Navegando por Autor "Stow, Jennifer L."
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Artigo Binding of the cytosolic p200 protein to Golgi membranes is regulated by heterotrimeric G proteins(Journal Of Cell Science, 1993) Almeida, Jose Bruno de; Doherty, Joanne; Ausiello, Dennis A.; Stow, Jennifer L.The formation of vesicles for protein trafficking requires the dynamic binding of cytosolic coat proteins onto Golgi membranes and this binding is regulated by a variety of GTPases, including heterotrimeric G proteins. We have previously shown the presence of the pertussis toxin-sensitive G i-3 protein on Golgi membranes and demonstrated a functional role for G i-3 in the trafficking of secretory proteins through the Golgi complex. We have also described a brefeldin A-sensitive phosphoprotein, p200, which is found in the cytoplasm and on Golgi membranes. The present study investigates the role of heterotrimeric G proteins in the regulation of p200 binding to Golgi membranes. An in vitro binding assay was used to measure the binding of cytosolic p200 to LLC-PK1 cell microsomal membranes and to purified rat liver Golgi membranes in the presence of specific activators of G proteins. The binding of p200 to Golgi membranes was compared to that of the coatomer protein -COP, for which G protein-dependent membrane binding has previously been established. Membrane binding of both p200 and -COP was induced maximally by activation of all G proteins in the presence of GTP S. More selective activation of the heterotrimeric G proteins, with AlFn or mastoparan, also induced membrane binding of p200 and -COP. Pertussis toxin pretreatment of Golgi membranes, to selectively inactivate G i-3, reduced the AlFn and mastoparan-induced binding of p200 to Golgi membranes, whereas no significant effect of pertussis toxin on -COP binding was found in this assay. The effect of pertussis toxin thus implicates G i-3, as one component of a regulatory pathway, in the binding of cytosolic p200 to Golgi membranes. The effects of AlFn and pertussis toxin on p200 membrane binding were also shown in intact cells by immunofluorescence staining. AlFn treatment of cells induced translocation of p200 from the cytoplasm onto the Golgi complex, resulting in a conformational change in some Golgi membranes. The translocation of p200 was blocked by pretreatment of intact NRK cells with pertussis toxin. The data presented here support the conclusion that the binding of the p200 protein to Golgi membranes involves regulation by the pertussis toxinsensitive heterotrimeric G proteins, specifically the G i-3 proteinArtigo Distribution and role of heterotrimeric G proteins in the secretory pathway of polarized epithelial cells(Journal Of Cell Science, 1993) Almeida, Jose Bruno de; Stow, Jennifer L.The movement of newly synthesized proteins in the constitutive secretory pathway, from their site of synthesis in the endoplasmic reticulum to the cell surface or to intracellular destinations, requires an orderly sequence of transport steps between membrane-bound compartments. Until recently, the trafficking and secretion of proteins through this pathway was thought to occur as a relatively automatic, unregulated series of events. Recent studies show that protein trafficking in the constitutive secretory pathway requires G T P hydrolysis by families of GTP-binding proteins (G proteins), which at multiple steps potentially provide regulation and specificity for protein trafficking. M any monomeric G proteins are known to be localized and functional on membrane compartments in the constitutive secretory pathway. Now, members of the heterotrimeric G protein family have also been localized on intracellular membranes and compartments such as the Golgi complex. We have studied the localization and targeting of G a subunits to distinct membrane domains in polarized epithelial cells. The distribution of different G a subunits on very specific membrane domains in cultured epithelial cells and in epithelial cells of the kidney cortex, is highly suggestive of roles for these G proteins in intracellular trafficking pathways. One of these G protein subunits, Gai-3, was localized on Golgi membranes. Studies on L L C -P K i cells overexpressing Gcti.3 provided evidence for its functional role in regulating the transport o f a constitutively secreted heparan sulfate proteoglycan through the Golgi complex. Inhibition or activation of heterotrimeric G proteins by pertussis toxin or by aluminium fluoride respectively, have provided further evidence for regulation of intracellular transport by pertussis toxin-sensitive G proteins. Although the functions of Golgi-associated G proteins are not yet understood at the molecular level, heterotrimeric G proteins have been implicated in the binding of cytosolic coat proteins and vesicle formation on Golgi membranes. Future studies will elucidate how multiple G proteins, of both the heterotrimeric and monomeric families, are involved in the regulation of Golgi function and protein trafficking in the secretory pathwayArtigo Entry of cholera toxin into polarized human intestinal epithelial cells. Identification of an early brefeldin a sensitive event required for A1-peptide generation(American Society for Clinical Investigation, 1993) Almeida, Jose Bruno de; Lencer, W. I.; Moe, S.; Stow, Jennifer L.; Ausiello, Dennis A.; Madara, J. L.The effect of brefeldin-A (BFA), a reversible inhibitor of vesicular transport, on cholera toxin (CT)-induced Cl- secretion (Isc) was examined in the polarized human intestinal cell line, T84. Pretreatment of T84 monolayers with 5 microM BFA reversibly inhibited Isc in response to apical or basolateral addition of 120 nM CT (2.4 +/- 0.5 vs. 68 +/- 3 microA/cm2, n = 5). In contrast, BFA did not inhibit Isc responses to the cAMP agonist VIP (63 +/- 7 microA/cm2). BFA had no effect on cell surface binding and endocytosis of a functional fluorescent CT analog or on the dose dependency of CT induced 32P-NAD ribosylation of Gs alpha in vitro. In contrast, BFA completely inhibited (> 95%) the ability of T84 cells to reduce CT to the enzymatically active A1-peptide. BFA had to be added within the first 10 min of CT exposure to inhibit CT-elicited Isc. The early BFA-sensitive step occurred before a temperature-sensitive step essential for apical CT action. These studies show that sequential steps are required for a biological response to apical CT: (a) binding to cell surfaces and rapid endocytosis; (b) early, BFA-sensitive vesicular transport essential for reduction of the A1-peptide; and (c) subsequent temperature-sensitive translocation of a signal (the A1-peptide or possibly ADP-ribose-Gs alpha) to the basolateral domainArtigo A heterotrimeric GProtein, G«i-3 , on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PKI epithelial cells(The Journal Of Cell Biology, 1991) Almeida, Jose Bruno de; Stow, Jennifer L.; Narula, Navneet; Holtzman, Eliezer J.; Ercolani, Louis; Ausiello, Dennis A.A heterotrimeric Gai subunit, «i- 3 , is localized on Golgi membranes in LLC-PKI and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence . The M-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The a;_3 subunit is found on isolated rat liver Golgi membranes by Western blotting and Gai -3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLCPKI cells were stably transfected with GO;-3 on an MT1, inducible promoter in order to overexpress ai-3 on Golgi membranes. The intracellular processing and constitutive secretion of the basement membrane heparan sulfate proteoglycan (HSPG) was measured in LLC-PK, cells. Overexpression of ai-3 on Golgi membranes in transfected cells retarded the secretion of HSPG and accumulated precursors in the medial-trans-Golgi . This effect was reversed by treatment of cells with pertussis toxin which results in ADP-ribosylation and functional uncoupling of Gai-3 on Golgi membranes. These results provide evidence for a novel role for the pertussis toxin sensitive Gai-3 protein in Golgi trafficking of a constitutively secreted protein in epithelial cellsArtigo Myosin II is associated with Golgi membranes: identification of p200 as nonmuscle myosin II on Golgi-derived vesicles(Journal Of Cell Science, 1997) Almeida, José Bruno de; Ikonen, Elina; Fath, Karl R.; Burgess, David R.; Ashman, Keith; Simons, Kai; Stow, Jennifer L.A variety of peripheral membrane proteins associate dynamically with Golgi membranes during the budding and trafficking of transport vesicles in eukaryotic cells. A monoclonal antibody (AD7) raised against Golgi membranes recognizes a peripheral membrane protein, p200, which associates with vesicles budding off the trans-Golgi network (TGN). Based on preliminary findings, a potential association between p200 and myosin on Golgi membranes was investigated. Immunofluorescence staining of cultured cells under a variety of fixation conditions was carried out using an antibody raised against chick brush border nonmuscle myosin II. We show that, in addition to being found in the cytoplasm or associated with stress fibres, nonmuscle myosin II is also specifically localized on Golgi membranes. Myosin II was also detected on Golgi membranes by immunoblotting and by immunogold labeling at the electron microscopy level where it was found to be concentrated on Golgi-derived vesicles. The association of myosin II with Golgi membranes is dynamic and was found to be enhanced following activation of G proteins. Myosin II staining of Golgi membranes was also disrupted by brefeldin A (BFA). Colocalization of the AD7 and myosin II antibodies at the light and electron microscopy levels led us to investigate the nature of the 200 kDa protein recognized by both antibodies. The 200 kDa protein immunoprecipiated by the AD7 antibody was isolated from MDCK cells and used for microsequencing. Amino acid sequence data enabled us to identify p200 as the heavy chain of nonmuscle myosin IIA. In addition, an extra protein (240 kDa) recognized by the AD7 antibody specifically in extracts of HeLa cells, was sequenced and identified as another actin-binding protein, filamin. These results show that nonmuscle myosin II is associated with Golgi membranes and that the vesicle-associated protein p200, is itself a heavy chain of myosin II.Artigo Purified epithelial Na+ channel complex contains the pertussis toxin-sensitive Gai-3 protein(Elsevier, 1992) Almeida, José Bruno de; Ausiello, Dennis A.; Stow, Jennifer L.; Cantiello, Horacio F.; Benos, Dale J.We have recently demonstrated that the amiloride-sensitive Na+ channel in the apical membrane of the renal epithelial cell line, A6, is modulated by the alpha i-3 subunit of the Gi-3 protein. We also showed that a 700-kDa protein complex can be purified from the membranes of A6 epithelia which (a) can reconstitute the amiloride-sensitive Na+ influx in liposomes and planar bilayer membranes and (b) consists of six major protein bands observed on reducing sodium dodecyl sulfate-polyacrylamide gels with molecular masses ranging from 35 to 320 kDa. The present study was undertaken to determine if the alpha i-3 subunit was a member of this Na+ channel complex. G alpha i structure and function were identified by Western blotting with specific G alpha i subunit antibodies and Na+ channel antibodies, through ADP-ribosylation with pertussis toxin, and by immunocytochemical localization of the Na+ channel and G alpha i proteins. We demonstrate that two protein substrates are ADP-ribosylated in the 700-kDa complex in the presence of pertussis toxin and are specifically immunoprecipitated with an anti-Na+ channel polyclonal antibody. One of these substrates, a 41-kDa protein, was identified as the alpha i-3 subunit of the Gi-3 protein on Western blots with specific antibodies. Na+ channel antibodies do not recognize G alpha i-3 on Western blots of Golgi membranes which contain alpha i-3 but not Na+ channel proteins, nor do they immunoprecipitate alpha i-3 from solubilized Golgi membranes; however, alpha i-3 is coprecipitated as part of the Na+ channel complex from A6 cell membranes by polyclonal Na+ channel antibodies. Both alpha i-3 and the Na+ channel have been localized in A6 cells by confocal imaging and immunofluorescence with specific antibodies and are found to be in distinct but adjacent domains of the apical cell surface. In functional studies, alpha i-3, but not alpha i-2, stimulates Na+ channel activity. These data are therefore consistent with the localization of Na+ channel activity and modulatory alpha i-3 protein at the apical plasma membrane, which together represent a specific signal transduction pathway for ion channel regulationArtigo Targeting of chimeric Gαi proteins to specific membrane domains(Journal of Cell Science, 1994) Almeida, Jose Bruno de; Holtzman, Eliezer J.; Peters, Philip; Ercolani, Louis; Ausiello, Dennis A.; Stow, Jennifer L.Heterotrimeric guanine nucleotide-regulatory (G) proteins are associated with a variety of intracellular membranes and specific plasma membrane domains. In polarized epithelial LLC-PK1 cells we have shown previously that endogenous Gαi-2 is localized on the basolateral plasma membrane, whereas Gαi-3 is localized on Golgi membranes. The targeting of these highly homologous Gαi proteins to distinct membrane domains was studied by the transfection and expression of chimeric Gαi proteins in LLC-PK1 cells. Chimeric cDNAs were constructed from the cDNAs for Gαi-3 and Gαi-2 and introduced into a pMXX eukaryotic expression vector containing a mouse metallothioneinI promotor. Stably transfected cell lines were produced that expressed either Gαi-2/3 or Gαi-3/2 chimeric proteins. Chimeric and endogenous Gαi proteins were detected in cells using specific carboxy-terminal peptide antibodies. Immunofluorescence staining was used to localize endogenous and chimeric Gαi proteins in LLC-PK1 cells. The staining of chimeric proteins was detected as an increased intensity of staining on membranes containing endogenous Gαi proteins. Using confocal microscopy and image analysis we localized Gαi-2 to a specific sub-domain of the lateral membrane of polarized cells, the chimeric Gαi-3/2 protein was then shown to colocalize with endognenous Gαi-2 in the same lateral plasma membrane domain. The chimeric Gαi-2/3 protein colocalized with endogenous Gαi-3 on Golgi membranes in LLC-PK1 cells. These results show that chimeric Gαi proteins were targeted to the same membrane domains as endogenous Gαi proteins and the specificity of their membrane targeting was conferred by the carboxy-terminal end of the proteins. These data provide the first evidence for specific targeting information contained in the carboxy termini of Gαi proteins, which appears to be independent of amino-terminal membrane attachment sites in these proteins