Regulation of constant cell elongation and Sfm pili synthesis in Escherichia coli via two active forms of FimZ orphan response regulator.

Escherichia coli (E. coli) has multiple copies of the chaperone-usher (CU) pili operon in five fimbria groups: CU pili, curli, type IV pili, type III secretion pili, and type IV secretion pili. Commensal E. coli K-12 contains 12 CU pili operons. Among these operons, Sfm is expressed by the sfmACDHF operon. Transcriptome analyses, reporter assays, and chromatin immunoprecipitation PCR analyses reported that FimZ directly binds to and activates the sfmA promoter, transcribing sfmACDHF. In addition, FimZ regularly induces constant cell elongation in E. coli, which is required for F-type ATPase function. The bacterial two-hybrid system showed a specific interaction between FimZ and the α subunit of the cytoplasmic F1 domain of F-type ATPase. Studies performed using mutated FimZs have revealed two active forms, I and II. Active form I is required for constant cell elongation involving amino acid residues K106 and D109. Active form II additionally required D56, a putative phosphorylation site, to activate the sfmA promoter. The chromosomal fimZ was hardly expressed in parent strain but functioned in phoB and phoP double-gene knockout strains. These insights may help to understand bacterial invasion restricted host environments by the sfm γ-type pili.

BabA-mediated adherence is a potentiator of the Helicobacter pylori type IV secretion system activity.

Chronic infection of Helicobacter pylori in the stomach mucosa with translocation of the bacterial cytotoxin-associated gene A (CagA) effector protein via the cag-Type IV secretion system (TFSS) into host epithelial cells are major risk factors for gastritis, gastric ulcers, and cancer. The blood group antigen-binding adhesin BabA mediates the adherence of H. pylori to ABO/Lewis b (Le(b)) blood group antigens in the gastric pit region of the human stomach mucosa. Here, we show both in vitro and in vivo that BabA-mediated binding of H. pylori to Le(b) on the epithelial surface augments TFSS-dependent H. pylori pathogenicity by triggering the production of proinflammatory cytokines and precancer-related factors. We successfully generated Le(b)-positive cell lineages by transfecting Le(b)-negative cells with several glycosyltransferase genes. Using these established cell lines, we found increased mRNA levels of proinflammatory cytokines (CCL5 and IL-8) as well as precancer-related factors (CDX2 and MUC2) after the infection of Le(b)-positive cells with WT H. pylori but not with babA or TFSS deletion mutants. This increased mRNA expression was abrogated when Le(b)-negative cells were infected with WT H. pylori. Thus, H. pylori can exploit BabA-Le(b) binding to trigger TFSS-dependent host cell signaling to induce the transcription of genes that enhance inflammation, development of intestinal metaplasia, and associated precancerous transformations.

Helicobacter pylori CagA phosphorylation-independent function in epithelial proliferation and inflammation.

CagA, a major virulence factor of Helicobacter pylori (Hp), is delivered into gastric epithelial cells and exists in phosphorylated and nonphosphorylated forms. The biological activity of the phosphorylated form is well established; however, function(s) of the nonphosphorylated form remain elusive. Here, we report that a conserved motif in the C-terminal region of CagA, which is distinct from the EPIYA motifs used for phosphorylation and which we designate CRPIA (conserved repeat responsible for phosphorylation-independent activity), plays pivotal roles in Hp pathogenesis. The CRPIA motif in nonphosphorylated CagA was involved in interacting with activated Met, the hepatocyte growth factor receptor, leading to the sustained activation of phosphatidylinositol 3-kinase/Akt signaling in response to Hp infection. This in turn led to the activation of beta-catenin and NF-kappaB signaling, which promote proliferation and inflammation, respectively. Thus, nonphosphorylated CagA activity contributes to the epithelial proliferative and proinflammatory responses associated with development of chronic gastritis and gastric cancer.

Helicobacter pylori dampens gut epithelial self-renewal by inhibiting apoptosis, a bacterial strategy to enhance colonization of the stomach.

Colonization of the gastric pits in the stomach by Helicobacter pylori (Hp) is a major risk factor for gastritis, gastric ulcers, and cancer. Normally, rapid self-renewal of gut epithelia, which occurs by a balance of progenitor proliferation and pit cell apoptosis, serves as a host defense mechanism to limit bacterial colonization. To investigate how Hp overcomes this host defense, we use the Mongolian gerbil model of Hp infection. Apoptotic loss of pit cells induced by a proapoptotic agent is suppressed by Hp. The ability of Hp to suppress apoptosis contributed to pit hyperplasia and persistent bacterial colonization of the stomach. Infection with WT Hp but not with a mutant in the virulence effector cagA increased levels of the prosurvival factor phospho-ERK and antiapoptotic protein MCL1 in the gastric pits. Thus, CagA activates host cell survival and antiapoptotic pathways to overcome self-renewal of the gastric epithelium and help sustain Hp infection.