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

Abstract

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.

Abnormal GRHL2 Methylation Confers Malignant Progression to Acute Leukemia

“…At present, epigenetics is mainly monitored by DNA methylation and mRNA detection [21]. Tumor suppressor gene methylation is one of the important links in the occurrence of malignant neoplastic diseases and substantially regulates the occurrence and development of malignant neoplastic diseases [22][23][24].…”

Crosstalk between DNA methylation and hypoxia in acute myeloid leukaemia

“…These effects are reversed with HIF1α inhibition, suppressing the growth of AML cell lines, and encouraging various apoptotic pathways [166]. The glycolytic switch induced by hypoxia can also promote AML cell growth, viability, and survival [160,[168][169][170][171][172]. A distinct glycolytic profile is observed in AML patients, with high levels of glycolytic metabolites predicting poor survival [173].…”

“…Until recently, the relationship between hypoxia and TET activity in AML had not been explored. In 2021, an analysis of KG-1 AML cells exposed to hypoxia (1–3% O 2 ) demonstrated a positive correlation between HIF1A and TET2 expression [ 170 ]. Enhanced TET2 transcription was also associated with increased binding of HIF1α to the TET2 promoter, which subsequently increased 5hmC and decreased 5mC.…”

Dissecting TET2 Regulatory Networks in Blood Differentiation and Cancer

“…Finally, although essential for TET catalytic activity, oxygen has been described as a minor direct regulator of TET function in physiological settings [55]. However, low oxygen levels might indirectly regulate TET2 expression and activity in leukemic cells through a mechanism involving the activation of the hypoxia-inducible factor 1α (HIF1α) [56].…”