Human S100B Research Articles

S100B as a predictor of delirium in critically ill obstetric patients: A nested case-control study.

Delirium is a neuropsychiatric illness that lasts for a short period of time. The incidence of delirium in the intensive care unit (ICU) varies from 20% to 80%. A nested case-control study was carried out in the obstetric ICU. Individuals were divided into three groups: critically ill obstetric women who had delirium on admission (Group A), women who developed delirium within follow-up of 7 days (Group B), and women who did not develop delirium after follow-up of 7 days (Group C). The APACHE II score was used to assess critical illness severity. The Richmond Agitation-Sedation Scale was used to assess the alertness or sedation level of patients, and the Confusion Assessment Method (ICU scale) was used to assess the presence of delirium. S100B was measured by human S100B calcium-binding protein B ELISA kit (Elabscience Biotechnology, Houston, USA). Severe preeclampsia and antepartum eclampsia were significantly associated with delirium. S100B levels in Group B were found to be significantly higher than those in Group C. S100B levels were higher in patients with >2 morbidities in comparison to patients with two morbidities. At a cutoff value of >169.25 pg/ml, S100B had a sensitivity of 74% and a specificity of 87.2% to discriminate cases of delirium from nondelirium. The rise in S100B levels was approximately three times greater in those who developed delirium as compared to those who did not. It is a more specific predictor of delirium.

Intracellular Protein S-Nitrosylation-A Cells Response to Extracellular S100B and RAGE Receptor.

Human S100B is a small, multifunctional protein. Its activity, inside and outside cells, contributes to the biology of the brain, muscle, skin, and adipocyte tissues. Overexpression of S100B occurs in Down Syndrome, Alzheimer’s disease, Creutzfeldt–Jakob disease, schizophrenia, multiple sclerosis, brain tumors, epilepsy, melanoma, myocardial infarction, muscle disorders, and sarcopenia. Modulating the activities of S100B, related to human diseases, without disturbing its physiological functions, is vital for drug and therapy design. This work focuses on the extracellular activity of S100B and one of its receptors, the Receptor for Advanced Glycation End products (RAGE). The functional outcome of extracellular S100B, partially, depends on the activation of intracellular signaling pathways. Here, we used Biotin Switch Technique enrichment and mass-spectrometry-based proteomics to show that the appearance of the S100B protein in the extracellular milieu of the mammalian Chinese Hamster Ovary (CHO) cells, and expression of the membrane-bound RAGE receptor, lead to changes in the intracellular S-nitrosylation of, at least, more than a hundred proteins. Treatment of the wild-type CHO cells with nanomolar or micromolar concentrations of extracellular S100B modulates the sets of S-nitrosylation targets inside cells. The cellular S-nitrosome is tuned differently, depending on the presence or absence of stable RAGE receptor expression. The presented results are a proof-of-concept study, suggesting that S-nitrosylation, like other post-translational modifications, should be considered in future research, and in developing tailored therapies for S100B and RAGE receptor-related diseases.

Evaluation of Human Serum S100B Protein as a Prognostic Factor in Nonmetastatic Breast Cancer Patients

Aim: The aim of this study was the evaluation of S100B prognostic role in nonmetastatic breast cancer patients, excluding confounding factors. Patients & method: 79 breast cancer patients, who fulfilled inclusion and exclusion criteria, were enrolled in the study. Before any adjuvant chemotherapy or surgery, the serum level of S100B was determined. All patients were followed up for 5 years, particularly regarding cancer recurrence and patients’ survival. Results: 42% of the patients experienced no recurrence after 5 years and cumulative risk of recurrence was 0.86. There was no significant correlation between serum level of protein S100B and recurrence rate in 5 years (p = 0.59). Conclusion: According to the results, the serum levels of S100B protein may have no prognostic role in nonmetastatic breast cancer.

1H and 15N chemical shift assignments of human S100B

1H and 15N chemical shift assignments of human S100B

Calcium-dependent interaction of monomeric S100P protein with serum albumin

S100 proteins are multifunctional (intra/extra)cellular mostly dimeric calcium-binding proteins engaged into numerous diseases. We have found that monomeric recombinant human S100P protein interacts with intact human serum albumin (HSA) in excess of calcium ions with equilibrium dissociation constant of 25–50nM, as evidenced by surface plasmon resonance spectroscopy and fluorescent titration by HSA of S100P labelled by fluorescein isothiocyanate. Calcium removal or S100P dimerization abolish the S100P-HSA interaction. The interaction is selective, since S100P does not bind bovine serum albumin and monomeric human S100B lacks interaction with HSA. In vitro glycation of HSA disables its binding to S100P. The revealed selective and highly specific conformation-dependent interaction between S100P and HSA shows that functional properties of monomeric and dimeric forms of S100 proteins are different, and raises concerns on validity of cell-based assays and animal models used for studies of (patho)physiological roles of extracellular S100 proteins.

Functional expression, characterization, and application of human S100B.

The EF-hand calcium-binding protein S100B presents a wide range of biological activities and functions. This binding protein is involved in various human diseases, including cancer, brain trauma and ischemia, neuro-degenerative disease (Alzheimer's disease), and psychiatric disorders. In this study, we prepared human S100B protein and its monoclonal antibodies. Human S100B protein was expressed in Escherichia coli, successfully purified by diethylaminoethyl cellulose anion-exchange chromatography, and then identified by western blot analysis. Monoclonal antibodies (mAbs) were produced by the standard hybridoma method and validated by enzyme-linked immunosorbent assay and western blot analysis. The prepared human S100B protein and its mAbs demonstrated potential biological activities. The KD of one mAb is approximately 4.72x10-8mol/l, and its cross reactivity is low with human S100A4, mouse S100A4, and human S100A1. Recombinant Soluble S100B can promote the migration and invasion of HeLa cells. The expression of S100B protein in tumor tissues can be detected effectively by using the prepared monoclonal antibodies. Increasing concentration of the anti-human S100B mAbs showed a reduced expression of the S100B protein. Subsequently, the expression of p53 increased significantly (P<0.05) in A375 cells. A significant increase in apoptosis in A375 cells was observed with increasing S100B mAb concentration. Results showed that our prepared S100B mAbs were suitable for detecting S100B expression in human tissues, furnishing promising tools for further functional investigation and clinical applications.

Serum S100B Protein Levels in Patients with Panic Disorder: Effect of Treatment with Selective Serotonine Reuptake Inhibitors.

ObjectiveAltered serum S100B protein levels have been shown in several psychiatric disorders. Our aim was to investigate whether plasma S100B is different in patients with panic disorder (PD) when compared with controls. Our second aim was to investigate whether treatment with SSRIs have an effect on S100B levels in patients with PD.MethodsThe sample included 32 patients diagnosed with PD (21 women, 11 men) per DSM-IV criteria and 21 healthy controls (11 women, 10 men). S100B levels were measured with BioVendor Human S100B ELISA (Enzyme Linked Immunosorbent Assay) kit.Results14 patients were not on drug treatment (43.8%) while 18 patients were taking various SSRIs. Median S100B value was 151.7 pg/mL (minimum-maximum: 120.4-164.7 pg/mL) in the control group, 147.4 pg/mL (minimum-maximum: 138.8-154.1 pg/mL) in the drug free group and 153.0 pg/mL (minimum-maximum: 137.9-164.7 pg/mL) in the treatment group. Kruskal-Wallis analysis showed a significant diffrerence among the three groups (z=9.9, df=2, p=0.007). Follow up Mann-Whitney-U tests indicated that while the control and the patients with treatment were not significantly different (z=-0.05, p=0.96), there were significant differences between the control group and untreated patients (z=-2.6, p=0.009) and treated and untreated patients (z=-3.0, p=0.003).ConclusionOur results suggested that, serum S100B protein level might be decreased in untreated PD patients and that patients who were treated with SSRIs had similar S100B level to healthy controls.

The Serum S100B Level as a Biomarker of Enteroglial Activation in Patients with Ulcerative Colitis

Objective. Recent studies have demonstrated that enteric glial cells (EGC) participate in the homeostasis of the gastrointestinal tract. This study investigated whether enteroglial markers, including S100B protein and glial fibrillary acidic protein (GFAP), can serve as noninvasive indicators of EGC activation and disease activity in UC patients. Methods. This clinical prospective study included 35 patients with UC and 40 age- and sex-matched controls. The diagnosis of UC was based on standard clinical, radiological, endoscopic, and histological criteria. Clinical disease activity was evaluated using the Modified Truelove-Witts Severity Index. Serum samples were analyzed for human GFAP and S100B using commercial enzyme-linked immunosorbent assay kits. Results. GFAP was not detected in the serum of either UC patients or controls (P > 0.05). However, we found a significant (P < 0.001) decrease in the serum S100B levels in the UC patients. No correlation between the serum S100B level and the disease activity or duration was observed (P > 0.05). The serum S100B levels did not differ between UC patients with active disease (24 patients, 68.6%) or in remission (11 patients, 31.4%) (P > 0.05). Conclusions. Ulcerative colitis patients had significantly lower serum S100B levels, while GFAP was of no diagnostic value in UC patients.

Structural Insights into Human S100B and Basic Fibroblast Growth Factor (FGF2) Interaction

Structural Insights into Human S100B and Basic Fibroblast Growth Factor (FGF2) Interaction

S100B as a glial cell marker in diabetic peripheral neuropathy

Evidence suggests that acute and chronic hyperglycemia can cause oxidative stress in the peripheral nervous system which, in turn, can promote the development of diabetic neuropathy. Recent studies have found increased expression of glial fibrillary acidic protein (GFAP) and S100B, both of which are indicators of glial reactivity, in the neural and retinal tissues of diabetic rats. For the first time in the literature, the serum levels of GFAP and S100B were assessed in patients with diabetes to evaluate the potential of these factors to serve as peripheral glial biomarkers of diabetes and to investigate their relationship to diabetic peripheral neuropathy. This prospective clinical study included 72 patients with type 2 diabetes mellitus and 50 age- and sex-matched control subjects. All diabetic patients were assessed with respect to diabetes-related microvascular complications, such as peripheral neuropathy, retinopathy, and nephropathy. Serum samples were analyzed for human GFAP and S100B using a commercially available Enzyme-linked Immuno Sorbent Assay kit. GFAP was not detected in the serum samples of either diabetic or control patients (p>0.05). However, we found a statistically significant decrease in S100B serum levels in patients with diabetes compared with control participants (p<0.001). No associations between serum S100B levels and the presence of diabetic peripheral neuropathy or other microvascular complications were observed (p>0.05). The findings of markedly decreased serum levels of S100B may possibly indicate a neuroprotective effect of S100B, whereas GFAP may be of no diagnostic value in human patients with diabetes.

Structural insights into the interaction of human S100B and basic fibroblast growth factor (FGF2): Effects on FGFR1 receptor signaling

S100B is a calcium sensing protein belonging to the S100 protein family with intracellular and extracellular roles. It is one of the EF hand homodimeric proteins, which is known to interact with various protein targets to regulate varied biological functions. Extracellular S100B has been recently reported to interact with FGF2 in a RAGE-independent manner. However, the recognition mechanism of S100B–FGF2 interaction at the molecular level remains unclear. In this study, the critical residues on S100B–FGF2 interface were mapped by combined information derived from NMR spectroscopy and site directed mutagenesis experiments. Utilizing NMR titration data, we generated the structural models of S100B–FGF2 complex from the computational docking program, HADDOCK which were further proved stable during 15ns unrestrained molecular dynamics (MD) simulations. Isothermal titration calorimetry studies indicated S100B interaction with FGF2 is an entropically favored process implying dominant role of hydrophobic contacts at the protein–protein interface. Residue level information of S100B interaction with FGF2 was useful to understand the varied target recognition ability of S100B and further explained its role in effecting extracellular signaling diversity. Mechanistic insights into the S100B–FGF2 complex interface and cell-based assay studies involving mutants led us to conclude the novel role of S100B in FGF2 mediated FGFR1 receptor inactivation.

The Effect of Optimising Cerebral Tissue Oxygen Saturation on Markers of Neurological Injury during Coronary Artery Bypass Graft Surgery

Surgical revascularisation of the coronary arteries is a cornerstone of cardiothoracic surgery. Advanced age and the incidence of preoperative co-morbidity in patients presenting for coronary artery bypass graft surgery increases the potential for stroke and other perioperative outcomes. It is hypothesised that by using interventions during cardiac surgery to improve cerebral oxygenation, the risk of patients enduring adverse neurological outcomes would be reduced. Forty patients (mean age 55.3, standard deviation 9.74 and range from 39 to 72 years) undergoing on-pump coronary artery bypass graft surgery were recruited at Inkosi Albert Luthuli Central Hospital, South Africa. Patients were randomised into a control group (n=20) and interventional group (n=20). Intraoperative regional cerebral oxygen saturation (rSO2) monitoring with active display and Murkin treatment intervention protocol was administered for the interventional group. Arterial blood samples for the measurement of serum S100B were taken pre and postoperatively. An enzyme immunoassay (ELISA) was used for the quantitative and comparative measurement of human S100B concentrations for both groups. A prioritised intraoperative management protocol to maintain rSO2 values above 75% of the baseline threshold during cardiopulmonary bypass was followed. There was a highly significant difference in the change in S100B concentrations post surgery between the interventional (37.3picograms per millilitre) and control groups (139.3pg/ml). The control group showed a significantly higher increase in S100B concentration over time than the intervention group (p<0.001). There was a significant difference in cerebral desaturation time (p<0.001) between the groups. The mean desaturation time for the control group was 63.85min as compared to 24.7min in the interventional group. Cerebral desaturation occurred predominantly during aortic cross clamping, distal anastomosis of coronary arteries and aortic cross clamp release. Predictors of cerebral oxygen desaturation included, partial pressure of carbon dioxide (pCO2), temperature, pump flow rate (LMP), mean arterial pressure (MAP), haematocrit, heart rate (HR) and patient oxygen saturation (SpO2). Monitoring brain oxygen saturation during on-pump CABG together with an effective treatment protocol to deal with cerebral desaturation must be advocated.

Identification of small-molecule inhibitors of the human S100B–p53 interaction and evaluation of their activity in human melanoma cells

The interaction between human S100 calcium-binding protein B (S100B) and the tumor suppressor protein p53 is considered to be a possible therapeutic target for malignant melanoma. To identify potent inhibitors of this interaction, we screened a fragment library of compounds by means of a fluorescence-based competition assay involving the S100B-binding C-terminal peptide of p53. Using active compounds from the fragment library as query compounds, we constructed a focused library by means of two-dimensional similarity searching of a large database. This simple, unbiased method allowed us to identify several inhibitors of the S100B-p53 interaction, and we elucidated preliminary structure–activity relationships. One of the identified compounds had the potential to inhibit the S100B–p53 interaction in melanoma cells.

Thermodynamic and kinetic analysis of peptides derived from CapZ, NDR, p53, HDM2, and HDM4 binding to human S100B.

S100B is a member of the S100 subfamily of EF-hand proteins that has been implicated in malignant melanoma and neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease. Calcium-induced conformational changes expose a hydrophobic binding cleft, facilitating interactions with a wide variety of nuclear, cytoplasmic, and extracellular target proteins. Previously, peptides derived from CapZ, p53, NDR, HDM2, and HDM4 have been shown to interact with S100B in a calcium-dependent manner. However, the thermodynamic and kinetic basis of these interactions remains largely unknown. To gain further insight, we screened these peptides against the S100B protein using isothermal titration calorimetry and nuclear magnetic resonance. All peptides were found to have binding affinities in the low micromolar to nanomolar range. Binding-induced changes in the line shapes of S100B backbone (1)H and (15)N resonances were monitored to obtain the dissociation constants and the kinetic binding parameters. The large microscopic K(on) rate constants observed in this study (≥1 × 10(7) M(-1) s(-1)) suggest that S100B utilizes a "fly casting mechanism" in the recognition of these peptide targets.

Abstract 1054: S100B affects cell signaling in malignant melanoma

Abstract Establishing the mechanism by which S100B effects ERK and its downstream proteins will provide valuable insight into the role of S100B in the progression of melanoma and potentially aid in developing new pharmacological drugs. S100B is a 21.5 kDa symmetric homodimer that is highly conserved and expressed in a number of tissues and cell lines, including melanocytes. Generally, low levels of S100B have trophic effects, while higher levels are problematic, as is the case in human malignant melanoma. S100B is an effective and widely used prognostic marker for malignant melanoma, with increased levels of serum S100B being predictive of disease stage, increased recurrence, and low overall survival. It has previously been found that S100B directly interacts with the tumor suppressor protein p53, down-regulating its protein levels, thereby allowing damaged cells to proliferate and mutations to propagate. S100B has also been implicated in several other signaling pathways, including the MAPK pathway (BRAF-MEK-ERK). The initial hypothesis tested was that S100B inhibits the phosphorylation of ERK targets in a calcium-dependent manner. To evaluate the significance of S100B in melanoma cell lines, stable S100B knock-down clones were created using lentiviral shRNA particles. The extent of the knock-down varies among the clones and shows a correlation between the level of remaining S100B and the level of phosphorylated ERK, where the clone with the least amount of S100B also has the lowest level of phosphorylated ERK. The clones also display a decreased rate of proliferation measured with both an MTT based assay, as well as with electrical impedance. Over-expression studies were also conducted where normal human S100B, but not a mutant S100B incapable of binding calcium, results in increased phosphorylated ERK, but decreased phosphorylated RSK at Thr573. To determine if S100B was interacting with RSK directly, pull-down assays were performed, and RSK was detected in S100B pull-downs in the presence of calcium; however, it was not detected in the presence of the calcium chelator EDTA. In conclusion, we demonstrate that the calcium-binding protein S100B affects the MAPK pathway by simultaneously increasing phosphorylated ERK and decreasing phosphorylated RSK, together which are consistent with the increased growth rates and cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1054. doi:10.1158/1538-7445.AM2011-1054

Human CD8+ T cells and NK cells express and secrete S100B upon stimulation

Previous studies have demonstrated the utility of S100B as a surrogate marker of brain-related pathologies, e.g. neuropsychiatric disorders, and melanoma progression, which have an inflammatory component. This study addresses the relevance of S100B+ lymphocytes in mediating such responses. S100B expression was determined in human peripheral blood leukocytes isolated from healthy volunteers using flow cytometry. S100B+ lymphocytes were characterised for phenotype, cytokine production and S100B secretion. In addition, we investigated whether S100B activates monocytes and neutrophils.S100B+ cells comprised 2–4% of all lymphocytes and the majority displayed a CD3+ CD8+ phenotype; fewer cells were CD3− CD56+ NK lymphocytes. Comparison of S100B+ and S100B− CD3+ CD8+ cells revealed no differences in production of interferon gamma (IFNγ) and interleukin-2 (IL-2). Stimulation of S100B+ CD3+ CD8+ lymphocytes with anti-CD3 or phytohaemagglutinin resulted in release of S100B. High concentrations of recombinant human S100B triggered upregulation of CD11b and membrane shedding of CD62L in granulocytes and monocytes.These findings set the stage for a new field of research addressing a S100B-mediated crosstalk between the innate and adaptive immune systems if close proximity of effector and responder cells accomplishes sufficient local S100B levels. In various physiological and pathological conditions S100B might function as an interface to immunological processes, distinct from known cytokine- and chemokine-mediated pathways.

Metabonomics Study of Brain-Specific Human S100B Transgenic Mice by Using High-Performance Liquid Chromatography Coupled with Quadrupole Time of Flight Mass Spectrometry

For the purpose of investigating the effects of S100B on the development of Parkinsion's disease (PD), a high-performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (HPLC/MS-ESI-TOF) metabonomic approach was established to study the mesencephalon profiling of brain-specific human S100B transgenic mice. In order to obtain more full-scale chemical information of metabolites, two kinds of separation mechanism, including reversed-phase (RP) column chromatography and hydrophilic interaction liquid chromatography (HILIC) column, were combined to use. Acquired data were subjected to principal component analysis (PCA) to investigate the effects of S100B protein on mice mesencephalon metabolite profiles. Potential biomarkers were screened by using Mass Hunter Prossional Profiller (MPP) and were identified by the accurate mass. Twelve metabolites in mesencephalon of S100B transgenic mice were identified as potential biomarkers, among which, glutamic acid (Glu) detected by RP/MS in negative ionization mode, gamma-aminobutyric acid (GABA) and tryptophan (Trp) detected by HILIC/MS in positive ionization mode, phenylalanine (Phe) and histidine (His) detected by HILIC/MS in negative ionization mode, related to metabolic pathway of neurotransmitters in mice central nervous system. The analytical technique used in this paper was able to detect biochemical changes in mesencephalon of S100B transgenic mice, which may be helpful to understand the action mechanism of S100B protein in the development of PD.

S100B Transgenic Mice Develop Features of Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. Until now, the cause and mechanism of PD are unknown, making further studies necessary. We undertook this study to establish the brain-specific S100B gene transgenic mice and investigate the role of S100B in the development of PD. The hS100B transgenic vector was constructed by inserting the human S100B gene downstream into platelet-derived growth factor (PDGF) promoter, followed by microinjection to produce transgenic mice. Motor coordination ability of mice in the S100B transgenic group (TG), S100B knockout group (KG) and the non-transgenic control group (CG) were measured by the Rota-rod test. The expressions of dopamine D1 receptor (D1DR), dopamine D2 receptor (D2DR), G protein-coupled receptor kinase2 (GRK2), G protein-coupled receptor kinase5 (GRK5), tyrosine hydroxylase (TH) in the brain tissue, and levels of dioxyphenylalanine (DOPA), dopamine (DA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the midbrain tissue were detected by RT-PCR, Western blotting, and high-performance liquid chromatography-fluorescence detection method (HPLC-FLD), respectively. Compared with CG, in TG, the motor coordination ability of mice, expressions ofD2DR and GRK2, and the level of 5-HT visibly decreased, while the levels of DOPA, DA and its metabolic product HVA increased, the expressions of D1DR, GRK5, TH and 5-HIAA were similar. Compared with CG, no obvious change of detection indexes was observed in KG. Overexpression of S100B in the brain resulted in motor coordination impairment, which may have resulted from the downregulation of D2DR and GRK2 expressions, increased DA synthesis and metabolism, and decreased 5-HT level. Therefore, S100B may be a potential cause of pathogenesis in PD.

The crystal structures of human S100B in the zinc- and calcium-loaded state at three pH values reveal zinc ligand swapping

S100B is a homodimeric zinc-, copper-, and calcium-binding protein of the family of EF-hand S100 proteins. Zn2+ binding to S100B increases its affinity towards Ca2+ as well as towards target peptides and proteins. Cu2+ and Zn2+ bind presumably to the same site in S100B. We determined the structures of human Zn2+- and Ca2+-loaded S100B at pH 6.5, pH 9, and pH 10 by X-ray crystallography at 1.5, 1.4, and 1.65Å resolution, respectively. Two Zn2+ ions are coordinated tetrahedrally at the dimer interface by His and Glu residues from both subunits. The crystal structures revealed that ligand swapping occurs for one of the four ligands in the Zn2+-binding sites. Whereas at pH 9, the Zn2+ ions are coordinated by His15, His25, His 85′, and His 90′, at pH 6.5 and pH 10, His90′ is replaced by Glu89′. The results document that the Zn2+-binding sites are flexible to accommodate other metal ions such as Cu2+. Moreover, we characterized the structural changes upon Zn2+ binding, which might lead to increased affinity towards Ca2+ as well as towards target proteins. We observed that in Zn2+–Ca2+-loaded S100B the C-termini of helix IV adopt a distinct conformation. Zn2+ binding induces a repositioning of residues Phe87 and Phe88, which are involved in target protein binding. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Abstract 4125: The effects of S100B on cell signaling in malignant melanoma

Abstract Establishing the mechanism by which S100B effects ERK and its downstream proteins will provide valuable insight into the role of S100B in the progression of melanoma and potentially aid in developing new pharmacological drugs. The protein S100B is an effective prognostic marker for human malignant melanoma. Increased levels of serum S100B are predictive of disease stage, increased recurrence, and low overall survival. It has previously been found that S100B directly interacts with the tumor suppressor protein p53, down-regulating its protein levels, thereby allowing damaged cells to proliferate and mutations to propagate. S100B has also been implicated in several other signaling pathways, including the MAPK pathway. The initial hypothesis tested was that S100B inhibits the phosphorylation of ERK targets in a calcium-dependent manner. The S100B binding motif has been found to overlap with the ERK binding motif, suggesting that S100B binds the targets and physically prevents ERK from interacting with and subsequently phosphorylating them. ERK kinase assays revealed that the addition of S100B in the presence of calcium decreased ERK phosphorylation of RSK, but more dramatically Elk-1. Additionally, RSK was detected in S100B pull-downs in the presence of calcium; however, it was not detected in the presence of the calcium chelator EDTA. Over-expression of normal human S100B, but not a mutant S100B incapable of binding calcium, results in decreased phosphorylated RSK at Thr573, yet increased phosphorylated ERK, interestingly. Since a rise in serum S100B levels is indicative of tumor progression, it was also of interest to see if the addition of extracellular S100B alone is sufficient to elicit the same signaling response. Preliminary data shows an increase in phosphorylated ERK after the addition of low concentrations of extracellular S100B, as well as effects on ERK targets. We demonstrate that the calcium-binding protein S100B affects the MAPK pathway by simultaneously increasing phosphorylated ERK and decreasing phosphorylated RSK and Elk-1, together which could have a significant impact on cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4125.