Silencing Bmi-1 enhances the senescence and decreases the metastasis of human gastric cancer cells

AIM:To evaluate the impact of Bmi-1 on cell senescence and metastasis of human gastric cancer cell line BGC823.METHODS:Two pairs of complementary small hairpin RNA(shRNA)oligonucleotides targeting the Bmi-1gene were designed,synthesized,annealed and cloned into the pRNAT-U6.2 vector.After DNA sequencing to verify the correct insertion of the shRNA sequences,the recombinant plasmids were transfected into BGC823 cells.The expression of Bmi-1 mRNA and protein was examined by reverse transcription-polymerase chain reaction(RT-PCR)and Western blotting.The effects of Bmi-1 knockdown on cell senescence and metastasis were determined by theβ-Gal activity assay and Boyden chamber assay,respectively.RESULTS:The double-stranded oligonucleotide fragments of Bmi-1 short interfering RNA(siRNA)cloned into pRNAT-U6.2 vector conformed to the inserted sequence.RT-PCR and Western blotting indicated that the expression levels of Bmi-1 gene mRNA and protein were markedly decreased in transfected BGC823 cells with pRNAT-U6.2-si1104 and pRNATU6.2-si1356,especially in transfected BGC823 cells with pRNAT-U6.2-si1104,compared with two control groups(empty vector and blank group).In particular,Bmi-1 protein expression was almost completely abolished in cells transfected with the recombinant vector harboring shRNA targeting the sequence GGAGGAGGTGAATGATAAA(nt1104-1122).Compared with untransfected cells and cells transfected with the empty vector,the mean percentage of senescent cells increased and the number of cells passing through the Matrigel decreased in cells transfected with the recombinant vectors.CONCLUSION:Silencing Bmi-1 by RNA interference can increase the senescent cell rate and effectively reduce the metastasis of gastric cancer cells.

Prognosis of patients with gastric cancer and solitary lymph node metastasis

AIM:To investigate the relationship of solitary lymph node metastasis(SLNM)and age with patient survival in gastric cancer(GC).METHODS:The medical records databases of China’s Beijing Cancer Hospital at the Peking University School of Oncology and Shanghai Tenth People’s Hospital affiliated to Tongji University were searched retrospectively to identify patients with histologically proven GC and SLNM who underwent surgical resection between October 2003 and December 2012.Patients with distant metastasis or gastric stump carcinoma following resection for benign disease were excluded from the analysis.In total,936 patients with GC+SLNM were selected for analysis and the recorded parameters of clinicopathological disease and follow-up(range:13-2925 d)were collected.The Kaplan-Meier method was used to stratify patients by age(≤50 years-old,n=198;50-64 years-old,n=321;≥65 years-old,n=446)and by metastatic lymph node ratio[MLR<0.04(1/25),n=180;0.04-0.06(1/25-1/15),n=687;≥0.06(1/15),n=98]for 5-year survival analysis.The significance of intergroup differences between the survival curves was assessed by a log-rank test. RESULTS:The 5-year survival rate of the entire GC+SLNM patient population was 49.9%.Stratification analysis showed significant differences in survival time(post-operative days)according to age:≤50 yearsold:950.7±79.0 vs 50-64 years-old:1697.8±65.9 vs≥65 years-old:1996.2±57.6,all P<0.05.In addition,younger age(≤50 years-old)correlated significantly with mean survival time(r=0.367,P<0.001).Stratification analysis also indicated an inverse relationship between increasing MLR and shorter survival time:<0.04:52.8%and 0.04-0.06:51.1%vs≥0.06:40.5%,P<0.05.The patients with the shortest survival times and rates were younger and had a high MLR(≥0.06):≤50 years-old:496.4±133.0 and 0.0%vs 50-65 years-old:1180.9±201.8 and 21.4%vs≥65 years-old:1538.4±72.4 and 37.3%,all P<0.05.The same significant trend in shorter survival times and rates for younger patients was seen with the mid-range MLR group(0.04-0.06),but the difference between the two older groups was not significant.No significant differences were found between the age groups of patients with MLR<0.04.Assessment of clinicopathological parameters identified age group,Borrmann type,histological type and tumor depth as the most important predictors of the survival rates and times observed for this study population.CONCLUSION:GC patients below 51 years of age with MLR of SLNM above 0.06 have shorter life expectancy than their older counterparts.