Effect of S-100 proteins and calmodulin on Ca2+-induced disassembly of brain microtubule proteins in vitro

Enhancement of S-100 beta protein in blood of patients with Down's syndrome

The human gene encoding the beta subunit of S-100 protein (S-100 beta) was mapped on chromosome 21. In order to confirm the expression of gene-dosage effect of S-100 beta in patients with Down's syndrome (DS), concentrations of immunoreactive S-100 alpha and S-100 beta proteins were determined in the blood plasma and lymphocytes fraction of the patients and control subjects. Cu/Zn-superoxide dismutase (SOD), a protein that is known to show the gene-dosage effect on the trisomy of chromosome 21, also was immunoassayed in the same blood samples as control proteins. In blood plasma, S-100 beta protein as well as Cu/Zn SOD was enhanced (P less than 0.001) in the patients (160 +/- 70 pg S-100 beta/ml and 87 +/- 83 ng SOD/ml, N = 44) as compared with control individuals (76 +/- 25 pg/ml, and 18 +/- 11 ng/ml, respectively, N = 28). However, concentrations of S-100 alpha in blood plasma of DS patients were similar to those of normal subjects. Concentrations of S-100 beta in lymphocyte fractions of DS patients (24.7 +/- 10.9 ng/mg protein) were also higher (P less than 0.001) than those of control subjects (10.1 +/- 5.8 ng/mg protein). These results indicate that gene-dosage effect of S-100 beta levels are expressed in DS patients.

Immunohistochemical differential distribution of S-100 alpha and S-100 beta in the peripheral nervous system of the rat

The localization of the alpha subunit of the S-100 protein (S-100 alpha) and beta subunit (S-100 beta) was studied in the peripheral nervous system of the rat. In peripheral nerves, S-100 alpha and S-100 beta were found in the cytoplasm of Schwann cells. Axons were positively stained in part by S-100 alpha and almost totally by S-100 beta. In the dorsal root ganglia, S-100 alpha was found in satellite cells and their processes and in some neurons. S-100 beta was found in more of the large neurons, but almost all of the small neurons were negative for S-100 beta. In the anterior horn cells, S-100 beta staining was stronger than that of S-100 alpha. In Schwann cells, both S-100 alpha and S-100 beta were present on the rough endoplasmic reticulum, free ribosomes, and nucleus, as seen by electron microscopy. The S-100 alpha and S-100 beta in axons were associated with microtubules and neurofilaments.

Transient modulation of Schwann cell antigens after peripheral nerve transection and subsequent regeneration

Schwann cells within the distal portion of a transected nerve undergo a series of poorly understood events in response to injury and loss of axonal contact. These events may influence the regeneration of PNS neurons. In this study we examined the alteration of antigens located in the basal lamina, plasma membrane and cytoplasm of Schwann cells within the distal nerve stump: (a) after a complete transection of the sciatic nerve, and (b) subsequent to reestablished contact between regenerating axons and dedifferentated Schwann cells separated from contact with neurons. Visualization of laminin and heparan sulphate proteoglycan molecules at various intervals after nerve transection always revealed intact basal lamina channels. In response to loss of axonal contact, vimentin expression by Schwann cells within the distal nerve stump increased, becoming a predominant intermediate filament protein of the cytoskeleton while glial fibrillary acid protein (GFAP) expression decreased. This reversal in the prominence of intermediate filament protein was maintained until the onset of axonal reinnervation, at which point expression of GFAP increased and vimentin decreased. Expression of the Schwann cell plasma membrane associated protein, C4, closely mimicked GFAP expression during axon degeneration and subsequent reinnervation. In the normal uninjured nerve, tissue plasminogen activator (tPA) and S-100 were localized in the region near the Schwann cell-axon interface and the outer Schwann cell plasma membrane. In response to loss of axonal contact, the S-100 and tPA immunoreactivity associated with the Schwann cell-axon interface was lost while that localized around the outer Schwann cell plasma membrane remained unchanged. The results of this study demonstrate that Schwann cells modulate a portion of their antigenic repertoire in response to a loss of axonal contact and after contact with regenerating axons.

Molecular interaction of S-100 proteins with microtubule proteins in vitro

Several procedures were employed to examine the in vitro interaction between S-100 proteins and microtubule proteins. Binding of S-100 to tau factors was observed under all experimental conditions. S-100 binding to microtubule-associated protein 2 (MAP2) was best detected by exposing nitrocellulose-immobilized MAP2 or MAPs to either 125I-labeled S-100 or biotinylated S-100. S-100 binding to tubulin was detected when the two protein fractions were first incubated with each other followed by exposure to the bifunctional cross-linker disuccinimidylsuberate, and then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transfered onto nitrocellulose paper. By this procedure, complex formation between S-100 and tubulin, as well as between S-100 and a relatively low-molecular-weight MAP, was evidenced by immunoblotting using an anti-S-100 antiserum. Alternatively, complex formation between biotinylated S-100 and either tubulin or MAPs was visualized by means of avidin-peroxidase, after SDS-PAGE of the complex mixtures and transfer of the separated proteins onto nitrocellulose. The interaction between S-100 and tubulin was strictly Ca2+ dependent, and resistant to high concentrations of KCl, colchicine, or vinblastine.

S-100a0 protein stimulates the basal (Mg2+-activated) adenylate cyclase activity associated with skeletal muscle membranes

S-100a0 protein, the alpha alpha isoform of the S-100 family, stimulates basal (Mg2+-activated) adenylate cyclase (AC) activity associated with the sarcolemma, longitudinal tubules and terminal cisternae of rat skeletal muscle cells. The stimulatory effect of S-100a0 on AC activity is maximal around 5 microM S-100a0 and half-maximal around 0.2 microM S-100a0. Also, the stimulatory effect is greatest on the AC activity associated with the terminal cisternae than on the other membrane fractions studied. These data are discussed in relation to the subcellular localization of S-100a0 in muscle cells.

Identification of S-100 proteins and S-100-binding proteins in a detergent-resistant EDTA/KCl-extractable fraction from bovine brain membranes

The Triton X-100-resistant residue of brain membranes contains appreciable amounts of S-100 proteins. This fraction of S-100 can be solubilized by high concentrations of EDTA plus or minus high concentrations of KCl. Whereas KCl (0.6 M) extracts the detergent-resistant S-100, NaCl (1 M) does not. Endogenous Ca2+ is required and is sufficient for S-100 to remain associated with the detergent-resistant residue. However, 0.6 M KCl extracts a further fraction of Triton X-100-resistant S-100. In contrast, the Triton X-100-extractable fraction of S-100 resists the action of EDTA. These data suggest that Ca2+ regulates the extent of association of S-100 with Triton X-100-resistant components in brain membranes, whereas the association of S-100 with the lipid bilayer of brain membranes and/or with some intrinsic membrane proteins is less Ca2+-regulated. Several S-100-binding proteins are identified in the detergent-resistant residue of brain membranes by an overlay procedure.

Interaction between S-100 proteins and steady-state and taxol-stabilized microtubules in vitro

S-100 proteins are a group of three 21-kilodalton, acidic, Ca2+-binding proteins of the "E-F hand" type shown to regulate several cell activities, including microtubule (MT) assembly-disassembly. We show here that S-100 proteins interact with MTs assembled from either whole microtubule protein or purified tubulin, both in the absence and in the presence of the MT-stabilizing drug taxol. Evidence for the binding of S-100 to MTs comes from both kinetic (turbidimetric) and binding studies. Kinetically, S-100 enhances the disassembly of steady-state MTs in the presence of high concentrations of colchicine or vinblastine at 10 microM free Ca2+ and disassembles taxol-stabilized MTs at high Ca2+ concentrations. Experiments performed using 125I-labeled S-100 show that S-100 binds Ca2+ independently to a single set of sites on taxol-stabilized MTs assembled from pure tubulin with an affinity of 6 x 10(-5) M and a stoichiometry of 0.15 mol of S-100/mol of polymerized tubulin. Under certain conditions, S-100 proteins also cosediment with MTs prepared by coassembly of S-100 with MTs, probably in the form of an S-100-tubulin complex. Because S-100 binds to MTs under conditions where this protein fraction does not produce observable effects on the kinetics of assembly-disassembly, e.g., in the absence of Ca2+ at pH 6.7, we conclude that the S-100 binding to MTs does not affect the stability of MTs per se, but rather creates conditions for increased sensitivity of MTs to Ca2+.

S-100 protein localization in human adult dental pulp

The pulp of third molar teeth was examined by immunofluorescence and immunoperoxidase using a specific antibody to detect S-100 protein-labelled cells. There was a strong positive reaction in macrophages and in Schwann cells ensheathing axons. The other cells within the pulp were negative.

Approaches to study the role of S100 proteins in calcium-dependent cellular responses

Calcium is necessary for the optimal growth and cellular functions of most living organisms. For example, Ca is involved in the processes of muscle contraction, stimulus-secretion coupling, bone formation, blood clotting, cell proliferation and motility, and fertilization. Many regulatory actions of Ca are mediated through Ca-binding proteins. Calcium-modulated proteins are a subclass of Ca-binding proteins that are thought to be the major signal transducers of Ca acting as a cellular second messenger. Most Ca-modulated proteins are not enzymes but are effector proteins capable of transducing a Ca signal into a biological response by their ability to bind Ca reversibly and modulate the activity of other proteins in a Ca-dependent manner. This review focuses on a set of Ca-modulated proteins, the S100 proteins, and their possible roles in mediating Ca-dependent cellular events.

Large-scale, one-step purification of oxidized and reduced forms of bovine brain S100b protein by HPLC

A rapid and simple method, using a reverse-phase column in a HPLC system, has been developed to purify high yields of both oxidized and reduced S100b proteins from a bovine brain S100 protein mixture. The final proteins were characterized by amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and absorbance and fluorescence spectroscopy. Both S100b subtypes appeared highly purified and differed only by their oxidation state: all four cysteinyl sulfhydryl groups were free in reduced S100b protein whereas two of them gave disulfide bridges in oxidized S100b protein. The stability of the oxidation state of the two isolated subtypes suggests that the two forms were not in rapid equilibrium and probably coexisted in vivo.

Proteolysis of tubulin and microtubule-associated proteins 1 and 2 by calpain I and II. Difference in sensitivity of assembled and disassembled microtubules

Calpain I and II (EC 3.4.22.17) are Ca2+-activated neutral thiol-proteases. Isolated brain tubulin and microtubule-associated proteins were found to be good substrates for proteolytic degradation by brain calpain I and II. The assembly of microtubules was totally inhibited when the calpains were allowed to act on microtubule proteins initially, and a complete disassembly was found after addition of calpain I to assembled microtubules. The high-molecular weight microtubule-associated proteins were degraded within a few minutes following incubation with calpain as shown by SDS-polyacrylamide gel electrophoresis and electron microscopy. When calpain was added to pre-formed microtubules, either in the presence or in the absence of microtubule-associated proteins, the proteolysis was significantly reduced. When tubulin was pre-assembled by taxol, the formation of proteolytic fragments was decreased indicating that assembly alters the availability of tubulin sites for proteolytic cleavage by calpain. Digested tubulin spontaneously formed aberrant polymers. No considerable change of apparent net charge was seen, thus indicating that calpain cleaves off fragments containing neutral amino acid residues and/or that the fragments of tubulin remain associated as an entity with the same charge as native tubulin. The results suggest that the calpains act as irreversible microtubule regulators.

Immunocytochemistry of intracranial meningiomas

Fifty meningiomas of four major histological types have been examined by immunocytochemical methods applied to formalin fixed paraffin embedded material and using readily available commercial antisera. The expression of GFAP, S100, NSE, vimentin, cytokeratin, fibronectin and desmoplakin was investigated. The majority of tumours contained NSE (86%) and S100 (78%), and all irrespective of histological type, contained vimentin and fibronectin. The epithelial marker cytokeratin was found in 56% of cases, but showed only focal expression. The relevance of these findings to histogenesis and metabolism is discussed and it is suggested that intermediate filament typing provides valuable information on meningiomas structure and function. The possible role of NSE and S100 in meningeal neoplasm is discussed.

Effect of sodium butyrate on S-100 protein levels and the cAMP response

Sodium butyrate (NaB), when added to cell cultures, produces a variety of morphological and biochemical changes. We examined its effects, in nM concentrations, on the expression of two glioma cell-associated proteins, glial fibrillary acidic protein (GFAP) and S-100 protein in human glioma-derived cell line (RF), and of S-100 protein in the C6 rat glioma cell line. GFAP levels decreased by about 50% in the RF cell line, and S-100 protein levels decreased protein levels decreased by about 40% after treatment with 1 mM NaB for 48 h. In the C6 rat glioma cell line, isoproterenol with theophylline was found to increase S-100 levels by two-fold over basal levels. NaB was found to inhibit the induction of S-100 protein but exhibited no effect on the basal levels of the protein. Other short chain fatty acids, including sodium propionate and sodium isobutyrate, exhibited partial inhibitory activity. NaB, at an EC50 of 1 mM, was also found to inhibit both the beta-adrenergic and the forskolin-mediated increase in cAMP levels in these cells. This suggests that NaB may inhibit cells from expressing S-100 protein by attenuating cAMP levels.

Characteristics of the effect of S-100 proteins on the assembly-disassembly of brain microtubule proteins at alkaline pH in vitro

The ability of S-100 proteins to inhibit the assembly of brain microtubule proteins (MTPs) in the presence of microM levels of Ca2+ increases as a function of pH. This seems to be due to an increasingly larger inhibitory effect of S-100 on the nucleation and, probably, on the elongation of microtubules (MTs) as the pH raises. In the presence of microM Ca2+ levels, the ability of S-100 to disassemble MTs also increases linearly with the pH, suggesting that the larger inhibitory effect of S-100 on MTP assembly at alkaline than at acidic pH may depend on both a decrease in the assembly rate and an increase in the disassembly rate. Also, S-100 inhibits the assembly of phosphocellulose-purified tubulin to a larger and larger extent as the pH raises. S-100 brings about its effect on MT assembly-disassembly probably by sequestering soluble tubulin, though additional mechanisms cannot be excluded. The present data are briefly discussed in relation to the role attributed to changes in intracellular pH in the regulation of the state of assembly of cytoplasmic MTs.

Quantitative analysis of the interaction between S-100 proteins and brain tubulin

S-100 was shown to regulate the in vitro assembly of brain microtubule proteins (MTPs) in a Ca2+-mediated way by acting on both the nucleation and the elongation of microtubules (MTs). Here data will be shown suggesting that S-100 binds to tubulin. The binding is time-, temperature-, Ca2+-, and pH-dependent, and saturable with respect to S-100. At pH 6.75, the saturation curve is biphasic, displaying a high affinity component (dissociation constant, Kd1, approximately 0.1 microM) and a low affinity component (Kd2 approximately 3.8 microM). At pH 6.75, as the free Ca2+ concentration raises from 0 to 100 microM, the overall binding capacity increases from 0.065 to 0.66 mol S-100/mol tubulin dimer. This finding, together with the observation that the S-100 effect on MTP assembly is Ca2+-dependent at that pH, suggests that the S-100-induced inhibition of MTP assembly depends on S-100 binding to the low affinity sites on the tubulin molecule. The S-100 binding to tubulin is pH-dependent; as the pH raises from 6.75 to 8.3, both binding components are affected, the major changes consisting of an increase in the binding capacity and a decrease in the overall affinity. Moreover, as the pH raises, Ca2+ is no longer required for S-100 to bind to tubulin. S-100 also interacts with a component of whole MTPs (probably tubulin, on the basis of the above results). No S-100 binding to microtubule-associated proteins (MAPs) could be evidenced by the techniques employed in this study. On the contrary, some competition between S-100 and MAPs for binding sites or tubulin seems to occur.

Increase in S-100b protein content in thyroid carcinoma

S-100b protein was detectable in the soluble fraction of thyroid tissue. The concentration of S-100b protein in thyroid carcinoma tissue was three to five times higher than in normal thyroid tissue and thyroid adenoma. It is, however, not higher in the thyroid tissue of Graves' disease. The increase of S-100b protein concentration was not remarkable in carcinomatous tissue of the stomach and other digestive organs. The calmodulin content in the thyroid carcinoma tissue increased but the increment was low compared to that of S-100b protein. These data suggest that S-100b protein may play a significant role in cell maturation or differentiation.

Tissue distribution of rat S100 alpha and S100 beta and S100-binding proteins

To understand the physiological role of the calcium-binding proteins S100 alpha and S100 beta, it is necessary to determine the distribution of these proteins and detect their intracellular targets in various tissues. The distribution of immunoreactive S100 alpha and S100 beta in various rat tissues was examined by radioimmunoassay. All tissues examined contained detectable S100, but the S100 beta/S100 alpha ratio in each tissue differed. Brain, adipose, and testes contained 18- to 40-fold more S100 beta than S100 alpha; skin and liver contained approximately equivalent amounts and kidney, spleen, and heart contained 8- to 75-fold more S100 alpha than S100 beta. Analysis of S100-binding proteins by gel overlay showed that each tissue possessed its own complement of binding proteins. The S100 beta-binding profile was indistinguishable from the S100 alpha-binding profile and both of these profiles were distinct from the calmodulin-binding profile. These observations suggest that the differential distribution and quantity of the individual S100 polypeptides and their binding proteins in various tissues may be important factors in determining S100 function.

Bimane- and acrylodan-labeled S100 proteins. Role of cysteines-85 alpha and -84 beta in the conformation and calcium binding properties of S100 alpha alpha and S100b (beta beta) proteins

Bovine brain S100 alpha alpha, S100a (alpha beta), and S100b (beta beta) protein dimers were labeled with the sulfydryl-specific fluorescent probes monobromo(trimethylammonio)bimane (bimane) and 6-acryloyl-2-(dimethylamino)naphthalene (acrylodan) at cysteines-85 alpha and -84 beta. The conformation and fluorescence properties of the S100 proteins derived were studied by means of anion-exchange chromatography on a Mono Q column using a fast protein chromatography system and fluorescence intensity, maximum emission wavelength, and polarization measurements. Spectroscopic studies on the intrinsic absorption and fluorescence properties of S100 alpha alpha and S100b proteins chemically modified on cysteines-85 alpha and -84 beta with iodoacetamide completed this study. Several arguments suggest that the alkylated S100 proteins undergo conformational changes that are mainly characterized by the destabilization of the quaternary protein structure, which provokes a slow dimer-monomer equilibrium at high protein concentrations and induces total subunit dissociation at low ones. Calcium binding studies on bimane-S100 alpha alpha and -S100b proteins showed that alkylated proteins had a much higher calcium binding affinity than native protein and that the antagonistic effect of KCl on calcium binding was much less pronounced. These results confirmed our previous observations that the affinities of calcium binding sites II alpha and II beta in S100 proteins are highly dependent on protein conformation [Baudier, J., & Gerard, D. (1986) J. Biol. Chem. 261, 8204-8212].

Effects of S-100 proteins on assembly of brain microtubule proteins: correlation between kinetic and ultrastructural data

Microtubules formed in vitro in the presence of S-100 proteins and micromolar Ca2+ concentrations are fewer in number and longer than those formed in the presence of Ca2+ alone. Moreover, microtubules growing after addition of microtubule fragments to a microtubule protein solution in the presence of S-100 are shorter than those growing in its absence. These data lend support to previous results of kinetic studies indicating that S-100 interferes with both the nucleation and the elongation of microtubules in vitro.

S-100 proteins

S-100 is a group of closely related, small, acidic Ca2+-binding proteins (S-100a0, S-100a and S-100b, which are alpha alpha, alpha beta, and beta beta in composition, respectively). S-100 is structurally related to calmodulin and other Ca2+-binding proteins. S-100 is abundant in the brain and is contained in well defined cell types of both neuroectodermal and non-neuroectodermal origin, as well as in their neoplastic counterparts. In the mammalian brain, S-100a and S-100b are confined to glial cells, while S-100a0 is neuronal in localization. Single S-100 isoforms bind Ca2+ with nearly the same affinity. K+ antagonizes the binding of Ca2+ to high affinity sites on S-100. S-100 binds Zn2+ with high affinity. S-100 is found in a soluble and a membrane-bound form and has the ability to interact with artificial and natural membranes. S-100 has no enzymatic activity. S-100 has been involved in several activities including memory processes, regulation of diffusion of monovalent cations across membranes, modulation of the physical state of membranes, regulation of the phosphorylation of several proteins, control of the assembly-disassembly of microtubules. Some of these effects are strictly Ca2+-dependent, while other are not. S-100 is being secreted or released to the extracellular space. In some cases, this event is hormonally regulated. Several S-100 binding proteins are being described.

Identity between cytoplasmic and membrane-bound S-100 proteins purified from bovine and rat brain

Cytoplasmic and membrane-bound S-100 proteins were purified to homogeneity from bovine and rat brain. Cytoplasmic and membrane-bound S-100 from single species are identical by immunological, electrophoretic, spectrophotometric, and functional criteria. Cytoplasmic and membrane-bound S-100 from bovine brain consists of nearly equal amounts of S-100a and S-100b, whereas cytoplasmic and membrane-bound S-100 from rat brain consists mostly of S-100b. The functional role of membrane-bound S-100 remains to be elucidated.

Evidence that S100 proteins regulate microtubule assembly and stability in rat brain extracts

Microtubule re-assembly in rat brain extracts was inhibited by antibodies to S100 proteins. Anti-S100 antibodies caused an increase in the cold-stability of microtubules and this effect was abolished by the presence of short lengths of microtubules formed under control conditions. Anti-S100 antibodies had no effect on the stimulation of assembly or the increase in microtubule stability caused by low zinc concentrations. Addition of exogenous S100a and S100b to brain extracts had different effects on assembly; S100a caused an inhibition of assembly while S100b stimulated the early phase of assembly. The data suggest that endogenous S100b is involved in the regulation of microtubule assembly in brain extracts.

S-100 proteins and microtubules: analysis of the effects of rat brain S-100 (S-100b) and ox brain S-100a0, S-100a and S-100b on microtubule assembly-disassembly

Rat brain S-100 (S-100b) and ox brain S-100a0, S-100a and S-100b have been tested for their ability to control the assembly and disassembly of brain microtubule proteins in the presence of either Ca2+ or Zn2+, in vitro. In the presence of Ca2+, single S-100 isoforms have similar, if not identical, effects, i.e. they inhibit assembly and promote disassembly. In the presence of Zn2+ from 0.1 to 1 mM (free concentration), rat S-100 and ox S-100a and S-100b inhibit assembly, while S-100a0 is without effect. These data are briefly discussed in relation to the cellular localization of single S-100 isoforms in the brain.

S-100 protein-induced changes in the physical state of synaptosomal particulate fractions as monitored by spin labels

This report documents changes in the physical state of synaptosomal particulate fractions (SYN) upon binding of S-100 protein, as monitored by spin labels. Studies were conducted on SYN labeled with either 5-doxylstearic acid or 16-doxylstearic acid, which probe the polar region and the hydrophobic core of the lipid bilayer, respectively. S-100 perturbs to some extent both the polar surface and the hydrophobic core of SYN in a time- and temperature-dependent manner. Ca2+ is essential for S-100 to perturb the membranes. K+ almost completely inhibits the S-100 perturbing effect if present in the incubation medium, but fails to reverse the S-100-induced changes if added after S-100 has interacted with SYN. At room temperature and below, the overall S-100 effect registered after about 30 min of association of the protein with SYN is an increase in the fluidity of both the surface and the interior of the membranes. Spectra registered at intervals at room temperature indicate that the S-100 perturbing effect on the membrane surface is practically monophasic, consisting of an increase in fluidity, while that on the membrane interior is multiphasic, consisting of a decrease in fluidity during the first 10 min of association, followed by an increase in fluidity during the subsequent 20 min and a return to starting values during the second 30 min of association. Around 37 degrees C, on the contrary, a decrease in fluidity is registered in both regions. The data suggest that S-100 induces a spatial rearrangement of membrane components (proteins) involved in the specific binding and/or partially penetrates into the lipid bilayer.

Differentiation markers (S-100, GFAP, NSE and D2) in fetal rat brain cells during malignant transformation in cell culture

Malignant cell lines obtained by ethylnitrosourea (EtNU)-induced transformation of fetal rat brain cells in culture express protein markers of different types of neural cells. These are the nervous system-characteristic S-100 protein; glial fibrillary acidic protein (GFAP); neuron-specific-enolase (NSE), and the D2-cell adhesion molecule. S-100 protein was absent in fetal brain cells in culture, but gradually appeared in the later stages of malignant transformation and further increased at onset of rapid growth of atypical cells (stage IV). GFAP and D2 were weakly expressed in primary fetal brain cells and did not change throughout malignant transformation. NSE was present in both normal and carcinogen-treated fetal brain cells, and increased at later stages of malignant transformation. From stage III (40-100 days) some cultures were strongly positive and some negative, and the same was seen in the resulting tumorigenic cells about 100 days later. In conclusion the stepwise process of malignant transformation of brain cells in culture ended with a stable phenotype of cells capable of expressing varying types of differentiation markers. The presence of these markers in rat brain cells undergoing malignant transformation may indicate that EtNU given at 18th days of gestation is acting on multipotent neuroectodermal cells.

The binding of Ruthenium red to tubulin

The inhibition of microtubule assembly by Ruthenium red (Deinum, J., Wallin, M., Kanje, M. and Lagercrantz, C. (1981) Biochim. Biophys. Acta 675, 209-213) could be counteracted by either taxol or dimethyl sulfoxide. Ruthenium red remained bound to the assembled microtubules. Microtubules assembled in the presence of Ruthenium red and taxol showed the typical taxol-dependent stability. The dimethyl sulfoxide-induced microtubules showed normal assembly characteristics, e.g., were GTP dependent, could be disassembled by cold, colchicine and Ca2+ and had no alterations in ultrastructure. The absolute disassembly induced by Ca2+ in the presence of dimethyl sulfoxide and Ruthenium red was dependent on the microtubule protein concentration, but independent in the absence of Ruthenium red. Ruthenium red was strongly bound to purified tubulin also in the presence of 8% (v/v) dimethyl sulfoxide. The dimethyl sulfoxide-induced assembly of purified tubulin in the presence of Ruthenium red was slightly stimulated, although the critical protein concentration was the same. It was found by resonance Raman spectroscopy with a flow technique that Ruthenium red did not bind to a specific calcium binding site on tubulin, although binding to a GTP binding site cannot be excluded. The wavenumbers of the lines in the region 375-500 cm-1 differ from those found for Ruthenium red bound to typical calcium-binding proteins such as calmodulin. Although Ruthenium red binds to serum albumin as well, the spectrum with albumin resembled that of the free dye.

Rat brain S100b protein: purification, characterization, and ion binding properties. A comparison with bovine S100b protein

We purified to homogeneity rat brain S100b protein, which constitutes about 90% of the soluble S100 protein fraction. Purified rat S100b protein comigrates with bovine S100b protein in nondenaturant system electrophoresis but differs in its amino acid composition and in its electrophoretic mobility in urea-sodium dodecyl sulfate-polyacrylamide gel with bovine S100b protein. The properties of the Ca2+ and Zn2+ binding sites on rat S100b protein were investigated by flow dialysis and by fluorometric titration, and the conformation of rat S100b in its metal-free form as well as in the presence of Ca2+ or Zn2+ was studied. The results were compared with those obtained for the bovine S100b protein. In the absence of KCl, rat brain S100b protein is characterized by two high-affinity Ca2+ binding sites with a KD of 2 X 10(-5) M and four lower affinity sites with KD about 10(-4) M. The calcium binding properties of rat S100b protein differ from bovine S100b only by the number of low-affinity calcium binding sites whereas similar Ca2+-induced conformational changes were observed for both proteins. In the presence of 120 mM KCl rat brain S100b protein bound two Zn2+-ions/mol of protein with a KD of 10(-7) M and four other with lower affinity (KD approximately equal to 10(-6) M). The occupancy of the two high-affinity Zn2+ binding sites was responsible for most of the Zn2+-induced conformational changes in the rat S100b protein. No increase in the tyrosine fluorescence quantum yield after Zn2+ binding to rat S100b was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of action of S-100 protein(s) on brain microtubule protein assembly

The inhibitory effect of S-100 on microtubule protein assembly is inversely related to the microtubule protein concentration and/or the temperature of assembly. Moreover, the S-100-induced decrease in the rate and extent of assembly is positively correlated with the length of the lag of assembly. When microtubule fragments are added to the microtubule protein solution, the S-100 effect is reduced but not abolished. These data suggest that S-100 interferes with both the nucleation and the elongation of microtubules. Since S-100 also inhibits the assembly of purified tubulin, S-100 is suggested to affect the microtubule assembly by interacting with and sequestering tubulin.

Hormonal regulation of adipose S-100 protein release

The release of S-100 protein from epididymal fat pads was enhanced by epinephrine in vitro, and about 50% of S-100 protein in the tissue was released into the medium after 2-h incubation at 37 degrees C with 10 microM epinephrine. Similar results were obtained with the incubation of isolated adipocytes. The S-100 protein release was also enhanced by isoproterenol, norepinephrine, ACTH, and dibutyryl cyclic AMP, which all increase the lipolysis by increasing cyclic AMP levels in the tissue. Propranolol, a beta-adrenergic blocker, could block the increase of S-100 protein release by catecholamines, indicating that the release was mediated by the beta-adrenergic effect of catecholamines. However propranolol had no suppressive effect on the enhancement of S-100 protein release by ACTH or dibutyryl cyclic AMP. Insulin had an inhibitory effect on the epinephrine-enhanced S-100 protein release. Epinephrine or ACTH could not stimulate the S-100 protein release in the absence of Ca2+, whereas the epinephrine-enhanced glycerol release was not affected under the same conditions. The increase in S-100 protein release was induced by only a pretreatment of the tissue with epinephrine. However, the lipolysis in the tissue was not enhanced by the pretreatment alone. These results indicate that the release of S-100 protein from adipocytes is regulated by the hormones that have been known to control the lipolysis with a manner slightly different from that of lipolysis.

S100a0 (alpha alpha) protein is present in neurons of the central and peripheral nervous system

The cellular distribution of S100 subunits in human brain and peripheral nerves was studied by means of an immunohistochemical technique using antibodies specific to the alpha subunit or the beta subunit of S100 protein. The results indicate that the distribution of the alpha subunit and the beta subunit is different among cell types in the nervous tissue, and that neurons in the brain and peripheral nerves contain only the alpha subunit, or S100a0 protein. The subunit distribution also appears to be different at an intracellular level, where the immunoreaction products for the alpha subunit show granular arrangement whereas those for the beta subunit are found diffusely in the cytoplasm.

Purification, characterization and ion binding properties of human brain S100b protein

Human brain S100b (beta beta) protein was purified using zinc-dependent affinity chromatography on phenyl-Sepharose. The calcium- and zinc-binding properties of the protein were studied by flow dialysis technique and the protein conformation both in the metal-free form and in the presence of Ca2+ or Zn2+ was investigated with ultraviolet spectroscopy, sulfhydryl reactivity and interaction with a hydrophobic fluorescence probe 6-(p-toluidino)naphthalene-2-sulfonic acid (TNS). Flow dialysis measurements of Ca2+ binding to human brain S100b (beta beta) protein revealed six Ca2+-binding sites which we assumed to represent three for each beta monomer, characterized by the macroscopic association constants K1 = 0.44 X 10(5) M-1; K2 = 0.1 X 10(5) M-1 and K3 = 0.08 X 10(5) M-1. In the presence of 120 mM KCl, the affinity of the protein for calcium is drastically reduced. Zinc-binding studies on human S100b protein showed that the protein bound two zinc ions per beta monomer, with macroscopic constants K1 = 4.47 X 10(7) M-1 and K2 = 0.1 X 10(7) M-1. Most of the Zn2+-induced conformational changes occurred after the binding of two zinc ions per mole of S100b protein. These results differ significantly from those for bovine protein and cast doubt on the conservation of the S100 structure during evolution. When calcium binding was studied in the presence of zinc, we noted an increase in the affinity of the protein for calcium, K1 = 4.4 X 10(5) M-1; K2 = 0.57 X 10(5) M-1; K3 = 0.023 X 10(5) M-1. These results indicated that the Ca2+- and Zn2+-binding sites on S100b protein are different and suggest that Zn2+ may regulate Ca2+ binding by increasing the affinity of the protein for calcium.

Chlorpromazine inhibits the calcium-mediated effects of S-100 protein(s) on assembled brain microtubule proteins, but not those on microtubule protein assembly

We have examined the S-100-chlorpromazine interplay at the level of brain microtubule proteins in vitro. The results indicate that in the presence of 0.12 M KCl and 10 microM free Ca2+ the inhibitory effect of S-100 on microtubule assembly is additive to that of chlorpromazine, but S-100 fails to potentiate the disassembling effect of 0.1 mM Ca2+ if added to assembled microtubule proteins after chlorpromazine and Ca2+, probably because of inhibition of S-100 by the phenothiazine. Chlorpromazine does not compete with S-100 for binding to purified tubulin.

S-100 modulates Ca2+-independent phosphorylation of an endogenous protein (Mr = 19K) in brain

A new brain enzyme (tentatively named protein kinase X), which catalyzes protamine phosphorylation modulated by S-100, was reported recently. An endogenous substrate protein (Mr = 19K) for protein kinase X was isolated from brain by means of S-100-Sepharose 4B affinity chromatography. S-100, but not calmodulin, promoted phosphorylation of the 19K Mr protein in a Ca2+-independent manner, and this reaction was inhibited by gossypol. The substrate protein, localized in the particulate fraction, was present at a much higher level in brain from adult than neonatal rats (2-day-old), a developmental change similar to that seen for protein kinase X. It is suggested that a protein phosphorylation system modulated by S-100 exists in brain, and that this process may be involved in regulation of certain neural functions.

Binding of chlorpromazine to S-100 protein

Chlorpromazine (CPZ) induces in S-100 conformational changes resulting in the exposure of titratable SH groups of the protein to the solvent. This effect is even greater in the presence of Mg2+ +/- Ca2+. S-100 possesses binding sites for CPZ. The binding of CPZ to 3 microM S-100 is half-saturated by 0.18 microM CPZ in the presence of Mg2+ plus Ca2+ and by 0.24 microM CPZ in the presence of Mg2+ plus EGTA. The extent of the binding is greater in the presence of Ca2+ than in the presence of EGTA, especially at low CPZ concentrations.