title: Effects of small interfering RNA inhibit Class I phosphoinositide 3-kinase on human gastric cancer cells.
abstract: OBJECTIVE
  To investigate the effects of small interfering RNA (siRNA)-mediated inhibition of Class I phosphoinositide 3-kinase (Class I PI3K) signal transduction on the proliferation, apoptosis, and autophagy of gastric cancer SGC7901 and MGC803 cells.
  
  
  METHODS
  We constructed the recombinant replication adenovirus PI3K(I)-RNA interference (RNAi)-green fluorescent protein (GFP) and control adenovirus NC-RNAi-GFP, and infected it into human gastric cancer cells. MTT assay was used to determine the growth rate of the gastric cancer cells. Activation of autophagy was monitored with monodansylcadaverine (MDC) staining after adenovirus PI3K(I)-RNAi-GFP and control adenovirus NC-RNAi-GFP treatment. Immunofluorescence staining was used to detect the expression of microtubule-associated protein 1 light chain 3 (LC3). Mitochondrial membrane potential was measured using the fluorescent probe JC-1. The expression of autophagy was monitored with MDC, LC3 staining, and transmission electron microscopy. Western blotting was used to detect p53, Beclin-1, Bcl-2, and LC3 protein expression in the culture supernatant.
  
  
  RESULTS
  The viability of gastric cancer cells was inhibited after siRNA targeting to the Class I PI3K blocked Class I PI3K signal pathway. MTT assays revealed that, after SGC7901 cancer cells were treated with adenovirus PI3K(I)-RNAi-GFP, the rate of inhibition reached 27.48% ± 2.71% at 24 h, 41.92% ± 2.02% at 48 h, and 50.85% ± 0.91% at 72 h. After MGC803 cancer cells were treated with adenovirus PI3K(I)-RNAi-GFP, the rate of inhibition reached 24.39% ± 0.93% at 24 h, 47.00% ± 0.87% at 48 h, and 70.30% ± 0.86% at 72 h (P < 0.05 compared to control group). It was determined that when 50 MOI, the transfection efficiency was 95% ± 2.4%. Adenovirus PI3K(I)-RNAi-GFP (50 MOI) induced mitochondrial dysfunction and activated cell apoptosis in SGC7901 cells, and the results described here prove that RNAi of Class I PI3K induced apoptosis in SGC7901 cells. The results showed that adenovirus PI3K(I)-RNAi-GFP transfection induced punctate distribution of LC3 immunoreactivity, indicating increased formation of autophagosomes. The results showed that the basal level of Beclin-1 and LC3 protein in SGC7901 cells was low. After incubating with adenovirus PI3K(I)-RNAi-GFP (50 MOI), Beclin-1, LC3, and p53 protein expression was significantly increased from 24 to 72 h. We also found that Bcl-2 protein expression down-regulated with the treatment of adenovirus PI3K(I)-RNAi-GFP (50 MOI). A number of isolated membranes, possibly derived from ribosome-free endoplasmic reticulum, were seen. These isolated membranes were elongated and curved to engulf a cytoplasmic fraction and organelles. We used transmission electron microscopy to identify ultrastructural changes in SGC7901 cells after adenovirus PI3K(I)-RNAi-GFP (50 MOI) treatment. Control cells showed a round shape and contained normal-looking organelles, nucleus, and chromatin, while adenovirus PI3K(I)-RNAi-GFP (50 MOI)-treated cells exhibited the typical signs of autophagy.
  
  
  CONCLUSIONS
  After the Class I PI3K signaling pathway has been blocked by siRNA, the proliferation of cells was inhibited and the apoptosis of gastric cancer cells was enhanced.
authors.affiliation: Department of General Surgery, The Second Affiliated Hospital, Soochow University, Suzhou 215004, Jiangsu Province, China.
authors.forename: Bao-Song
authors.initials: BS
authors.lastname: Zhu
authors.forename: Li-Yan
authors.initials: LY
authors.lastname: Yu
authors.forename: Kui
authors.initials: K
authors.lastname: Zhao
authors.forename: Yong-You
authors.initials: YY
authors.lastname: Wu
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Cheng
authors.forename: Yong
authors.initials: Y
authors.lastname: Wu
authors.forename: Feng-Yun
authors.initials: FY
authors.lastname: Zhong
authors.forename: Wei
authors.initials: W
authors.lastname: Gong
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chen
authors.forename: Chun-Gen
authors.initials: CG
authors.lastname: Xing
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy; D000071186:Beclin-1; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D058534:Class I Phosphatidylinositol 3-Kinases / Q000235:genetics* / Q000378:metabolism; D005822:Genetic Vectors; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism*; D015398:Signal Transduction; D013274:Stomach Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D013997:Time Factors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D058534:Class I Phosphatidylinositol 3-Kinases
keywords: Apoptosis; Autophagy; Class I phosphoinositide 3-kinase; Gastric cancer cells; RNA interference
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