In Vivo and In Vitro Studies of Cytosolic Phospholipase A₂Expression inHelicobacter pyloriInfection

Abstract

Modifications of mucosal phospholipids have been detected in samples from patients with Helicobacter pylori-positive gastritis. These alterations appear secondary to increased phospholipase A 2 activity (PLA 2 ). The cytosolic form of this enzyme (cPLA 2 ), normally involved in cellular signaling and growth, has been implicated in cancer pathogenesis. The aim of this study was to investigate cPLA 2 expression and PLA 2 activity in the gastric mucosae of patients with and without H. pylori infection. In gastric biopsies from 10 H. pylori-positive patients, cPLA 2 levels, levels of mRNA as determined by reverse transcriptase PCR, levels of protein as determined by immunohistochemistry, and total PLA 2 activity were higher than in 10 H. pylori-negative gastritis patients. To clarify whether H. pylori had a direct effect on the cellular expression of cPLA 2 , we studied cPLA 2 expression in vitro with different human epithelial cell lines, one from a patient with larynx carcinoma (i.e., HEp-2 cells) and two from patients with gastric adenocarcinoma (i.e., AGS and MKN 28 cells), incubated with different H. pylori strains. The levels of cPLA 2 , mRNA, and protein expression were unchanged in Hep-2 cells independently of cellular adhesion or invasion of the bacteria. Moreover, no change in cPLA 2 protein expression was observed in AGS or MKN 28 cells treated with wild-type H. pylori. In conclusion, our study shows increased cPLA 2 expression and PLA 2 activity in the gastric mucosae of patients with H. pylori infection and no change in epithelial cell lines exposed to H. pylori.Helicobacter pylori infection of the gastric mucosa is present worldwide and may be associated with several pathologic alterations, including gastric cancer (30). The relationship between this organism and the development of gastric cancer has been postulated mainly on the basis of epidemiological investigations and animal models of H. pylori infection (13,15,17,21,39,40,53). This relationship is further supported by the finding that some patients with H. pylori infection show the genetic abnormalities of dysplasia and metaplasia in mucosal areas before the development of carcinoma (35, 50). However, the molecular mechanisms underlying the multistep process of gastric carcinogenesis related to H. pylori infection remain undefined (57). It has been shown that H. pylori damages the gastric barrier function and induces a dramatic change in mucosal phospholipid composition (34). This is likely due to a local increase in phospholipase A 2 (PLA 2 ) activity (4, 27). The cytosolic form (cPLA 2 ), but not the secretory form, of this enzyme is involved in cellular signaling and growth (2,25,26,28,31,38,51) and has recently been implicated in the pathogenesis of malignant transformation (11,22,32,48,49,55,56). Furthermore, many human tumors have been reported to exhibit increased synthesis of prostaglandins, the formation of which is dependent on an increase in cPLA 2 activity (16,18,19,29).In this study, we analyzed cPLA 2 expression in gastric-mucosal b...

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