Effects of hypoxia on DNA hydroxymethylase Tet methylcytosine dioxygenase 2 in a KG-1 human acute myeloid leukemia cell line and its mechanism

Hypoxia is involved in the epigenetic modification of leukemia. As an important DNA hydroxymethylase and a tumor suppressor gene, the expression regulating mechanism of Tet methylcytosine dioxygenase 2 (TET2) remains unclear. The aim of the present study was to explore whether hypoxia and hypoxia-inducible factor 1α (HIF-1α) regulate TET2 gene expression and its demethylation function in acute myeloid leukemia (AML). The human AML cell line KG-1 was used in the present study. The results demonstrated that hypoxia could increase proliferation, enhance metabolism and inhibit apoptosis in KG-1 cells, as detected by the cell counting kit-8 assay, lactate dehydrogenase assay and Annexin V-FITC/propidium iodide staining, respectively. Hypoxia reduced the genome methylation status in KG-1 cells detected using 5-methylcytosine and 5-hydroxymethylcytosine detection kits. In addition, HIF-1α overexpression increased TET2 expression, 5-hmC level and cyclin-dependent kinase inhibitor 2B [p15(INK4B)] gene demethylation compared with the HIF-1α non-overexpression group in KG-1 cells detected by reverse transcription-quantitative PCR, western blotting, 5-hydroxymethylcytosine detection kits and methylation-specific PCR, respectively. The inhibition of HIF-1α by inhibitor YC-1 reduced demethylation in KG-1 cells by decreasing TET2 expression. It was also revealed that HIF-1α could enhance TET2 transcriptional activity by binding to the hypoxia response element of the TET2 gene promoter region using chromatin immunoprecipitation and luciferase reporter gene assays. TET2 may be a potential target gene regulated by HIF-1α. Hypoxia was demonstrated to regulate the expression of TET2 by HIF-1α, which in turn affected the methylation and expression of downstream target genes and served a role in the occurrence and progression of leukemia. In the present study, the association between hypoxia metabolism and epigenetic regulation in AML was investigated and the findings provided a new idea and experimental basis for the diagnosis and treatment of hematologic malignancies.