ABSTRACT
Hypoxia-inducible factor 1alpha (HIF-1alpha), which transactivates a variety of hypoxia-induced genes, is rapidly degraded under nomoxia through the hydroxylation-ubiquitination-proteasome pathway. In this study, we addressed how HIF-1alpha is stabilized by proteasome inhibitors. The ubiquitin pool was rapidly reduced after proteasome inhibition, followed by the accumulation of non-ubiquitinated HIF-1alpha. The poly-ubiquitination of HIF-1alpha was resumed by restoration of free ubiquitin, which suggests that the HIF-1alpha stabilization under proteasome inhibition is attributed to depletion of the free ubiquitin pool. Ni2+ and Zn2+ also stabilized HIF-1alpha with depletion of the free ubiquitin pool and these effects of metal ions were attenuated by restoration of free ubiquitin. Ni2+ and Zn2+ may disturb the recycling of free ubiquitin, as MG132 does. Based on these results, the state of the ubiquitin pool seems to be another critical factor determining the cellular level of HIF-1alpha.
Subject(s)
Humans , Cell Hypoxia/physiology , Cell Line, Tumor , HCT116 Cells , HEK293 Cells , Hypoxia-Inducible Factor 1, alpha Subunit/biosynthesis , Leupeptins/pharmacology , Nickel/chemistry , Proteasome Endopeptidase Complex/metabolism , Proteasome Inhibitors/pharmacology , Ubiquitin/metabolism , Ubiquitination/physiology , Up-Regulation , Zinc/chemistryABSTRACT
To study the expression of hypoxia inducible factor-1alpha (HIF-1alpha) protein in prostate cancer (Pca) and its biological significance, the expression of HIF-1alpha was assayed by means of immunohistochemical technique in 42 prostate cancer, 12 prostatic intraepithelial neoplasm (PIN) and 9 normal prostate tissue (NP) specimens. Western blot was used to examine the expression of HIF-1alpha in prostate cancer cell line (PC-3M) induced by different oxygen tension. HIF-1alpha expression was positive in 33 Pca and 9 PIN specimens, and the positive rate of HIF-1alpha was higher in distant metastasis patients than in patients without metastasis of prostate cancer (P<0.05), while there was no expression of HIF-1alpha in NP. The level of HIF-1alpha in PC-3M significantly increased with the decrease of oxygen tension (P<0.01). Overexpression of HIF-1alpha is the preliminary event of the formation of Pca, which may induce carcinoma into malignant phenotype. Thus it may serve as an early diagnosis marker and the novel target for Pca treatment.