S100 protein and Down syndrome

Astroglial and microglial pathology in Down syndrome: Focus on Alzheimer's disease

Down syndrome (DS) arises from the triplication of human chromosome 21 and is considered the most common genetic cause of intellectual disability. Glial cells, specifically astroglia and microglia, display pathological alterations that might contribute to DS neuropathological alterations. Further, in middle adulthood, people with DS develop clinical symptoms associated with premature aging and Alzheimer's disease (AD). Overexpression of the amyloid precursor protein (APP) gene, encoded on chromosome 21, leads to increased amyloid-β (Aβ) levels and subsequent formation of Aβ plaques in the brains of individuals with DS. Amyloid-β deposition might contribute to astroglial and microglial reactivity, leading to neurotoxic effects and elevated secretion of inflammatory mediators. This review discusses evidence of astroglial and microglial alterations that might be associated with the AD continuum in DS.

Influence of S100A2 in Human Diseases

S100 proteins are a family of low-molecular-weight proteins characterized by two calcium-binding sites with a helix-loop-helix (“EF-hand-type”) domain. The S100 family of proteins is distributed across various organs and can interact with diverse molecules. Among the proteins of the S100 family, S100 calcium-binding protein A2 (S100A2) has been identified in mammary epithelial cells, glands, lungs, kidneys, and prostate gland, exhibiting various physiological and pathological actions in human disorders, such as inflammatory diseases and malignant tumors. In this review, we introduce basic knowledge regarding S100A2 regulatory mechanisms. Although S100A2 is a tumor suppressor, we describe the various influences of S100A2 on cancer and inflammatory diseases.

S100A16 is a prognostic marker for colorectal cancer

BACKGROUND

S100 is a superfamily of calcium-binding proteins that regulate multiple biological processes and are involved in many diseases. S100A16 has recently been identified to be involved in several cancers such as bladder cancer, lung cancer, and oral squamous cell carcinoma. However, the role of S100A16 expression in the colorectal cancer (CRC) has not been investigated.

METHODS

S100A16 protein expression was detected by immunohistochemistry in 296 cases of CRC. Kaplan-Meier survival analysis and Cox regression analysis were performed to evaluate the prognostic significance of S100A16.

RESULT

The results showed that the overall survival (OS) of patients with low membrane S100A16 expression was significantly shorter than patients with high expression (P < 0.05). Chi-square analysis showed that S100A16 expression had a positive correlation with tumor grade (P = 0.02). Multivariate analysis identified membrane S100A16 expression as an independent prognostic marker for OS in CRC patients. (P < 0.05). Univariate analysis showed no significant association between cytoplasmic/nuclear S100A16 expression and OS.

CONCLUSION

Membrane S100A16 is associated with the prognosis of CRC patients, indicating that S100A16 may be a potential prognostic biomarker and therapeutic target for CRC.

Search for melanoma markers in plasma and serum samples

Fourteen blood samples from patients with melanoma and eleven blood samples from healthy subjects were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The study was focussed on species of low molecular weight, in the range 800-5000 Da, present in plasma and sera. While for healthy subjects plasma samples lead to the production of a higher number of ionic species, for melanoma patients a high number of diagnostic ions, present with high frequency and with quite high relative abundance, are present in particular in serum samples and to a lesser extent also in plasma. Since plasma samples are obtained more easily in comparison to sera, it is possible to suggest that also plasma can be used for these studies.

Over-expression of S100B protein in children with cerebral palsy or delayed development

S100B protein plays a role in promoting the maturation of a variety of neurons in many different CNS regions. Behavioral dysfunction in S100B over-expressed transgenic mice and the chronic elevation of S100B in Down's syndrome and in schizophrenia suggest that S100B over-expression is related to abnormal brain function. Therefore, we believed that the over-expression of S100B protein might be implicated in developmental brain dysfunction. The purpose of this study was to evaluate the serum S100B protein levels in patients with developmental brain dysfunction, such as cerebral palsy and delayed development, and to determine the clinical relevance of serum S100B protein in these patients. The mean values of serum S100B protein were significantly increased in both conditions. Patients with cerebral palsy had a S100B protein level of 3455.8 +/- 5004.6 ng/L and those with delayed development of 2557.0 +/- 2321.0 ng/L, compared with a normal control level of 583.8 +/- 483.0 ng/L (P < 0.05). The over-expression of S100B (defined as the normal mean plus three standard deviations) was found in 47.1% of the total patient group (delayed development (47.5%) and cerebral palsy (47.0%)). The frequency of over-expression was not significantly related to clinical diagnosis, disease severity or to brain MRI findings. However, patients who had periventricular leukomalacia by brain MRI showed a wide range and very high levels of S100B exceeding 10,000 ng/L in some cases. These findings suggest that the pathogenesis implied by the over-expression of S100B protein during brain development may play a role in developmental brain dysfunction.

Enhanced calcium transients in glial cells in neonatal cerebellar cultures derived from S100B null mice

S100B is the major low-affinity Ca(2+)-binding protein in astrocytes. In order to study the role of S100B in the maintenance of Ca(2+) homeostasis, we generated S100B null mice by a targeted inactivation of the S100B gene. Absence of S100B expression was demonstrated by Northern and Western blotting for S100B mRNA and protein, respectively, and immunoperoxidase staining of sections of various brain regions. S100B null mice were viable, fertile, and exhibited no overt behavioral abnormalities up to 12 months of age. On the basis of light microscopy and immunohistochemical staining, there were no discernable alterations in the distribution and morphology of astrocytes or neurons in sections of adult brains of these mice. Astrocytes in cerebellar cultures derived from 6-day-old S100B null mice exhibited enhanced Ca(2+) transients in response to treatment with KCl or caffeine. On the other hand, granule neurons, in the same cultures, exhibited normal Ca(2+) transients in response to treatment with KCl, caffeine, or N-methyl-d-aspartate. These results demonstrate a specific decrease in Ca(2+)-handling capacity in astrocytes derived from S100B null mice and suggest that S100B plays a role in the maintenance of Ca(2+) homeostasis in astrocytes.

Ca(2+)-dependent association of S100A6 (Calcyclin) with the plasma membrane and the nuclear envelope

Expression of S100A6 (Calcyclin), a member of the S100 family and of Zn(2+)-binding proteins is elevated in a number of malignant tumors. In vitro the protein associates with several actin-binding proteins and annexins in a Ca(2+)-dependent manner. We have now studied the subcellular localization of S100A6 using a new, specific monoclonal antibody. Immunofluorescence microscopy of unfixed, ultrathin, frozen sections demonstrated a dual localization of S100A6 at the nuclear envelope and the plasma membrane of porcine smooth muscle only in the presence of Ca(2+). The same localization was found by immunofluorescence and immunogold electron microscopy as well as by confocal laser scanning microscopy with cultured, fixed, human CaKi-2 and porcine ST interphase cells. Upon cell division, however, S100A6 was found exclusively in the cytoplasm. Cell fractionation studies showed that S100A6 was present in the microsomal fraction in the presence of Ca(2+) and was released from this fraction by the addition of EGTA/EDTA but not by Triton X-100. The data demonstrate that S100A6 is localized both at the plasma membrane and the nuclear envelope in vivo and suggest a Ca(2+)-dependent interaction with annexins or other components of the nuclear envelope.

Ca2+-dependent interaction of S100A2 with muscle and nonmuscle tropomyosins

Zero-length chemical crosslinking with 1-ethyl-3-[3-(dimethyl amino)propyl]carbodiimide (EDC) indicated an association of the Ca2+-binding protein S100A2 with tropomyosin (TM) in vitro. The mobility of the crosslinked product on SDS-PAGE gels indicated the formation of a 1:1 complex between S100A2 and TM and the interaction was Ca2+ dependent. Monoclonal antibodies were raised against S100A2 and used to determine its cellular localization in the porcine epithelial cell line LLC PK1. It was found that the localization of S100A2 depended on the differentiation state of the cells, being absent from actin stress fibers in sparsely seeded cultures, but present in the actin-containing microvilli characteristic of differentiated cells. Immunoprecipitations of [35S]methionine-labeled extracts using S100A2 as well as TM-specific antibodies failed to co-precipitate TM and S100A2, indicating a transient association between these two molecules in solution. Affinity chromatography of cell extracts on immobilized recombinant TMs, however, confirmed the Ca2+-dependent interaction between S100A2 and both muscle TMs as well as with high and low molecular mass nonmuscle TMs, suggesting that the binding site resides in one of the conserved regions of TM. Our data demonstrate the possible interaction of S100A2 with TM that is not bound to the microfilaments and indicate a differentiation-related function for S100A2 in LLC PK1 cells. The possible functional implications of this interaction are discussed.

Accumulation of S100 beta mRNA and protein in cerebellum during infancy in Down syndrome and control subjects

S100 protein is a 20 kDA calcium-binding protein that accumulates during CNS maturation in mammals. The human gene coding for the beta subunit of S100 protein (S100 beta) is located on chromosome 21, in a subtelomeric position in 21q22.3. In order to investigate the effect of trisomy 21 on S100 beta gene expression, we performed Southern, Northern and Western blot analysis on DNA, RNA and protein, respectively, extracted from the cerebellum of control and Down syndrome (DS) subjects aged 1-18 months. Southern blot analysis revealed a novel EcoRI polymorphism in the S100 beta gene in two of 15 DNA samples examined, and a 1.5 gene dosage for S100 beta in DS. Northern and Western blot analysis showed an approximately 10-fold increase in S100 beta mRNA and protein levels between 1 and 18 months. No differences in the rates of accumulation of S100 beta mRNA and protein were observed between DS and normal subjects. These results demonstrate an increase in S100 beta mRNA and protein levels during infancy indicative of postnatal astrocytic maturation and show that there is no gross deregulation in the expression of the S100 beta gene in DS as a consequence of trisomy 21.

The S100 protein family: history, function, and expression

The S100 family of calcium binding proteins contains approximately 16 members each of which exhibits a unique pattern of tissue/cell type specific expression. Although the distribution of these proteins is not restricted to the nervous system, the implication of several members of this family in nervous system development, function, and disease has sparked new interest in these proteins. We now know that the original two members of this family, S100A1 and S100B, can regulate a diverse group of cellular functions including cell-cell communication, cell growth, cell structure, energy metabolism, contraction and intracellular signal transduction. Although some members of the family may function extracellularly, most appear to function as intracellular calcium-modulated proteins and couple extracellular stimuli to cellular responses via interaction with other cellular proteins called target proteins. Interaction of these proteins with target proteins appear to involve cysteine residues (one in S100A1 and two in S100B), as well as a stretch of 13 amino acids, in the middle of the molecule called the linker region, which connects the two EF-hand calcium binding domains. In addition to the amino acid sequence and secondary structures of these proteins, the structures of the genes encoding these proteins are highly conserved. Studies on the expression of these proteins have demonstrated that a complex mixture of transcriptional and postranscriptional mechanisms regulate S100 expression. Further analysis of the function and expression of these proteins in both nervous and nonnervous tissues will provide important information regarding the role of altered S100 expression in nervous system development, function and disease.