Objective  To analyze the expression level of miR-221 in cancer tissues, normal tissues and plasma of patients with liver cancer and its correlation with clinicopathological characteristics, diagnosis and prognosis. And further analyze and explore its mechanism of action in the occurrence and development of liver cancer.

  Methods  The two chip data sets in the Gene Expression Omnibus (GEO) were used to analyze the expression level of miR-221 in liver cancer tissues and non-tumor tissues. Real-time fluorescent quantitative PCR method was used to verify the expression level of miR-221 in tumor tissues and corresponding adjacent tissues of 74 patients with liver cancer, and to further detect the expression level of miR-221 in plasma of 25 patients with liver cancer and normal human plasma. Further analyze the value of miR-221 in the diagnosis and prognosis of liver cancer. Predict the target genes of miR-221 for functional enrichment analysis, and further use MTS, clone formation experiment and traswell chamber experiment to detect the effect of miR-221 on the proliferation, invasion and epithelial-mesenchymal transition (EMT) process of liver cancer cells.

  Results   The results of GEO database analysis showed that the expression level of miR-221 in liver cancer tissues was significantly higher than that in non-tumor liver tissues (P<0.05). Also verified by real-time fluorescent quantitative PCR results showed that miR-221 was significantly higher in tumor tissues and plasma of liver cancer patients than those of normal people. And the expression of miR-221 is significantly related to the TNM stage and tumor size of liver cancer patients. The decrease in the expression level of MiR-221 is significantly related to the prolonged overall survival time and disease-free survival time of liver cancer patients. Functional enrichment analysis found that the signal pathways involved in miR-221 were mainly p53 signal pathway, ErbB signal pathway, RNA transport and mTOR signal pathway, and in vitro experiments showed that low expression of miR-221 significantly inhibited the proliferation and invasion of liver cancer cells At the same time, the expression levels of E-cadherin mRNA and protein in liver cancer HepG2 and MHCC97H cells were significantly increased (P<0.01), while the expression levels of N-cadherin and vimentin mRNA and protein were significantly reduced.

  Conclusions   MiR-221 is highly expressed in liver cancer tissues and plasma, and is significantly related to the poor prognosis of liver cancer patients. It mainly plays a role in liver cancer through the EMT process.