 expression showed a significantly shorter survival than those without (P = 0.0045). This was not the case for cytoplasmic S100A4 expression. Ovarian carcinoma cell lines were shown to express S100A4, and secrete S100A4 into the culture media. Treatment with recombinant S100A4 resulted in the upregulation of S100A4 expression, translocation of S100A4 into the nucleus, and enhancement of invasiveness, which was associated with the upregulation of small GTPase, RhoA. These findings suggest that the nuclear expression of S100A4 is involved in the aggressive behavior of ovarian carcinoma and S100A4 is an autocrine/paracrine factor that plays an important role in the aggressiveness of ovarian carcinoma cells.

Sensory neurite outgrowth on white matter astrocytes is influenced by intracellular and extracellular S100A4 protein

The central nervous system (CNS) is considered a nonpermissive environment for axonal regeneration because of the presence of myelin and associated repulsive molecules. However, neural cells transplanted to the CNS preferably migrate and extend their fibers in white matter areas. We previously showed that white matter astrocytes in vivo express the calcium-binding protein S100A4, which is strongly up-regulated in areas of white matter degeneration. To investigate the role of white matter astrocytes and their specific protein S100A4 in axonal regeneration, we developed white matter astrocyte cultures with strong S100A4 expression and grew dissociated adult dorsal root ganglion (DRG) cells on top of astrocytes for 24 hr. By using small interfering S100A4 RNA, we were able to eliminate S100A4 expression and compare growth of DRG cell neurites on S100A4-silenced and S100A4-expressing astrocytes. In addition, we studied whether extracellular S100A4 has an effect on neurite growth from adult DRG cells cultured on S100A4-expressing white matter astrocytes. Our data show that white matter astrocytes are permissive for neurite growth, although high levels of S100A4 in white matter astrocytes have a negative effect on this growth. Extracellular application of S100A4 induced extensive growth of DRG cell neurites on white matter astrocytes. These findings suggest that white matter astrocytes are able to support axonal regeneration and, furthermore, that administration of extracellular S100A4 provides strong additional support for axonal regeneration.

Amyloid Fibrils of Mammalian Prion Protein Are Highly Toxic to Cultured Cells and Primary Neurons

A growing body of evidence indicates that small, soluble oligomeric species generated from a variety of proteins and peptides rather than mature amyloid fibrils are inherently highly cytotoxic. Here, we show for the first time that mature amyloid fibrils produced from full-length recombinant mammalian prion protein (rPrP) were highly toxic to cultured cells and primary hippocampal and cerebella neurons. Fibrils induced apoptotic cell death in a time- and dose-dependent manner. The toxic effect of fibrils was comparable with that exhibited by soluble small beta-oligomers generated from the same protein. Fibrils prepared from insulin were not toxic, suggesting that the toxic effect was not solely due to the highly polymeric nature of the fibrillar form. The cell death caused by rPrP fibrils or beta-oligomers was substantially reduced when expression of endogenous PrP(C) was down-regulated by small interfering RNAs. In opposition to the beta-oligomer and amyloid fibrils of rPrP, the monomeric alpha-helical form of rPrP stimulated neurite out-growth and survival of neurons. These studies illustrated that both soluble beta-oligomer and amyloid fibrils of the prion protein are intrinsically toxic and confirmed that endogenously expressed PrP(C) is required for mediating the toxicity of abnormally folded external PrP aggregates.

Parietal endoderm secreted S100A4 promotes early cardiomyogenesis in embryoid bodies

Cardiomyogenesis is influenced by factors secreted by anterior-lateral and extra-embryonic endoderm. Differentiation of embryonic stem cells in embryoid bodies allows to study the influence of growth factors on cardiomyogenesis. By these means SPARC was identified as a new factor enhancing cardiomyogenesis [M. Stary, W. Pasteiner, A. Summer, A. Hrdina, A. Eger, G. Weitzer, Parietal endoderm secreted SPARC promotes early cardiomyogenesis in vitro, Exp. Cell Res. 310 (2005) 331-341]. Here we report a similar and new function for S100A4, a calcium-binding protein of the EF-hand type. S100A4 is secreted by parietal endoderm and promotes early differentiation and proliferation of cardiomyocytes. Oligomeric S100A4 supports cardiomyogenesis in a concentration-dependent manner, whereas inhibition of autocrine S100A4 severely attenuates cardiomyogenesis. S100A4 specifically influences transcription in differentiating cardiomyocytes, as evident from increased expression of cardiac transcription factor genes nkx2.5 and mef2C. These data suggest that S100A4, like SPARC, plays a supportive role in early in vitro cardiomyogenesis.

Molecular mechanisms of Ca(2+) signaling in neurons induced by the S100A4 protein

The S100A4 protein belongs to the S100 family of vertebrate-specific proteins possessing both intra- and extracellular functions. In the nervous system, high levels of S100A4 expression are observed at sites of neurogenesis and lesions, suggesting a role of the protein in neuronal plasticity. Extracellular oligomeric S100A4 is a potent promoter of neurite outgrowth and survival from cultured primary neurons; however, the molecular mechanism of this effect has not been established. Here we demonstrate that oligomeric S100A4 increases the intracellular calcium concentration in primary neurons. We present evidence that both S100A4-induced Ca(2+) signaling and neurite extension require activation of a cascade including a heterotrimeric G protein(s), phosphoinositide-specific phospholipase C, and diacylglycerol-lipase, resulting in Ca(2+) entry via nonselective cation channels and via T- and L-type voltage-gated Ca(2+) channels. We demonstrate that S100A4-induced neurite outgrowth is not mediated by the receptor for advanced glycation end products, a known target for other extracellular S100 proteins. However, S100A4-induced signaling depends on interactions with heparan sulfate proteoglycans at the cell surface. Thus, glycosaminoglycans may act as coreceptors of S100 proteins in neurons. This may provide a mechanism by which S100 proteins could locally regulate neuronal plasticity in connection with brain lesions and neurological disorders.

Calcium-dependent tetramer formation of S100A8 and S100A9 is essential for biological activity

S100 proteins comprise the largest family of calcium-binding proteins. Members of this family usually form homo- or heterodimers, which may associate to higher-order oligomers in a calcium-dependent manner. The heterodimers of S100A8 and S100A9 represent the major calcium-binding proteins in phagocytes. Both proteins regulate migration of these cells via modulation of tubulin polymerization. Calcium binding induces formation of (S100A8/S100A9)2 tetramers. The functional relevance of these higher-order oligomers of S100 proteins, however, is not yet clear. To investigate the importance of higher-order oligomerization for S100 proteins, we created a set of mutations within S100A9 (N69A, E78A, N69A+E78A) destroying the high-affinity C-terminal calcium-binding site (EF-hand II). Mutations in EF-hand II did not interfere with formation of the S100A8/S100A9 heterodimer as demonstrated by yeast two-hybrid experiments and pull-down assays. In contrast, mass spectrometric analysis and density gradient centrifugation revealed that calcium-induced association of (S100A8/S100A9)2 tetramers was strictly dependent on a functional EF-hand II in S100A9. Failure of tetramer formation was associated with a lack of functional activity of S100A8/S100A9 complexes in promoting the formation of microtubules. Thus, our data demonstrate that calcium-dependent formation of (S100A8/S100A9)2 tetramers is an essential prerequisite for biological function. This is the first report showing a functional relevance of calcium-induced higher-order oligomerization in the S100 family.

The metastasis associated protein S100A4: role in tumour progression and metastasis

The metastasis associated protein S100A4 is a small calcium binding protein that is associated with metastatic tumors and appears to be a molecular marker for clinical prognosis. Below we discuss its biochemical properties and possible cellular functions in metastasis including cell motility, invasion, apoptosis, angiogenesis and differentiation.

A procedure for culturing astrocytes from white matter and the application of the siRNA technique for silencing the expression of their specific marker, S100A4

White matter astrocytes have physiological functions which are distinct from those of astrocytes in gray matter. White matter becomes highly non-permissive to neurite growth after injury, but the role of white matter astrocytes in this process is incompletely understood. Current protocols for making primary astroglial cultures are inadequate for exploring the specific properties of white matter astrocytes in vitro. We describe a procedure for obtaining cultures of white matter astrocytes from the rodent corpus callosum. In this procedure, we take advantage of our previous finding that white, but not gray matter astrocytes express the calcium-binding protein S100A4. S100A4 expressing astrocytes are abundant in the corpus callosum, and we show that cultures, highly enriched in S100A4 expressing white matter astrocytes, can be reproducibly generated from this area. Key factors for successful cultures are (i) meticulous dissection of the corpus callosum from 4-day-old rats, and (ii) Percoll density gradient centrifugation to purify astrocytes. As a means of exploring the possible role of S100A4 in white matter astrocytes, we describe the use of the siRNA technique to eliminate the expression of S100A4 in our in vitro system.

Suppression of tumor development and metastasis formation in mice lacking the S100A4(mts1) gene

The S100A4(mts1) protein stimulates metastatic spread of tumor cells. An elevated expression of S100A4 is associated with poor prognosis in many human cancers. Dynamics of tumor development were studied in S100A4-deficient mice using grafts of CSML100, highly metastatic mouse mammary carcinoma cells. A significant delay in tumor uptake and decreased tumor incidences were observed in S100A4(-/-) mice compared with the wild-type controls. Moreover, tumors developed in S100A4(-/-) mice never metastasize. Immunohistochemical analyses of these tumors revealed reduced vascularity and abnormal distribution of host-derived stroma cells. Coinjection of CSML100 cells with immortalized S100A4(+/+) fibroblasts partially restored the dynamics of tumor development and the ability to form metastasis. These fibroblasts were characterized by an enhanced motility and invasiveness in comparison with S100A4(-/-) fibroblasts, as well as by the ability to release S100A4 into the tumor environment. Taken together, our results point to a determinative role of host-derived stroma cells expressing S100A4 in tumor progression and metastasis.

Gene expression profiling in phosphatidylethanolamine N-methyltransferase knockout mice

Choline is derived from the diet as well as from de novo methylation of phosphatidylethanolamine catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). Pemt knockout mice have no endogenous synthesis of choline molecules. We previously reported that these mice have excess S-adenosylmethionine and hypermethylated DNA in brain, as well as increased mitosis in neural progenitor cells of the hippocampus in embryonic day 17 (E17) brain. In the present study, E17 fetal brains and adult brains were harvested and total RNA was extracted. In fetal brain, using gene expression profiling and Significance Analysis of Microarrays, we identified 107 significant genes with increased expression and 379 significant genes with decreased expression. In adult brain, we identified 381 significant genes with increased expression and 1037 significant genes with decreased expression. We observed significant changes in expression of genes regulating cell cycle (such as TP53, Fgf4, and Ing1), differentiation and neurogenesis (such as S100A4 and D14Ws), and phospholipid metabolism (such as Pip5k1a, Pitpn, and Pla2g6) as well as in a number of methyltransferase genes (including Gnmt). Some genes with expression known to be regulated by promoter methylation were suppressed in Pemt knockout brain (such as S100a4 and TP53). These findings are consistent with the biochemical changes that we previous reported in fetal brains from Pemt knockout mice. This is the first report of gene profiling in Pemt(-/-) mouse brain.

Metastasis-associated protein S100A4 induces angiogenesis through interaction with Annexin II and accelerated plasmin formation

Many advanced tumors overexpress and secrete the S100A4 protein that is known to promote angiogenesis and metastasis development. The mechanisms of this effect and the endothelial receptor for S100A4 are both still unknown. Here we report that extracellular S100A4 interacts with annexin II, an endothelial plasminogen co-receptor. Co-localization and direct binding of S100A4 and annexin II were demonstrated, and the binding site was identified in the N-terminal region of annexin II. S100A4 alone or in a complex with annexin II accelerated tissue plasminogen activator-mediated plasminogen activation in solution and on the endothelial cell surface through interaction of the S100A4 C-terminal lysines with the lysine-binding domains of plasminogen. A synthetic peptide corresponding to the N terminus of annexin II prevented S100A4-induced plasmin formation in the endothelial cell culture. Local plasmin formation induced by circulating S100A4 could contribute to tumor-induced angiogenesis and metastasis formation that makes this protein an attractive target for new anti-cancer and anti-angiogenic therapies.

Distinct subcellular location of the Ca2+-binding protein S100A1 differentially modulates Ca2+-cycling in ventricular rat cardiomyocytes

Calcium is a key regulator of cardiac function and is modulated through the Ca2+-sensor protein S100A1. S100 proteins are considered to exert both intracellular and extracellular functions on their target cells. Here we report the impact of an increased intracellular S100A1 protein level on Ca2+-homeostasis in neonatal ventricular cardiomyocytes in vitro. Specifically, we compare the effects of exogenously added recombinant S100A1 to those resulting from the overexpression of a transduced S100A1 gene. Extracellularly added S100A1 enhanced the Ca2+-transient amplitude in neonatal ventricular cardiomyocytes (NVCMs) through a marked decrease in intracellular diastolic Ca2+-concentrations ([Ca2+]i). The decrease in [Ca2+]i was independent of sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) activity and was probably the result of an increased sarcolemmal Ca2+-extrusion through the sodium-calcium exchanger (NCX). At the same time the Ca2+-content of the sarcoplasmic reticulum (SR) decreased. These effects were dependent on the uptake of extracellularly added S100A1 protein and its subsequent routing to the endosomal compartment. Phospholipase C and protein kinase C, which are tightly associated with this subcellular compartment, were found to be activated by endocytosed S100A1.

By contrast, adenoviral-mediated intracellular S100A1 overexpression enhanced the Ca2+-transient amplitude in NVCMs mainly through an increase in systolic [Ca2+]i. The increased Ca2+-load in the SR was based on an enhanced SERCA2a activity while NCX function was unaltered. Overexpressed S100A1 colocalized with SERCA2a and other Ca2+-regulatory proteins at the SR, whereas recombinant S100A1 protein that had been endocytosed did not colocalize with SR proteins. This study provides the first evidence that intracellular S100A1, depending on its subcellular location, modulates cardiac Ca2+-turnover via different Ca2+-regulatory proteins.