scholarly journals Activation of the Phosphatidylinositol 3-Kinase/Akt Pathway Contributes to Survival of Primary Epithelial Cells Infected with the Periodontal Pathogen Porphyromonas gingivalis

2004 ◽  
Vol 72 (7) ◽  
pp. 3743-3751 ◽  
Author(s):  
Özlem Yilmaz ◽  
Thomas Jungas ◽  
Philippe Verbeke ◽  
David M. Ojcius
Keyword(s):  
Epithelial Cells ◽  
Host Cell ◽  
Porphyromonas Gingivalis ◽  
Periodontal Pathogen ◽  
Akt Pathway ◽  
Phosphatidylinositol 3 Kinase ◽  
Pi3k Inhibitor Ly294002 ◽  
Mitochondrial Membrane Depolarization ◽  
Infected Cells ◽  
Phosphatidylinositol 3

ABSTRACT Porphyromonas gingivalis, an important periodontal pathogen, infects primary gingival epithelial cells (GECs). Despite the large number of bacteria that replicate inside the GECs, the host cell remains viable. We demonstrate that P. gingivalis triggers rapid and reversible surface phosphatidylserine exposure through a mechanism requiring caspase activation. However, after 1 day of infection, the bacteria no longer induce phosphatidylserine externalization and instead protect infected cells against apoptosis. Infection exerts its effect at the level of mitochondria, as P. gingivalis also blocks depolarization of the mitochondrial transmembrane potential and cytochrome c release. Interestingly, protein kinase B/Akt is phosphorylated during infection, which can be blocked with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. Suppression of the PI3K/Akt pathway following staurosporine treatment results in mitochondrial-membrane depolarization, cytochrome c release, DNA fragmentation, and increased apoptosis of infected GECs. Thus, P. gingivalis stimulates early surface exposure of phosphatidylserine, which could downmodulate the inflammatory response, while also promoting host cell survival through the PI3K/Akt pathway.

scholarly journals Phosphatidylinositol 3-Kinase-Mediated Effects of Glucose on Vacuolar H+-ATPase Assembly, Translocation, and Acidification of Intracellular Compartments in Renal Epithelial Cells

2005 ◽  
Vol 25 (2) ◽  
pp. 575-589 ◽  
Author(s):  
Yuri Y. Sautin ◽  
Ming Lu ◽  
Andrew Gaugler ◽  
Li Zhang ◽  
Stephen L. Gluck
Keyword(s):  
Epithelial Cells ◽  
Apical Plasma Membrane ◽  
Proton Pumps ◽  
Coupling Mechanism ◽  
Phosphatidylinositol 3 Kinase ◽  
Ph Gradients ◽  
Renal Epithelial Cells ◽  
Pi3k Inhibitor Ly294002 ◽  
Intracellular Compartments ◽  
Phosphatidylinositol 3

ABSTRACT Vacuolar H+-ATPases (V-ATPases) are a family of ATP-driven proton pumps. They maintain pH gradients between intracellular compartments and are required for proton secretion out of the cytoplasm. Mechanisms of extrinsic control of V-ATPase are poorly understood. Previous studies showed that glucose is an important regulator of V-ATPase assembly in Saccharomyces cerevisiae. Human V-ATPase directly interacts with aldolase, providing a coupling mechanism for glucose metabolism and V-ATPase function. Here we show that glucose is a crucial regulator of V-ATPase in renal epithelial cells and that the effect of glucose is mediated by phosphatidylinositol 3-kinase (PI3K). Glucose stimulates V-ATPase-dependent acidification of the intracellular compartments in human proximal tubular cells HK-2 and porcine renal epithelial cells LLC-PK1. Glucose induces rapid ATP-independent assembly of the V1 and Vo domains of V-ATPase and extensive translocation of the V-ATPase V1 and Vo domains between different membrane pools and between membranes and the cytoplasm. In HK-2 cells, glucose stimulates polarized translocation of V-ATPase to the apical plasma membrane. The effects of glucose on V-ATPase trafficking and assembly can be abolished by pretreatment with the PI3K inhibitor LY294002 and can be reproduced in glucose-deprived cells by adenoviral expression of the constitutively active catalytic subunit p110α of PI3K. Taken together these data provide evidence that, in renal epithelial cells, glucose plays an important role in the control of V-ATPase-dependent acidification of intracellular compartments and V-ATPase assembly and trafficking and that the effects of glucose are mediated by PI3K-dependent signaling.

scholarly journals Intercellular Spreading of Porphyromonas gingivalis Infection in Primary Gingival Epithelial Cells

2006 ◽  
Vol 74 (1) ◽  
pp. 703-710 ◽  
Author(s):  
Özlem Yilmaz ◽  
Philippe Verbeke ◽  
Richard J. Lamont ◽  
David M. Ojcius
Keyword(s):  
Epithelial Cells ◽  
Porphyromonas Gingivalis ◽  
Propagation Rate ◽  
Significant Inhibition ◽  
Periodontal Pathogen ◽  
Extracellular Medium ◽  
Flow Cytofluorometry ◽  
Gingival Epithelial Cells ◽  
Infected Cells ◽  
Over Time

ABSTRACTPorphyromonas gingivalis, an important periodontal pathogen, is an effective colonizer of oral tissues. The organism successfully invades, multiplies in, and survives for extended periods in primary gingival epithelial cells (GECs). It is unknown whetherP. gingivalisresides in the cytoplasm of infected cells throughout the infection or can spread to adjacent cells over time. We developed a technique based on flow cytofluorometry and fluorescence microscopy to study propagation of the organism at different stages of infection of GECs. Results showed thatP. gingivalisspreads cell to cell and that the amount of spreading increases gradually over time. There was a very low level of propagation of bacteria to uninfected cells early in the infection (3 h postinfection), but there were 20-fold and 45-fold increases in the propagation rate after 24 h and 48 h, respectively, of infection. Immunofluorescence microscopy of infected cells suggested that intercellular translocation ofP. gingivalismay be mediated through actin-based membrane protrusions, bypassing the need for release of bacteria into extracellular medium. Consistent with these observations, cytochalasin D treatment of infected cells resulted in significant inhibition of bacterial spreading. This study shows for the first time thatP. gingivalisdisseminates from cell to cell without passing through the extracellular space. This mechanism of spreading may allowP. gingivalisto colonize oral tissues without exposure to the humoral immune response.

scholarly journals Enterococcus faecalis Infection Activates Phosphatidylinositol 3-Kinase Signaling To Block Apoptotic Cell Death in Macrophages

2014 ◽  
Vol 82 (12) ◽  
pp. 5132-5142 ◽  
Author(s):  
Jun Zou ◽  
Nathan Shankar
Keyword(s):  
Host Cell ◽  
Enterococcus Faecalis ◽  
Caspase 3 ◽  
Defense Mechanism ◽  
Apoptotic Cell ◽  
Immune Defense ◽  
Phosphatidylinositol 3 Kinase ◽  
Content Type ◽  
Infected Cells ◽  
Phosphatidylinositol 3

ABSTRACTApoptosis is an intrinsic immune defense mechanism in the host response to microbial infection. Not surprisingly, many pathogens have evolved various strategies to manipulate this important pathway to benefit their own survival and dissemination in the host during infection. To our knowledge, no attempts have been made to explore the host cell survival signals modulated by the bacteriumEnterococcus faecalis. Here, we show for the first time that during early stages of infection, internalized enterococci can prevent host cell (RAW264.7 cells, primary macrophages, and mouse embryonic fibroblasts [MEFs]) apoptosis induced by a wide spectrum of proapoptotic stimuli. Activation of caspase 3 and cleavage of the caspase 3 substrate poly(ADP-ribose) polymerase were inhibited inE. faecalis-infected cells, indicating thatE. faecalisprotects macrophages from apoptosis by inhibiting caspase 3 activation. This antiapoptotic activity inE. faecalis-infected cells was dependent on the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, which resulted in the increased expression of the antiapoptotic factor Bcl-2 and decreased expression of the proapoptotic factor Bax. Further analysis revealed that activeE. faecalisphysiology was important for inhibition of host cell apoptosis, and this feature seemed to be a strain-independent trait amongE. faecalisisolates. Employing a mouse peritonitis model, we also determined that cells collected from the peritoneal lavage fluid ofE. faecalis-infected mice showed reduced levels of apoptosis compared to cells from uninfected mice. These results show early modulation of apoptosis during infection and have important implications for enterococcal pathogenesis.

Phosphatidylinositol 3-Kinase/AKT Pathway Activation in Human Vestibular Schwannoma

2008 ◽  
Vol 29 (1) ◽  
pp. 58-68 ◽  
Author(s):  
Abraham Jacob ◽  
Tina X. Lee ◽  
Brian A. Neff ◽  
Shyra Miller ◽  
Bradley Welling ◽  
...  
Keyword(s):  
Vestibular Schwannoma ◽  
Akt Pathway ◽  
Phosphatidylinositol 3 Kinase ◽  
Pathway Activation ◽  
Phosphatidylinositol 3
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