[show abstract][hide abstract] ABSTRACT: Enterotoxigenic Bacteroides fragilis (ETBF) produces an approximately 20-kDa heat-labile enterotoxin (BFT) that plays an essential role in mucosal inflammation. Although spontaneous disappearance of ETBF infection is common, little information is available on regulated expression of antibacterial factors in response to BFT stimulation. This study investigates the role of BFT in human beta-defensin 2 (hBD-2) induction from intestinal epithelial cells. Stimulation of HT-29 and Caco-2 intestinal epithelial cell lines with BFT resulted in the induction of hBD-2. Activation of a reporter gene for hBD-2 was dependent on the presence of NF-kappaB binding sites. In contrast, suppression of AP-1 did not affect hBD-2 expression in BFT-stimulated cells. Inhibition of p38 mitogen-activated protein kinase (MAPK) using SB203580 and small interfering RNA (siRNA) transfection resulted in a significant reduction in BFT-induced I kappaB kinase (IKK)/NF-kappaB activation and hBD-2 expression. Our results suggest that a pathway including p38 MAPK, IKK, and NF-kappaB activation is required for hBD-2 induction in intestinal epithelial cells exposed to BFT, and may be involved in the host defense following infection with ETBF.
Infection and immunity 03/2010; 78(5):2024-33. · 4.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bacteroides fragilis produces an approximately 20-kDa heat-labile toxin (B. fragilis enterotoxin, BFT) which is known to be associated with diarrhea. To determine whether cyclooxygenase (COX)-2, via NF-kappaB activation, can contribute to BFT-induced diarrhea, the relationship between COX-2 expression and fluid secretion in BFT-stimulated human intestinal epithelial cells was examined. BFT stimulation increased the expression of COX-2, but not COX-1, in human intestinal epithelial cells. Suppression of the NF-kappaB signal significantly decreased COX-2 expression in response to BFT stimulation. Prostaglandin E2 (PGE2) levels were increased in parallel with COX-2 expression, and, conversely, PGE2 production was significantly inhibited when COX-2 or NF-kappaB activities were suppressed using COX-2 small interfering RNA (siRNA), p65 NF-kappaB subunit siRNA, or a retrovirus encoding the IkappaBalpha superrepressor. In addition, a selective COX-2 inhibitor, NS-398, significantly inhibited the increased cAMP level induced by BFT stimulation. Furthermore, a selective COX-2 inhibitor prevented BFT-induced PGE2 production and ileal fluid secretion in a mouse ileal loop model. These results suggest that the secretory response to BFT stimulation may be mediated by the production of PGE2, through NF-kappaB activation and the up-regulation of COX-2 in intestinal epithelial cells.
European Journal of Immunology 10/2006; 36(9):2446-56. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: WD repeats are implicated in protein-protein interactions and regulate a wide variety of cellular functions, including chromatin remodeling and transcription. The WD repeats of the Bub3 and Cdc20 kinetochore proteins are important for the physical interactions of these proteins with Mad2 and BubR1 to yield a kinetochore protein complex capable of delaying anaphase by inhibiting ubiquitin ligation via the anaphase-promoting complex/cyclosome. Here, we show that Bub3 and Cdc20 form a complex with histone deacetylases; this interaction appears to confer transcriptional repressor activity in a heterologous DNA-binding context. In addition, inhibition of Bub3 and Cdc20 expression significantly impairs interphase cell cycle. These results indicate that Bub3 and Cdc20 play additional roles in the integration of cell cycle arrest as transcriptional repressors.
[show abstract][hide abstract] ABSTRACT: The differentiated phenotype of chondrocyte is rapidly lost during in vitro culture by a process designated "dedifferentiation." In this study, we investigate the roles of protein kinase C (PKC) and extracellular signal-regulated protein kinase (ERK) in the maintenance of the differentiated chondrocyte phenotype. Chondrocytes isolated from rabbit articular cartilage underwent dedifferentiation upon serial monolayer culture with cessation of type II collagen expression and proteoglycan synthesis, which was reversed by culturing dedifferentiated cells in alginate gel. The expression pattern of PKC alpha was essentially the same as that of type II collagen during de- and redifferentiation, in that expression was decreased during dedifferentiation and increased during redifferentiation. In contrast to PKC alpha, ERK activity increased 15-fold during dedifferentiation. This enhanced activity was terminated during redifferentiation. Down-regulation of PKC alpha in passage 0 chondrocytes resulted in dedifferentiation. However, overexpression of PKC alpha did not affect type II collagen levels, suggesting that PKC alpha expression is not sufficient to maintain the differentiated phenotype. However, inhibition of ERK by PD98059 enhanced type II collagen expression and proteoglycan synthesis in passage 0 cells, retarded dedifferentiation during monolayer cultures, and reversed dedifferentiation caused by down-regulation of PKC. Unlike PKC-dependent ERK regulation of chondrogenesis, PKC and ERK independently modulated chondrocyte dedifferentiation, as confirmed by observations that PKC down-regulation and ERK inhibition did not alter ERK phosphorylation and PKC expression, respectively. In addition, expression of N-cadherin, alpha-catenin, and beta-catenin, which are oppositely regulated to type II collagen during phenotype alterations, were modulated by PKC and ERK during chondrogenesis but not dedifferentiation, supporting distinct mechanisms for the regulation of chondrocyte differentiation and maintenance of differentiated phenotype by these two protein kinases.
Journal of Biological Chemistry 04/2002; 277(10):8412-20. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nitric oxide regulates cartilage destruction by causing dedifferentiation and apoptosis of chondrocytes. We investigated the role of the mitogen-activated protein kinase subtypes, extracellular signal-regulated protein kinase (ERK)-1/2, and p38 kinase in NO-induced apoptosis of rabbit articular chondrocytes and their involvement in dedifferentiation. Generation of NO with sodium nitroprusside (SNP) caused dedifferentiation, as indicated by the inhibition of type II collagen expression and proteoglycan synthesis. NO additionally caused apoptosis, accompanied by p53 accumulation and caspase-3 activation. SNP treatment stimulated activation of ERK-1/2 and p38 kinase. Inhibition of ERK-1/2 with PD98059 rescued SNP-induced dedifferentiation but enhanced apoptosis up to 2-fold, whereas inhibition of p38 kinase with SB203580 enhanced dedifferentiation, with significant blockage of apoptosis. The stimulation of apoptosis by ERK inhibition was accompanied by increased p53 accumulation and caspase-3 activity, whereas the inhibitory effect of p38 kinase blockade was associated with reduced p53 accumulation and caspase-3 activity. Our results indicate that NO-induced p38 kinase functions as an induction signal for apoptosis and in the maintenance of chondrocyte phenotype, whereas ERK activity causes dedifferentiation and operates as an anti-apoptotic signal. NO generation is less proapoptotic in chondrocytes that are dedifferentiated by serial monolayer culture or phorbol ester treatment. NO-induced p38 kinase activity is low in dedifferentiated cells compared with that in differentiated chondrocytes, with lower levels of p53 accumulation and caspase-3 activity. Our findings collectively suggest that ERK-1/2 and p38 kinase oppositely regulate NO-induced apoptosis of chondrocytes, in association with p53 accumulation, caspase-3 activation, and differentiation status.
Journal of Biological Chemistry 02/2002; 277(2):1332-9. · 4.65 Impact Factor