Analysis of SEMA3B methylation and expression patterns in gastric cancer tissue and cell lines

The family of semaphorins has been demonstrated to possess tumor suppressor activity, in which semaphorin 3B (SEMA3B) is differentially expressed in several types of tumors. The relationship between SEMA3B expression and its clinical significance in gastric cancer (GC) is currently unclear. In the present study, the expression and methylation status of the SEMA3B gene were detected by quantitative PCR and bisulfite sequencing PCR (BSP). Data indicated that the levels of SEMA3B mRNA decreased in gastric tumor tissues and the methylation status of SEMA3B in the tumor group was higher than the paired normal tissues. By BSP, the SEMA3B gene showed high methylated status which was detected in all 4 cell lines (AGS, BGC-823, MGC-803 and SGC-7901). Treatment of the cells with 5-Aza-2'-deoxycytidine revealed clearly elevated mRNA levels of SEMA3B. These results were further confirmed by western blot analysis of Sema3b protein expression. At the same time, increased expression of p53 mRNA in BGC-823, MGC-803 was detected and indicated that p53 may be involved in the regulation of SEMA3B expression in specific genetic background. Downregulation of SEMA3B was negatively correlated with tumor size and N staging in GC (p<0.05). In conclusion, CpG methylation of SEMA3B epigenetically regulates SEMA3B expression during development of GC. Furthermore, 5-Aza-2'-deoxycytidine could reverse the hypermethylation status of SEMA3B, which may benefit future studies exploring the application of demethylating agents in clinical usage of GC.