Similarity in the functions of HIF-1α and HIF-2α proteins in cervical cancer cells

Hypoxia Enhances HIF1α Transcription Activity by Upregulating KDM4A and Mediating H3K9me3, Thus Inducing Ferroptosis Resistance in Cervical Cancer Cells

Objective

Cervical cancer (CC) is a prevalent cancer in women. Hypoxia plays a critical role in CC cell ferroptosis resistance. This study explored the mechanism of hypoxia in CC cell ferroptosis resistance by regulating HIF1α/KDM4A/H3K9me3.

Methods

Cultured SiHa and Hela cells were exposed to CoCl2 and treated with Erastin. Cell viability was detected by MTT assay, and concentrations of iron ion, MDA and GSH were determined using corresponding kits. Expressions of KDM4A, HIF1α, TfR1, DMT1, and H3k9me3 were detected by RT-qPCR, Western blot, and ChIP assay. The correlation of KDM4A and HIF1α was analyzed on Oncomine, UALCAN, and Starbase. CC cells were co-transfected with shKDM4A or/and pcDNA3.1-HIF1α. Iron uptake and release were assessed using the isotopic tracer method. The binding relationship between HIF1α and HRE sequence was verified by dual-luciferase assay.

Results

Cell viability and GSH were decreased while iron concentration, MDA, KDM4A, and HIF1α levels were increased in hypoxia conditions. The 2-h hypoxia induced ferroptosis resistance. KDM4A and HIF1α were highly-expressed in CC tissues and positively correlated with each other. KDM4A knockdown attenuated cell resistance to Erastin, increased H3K9me3 level in the HIF1α promoter region, and downregulated HIF1α transcription and translation. H3K9me3 level was increased in the HIF1α promoter after hypoxia. HIF1α overexpression abrogated the function of KDM4A knockdown on ferroptosis in hypoxia conditions. Iron uptake/release and TfR1/DMT1 levels were increased after hypoxia. Hypoxia activated HRE sequence in TfR1 and DMT1 promoters.

Conclusion

Hypoxia upregulated KDM4A, enhanced HIF1α transcription, and activated HRE sequence in TfR1 and DMT1 promoters via H3K9me3, thus inducing ferroptosis resistance in CC cells.

HIF2A overexpression reduces cisplatin sensitivity in cervical cancer by inducing excessive autophagy

Background

Hypoxia-induced autophagy is a crucial factor that induces chemotherapy resistance in tumor cells. As a key regulator facilitating the adaptation of solid tumors to hypoxia, the role of hypoxia-inducible factors (HIFs) in regulating hypoxia-induced chemotherapy resistance and autophagy has been extensively studied. However, the majority of studies have mainly focused on HIF-1. Direct evidence concerning the role of HIF2A in cisplatin resistance is sparse, and its underlying mechanism is not yet known.

Methods

Animal models were constructed by subcutaneously injecting cervical cancer cells stably overexpressing HIF2A (LV-HIF2A) with or without intraperitoneal injection of cisplatin. Tumor size and weight were evaluated to determine tumor growth. Apoptosis was detected by TUNEL assay and protein expression by western blotting.

Results

Nude mice injected with cells overexpressing HIF2A showed larger and heavier tumors than those in mice injected with negative control lentivirus (LV-NC)-infected cells, with or without cisplatin. Fewer apoptotic cells were noted in tumor tissues from the LV-HIF2A group than from the LV-NC group, with or without cisplatin. Additionally, expression of the anti-apoptotic protein, B-cell lymphoma 2 (BCL2), and autophagy-related proteins, beclin 1 and autophagy related 5 (ATG5), were found to be higher in the LV-HIF2A group than in the LV-NC group, regardless of cisplatin treatment. Moreover, expression of the pro-apoptotic protein, BCL2-associated X (BAX), was lower in tumor tissues from the LV-HIF2A group than from the LV-NC group. Effect of HIF2A overexpression on cisplatin sensitivity was found to be alleviated in vivo by the autophagy inhibitor, 3-methyladenine (3-MA).

Conclusions

HIF2A overexpression promoted tumor growth and autophagy but suppressed apoptosis in vivo, with or without cisplatin. The HIF2A overexpression-affected cisplatin sensitivity was alleviated by 3-MA. Therefore, we suggest that HIF2A overexpression reduces cisplatin sensitivity in cervical cancer by inducing excessive autophagy.

MicroRNA-519d-3p Inhibits Proliferation and Promotes Apoptosis by Targeting HIF-2α in Cervical Cancer Under Hypoxic Conditions

HIF-2α knockdown inhibits proliferation, arrests the cell cycle, and promotes apoptosis and autophagy under hypoxic conditions in cervical cancer. However, the upstream regulatory mechanism of HIF-2α expression is unclear. MicroRNAs (miRNAs) degrade target mRNAs by binding to the 3′-untranslated region of mRNAs. In this study, we investigated the role of miRNAs in the regulation of HIF-2α expression in cervical cancer under hypoxic conditions. miRNAs regulating HIF-2α expression were predicted using TargetScan and miRanda and were determined in cervical cancer under hypoxic conditions by qRT-PCR. Additionally, the targeted regulation of HIF-2α by miR-519d-3p was evaluated by Western blot and luciferase reporter assays. Effects of miR-519d-3p and HIF-2α on cell proliferation, cell cycle, and apoptosis were analyzed by CCK-8 and flow cytometry assays, respectively. miR-106a-5p, miR-17-5p, miR-519d-3p, miR-526b-3p, and miR-20b-5p are potentially regulatory miRNAs that bound to the HIF-2α 3′-untranslated region as per TargetScan and miRanda predictions. Expression of the five miRNAs was inhibited in HeLa cells under hypoxic conditions compared to normoxic conditions, and the expression of miR-519d-3p was lower than that of other miRNAs. Luciferase reporter assays showed that HIF-2α was a target of miR-519d-3p. Additionally, miR-519d-3p overexpression inhibited cell proliferation, arrested the cell cycle transition from the G₁ stage to the S stage, and promoted cell apoptosis under hypoxic conditions in cervical cancer. HIF-2α overexpression partially reversed the effect of miR-519d-3p. In conclusion, miR-519d-3p overexpression suppressed proliferation, inhibited the cell cycle, and promoted apoptosis of HeLa cells by targeting HIF-2α under hypoxic conditions.