Effect Of Apoptin On Apoptosis Induced By HSP70 Stress In HepG2 Cells

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death with an estimated worldwide incidence of over one million new cases per year. surgery offers a cure, but tumor resection is feasible for 10-20% of patients, and recurrence rates remain as high as 50% after tumor resection. Due to the aggressive features of HCC including rapid growth, resistance to chemotherapy, and lack of effective adjunct therapy after surgery. Despite extensive exploration for novel anticancer drugs and therapeutic strategies, there has been little success in improving the treatment of HCC. Therefore, effective treatment is urgently required for HCC patients.Apoptin is a protein of 121 amino acids encoded by the VP3 gene of chicken anemia virus. Up to now, apoptin has been shown to induce apoptosis of a variety of human tumor cell lines without causing any effect to normal cells. Notably, apoptin induces apoptosis of tumor cells in a p53-independent manner and its tumoricidal activity is not affected by the overexpression of B-cell lymphoma 2 (Bcl-2). As the mutation of p53 and Bcl-2 overexpression in tumor cells are important mechanisms for chemotherapeutic drug resistance, the unique antitumor properties of apoptin suggest that it is a promising agent for anticancer therapy.Objective:Observe the localization of Apoptin in tumor and normal cells, and explore the mechanism of tumor-specific apoptosis induced by Apoptin. This study aimed to investigate the molecularmechanism underlying the selective antitumor effects of apoptin. Methods:HepG2 cells were treated with apoptin or transfected with apoptin expression vector. Heat shock protein 70 (HSP70) expression was examined by Western blot. The binding of apoptin to HSP70 promoter was detected by electrophoretic mobility shift assay, chromatin immunoprecipitation, and luciferase assay. Results:The results showed that apoptin inhibited HSP70 expression in HepG2 cells and apoptin-induced apoptosis of HepG2 cells was dependent on the expression level of HSP70. Conclusion:Furthermore, apoptin promoted HSF1 trimer depolymerization and inhibited HSF1-mediated HSP70 transcription. In addition, apoptin competed with HSF1 to bind heat shock element in HSP70 promoter, leading to reduced HSP70 transcription. Both these mechanisms contribute to the suppression of HSP70 transcription and expression. Our findings provide the first evidence that apoptin induces tumor cell apoptosis by specifically downregulating the expression of HSP70, which helps explain the specific antitumor effects of apoptin.