Helicobacter pylori CagA Causes Mitotic Impairment and Induces Chromosomal Instability

Abstract

Infection with cagA-positive Helicobacter pylori is the strongest risk factor for the development of gastric carcinoma. The cagA gene product CagA, which is delivered into gastric epithelial cells, specifically binds to and aberrantly activates SHP-2 oncoprotein. CagA also interacts with and inhibits partitioningdefective 1 (PAR1)/MARK kinase, which phosphorylates microtubule-associated proteins to destabilize microtubules and thereby causes epithelial polarity defects. In light of the notion that microtubules are not only required for polarity regulation but also essential for the formation of mitotic spindles, we hypothesized that CagA-mediated PAR1 inhibition also influences mitosis. Here, we investigated the effect of CagA on the progression of mitosis. In the presence of CagA, cells displayed a delay in the transition from prophase to metaphase. Furthermore, a fraction of the CagA-expressing cells showed spindle misorientation at the onset of anaphase, followed by chromosomal segregation with abnormal division axis. The effect of CagA on mitosis was abolished by elevated PAR1 expression. Conversely, inhibition of PAR1 kinase elicited mitotic delay similar to that induced by CagA. Thus, CagA-mediated inhibition of PAR1, which perturbs microtubule stability and thereby causes microtubule-based spindle dysfunction, is involved in the prophase/metaphase delay and subsequent spindle misorientation. Consequently, chronic exposure of cells to CagA induces chromosomal instability. Our findings reveal a bifunctional role of CagA as an oncoprotein: CagA elicits uncontrolled cell proliferation by aberrantly activating SHP-2 and at the same time induces chromosomal instability by perturbing the microtubule-based mitotic spindle. The dual function of CagA may cooperatively contribute to the progression of multistep gastric carcinogenesis.Helicobacter pylori is a spiral-shaped bacterium first described in 1984 by Marshall and Warren (1). H. pylori inhabits at least half of the world's human population. Clinically isolated H. pylori strains can be divided into two major subtypes based on their ability to produce a 120-to 145-kDa protein called cytotoxin-associated gene A antigen (CagA) 2 (2-5). More than 90 -95% of H. pylori strains isolated in East Asian countries such as Japan, Korea, and China are cagA-positive, whereas 40 -50% of those isolated in Western countries are cagA-negative. Infection with a cagA-positive H. pylori strain is associated with severe atrophic gastritis, peptic ulcerations, and gastric adenocarcinoma (6 -12).H. pylori cagA-positive strains deliver the CagA protein into host cells via the cag pathogenicity island-encoded type IV secretion system (4, 5, 13, 14). Translocated CagA then localizes to the inner surface of the plasma membrane, where it undergoes tyrosine phosphorylation by Src family kinases or Abl kinase at the Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs present in the C-terminal region of CagA (15-17). Tyrosine-phosphorylated CagA then binds specifically to SHP-2 tyrosine phosphatase and dereg...

Helicobacter pyloriand Gastric Cancer: Factors That Modulate Disease Risk

“…Nonphosphorylated CagA associates with the epithelial tight junction scaffolding protein zonula occludens 1 (ZO-1) and the transmembrane protein junctional adhesion molecule A (JAM-A), leading to nascent but incomplete assembly of tight junctions at ectopic sites of bacterial attachment (13). Recently, CagA was shown to directly bind PAR1b/MARK2, a central regulator of cell polarity, and to inhibit its kinase activity as well as to dysregulate mitotic spindle formation, thus promoting a loss of cell polarity (see "Apical-Junctional Complexes") (179,269,320). While it is evident that non-tyrosine-phosphorylated mutant forms of CagA exert effects within gastric epithelial cells, to our knowledge, there is currently no direct evidence for nonphosphorylated CagA within the host cell.…”

Microbe-Induced Epigenetic Alterations

“…It is interesting to note that although chronic gastritis appears to be associated with the development of gastric carcinoma in humans, there were no signs of gastritis or systemic in fl ammation in CagA transgenic mice, including those with gastrointestinal carcinomas. Interaction of CagA with PAR1/MARK (partitioning defective 1/ microtubule af fi nity-regulating kinase) may also contribute to the carcinogenic process because it induces chromosomal instability by destabilizing the microtubules during mitosis (Umeda et al 2009 ) .…”

When our genome is targeted by pathogenic bacteria

“…Indeed, mutation frequencies are more elevated in mice infected with H. pylori, with a prevalence of transversion mutations (AT to GC and GC to AT), resulting from oxidative DNA damage [14]. Umeda and co-workers showed that CagA, a virulence factor delivered into H. pylori-infected cells delays prophase and metaphase, resulting in the incorrect orientation of the mitotic spindle and an abnormal division axis, generating anomalies in chromosome segregation and genomic instability [15]. H. pylori also alters the level of the pro-apoptotic regulator p53 through the promotion of ubiquitin-dependent proteasome degradation in a CagA-dependent manner [16,17].…”