Mo1587 Epstein-Barr Virus Positivity as a Prognostic Indicator in Gastric Cancer: an International Pooled Analysis

Abstract

to evaluate the expression of P-gp in human fetal stomach and in Hp-related gastric preneoplastic and neoplastic lesions and the effect of selective silencing of P-gp on cell survival in an In Vitro model. Materials and Methods: P-gp and Bcl-xL expression was evaluated by immunohistochemistry on gastric mucosa of 28 human fetuses, 66 Hp-negative subjects, 138 Hp-positive CG patients (28 with IM) and 45 intestinal type GCs. Protocol was repeated in Hp-positive subjects one-year after eradication therapy. P-gp/Bcl-xL co-localization and protein-protein interaction were investigated by confocal microscopy and co-immunoprecipitation, respectively, in AGS and MKN-28 GC cell lines. The role of P-gp in controlling apoptosis was evaluated by knocking down its expression by small interfering RNA (siRNAs). After transfection, the percentage of viable, necrotic and apoptotic cells was analyzed by FACS, baseline and after 6 h incubation with 3% H2O2. Results: P-gp was expressed in the stomach of all human fetuses, undetectable in adult normal mucosa and re-expressed in 30/110 Hp-positive non IM-CG, 28/28 IM-CG and 40/45 GCs. Bcl-xL expression paralleled that of P-gp. After successful Hp eradication therapy (88/138), Pg-p and Bcl-xL were expressed only in IM areas while they were undetectable in the remaining cases. In GC cell lines, Pgp co-localized with Bcl-xL on the mithocondria. Co-immunoprecipitation confirmed the physical interaction between P-gp and Bcl-xL. Selective silencing of P-gp significantly increased the apoptotic index in both GC cell lines exposed to oxidative stress (AGS: from 22.6 to 90.3 %; p<0.0001 and MKN-28: from 7.3 to 56.2 ± 1.1%; p<0.0001). Conclusion: P-gp behaves as a gastric oncofetal protein, that acting as an anti-apoptotic agent, confers a strong survival advantage to cells by cross-talking with Bcl-xL. The expression of P-gp in pre-neoplastic gastric mucosa could indicate a functional implication of this protein in Hprelated gastric carcinogenesis.