Helicobacter pylorivacuolating cytotoxin에 의한 호산구 apoptosis에 대한 연구

Abstract

Persistent Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer, gastric cancer, and gastric lymphoma. The H. pylori vacuolating cytotoxin (VacA) is one of the major pathogenic products of H. pylori and induces vacuoles within various types of cultured cells. Although H. pylori-infected gastric mucosa is characterized by infiltration of inflammatory cells such as eosinophils, pathogenic roles of eosinophils in response to VacA have not been elucidated. This study investigates the role of VacA in apoptosis of human eosinophils. Treatment of human eosinophils with H. pylori VacA showed an induction of apoptosis as a relatively late event. During the early period of VacA stimulation, expression of cellular inhibitor of apoptosis protein-2 (c-IAP2) increased, and inhibition of c-IAP2 augmented the apoptotic cell death. VacA caused the translocation of cytoplasmic Bax to mitochondria and increased cytochrome c release from mitochondria. Transfection with Bax siRNA decreased the release of cytochrome c and DNA fragmentation. In addition, the apoptosis through Bax and cytochrome c was mainly regulated by a p38 mitogen-activated protein kinase (MAPK). These results suggest that the apoptosis is mediated by a sequential pathway, including p38 MAPK, Bax translocation, and cytochrome c in response to stimulation of human eosinophils with H. pylori VacA.; Helicobacter pylori는 만성 위염, 위십이지장 궤양뿐만 아니라, 위암 및 위림프종의 위험도를 증가시키는 균으로 알려져 있다. 이들 질병과 연관된 H. pylori의 독성인자 중에서 분자량 87 kDa인vacuolating cytotoxin (VacA)은 세포질의 공포화(vacuolation)를 유발하는 단백질이다. 그런데 H. pylori에 감염된 환자의 위조직에 호산구(eosinophil)가 자주 관찰됨에도 불구하고 아직까지 H. pylori VacA에 대한 호산구의 병원적 역할에 대해서는 알려진 바가 없다. 본 연구에서는 사람 호산구의 apoptosis에 대한 VacA 역할에 대해 규명하였다. 연구 결과, H. pylori VacA를 사람 호산구에 처리했을 때 apoptosis가 후기 반응으로 관찰되었다. 반면, VacA 자극 초기에는cellular inhibitor of apoptosis protein-2 (c-IAP2) 발현이 유도되었다. 이 때, c-IAP2의 발현을 억제시키면 apoptosis에 의한 세포사멸이증가하였다. VacA는 세포질 내 Bax를 mitochondria로 translocation 시켰고, mitochondria로부터 cytochrome c의 분비를 촉진시켰다. Bax siRNA를transfection 시켜 Bax 시그널을 차단하였을 때, cytochrome c의 분비와 DNA fragmentation이 억제되었다. 이와 더불어 Bax와cytochrome c를 통한 apoptosis의 신호전달에 p38 mitogen-activated protein kinase (MAPK)가 관여함을 확인할 수 있었다. 이와 같은 결과들로 미루어 H. pylori VacA 자극을 받은 호산구는p38 MAPK, Bax translocation, cytochrome c 분비라는 일련의 신호전달 체계를 통해 apoptosis를 유도할 것으로 추정된다. |Persistent Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer, gastric cancer, and gastric lymphoma. The H. pylori vacuolating cytotoxin (VacA) is one of the major pathogenic products of H. pylori and induces vacuoles within various types of cultured cells. Although H. pylori-infected gastric mucosa is characterized by infiltration of inflammatory cells such as eosinophils, pathogenic roles of eosinophils in response to VacA have not been elucidated. This study investigates the role of VacA in apoptosis of human eosinophils. Treatment of human eosinophils with H. pylori VacA showed an induction of apoptosis as a relatively late event. During the early period of VacA stimulation, expression of cellular inhibitor of apoptosis protein-2 (c-IAP2) increased, and inhibition of c-IAP2 augmented the apoptotic cell death. VacA caused the translocation of cytoplasmic Bax to mitochondria and increased cytochrome c release from mitochondria. Transfection with Bax siRNA decreased the release of cytochrome c and DNA fragmentation. In addition, the apoptosis through Bax and cytochrome c was mainly regulated by a p38 mitogen-activated protein kinase (MAPK). These results suggest that the apoptosis is mediated by a sequential pathway, including p38 MAPK, Bax translocation, and cytochrome c in response to stimulation of human eosinophils with H. pylori VacA.