Effect of hypoxia-inducible factor 1-alpha (HIF-1α) on proliferation and apoptosis of adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma cells

Abstract

To understand whether hypoxia-inducible factor 1-alpha (HIF-1α) could protect AtT-20 cells from hypoxia induced apoptosis, we investigated the effects of HIF-1α on proliferation and apoptosis of adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma cells (AtT-20 cells). AtT-20 cells were treated with various concentrations of CoCl₂ to induce hypoxia. 3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide, a yellow tetrazole (MTT) was applied to detect the proliferation of these cells. Western blot assay and real time polymerase chain reaction (PCR) were used to determine the protein and mRNA expressions of HIF-1α, respectively. In addition, AtT-20 cells were transfected with siRNA targeting HIF-1α and treated with different concentrations of CoCl₂. The transfection efficacy was assessed by real-time PCR and western blot assay. Apoptosis was measured by fluorescein isothiocyanate (FITC)-annexin V/ propidium iodide (PI) staining and TUNEL staining. The effect of CoCl₂ on the proliferation of AtT-20 cells was in a concentration and time dependent manner. When the concentration of CoCl₂ was ≤100 μM and/or duration of CoCl₂ treatment was ≤48 h, CoCl₂ triggered the proliferation of AtT-20 cells. Nevertheless, the apoptosis rate of cells transfected with HIF-1α-siRNA was markedly increased after CoCl₂ treatment. These findings suggest that, HIF-1α can promote the proliferation of AtT-20 cells and exert anti-apoptotic effect under hypoxic condition.

Key words: Hypoxia inducible factor–1α, cobalt chloride, apoptosis, pituitary adenoma