scholarly journals Acid-Resistant Bovine Pestivirus Requires Activation for pH-Triggered Fusion during Entry

2005 ◽  
Vol 79 (7) ◽  
pp. 4191-4200 ◽  
Author(s):  
Thomas Krey ◽  
Heinz-Jürgen Thiel ◽  
Till Rümenapf
Keyword(s):  
Disulfide Bonds ◽  
Low Ph ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Acidic Ph ◽  
Diarrhea Virus ◽  
Endosomal Membrane ◽  
Endosomal Acidification ◽  
Mdbk Cells ◽  
Low Efficiency

ABSTRACT The route of internalization of the pestivirus bovine viral diarrhea virus (BVDV) was studied by using different chemical and biophysical inhibitors of endocytosis. Expression of the dominant-negative mutant DynK44A of the GTPase dynamin in MDBK cells, as well as the treatment of the cells with chlorpromazine and β-methyl-cyclodextrin inhibited BVDV entry. BVDV infection was also abolished by potassium (K+) depletion, hyperosmolarity, and different inhibitors of endosomal acidification. We conclude that BVDV likely enters the cell by clathrin-dependent endocytosis and that acidification initiates fusion with the endosomal membrane. Further studies revealed that BVDV was unable to undergo “fusion from without” at low pH. The finding that low pH is not sufficient to force adsorbed BVDV into fusion with the plasma membrane is compatible with the remarkable resistance of pestiviruses to inactivation by low pH. The importance of the abundant intra- and intermolecular disulfide bonds in BVDV glycoproteins for virus stability was studied by the use of reducing agents. The combination of dithiothreitol and acidic pH led to partial inactivation of BVDV and allowed fusion from without at low efficiency. Evidence is provided here that acid-resistant BVDV is destabilized during endocytosis to become fusogenic at an endosomal acidic pH. We suggest that destabilization of the virion occurs by breakage of disulfide bonds in the glycoproteins by an unknown mechanism.

The exosome pathway in K562 cells is regulated by Rab11

2002 ◽  
Vol 115 (12) ◽  
pp. 2505-2515 ◽  
Author(s):  
Ariel Savina ◽  
Michel Vidal ◽  
Maria I. Colombo
Keyword(s):  
Transferrin Receptor ◽  
K562 Cells ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Rab Proteins ◽  
Multivesicular Bodies ◽  
Red Cell ◽  
Cell Type ◽  
Extracellular Medium ◽  
Endosomal Membrane

During maturation, reticulocytes lose some membrane proteins that are not required on the mature red cell surface. The proteins are released into the extracellular medium associated with vesicles that are formed by budding of the endosomal membrane into the lumen of the compartment; this process results in the formation of multivesicular bodies (MVBs). Fusion of MVBs with the plasma membrane results in secretion of the small internal vesicles, termed exosomes. K562 cells release exosomes with similar characteristics to reticulocyte exosomes, in particular the transferrin receptor (TfR) is found associated with the vesicles. Interestingly, this cell line has been shown to possess high amounts of Rab11 compared with other Rab proteins. To assess the regulation of transferrin receptor release via exosome secretion by Rab11 in this cell type, K562 cells were stably transfected with GFP-Rab11wt or the GTP- and GDP-locked mutants. The distribution of the proteins was assessed by fluorescence microscopy. Transferrin recycling and the number of TfRs present on the surface of the transfected cells were reduced by overexpression of either Rab11wt or the mutants. The amount of released exosomes was analyzed by measuring different molecular markers present on these vesicles either biochemically or by western blot. Overexpression of the dominant-negative mutant Rab11S25N inhibited exosome release, whereas the secretion of exosomes was slightly stimulated in cells transfected with Rab11wt. Taken together, the results demonstrate that in K562 cells Rab11 modulates the exosome pathway although the exact step involved is still not known.

scholarly journals Mouse Polyomavirus Enters Early Endosomes, Requires Their Acidic pH for Productive Infection, and Meets Transferrin Cargo in Rab11-Positive Endosomes

2006 ◽  
Vol 80 (9) ◽  
pp. 4610-4622 ◽  
Author(s):  
David Liebl ◽  
Francesco Difato ◽  
Lenka Horníková ◽  
Petra Mannová ◽  
Jitka Štokrová ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Dominant Negative ◽  
Jurkat Cells ◽  
Productive Infection ◽  
Dominant Negative Mutant ◽  
Acidic Ph ◽  
Recycling Endosome ◽  
Mouse Fibroblasts ◽  
Caveolin 1 ◽  
Early Endosomes

ABSTRACT Mouse polyomavirus (PyV) virions enter cells by internalization into smooth monopinocytic vesicles, which fuse under the cell membrane with larger endosomes. Caveolin-1 was detected on monopinocytic vesicles carrying PyV particles in mouse fibroblasts and epithelial cells (33). Here, we show that PyV can be efficiently internalized by Jurkat cells, which do not express caveolin-1 and lack caveolae, and that overexpression of a caveolin-1 dominant-negative mutant in mouse epithelial cells does not prevent their productive infection. Strong colocalization of VP1 with early endosome antigen 1 (EEA1) and of EEA1 with caveolin-1 in mouse fibroblasts and epithelial cells suggests that the monopinocytic vesicles carrying the virus (and vesicles containing caveolin-1) fuse with EEA1-positive early endosomes. In contrast to SV40, PyV infection is dependent on the acidic pH of endosomes. Bafilomycin A1 abolished PyV infection, and an increase in endosomal pH by NH4Cl markedly reduced its efficiency when drugs were applied during virion transport towards the cell nucleus. The block of acidification resulted in the retention of a fraction of virions in early endosomes. To monitor further trafficking of PyV, we used fluorescent resonance energy transfer (FRET) to determine mutual localization of PyV VP1 with transferrin and Rab11 GTPase at a 2- to 10-nm resolution. Positive FRET between PyV VP1 and transferrin cargo and between PyV VP1 and Rab11 suggests that during later times postinfection (1.5 to 3 h), the virus meets up with transferrin in the Rab11-positive recycling endosome. These results point to a convergence of the virus and the cargo internalized by different pathways in common transitional compartments.

scholarly journals Time- and Temperature-Dependent Activation of Hepatitis C Virus for Low-pH-Triggered Entry

2006 ◽  
Vol 80 (4) ◽  
pp. 1734-1741 ◽  
Author(s):  
Donna M. Tscherne ◽  
Christopher T. Jones ◽  
Matthew J. Evans ◽  
Brett D. Lindenbach ◽  
Jane A. McKeating ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Viral Entry ◽  
Ebola Virus ◽  
Virus Production ◽  
Low Ph ◽  
Acidic Ph ◽  
Prolonged Incubation ◽  
Diarrhea Virus ◽  
Concanamycin A

ABSTRACT Hepatitis C virus (HCV) is an important human pathogen associated with chronic liver disease. Recently, based on a genotype 2a isolate, tissue culture systems supporting complete replication and infectious virus production have been developed. In this study, we used cell culture-produced infectious HCV to analyze the viral entry pathway into Huh-7.5 cells. Bafilomycin A1 and concanamycin A, inhibitors of vacuolar ATPases, prevented HCV entry when they were present prior to infection and had minimal effect on downstream replication events. HCV entry therefore appears to be pH dependent, requiring an acidified intracellular compartment. For many other enveloped viruses, acidic pH triggers an irreversible conformational change, which promotes virion-endosomal membrane fusion. Such viruses are often inactivated by low pH. In the case of HCV, exposure of virions to acidic pH followed by return to neutral pH did not affect their infectivity. This parallels the observation made for the related pestivirus bovine viral diarrhea virus. Low pH could activate the entry of cell surface-bound HCV but only after prolonged incubation at 37°C. This suggests that there are rate-limiting, postbinding events that are needed to render HCV competent for low-pH-triggered entry. Such events may involve interaction with a cellular coreceptor or other factors but do not require cathepsins B and L, late endosomal proteases that activate Ebola virus and reovirus for entry.

scholarly journals Bovine Viral Diarrhea Virus Entry Is Dependent on Clathrin-Mediated Endocytosis

2005 ◽  
Vol 79 (16) ◽  
pp. 10826-10829 ◽  
Author(s):  
Steve Lecot ◽  
Sandrine Belouzard ◽  
Jean Dubuisson ◽  
Yves Rouillé
Keyword(s):  
Bovine Viral Diarrhea Virus ◽  
Kinase Inhibitor ◽  
Dominant Negative ◽  
Endocytic Pathway ◽  
Bovine Viral Diarrhea ◽  
Cellular Mechanisms ◽  
Diarrhea Virus ◽  
Viral Diarrhea ◽  
Mdbk Cells ◽  
Viral Diarrhea Virus

ABSTRACT Cellular mechanisms of bovine viral diarrhea virus (BVDV) entry in MDBK cells were investigated. Chloroquine, bafilomycin A1, or ammonium chloride inhibited BVDV infection, indicating that an acidic endosomal pH is required for BVDV entry. The tyrosine kinase inhibitor genistein partially inhibited BVDV infection at a postentry step, whereas BVDV entry was strongly inhibited by chlorpromazine or by the overexpression of a dominant-negative form of EPS15, a protein essential for the formation of clathrin-coated vesicles at the plasma membrane. Together, these data indicate that BVDV infection requires an active clathrin-dependent endocytic pathway.

scholarly journals Jaagsiekte Sheep Retrovirus Utilizes a pH-Dependent Endocytosis Pathway for Entry

2007 ◽  
Vol 82 (5) ◽  
pp. 2555-2559 ◽  
Author(s):  
Pascale Bertrand ◽  
Marceline Côté ◽  
Yi-Min Zheng ◽  
Lorraine M. Albritton ◽  
Shan-Lu Liu
Keyword(s):  
Leukemia Virus ◽  
Low Ph ◽  
Dominant Negative ◽  
Moloney Murine Leukemia Virus ◽  
Dominant Negative Mutant ◽  
Jaagsiekte Sheep Retrovirus ◽  
Early Entry ◽  
Ph Inactivation ◽  
Endocytosis Pathway ◽  
Ph Dependent

ABSTRACT Using Moloney murine leukemia virus pseudovirions bearing the envelope protein of Jaagsiekte sheep retrovirus (JSRV), we report here that entry was weakly inhibited by lysosomotropic agents but was profoundly blocked by bafilomycin A1 (BafA1). Kinetics studies revealed that JSRV entry is a slow process and was substantially blocked by a dominant-negative mutant of dynamin. Interestingly, a low-pH pulse overcame the BafA1 block to JSRV infection, although this occurred only if virus-bound cells were preincubated at 37°C, consistent with a very early entry event such as endocytosis being required before the low-pH-dependent step occurs. Moreover, JSRV pseudovirions were resistant to low-pH inactivation. Altogether, this study reveals that JSRV utilizes a pH-dependent, dynamin-associated endocytosis pathway for entry that differs from the classical pH-dependent entry pathway of vesicular stomatitis virus.

scholarly journals Protein kinase C-theta isoenzyme selective stimulation of the transcription factor complex AP-1 in T lymphocytes.

1996 ◽  
Vol 16 (4) ◽  
pp. 1842-1850 ◽  
Author(s):  
G Baier-Bitterlich ◽  
F Uberall ◽  
B Bauer ◽  
F Fresser ◽  
H Wachter ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Transcriptional Activation ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Kinase C ◽  
Pkc Isoforms ◽  
Pkc Alpha ◽  
Transcriptional Complex ◽  
Induced Signal ◽  
Transcription Factor Complex

T-lymphocyte stimulation requires activation of several protein kinases, including the major phorbol ester receptor protein kinase C (PKC), ultimately leading to induction of lymphokines, such as interleukin-2 (IL-2). The revelant PKC isoforms which are involved in the activation cascades of nuclear transcription factors involved in IL-2 production have not yet been clearly defined. We have examined the potential role of two representative PKC isoforms in the induction of the IL-2 gene, i.e., PKC-alpha and PKC-theta, the latter being expressed predominantly in hematopoietic cell lines, particularly T cells. Similar to that of PKC-alpha, PKC-theta overexpression in murine EL4 thymoma cells caused a significant increase in phorbol 12-myristate 13-acetate (PMA)-induced transcriptional activation of full-length IL-2-chloramphenicol acetyltransferase (CAT) and NF-AT-CAT but not of NF-IL2A-CAT or NF-kappaB promoter-CAT reporter gene constructs. Importantly, the critical AP-1 enhancer element was differentially modulated by these two distinct PKC isoenzymes, since only PKC-theta but not PKC-alpha overexpression resulted in an approximately 2.8-fold increase in AP-1-collagenase promoter CAT expression in comparison with the vector control. Deletion of the AP-1 enhancer site in the collagenase promoter rendered it unresponsive to PKC-theta. Expression of a constitutively active mutant PKC-theta A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-theta K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-RasS17N completely inhibited the PKC-O A148E-induced signal, PKC-O. Expression of a constitutively active mutant PKC-O A148E (but not PKC-alpha A25E) was sufficient to induce activation of AP-1 transcription factor complex in the absence of PMA stimulation. Conversely, a catalytically inactive PKC-O K409R (but not PKC-alpha K368R) mutant abrogated endogenous PMA-mediated activation of AP-1 transcriptional complex. Dominant negative mutant Ha-enRasS17N completely inhibited in the PKC-O A148E-induced signal, identifying PKC-theta as a specific constituent upstream of or parallel to Ras in the signaling cascade leading to AP transcriptional activation.

scholarly journals A Dominant-negative Mutant of Androgen Receptor Coregulator ARA54 Inhibits Androgen Receptor-mediated Prostate Cancer Growth

2001 ◽  
Vol 277 (7) ◽  
pp. 4609-4617 ◽  
Author(s):  
Hiroshi Miyamoto ◽  
Mujib Rahman ◽  
Hiroshi Takatera ◽  
Hong-Yo Kang ◽  
Shuyuan Yeh ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Androgen Receptor ◽  
Dominant Negative ◽  
Cancer Growth ◽  
Dominant Negative Mutant ◽  
Negative Mutant

Targeting mitochondria to overcome conventional and bortezomib/proteasome inhibitor PS-341 resistance in multiple myeloma (MM) cells

Blood ◽  
2004 ◽  
Vol 104 (8) ◽  
pp. 2458-2466 ◽  
Author(s):  
Dharminder Chauhan ◽  
Guilan Li ◽  
Klaus Podar ◽  
Teru Hideshima ◽  
Constantine Mitsiades ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Drug Exposure ◽  
Low Dose ◽  
Benzodiazepine Receptors ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Superoxide Generation ◽  
Insulin Growth Factor ◽  
Bortezomib Treatment ◽  
Induced Apoptosis

Abstract Bortezomib (PS-341), a selective inhibitor of proteasomes, induces apoptosis in multiple myeloma (MM) cells; however, prolonged drug exposure may result in cumulative toxicity and the development of chemoresistance. Here we show that combining PK-11195 (PK), an antagonist to mitochondrial peripheral benzodiazepine receptors (PBRs), with bortezomib triggers synergistic anti-MM activity even in doxorubicin-, melphalan-, thalidomide-, dexamethasone-, and bortezomib-resistant MM cells. No significant cytotoxicity was noted in normal lymphocytes. Low-dose combined PK and bortezomib treatment overcomes the growth, survival, and drug resistance conferred by interleukin-6 or insulin growth factor within the MM bone marrow milieu. The mechanism of PK + bortezomib–induced apoptosis includes: loss of mitochondrial membrane potential; superoxide generation; release of mitochondrial proteins cytochrome-c (cyto-c) and Smac; and activation of caspases-8/-9/-3. Furthermore, PK + bortezomib activates c-Jun NH2 terminal kinase (JNK), which translocates to mitochondria, thereby facilitating release of cyto-c and Smac from mitochondria to cytosol. Blocking JNK, by either dominant-negative mutant (DN-JNK) or cotreatment with a specific JNK inhibitor SP600125, abrogates both PK + bortezomib–induced release of cyto-c/Smac and induction of apoptosis. Together, these preclinical studies suggest that combining bortezomib with PK may enhance its clinical efficacy, reduce attendant toxicity, and overcome conventional and bortezomib resistance in patients with relapsed refractory MM.

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