Knockdown of MDC1 relieves the inhibitory effect of MDC1-AS on human gastric cancer cell proliferation. (A) The relative mRNA expression of MDC1-AS and MDC1 were examined by RT-qPCR in the three MKN28 cell treatment groups, the control group, MDC1-AS-expressing plasmid transfected group and MDC1-AS-expressing plasmid/siMDC1 co-transfected group. (B) The relative expression of MDC1-AS and MDC1 mRNA was explored by RT-qPCR analysis in three MKN45 cell treatment groups, the control group, the shMDC1-AS transfected group and the shMDC1-AS/MDC1-expressing plasmid co-transfected group. Cell proliferation was determined in (D) MKN28 cells transfected with the MDC1-AS expressing plasmid in the presence or absence of siMDC1 and (C) MKN45 cells transfected with shMDC1-AS with or without the MDC1-expressing plasmid. *P<0.05 vs. the control group for MDC1-AS; #P<0.05 vs. the control group for MDC1; &P<0.05 vs. as indicated. MDC1, mediator of DNA damage checkpoint protein 1; MDC1-AS, MDC1-antisense RNA; shMDC1-AS, small hairpin RNA directed against MDC1-AS; siMDC1, small interfering RNA directed against MDC1; RT-qPCR, reverse transcription-quantitative polymerase chain reaction.