| Gastric cancer is one of the most common disease of malignant tumors threatening the life of people.In China,incidence and mortality of the disease have been highest in all kinds of cancers in recent one hundred years.Despite enormous progress made in the gastric cancer research field,a multitude of unresolved issues remain outstanding regarding the molecular basis of carcinogenesis.There is increasing evidence supporting that cancer cells are in many aspects similar to the stem cells.In particular,we focus on three aspects of the relationship between stem cells and cancer cells:first,the similarities in the mechanisms that regular self-renewal of normal stem cells and cancer cells; second,the possibility that tumor cells might arise from normal stem cells;and third,the notion that tumors contain 'cancer stem cells'—rare cells with indefinite proliferative potential that drive the formation and growth of tumors.The cancer stem cell hypothesis presumes that it is the cancer initiating cells responsible for tumorigenesis and contribute to cancer resistance.Cancer stem cells have been the hot spot of cancer research field.According to this theory,we suppose that gastric cancer cells may originate from stem cells and it is a stem cell disease.The most important problem of cancer stem cells is isolation and identification.Nevertheless,there are short of typical markers of stem cells, thereby it is very difficult to isolate and identificate cancer stem cells.ABCG2 is a member of the ATP-binding cassette(ABC)family of cell surface transport protein.ABCG2 expression occurs in a variety of normal tissues,and is relatively limited to primitive stem cells.ABCG2 expression is associated with the side population(SP)phenotype of Hoechst 33342 efflux.Side populations,as defined by Hoechst exclusion in flow cytometry,express high levels of various members of ABCG2,which is responsible for drug resistance.SP appear to be enriched in stem cells,cells that play a pivotal role in normal development and cancer biology. Thus,they could provide a useful tool and a readily accessible source for stem cell studies in both the normal and cancerous settings.At present,gastric cancer stem cell research is at the exploratory stage.Due to the complexity of gastric cancer,its stem cell research is progressing slowly. Up to now,the specific surface marker of gastric cancer stem cell has not been found and gastric cancer stem cell has not been isolated and identificated.Aim:①To investigate the expression of ABCG2 in human gastric carcinoma and its clinical significance.②To isolate and preliminarily identify the side population(SP)of cancer stem-like cells in gastric cancer cell lines.Methods:①Expression of ABCG2 was examined with immunohistochemical technique in the specimens from 45 gastric carcinoma tissues and 30 surrounding normal tissues.②The mRNA expression of ABCG2 was measured by RT-PCR and real-time quantitative PCR in 30 cases of gastric carcinoma and normal gastric mucosa respectively.③The protein expression of ABCG2 was examined by Western blotting.④Expression of ABCG2 in gastric cancer cell line was determined by immunocytochemical stain.⑤Tumor cells suspension was stained with Hoechst33342 and PI in the absence or presence of verapamil.Then the SP was analyzed in the fluorescence-activated cell sorter.⑥The mRNA expression of some stem markers were measured by RT-PCR in SP and non-SP respectively.Results:ABCG2 expression was observed in 28 of 45(62.2%)cases by immunohistochemical analysis.In ABCG2-positive tumors,adjacent non-neoplastic tissue was similarly analyzed,revealing that ABCG2 is upregulated in gastric carcinoma.ABCG2 expression in poorly differentiated/undifferentiated carcinoma was significantly higher than that in well/moderately-differentiated carcinoma(P＜0.05).The mRNA and protein expression of ABCG2 was significantly higher than that in normal gastric mucosa (P＜0.05).SP cells accounted for 0.25%of the MKN-28 gastric cancer cells, which were decreased to 0.05%by treating with verapamil.Whereas,there were not SP in BGC-823 and SGC-7901 gastric cancer cell lines.The mRNA of ABCG2 in SP was significantly higher than that in non-SP(P＜0.05).The mRNA level of EGFR in SP and non-SP was not significant deviation.There were not CD133,Musashi-1,OCT4 and SOX2 mRNA expression in SP and non-SP.Conclusions:ABCG2 plays an important role in the multi-drug resistance of gastric carcinoma.ABCG2 might be an important factor in the research of gastric cancer stem cell.Gastric cancer cell line MKN-28 contains SP which can be decreased by verapamil.Not all gastric cancer cell lines contain SP.
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