Ubiquitin-proteasome inhibition enhances tumor necrosis factor-a-induced apoptosis of nontransformed gastric epithelial cells

ABSTRACT Following infection with Neisseria gonorrhoeae, bacteria may ascend into the Fallopian tubes (FT) and induce salpingitis, a major cause of infertility. In the FT, interactions between mucosal epithelial cells and gonococci are pivotal events in the pathogen's infection cycle and the inflammatory response. In the current study, primary FT epithelial cells were infected in vitro with different multiplicities of infection (MOI) of Pil+ Opa+ gonococci. Bacteria showed a dose-dependent association with cells and induced the secretion of tumor necrosis factor alpha (TNF-α). A significant finding was that gonococcal infection (MOI = 1) induced apoptosis in approximately 30% of cells, whereas increasing numbers of bacteria (MOI = 10 to 100) did not induce apoptosis. Apoptosis was observed in only 11% of cells with associated bacteria, whereas >84% of cells with no adherent bacteria were apoptotic. TNF-α was a key contributor to apoptosis, since (i) culture supernatants from cells infected with gonococci (MOI = 1) induced apoptosis in naïve cultures, suggesting that a soluble factor was responsible; (ii) gonococcal infection-induced apoptosis was inhibited with anti-TNF-α antibodies; and (iii) the addition of exogenous TNF-α induced apoptosis, which was inhibited by the presence of increasing numbers of bacteria (MOI = 10 to 100). These data suggest that TNF-α-mediated apoptosis of FT epithelial cells is likely a primary host defense mechanism to prevent pathogen colonization. However, epithelial cell-associated gonococci have evolved a mechanism to protect the cells from undergoing TNF-α-mediated apoptosis, and this modulation of the host innate response may contribute to establishment of infection. Understanding the antiapoptotic mechanisms used by Neisseria gonorrhoeae will inform the pathogenesis of salpingitis and could suggest new intervention strategies for prevention and treatment of the disease.

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Keratin attenuates tumor necrosis factor–induced cytotoxicity through association with TRADD

The Journal of Cell Biology ◽

10.1083/jcb.200103078 ◽

2001 ◽

Vol 155 (3) ◽

pp. 415-426 ◽

Cited By ~ 117

Author(s):

Hiroyasu Inada ◽

Ichiro Izawa ◽

Miwako Nishizawa ◽

Eriko Fujita ◽

Tohru Kiyono ◽

...

Keyword(s):

Tumor Necrosis Factor ◽

Epithelial Cells ◽

Tumor Necrosis ◽

Mammary Epithelial Cells ◽

Mammary Epithelial ◽

Type I ◽

Death Domain ◽

Interacting Protein ◽

Induced Apoptosis ◽

Necrosis Factor

Keratin 8 and 18 (K8/18) are the major components of intermediate filament (IF) proteins of simple or single-layered epithelia. Recent data show that normal and malignant epithelial cells deficient in K8/18 are nearly 100 times more sensitive to tumor necrosis factor (TNF)–induced cell death. We have now identified human TNF receptor type 1 (TNFR1)–associated death domain protein (TRADD) to be the K18-interacting protein. Among IF proteins tested in two-hybrid systems, TRADD specifically bound K18 and K14, type I (acidic) keratins. The COOH-terminal region of TRADD interacted with the coil Ia of the rod domain of K18. Endogenous TRADD coimmunoprecipitated with K18, and colocalized with K8/18 filaments in human mammary epithelial cells. Overexpression of the NH2 terminus (amino acids 1–270) of K18 containing the TRADD-binding domain as well as overexpression of K8/18 in SW13 cells, which are devoid of keratins, rendered the cells more resistant to killing by TNF. We also showed that overexpressed NH2 termini of K18 and K8/18 were associated with endogenous TRADD in SW13 cells, resulting in the inhibition of caspase-8 activation. These results indicate that K18 may sequester TRADD to attenuate interactions between TRADD and activated TNFR1 and moderate TNF-induced apoptosis in simple epithelial cells.

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Ammonia as an Accelerator of Tumor Necrosis Factor Alpha-Induced Apoptosis of Gastric Epithelial Cells inHelicobacter pylori Infection

Infection and Immunity ◽

10.1128/iai.69.2.816-821.2001 ◽

2001 ◽

Vol 69 (2) ◽

pp. 816-821 ◽

Cited By ~ 27

Author(s):

Muneki Igarashi ◽

Yukie Kitada ◽

Hironori Yoshiyama ◽

Atsushi Takagi ◽

Takeshi Miwa ◽

...

Keyword(s):

Tumor Necrosis Factor ◽

Tumor Necrosis ◽

Significant Degree ◽

Gastric Epithelial Cells ◽

Necrosis Factor Alpha ◽

Tnf Α ◽

Factor Alpha ◽

H Pylori ◽

Induced Apoptosis ◽

Necrosis Factor

ABSTRACT The mechanism by which Helicobacter pylori induces apoptosis remains unclear. In a previous study using biopsy samples, we found a significant correlation between the urease activity of anH. pylori strain and the apoptosis level induced by this strain. Therefore, in this study, we investigated whether urease and/or the ammonia generated by urease can induce apoptosis. Human gastric epithelial cell lines were cocultured with H. pylori, and the levels of apoptosis and ammonia production were measured. The medium was supplemented (or not supplemented) with urea and cytokines. While a large amount of ammonia (>30 mM) accumulated in the coculture containing urease-positive H. pylori and urea, no significant degree of apoptosis occurred. In the presence of tumor necrosis factor alpha (TNF-α), however, a marked acceleration of apoptosis was found in this coculture. Such enhancement of apoptosis was also induced by the addition of 4 to 8 mM ammonia to the cell culture without either H. pylori or urea but containing TNF-α. These results suggested that ammonia accelerates cytokine-induced apoptosis in gastric epithelial cells, while ammonia or urease molecules alone are unable to induce a significant degree of apoptosis.

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