Characterization of the cell-cycle-regulated protein calcyclin from Ehrlich ascites tumor cells. Identification of two binding proteins obtained by Ca2(+)-dependent affinity chromatography

S100A6: molecular function and biomarker role

S100A6 (also called calcyclin) is a Ca2+-binding protein that belongs to the S100 protein family. S100A6 has many functions related to the cytoskeleton, cell stress, proliferation, and differentiation. S100A6 also has many interacting proteins that are distributed in the cytoplasm, nucleus, cell membrane, and outside the cell. Almost all these proteins interact with S100A6 in a Ca2+-dependent manner, and some also have specific motifs responsible for binding to S100A6. The expression of S100A6 is regulated by several transcription factors (such as c-Myc, P53, NF-κB, USF, Nrf2, etc.). The expression level depends on the specific cell type and the transcription factors activated in specific physical and chemical environments, and is also related to histone acetylation, DNA methylation, and other epigenetic modifications. The differential expression of S100A6 in various diseases, and at different stages of those diseases, makes it a good biomarker for differential diagnosis and prognosis evaluation, as well as a potential therapeutic target. In this review, we mainly focus on the S100A6 ligand and its transcriptional regulation, molecular function (cytoskeleton, cell stress, cell differentiation), and role as a biomarker in human disease and stem cells.

Francisella tularensis Glyceraldehyde-3-Phosphate Dehydrogenase Is Relocalized during Intracellular Infection and Reveals Effect on Cytokine Gene Expression and Signaling

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is known for its multifunctionality in several pathogenic bacteria. Our previously reported data suggest that the GAPDH homologue of Francisella tularensis, GapA, might also be involved in other processes beyond metabolism. In the present study, we explored GapA's potential implication in pathogenic processes at the host cell level. Using immunoelectron microscopy, we demonstrated the localization of this bacterial protein inside infected macrophages and its peripheral distribution in bacterial cells increasing with infection time. A quantitative proteomic approach based on stable isotope labeling of amino acids in cell culture (SILAC) combined with pull-down assay enabled the identification of several of GapA's potential interacting partners within the host cell proteome. Two of these partners were further confirmed by alternative methods. We also investigated the impact of gapA deletion on the transcription of selected cytokine genes and the activation of the main signaling pathways. Our results show that ∆gapA-induced transcription of genes encoding several cytokines whose expressions were not affected in cells infected with a fully virulent wild-type strain. That might be caused, at least in part, by the detected differences in ERK/MAPK signaling activation. The experimental observations together demonstrate that the F. tularensis GAPDH homologue is directly implicated in multiple host cellular processes and, thereby, that it participates in several molecular mechanisms of pathogenesis.

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.

Differentially expressed genes of human microvascular endothelial cells in response to anti-dengue virus NS1 antibodies by suppression subtractive hybridization

It has been previously shown that anti-dengue virus (DENV) nonstructural protein NS1 antibodies could act as autoantibodies that direct against one or more of the host's own proteins, which has potential implications for dengue hemorrhagic fever pathogenesis. In the present study, we have employed suppression subtractive hybridization (SSH) to identify the differentially expressed genes from human microvascular endothelial cells (HMEC-1) in response to anti-dengue virus type 2 NS1 antibodies (anti-DENV2 NS1 Abs). A total of 35 clones from the SSH cDNA library were randomly selected for further analysis using bioinformatics tools after vector screening. After searching for sequence homology in NCBI GenBank database with BLASTN and BLASTX programs, 23 obtained sequences with significant matches (E-values <1×10(-4)) in the SSH library. The predicted genes in the subtracted library include immune response molecules (CD59 antigen preproprotein preproprotein, MURR1), signal transduction molecules (Nuclear casein kinase and cyclin-dependent kinase substrate 1), calcium-binding proteins (S100A6, Annexin A2 isoform 1/2), and cell-membrane component (Yip1 domain family). From these clones, 5 upregulated genes were selected for differential expression profiling by real-time RT-PCR to confirm their upregulated status. The results confirmed their differential upregulation, and thus verified the success of SSHs and the likely involvement of these genes in dengue pathogenesis.

The S100A6 calcium-binding protein regulates endothelial cell-cycle progression and senescence

Endothelial cells regulate many aspects of vascular physiology, including vasculogenesis and angiogenesis. The S100 family of calcium-binding proteins regulates many aspects of cell function but their roles in vascular physiology are less well understood. Herein, we investigated the expression and function of S100-related family members in endothelial cells. Analysis of total endothelial mRNAs using a human gene chip array revealed significant gene expression of the S100 calcium-binding protein family members S100A6, S100A10, S100A11 and S100A13. We then examined the expression and functional properties of the major S100 family member, S100A6, in vascular endothelial cells. Comparison of primary and transformed human cells revealed significant differences in S100A6 protein levels in these cells. In primary human endothelial cells, S100A6 was present in both the nucleus and the cytoplasm. To assess the function of endothelial S100A6, we depleted protein levels using RNA interference and this caused increased cell-cycle arrest in the G2/M phase under different conditions. S100A6 depletion caused a decrease in both cyclin-dependent kinase 1 (CDK1) and phospho-CDK1 levels, which are essential for eukaryote cell-cycle progression. S100A6 depletion also decreased expression of CDK1, cyclin A1 (CCNA1) and cyclin B (CCNB1) genes with effects on cell-cycle progression. Depletion of endothelial S100A6 levels also elevated β-galactosidase expression, which is an important hallmark of cellular senescence and exit from the mammalian cell cycle. We thus propose that S100A6 has an important role in regulating endothelial commitment to, and progression through, the cell cycle.

Binding of S100 proteins to RAGE: an update

The Receptor for Advanced Glycation Endproducts (RAGE) is a multi-ligand receptor of the immunoglobulin family. RAGE interacts with structurally different ligands probably through the oligomerization of the receptor on the cell surface. However, the exact mechanism is unknown. Among RAGE ligands are members of the S100 protein family. S100 proteins are small calcium binding proteins with high structural homology. Several members of the family have been shown to interact with RAGE in vitro or in cell-based assays. Interestingly, many RAGE ligands appear to interact with distinct domains of the extracellular portion of RAGE and to trigger various cellular effects. In this review, we summarize the modes of S100 protein-RAGE interaction with regard to their cellular functions.

Insights into S100 target specificity examined by a new interaction between S100A11 and annexin A2

S100 proteins are a group of EF-hand calcium-signaling proteins, many of which interact with members of the calcium- and phospholipid-binding annexin family of proteins. This calcium-sensitive interaction enables two neighboring membrane surfaces, complexed to different annexin proteins, to be brought into close proximity for membrane reorganization, using the S100 protein as a bridging molecule. S100A11 and S100A10 are two members of the S100 family found to interact with the N-termini of annexins A1 and A2, respectively. Despite the high degree of structural similarity between these two complexes and the sequences of the peptides, earlier studies have shown that there is little or no cross-reactivity between these two S100s and the annexin peptides. In the current work the specificity and the affinity of the interaction of the N-terminal sequences of annexins A1 and A2 with Ca2+-S100A11 were investigated. Through the use of alanine-scanning peptide array experiments and NMR spectroscopy, an approximate 5-fold tighter interaction was identified between Ca2+-S100A11 and annexin A2 (approximately 3 microM) compared to annexin A1 (approximately 15 microM). Chemical shift mapping revealed that the binding site for annexin A2 on S100A11 was similar to that observed for the annexin A1 but with distinct differences involving the C-terminus of the annexin A2 peptide. In addition, kinetic measurements based on NMR titration data showed that annexin A2 binding to Ca2+-S100A11 occurs at a comparable rate (approximately 120 s(-1)) to that observed for membrane fusion processes such as endo- and exocytosis.

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.

Calcium-binding proteins annexin A2 and S100A6 are sensors of tubular injury and recovery in acute renal failure

BACKGROUND

Rise in cellular calcium is associated with acute tubular necrosis, the most common cause of acute renal failure (ARF). The mechanisms that calcium signaling induce in the quiescent tubular cells to proliferate and differentiate during acute tubular necrosis have not been elucidated.

METHODS

Acute tubular necrosis induced in mice by single intravenous injection of uranyl nitrate and examined after 1, 3, 7, and 14 days. Renal function was monitored and kidneys were evaluated by histology, immunohistochemistry, Western blotting, in situ hybridization, and real-time reverse transcription-polymerase chain reaction (RT-PCR). Models of folic acid induced-ARF and ischemic/reperfusion (I/R) injury were similarly investigated.

RESULTS

Analysis of mRNA expression of intracellular calcium and phospholipid-binding proteins demonstrated selective expression of S100A6 and Annexin A2 (Anxa2) in the renal cortex with marked elevation on day 3, and gradually decline on day 7 and further attenuation on day 14. Similarly, the expression of both proteins, as demonstrated by immunohistochemistry and Western blot analysis, was increased and reached the peak level on day 7 and then gradually declined by day 14. Vimentin, a marker of dedifferentiated cells, was highly expressed during the recovery phase. Combined in situ hybridization immunohistochemistry revealed colocalization of both S100A6 and Anxa2 with proliferating cell nuclear antigen (PCNA). The universality of this phenomenon was confirmed in two other mouse acute tubular necrosis models, the ischemic-reperfusion injury and folic acid-induced ARF.

CONCLUSION

Collectively, these findings demonstrate that S100A6 and Anxa2 expression, initiated in response to tubular injury, persist in parallel throughout the recovery process of tubular cells in acute renal failure.

Cancer-related diseases of the eye: the role of calcium and calcium-binding proteins

The eye provides unique opportunities to study complex biochemical pathways and to describe how components of these pathways contribute to the molecular basis of disease. In this article, the role of calcium-binding proteins in cancer-related diseases of the eye is reviewed. First, paraneoplastic syndromes, or so-called remote effects of cancer, arise from damage to tissues distant from any tumor or its metastases. Many of these syndromes are believed to be immune-mediated. Cancer-associated retinopathy (CAR), a blinding disease due to the degeneration of retinal photoreceptor cells, is one of the best characterized of the paraneoplastic syndromes. The CAR autoantigen has been identified as recoverin, a calcium-binding protein of the EF-hand superfamily. Its features as a calcium-binding protein, along with its function in photoreceptor cells and its role as the CAR autoantigen, are discussed. Next, unlike visual symptoms instigated by a distant tumor, ocular melanoma is the primary malignancy originating in the eye. ALG-2 encodes a pro-apoptotic calcium-binding protein that is down-regulated in ocular melanoma, thus providing these tumor cells with a selective advantage. In addition to background discussion of ALG-2, data describing the expression, cellular localization, and dimerization characteristics of ALG-2 in melanoma cells are presented. Biochemical studies of ALG-2 and its interactions with its target Alix/AIP1 also are presented. Finally, the function of ALG-2 in calcium-induced cell death is discussed. Additional calcium-binding proteins in retina and in ocular tumors are described in relation to different disease entities. Such proteins and their expression in the eye provide valuable examples bridging studies of protein chemistry, cellular function, and human disease.

Identification of intracellular target proteins of the calcium-signaling protein S100A12

In this report, we have focused our attention on identifying intracellular mammalian proteins that bind S100A12 in a Ca2+-dependent manner. Using S100A12 affinity chromatography, we have identified cytosolic NADP+-dependent isocitrate dehydrogenase (IDH), fructose-1,6-bisphosphate aldolase A (aldolase), glyceraldehyde-3-phosphate dehydrogenese (GAPDH), annexin V, S100A9, and S100A12 itself as S100A12-binding proteins. Immunoprecipitation experiments indicated the formation of stable complexes between S100A12 and IDH, aldolase, GAPDH, annexin V and S100A9 in vivo. Surface plasmon resonance analysis showed that the binding to S100A12, of S100A12, S100A9 and annexin V, was strictly Ca2+-dependent, whereas that of GAPDH and IDH was only weakly Ca2+-dependent. To localize the site of S100A12 interaction, we examined the binding of a series of C-terminal truncation mutants to the S100A12-immobilized sensor chip. The results indicated that the S100A12-binding site on S100A12 itself is located at the C-terminus (residues 87-92). However, cross-linking experiments with the truncation mutants indicated that residues 87-92 were not essential for S100A12 dimerization. Thus, the interaction between S100A12 and S100A9 or immobilized S100A12 should not be viewed as a typical S100 homo- or heterodimerization model. Ca2+-dependent affinity chromatography revealed that C-terminal residues 75-92 are not necessary for the interaction of S100A12 with IDH, aldolase, GAPDH and annexin V. To analyze the functional properties of S100A12, we studied its action in protein folding reactions in vitro. The thermal aggregation of IDH or GAPDH was facilitated by S100A12 in the absence of Ca2+, whereas in the presence of Ca2+ the protein suppressed the aggregation of aldolase to less than 50%. These results suggest that S100A12 may have a chaperone/antichaperone-like function which is Ca2+-dependent.

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.

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

Calcyclin (S100A6) is an S100 calcium-binding protein whose expression is up-regulated in proliferating and differentiating cells. A novel 30-kDa protein exhibiting calcium-dependent calcyclin-binding (calcyclin-binding protein, CacyBP) had been identified, purified, and cloned previously (Filipek, A., and Kuznicki, J. (1998) J. Neurochem. 70, 1793-1798). Here, we have defined the calcyclin binding region using limited proteolysis and a set of deletion mutants of CacyBP. A fragment encompassing residues 178-229 (CacyBP-(178-229)) was capable of full binding to calcyclin. CacyBP-(178-229) was expressed in Escherichia coli as a glutathione S-transferase fusion protein and purified. The protein fragment cleaved from the glutathione S-transferase fusion protein was shown by CD to contain 5% alpha-helix, 15% beta -sheet, and 81% random coil. Fluorescence spectroscopy was used to determine calcyclin dissociation constants of 0.96 and 1.2 microm for intact CacyBP and CacyBP-(178-229), respectively, indicating that the fragment can be used for characterization of calcyclin-CacyBP interactions. NMR analysis of CacyBP-(178-229) binding-induced changes in the chemical shifts of (15)N-enriched calcyclin revealed that CacyBP binding occurs at a discrete site on calcyclin with micromolar affinity.

Calcyclin (S100A6) binding protein (CacyBP) is highly expressed in brain neurons

The expression of a novel calcyclin (S100A6) binding protein (CacyBP) in different rat tissues was determined by Western and Northern blotting. Polyclonal antibodies against recombinant CacyBP purified from E. coli exhibited the highest reaction in the brain and weaker reaction in liver, spleen, and stomach. CacyBP immunoreactivity was also detected in lung and kidney. Densitometric analysis showed that the concentration of CacyBP in the soluble fractions of total brain and cerebellum is approximately 0.17 and 0. 34 ng/microg protein, respectively. Northern blotting with a specific cDNA probe confirmed the high level of CacyBP expression in the rat brain and lower levels in other tissues examined. Immunohistochemistry and in situ hybridization of rat brain sections revealed strong expression of CacyBP in neurons of the cerebellum, hippocampus, and cortex. The in situ hybridization detected CacyBP in hippocampus as early as P7 (postnatal day 7) and a peak of expression at P21, and the expression signal was preserved until adulthood. In the entorhinal cortex, the peak of expression was observed at P7, whereas in the cerebellum it was seen at P21. The results presented here show that CacyBP is predominantly a neuronal protein. (J Histochem Cytochem 48:1195-1202)

Differential expression of S100B and S100A6(1) in the human fetal and aged cerebral cortex

S100B and S100A6 (calcylin) are two members of the S100 Ca(2+)-binding protein family and have been localized in the mammalian nervous system. However, information on their distribution in the human nervous system, especially in the developing human fetal brain, is scarce. In the present study, an immunocytochemical method was used to examine the spatio-temporal protein expression patterns of S100B and S100A6 in normal human fetal hippocampus, entorhinal cortex and occipital cortex. Normal aged adult human brain specimens were also included for comparison. From week 15 onwards, an increase with advancing gestation age in both the number and staining intensity of S100B positive, astrocyte-like cells was found in the pyramidal layer of the hippocampus, while both the molecular and polymorphic layers showed similar S100B immunoreactivities at all stages examined. A decrease in the immunoreactivities was found in the molecular layer of the aged adult hippocampus while other layers exhibited immunoreactivities similar to those of the late fetus. At week 15, the molecular, pyramidal and ganglionic/multiform layers of the entorhinal cortex also showed positive S100B immunoreactivities which were maintained throughout the rest of the gestation and in adult specimens. In the occipital cortex, the numbers of positive cells for all layers were about twofold higher than those found in the hippocampus and entorhinal cortex, and immunoreactivities detected in the granular layer increased from week 21, reaching a plateau at around week 27. S100B positive fibers were also found at week 30 but were not observed in aged adult specimens. S100A6 positive cells were on the whole fewer in number than those of S100B in the brain regions examined. The S100A6 immunoreactivities which were localized in some pyramidal neuron-like and some glial-like cells of the pyramidal and molecular layers of the hippocampus increased by midgestation and became weak in the late fetus and in aged adult specimens. Weakly stained S100A6 positive cells were also observed in the entorhinal cortex throughout the gestation and in aged adult cortex. S100A6 immunoreactivities were weak in the fetal occipital cortex. They were also localized in the glial-like cells of the aged adult occipital cortex. The differential spatio-temporal expression of S100B and S100A6 proteins suggests that the proteins play different roles in different brain regions during development and in adulthood.

The identification and differential expression of calcium-binding proteins associated with ocular melanoma

Calcium-binding proteins may endow tumor cells with properties related to their malignancy and metastatic phenotype. Chromatographic procedures and amino acid sequence analysis were used in this study to identify seven calcium-binding proteins, annexin VI, cap g, annexin V, calmodulin, S100A11, S100B and S100A6, associated with uveal melanoma, the primary ocular tumor of adults. This series of calcium-binding proteins was identified in both primary tumors and cell lines of uveal melanoma. Several of the proteins were shown by immunochemical methods to be differentially expressed between normal uveal melanocytes and malignant melanomas of the uvea. In addition, the expression of S100A6 may correlate with the malignant properties of the tumor.

Annexin VI binds S100A1 and S100B and blocks the ability of S100A1 and S100B to inhibit desmin and GFAP assemblies into intermediate filaments

Annexin VI, a member of a family of Ca(2+)-dependent phospholipid- and membrane-binding proteins, interacts with the Ca(2+)-regulated EF-hand proteins, S100A1 and S100B, and blocks the ability of these two proteins to inhibit the assembly of desmin and glial fibrillary acidic protein (GFAP) into intermediate filaments in a Ca(2+)- and dose-dependent manner. S100A1 and S100B each possess one annexin VI binding site, characterized by an affinity for annexin VI in the submicromolar range. Binding of annexin VI to either S100 protein occurs at a site that appears to differ in some parts from that recognizing desmin and GFAP. As S100A1 and S100B exist in solution as homodimers in which the two monomers are related by a 2-fold symmetry axis, each of the above S100 homodimers likely crosslinks two annexin VI molecules, a situation that appears typical of all the annexin-S100 protein complexes described thus far. However, whereas in the cases of other annexin-S100 complexes the C-terminal extension of the S100 molecule appears indispensable for annexin binding, the annexin VI binding site cannot be restricted to the S100A1 and S100B C-terminal extension. We speculate that the annexin VI site on S100A1/B may only partially overlap to the desmin/GFAP site. In contrast, no effects of annexin V on the ability of S100A1 or S100B to affect the desmin and GFAP assemblies could be documented, although binding of annexin V to S100A1 and S100B could be detected at relatively high Ca2+ concentrations. The present data suggest that annexin VI might regulate S100A1 and S100B activities and vice versa.

p30, a novel protein target of mouse calcyclin (S100A6)

A novel protein target of mouse calcyclin (S100A6) was detected by a gel overlay method with 125I-labelled calcyclin. Interaction of calcyclin with its 30 kDa target protein (p30) present in Ehrlich ascites tumour (EAT) cells depended on the presence of Ca2+ ions. The binding of p30, evidenced by the reaction with 125I-labelled calcyclin, was found to be of higher affinity than the binding between mouse calcyclin and annexin II or glyceraldehyde-3-phosphate dehydrogenase. Examination of tissue extracts by the gel overlay method has shown that p30 is present not only in the EAT cells but also in mouse brain and spleen. This novel target protein of mouse calcyclin was purified to homogeneity from EAT cells by means of Phenyl-Sepharose chromatography, affinity chromatography and CM-cellulose chromatography. Purified p30 was digested with alpha-chymotrypsin and a partial amino acid sequence of one of the resulting peptides was established. A database search analysis revealed that the sequence is unique, with a similarity of less than 55% to any other known protein sequence.

Annexin II in exocytosis: catecholamine secretion requires the translocation of p36 to the subplasmalemmal region in chromaffin cells

Annexin II is a Ca(2+)-dependent membrane-binding protein present in a wide variety of cells and tissues. Within cells, annexin II is found either as a 36-kD monomer (p36) or as a heterotetrameric complex (p90) coupled with the S-100-related protein, p11. Annexin II has been suggested to be involved in exocytosis as it can restore the secretory responsiveness of permeabilized chromaffin cells. By quantitative confocal immunofluorescence, immunoreplica analysis and immunoprecipitation, we show here the translocation of p36 from the cytosol to a subplasmalemmal Triton X-100 insoluble fraction in chromaffin cells following nicotinic stimulation. A synthetic peptide corresponding to the NH2-terminal domain of p36 which contains the phosphorylation sites was microinjected into individual chromaffin cells and catecholamine secretion was monitored by amperometry. This peptide blocked completely the nicotine-induced recruitment of p36 to the cell periphery and strongly inhibited exocytosis evoked by either nicotine or high K+. The light chain of annexin II, p11, was selectively expressed by adrenergic chromaffin cells, and was only present in the subplasmalemmal Triton X-100 insoluble protein fraction of both resting and stimulated cells. p11 can modify the Ca(2+)- and/or the phospholipid-binding properties of p36. We found that loss Ca2+ was required to stimulate the translocation of p36 and to trigger exocytosis in adrenergic chromaffin cells. Our findings suggest that the translocation of p36 to the subplasmalemmal region is an essential event in regulated exocytosis and support the idea that the presence of p11 in adrenergic cells may confer a higher Ca2+ affinity to the exocytotic pathway in these cells.

Calcium-dependent binding of the plasma protein apolipoprotein A-I to two members of the annexin family

Affinity chromatography with purified annexins coupled to CNBr-activated Sepharose 4B was used to determine the capacity of proteins found in cytosolic fractions of the bovine adrenal medulla to bind to an immobilized annexin in a Ca2+-dependent manner. Several proteins were eluted from a recombinant annexin I column in the presence of 2 mM EGTA, including protein kinase C (PKC), members of the annexin family, and a 26 kDa protein that appeared as the most prominent band on SDS-PAGE. The identities of PKC, annexin I, annexin IV, annexin VI, and annexin VII were confirmed by Western blotting. The 26 kDa protein was purified by anion exchange chromatography on a Poros Q column and determined to be apolipoprotein A-I (apoA-I) by peptide sequencing. Comigration of apoA-I and chromobindin 2 on two-dimensional gels identified apoA-I as chromobindin 2. Overlay assays were performed to verify the apoA-I-annexin I interaction using apoA-I immobilized on nitrocellulose and annexin I in solution with binding detected using anti-annexin I antiserum. Additionally, the ability of biotin-labeled apoA-I in solution to bind to several purified annexins immobilized on nitrocellulose was determined by detection with horseradish peroxidase-conjugated avidin. Using these methods, it was shown that both annexin I and annexin VII bind to bovine apoA-I in a Ca2+-dependent manner. Other annexins, such as annexin IV and annexin VI, do not exhibit this binding. The results suggest that certain annexins may function as extracellular binding sites for plasma proteins.

Studies on associations of glycolytic and glutaminolytic enzymes in MCF-7 cells: role of P36

Isoelectric focusing of MCF-7 cell extracts revealed an association of the glycolytic enzymes glyceraldehyde 3-phosphate-dehydrogenase, phosphoglycerate kinase, enolase, and pyruvate kinase. This complex between the glycolytic enzymes is sensitive to RNase. p36 could not be detected within this association of glycolytic enzymes; however an association of p36 with a specific form of malate dehydrogenase was found. In MCF-7 cells three forms of malate dehydrogenase can be detected by isoelectric focusing: the mitochondrial form with an isoelectric point between 8.9 and 9.5, the cytosolic form with pl 5.0, and a p36-associated form with pl 7.8. The mitochondrial form comprises the mature mitochondrial isoenzyme (pl 9.5) and its precursor form (pl 8.9). Refocusing of the pl 7.8 form of malate dehydrogenase also gave rise to the mitochondrial isoenzyme. Thus, the pl 7.8 form of malate dehydrogenase is actually the mitochondrial isoenzyme retained in the cytosol by the association with p36. Addition of fructose 1,6-bisphosphate to the initial focusing column induced a quantitative shift of the pl 7.8 form of malate dehydrogenase to the mitochondrial forms (pl 8.9 and 9.5). In MCF-7 cells p36 is not phosphorylated in tyrosine. Kinetic measurements revealed that the pl 7.8 form of malate dehydrogenase has the lowest affinity for NADH. Compared to both mitochondrial forms the cytosolic isoenzyme has a high capacity when measured in the NAD --> NADH direction (malate --> oxaloacetate direction). The association of p36 with the mitochondrial isoenzyme may favor the flow of hydrogen from the cytosol into the mitochondria. Inhibition of cell proliferation by AMP which leads to an inhibition of glycolysis has no effect on complex formation by glycolytic and glutaminolytic enzymes in MCF-7 cells. AMP treatment leads to an activation of malate dehydrogenase, which correlates with the increase of pyruvate and the decrease of lactate levels, but has no effect on the distribution of the various malate dehydrogenase forms.

Characterization of chicken gizzard calcyclin and examination of its interaction with caldesmon

Using a procedure developed to purify calcyclin from mouse Ehrlich ascites tumor cells calcyclin was purified from smooth muscle of chicken gizzard. Chicken gizzard calcyclin bound to phenyl-Sepharose in a calcium dependent manner as did mouse EAT cells and rabbit lung calcyclin but appeared to be more acidic than its mammalian counterparts as revealed by ion exchange chromatography on Mono Q. Chicken gizzard calcyclin bound 45Ca2+ on nitrocellulose filters and exhibited a shift in electrophoretic mobility on urea-PAGE depending on Ca2+ concentration. Crosslinking experiments with BS3 showed that chicken gizzard calcyclin was able to form noncovalent dimers. As indicated by a decrease in maximum tryptophan fluorescence emission of caldesmon (about 14% at 1:1 molar ratio) and displacement of calmodulin from its complex with caldesmon, chicken gizzard calcyclin binds caldesmon. This binding was, however, much weaker than that of calmodulin and could not influence the interaction of caldesmon with actin. In consequence, calcyclin was unable to reverse the inhibitory effect of caldesmon on actin-activated Mg(2+)-ATPase activity of myosin in the presence of Ca2+.

Interaction of calcyclin and its cyanogen bromide fragments with annexin II and glyceraldehyde 3-phosphate dehydrogenase

The structural properties of calcyclin protein are quite well characterized but its function remains obscure. To help elucidate the biological role of calcyclin we have performed the in vitro studies of the Ca(2+)-dependent interaction of Ehrlich ascites tumor cells calcyclin and its cyanogen bromide fragments with two potential calcyclin targets: annexin II and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). The binding of annexin II, evidenced by the reaction with 125I-calcyclin, was found to be very weak and occurred only for intact calcyclin. On the other hand the interaction between calcyclin and GAPDH was of high affinity and could be assigned to the N-terminal region of calcyclin. Intact calcyclin and its N-terminal fragment bound to GAPDH in the gel overlay and affinity chromatography assay. When examined in the presence of a crosslinking agent the interaction resulted in the formation of 46K covalent adduct between calcyclin monomer and GAPDH subunit. Fluorescence of 5-iodoacetamido-fluorescein-labelled calcyclin was efficiently quenched by GAPDH in the presence of Ca2+. Titration experiments revealed the stoichiometry of one calcyclin monomer binding to each of GAPDH subunits with a binding constant of 10(8) M-1. The results of this work suggest that the binding between calcyclin and GAPDH may have bearing on calcyclin function.

S100 beta is a target protein of neurocalcin delta, an abundant isoform in glial cells

To clarify the function of neurocalcin delta, an isoform found abundantly in glial cells, we attempted to find its target proteins by using neurocalcin delta-affinity chromatography and the 125I-neurocalcin delta gel-overlay method. The 10, 14, 27, 36 and 50 kDa bands found on SDS/PAGE bound to 125I-neurocalcin delta, and 10, 11, 19, 24, 26, 50 and 70 kDa proteins were eluted from a neurocalcin delta-affinity column in a Ca(2+)-dependent manner. Sequence analysis of proteolytic peptides revealed the following identities: S100 beta (10 kDa), S100 alpha (11 kDa), myelin basic protein (19 kDa), glyceraldehyde-3-phosphate dehydrogenase (36 kDa) and tubulin beta-chain (50 kDa). A zero-length cross-linking study indicated that 1 mol of S100 beta bound to 1 mol of neurocalcin delta. With the gel-overlay method, purified S100 beta protein and calcyclin bound to 125I-neurocalcin delta whereas calgizarrin and calvasculin, other members of the S100 family, did not. These findings suggest that S100 beta is one of the target proteins of neurocalcin delta, and the neurocalcin delta-S100 beta complex may be involved in Ca(2+)-signalling in the glial cell.

Calcyclin from mouse Ehrlich ascites tumor cells and rabbit lung form non-covalent dimers

Crosslinking treatments of fresh cytosol from mouse Ehrlich ascites tumor (EAT) cells revealed the existence of calcyclin dimers which were sensitive to SDS, but not to reducing agents, which suggests the existence of non-covalent dimers. In stored EAT cell cytosol and preparations of purified calcyclin dimers were also formed by S-S bridging (covalent dimers). The S-S dimers did not bind to organomercurial Agarose and could be separated from reduced forms of calcyclin that bound to the resin. Calcyclin eluted from the resin with DTT was a mixture of monomers and non-covalent dimers as shown by crosslinking and subsequent immunoblotting. Calcyclin from rabbit lung, lacking a cysteine residue, could also be crosslinked as a dimer. It is suggested that the ability of calcyclin to form non-covalent dimers is of physiological significance.

Identification of an AP-1-like sequence in the promoter region of calcyclin, a S-100-like gene. Enhancement of binding during retinoic acid-induced neuroblastoma cell differentiation

The promoter region of genes involved in cell growth and differentiation is bound by specific transcription factors which regulate its expression. Our previous study showed that the calcyclin gene, which belongs to the large family of Ca2+-binding proteins, is differently expressed in SK-N-BE(2)C and LA-N-5 neuroblastoma cell lines. We analysed the region upstream the transcription initiation site of the gene before and during retinoic acid (RA)-induced differentiation. Gel-shift analysis showed that the -161,-135 untranslated region is bound by an AP-1-like protein both in SK-N-BE(2)C and LA-N-5 cells. Competition assay demonstrated that AP-2,AP-3 and NF1 transcription factors did not bind in the same region. Calcyclin mRNA is induced in RA-treated LA-N-5 cells and reaches maximal expression at 96 h, suggesting that its gene is involved in cell differentiation. Gel-shift analysis shows a strong signal of binding after 96 h of RA treatment. Our results indicate that RA induces an increase in the binding protein or improves its affinity for the AP-1-like region during neuronal differentiation. These preliminary data suggest that the calcyclin gene is involved in neuronal pathway differentiation and that AP-1-like binding sequence could be one of the gene regions that is under transcriptional factor control during cell differentiation.

Purification and characterization of a novel calcium-binding protein, S100C, from porcine heart

A novel Ca(2+)-binding protein, which we have named S100C (Ohta et al. (1991) FEBS Lett. 295, 93-96), was purified to homogeneity from porcine heart by Ca(2+)-dependent dye-affinity chromatography. S100C possesses some properties of S100 proteins, such as self-association and exposure of a hydrophobic site upon binding of Ca2+ but it differs from S100 proteins in forms of its isoelectric point (pI = 6.2), cross-reactivity with antibodies, staining by Stains-all, and its Ca(2+)-dependent interaction with the immobilized dye. S100C bound to cytoskeletal components at physiological concentrations of Ca2+. Moreover, it was found that 125I-labeled S100C interacted with annexin I in a Ca(2+)-dependent manner. S100C also inhibited the phosphorylation of annexin I by protein kinase C. These data suggest that S100C might act to regulate the cytoskeleton in a Ca(2+)-dependent manner via interactions with annexin I.

Transduction of Ca2+ signals upon fertilization of eggs; identification of an S-100 protein as a major Ca(2+)-binding protein

A transient increase in the level of free cytosolic Ca2+ is observed upon fertilization of the eggs of many species and is thought to represent a key event in the initiation of development. To identify components in the egg which could be involved in mediating such Ca2+ signals we searched for Ca(2+)-binding proteins in eggs of the fresh-water fish Misgurnus fossilis (loach). We show that loach eggs contain two major Ca(2+)-binding proteins which can be purified through their Ca(2+)-dependent interaction with a hydrophobic matrix. Protein sequencing revealed that the larger 18 kDa protein is calmodulin, while the smaller polypeptide of 10 kDa is a member of the S-100 protein family. This is the first report of the presence of an S-100 protein in vertebrate eggs and shows that this protein is found in two fold higher concentration than calmodulin. Since the 10 kDa protein shares 68% sequence identity with S-100 alpha from bovine brain, it can be considered as the loach homologue of mammalian S-100 alpha. During early embryonic development, de novo protein synthesis of calmodulin is observed at the earliest stages analyzed (mid-blastula), while de novo protein synthesis of the S-100 alpha homologue begins with the mid-gastrula stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of calcyclin fragments obtained by CNBr-cleavage

1. Two calcyclin fragments were obtained by CNBr-cleavage. 2. One fragment represented N-terminal end of a molecule (residues 1-56), and another one a C-terminal end (residues 57-89). 3. Properties of intact calcyclin such as binding of calcium, binding to hydrophobic resins and interaction with calcyclin specific antibodies were not retained by these fragments. 4. However, both fragments were able to form dimers and higher forms of aggregates as seen for uncleaved calcyclin. 5. This indicates that both halves of the molecule contain the regions responsible for non-covalent interaction which might participate in dimer formation.

Identification of annexin II, annexin VI and glyceraldehyde-3-phosphate dehydrogenase as calcyclin-binding proteins in bovine heart

1. Matrix-immobilized calcyclin as affinity ligand in chromatography led to purification of three protein bands at 68, 36 and 35 kDa from bovine heart that required Ca2+ for binding. 2. Polyacrylamide-immobilized phosphatidylserine separated this fraction into a phospholipid-binding part (68 kDa, 35 kDa), also attaching to phospholipid vesicles even in the presence of calcyclin, and a flow-through part, constituting approx 30% of the total fraction (36 kDa). 3. Enzyme assays and electrophoretic mobility showed an at least close relationship of the 36 kDa band to glyceraldehyde-3-phosphate dehydrogenase. Interaction between enzyme and calcyclin in a solid-phase assay was inhibited by sialoglycoproteins and depended strongly on the integrity of carboxyl and hydrophobic groups of the enzyme. The interaction between the two proteins had a KD value of 110 nM. 4. Application of annexin-specific antibodies revealed an immunological relationship of the 35 and 68 kDa calcyclin-binding proteins to members of the annexin family, namely to annexin II (35 kDa) and annexin VI (68 kDa). The N-terminal amino acid sequence of a cleavage peptide of the 68 kDa protein was identical to a sequence stretch in human annexin VI, corroborating this evidence.

The gene encoding the calcium binding protein calcyclin is expressed at sites of exocytosis in the mouse

Calcyclin is a member of the S100 family of calcium binding proteins. We have found by in situ hybridization that calcyclin transcripts are restricted to specific cell types within a limited number of mouse organs. High levels of expression in the epithelia lining the gastrointestinal, respiratory and urinary tracts, and specific localization of the transcripts to the goblet cells in the small intestine, lead us to suggest a role for calcyclin in the process of mucus secretion. In addition, calcyclin expression was detected in the corpus luteum, placenta and nerves within the gut wall, which are all sites of regulated exocytosis. We propose that this S100-like protein may be part of a calcium signalling pathway utilized in the secretion of various products by different cell types.

Site-directed mutation makes rabbit calcyclin dimer

Unlike human, rat and mouse calcyclin, purified rabbit calcyclin did not form a dimer on Tricine SDS-PAGE under non-reduced conditions. Based on the internal peptide sequence of rabbit calcylin, we isolated and sequenced a cDNA clone encoding calcyclin. The sequence of this clone (pCalC) is 629 bp long and codes 90 amino acid residues of a protein with a molecular mass of 10,153 Da. By Northern blot analysis, a major band of 0.9 kbp and a minor band of 2.6 kbp were detected in the lung. The recombinant calcyclin mutated serine at the third position to cysteine was expressed in E. coli and made dimer formation under non-reduced conditions on SDS-PAGE. Whether or not this type of mutation which prevents dimer formation of calcyclin plays a physiological role in the rabbit lung is the subject of an ongoing study.

A growth-dependent post-translational modification of annexin VI

Annexin VI (p68, 67-kDa calelectrin) is a member of a family of Ca2+/phospholipid-binding proteins, that includes p35 (annexin I) and p36 (annexin II), the major cellular substrates for phosphorylation by the epidermal growth factor receptor and pp60v-src tyrosine kinase activities, respectively. We report here that like annexins I and II, annexin VI is phosphorylated in vivo, but that in contrast, annexin VI phosphorylation is associated with cell growth. In both Swiss 3T3 fibroblasts and human T-lymphoblasts the pattern of phosphorylation followed an almost identical profile. In particular, annexin VI was not phosphorylated in quiescent cells, but was phosphorylated on serine and to a lesser extent threonine, several hours following cell stimulation. Furthermore, annexin VI also incorporated phosphate in a growth-dependent manner, in a form other than a phosphoamino-acid. The phosphate was visualised following acid hydrolysis of immunoprecipitated annexin VI, as part of a complex having high mobility on 2-D thin-layer electrophoresis. The identity of this complex is not known. The results suggest that a post-translational modification other than direct protein phosphorylation may influence the activity of annexin VI and provide evidence linking cell growth with regulation of annexin VI function.

S-100 protein binds to annexin II and p11, the heavy and light chains of calpactin I

S-100 protein, a dimeric, Ca(2+)-binding protein of the EF-hand type, interacts with annexin II (p36, the heavy chain of the cytoskeletal protein complex, calpactin I), with p11 (the light and regulatory chain of calpactin I) and with the hetero-tetramer annexin II2-p11(2) (calpactin I) in a Ca(2+)-regulated way, but not with annexins I, V and VI. The interaction of S-100 protein with the above proteins was investigated by fluorescence spectroscopy using acrylodan-S-100 protein and acrylodan-annexin II and by cross-linking experiments using the bifunctional cross-linker disuccinimidyl suberate (DSS). S-100 protein binds with the highest affinity to annexin II (Kd approx. 0.4 microM) and with the lowest affinity to calpactin I (Kd approx. 10 microM), with a constant stoichiometry of about 2 mol of protein/S-100 dimer. Thus, S-100 protein could substitute for p11 in regulating the activities of annexin II in cells which do not express p11 and/or act synergistically with p11 in cells expressing both p11 and S-100. The binding of S-100 protein to p11 could reflect the natural tendency of S-100 subunits and p11 to dimerize. Chimeric p11-S-100 alpha and p11-S-100-beta proteins could therefore form in a Ca(2+)-regulated way. The interaction of S-100 protein with calpactin I appears of doubtful physiological importance, because of the low binding affinity, of the small extent of fluorescence changes induced by calpactin I in acrylodan-S-100 protein and of lack of DSS-induced complex formation between the two protein species.

Calcyclin as a marker of human epithelial cells and fibroblasts

The distribution of calcyclin in human tissues was studied using polyclonal antibodies against this protein. In all organs examined (breast, heart, intestine, kidney, liver, ovary, placenta, stomach, thymus, and uterus) only epithelial cells and fibroblasts were stained. This suggests that calcyclin expression is related either to proliferation rate or secretion activity. The data show that calcyclin might be considered as a marker of some human epithelial cells and fibroblasts.

Evolution of EF-hand calcium-modulated proteins. II. Domains of several subfamilies have diverse evolutionary histories

In the first report in this series we described the relationships and evolution of 152 individual proteins of the EF-hand subfamilies. Here we add 66 additional proteins and define eight (CDC, TPNV, CLNB, LPS, DGK, 1F8, VIS, TCBP) new subfamilies and seven (CAL, SQUD, CDPK, EFH5, TPP, LAV, CRGP) new unique proteins, which we assume represent new subfamilies. The main focus of this study is the classification of individual EF-hand domains. Five subfamilies--calmodulin, troponin C, essential light chain, regulatory light chain, CDC31/caltractin--and three uniques--call, squidulin, and calcium-dependent protein kinase--are congruent in that all evolved from a common four-domain precursor. In contrast calpain and sarcoplasmic calcium-binding protein (SARC) each evolved from its own one-domain precursor. The remaining 19 subfamilies and uniques appear to have evolved by translocation and splicing of genes encoding the EF-hand domains that were precursors to the congruent eight and to calpain and to SARC. The rates of evolution of the EF-hand domains are slower following formation of the subfamilies and establishment of their functions. Subfamilies are not readily classified by patterns of calcium coordination, interdomain linker stability, and glycine and proline distribution. There are many homoplasies indicating that similar variants of the EF-hand evolved by independent pathways.