Sencond, XWLC-05, YTMLC-90, and H157 cells were transfected with pGCMV/EGFP-hsa-miR-34a or pGCMV/EGFP-hsa-miR-NC plasmids to demonstrate whether high expression levels of miR-34a correlated with the expression of PTEN, CDK6, and YY1 in lung cancer. The gene discussed is YY1; the disease is lung cancer.