Ca2+ release from host intracellular stores and related signal transduction during Campylobacter jejuni 81-176 internalization into human intestinal cells
ABSTRACT Campylobacter jejuni is the leading bacterial cause of human diarrhoeal disease in many parts of the world, including the USA. The ability of C. jejuni to invade the host intestinal epithelium is an important determinant of virulence. A common theme among pathogenic invasive micro-organisms is their ability to usurp the eukaryotic cell-signalling systems both to allow for invasion and to trigger disease pathogenesis. Ca(2+) is very important in a great variety of eukaryotic cell-signalling processes (e.g. calmodulin-activated enzymes, nuclear transcriptional upregulation, and cytoskeletal rearrangements). This study analyses the effects of Ca(2+) availability on invasion of human INT407 intestinal epithelial cells by C. jejuni strain 81-176. The ability of C. jejuni to invade INT407 cells was not blocked by chelation of any remaining extracellular Ca(2+) from host cells incubated in Ca(2+)-free, serum-free media. In contrast, C. jejuni invasion was markedly reduced either by chelating host intracellular Ca(2+) with 1,2-bis-(2-)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA, AM) or by blocking the release of Ca(2+) from intracellular stores with dantrolene or U73122. Moreover, Bay K8644, a plasma-membrane Ca(2+)-channel agonist, was observed to stimulate C. jejuni invasion, presumably by increasing host intracellular free Ca(2+) levels. Measurement of host-cell cytosolic Ca(2+) via spectrofluorimetry and fluorescence microscopy revealed an increase in Ca(2+) from 10 min post-infection. Monolayer pretreatment with either a calmodulin antagonist or a specific inhibitor of protein kinase C was found to cause a marked reduction in C. jejuni invasion, suggesting roles for these Ca(2+)-activated modulators in signal-transduction events involved in C. jejuni invasion. These results demonstrate that C. jejuni induces the mobilization of Ca(2+) from host intracellular stores, which is an essential step in the invasion of intestinal cells by this pathogen.
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ABSTRACT: The enteropathogen Campylobacter jejuni is a major worldwide health and economic burden, being one of the leading causes of bacterial gastroenteritis and commonly linked to postinfectious onset of autoimmune disease. Chickens are a major vector for human infection and even though variation in avian colonization level is heritable, no previous studies have identified regions of the genome associated with colonization resistance. We performed a genome-wide association study of resistance to C. jejuni colonization in the avian intestine, controlling for population structure which revealed a risk locus with genome-wide significance spanning the T-cadherin (CDH13) gene. A second possible risk locus was also identified close to calmodulin (CALM1), a calcium-activated modulator of cadherin function. In addition, gene expression analysis of mRNA sequencing profiles revealed that the relative expression of the two genes is significantly associated with colonization resistance. Functional studies have previously demonstrated involvement of cadherins and calmodulin in C. jejuni intracellular invasion and colonization of human intestinal epithelial cells in vitro. Consistent with this, our analysis reveals that variation surrounding these genes is associated with avian colonization resistance in vivo and highlights their potential as possible targets for control of the bacterium in avian and human populations.G3-Genes Genomes Genetics 03/2013; 3(5). DOI:10.1534/g3.113.006031 · 2.51 Impact Factor
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ABSTRACT: Calcium signaling has been implicated in various steps in bacterial pathogenesis. Here, we investigated the role of Ca(2+) signaling in intracellular invasion of non-phagocytic host cells infected with Orientia tsutsugamushi, the causative agent of scrub typhus. The bacteria induced a transient Ca(2+) increase in HeLa cells immediately after infection and the source of the mobilized Ca(2+) appears to be intracellular stores, not the extracellular milieu, as determined using extracellular (EGTA) or intracellular (BAPTA-AM) Ca(2+) chelators. O. tsutsugamushi rapidly induced activation of PLC-γ1, as indicated by tyrosine phosphorylation. PLC-γ1 activity increased within 1 min of infection and returned to the basal level by 5 min. Pretreatment of host cells with inhibitors of PLC-γ1 (U73122) or IP3R channel activity (2-APB) significantly blocked bacterial entry without affecting bacterial attachment. In addition, these chemical inhibitors were effective in suppressing not only the activation of ERK MAP kinase but also the expression of the chemokine MCP-1. Taken together, Ca(2+) signaling induced by O. tsutsugamushi may play a crucial role in bacterial pathogenesis including inflammatory reactions as well as intracellular invasion into non-phagocytic host cells.Microbial Pathogenesis 02/2011; 50(6):326-30. DOI:10.1016/j.micpath.2011.02.007 · 2.00 Impact Factor
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ABSTRACT: The invasion-associated type III secretion system (T3SS-1) of S. Typhimurium is required to initiate and sustain an acute inflammatory response in the intestine. We investigated the relationship of S. Typhimurium T3SS-1-induced IL-8 expression and invasion with intracellular Ca(2+) mobilization in HeLa cells. Compared to the sipAsopABDE2 mutant, strains carrying a mutation in sipA, or mutations in sopABDE2 induced higher levels of IL-8 and greater bacterial internalization despite the fact that these mutants elicited similarly low intracellular concentrations of Ca(2+). Likewise, complemented sipAsopABDE2 mutant with sopE2 did not affect intracellular Ca(2+) concentrations or IL-8 expression, but significantly increased bacterial internalization. Treating HeLa cells with the calcium chelator BAPTA-AM or with D-BAPTA-AM, a derivative with greatly reduced Ca(2+) chelating activity, yielded strong evidence that BAPTA-AM does not affect invasion and inhibits IL-8 secretion by a calcium-dependent mechanism. These findings suggest that, although wild-type S. Typhimurium-induced IL-8 expression and bacterial internalization in HeLa cells coincides with increased cytosolic Ca(2+), the differing levels of IL-8 and invasion induced by strains carrying different effector proteins are unrelated to levels of intracellular Ca(2+).Microbes and Infection 06/2009; 11(10-11):850-8. DOI:10.1016/j.micinf.2009.05.003 · 2.73 Impact Factor