Bacterial CagA protein induces degradation of p53 protein in a p14ARF-dependent manner

Abstract

Objective Infection with Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the stomach. Tumorigenic transformation of gastric epithelium induced by H. pylori is a highly complex process driven by an active interplay between bacterial virulence and host factors, many aspects of which remain obscure. In this work, we investigated the degradation of p53 tumour suppressor induced by H. pylori. Design Expression of p53 protein in gastric biopsies was assessed by immunohistochemistry. Gastric cells were co-cultured with H. pylori strains isolated from high-gastric risk and low-gastric risk areas and assessed for expression of p53, p14ARF and cytotoxin-associated gene A (CagA) by immunoblotting. siRNA was used to inhibit activities of ARF-BP1 and Human Double Minute 2 (HDM2) proteins. Results Our analysis demonstrated that H. pylori strains expressing high levels of CagA virulence factor and associated with a higher gastric cancer risk more strongly suppress p53 compared with low-risk strains in vivo and in vitro. We found that degradation of p53 induced by bacterial CagA protein is mediated by host HDM2 and ARF-BP1 E3 ubiquitin ligases, while the p14ARF protein counteracts H. pylori-induced signalling. Conclusions Our results provide novel evidence that tumorigenicity associated with H. pylori infection is linked to inhibition of p53 protein by CagA. We propose a model in which CagA-induced degradation of p53 protein is determined by a relative level of p14ARF. In cells in which p14ARF levels were decreased due to hypermethylation or deletion of the p14ARF gene, H. pylori efficiently degraded p53, whereas p53 is protected in cells expressing high levels of p14ARF.

Pathobiology of Helicobacter pylori–Induced Gastric Cancer

“…These broadly include stimulating cell proliferation through mitotic signaling pathways such as the PI3 kinase–AKT 28, 29 , SHP2, GRB2 and MEK–ERK, 30–32 and β-catenin–WNT pathways. 33–35 CagA also reduces epithelial cell apoptosis by interfering with tumor suppressors such as p53 36, 37 and RUNX3 38 . CagA alters epithelial cell polarity through direct interactions with the polarity protein MAP/microtubule affinity-regulating kinase 2 (MARK2 or PAR1b) 39, 40 , and disrupts assembly and signaling through the cell junctions 41, 42 .…”

Bacterial Pathogen Helicobacter pylori: A Bad AKT or Inhibits p53 Protein Activity

“…The authors speculated that the level of p53 is determined by a balance between upregulation of p53 protein expression by DNA damage and p53 degradation by MDM2 induced by H. pylori . Although it was not explored in this study, another possibility is that p53 is upregulated via inhibition of MDM2 by p14ARF protein, as has been reported previously [5]. …”

“…1). H. pylori efficiently degrades p53 protein in ARF-deficient cells, whereas degradation of p53 is halted and its level is increased in H. pylori infected cells expressing ARF [5]. …”

The role of intestinal bacteria in the development and progression of gastrointestinal tract neoplasms

“…Helicobacter pylori expresses the cytotoxin-associated gene A (CagA) protein, a virulence factor that has been shown to promote cell proliferation through the activation of the PI3K-AKT, WNT, and NFKB signaling pathways [25–27], and reduce epithelial cell apoptosis by the inhibition of TP53 [28]. In addition, accumulating evidence suggests that CagA can activate stemness properties and induce the epithelial-mesenchymal transition in gastric epithelial cells [29–35].…”