Identification of visual arrestin (S-antigen) in retinal pigmented epithelial cells

PURPOSE

Inactivation of photolyzed rhodopsin requires phosphorylation of this receptor and binding of the 48 kDa regulatory protein arrestin (S-antigen). Arrestin is also to cause an autoimmune disease, uveoretinits, that resembles uveitis in humans. In this study we demonstrate the presence of visual arrestin in retinal pigment epithelial cells (RPE) in culture.

METHODS

Bovine RPE were isolated. Mouse and rat monoclonal and rabbit polyclonal antibodies against visual arrestin, and a synthetic peptide "GFLGELTSSEVATEVPFRLM" (a pathogenic sequence corresponding to residues 340 to 359 of human visual arrestin), and rabbit polyclonal antibody against the specific peptide "EDPDTAKESFQ" for bovine visual arrestin were used to detect arrestin in RPE cells. Using visual arrestin specific primer, RT-PCR of RNA from RPE was performed.

RESULTS

By western blots analysis a 48 kDa protein, corresponding to visual arrestin was detected with both mAb and polyclonal antibodies in extracts of RPE cells. RT-PCR analysis of RNA from RPE cells confirmed the presence of arrestin mRNA of predicted 377 bp and exhibited 100% homology with visual arrestin 48 kDa.

CONCLUSION

Visual arrestin proteins present in RPE may be involved in the desensitization of G-protein-coupled receptors in RPE cells and in arrestin uveopathogenesis.

The epithelial sodium channel (ENaC) in rodent retina, ontogeny and molecular identity

PURPOSE

To assess the appearance of the epithelial sodium channels (ENaC) during retinal development and establish its molecular identity.

METHODS

Photoreceptors were isolated by horizontal sectioning of rat retina with a vibratome series 1000. Intact retina and isolated photoreceptors were analyzed for the developmental appearance of ENaC using the Polymerase Chain Reaction (PCR) technique. Immunofluorescence was conducted with the aid of an antibody raised against the 14 amino acids peptide QGLGKGDKREEQGL, corresponding to the N-terminal region (44-58 aa) of alpha ENaC.

RESULTS

ENaC message was present in rat retina photoreceptors, isolated just one day after birth. The bipolar and ganglion cell layers, separated from whole retina by vibratome, also contained the ENaC message. The partial sequence of the photoreceptor ENaC (496 base) exhibited one hundred percent homology with the channel from rat known sources. Immunochemistry revealed that only the outer nuclear layer was positive for the ENaC in one-day-old rat; the inner segment became immunopositive at the age of 9 days.

CONCLUSION

The ENaC is present in the retina and visible soon after birth. These observations suggest that ENaC may prove to have physiological importance in the retina but until now its function is unknown.

Thrombotic dysfibrinogenemia. Fibrinogen "Caracas V" relation between very tight fibrin network and defective clot degradability

Fibrinogen Caracas V is a thrombotic dysfibrinogenemia with an Aalpha 532 Ser-->Cys mutation characterized by a tight fibrin network formed of thin fibers responsible for a less porous clot than a normal one. In the present work, fibrinogen Caracas V is further characterized in order to understand the relationship between the structural defect and thrombophilia. This thrombotic disorder has been attributed to a tight fibrin network responsible for a decreased permeation of flow through the clot, leading to defective thrombus lysis due to a diminished availability of fibrinolytic enzymes to the inner fibrin surface. Correction of clot structure anomaly, by addition of dextran 40 to fibrinogen before clotting, induces an improvement in fibrin degradation that was attributed to an increase in porosity. The pulmonary embolism observed in this family has been related to an hyper rigidity of the clot, an anomaly that is also corrected by dextran. Furthermore, this abnormal fibrinogen binds more albumin than does normal fibrinogen, a phenomenon attributed to the mutation of serine in Aalpha-532 by cysteine. Therefore, this fibrinogen shows a striking similarity to the fibrinogen Dusart, allowing us to confirm that the alphaC-terminal part of fibrinogen plays an important role in fibrin structure, and to conclude that the anomaly of fibrin network observed in fibrinogen Caracas V is responsible for a deficient thrombus lysis.

Demonstration of the mineralocorticoid hormone receptor and action in human leukemic cell lines

We studied the expression of the mineralocorticoid receptor (MCR), and of the amiloride-sensitive sodium channel (ASSC) regulated by the MCR, in human leukemic cell lines. Cell extracts from TF1 (proerythroblastic), HEL (human erythroblastic leukemia) and U937 (myeloblastic) cell line were positive for the ASSC, as a 82 kDa band in Western blots developed with the aid of a polyclonal antibody raised against the peptide QGLGKGDKREEQGL, corresponding to the region 44-58 of the alpha subunit of the epithelial sodium channel (ENaC) cloned from rat colon, linked to KLH. The polyclonal antibody against the MCR revealed a single band of about 102 kDa in extracts from HEL and TF1 cells. The immunofluorescent labelling of the MCR in all cell lines showed a nucleocytoplasmic localization of the receptor but the ASSC was exclusively membrane-bound and these results were confirmed by confocal microscopy. The expression of the MCR in the HEL cells was evident as a predicted band of 843 bp (234 amino acids) in electrophoresis of the PCR product obtained after total RNA had been reverse transcribed and then amplified using the primers 5'-AGGCTACCACAGTCTCCCTG-3' and 5'-GCAGTGTAAAATCTCCAGTC-3' (sense and antisense, respectively). The ENaC was similarly evident with the aid of the primers 5'-CTGCCmATG GATGATGGT-3' (sense) and 5'-GTTCAGCTCGAAGAAGA-3' (antisense) as a predicted band of 520 bp. In both cases, 100% identity was observed between the sequences of the PCR products compared to those from known human sources. The multiplication of the HEL cells was influenced by antagonists (RU 26752, ZK 91587) targeted for specificity to the MCR and this was selectively reversed by the natural hormone aldosterone. These steroids also provoked chromatin condensation in the HEL population. These permit new and novel possibilities to understand the pathobiology of human leukemia and to delineate sodium-water homeostasis in nonepithelial cells.

Paradoxical effects of mineralocorticoids on the ion gated sodium channel in embryologically diverse cells

PCR analysis and Western blotting revealed the expression of the mineralocorticoid receptor (MCR) and the epithelial sodium channel (ENaC) genes at the level of RNA, DNA, and protein in several leukemic cell lines, fibroblasts from human cornea, and epithelial cells from ocular tissues. Following immunofluorescence, the MCR appeared to be primarily nuclear whereas the ENaC was almost exclusively membrane-bound. Paradoxically, the MCR-specific antagonist ZK 91587 actually stimulated the multiplication of human erythroblastic leukemia cells, contrary to the inhibitory effect of the antagonist RU 26752 on the multiplication of corneal fibroblasts; both effects were opposed by aldosterone. In quantitative PCR, both basal and aldosterone-induced levels of ENaC were diminished by ZK 91587 in the corneal fibroblast, in contrast to the stimulation observed in the retinal pigmentary epithelium. Thus, contrary to the existing notions, (a) antimineralocorticoids can act both as agonists and antagonists, and (b) the receptor-mediated action of mineralocorticoids on the sodium channel is not restricted to the epithelial cell.

Development of a sensitive method for the determination of ganciclovir by reversed-phase high-performance liquid chromatography

Ganciclovir is a nucleoside analogue widely used in the treatment of cytomegalovirus infections, which affects mainly immunocompromised patients. Recently, new pharmaceutical dosage forms based on the use of albumin nanoparticles have been developed for improving the efficacy of this drug. The aim of this study was to develop an analytical HPLC method for the determination of ganciclovir in both pharmaceuticals (i.e. albumin nanoparticles) and biological medium samples. The chromatography was performed on a reversed-phase encapped column (LiChrospher Select B C8) with a mobile phase consisting of acetonitrile in 0.05 M ammonium acetate (pH 6.5; 2: 98, v/v). Acyclovir was used as internal standard and the detection wavelength was 254 nm. The limit of quantitation of ganciclovir was 50 ng/ml and the average recoveries over a concentration range of 0.05-10 microg/ml ranged from 98 to 102%. Precision did not exceed 5%. In summary, this assay is a selective, sensitive and reproducible method for the determination of the ganciclovir in albumin nanoparticles. It can be successfully applied to the estimation of the ganciclovir uptake by cultured human corneal fibroblasts.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Abnormal fibrin clot architecture in nephrotic patients is related to hypofibrinolysis: influence of plasma biochemical modifications: a possible mechanism for the high thrombotic tendency?

Porosity, viscoelasticity and morphological properties of plasma fibrin from 16 nephrotic patients and 16 healthy volunteers were compared. Nephrotic patients were characterized by formation of tight and rigid plasma fibrin gels which resulted in a slower rate of fibrin lysis studied either under pressure-driven permeation or diffusional transport of fibrinolytic agents. These latter findings indicated that both abnormal fibrin network conformation and abnormal fibrin fiber structure were involved in hypofibrinolysis. Albumin supplementation up to 40 mg/ml partially restored normal fibrin architecture and increased the rate of fibrinolysis in these patients. Multiparametric analysis showed that nephrotic patients were mainly characterized by a low plasma albumin level (R = -0.85), a low albumin to fibrinogen ratio (R = -0.89) and a high resistance to lysis (R = -0.82). High triglycerides level was the only plasma modification related to the slower fibrin lysis rate (R = -0.54). High fibrin rigidity (G') was the only fibrin parameter simultaneously related to the nephrotic state (R = 0.75) and the lysis resistance (R = -0.71). After eliminating the effects of age, albumin and fibrinogen levels, low fibrin porosity (Ks) and low fiber mass-length ratio (mu) were the main features of the nephrotic state. These findings are discussed in relation to both the pathophysiology of thrombotic complications in nephrotic syndrome and their pharmacological prevention.

Immunochemical analysis of the sodium channel in rodent and human eye

The presence of the amiloride-sensitive sodium channel (ASSC) in ocular tissues was studied with the aid of a polyclonal antiserum raised against the 14 amino acid peptide QGLGKGDKREEQGL. This sequence corresponds to the region 44-58 of the alpha subunit of the channel, termed ENaC, cloned from rat colon. The antibody titers, measured by the ELISA technique, rose to 1∶2560 4 weeks after immunization, and this bleed was used in all subsequent experiments. Immunoblotting with the polyclonal anti-alphaENaC serum, revealed a major band of 82-86 kDa in extracts prepared from whole bovine or rat retina; a minor component of 92 kDa in the extract from bovine ciliary body may represent a glycosylated species. Immunohistochemistry, using the alphaENaC-specific antiserum, revealed strong fluorescence in specific areas of the rat and human eye. Pronounced labelling was observed in the epithelial cell layer of the retina, the lens, as well as both the pigmented and the nonpigmented epithelium of the ciliary body and the iris. All of the cell layers (epithelium, endothelium and fibroblasts) in the cornea, the blood vessels in the iris, and iris epithelium, were also strongly immunopositive. The somatic body of the photoreceptor cells (cones and rods) in the inner and outer segments could be traced to forming a synapse in both the internal and external portions of the internal nuclear layer. The bipolar cells and ganglia in the neuronal compartment also exhibited occasional immunofluorescence. The method of fixation and the source of the tissue were important parameters for the immunochemical localization of the ENaC. The resolution was very poor when rat eye was fixed in Bouin's solution but this method was satisfactory for human tissues. For rat eye, optimum resolution was obtained with AMeX fixation. This widespread distribution of the ENaC generally colocalizes with the previously observed immunopositivity for the mineralocorticoid receptor such that steroid hormone-mediated ion regulation would appear to add a new parameter to the functional expression of ocular tissues.

Beta-arrestin-related proteins in ocular tissues

PURPOSE

Proteins of the arrestin family contribute to the regulation of G-protein-mediated transduction. In this study, the presence of beta-arrestins in ocular tissues was investigated.

METHODS

Mouse monoclonal and rabbit polyclonal antibodies were raised against the peptide Val-Asp-Thr-Asn-Ile-Leu-Glu-Leu-Asp-Thr-Asn-Asp-Asp-Asp-Ile, a sequence present in beta-arrestins 1 and 2 but absent from visual arrestin. These antibodies were used for the immunohistologic detection of beta-arrestins in parafin sections of rodent eyes fixed in Bouin's solution. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of RNA from bovine retina, retinal pigmented epithelial (RPE) cells, lens epithelial cells, and human corneal fibroblasts was performed using beta-1 arrestin primers.

RESULTS

In the eye, bet-arrestin staining predominated in RPE, inner segments of photoreceptors, synaptic spherules of rods, inner plexiform layer and ganglion cell fibers, epithelial cells from ciliary body, and vessels. RT-PCR amplified a 480 bp product, corresponding to the predicted length. The sequence of PCR products from bovine retina and RPE cells was identical with the bovine beta-arrestin mRNA.

CONCLUSIONS

beta-arrestins were detected in several ocular tissues. In photoreceptor cells, their specific localization in the synaptic terminals and plexiform layer suggests a role of beta-arrestin in synaptic transmission. In other ocular tissues, the presence of beta-arrestin may be related either to adrenergic signal transduction or to signal transduction mediated by other G-protein-coupled receptors.

Copurification of selected glycolytic enzymes with retinal S-antigen (arrestin) by hydroxyapatite agarose chromatography of bovine retina

PURPOSE

A variety of methods have been developed for the purification of S-antigen but a simple and rapid procedure based on hydroxyapatite-agarose (HA) adsorbtion is most widely used. In the present study, we investigated the nature of proteins purified with the aid of HA chromatography.

METHODS

After elimination of retinal S-antigen by HA, the soluble extract of retinal tissue was readsorbed on HA. The proteins were thereafter desorbed by 10 to 500 mM phosphate buffer gradient. Two peaks obtained by SDS-PAGE were used for the generation of specific antisera for subsequent analysis by ELISA and Western blotting.

RESULTS

Four proteins (two 48 kDa , one 50 kDa and one 46 kDa) were obtained in this manner. Partial amino acid sequencing permitted the identification of these proteins as alpha-enolase (48 kDa), gamma-enolase (48 kDa), Glucose-6-phosphate-Isomerase (50 kDa) and aspartate-amino-transferase (46 kDa).

CONCLUSION

The selected glycolytic enzymes co-purified with retinal S-antigen by hydroxyapatite agarose chromatography of bovine retina.

Thrombus generation after adenovirus-mediated gene transfer into atherosclerotic arteries

Thrombosis represents a major issue during arterial local delivery. We evaluated the occurrence of thrombosis after adenovirus (Ad)-mediated gene transfer into normal and atherosclerotic arteries. A replication-deficient Ad vector expressing the beta-galactosidase reporter gene (Ad.RSV betagal; 4 x 10(9) PFU) was injected into normal and atherosclerotic arteries (n = 11 in both groups). The contralateral artery received either an Ad vector carrying no transgene (Ad.MLPnull) (n = 7 in both groups, 4 x 10(9) PFU) or vehicle buffer (n = 4 in normal group, n = 8 in atherosclerotic group). Animals were sacrificed 3 days following gene transfer for thrombus detection and assessment of beta-galactosidase activity. Thrombus was absent in normal arteries and in atherosclerotic arteries injected with vehicle buffer only. In contrast, nonocclusive thrombus was present in atherosclerotic arteries injected with either Ad.RSV betagal (5 of 11) or Ad.MLPnull (3 of 7). Beta-galactosidase activity was predominantly found in the endothelial layer of the transfected arteries. Gene transfer and expression occurred despite the presence of the thrombus (4 of 5), and its efficiency did not significantly differ regardless of the thrombus. We conclude that thrombus frequently occurred in atherosclerotic arteries after Ad-mediated gene transfer. Further studies are warranted to identify the mechanisms of thrombus generation after Ad-mediated gene transfer into atherosclerotic arteries.

Mineralocorticoid hormone receptor and the epithelial sodium channel in a human leukemic cell line

A Cell extract from the HEL (human erythroblastic leukemia) cell line was positive for both the epithelial sodium channel (ENaC) and the mineralocorticoid receptor (MCR) as glycosylated 82-84 kDa bands, and a single 102 kDa band, respectively, in Western blots using polyclonal antibodies raised against these proteins. The immunofluorescent labeling of the MCR in all cell lines showed a nucleocytoplasmic localization of the receptor whereas the ENaC was exclusively membrane-bound. These results were confirmed by confocal microscopy. The expression of the MCR in HEL cells was evident as a predicted band of 843 bp (234 amino acids) after total RNA from HEL cells had been reverse transcribed and then amplified by PCR; the ENaC was similarly evident as a predicted band of 520 bp. In both cases, near 100% identity was observed between the deduced amino acid sequences of the PCR products and those from known human sources. The multiplication of HEL cells was influenced by antagonists (RU 26752, ZK 91587) targeted for specificity to the MCR and this was reversed by the natural hormone aldosterone. These steroids also provoked chromatin condensation in the HEL population.

Enhanced activation of the mineralocorticoid receptor in genetically hypertensive rats

The relative abundance and availability of the mineralocorticoid receptor (MCR) appeared to be similar in the heart, kidney and ocular tissues of the genetically hypertensive SHR and normotensive WKY rats by a number of criteria including Western blotting, immunoprecipitation, dot blot analysis, and immunohistochemistry. On the other hand, the activation of the MCR, as judged by binding to DNA cellulose, was significantly enhanced in the hearts and kidneys of 14 week-old, hypertensive, SHR rats compared to the normotensive WKY animals. The activation of the renal MCR was elevated in the SHR strain even at the age of six weeks when the tail arterial pressure was statistically identical to that of the WKY strain. Thus, precocious receptor activation may represent a primary lesion leading to hypertension in the SHR strain, thereby providing a new model to elucidate the hypertensive state.

Cellular source of human platelet secretory phospholipase A2

Platelets are one source of the group II extracellular form of phospholipase A2 (sPLA2) which is involved in the amplification of local and systemic inflammation. Although sPLA2 protein has been described in human platelets, its presence in human megakaryocytes has not been yet established. We demonstrated in this study that the human erythroleukaemia (HEL) cell line, which has megakaryoblastic features, constitutively expresses sPLA2. Using an anti-rhsPLA2 monoclonal antibody (mAb BA11) and dot-blot detection, we showed that HEL cells and platelets release sPLA2 into incubation medium upon stimulation by thrombin. Similar results were obtained for sPLA2 activity detected by a spectrofluorescence assay. Enzymatic activity was abolished by mAb BA11 and by protamine. In both cell types, although released, the major part of sPLA2 remained in the cell pellet, and was probably adsorbed at non-specific membrane sites. Double labelling experiments using mAb BA11 and an anti-GPIIb antiserum revealed the presence of sPLA2 in human bone-marrow megakaryocytes. The use of reverse transcription-polymerase chain reaction conjugated with hybridization analysis demonstrated the presence of mRNA encoding for sPLA2 in platelets and HEL cells. Expression of sPLA2 in platelets and megakaryocytes at both transcriptional and post-translational levels strongly argues in favour of a megakaryocytic origin of platelet sPLA2 and rules out a role for endocytosis of the enzyme from plasma by circulating platelets.

Immunodetection of a protein related to mammalian arrestin in Euglena gracilis

Six monoclonal antibodies directed against different epitopes of bovine retinal arrestin recognized a single polypeptide in extracts of achlorophyllous Euglena gracilis cells. This polypeptide had an apparent molecular weight slightly lower: 45kDa vs. 48 kDa, and a more basic isoelectric point compared to that of bovine visual arrestin. It was located in an insoluble cytoplasmic fraction. Immunofluorescence assays show a cytoplasmic punctuated pattern suggesting a cluster distribution or a linkage to some cell structure. The presence of arrestine-like molecules in achlorophyllous Euglena gracilis cells suggests that these proteins might be involved in a peculiar step of chemical signal transduction processes.

Immunological detection of potential signal-transduction proteins expressed during wheat somatic tissue culture

An immunochemical approach was used to detect the expression of putative guanine nucleotide-binding proteins (G-proteins), arrestin, and nucleoside diphosphate kinases during wheat (Triticum aestivum) tissue culture initiated from immature embryos. Both the soluble and membrane extracts from the immature embryos revealed bands of 58, 40, and 16 kD with antibodies to G-protein (alpha subunit), arrestin, and nucleoside diphosphate kinase, respectively. These proteins were overexpressed in vitro in both nonembryogenic callus and embryogenic cultures. An additional soluble protein (32 kD) was detected by anti-G alpha antibodies in cultured tissues but not in immature embryos, suggesting a possible function in cell multiplication. Moreover, somatic embryogenesis was associated with the appearance of a 29-kD protein reactive with anti-arrstin antibodies, both in soluble and membrane fractions. Tissue-cultured genetic stocks of Chinese Spring wheat, including the disomic, 36 ditelosomic, and 6 nullisomic-tetrasomic wheat lines, were used to ascertain the chromosomal location of the genes encoding the 29-kD arrestin-like protein. The lack of a signal with the nonembryogenic ditelosomic 3 D short chromosome arm line suggests that the 3 D long chromosome arm possesses at least one gene involved in the expression of the 29-kD protein. The putative role of the 29-kD protein in signal-transduction regulating embryogenesis is discussed.

Immunochemical demonstration of the mineralocorticoid receptor in ocular tissues

We studied the presence of the mineralocorticoid receptor (MCR) in the eye with the aid of a number of immunochemical techniques. Immunoblotting with a polyclonal antibody, directed against the rat renal MCR, revealed a single band of about 102 kD in extracts prepared from whole bovine or rat retina similar to that observed in cytosol from the kidney and myocardium from these species. Isolated cells of the bovine retinal pigment epithelium (RPE) similarly exhibited a 98- to 102-kD band in Western blots developed with the aid of anti-MCR antiserum. The 98- to 102-kD band was also obtained following autoradiography of RPE cytosol irradiated in the presence of 3H-R 5020. This fluorographic pattern was abolished when RU 26752, an antagonist specific to the MCR, was allowed to compete with radiolabelled promegestone. The MCR-3H-RU 26752 complex in RPE cytosol underwent heat activation, as judged by binding to DNA cellusose, and could also be precipitated by anti-MCR IgG. In primary cultures, the proliferation of the RPE cells was inhibited by the two MCR-specific antagonists RU 26752 and ZK 91587. The loss of the MCR-specific immunofluorescence in RPE cells after only 3 passages in culture was associated with refractoriness to the inhibitory effect of both of these spironolactones. Immunohistochemistry, using MCR-specific antiserum, revealed strong fluorescence in specific areas of the rat eye. In the retina, immunopositivity was observed in Müller cells, external and internal limiting membranes, the vitreous base lining and in the pigment epithelium. Epithelial cells of the ciliary body, iris and cornea also exhibited strong MCR-specific immunofluorescence. Thus, both the epithelial and the nonepithelial compartments of the ocular tissues form interesting new targets to delineate the mechanism of action of mineralotropic hormones.

Evidence for receptor-mediated mineralocorticoid action in rat osteoblastic cells

Aldosterone significantly enhanced the proliferation of osteoblastic cells from rat calvaria, and this effect was inhibited by RU 26752 and ZK 91587, two antagonists specific to the mineralocorticoid receptor (MCR). In addition, aldosterone inhibited the activity of alkaline phosphatase, a marker of the osteoblastic phenotype, and this effect was also reversed by RU 26752. Cytoplasmic staining of MCR was observed in rat calvaria osteoblasts incubated with a specific polyclonal antiserum raised against rat kidney MCR. This anti-MCR immunoglobulin G immunoprecipitated and macroaggregated the MCR-[3H]RU 26752 complex in osteoblastic cytosol. A single 98-kDa band was observed when osteoblastic cytosol was analyzed by Western blotting with anti-MCR serum. The 98-kDa band was also obtained after autoradiography of irradiated osteoblastic cytosol-[3H]R 5020 complex, and this was abolished in the presence of RU 26752. A p26MR probe, specific to COOH-terminal end of MCR, hybridized with the predicted product after amplification of total cell RNA by polymerase chain reaction technique. Furthermore, hybridization of poly(A)+ mRNA from at calvaria osteoblastic cells with the p26MR probe revealed a major band of approximately 4.2 kb. Collectively, our studies demonstrate the existence of a functional MCR in rat calvaria osteoblasts.

Effect of interferon gamma and TNF alpha on the differentiation/activation of human glial cells: implication for the TNF alpha receptor 1

This study focused on the activation/differentiation of human microglial cells and astrocytes, which is a prerequisite for HIV1 replication. In vitro, IFN gamma induced a differentiation-like morphological change in embryonic microglia and astrocytes, in both primary and in purified culture. This effect was enhanced by TNF alpha which in itself had no effect. IFN gamma did not increase the low level of endogenous TNF alpha, which is not secreted by embryonic cells, but stimulated the expression of TNF alpha R1, although to a relatively low extent. IFN gamma facilitated TNF alpha response through an increase in TNF alpha R1 expression, but probably also through interaction with different intracellular signal transduction pathways.

The mineralocorticoid hormone receptor and action in the eye

Immunoblotting with a polyclonal antibody, directed against the mineralocorticoid receptor protein purified from rat kidney in presence of the receptor-specific ligand RU 26752, labeled a single 98-102 kDa band in soluble extracts from bovine retina and from cultured bovine retinal pigment epithelial cells, identical to the receptor in several other tissues from the rat. The antibody also immunoprecipitated the receptor-3H-RU 26752 complex in bovine retinal extract. The growth of the isolated pigment epithelial cells was inhibited by RU 26752 and ZK91587, two ligands specific to the mineralocorticoid receptor. Successive passages in culture led to the disappearance of immunoreactivity in Western blots, concurrently with the refractoriness of the cells to growth inhibition by the two antagonists. On sections of the human eye, mineralocorticoid receptor-specific immunofluorescence was observed in retinal cone cells, pigment epithelium, epithelium of ciliary body, iris, cornea and lens. To our knowledge, this is the first ever demonstration of the mineralocorticoid receptor in ocular tissues.

Fibrinogen Dusart: electron microscopy of molecules, fibers and clots, and viscoelastic properties of clots

Ultrastructural perturbations resulting from defects in polymerization of fibrinogen Dusart, a congenital dysfibrinogenemia with the amino acid substitution A alpha 554 arginine to cysteine, were investigated by a variety of electron microscope studies. Polymerization of this mutant fibrinogen on addition of thrombin is impaired, producing clots with decreased porosity and increased resistance to fibrinolysis, resulting in thrombotic complications in the family members with this dysfibrinogenemia. Electron microscopy of rotary-shadowed individual molecules revealed that, in contrast to control fibrinogen, most of the alpha C domains of fibrinogen or fibrin Dusart appeared to be free-swimming appendages that do not exhibit intra- or intermolecular interactions either with each other or with the central domains. The location of albumin on the alpha C domains was demonstrated by electron microscopy using anti-albumin antibodies. Electron microscopy of negatively contrasted fibrin Dusart fibers indicated that they were less ordered than control fibers and had additional mass visible. Electron microscopy of freeze-dried, unidirectionally shadowed fibers showed that they were twisted with a shorter pitch. Scanning electron microscopy revealed that intact clots were made up of thin fibers with many branch points and very small pore sizes. The viscoelastic properties of Dusart fibrin clots measured with a torsion pendulum indicated a marked increase in stiffness consistent with the structural observations.