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E Carafoli

Publications and source records attributed to E Carafoli.

At least 91 records · Page 5Linked to original sources
PubMed1994

Differentiation-specific isoform mRNA expression of the calmodulin-dependent plasma membrane Ca(2+)-ATPase.

The functional significance of the isoform diversity of the calmodulin-dependent plasma membrane Ca(2+)-ATPase (PMCA) is largely unknown. To determine whether the mRNA synthesis of different isoforms of the enzyme is regulated in a differentiation-specific manner, we investigated the expression of isoform-specific mRNAs in muscle and neuronal cells during differentiation by reverse transcription PCR. In the rat, the ubiquitous PMCA splicing variants 1b and 4b formed the typical PMCA isoform pattern of L6 myoblasts, the heart-derived cell line H9c2(2-1), two different fibroblast cell lines (FR and NRK-49F), smooth muscle, and endothelial cells. In addition to these two enzymes, novel expression of the splicing variants 1c, 1d, and 4a was induced during myogenic differentiation of L6 and H9c2(2-1) cells. A similar isoform subtype switch could be detected during differentiation of the neuronal PC-12 cells induced by nerve growth factor (NGF). The isoform-specific mRNAs 1c, 1d, and 4a were not expressed in cells other than myocytes and neurons, and therefore may be specific for excitable cells. The mRNA for isoform 1d was heart- and skeletal muscle-specific. To determine whether expression of a differentiation-specific PMCA mRNA pattern is under control of a myogenic determination factor, myogenin was constitutively expressed in rat fibroblasts. These cells converted to multinucleated myotubes, which displayed the PMCA isoform-specific mRNAs 1c, 1d, and 4a, typical of differentiated muscle cells. We conclude that: 1) the distribution of the various PMCA isoform-specific mRNAs and their splicing variants is cell type- and development-specific; 2) expression of the myogenic determination factor myogenin is sufficient to direct alternative splicing generating muscle-specific PMCA mRNA species; and 3) PMCA isoforms and/or splicing variants may play a role in determining functions of terminally differentiated muscle and neuronal cells and possibly during the differentiation process itself.

Alternative Splicing↗
PubMed1994

The plasma membrane calcium pump: functional domains, regulation of the activity, and tissue specificity of isoform expression.

The plasma membrane Ca2+ pump is responsible for the fine regulation of the intracellular Ca2+ level and is thus involved in the control of several cellular processes. The activity of the pump is regulated by a multiplicity of mechanisms, among which are calmodulin, acidic phospholipids, kinase-mediated phosphorylation, or an oligomerization process. The C-terminal part of the molecule interacts with the region of the pump close to the active site, leading to the decrease of the activity in the resting state. Four genes coding for different isoforms of the plasma membrane Ca2+ ATPase are known in humans. Isoform 1 and 4 represent housekeeping isoforms, whereas isoforms 2 and 3 are only present in specialized tissues. The variability of the protein is further increased by alternative RNA splicing at two sites (A, C). Alternative splicing occurs within (splice site C) or near (splice site A) regions coding for regulatory domains of the protein. In all isoforms a corresponding splice form exists at both splice sites. These common splice forms are present in all tissues, whereas isoform unique splice forms are normally only present in specialized tissues. In neuronal tissues all isoforms and almost the complete set of splice forms are found. The transcripts of the different isoforms are distributed in a region-specific manner in neuronal tissues.

Animals↗
PubMed1994

Protein identification in DNA databases by peptide mass fingerprinting.

Proteins can be identified using a set of peptide fragment weights produced by a specific digestion to search a protein database in which sequences have been replaced by fragment weights calculated for various cleavage methods. We present a method using multidimensional searches that greatly increases the confidence level for identification, allowing DNA sequence databases to be examined. This method provides a link between 2-dimensional gel electrophoresis protein databases and genome sequencing projects. Moreover, the increased confidence level allows unknown proteins to be matched to expressed sequence tags, potentially eliminating the need to obtain sequence information for cloning. Database searching from a mass profile is offered as a free service by an automatic server at the ETH, Zürich. For information, send an electronic message to the address cbrg/inf.ethz.ch with the line: help mass search, or help all.

Animals↗
PubMed1994

The plasma membrane calcium pump is the preferred calpain substrate within the erythrocyte.

The activation of calpain in normal human erythrocytes incubated in the presence of Ca2+ and the Ca2+ ionophore A23187 led to the decline of the Ca(2+)-dependent ATPase activity of the cells. Preloading of the erythrocyte with an anticalpain antibody prevented the decline. The pump was also inactivated by applied to isolated erythrocyte plasma membranes. The decline of the pump activity corresponded to the degradation of the pump protein and was inversely correlated to the amount of the natural inhibitor of calpain, calpastatin, present in the cells. In erythrocytes containing only 50% of the normal level the degradation started at a concentration of Ca2+ significantly lower than in normal cells. A comparison of the concentrations of Ca2+ required for the degradation of a number of erythrocyte membrane proteins showed that the Ca2+ pump and band 3 were the most sensitive. All other membrane proteins tested were attacked at higher levels of intracellular Ca2+. Thus, the degradation of the Ca2+ pump protein may be a simple and sensitive means to monitor calpain activation in vivo. Furthermore, the results have shown that the calpastatin level correlated directly with the amount of activable calpain and with the concentration of Ca2+ required to trigger the activation process.

Calcium↗
PubMed1994

Facilitated nuclear transport of calmodulin in tissue culture cells.

Calmodulin (CaM) potentiates Ca(2+)-dependent signaling pathways in both the cytoplasm and nucleus. We have investigated the mechanism of CaM nuclear transport using tissue culture cell microinjection and a permeabilized cell import assay. The inhibition of CaM import by the translocation inhibitor wheat germ agglutinin (WGA) and by chilling, indicates that CaM import is facilitated, but because ATP depletion does not affect CaM import, the mechanism does not appear to be active. Chilling and WGA arrest persist in ATP-depleted cells, indicating that CaM is not retained in the cytoplasm by an ATP-dependent mechanism. In permeabilized cells, both Ca(2+)-CaM and Ca(2+)-free CaM are sensitive to extract-dependent WGA and chilling import inhibition. Titration experiments in microinjected and permeabilized cells indicate that a saturable cytosolic factor(s) mediates chilling and WGA arrest.

Adenosine Triphosphate↗
PubMed1994

Localization of two genes encoding plasma membrane Ca2+ ATPases isoforms 2 (ATP2B2) and 3 (ATP2B3) to human chromosomes 3p26-->p25 and Xq28, respectively.

The plasma membrane Ca2+ ATPases (PMCA) represent a highly conserved, widely dispersed, multigene family in eukaryotes consisting of at least four functional genes. The genes for PMCA isoforms 1 and 4 (ATP2B1 and ATP2B4) have been previously localized to human chromosomes 12q21-->q23 and 1q25-->q32, respectively. Based upon results of fluorescence in situ hybridization (FISH), analysis of somatic cell hybrids, and genetic linkage analyses, we now report localization of ATP2B3 (PMCA isoform 3) to human chromosome Xq28, and confirm the recent localization of ATP2B2 (PMCA isoform 2) to chromosome 3p26-->p25. In contrast to ATP2B1 and ATP2B4, recent studies have suggested tissue specific regulation of expression of both ATP2B2 and ATP2B3 particularly in the nervous system. The genes for several neurological and neuromuscular diseases have been assigned to the distal portion of Xq, and ATP2B3 is a candidate gene for these diseases.

Calcium-Transporting ATPases↗
PubMed1994

The signaling function of calcium and its regulation.

CALCIUM COMPLEXATION WITH SOLUBLE PROTEINS: The signaling function of calcium is controlled by reversible complexation to specific proteins. Most of the soluble proteins belong to the exchange factor (EF)-hand family and act as decoders of the calcium information. They do so by changing conformation twice, once upon complexing calcium and later, upon interacting with target enzymes. The most important among the EF-hand proteins is calmodulin. MEMBRANE-INTRINSIC CALCIUM-CONTROLLING PROTEINS: Other calcium-controlling proteins are membrane-intrinsic (plasma membranes and organelles), and interact with calcium with high affinity (pumps) or with low affinity (sodium-calcium exchange, calcium channels, electrophoretic uptake by mitochondria). The fine and rapid tuning of cellular calcium is performed essentially by pumps, although in excitable tissues, plasma membrane sodium-calcium exchange is also important. Long-term, low-affinity calcium regulation, particularly in the presence of pathological increases in calcium entry, is probably performed by mitochondrial uptake/release systems.

Animals↗
PubMed1994

Biogenesis: plasma membrane calcium ATPase: 15 years of work on the purified enzyme.

The plasma membrane calcium pump is the system that ejects Ca2+ out of eukaryotic cells: this is documented in all animal and plant cells, although knowledge on the latter is only now beginning to be established. Information on lower eukaryotic cells, e.g., yeast, is still scarce, but it also is beginning to develop. The pump shares the catalytic properties of ion-motive ATPases of the P-type family, but has distinctive regulation properties: it is modulated by calmodulin, acidic phospholipids, a number of protein kinases, possibly by the interaction of calcium with its COOH-terminal region, and by aggregation (dimerization) through the calmodulin binding domain. The latter acts as an endogenous inhibitor of pump activity, much as phospholamban does for the sarcoplasmic reticulum pump. The analogy of the regulation mechanisms of the two pumps is heightened by the finding that phosphorylation of the calmodulin binding domain by protein kinase C removes its autoinhibiting function, as other kinases do in the case of phospholamban. The pump is the product of a family of four genes located on different human chromosomes. The isoform diversity is dramatically enhanced by alternative splicing of the transcripts, occurring at "hot spot" A (NH2-terminal) and C (COOH-terminal). At present more than 20 different transcripts with striking tissue and developmental specificity have been detected.

Amino Acid Sequence↗
PubMed1993

Quantitative analysis of alternative splicing options of human plasma membrane calcium pump genes.

The alternative splicing options and the quantitative tissue distribution of the transcripts of the four currently known human plasma membrane calcium pump (PMCA) genes have been analyzed in seven tissues (cerebral cortex, skeletal and heart muscle, stomach, liver, lung, and kidney) by quantitative polymerase chain reaction on reverse transcribed mRNA with glyceraldehyde-3-phosphate dehydrogenase as the internal standard. The mRNAs of genes 1 and 4 were found to be present in similar amounts in all tissues, whereas the transcripts of genes 2 and 3 were expressed in a tissue-specific manner, i.e. their amounts were highest in fetal skeletal muscle and brain. Alternative splicing was found to occur in the PMCA transcripts at two major regulatory sites (sites A and C), adjacent to the amino-terminal phospholipid-responsive region and within the carboxyl-terminal calmodulin binding domain, respectively. Novel splicing variants not described previously for human genes were detected for hPMCA3 and 4 at site A and for hPMCA1, 2, and 3 at site C. For all genes a common splice variant was found at both splice sites. The common splice variant at site A was characterized by the inclusion of a small exon (hPMCA1, 39 base pairs (bp); hPMCA2, 42 bp; hPMCA3, 42 bp; hPMCA4, 36 bp). In the common splice variant at site C, an exon (hPMCA1, 154 bp; hPMCA2, 227 bp; hPMCA3, 154 bp; hPMCA4, 178 bp) was excluded in the mRNA. All genes normally express these main splice variants in all tissues in which the corresponding isoform is present. The splicing complexity at site C was found to be augmented in the transcripts of PMCA2 and PMCA3 through the use of additional exons, and in PMCA1 and 3 through the use of additional internal splice sites in the single alternatively spliced 154-base pair exon.

Aged↗
PubMed1993

Structure of the gene encoding the human plasma membrane calcium pump isoform 1.

The complete structure of the gene for the human plasma membrane calcium ATPase isoform 1 (hPMCA1) has been elucidated. The protein is encoded by 21 exons present on overlapping clones covering more than 100 kilobases (kb) of DNA. An intron of over 35 kb separates the 5'-untranslated exon 1 from the exon containing the translational start codon. The entire putative promoter and 5'-flanking region is embedded in a CpG island and is characterized by the presence of numerous Sp1 factor-binding sequences and by the absence of a TATA box. In accordance with the ubiquitous tissue distribution of its mRNA these results suggest that the hPMCA1 gene is of the housekeeping type. No alternative splicing comparable to that identified in PMCA2 RNAs at site "A" and in PMCA3 RNAs close to site "C" seems to occur in hPMCA1 transcripts; however, a region in intron 6 shows significant resemblance to the site "A" alternatively spliced exons in PMCA2 and may represent a pseudoexon or a functional exon not yet detected in any PMCA1 mRNA. At six positions, intron interruptions in the hPMCA1 gene correlate with the boundaries of putative transmembrane domains in the protein, whereas most of the remaining intron positions do not show an obvious correlation with the proposed pump domain structure. The limited conservation of intron positions in different P-type pump genes indicates their early separation from a common ancestor.

Amino Acid Sequence↗
PubMed1993

Protein identification by mass profile fingerprinting.

We have developed an algorithm for identifying proteins at the sub-microgram level without sequence determination by chemical degradation. The protein, usually isolated by one- or two-dimensional gel electrophoresis, is digested by enzymatic or chemical means and the masses of the resulting peptides are determined by mass spectrometry. The resulting mass profile, i.e., the list of the molecular masses of peptides produced by the digestion, serves as a fingerprint which uniquely defines a particular protein. This fingerprint may be used to search the database of known sequences to find proteins with a similar profile. If the protein is not yet sequenced the profile can serve as a unique marker. This provides a rapid and sensitive link between genomic sequences and 2D gel electrophoresis mapping of cellular proteins.

Algorithms↗
PubMed1993

Calmodulin can modulate protein phosphorylation in rat liver cells nuclei.

This report describes the immunological identification of a 60-kDa calmodulin-binding protein, previously detected in the nuclei of rat liver cells (Bachs, O., Lanini, L., Serratosa, J., Coll, M.J., Bastos, R., Aligué, R., Rius, E., and Carafoli, E. (1990) J. Biol. Chem. 265, 18595-18600), as the calmodulin-dependent protein phosphatase calcineurin. Calcineurin could be extracted from the nuclei by incubation with DNase and RNase, indicating that it is associated with nuclear structures sensitive to the action of nucleases (chromatin or/and ribonucleoproteins). The presence of calcineurin in the nuclei of rat liver cells indicates that calmodulin may modulate the phosphorylation level of nuclear proteins by promoting their dephosphorylation. This report also shows that calmodulin inhibits the activity of casein kinase-2 in the nuclear fractions obtained by nuclease extraction. Phosphorylation experiments indicate that casein kinase-2 phosphorylates three major substrates of 100, 42-44, and 37 kDa as well as other minor proteins in the nuclease extracts. Calmodulin reduces the phosphorylation level of the two latter major proteins and of a minor band of 50 kDa. Thus, nuclear calmodulin in rat liver cells could regulate phosphorylation of nuclear proteins by at least two mechanisms: 1) activation of calcineurin and 2) inhibition of casein kinase-2.

Animals↗
PubMed1993

Synthetic peptides corresponding to the calmodulin-binding domains of skeletal muscle myosin light chain kinase and human erythrocyte Ca2+ pump interact with and permeabilize liposomes and cell membranes.

Synthetic calmodulin-binding (CaM-binding) peptides (CBPs) representing CaM-binding domains of Ca2+/CaM-dependent enzymes have been reported to interfere with the activity of the melanocyte-stimulating hormone (MSH) receptor function in melanoma cells [Gerst, J. E., & Salomon, Y. (1988) J. Biol. Chem. 263, 7073-7078]. We postulated that membrane lipids may play an important role in the mode of action of CBPs on cells. We therefore tested the ability of CBPs to interact with membrane bilayers. Using artificial phospholipid vesicles, or M2R melanoma cells and cell membranes derived therefrom, as models, we report here that synthetic peptides representing the CaM-binding domains of skeletal muscle myosin light chain kinase (M5) and the human erythrocyte calcium pump (C28W), as well as other CBPs, interact with lipid bilayers and cell membranes. Significant interactions of CBPs with the lipid bilayer were detected in both model systems. M5 and C28W were found to partition into the lipid bilayer of melanoma cell membranes and soybean lecithin vesicles, and surface partition constants obtained (for the liposome model) were in the range 10(3)-10(4) M-1. In addition, C28W and its N-modified NBD derivative were found to inhibit [125I]iodo-[Nle4,D-Phe7]alpha MSH binding to cultured M2R melanoma cells. These and other CBPs were also found to induce the release of cations and calcein from liposomes, suggesting that the interaction of CBPs with the lipid bilayer increases membrane permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

The calmodulin binding domain of nitric oxide synthase and adenylyl cyclase.

Peptides corresponding to regions of the calmodulin-activated NO-synthase and of the calmodulin dependent adenylyl cyclase, which could represent the calmodulin binding domains of the two proteins, have been synthesized and tested for calmodulin binding. The chosen peptides were those in the sequence of the two proteins which most closely corresponded to the accepted general properties of the calmodulin binding domains, i.e., a hydrophobic sequence containing basic amino acids. In the case of the NO-synthase, the putative high-affinity calmodulin binding domain was identified by urea gel electrophoresis and fluorescence spectroscopy with dansylcalmodulin as peptide NO-30 (amino acids 725-754). The highest affinity calmodulin binding site of the calmodulin-dependent adenylyl cyclase was assigned to peptide AC-28 (amino acids 495-522) by titration with dansylcalmodulin and by the ability to inhibit the calmodulin-stimulated activity of purified calmodulin-stimulated adenylyl cyclase. The sequence 495-522 is located in the unit protruding into the cytosol from the sixth putative transmembrane domain of the molecule. It has the typical hydrophobic/basic composition of canonical calmodulin binding domains, and also contains, like most calmodulin binding domains, an aromatic amino acid in its N-terminal portion. It also contains two Cys residues in the central portion, which is an unusual feature of the calmodulin binding domain of this enzyme.

Adenylyl Cyclases↗
PubMed1993

The C-terminal domain of the plasma membrane Ca2+ pump contains three high affinity Ca2+ binding sites.

The C-terminal portion of the plasma membrane Ca(2+)-ATPase contains different regulatory domains. A recombinant C-terminal fragment of the human plasma membrane Ca(2+)-ATPase 1b isoform (E1079-P1180) was used to study the role of two acidic amino acid stretches located on either side of the calmodulin binding domain, corresponding to synthetic peptides A18 (Vorherr, T., James, P., Krebs, J., Enyedi, A., McCormick, D. J., Penniston, J. T., and Carafoli, E. (1990) Biochemistry 29, 355-365) and B28 (James, P., Pruschy, M., Vorherr, T., Penniston, J. T., and Carafoli, E. (1989) Biochemistry 28, 4253-4258), respectively. The molecular mass of the recombinant C-terminal fragment, as determined by electrospray ionization mass spectrometry, was higher by 39 mass units than the calculated value (12,055 Da). This difference was the result of an EGTA-insensitive Ca2+ ion, which was located by chymotryptic proteolysis in a fragment corresponding to the last 37 amino acids of the expressed protein. Fluorescence experiments on the dansylated recombinant C-terminal fragment titrated with increasing amounts of free Ca2+ revealed two additional Ca2+ binding sites with affinities corresponding to KD values of about 30 and 300 nM, respectively. Stains All spectra of different synthetic peptides, corresponding to subdomains of the expressed protein, indicated that the site with the KD of 30 nM was probably located in the acidic sequence on the N-terminal side of the calmodulin binding domain (peptide A18); the site with the 300 nM KD was apparently located on the C-terminal side of the calmodulin binding domain (peptide B28) or, alternatively, formed by the cooperation of distant residues of the domain.

Amino Acid Sequence↗
PubMed1993

Total synthesis and functional properties of the membrane-intrinsic protein phospholamban.

The membrane-intrinsic protein phospholamban (PLN), the regulatory protein of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, was chemically synthesized. The synthesis was accomplished by double couplings and efficient capping procedures, thus eliminating hydrophobic failure sequences. The crude peptide was purified by high-performance liquid chromatographic ion exchange and gel permeation chromatography in chloroform-methanol mixtures. Ion spray mass spectroscopy showed that the product had the correct molecular mass. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis runs produced the typical monomer-pentamer structural pattern. A predominantly helical CD spectrum was obtained in 0.075% C12E8 (67.9% helix, 1.8% beta, 12.2% turn, 18.1% random coil). Synthetic PLN was phosphorylated in detergent solutions by protein kinase A with a stoichiometry close to 1:1 (Pi to PLN monomer). Reconstitution of the isolated skeletal muscle SR Ca2+ ATPase in phosphatidylcholine membranes in the presence of PLN using the freezing and thawing technique yielded a preparation with lower Ca(2+)-dependent ATPase activity. The inhibition was mainly due to a decrease in the affinity (Km(Ca)) of the ATPase for Ca2+ and was partially reversed by PLN phosphorylation with protein kinase A. By contrast, addition of PLN to diluted intact SR vesicles uncoupled the Ca(2+)-transport reaction, suggesting an ionophoric effect of PLN. Because this effect was observed at very high PLN-to-SR vesicle ratios and was not influenced by PLN phosphorylation, its biological function is doubtful.

Amino Acid Sequence↗
PubMed1992

Fluorescence energy transfer analysis of calmodulin-peptide complexes.

The interactions between calmodulin and the tryptophan residues of synthetic peptides corresponding to the calmodulin binding domains of skeletal muscle myosin light-chain kinase and the plasma membrane calcium pump were examined. The single tryptophan residue contained in each peptide became relatively immobilized and inaccessible to iodide ion upon binding to calmodulin, indicating that the indole side chain was inserted into a hydrophobic cleft in the surface of calmodulin. Fluorescence energy transfer from peptidyl tryptophan residues to an AEDANS moiety attached to cysteine-26 of spinach calmodulin was measured. Included in these analyses was a tryptophan-containing peptide analog of the calmodulin binding domain of neuromodulin. These data indicated that the indole ring of each peptide inserted 32-35 A away from cysteine-26 and may therefore interact with the carboxyl-terminal lobe of CaM in its "bent" conformation [Persechini & Kretsinger (1988a) J. Cardiovasc. Pharmacol. 12 (Suppl 5), S1-S12; Ikura et al. (1992) Science 256, 632-638; Vorherr et al. (1992) Eur. J. Biochem. 204, 931-937]. The interchange of tryptophan-3 and phenylalanine-21 of the calcium pump peptide increased the efficiency of energy transfer to the AEDANS-moiety approximately 12-fold, reducing the calculated distance to 20 A. These data suggest that phenylalanine-21 of the calcium pump peptide interacts with the hydrophobic cleft in the amino-terminal lobe of CaM.

Amino Acid Sequence↗