Showing papers on "Secretion published in 1996"
Journal Article•
TL;DR: The general protein apparatus used by all eukaryotes for intracellular transport, including secretion and endocytosis, and for triggered exocyTosis of hormones and neurotransmitters, is uncovered.
Abstract: Recent advances have uncovered the general protein apparatus used by all eukaryotes for intracellular transport, including secretion and endocytosis, and for triggered exocytosis of hormones and neurotransmitters. Membranes are shaped into vesicles by cytoplasmic coats which then dissociate upon GTP hydrolysis. Both vesicles and their acceptor membranes carry targeting proteins which interact specifically to initiate docking. A general apparatus then assembles at the docking site and fuses the vesicle with its target.
2,174 citations
TL;DR: It is indicated that IL-12 plays an essential role in regulating IFNγ production and in facilitating normal DTH responses and other phenomena associated with Th1 responses and cell-mediated immunity, i.e., IL-2 secretion and CTL generation, were not compromised in the absence of IL- 12.
984 citations
TL;DR: The trafficking of proteins within eukaryotic cells is achieved by the capture of cargo and targeting molecules into vesicles that bud from a donor membrane and deliver their contents to a receiving compartment.
Abstract: The trafficking of proteins within eukaryotic cells is achieved by the capture of cargo and targeting molecules into vesicles that bud from a donor membrane and deliver their contents to a receiving compartment. This process is bidirectional and may involve multiple organelles within a cell. Distinct coat proteins mediate each budding event, serving both to shape the transport vesicle and to select by direct or indirect interaction the desired set of cargo molecules. Secretion, which has been viewed as a default pathway, may require sorting and packaging signals on transported molecules to ensure their rapid delivery to the cell surface.
974 citations
TL;DR: After stable transfection of epithelial LLC-PK1 cells, MDR1 and MDR3 Pgp were localized in the apical membrane and newly synthesized short-chain analogs of various membrane lipids were recovered in theApical albumin-containing medium of MDR 1 cells but not control cells.
853 citations
Journal Article•
TL;DR: In limited studies of animal models of autoimmunity, specific MMP inhibitors have significantly decreased edema and inflammatory tissue damage, suggesting possible therapeutic benefits.
Abstract: Matrix metalloproteinases (MMPs) are a family of zinc-containing endo-proteinases that share structural domains but differ in substrate specificity, cellular sources, and inducibility. Macrophage production and secretion of large quantities of many MMPs, after contact with matrix proteins, is enhanced by surface determinants on activated T cells and suppressed by cytokines from Th1 and Th2 cells. T cells secrete predominantly the gelatinases MMP-2 and -9, after beta 1, integrin- or vascular cell adhesion molecule (VCAM)-1-dependent stimulation by cytokines and inflammatory mediators. MMPs of both T cells and macrophages facilitate secretion of TNF-alpha, by cleavage of the membrane-bound form. T cell MMPs prepare connective tissue matrices for T cell chemotaxis across basement membranes and through tissues. The greater amounts of diverse MMPs from macrophages are capable of degrading connective tissues, which may release stored growth factors. In limited studies of animal models of autoimmunity, specific MMP inhibitors have significantly decreased edema and inflammatory tissue damage, suggesting possible therapeutic benefits.
566 citations
TL;DR: Its expression by cells and tissues not normally exposed to pancreatic trypsin suggests that other proteases could serve as physiological activators and PAR-2 may serve as aTrypsin sensor in the gut.
Abstract: We used PCR to amplify proteinase activated receptor-2 (PAR-2) from human kidney cDNA. The open reading frame comprised 1191 bp and encoded a protein of 397 residues with 83% identity with mouse PAR-2. In KNRK cells (a line of kirsten murine sarcoma virus-transformed rat kidney epithelial cells) transfected with this cDNA, trypsin and activating peptide (AP) corresponding to the tethered ligand exposed by trypsin cleavage (SLIGKV-NH2) induced a prompt increase in cytosolic calcium ion concentration ([Ca2+]i). Human PAR-2 (hPAR-2) resided both on the plasma membrane and in the Golgi apparatus. hPAR-2 mRNA was highly expressed in human pancreas, kidney, colon, liver and small intestine, and by A549 lung and SW480 colon adenocarcinoma cells. Hybridization in situ revealed high expression in intestinal epithelial cells throughout the gut. Trypsin and AP stimulated an increase in [Ca2+]i in a rat intestinal epithelial cell line (hBRIE 380) and stimulated amylase secretion in isolated pancreatic acini. In A549 cells, which also responded to trypsin and AP with mobilization of cytosolic Ca2+, AP inhibited colony formation. Thus PAR-2 may serve as a trypsin sensor in the gut. Its expression by cells and tissues not normally exposed to pancreatic trypsin suggests that other proteases could serve as physiological activators.
463 citations
TL;DR: A key role is suggested for the type III secretion system of pathogenic bacteria to coordinate secretion with expression of virulence factors after physical contact with the target cell.
Abstract: Upon contact with the eukaryotic cell, Yersinia pseudotuberculosis increased the rate of transcription of virulence genes (yop), as determined by in situ monitoring of light emission from individual bacteria expressing luciferase under the control of the yopE promoter. The microbe-host interaction triggered export of LcrQ, a negative regulator of Yop expression, via the Yop-type III secretion system. The intracellular concentration of LcrQ was thereby lowered, resulting in increased expression of Yops. These results suggest a key role for the type III secretion system of pathogenic bacteria to coordinate secretion with expression of virulence factors after physical contact with the target cell.
424 citations
TL;DR: Results indicate a close correlation between the mechanisms of bacterial internalization into non‐phagocytic cells and those that lead to macrophage cytotoxicity.
Abstract: We have shown by a variety of microscopical and biochemical techniques that Salmonella spp. are cytotoxic for cultured J774A.1 and bone marrow-derived murine macrophages. The cytotoxicity is initially manifested by inhibition of membrane ruffling and macropinocytosis in infected macrophages, and is followed by cell death. Macrophages killed by Salmonella spp. exhibited features of apoptosis such as condensation and fragmentation of chromatin, membrane blebbing, and the presence of cytoplasmic nucleosomes and apoptotic bodies. Cytotoxicity does not require bacterial internalization as cytochalasin D, a drug that prevents bacterial uptake, did not prevent Salmonella-induced macrophage cell death. However, the cytotoxic effects are strictly dependent upon the expression of the invasion-associated Type III protein-secretion system encoded at centisome 63 of the Salmonella chromosome. Wild-type Salmonella typhimurium grown under conditions that do not allow optical expression of this system or strains of Salmonella carrying mutations in genes that encode components of this protein-secretion system were devoid of macrophage cytotoxicity. In addition, mutations in invJ, spaO, sipB, sipC and sipD, which encode proteins that are secreted via this secretion apparatus and are required for bacterial entry into non-phagocytic cells, also abolished the toxicity. In contrast, mutations in sipA and sptP, which encode secreted proteins that are not required for bacterial invasion, had no effect on macrophage cytotoxicity. These results indicate a close correlation between the mechanisms of bacterial internalization into non-phagocytic cells and those that lead to macrophage cytotoxicity. Host-adapted serotypes of Salmonella such as S. typhi, S. gallinarum and S. dublin were also toxic for murine macrophages, indicating that this virulence property is probably present in most Salmonella spp. and is not associated with the mechanisms responsible for host range.
420 citations
01 Sep 1996
TL;DR: It is suggested that the central nervous system may regulate IL-12 and IL-10 secretion and, hence, TH1/TH2 balance via the peripheral end-effectors of the stress system, which may cause a selective suppression of TH1 functions and a shift toward a TH2 cytokine pattern rather than generalized TH suppression.
Abstract: Interleukin-12 (IL-12) is a key inducer of differentiation of uncommitted T helper (TH) cells toward the TH1 phenotype, which regulates cellular immunity, whereas IL-10 inhibits TH1 functions and potentiates TH2-regulated responses (ie, humoral immunity) To examine the potential effects of stress on TH1/TH2 balance, we studied the ability of three prototype stress hormones-dexamethasone (a synthetic glucocorticoid) and the catecholamines norepinephrine and epinephrine-to alter the production of IL-12 (p70) and IL-10 induced by bacterial lipopolysaccharide (LPS) in human whole blood Dexamethasone inhibited LPS-induced bioactive IL-12 production in a dose-dependent fashion and at physiologically relevant concentrations; it had no effect on IL-10 secretion The glucocorticoid-induced reduction of IL-12 production was antagonized by RU 486, a glucocorticoid-receptor antagonist, suggesting that it was mediated by the glucocorticoid receptor Norepinephrine and epinephrine also suppressed IL-12 production in a dose-dependent fashion and at physiological concentrations; both catecholamines, however, dose-dependently increased the production of IL-10 The effects of either catecholamine on IL-12 or IL-10 secretion were blocked completely by propranolol, a beta-adrenoreceptor antagonist, indicating that they were mediated by the beta-adrenergic receptor These findings suggest that the central nervous system may regulate IL-12 and IL-10 secretion and, hence, TH1/TH2 balance via the peripheral end-effectors of the stress system Thus, stress may cause a selective suppression of TH1 functions and a shift toward a TH2 cytokine pattern rather than generalized TH suppression The TH1-to-TH2 shift may be responsible for the stress-induced susceptibility of the organism to certain infections Through the same or a reciprocal mechanism, states associated with chronic hyperactivity or hypoactivity of the stress system might influence the susceptibility of an individual to certain autoimmune, allergic, infectious, or neoplastic diseases
416 citations
TL;DR: It is proposed that YopB is essential for the formation of a pore in the target cell membrane that is required for the cell‐to‐cell transfer of Yop effector proteins.
Abstract: During infection of cultured epithelial cells, surface-located Yersinia pseudotuberculosis deliver Yop (Yersinia outer protein) virulence factors into the cytoplasm of the target cell. A non-polar yopB mutant strain displays a wild-type phenotype with respect to in vitro Yop regulation and secretion but fails to elicit a cytotoxic response in cultured HeLa cells and is unable to inhibit phagocytosis by macrophage-like J774 cells. Additionally, the yopB mutant strain was avirulent in the mouse model. No YopE or YopH protein were observed within HeLa cells infected with the yopB mutant strain, suggesting that the loss of virulence of the mutant strain was due to its inability to translocate Yop effector proteins through the target cell plasma membrane. Expression of YopB is necessary for Yersinia-induced lysis of sheep erythrocytes. Purified YopB was shown to have membrane disruptive activity in vitro. YopB-dependent haemolytic activity required cell contact between the bacteria and the erythrocytes and could be inhibited by high, but not low, molecular weight carbohydrates. Similarly, expression of YopE reduced haemolytic activity. Therefore, we propose that YopB is essential for the formation of a pore in the target cell membrane that is required for the cell-to-cell transfer of Yop effector proteins.
412 citations
TL;DR: Using cells from TCR transgenic mice that do or do not express Fas, it is shown that there are two mechanistically distinct forms of apoptosis in CD4+ T cells and that peripheral tolerance may be induced in vivo independent of Fas-mediated cell death.
TL;DR: The proteins found to function in the synapse are related to those in yeast and other organisms, demonstrating that the mechanisms that mediate vesicle trafficking are conserved in all eukaryotic species.
Abstract: Secretion of neurotransmitter is the primary means of intercellular communication within the nervous system. This process is regulated by a highly orchestrated cycle of membrane trafficking within the presynaptic nerve terminal. Characterization of proteins localized to the synaptic vesicle and the subsequent studies of their properties have led to a model for the biochemical pathway that underlies vesicle docking, activation, and fusion. The proteins found to function in the synapse are related to those in yeast and other organisms, demonstrating that the mechanisms that mediate vesicle trafficking are conserved in all eukaryotic species.
TL;DR: The dramatic effects of interferon beta‐1b on gelatinase expression and migration raise the possibility that its beneficial effects in multiple sclerosis may result from interference with the capacity of activated T cells to traverse the basement membrane and migrate to the central nervous system.
Abstract: Treatment with interferon beta-1b has substantial clinical benefit in the demyelinating disease multiple sclerosis, yet the mechanism of action in the disease remains largely unknown. Gelatinase A (matrix metalloproteinase-2, 72-kd gelatinase) and B (matrix metalloproteinase-9, 92-kd gelatinase) are matrix metalloproteinases capable of enzymatic digestion of subendothelial basement membrane constituents. In human T cells, interleukin-2 induces gelatinase secretion and enhances gelatinase-dependent migration across an artificial basement membrane-like layer in vitro. Pretreatment of T cells with interferon beta-1b for 48 hours decreased interleukin-2-induced gelatinase production and secretion as determined by zymography. In parallel to the downregulation of gelatinase secretion, pretreatment with interferon beta-1b inhibited T-cell migration across the basement membrane in vitro by up to 90%, but had only a minor impact on cell locomotion per se. For both gelatinase secretion and T-cell migration, the inhibitory effect mediated by exposure to interferon beta-1b was dose dependent. Fluorescence-activated cell sorter analysis also showed that interferon beta-1b downregulates the interleukin-2 receptor alpha-chain and lowered the affinity of interleukin-2 to the cell surface by 30%, which may represent an additional mechanism for the observed effects of interferon beta-1b. The dramatic effects of interferon beta-1b on gelatinase expression and migration raise the possibility that its beneficial effects in multiple sclerosis may result from interference with the capacity of activated T cells to traverse the basement membrane and migrate to the central nervous system.
TL;DR: Hsp47 is a novel stress protein in the endoplasmic reticulum that binds specifically to various types of collagens and procollagens, and is involved in collagen processing and/or secretion under normal conditions.
TL;DR: It is shown that Zn-SMase activity is secreted by human and murine macrophages, human skin fibroblasts, microglial cells, and several other cells in culture and is markedly up-regulated during differentiation of human monocytes to macrophage.
TL;DR: The results provide the basis for the conclusion that the maintenance of pH gradients between acidic vesicular compartments and a mildly alkaline cytoplasm is an essential biochemical requirement for the correct functioning of the endocytotic and secretory machinery.
Abstract: Alkalinization of normally acidic intracellular compartments or acidification of a mildly alkaline cytoplasm by biochemical or genetic manipulation has been demonstrated to inhibit both endocytosis and secretion (Tartakoff, 1983a; Cosson et al., 1989; Mellman et al., 1986; Davoust et al., 1987; Cosson et al., 1989; van Deurs et al., 1989; Maxfield & Yamashiro, 1991; Hansen et al., 1993). These results provide the basis for the conclusion that the maintenance of pH gradients between acidic vesicular compartments and a mildly alkaline cytoplasm is an essential biochemical requirement for the correct functioning of the endocytotic and secretory machinery. Tumor cells have been shown to have an abnormally acidic cytoplasmic pH (Warburg, 1956; Simon & Schindler, 1994). Here we report that the intracellular vesicular compartments in tumor cells (MCF-7) derived from a human breast cancer fail to acidify. This failure results in a significant decrease in the pH gradient (0.9 pH unit) between the vesicular luminal compartments and the cytoplasm. These defects are correlated with a disruption in the organization and function of the trans-Golgi network (TGN) and the pericentriolar recycling compartment (PRC). In marked distinction, drug-resistant tumor cells (MCF-7adr) derived from the MCF-7 line that are resistant to the most widely employed chemotherapeutic drug, adriamycin, appear normal in both acidification and organization of the PRC and TGN. Treatment of drug-resistant MCF-7adr cells with nigericin and monensin, ionophores demonstrated to disrupt vesicular acidification (Tartakoff, 1983b), leads to a resensitization of these cells to adriamycin. Drug sensitivity is proposed to result from an acidification defect within vesicles of the recycling and secretory pathways. A functional consequence of this defect is the diminished capacity of cells to remove cytotoxic drugs from the cytoplasm by sequestration of protonated drugs within the vesicles, followed by drug secretion through the activity of the secretory and recycling pathways.
Journal Article•
TL;DR: The human T cell response to Ags prepared from Yersinia enterocolitica and Ascaris suum with respect to cytokine mRNA-synthesis and secretion is analyzed to determine whether a subset of human chemokines is associated with a specific type of immune response.
Abstract: Lymphocytes regulate the immune response by secreting cytokines that control the activity and function of effector cells. Chemokine subsets are ideal candidates for recruitment of specific effector cells to inflammatory sites or to other lesions because of their selective chemoattractant activities. Given the Th1-Th2 model of immune regulation and the particular role of leukocyte recruitment for the outcome of the response, we analyzed whether a subset of human chemokines is associated with a specific type of immune response. Therefore, we have analyzed the human T cell response to Ags prepared from Yersinia enterocolitica and Ascaris suum with respect to cytokine mRNA-synthesis and secretion. For the Gram-negative bacterium Y. enterocolitica, induction of a type 1 response is indicated by IL-2 and IFN-gamma production, and for the nematode A. suum, a type 2 response is based on IL-4 and IL-5 production. Interestingly, expression of three CC-chemokines (i.e., MIP-1alpha, MIP-1beta, and RANTES) correlated with the type 1 response induced by Y. enterocolitica Ag. Chemokine secretion is not restricted to T lymphocytes; therefore, synthesis of MIP-1alpha, MIP-1beta, and RANTES was also characterized in human T cell clones that display a cytokine pattern indicative of the Th2, Th0, or Th1 phenotype. Again CC-chemokine secretion correlated with the Th1-like phenotype. In six analyzed IL-2- and IFN-gamma- secreting Th1 clones and in two Th0 clones, MIP-1alpha, MIP-1beta, and RANTES were detected, while none or only minimal secretion of these CC-chemokines was observed in three IL-4- and IL-5-producing Th2 cell clones.
Journal Article•
TL;DR: Results indicate that IFN-gamma produced by T and NK cells after CpG DNA stimulation contributes to the B cell production of IL-6 and the subsequent Ig production, providing further evidence that the immune system responds to C pG motifs in bacterial DNA by activating a coordinated set of humoral and cellular responses.
Abstract: Lymphocyte recognition of characteristic structural features in microbial DNA may contribute to immune defense by promoting protective immune responses The dinucleotide CpG is significantly under-represented in vertebrate DNA and is usually methylated In contrast, CpG dinucleotides are generally present at the expected frequency in bacterial DNA and are unmethylated These unmethylated CpG motifs induce B cells to secrete IL-6 and IgM, and can induce NK and CD4+ T cells to produce the immunoregulatory Th1 cytokine, IFN-gamma IFN-gamma inhibits IgM secretion that is triggered by a different bacterial product, LPS The present study demonstrates that in contrast to its antagonistic interaction with LPS, IFN-gamma causes a dose-dependent increase in the level of IgM secretion induced by CpG DNA Like IgM secretion, B cell secretion of IL-6 more than doubles after the addition of exogenous IFN-gamma Mice with disrupted IFN-gamma genes produced less than half as much IL-6 and IgM in response to CpG DNA, supporting the hypothesis that CpG-induced IFN-gamma production contributes to the B cell response In contrast to its promotion of IL-6 and IgM secretion, IFN-gamma did not significantly affect the spleen cell proliferation activated by CpG motifs These results indicate that IFN-gamma produced by T and NK cells after CpG DNA stimulation contributes to the B cell production of IL-6 and the subsequent Ig production These studies provide further evidence that the immune system responds to CpG motifs in bacterial DNA by activating a coordinated set of humoral and cellular responses
TL;DR: It is speculated that tension is a global parameter that the cell uses to control physically plasma membrane dynamics, cell shape and cell motility.
TL;DR: It is suggested that TGF-beta1 is produced in MM by both tumor cells and BMSCs, with related tumore cell growth, and that MM cell growth may be enhanced by resistance of tumor cells to the inhibitory effects of TGF -beta1 on normal B-cell proliferation and Ig secretion.
TL;DR: SirA, a gene located outside the pathogenicity island that is essential for induction of prgHIJK and hilA transcription, is identified and SirA phosphorylation is predicted to initiate a cascade of transcription‐factor synthesis which results in invasion‐gene transcription, Ssp secretion, and bacterial invasion of epithelia.
Abstract: The Salmonella typhimurium PhoP-repressed locus prgHIJK encodes components of a sec-independent type III secretion apparatus. This apparatus is composed of at least 17 proteins encoded on a 40 kb pathogenicity Island located at centisome 63 on the S. typhimurium chromosome. The secretion apparatus and some of its targets, SapB, SapC and SspD, are necessary for epithelial cell invasion. The transcription of many invasion genes, including prgHIJK, is coordinately activated by HilA, a transcription factor encoded within the pathogenicity island. In this report we identify sirA, a gene located outside the pathogenicity island that is essential for induction of prgHIJK and hilA transcription. sirA encodes a 234-amino-acid protein that is essential for S. typhimurium Ssp (Salmonella secreted protein) secretion and invasion and is similar to response regulators of two-component regulatory systems. sirA-mutant phenotypes could be suppressed by two DNA clones from unlinked loci, designated sirB and sirC. These data suggest that SirA may be phosphorylated in response to S. typhimurium sensing a mammalian microenvironment. Furthermore, SirA phosphorylation is predicted to initiate a cascade of transcription-factor synthesis which results in invasion-gene transcription, Ssp secretion, and bacterial invasion of epithelia.
TL;DR: Serotonin receptors provide a novel pharmacological target to reduce these derivatives in Alzheimer's disease as generation of APPs precludes the formation of amyloidogenic derivatives.
TL;DR: The Yop secretory apparatus, called Ysc, for Yop secretion, is the archetype of type III secretion systems (which serve for the secretion of virulence proteins by several animal and plant pathogens) and is related to the flagellar assembly apparatus.
Abstract: Pathogenic yersiniae secrete about a dozen anti-host proteins, the Yops, by a pathway which does not involve cleavage of a classical signal peptide. The Yop secretory apparatus, called Ysc, for Yop secretion, is the archetype of type III secretion systems (which serve for the secretion of virulence proteins by several animal and plant pathogens) and is related to the flagellar assembly apparatus. The Yop secretion signal is N-terminal but has not been defined to date. Apart from the Ysc machinery, secretion of at least four Yops requires cytoplasmic proteins called Syc (for specific Yop chaperone). Each Syc protein binds to its cognate Yop. Unlike most cytoplasmic chaperones, these proteins do not have an ATP-binding domain, and are presumably devoid of ATPase activity. They share a few common properties: an acidic pl, a size in the range of 15-20 kDa, and a putative amphipathic alpha-helix in the C-terminal portion. They were recently shown to have counterparts in other pathogenic bacteria, where they appear to have a similar function.
TL;DR: Galectin-1 is expressed in yeast and this export does not require the classical secretory pathway nor the yeast multidrug resistance-like protein Ste6p, the transporter for the peptide a factor, to be exported.
Abstract: Several physiologically important proteins lack a classical secretory signal sequence, yet they are secreted from cells. To investigate the secretion mechanism of such proteins, a representative mammalian protein that is exported by a nonclassical mechanism, galectin-1, has been expressed in yeast. Galectin-1 is exported across the yeast plasma membrane, and this export does not require the classical secretory pathway nor the yeast multidrug resistance-like protein Ste6p, the transporter for the peptide a factor. A screen for components of the export machinery has identified genes that are involved in nonclassical export. These findings demonstrate a new pathway for protein export that is distinct from the classical secretory pathway in yeast.
TL;DR: Because posttranslational modifications of proteins determine their activity and stability, alterations in the extent and level of various modifications such as phosphorylation, methylation, ADP-ribosylation, oxidation, glycation, and conformations during aging are being studied.
TL;DR: The primary difference between 1 and 4 d of hyperinsulinemia in conjunction with carbohydrate hyperalimentation is the increase in hepatic secretion of preformed FA into VLDL-TG.
Abstract: Triglycerides (TG) are synthesized in the liver principally from two sources of fatty acids (FA): FA synthesized de novo in the liver and preformed FA. We have measured the rate of secretion of de novo synthesized FA and total secretion of FA bound to VLDL-TG in healthy men (n = 5) in the basal state, and after 1 (day 1) and 4 d (day 4) of a hypercaloric carbohydrate diet (approximately 2.5 times energy expenditure) that generated a moderate endogenous hyperinsulinemia (plasma insulin approximately 60 microU/ml). Prolonged carbohydrate hyperalimentation/hyperinsulinemia increased plasma VLDL-TG approximately 10-fold in part due to a 3.4-fold increase in total VLDL-TG secretion rate (basal state = 72+/-23, day 4 = 242+/-78 micromol TG/kg/d). Although the secretion of de novo synthesized FA increased throughout the study (basal state = 1.1+/-0.4, day 1 = 15.9+/-7.9, day 4 = 50.0+/-18.8 micromol TG/ kg/d), the 2.7-fold increase in secretion rate of preformed FA (basal state = 70+/-23, day 4 = 191+/-57 micromol TG/kg/d) quantitatively contributed the most to total VLDL-TG secretion rate. Decreased catabolism of VLDL-TG also contributed to the hypertriglyceridemia as reflected by an approximately fourfold decrease in both fractional turnover rate (basal state = 9.2+/-3.8, day 1 = 2.1+/-0.2, day 4 = 2.1+/-0.3 pools/d) and rate of clearance (basal state = 0.35+/-0.08, day 1 = 0.11+/-0.01, day 4 = 0.09+/-0.01 liter/kg/d) of VLDL-TG. Thus, the primary difference between 1 and 4 d of hyperinsulinemia in conjunction with carbohydrate hyperalimentation is the increase in hepatic secretion of preformed FA into VLDL-TG.
TL;DR: It is demonstrated that increased levels of activin signaling through ActRII in hepatocytes and the glandular stomach causes the hepatocellular necrosis and depletion of parietal cells in the glandsular stomach as well as the severe weight loss in vivo.
Abstract: Activins and inhibins, members of the transforming growth factor-beta superfamily, are involved in diverse physiological and developmental processes. We have previously shown that mice deficient in alpha-inhibin develop gonadal sex cord-stromal tumors at an early age. The tumor development is rapidly followed by a wasting syndrome that includes severe weight loss, hepatocellular necrosis around the central vein, and depletion of the parietal cells in the glandular stomach. The liver histology in inhibin-deficient mice is similar to the pathological effects of short-term treatment of rats and mice with recombinant activin A. Consistent with these findings, we have shown that the gonadal tumors in the inhibin-deficient mice secrete high levels of activins. In addition, Northern blot analysis has localized activin receptor type II (ActRII) to the liver. Based on these studies, we postulated that tumor-produced activins act through ActRII to cause the wasting syndrome in inhibin-deficient mice. To test this hypothesis and determine the significance of elevated levels of activin signaling through ActRII in vivo, we generated compound homozygous mutant mice deficient in both alpha-inhibin and ActRII. Despite the continued development of gonadal sex cord-stromal tumors and elevated serum levels of activin A and B, the compound homozygous mutant mice suffered no unusual weight loss, and the stomachs and livers of the majority of the mice were histologically normal. These results demonstrate that increased levels of activin signaling through ActRII in hepatocytes and the glandular stomach causes the hepatocellular necrosis and depletion of parietal cells in the glandular stomach as well as the severe weight loss in vivo.
TL;DR: To identify the regions of YopE from Yersinia pseudotuberculosis that are necessary for its translocation across the bacterial and eukaryotic cellular membranes, a series of hybrid genes were constructed which consisted of various amounts of yopE fused to the adenylate cyclase-encoding domain of the cyclolysin gene (cyaA) of Bordetella pertussis.
Abstract: Pathogenic yersiniae deliver a number of different effector molecules, which are referred to as Yops, into the cytosol of eukaryotic cells via a type III secretion system. To identify the regions of YopE from Yersinia pseudotuberculosis that are necessary for its translocation across the bacterial and eukaryotic cellular membranes, we constructed a series of hybrid genes which consisted of various amounts of yopE fused to the adenylate cyclase-encoding domain of the cyclolysin gene (cyaA) of Bordetella pertussis. By assaying intact cells for adenylate cyclase activity, we show that a YopE-Cya protein containing just the 11 amino-terminal residues of YopE is efficiently exported to the exterior surface of the bacterial cell. Single amino acid replacements of the first seven YopE residues significantly decreased the amount of reporter protein detected on the cell surface, suggesting that the extreme amino-terminal region of YopE is recognized by the secretion machinery. As has recently been shown for the Y. enterocolitica YopE protein (M.-P. Sory, A. Boland, I. Lambermont, and G. R. Cornelis, Proc. Natl. Acad. Sci. USA 92:11998-12002, 1995), we found that export to the cell surface was not sufficient for YopE-Cya proteins to be delivered into the eukaryotic cytoplasm. For traversing the HeLa cell membrane, at least 49 yopE-encoded residues were required. Replacement of leucine 43 of YopE with glycine severely affected the delivery of the reporter protein into HeLa cells. Surprisingly, export from the bacterial cell was also not sufficient for YopE-Cya proteins to be released from the bacterial cell surface into the culture supernatant. At least 75 residues of YopE were required to detect activity of the corresponding reporter protein in the culture supernatant, suggesting that a release domain exists in this region of YopE. We also show that the chaperone-like protein YerA required at least 75 YopE residues to form a stable complex in vitro with YopE-Cya proteins and, furthermore, that YerA is not required to target YopE-Cya proteins to the secretion complex. Taken together, our results suggest that traversing the bacterial and eukaryotic membranes occurs by separate processes that recognize distinct domains of YopE and that these processes are not dependent on YerA activity.
TL;DR: This review emphasizes important structural and functional features of proton-secreting cells, describes the tissue distribution of these cells and discusses the known functions ofThese cells in their respective epithelia.
Abstract: Several transporting epithelia in vertebrates and invertebrates contain cells that are specialized for proton or bicarbonate secretion. These characteristic 'mitochondria-rich' (MR) cells have several typical features, the most important of which is an extremely high expression of a vacuolar-type proton-pumping ATPase (H+V-ATPase) both on intracellular vesicles and on specific domains of their plasma membrane. Physiological modulation of proton secretion is achieved by recycling the H+V-ATPase between the plasma membrane and the cytoplasm in a novel type of nonclathrin-coated vesicle. In the kidney, these cells are involved in urinary acidification, while in the epididymis and vas deferens they acidify the luminal environment to allow normal sperm development. Osteoclasts are non-epithelial MR cells that use H+V-ATPase activity for bone remodeling. In some insects, similar cells in the midgut energize K+ secretion by means of a plasma membrane H+V-ATPase. This review emphasizes important structural and functional features of proton-secreting cells, describes the tissue distribution of these cells and discusses the known functions of these cells in their respective epithelia.
TL;DR: It is proposed that mechanisms similar to those reported here may contribute to adrenergic and peptidergic inhibition of secretion in other neuroendocrine cells and in nerve terminals.