Differential localization and functional role of calsequestrin in growing and differentiated myoblasts.

Calsequestrin (CSQ) is the low affinity, high capacity Ca(2+)-binding protein concentrated within specialized areas of the muscle fiber sarcoplasmic reticulum (a part of the ER) where it is believed to buffer large amounts of Ca2+. Upon activation of intracellular channels this Ca2+ pool is released, giving rise to the [Ca2+]i increases that sustain contraction. In order to investigate the ER retention and the functional role of the protein, L6 rat myoblasts were infected with a viral vector with or without the cDNA of chicken CSQ, and stable clones were investigated before and after differentiation to myotubes. In the undifferentiated L6 cells, expression of considerable amounts of heterologous CSQ occurred with no major changes of other ER components. Ca2+ release from the ER, induced by the peptide hormone vasopressin, remained however unchanged, and the same occurred when other treatments were given in sequence to deplete the ER and other intracellular stores: with the Ca2+ pump blocker, thapsigargin; and with the Ca2+ ionophore, ionomycin, followed by the Na+/H+ ionophore, monensin. The lack of effect of CSQ expression on the vasopressin-induced [Ca2+]i responses was explained by immunocytochemistry showing the heterologous protein to be localized not in the ER but in large vacuoles of acidic content, positive also for the lysosomal enzyme, cathepsin D, corresponding to a lysosomal subpopulation. After differentiation, all L6 cells expressed small amounts of homologous CSQ. In the infected cells the heterologous protein progressively decreased, yet the [Ca2+]i responses to vasopressin were now larger with respect to both control and undifferentiated cells. This change correlated with the drop of the vacuoles and with the accumulation of CSQ within the ER lumen, where a clustered distribution was observed as recently shown in developing muscle fibers. These results provide direct evidence for the contribution of CSQ, when appropriately retained, to the Ca2+ capacity of the rapidly exchanging, ER-located Ca2+ stores; and for the existence of specific mechanism(s) (that in L6 cells develop in the course of differentiation) for the ER retention of the protein. In the growing L6 myoblasts the Ca(2+)-binding protein appears in contrast to travel along the exocytic pathway, down to post-Golgi, lysosome-related vacuoles which, based on the lack of [Ca2+]i response to ionomycin-monensin, appear to be incompetent for Ca2+ accumulation.

Expression of muscle calsequestrin in epithelial HeLa cells: distribution and functional role.

Calsequestrin is a Ca2+ binding protein expressed by a few cell types (mostly muscle fibers). In these cells the distribution of the protein is within the endoplasmic/sarcoplasmic reticulum, however, not uniformly throughout but at discrete sites of the lumen. In order to investigate the mechanisms of this unusual intracellular distribution together with the possible functions of the protein, we have studied stable transfected clones of epithelial HeLa cells. Treatment of these cells with butyric acid induced a rapid (24 h) and massive (approx. 10-fold) increase of the transfected protein, whereas the other lumenal and membrane proteins of the endoplasmic reticulum were either modified slightly or unchanged. When butyric acid treatment was interrupted the calsequestrin levels returned rapidly (within 24 h) to the pre-treatment level. Such a rapid turnover was due in part to secretion, sustained by both spontaneous and Ca(2+)-dependent release of calsequestrin to the extracellular medium. From the physiological point of view, the transfected cells exhibited only moderate increases of the Ca2+ release responses triggered by either ATP (a ligand addressed to the P2u receptor and working through IP3 generation) or thapsigargin (a blocker of the endoplasmic reticulum Ca2+ ATPase), with no further increase after butyric acid induction of calsequestrin. This result appears to correlate with the occurrence of only small amounts of calsequestrin within the endoplasmic reticulum lumen of all transfected cells. The bulk of calsequestrin, in contrast, was found sequestered within large vacuoles distributed both near the cell surface and, after butyric acid treatment, also in the deep cytoplasm. These vacuoles (possibly a lysosomal subcompartment) appear to contain no Ca2+ as no difference in 45Ca release from transfected cells was observed without or with butyric acid pretreatment when exposed to ionomycin, alone or combined with monensin. We conclude that HeLa cells possess no adequate mechanisms to keep calsequestrin in its physiologically relevant location, the endoplasmic reticulum. In the transfected cell the protein seems therefore to be diverted (possibly by default) to vacuoles destined to be rapidly eliminated by the cell.

Towards an alternative testing strategy for nanomaterials used in nanomedicine: lessons from NanoTEST.

In spite of recent advances in describing the health outcomes of exposure to nanoparticles (NPs), it still remains unclear how exactly NPs interact with their cellular targets. Size, surface, mass, geometry, and composition may all play a beneficial role as well as causing toxicity. Concerns of scientists, politicians and the public about potential health hazards associated with NPs need to be answered. With the variety of exposure routes available, there is potential for NPs to reach every organ in the body but we know little about the impact this might have. The main objective of the FP7 NanoTEST project ( www.nanotest-fp7.eu ) was a better understanding of mechanisms of interactions of NPs employed in nanomedicine with cells, tissues and organs and to address critical issues relating to toxicity testing especially with respect to alternatives to tests on animals. Here we describe an approach towards alternative testing strategies for hazard and risk assessment of nanomaterials, highlighting the adaptation of standard methods demanded by the special physicochemical features of nanomaterials and bioavailability studies. The work has assessed a broad range of toxicity tests, cell models and NP types and concentrations taking into account the inherent impact of NP properties and the effects of changes in experimental conditions using well-characterized NPs. The results of the studies have been used to generate recommendations for a suitable and robust testing strategy which can be applied to new medical NPs as they are developed.

Novel potent inhibitors of lipid peroxidation with protective effects against reperfusion arrhythmias.

A series of new compounds that contain lipoic acid and trolox connected through spacers were synthesized and examined for their antioxidant activity and their protective effects against reperfusion arrhythmias in isolated heart preparations. All compounds tested are strong inhibitors of lipid peroxidation in rat liver microsomal membranes induced by ferrous ions and ascorbate. N-(3,4-Dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carbonyl)-N'-(1,2-dithiolane-3-pentanoyl)-1,2-phenylenediamine (13) exhibits anti-lipid peroxidation activity at the nanomolar range. N-(3,4-Dihydro-6-hydroxy-2,5,7,8-tetramethyl-2H-1-benzopyran-2-carbonyl)-N'-(1,2-dithiolane-3-pentanoyl)ethylenediamine (10) and 13 totally suppressed reperfusion arrhythmias.

Opioids modify the release of LH at the pituitary level: in vitro studies with entire rat pituitaries.

It is currently accepted that opioids modify the secretion of LH by affecting the release of GnRH in the hypothalamus. A direct action of opioids at the pituitary level is not yet fully established. To this end, we tested the effects of opioids on the release of LH by the entire pituitary in adult male rats. Opioid agonists with mu (DAGO), delta (DS-LET) and kappa (U-50488H) specificity were tested at 0.01 to 10 microM in static incubations. DAGO inhibited dose-dependently the spontaneous and GnRH-induced release of LH. DSLET inhibited only the GnRH-induced release of LH. On the other hand, U-50488H increased spontaneous LH release dose-dependently. The opioid antagonists naloxone, diallyl-G (delta antagonist) and MR 2266 (kappa antagonist) blocked the effects induced by DAGO, DSLET or U-50488H respectively, implying an opioid receptor-mediated effect. The above results showed that opioids with mu, delta and kappa specificity act on the entire pituitary and modify differentially the release of LH. In this study we also compared spontaneous and GnRH-induced LH release by anterior and entire pituitaries and found that the amount of LH released by the anterior lobe was twofold higher, suggesting that inhibitory factors present in the neurointermediate part may affect the release of LH.

Ageing affects cytosolic Ca2+ binding proteins and synaptic markers in the retina but not in cerebral cortex neurons of the rat.

Two cerebral cortex areas (frontal and occipital) and the retina of rats varying in age from 0.4 to 30 months were investigated for the expression levels and distribution of two cytosolic high affinity Ca2+ binding proteins, calbindin-28 and calretinin, and of two presynaptic protein markers. Of these latter proteins, one is integral (synaptophysin) the other peripheral (synapsin I) to the synaptic vesicle membranes. In the cortex areas, no significant changes of the markers were observed, except for a drop of calretinin from 0.4 to 2 months, probably related to a stage of neuronal development. In the retina, calbindin-28 decreased progressively during ageing (-40% at 30 months) while calretinin remained unchanged. Concomitantly, the two synaptic vesicle proteins dropped, synaptophysin > 50% and synapsin I > 85%. The role of these changes in sustaining the functional alterations previously described in the retina of aged animals remains to be investigated.

Induction of micronuclei in human lymphocytes by organic solvents in vitro.

Our work is focused on identifying micronuclei (MN) induced in whole blood lymphocyte cultures after treatment with the organic solvents toluene, benzene, and acetone. We used the micronucleus test as a cytogenetic biomarker for genotoxicity and treated whole blood cultures with different concentrations of these solvents (0.1 to 5 mM) and mixtures of them (toluene plus acetone, toluene plus benzene). Our results did not show a significant increase in the number of micronuclei in binucleated lymphocytes after 48 hr of in vitro treatment. The addition of an external metabolic factor (10% S9 mix for 2 hr) in blood cultures treated with the organic solvents or their mixtures did not cause induction of MN. These results indicate the lack of genotoxic activity of toluene, benzene, and acetone in vitro.

Regulation of ornithine decarboxylase in murine erythroleukemic cells by N,N'-diacetyl-1,6-hexanediamine and N-acetyl-1,6-hexanediamine.

The levels at which the ornithine decarboxylase gene is regulated in murine erythroleukemic cells treated with N,N'-hexamethylene bisacetamide (N,N' diacetyl-1,6-hexanediamine) and with N-acetyl-1,6-hexanediamine, the monoacetylated catabolite of this inducer of erythrodifferentiation, have been investigated. Although these two molecules are structurally related and both cause a decrease in ornithine decarboxylase activity, they did not similarly affect ornithine decarboxylase mRNA. In the presence of 4 mM N,N'-hexamethylenebisacetamide, at the concentration generally used to induce differentiation in these cells, a decreased steady-state level of ornithine decarboxylase mRNA, due to decreased gene transcription, was observed. In the presence of N-acetyl-1,6-hexanediamine the decrease in enzyme activity was shown to be associated with a decrease in the half-life of the enzyme in the absence of a change in gene transcription. These results show that in proliferating cultured cells changes in ornithine-decarboxylase-gene transcription can be uncoupled from changes in cell growth and that N-acetyl-1,6-hexanediamine only regulates ornithine decarboxylase expression post-transcriptionally.

Effect of alpha-difluoromethylornithine on DNA methylation in murine erythroleukaemic cells. Relationship to stimulation of induced differentiation.

Murine erythroleukaemic (MEL) cells cultured with alpha-difluoromethylornithine (DFMO) accumulated decarboxylated S-adenosylmethionine(decarboxylated AdoMet). In the absence of the inducer hexamethylenebisacetamide (HMBA), this accumulation of decarboxylated AdoMet was associated with a concomitant and proportional increase in DNA hypomethylation. In the presence of HMBA, DFMO, which stimulates the erythrodifferentiation of MEL cells, enhanced the differentiation-associated DNA hypomethylation. However, this differentiation-associated DNA hypomethylation was neither temporally nor quantitatively correlated with the accumulation of decarboxylated AdoMet in these cells. Therefore DFMO probably stimulates the HMBA-induced differentiation of MEL cells and the associated DNA hypomethylation via the effect of this drug on polyamine biosynthesis.

Calstorin, a new Ca2+ binding protein of the microsome lumen which is abundant in the rat brain.

A new Ca2+ binding protein (apparent Mr: 54 KDa; pI: 4.37; Stains All positive) which, based on N terminal sequence and immunological criteria, appears different from calsequestrin, calreticulin and the chaperonins, has been identified in the rat brain and recovered primarily in the microsome fraction. Carbonate extraction and trypsin digestion experiments suggest the protein to be located within the microsome lumen. Its expression levels are considerable especially in the cerebellum (65% with respect to calreticulin). 45Ca binding experiments on 2D blots suggest the protein to be of high capacity (higher than calreticulin) and low affinity (apparent Kd: 3 mM). These properties are typical of the proteins participating in the storage of Ca2+ within rapidly exchanging organelles. The tentative name of calstorin (calcium-storage-protein, CST) is therefore proposed.

Various divalent cations protect the isolated perfused pigeon heart against a calcium paradox.

The protective effects of various divalent cations against the irreversible damage of myocardium, a phenomenon termed "the Ca2+-paradox", were examined in the isolated perfused pigeon heart. All cations examined were added at a concentration of 200 micromol l(-1) in the "calcium-free" medium. In hearts perfused with low calcium, upon normal calcium repletion, the maximal recovery of the contractile tension (in the 2nd minute) was approximately 115% and the recovery obtained at the end of reperfusion was 81.5% (compared to the equilibration period value). From the other divalent cations examined, the presence of cobalt, nickel, manganese or barium during calcium depletion powerfully protected the pigeon heart. Upon calcium repletion, the maximal recovery of contractile tension was approximately 60%, 76.5%, 100% and 85%, the recovery estimated at the end of reperfusion was 40%, 12%, 70% and 53%, and the resting tension estimated at the end of reperfusion was 2.69+/-0.18 g, 6.40+/-0.50 g, 1.20+/-0.10 g and 1.90+/-0.10 g for cobalt, nickel, manganese and barium, respectively. On the contrary, strontium exerted no protective effects. The protective effects were also indicated by reduced total protein and lactate dehydrogenase activity release into the effluent perfusate and maintenance of electrical activity. The effectiveness of the added divalent cations (with the exception of strontium) showed a strong dependence upon their ionic radius. The most potent inhibitors of this phenomenon in the pigeon heart were the divalent cations having an ionic radius closer to the ionic radius of calcium. These results are discussed in terms of the possible mechanisms involved in the protective effects of these cations.

Promoter elements and factors involved in hepatic transcription of the human ApoA-I gene positive and negative regulators bind to overlapping sites.

DNase I footprinting analysis of the proximal apoA-I promoter sequences with rat liver nuclear extracts identified four protected regions: A, -22 to +17; B, -128 to -77; C, -175 to -148; and D, -220 to -190. Region D (-220 to -190) binds at least two distinct activities, designated AID1 and AID2, respectively, which can be separated by ion exchange chromatography. Region C (-175 to -148) forms five DNA protein complexes. Three of the complexes (2, 4, and 5) originate from the binding of more than one heat-stable nuclear factor, and two (1 and 3), from the binding of two heat-labile factors. The heat-stable factors bind in the -175 to -148 region and can be distinguished from C/EBP, which recognizes the same region, with DNA binding gel electrophoretic assays. Both factors 1 and 3 bind in the -168 to -148 apoA-I region. Despite the lack of a CCAAT motif in this region, the binding of factor 1 is competed out by oligonucleotides containing the binding sites of NFY and NFY*. Mutagenesis of the promoter region showed that mutations in the -171 to -166 and -158 to -153 regions diminished the binding of the heat-stable factors and reduced hepatic transcription to 14 and 8% of control, respectively. In contrast, a mutation in the -164 to -159 region abolished the binding of factor 1 and was associated with a 4.6-fold increase in hepatic transcription. These findings suggest that the heat-stable factors act as positive regulators, whereas factor 1 acts as a negative regulator in apoA-I gene transcription.