Characterization of the interaction of calcyclin (S100A6) and calcyclin-binding protein

S100A6 Protein-Expression and Function in Norm and Pathology

S100A6, also known as calcyclin, is a calcium-binding protein belonging to the S100 protein family. It was first identified and purified more than 30 years ago. Initial structural studies, focused mostly on the mode and affinity of Ca²⁺ binding and resolution of the resultant conformational changes, were soon complemented by research on its expression, localization and identification of binding partners. With time, the use of biophysical methods helped to resolve the structure and versatility of S100A6 complexes with some of its ligands. Meanwhile, it became clear that S100A6 expression was altered in various pathological states and correlated with the stage/progression of many diseases, including cancers, indicative of its important, and possibly causative, role in some of these diseases. This, in turn, prompted researchers to look for the mechanism of S100A6 action and to identify the intermediary signaling pathways and effectors. After all these years, our knowledge on various aspects of S100A6 biology is robust but still incomplete. The list of S100A6 ligands is growing all the time, as is our understanding of the physiological importance of these interactions. The present review summarizes available data concerning S100A6 expression/localization, interaction with intracellular and extracellular targets, involvement in Ca²⁺-dependent cellular processes and association with various pathologies.

Siah-1-interacting protein regulates mutated huntingtin protein aggregation in Huntington’s disease models

Background

Huntington’s disease (HD) is a neurodegenerative disorder whereby mutated huntingtin protein (mHTT) aggregates when polyglutamine repeats in the N-terminal of mHTT exceeds 36 glutamines (Q). However, the mechanism of this pathology is unknown. Siah1-interacting protein (SIP) acts as an adaptor protein in the ubiquitination complex and mediates degradation of other proteins. We hypothesized that mHTT aggregation depends on the dysregulation of SIP activity in this pathway in HD.

Results

A higher SIP dimer/monomer ratio was observed in the striatum in young YAC128 mice, which overexpress mHTT. We found that SIP interacted with HTT. In a cellular HD model, we found that wildtype SIP increased mHTT ubiquitination, attenuated mHTT protein levels, and decreased HTT aggregation. We predicted mutations that should stabilize SIP dimerization and found that SIP mutant-overexpressing cells formed more stable dimers and had lower activity in facilitating mHTT ubiquitination and preventing exon 1 mHTT aggregation compared with wildtype SIP.

Conclusions

Our data suggest that an increase in SIP dimerization in HD medium spiny neurons leads to a decrease in SIP function in the degradation of mHTT through a ubiquitin–proteasome pathway and consequently an increase in mHTT aggregation. Therefore, SIP could be considered a potential target for anti-HD therapy during the early stage of HD pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00755-0.

Mitosis, Focus on Calcium

The transformation of a single fertilised egg into an adult human consisting of tens of trillions of highly diverse cell types is a marvel of biology. The expansion is largely achieved by cell duplication through the process of mitosis. Mitosis is essential for normal growth, development, and tissue repair and is one of the most tightly regulated biological processes studied. This regulation is designed to ensure accurate segregation of chromosomes into each new daughter cell since errors in this process can lead to genetic imbalances, aneuploidy, that can lead to diseases including cancer. Understanding how mitosis operates and the molecular mechanisms that ensure its fidelity are therefore not only of significant intellectual value but provide unique insights into disease pathology. The purpose of this review is to revisit historical evidence that mitosis can be influenced by the ubiquitous second messenger calcium and to discuss this in the context of new findings revealing exciting new information about its role in cell division.

Downregulation of CacyBP by CRISPR/dCas9-KRAB Prevents Bladder Cancer Progression

Bladder cancer (BCa) is a leading cause of cancer-related death in the world. CacyBP is initially described as a binding partner of calcyclin and has been shown to be involved in a wide range of cellular processes, including cell differentiation, proliferation, protein ubiquitination, cytoskeletal dynamics and tumorigenesis. In the present study, we found that CacyBP expression was significantly upregulated in BCa tissues compared with adjacent normal tissues. Moreover, its expression was negatively correlated with overall survival time. Secondly, CacyBP had higher expressions in BCa cell lines than normal urothelial cells which was consistent with the results of BCa tissues. Finally, knockdown of CacyBP by CRIPSR-dCas9-KRAB in T24 and 5,637 BCa cells inhibited cell proliferation and migration by CCK-8 assay and scratch assay, and promoted apoptosis by caspase-3/ELISA. These data elucidate that CacyBP is an important oncogene contributing to malignant behavior of BCa and provide a potentially molecular target for treatment of BCa.

High Throughput Proteomic Exploration of Hypothermic Preservation Reveals Active Processes within the Cell Associated with Cold Ischemia Kinetic

The demand for organs to be transplanted increases pressure on procurement centers, to the detriment of organ quality, increasing complications. New preservation protocols are urgently needed, requiring an in-depth understanding of ischemia-reperfusion mechanisms. We performed a proteomic analysis using LC-MS/MS-TOF data analyzed through R software and Cytoscape's ClueGO application, comparing the proteome of kidney endothelial cells, key cell type, subjected to 3, 6, 12, 19, and 24 h of cold ischemia and 6 h reperfusion. Critical pathways such as energy metabolism, cytoskeleton structure/transport system, and gene transcription/translation were modulated. Important time windows were revealed: a-during the first 3 h, central proteins were upregulated within these pathways; b-the majority of these upregulations were maintained until 12 h cold ischemia time (CIT); c-after that time, the overall decrease in protein expression was observed; d-at reperfusion, proteins expressed in response to cold ischemia were all downregulated. This shows that cold ischemia is not a simple slowing down of metabolism, as deep changes take place within the proteome on major pathways. Time-sensitive expression of key protein reveals possible quality biomarkers as well as potential targets for new strategies to maintain or optimize organ quality.

Sex differences in distribution of cannabinoid receptors (CB1 and CB2), S100A6 and CacyBP/SIP in human ageing hearts

Background

Women live about 4 years longer due to lower prevalence of cardiovascular complication with ageing. However, the mechanisms involved in the preservation of heart functionality in women have not been fully elucidated.

The endocannabinoid system fulfils a significant role in the regulation of cardiovascular system functioning. Cannabinoids, acting through specific receptors (CB1 and CB2), influence on blood pressure, heart rate and myocardial contractility. The function of cardiac muscle cells is strictly dependent on calcium ions. Calcium homeostasis in cardiomyocytes is subjected to complex regulation via calcium-binding proteins. Among them, increasing attention has been paid to the recently discovered S100A6 and CacyBP/SIP.

In order to better understand sex differences in the regulation of cardiomyocyte function during ageing, we undertook the present research aimed at immunohistochemical identification and comparative evaluation of cannabinoid receptors, S100A6 and CacyBP/SIP, in the myocardium of ageing men and women.

Methods

The study was conducted on the hearts of 12 men and 10 women (organ donors) without a history of cardiovascular disease. The subjects were divided into two age groups: subjects older than 50 years and subjects under 50 years old. Paraffin heart sections were processed by immunohistochemistry for detection of cannabinoids receptors, S100A6 and CacyBP/SIP. In the heart samples from each study, participant’s expression of genes coding for CB1, CB2, S100A6 and CacyBP/SIP using real-time PCR method was measured.

Results

CB1 and CB2 immunoreactivity in the cytoplasm of cardiomyocytes in the heart of subjects over 50 was weaker than in younger individuals. In the heart of younger men, CB1-immunoreactivity was weaker and CB2-immunoreaction was stronger compared to women. In the hearts of older men, the CB1-immunostaining was more intense and CB2-immunoreactivity was weaker than in women. Immunodetection of CB1 shoved the presence of receptor in the intercalated discs, but only in the hearts of individuals over the 50 years old. In the hearts of older individuals, stronger immunolabelling was observed for S100A6 and CacyBP/SIP. Male hearts had greater S100A6-immunoreactivity (both age groups) but less CacyBP/SIP immunostaining (individuals over 50 years) compared to the age-matched women. The expression of genes coding CB1, CB2, S100A6 and CacyBP/SIP in the human heart was sex and age-dependent. Observed changes between men and women as well as between subject under and over 50 years were consistent with immunohistochemically stated changes in peptide content.

Conclusion

Together, the data presented here indicate a close interaction between ageing and sex on the distribution and levels of cannabinoid receptors (CB1, CB2), S100A6 and CacyBP/SIP in the human heart.

Cardiac Overexpression of S100A6 Attenuates Cardiomyocyte Apoptosis and Reduces Infarct Size After Myocardial Ischemia-Reperfusion

Background

Cardiomyocyte‐specific transgenic mice overexpressing S100A6, a member of the family of EF‐hand calcium‐binding proteins, develop less cardiac hypertrophy, interstitial fibrosis, and myocyte apoptosis after permanent coronary ligation, findings that support S100A6 as a potential therapeutic target after acute myocardial infarction. Our purpose was to investigate S100A6 gene therapy for acute myocardial ischemia‐reperfusion.

Methods and Results

We first performed in vitro studies to examine the effects of S100A6 overexpression and knockdown in rat neonatal cardiomyocytes. S100A6 overexpression improved calcium transients and protected against apoptosis induced by hypoxia‐reoxygenation via enhanced calcineurin activity, whereas knockdown of S100A6 had detrimental effects. For in vivo studies, human S100A6 plasmid or empty plasmid was delivered to the left ventricular myocardium by ultrasound‐targeted microbubble destruction in Fischer‐344 rats 2 days prior to a 30‐minute ligation of the left anterior descending coronary artery followed by reperfusion. Control animals received no therapy. Pretreatment with S100A6 gene therapy yielded a survival advantage compared to empty‐plasmid and nontreated controls. S100A6‐pretreated animals had reduced infarct size and improved left ventricular systolic function, with less myocyte apoptosis, attenuated cardiac hypertrophy, and less cardiac fibrosis.

Conclusions

S100A6 overexpression by ultrasound‐targeted microbubble destruction helps ameliorate myocardial ischemia‐reperfusion, resulting in lower mortality and improved left ventricular systolic function post–ischemia‐reperfusion via attenuation of apoptosis, reduction in cardiac hypertrophy, and reduced infarct size. Our results indicate that S100A6 is a potential therapeutic target for acute myocardial infarction.

Influence of S100A6 on CacyBP/SIP Phosphorylation and Elk-1 Transcriptional Activity in Neuroblastoma NB2a Cells

In this work, we have found that casein kinase II (CKII) phosphorylates the CacyBP/SIP protein under in vitro conditions and have mapped the phosphorylation site to threonine 184. Moreover, we present evidence that S100A6, a CacyBP/SIP interacting protein, inhibits this phosphorylation in the presence of Ca(2+). CacyBP/SIP phosphorylation by CKII was also observed in neuroblastoma NB2a cells. Interestingly, we have found that the effect of DRB, a CKII inhibitor, on CacyBP/SIP phosphorylation state is similar to that of S100A6 overexpression. Phosphorylation at threonine 184 seems to have an effect on CacyBP/SIP phosphatase activity since the T184E phosphorylation mimic mutant overexpressed in NB2a cells has lower phosphatase activity toward p-ERK1/2 when compared to the non-phosphorylable T184A mutant or to the wild-type protein. In conclusion, our data suggest that S100A6 and Ca(2+), through inhibiting CacyBP/SIP phosphorylation on threonine 184, are important regulators of CacyBP/SIP phosphatase activity and of ERK1/2-Elk-1 signaling pathway.

The potential role of CacyBP/SIP in tumorigenesis

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) was initially described as a binding partner of S100A6 in the Ehrlich ascites tumor cells and later as a Siah-1-interacting protein. This 30 kDa protein includes three domains and is involved in cell proliferation, differentiation, cytoskeletal rearrangement, and transcriptional regulation via binding to various proteins. Studies have also shown that the CacyBP/SIP is a critical protein in tumorigenesis. But, its promotion or suppression of cancer progression may depend on the cell type. In this review, the biological characteristics and target proteins of CacyBP/SIP have been described. Moreover, the exact role of CacyBP/SIP in various cancers is discussed.

CacyBP/SIP--Structure and variety of functions

BACKGROUND

CacyBP/SIP (Calcyclin-Binding Protein and Siah-1 Interacting Protein) is a small modular protein implicated in a wide range of cellular processes. It is expressed in different tissues of mammals but homologs are also found in some lower organisms. In mammals, a high level of CacyBP/SIP is present in tumor cells and in neurons. CacyBP/SIP binds several target proteins such as members of the S100 family, components of a ubiquitin ligase complex, and cytoskeletal proteins.

SCOPE OF REVIEW

CacyBP/SIP has been shown to be involved in protein de-phosphorylation, ubiquitination, cytoskeletal dynamics, regulation of gene expression, cell proliferation, differentiation, and tumorigenesis. This review focuses on very recent reports on CacyBP/SIP structure and function in these important cellular processes.

MAJOR CONCLUSIONS

CacyBP/SIP is a multi-domain and multi-functional protein. Altered levels of CacyBP/SIP in several cancers implicate its involvement in the maintenance of cell homeostasis. Changes in CacyBP/SIP subcellular localization in neurons of AD brains suggest that this protein is strongly linked to neurodegenerative diseases. Elucidation of CacyBP/SIP structure and cellular function is leading to greater understanding of its role in normal physiology and disease pathologies.

GENERAL SIGNIFICANCE

The available results suggest that CacyBP/SIP is a key player in multiple biological processes. Detailed characterization of the physical, biochemical and biological properties of CacyBP/SIP will provide better insight into the regulation of its diverse functions in vivo, and given the association with specific diseases, will help clarify the potential of therapeutic targeting of this protein.

Differences in brain gene transcription profiles advocate for an important role of cognitive function in upstream migration and water obstacles crossing in European eel

BACKGROUND

European eel is a panmictic species, whose decline has been recorded since the last 20 years. Among human-induced environmental factors of decline, the impact of water dams during species migration is questioned. The main issue of this study was to pinpoint phenotypic traits that predisposed glass eels to successful passage by water barriers. The approach of the study was individual-centred and without any a priori hypothesis on traits involved in the putative obstacles selective pressure. We analyzed the transcription level of 14,913 genes.

RESULTS

Transcriptome analysis of three tissues (brain, liver and muscle) from individuals sampled on three successive forebays separated by water obstacles indicated different gene transcription profiles in brain between the two upstream forebays. No differences in gene transcription levels were observed in liver and muscle samples among segments. A total of 26 genes were differentially transcribed in brain. These genes encode for, among others, keratins, cytokeratins, calcium binding proteins (S100 family), cofilin, calmodulin, claudin and thy-1 membrane glycoprotein. The functional analysis of these genes highlighted a putative role of cytoskeletal dynamics and synaptic plasticity in fish upstream migration.

CONCLUSION

Synaptic connections in brain are solicited while eels are climbing the obstacles with poorly designed fishways. Successful passage by such barriers can be related to spatial learning and spatial orientation abilities when fish is out of the water.

S100 calcium-binding protein A6 promotes epithelial-mesenchymal transition through β-catenin in pancreatic cancer cell line

The pathogenesis of pancreatic ductal adenocarcinoma (PDAC) remains poorly understood. S100 calcium-binding protein A6 (S100A6) has been associated with PDAC; however, the effect of S100A6 on PDAC migration and invasion has not yet been explored. In this study, Panc-1 cells were transfected with a plasmid to induce overexpression of S100A6, and β-catenin was knocked down using a specific short hairpin RNA (shRNA). The wound-healing and Transwell assays demonstrated that S100A6 promoted PDAC cell migration and invasion. Furthermore, β-catenin shRNA inhibited the migration and invasion of PDAC cells. We confirmed that S100A6 induces PDAC cell migration and invasion via activation of β-catenin in vitro. Assessment of mRNA and protein levels revealed that S100A6 induces increased expression of β-catenin, N-cadherin and vimentin, and decreased expression of E-cadherin in PDAC cells. β-catenin shRNA also altered the expression of epithelial-mesenchymal transition (EMT)-related markers in PDAC cells. Specifically, expression of E-cadherin was increased, whereas expression of N-cadherin and vimentin was decreased. Finally, we demonstrated that S100A6 alters the expression of EMT-related markers via β-catenin activation. In conclusion, S100A6 induces EMT and promotes cell migration and invasion in a β-catenin-dependent manner. S100A6 may therefore represent a novel potential therapeutic target for the treatment of pancreatic cancer.

Predictive proteomic biomarkers for inflammatory bowel disease-associated cancer: Where are we now in the era of the next generation proteomics?

Recent advances in genomic medicine have opened up the possibility of tailored medicine that may eventually replace traditional “one-size-fits all” approaches to the treatment of inflammatory bowel disease (IBD). In addition to exploring the interactions between hosts and microbes, referred to as the microbiome, a variety of strategies that can be tailored to an individual in the coming era of personalized medicine in the treatment of IBD are being investigated. These include prompt genomic screening of patients at risk of developing IBD, the utility of molecular discrimination of IBD subtypes among patients diagnosed with IBD, and the discovery of proteome biomarkers to diagnose or predict cancer risks. Host genetic factors influence the etiology of IBD, as do microbial ecosystems in the human bowel, which are not uniform, but instead represent many different microhabitats that can be influenced by diet and might affect processes essential to bowel metabolism. Further advances in basic research regarding intestinal inflammation may reveal new insights into the role of inflammatory mediators, referred to as the inflammasome, and the macromolecular complex of metabolites formed by intestinal bacteria. Collectively, knowledge of the inflammasome and metagenomics will lead to the development of biomarkers for IBD that target specific pathogenic mechanisms involved in the spontaneous progress of IBD. In this review article, our recent results regarding the discovery of potential proteomic biomarkers using a label-free quantification technique are introduced and on-going projects contributing to either the discrimination of IBD subtypes or to the prediction of cancer risks are accompanied by updated information from IBD biomarker research.

Low-resolution structure of the full-length barley (Hordeum vulgare) SGT1 protein in solution, obtained using small-angle X-ray scattering

SGT1 is an evolutionarily conserved eukaryotic protein involved in many important cellular processes. In plants, SGT1 is involved in resistance to disease. In a low ionic strength environment, the SGT1 protein tends to form dimers. The protein consists of three structurally independent domains (the tetratricopeptide repeats domain (TPR), the CHORD- and SGT1-containing domain (CS), and the SGT1-specific domain (SGS)), and two less conserved variable regions (VR1 and VR2). In the present study, we provide the low-resolution structure of the barley (Hordeum vulgare) SGT1 protein in solution and its dimer/monomer equilibrium using small-angle scattering of synchrotron radiation, ab-initio modeling and circular dichroism spectroscopy. The multivariate curve resolution least-square method (MCR-ALS) was applied to separate the scattering data of the monomeric and dimeric species from a complex mixture. The models of the barley SGT1 dimer and monomer were formulated using rigid body modeling with ab-initio structure prediction. Both oligomeric forms of barley SGT1 have elongated shapes with unfolded inter-domain regions. Circular dichroism spectroscopy confirmed that the barley SGT1 protein had a modular architecture, with an α-helical TPR domain, a β-sheet sandwich CS domain, and a disordered SGS domain separated by VR1 and VR2 regions. Using molecular docking and ab-initio protein structure prediction, a model of dimerization of the TPR domains was proposed.

iTRAQ based quantitative proteomics approach validated the role of calcyclin binding protein (CacyBP) in promoting colorectal cancer metastasis

Keeping continuity with our previous study that revealed direct correlations between CRC metastasis and enhanced CacyBP protein levels, here we attempt to improve our understanding of the mechanisms involved within this enigmatic process. Overexpression of CacyBP (CacyBP-OE) in primary CRC cell and its knock down (CacyBP-KD) in the metastatic CRC cells revealed (through phenotypic studies) the positive impact of the protein on metastasis. Additionally, two individual 4-plex iTRAQ based comparative proteomics experiments were carried out on the CacyBP-OE and CacyBP-KD cells, each with two biological replicates. Mining of proteomics data identified total 279 (63.80% up-regulated and 36.20% down-regulated) proteins to be significantly altered in expression level for the OE set and in the KD set, this number was 328 (48.78% up-regulated and 51.22% down-regulated). Functional implications of these significantly regulated proteins were related to metastatic phenotypes such as cell migration, invasion, adhesion and proliferation. Gene ontology analysis identified integrin signaling as the topmost network regulated within CacyBP-OE. Further detection of caveolar mediated endocytosis in the top hit list correlated this phenomenon with the dissociation of integrins from the focal adhesion complex which are known to provide the traction force for cell movement when transported back to the leading edge. This finding was further supported by the data obtained from CacyBP-KD data set showing down-regulation of proteins necessary for integrin endocytosis. Furthermore, intracellular calcium levels (known to influence integrin mediated cell migration) were found to be lowered in CacyBP-KD cells indicating decreased cell motility and vice versa for the CacyBP-OE cells. Actin nucleation by ARP-WASP complex, known to promote cell migration, was also identified as one of the top regulated pathways in CacyBP-OE cells. In short, this study presents CacyBP as a promising candidate biomarker for CRC metastasis and also sheds light on the underlying molecular mechanism by which CacyBP promotes CRC metastasis.

S100A6 binding protein and Siah-1 interacting protein (CacyBP/SIP): spotlight on properties and cellular function

The CacyBP/SIP protein (S100A6 binding protein and Siah-1 interacting protein) was originally discovered in Ehrlich ascites tumor cells as a S100A6 (calcyclin) target (Filipek and Wojda in Biochem J 320:585-587, 1996; Filipek and Kuźnicki in J Neurochem 70(5):1793-1798, 1998) and later on as a Siah-1 interacting protein (Matsuzawa and Reed in Mol Cell 7(5):915-926, 2001). CacyBP/SIP binds several target proteins such as some calcium binding proteins of the S100 family (Filipek et al. in J Biol Chem 277(32):28848-28852, 2002), Skp1 (Matsuzawa and Reed in Mol Cell 7(5):915-926, 2001), tubulin (Schneider et al. in Biochim Biophys Acta 1773(11):1628-1636, 2007) and ERK1/2 (Kilanczyk et al. in Biochem Biophys Res Commun 380:54-59, 2009). Studies concerning distribution of CacyBP/SIP show that it is present in various tissues and that a particularly high level of CacyBP/SIP is observed in brain (Jastrzebska et al. in J Histochem Cytochem 48(9):1195-1202, 2000). Regarding the function of CacyBP/SIP, there are some reports suggesting its role in cellular processes such as ubiquitination, proliferation, differentiation, tumorigenesis, cytoskeletal rearrangement or regulation of transcription. This review describes the properties of CacyBP/SIP and summarizes all findings concerning its cellular function.

CacyBP/SIP binds ERK1/2 and affects transcriptional activity of Elk-1

In this work we showed for the first time that mouse CacyBP/SIP interacts with extracellular signal regulated kinases 1 and 2 (ERK1/2). We also established that a calcium binding protein, S100A6, competes for this interaction. Moreover, the E217K mutant of CacyBP/SIP does not bind significantly to ERK1/2 although it retains the ability to interact with S100A6. Molecular modeling shows that the E217K mutation in the 189-219 CacyBP/SIP fragment markedly changes its electrostatic potential, suggesting that the binding with ERK1/2 might have an electrostatic character. We also demonstrate that CacyBP/SIP-ERK1/2 interaction inhibits phosphorylation of the Elk-1 transcription factor in vitro and in the nuclear fraction of NB2a cells. Altogether, our data suggest that the binding of CacyBP/SIP with ERK1/2 might regulate Elk-1 phosphorylation/transcriptional activity and that S100A6 might further modulate this effect via Ca(2+)-dependent interaction with CacyBP/SIP and competition with ERK1/2.

Structure of the S100A6 complex with a fragment from the C-terminal domain of Siah-1 interacting protein: a novel mode for S100 protein target recognition

S100A6 is a member of the S100 subfamily of EF-hand Ca (2+) binding proteins that has been shown to interact with calcyclin binding protein/Siah-1 interacting protein (CacyBP/SIP or SIP), a subunit of an SCF-like E3 ubiquitin ligase complex (SCF-TBL1) formed under genotoxic stress. SIP serves as a scaffold in this complex, linking the E2-recruiting module Siah-1 to the substrate-recruiting module Skp1-TBL1. A cell-based functional assay suggests that S100A6 modulates the activity of SCF-TBL1. The results from the cell-based experiments could be enhanced if it were possible to selectively inhibit S100A6-SIP interactions without perturbing any other functions of the two proteins. To this end, the structure of the S100A6-SIP complex was determined in solution by NMR and the strength of the interaction was characterized by isothermal titration calorimetry. In an initial step, the minimal S100A6 binding region in SIP was mapped to a 31-residue fragment (Ser189-Arg219) in the C-terminal domain. The structure of the S100A6-SIP(189-219) complex revealed that SIP(189-219) forms two helices, the first of which (Met193-Tyr200) interacts with S100A6 in a canonical binding mode. The second helix (Met207-Val216) lies over the S100A6 dimer interface, a mode of binding to S100A6 that has not previously been observed for any target bound to an S100 protein. A series of structure-based SIP mutations showed reduced S100A6 binding affinity, setting the stage for direct functional analysis of S100A6-SIP interactions.

Upregulated expression of S100A6 in human gastric cancer

OBJECTIVE

The expression of S100A6 (calcyclin), a member of the S100 calcium binding protein family, is elevated in a number of malignant tumors, but there have been few reports about its expression in gastric cancer. The aim of this study was to investigate its expression regulations in human gastric cancer and noncancerous mucosa, and the response to chemotherapeutic drugs in the gastric cancer cell line.

MATERIALS AND METHODS

In one matched gastric cancer sample pair, the serial analysis of gene expression (SAGE) experiment was conducted to compare the gene expression profiles between cancerous and adjacent tissues. To detect the expression regulations among more cancerous tissues, microarrays were carried out and real-time RT-PCR was conducted to validate the results. At the protein level, Western blot and tissue microarray (TMA) examination were further used to verify S100A6 expression. The regulation detection of S100A6 with flurouracil and doxorubicin at the mRNA and protein level was performed in the SGC7901 cell line.

RESULTS

With the SAGE strategy, five times more S100A6 tags were identified in cancer tissues than in normal tissues. With the cDNA microarray, S100A6 was found to be significantly upregulated in 21 of 42 (50%) nonselective gastric cancers. In 10 other paired samples, the upregulation of S100A6 was consolidated with RT-PCR and Western blot analysis as well. A total of 14 endoscopy-sectioned gastric noncancerous lesions and corresponding normal gastric mucosa were also applied to profile the gene expression; both cDNA microarray and RT-PCR demonstrated no significant alterations of S100A6 at the mRNA level. TMA examination showed that 34 of 52 (65.4%) cancer samples were positively stained, while only 17 of 80 (21.3%) noncancerous lesions were positively detected and all nine normal mucosae were detected to be negative. An in vitro experiment showed that in the gastric cell line SGC-7901, S100A6 mRNA was detected to be upregulated from 24 to 72 h after treatment with 5 mg/L 5-flurouracil or 0.3 mg/L doxorubicin, and there were two wave upregulations of the S100A6 protein.

CONCLUSION

The observed regulated expression of S100A6 suggests that it is associated with gastric cancer tumorigenesis and quantitation of S100A6 is a promising tool for diagnosis of gastric cancer.

CacyBP/SIP interacts with tubulin in neuroblastoma NB2a cells and induces formation of globular tubulin assemblies

CacyBP/SIP, originally identified as a S100A6 (calcyclin) target, was later shown to interact with some other members of the S100 family as well as with Siah-1 and Skp1 proteins. Recently, it has been shown that CacyBP/SIP is up-regulated during differentiation of cardiomyocytes. In this work we show that the level of CacyBP/SIP is higher in differentiated neuroblastoma NB2a cells than in undifferentiated ones and that in cells overexpressing CacyBP/SIP the level of GAP-43, a marker of differentiation, was increased. Since the process of differentiation is accompanied by an extensive rearrangement of microtubules, we examined whether CacyBP/SIP interacted with tubulin. By applying cross-linking experiments we found that these two proteins bind directly. The dissociation constant of the tubulin-CacyBP/SIP complex determined by the surface plasmon resonance technique is 1.57 x 10(-7 )M which suggests that the interaction is tight. The interaction and co-localization of CacyBP/SIP and tubulin was also demonstrated by co-immunoprecipitation, affinity chromatography and immunofluorescence methods. Light scattering measurements and electron microscopy studies revealed that CacyBP/SIP, but not its homologue, Sgt1, increased tubulin oligomerization. Altogether, our results suggest that CacyBP/SIP, via its interaction with tubulin, might contribute to the differentiation of neuroblastoma NB2a cells.

Calcyclin binding protein promotes DNA synthesis and differentiation in rat neonatal cardiomyocytes

During cardiac muscle development, most cardiomyocytes permanently withdraw from the cell cycle. Previously, by suppressive subtractive hybridization, we identified calcyclin-binding protein/Siah-interacting protein (CacyBP/SIP) as one of the candidates being upregulated in the hyperplastic to hypertrophic switch, suggesting an important role of CacyBP/SIP in cardiac development. To show the importance of CacyBP/SIP during myoblast differentiation, we report here that CacyBP/SIP is developmentally regulated in postnatal rat hearts. The overexpression of CacyBP/SIP promotes the differentiation and DNA synthesis of H9C2 cells and primary rat cardiomyocytes, as well as downregulates the expression of beta-catenin. Besides, CacyBP/SIP promotes the formation of myotubes and multinucleation upon differentiation. To investigate the cardioprotective role of CacyBP/SIP in cardiomyocytes, a hypoxia/reoxygenation model was employed. We found that CacyBP/SIP was upregulated during myocardial infarction (MI) and hypoxia/reoxygenation. As a conclusion, CacyBP/SIP may play a role in cardiomyogenic differentiation and possibly protection of cardiomyocytes during hypoxia/reoxygenation injury.

Calcium-dependent and -independent interactions of the S100 protein family

The S100 proteins comprise at least 25 members, forming the largest group of EF-hand signalling proteins in humans. Although the proteins are expressed in many tissues, each S100 protein has generally been shown to have a preference for expression in one particular tissue or cell type. Three-dimensional structures of several S100 family members have shown that the proteins assume a dimeric structure consisting of two EF-hand motifs per monomer. Calcium binding to these S100 proteins, with the exception of S100A10, results in an approx. 40 degrees alteration in the position of helix III, exposing a broad hydrophobic surface that enables the S100 proteins to interact with a variety of target proteins. More than 90 potential target proteins have been documented for the S100 proteins, including the cytoskeletal proteins tubulin, glial fibrillary acidic protein and F-actin, which have been identified mostly from in vitro experiments. In the last 5 years, efforts have concentrated on quantifying the protein interactions of the S100 proteins, identifying in vivo protein partners and understanding the molecular specificity for target protein interactions. Furthermore, the S100 proteins are the only EF-hand proteins that are known to form both homo- and hetero-dimers, and efforts are underway to determine the stabilities of these complexes and structural rationales for their formation and potential differences in their biological roles. This review highlights both the calcium-dependent and -independent interactions of the S100 proteins, with a focus on the structures of the complexes, differences and similarities in the strengths of the interactions, and preferences for homo- compared with hetero-dimeric S100 protein assembly.

Proteomic characterization of the cytotoxic mechanism of gold (III) porphyrin 1a, a potential anticancer drug

There has been increasing interest in the potential applications of gold (III) complexes as anticancer drugs with higher cytotoxicity and fewer side effects than existing metal anticancer drugs. Our previous findings demonstrated that gold (III) porphyrin 1a preferentially induced apoptosis in a cancer cell line (SUNE1). In this study, we identified differentially expressed proteins related to the drug's cytotoxic action by comparing the protein alterations induced by gold (III) porphyrin 1a and cisplatin treatments. Several clusters of altered proteins were identified, including cellular structure and stress-related chaperone proteins, proteins involved in reactive oxygen species and enzyme proteins, translation factors, proteins that mediate cell proliferation or differentiation, and proteins participating in the internal degradation systems. Our results indicated that multiple factors leading to apoptosis were involved in drug cytotoxicity in SUNE1 cells. The balance between pro-apoptotic and anti-apoptotic signals determined the final fate of cancer cells.

Effects of cadmium on structure and enzymatic activity of Cu,Zn-SOD and oxidative status in neural cells

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder disease. Ten percent of the ALS patients are congenital (familial ALS), and the other 90% are sporadic ALS (SALS). It has been shown that mutations found in the Cu,Zn-SOD cause 20% of the familial ALS due to its low enzyme activity. We hypothesized that heavy metals may interfere the structure of Cu,Zn-SOD protein to suppress its activity in some of the SALS. In this study, we expressed and characterized the recombinant human Cu,Zn-SOD under various concentrations of Cu(2+), Zn(2+), and Cd(2+). By atomic absorption spectrophotometry, we demonstrated that adding of cadmium significantly increased the content of cadmium ion, but reduced its Zn(2+) content and enzyme activity of the Cu,Zn-SOD protein. The data of circular dichroism spectra demonstrated that the secondary structure of Cu,Zn-SOD/Cd is different from Cu,Zn-SOD, but close to apo-SOD. In addition to the effect of cadmium on Cu,Zn-SOD, cadmium was also shown to induce neural cell apoptosis. To further investigate the mechanism of neural cell apoptosis induced by cadmium, we used proteomics to analyze the altered protein expressions in neural cells treated with cadmium. The altered proteins include cellular structural proteins, stress-related and chaperone proteins, proteins involved in reactive oxygen species (ROS), enzyme proteins, and proteins that mediated cell death and survival signaling. Taken together, in this paper, we demonstrate that cadmium decreases the content of Zn(2+), changes the conformation of Cu,Zn-SOD protein to decrease its enzyme activity, and causes oxidative stress-induced neural cell apoptosis.

Expression and hormonal regulation of calcyclin-binding protein (CacyBP) in the mouse uterus during early pregnancy

Calcyclin-binding protein (Siah-1-Interacting Protein, CacyBP/SIP), is a calcium signaling protein involved in the degradation of beta-catenin, however, little is known about its role in reproductive biology. The present study was to character its temporospatial expression pattern and regulation in mouse uterus and to investigate whether it plays a role in the regulation of normal endometrial events. While prominently expressed in both luminal and glandular epithelia, CacyBP underwent dynamic changes during early pregnancy. CacyBP expression was observed weakly from days 1-4. An intense accumulation in luminal and glandular epithelia as well as decidua surrounding the embryo at later stages (days 5-7) was observed. Most notably, CacyBP accumulation in trophoblast was pronounced at day 7. Using ovariectomized and pseudopregnant mice, we found that progesterone (P(4)) and 17beta-estradiol (E(2)) led to increased expression of CacyBP gene and this could be abolished by Ru486 and tamoxifen, respectively. Antisense oligonucleotides (ODNs) against CacyBP significantly inhibited cultured endometrial stromal cells' (ESCs) apoptosis induced by UV irradiation. Injection of antisense ODNs into mouse uterine horn severely impaired the number of implanted blastocysts. Taken together, our results suggested that CacyBP expression was positively regulated by P(4) and E(2). CacyBP may be involved in the regulation of endometrial cell apoptosis during early pregnancy and play an important role in mouse endometrial events such as pregrancy establishment.

A microarray study of MPP+-treated PC12 Cells: Mechanisms of toxicity (MOT) analysis using bioinformatics tools

Background

This paper describes a microarray study including data quality control, data analysis and the analysis of the mechanism of toxicity (MOT) induced by 1-methyl-4-phenylpyridinium (MPP⁺) in a rat adrenal pheochromocytoma cell line (PC12 cells) using bioinformatics tools. MPP⁺ depletes dopamine content and elicits cell death in PC12 cells. However, the mechanism of MPP⁺-induced neurotoxicity is still unclear.

Results

In this study, Agilent rat oligo 22K microarrays were used to examine alterations in gene expression of PC12 cells after 500 μM MPP⁺ treatment. Relative gene expression of control and treated cells represented by spot intensities on the array chips was analyzed using bioinformatics tools. Raw data from each array were input into the NCTR ArrayTrack database, and normalized using a Lowess normalization method. Data quality was monitored in ArrayTrack. The means of the averaged log ratio of the paired samples were used to identify the fold changes of gene expression in PC12 cells after MPP⁺ treatment. Our data showed that 106 genes and ESTs (Expressed Sequence Tags) were changed 2-fold and above with MPP⁺ treatment; among these, 75 genes had gene symbols and 59 genes had known functions according to the Agilent gene Refguide and ArrayTrack-linked gene library. The mechanism of MPP⁺-induced toxicity in PC12 cells was analyzed based on their genes functions, biological process, pathways and previous published literatures.

Conclusion

Multiple pathways were suggested to be involved in the mechanism of MPP⁺-induced toxicity, including oxidative stress, DNA and protein damage, cell cycling arrest, and apoptosis.

The Modular Structure of SIP Facilitates Its Role in Stabilizing Multiprotein Assemblies,

Siah-interacting protein (SIP) was identified as a novel adaptor that physically links the E3 ubiquitin ligase activity of Siah-1 with Skp1 and Ebi F-Box protein in the degradation of beta-catenin, a transcriptional activator of TCF/LEF genes. In this study, we have used solution NMR spectroscopy to characterize the domain structure of SIP, which includes a novel helical hairpin domain at the N-terminus flexibly linked to a CS domain and an unstructured carboxy terminal SGS domain. These studies have been complemented by mapping the sites of functionally important protein-protein interactions involving Siah-1 and Skp1 to individual domains of SIP. NMR-based chemical shift perturbation assays show that Siah-1 interacts with the flexible linker between SIP N and CS domains. This site for interaction in the linker does not perturb residues in the structured region at the N-terminus but does appear to restrict the rotational freedom of the SIP CS domain in the context of the full-length protein. In contrast, Skp1 engages the SIP CS domain exclusively through weak interactions that are not coupled to the other domains. The principal role of the modular structure of SIP appears to be in bringing these two proteins into physical proximity and orchestrating the orientation required for polyubiquitination of beta-catenin in the intact SCF-type complex.

Human Sgt1 binds HSP90 through the CHORD-Sgt1 domain and not the tetratricopeptide repeat domain

Sgt1 has been identified as a subunit of both core kinetochore and SCF (Skp1-Cul1-F-box) ubiquitin ligase complexes and is also implicated in plant disease resistance. Sgt1 has two putative HSP90 binding domains, a tetratricopeptide repeat and a p23-like CHORD and Sgt1 (CS) domain. Using NMR spectroscopy, we show that only the CS domain of human Sgt1 physically interacts with HSP90. The tetratricopeptide repeat domain does not bind to either HSP90 or HSP70. Determination of the three-dimensional structure showed that the Sgt1-CS domain shares the same beta-sandwich fold as p23 but lacks the last highly conserved beta-strand in p23. Analysis of the structures of Sgt1-CS and p23 revealed a similar charge distribution on one of two opposing surfaces that suggests that it is the binding region for HSP90 in Sgt1. Although ATP is absolutely required for p23 binding to HSP90, Sgt1 binds to HSP90 also in the absence of the non-hydrolyzable analog ATPgammaS. Our findings suggest the CS domain is a binding module for HSP90 distinct from p23-like domains, which implies that Sgt1 and related proteins function in recruiting heat shock protein activities to multiprotein assemblies.

Identification of genes that are induced after cadmium exposure by suppression subtractive hybridization

The heavy metal cadmium is a xenobiotic toxicant of environmental and occupational concern and it has been classified as a human carcinogen. Inhalation of cadmium has been implicated in the development of emphysema and pulmonary fibrosis, but, the detailed mechanism by which cadmium induces adverse biological effects is not yet known. Therefore, we undertook the investigation of genes that are induced after cadmium exposure to illustrate the mechanism of cadmium toxicity. For this purpose, we employed the polymerase chain reaction (PCR)-based suppression subtractive hybridization (SSH) technique. We identified 29 different cadmium-inducible genes in human peripheral blood mononuclear cells (PBMCs), such as macrophage migration inhibitory factor (MIF), lysophosphatidic acid acyltransferase-alpha, enolase-1alpha, VEGF, Bax, and neuron-derived orphan receptor-1 (Nor-1), which are known to be associated with inflammation, cell survival, and apoptosis. Induction of these genes by cadmium treatment was further confirmed by semi-quantitative reverse-transcription PCR. Further, we found that these genes were also induced after cadmium exposure in normal human lung fibroblast cell line, WI-38, suggesting potential use of this induction profile to monitor cadmium toxicity in the lung.

Calcium-regulated interaction of Sgt1 with S100A6 (calcyclin) and other S100 proteins

S100A6 (calcyclin), a small calcium-binding protein from the S100 family, interacts with several target proteins in a calcium-regulated manner. One target is Calcyclin-Binding Protein/Siah-1-Interacting Protein (CacyBP/SIP), a component of a novel pathway of beta-catenin ubiquitination. A recently discovered yeast homolog of CacyBP/SIP, Sgt1, associates with Skp1 and regulates its function in the Skp1/Cullin1/F-box complex ubiquitin ligase and in kinetochore complexes. S100A6-binding domain of CacyBP/SIP is in its C-terminal region, where the homology between CacyBP/SIP and Sgt1 is the greatest. Therefore, we hypothesized that Sgt1, through its C-terminal region, interacts with S100A6. We tested this hypothesis by performing affinity chromatography and chemical cross-linking experiments. Our results showed that Sgt1 binds to S100A6 in a calcium-regulated manner and that the S100A6-binding domain in Sgt1 is comprised of 71 C-terminal residues. Moreover, S100A6 does not influence Skp1-Sgt1 binding, a result suggesting that separate Sgt1 domains are responsible for interactions with S100A6 and Skp1. Sgt1 binds not only to S100A6 but also to S100B and S100P, other members of the S100 family. The interaction between S100A6 and Sgt1 is likely to be physiologically relevant because both proteins were co-immunoprecipitated from HEp-2 cell line extract using monoclonal anti-S100A6 antibody. Phosphorylation of the S100A6-binding domain of Sgt1 by casein kinase II was inhibited by S100A6, a result suggesting that the role of S100A6 binding is to regulate the phosphorylation of Sgt1. These findings suggest that protein ubiquitination via Sgt1-dependent pathway can be regulated by S100 proteins.

Calcium: a potential central regulator in wound healing in the skin

Calcium has an established role in the normal homeostasis of mammalian skin and serves as a modulator in keratinocyte proliferation and differentiation. Gradients of calcium concentration increasing from 0.5 mM in the basal layer to > 1.4 mM in the stratum granulosum are consistent with migration patterns in response to minor abrasion (normal wear). Dermal fibroblasts require calcium but are approximately 100 times less sensitive than keratinocytes. Normal calcium metabolism in the skin is dependent on cell membrane and cytosolic calcium binding proteins (calmodulin, cadherins, etc.), but their modulation through parathyroid hormone, vitamin D or growth factors in normal or damaged tissue is not well documented. In wound repair, calcium is predominantly involved as Factor IV in the hemostatic phase, but it is expected to be required in epidermal cell migration and regeneration patterns in later stages of healing. Calcium alginate dressings are designed to liberate calcium early in the acute phase to promote hemostasis, but it is presently unclear whether the supplementary calcium influences the intracellular environment at later stages of wound repair, notably during the remodeling phase. Although experimental studies suggest that control of calcium is obligatory in wound management, we know very little as to how calcium in the wound bed is modulated through hormones, vitamin D, or various growth factors. Also, there is limited information as to how calcium released either from dressings, platelets, or from the circulation through the action of parathyroid hormone, growth factors or other modulators influences cell migration and remodeling in skin wounds, although experimental models suggest that management of calcium is essential in wound management.

CacyBP/SIP, a calcyclin and Siah-1-interacting protein, binds EF-hand proteins of the S100 family

Recently, a human ortholog of mouse calcyclin (S100A6)-binding protein (CacyBP) called SIP (Siah-1-interacting protein) was shown to be a component of a novel ubiquitinylation pathway regulating beta-catenin degradation (Matsuzawa, S., and Reed, J. C. (2001) Mol. Cell 7, 915-926). In murine brain, CacyBP/SIP is expressed at a high level, but S100A6 is expressed at a very low level. Consequently we carried out experiments to determine if CacyBP/SIP binds to other S100 proteins in this tissue. Using CacyBP/SIP affinity chromatography, we found that S100B from the brain extract binds to CacyBP/SIP in a Ca2+-dependent manner. Using a nitrocellulose overlay assay with 125I-CacyBP/SIP and CacyBP/SIP affinity chromatography, we found that this protein binds purified S100A1, S100A6, S100A12, S100B, and S100P but not S100A4, calbindin D(9k), parvalbumin, and calmodulin. The interaction of S100 proteins with CacyBP/SIP occurs via its C-terminal fragment (residues 155-229). Co-immunoprecipitation of CacyBP/SIP with S100B from brain and with S100A6 from Ehrlich ascites tumor cells suggests that these interactions are physiologically relevant and that the ubiquitinylation complex involving CacyBP/SIP might be regulated by S100 proteins.

Ca2+-dependent translocation of the calcyclin-binding protein in neurons and neuroblastoma NB-2a cells

The calcyclin-binding protein (CacyBP) binds calcyclin (S100A6) at physiological levels of [Ca(2+)] and is highly expressed in brain neurons. Subcellular localization of CacyBP was examined in neurons and neuroblastoma NB-2a cells at different [Ca(2+)](i). Immunostaining indicates that CacyBP is present in the cytoplasm of unstimulated cultured neurons in which resting [Ca(2+)](i) is known to be approximately 50 nm. When [Ca(2+)](i) was increased to above 300 nm by KCl treatment, the immunostaining was mainly apparent as a ring around the nucleus. Such perinuclear localization of CacyBP was observed in untreated neuroblastoma NB-2a cells in which [Ca(2+)](i) is approximately 120 nm. An additional increase in [Ca(2+)](i) to above 300 nm by thapsigargin treatment did not change CacyBP localization. However, when [Ca(2+)](i) in NB-2a cells dropped to 70 nm, because of BAPTA/AM treatment, perinuclear localization was diminished. Ca(2+)-induced translocation of CacyBP was confirmed by immunogold electron microscopy and by fluorescence of NB-2a cells transfected with an EGFP-CacyBP vector. Recombinant CacyBP can be phosphorylated by protein kinase C in vitro. In untreated neuroblastoma NB-2a cells, CacyBP is phosphorylated on a serine residue(s), but exists in the dephosphorylated form in BAPTA/AM-treated cells. Thus, phosphorylation of CacyBP occurs in the same [Ca(2+)](i) range that leads to its perinuclear translocation.

A structural basis for S100 protein specificity derived from comparative analysis of apo and Ca(2+)-calcyclin

Calcyclin is a homodimeric protein belonging to the S100 subfamily of EF-hand Ca(2+)-binding proteins, which function in Ca(2+) signal transduction processes. A refined high-resolution solution structure of Ca(2+)-bound rabbit calcyclin has been determined by heteronuclear solution NMR. In order to understand the Ca(2+)-induced structural changes in S100 proteins, in-depth comparative structural analyses were used to compare the apo and Ca(2+)-bound states of calcyclin, the closely related S100B, and the prototypical Ca(2+)-sensor protein calmodulin. Upon Ca(2+) binding, the position and orientation of helix III in the second EF-hand is altered, whereas the rest of the protein, including the dimer interface, remains virtually unchanged. This Ca(2+)-induced structural change is much less drastic than the "opening" of the globular EF-hand domains that occurs in classical Ca(2+) sensors, such as calmodulin. Using homology models of calcyclin based on S100B, a binding site in calcyclin has been proposed for the N-terminal domain of annexin XI and the C-terminal domain of the neuronal calcyclin-binding protein. The structural basis for the specificity of S100 proteins is discussed in terms of the variation in sequence of critical contact residues in the common S100 target-binding site.