A prolyl-hydroxylase inhibitor, ethyl-3,4-dihydroxybenzoate, induces haem oxygenase-1 expression in human cells through a mechanism independent of hypoxia-inducible factor-1alpha.
Hypoxia-inducible factor (HIF)-1 is important for cellular homeostasis under hypoxia. Expression of haem oxygenase-1 (HO-1), an essential enzyme in haem catabolism, varies under hypoxia, depending on cell types. Here, we studied the role of HIF-1alpha, a component of HIF-1, in the regulation of HO-1 expression using three human cell lines: HeLa cervical cancer, and ARPE-19 and D407 retinal pigment epithelial cells. Under hypoxia (1% O(2)), the expression of HO-1 mRNA was decreased in HeLa cells, increased in D407 cells, and unchanged in ARPE-19 cells, while HIF-1alpha protein was accumulated in these cell lines. Thus, HIF-1alpha is unlikely to function as a key regulator for HO-1 expression under hypoxia. We then used ethyl-3,4-dihydroxybenzoate (EDHB), an inhibitor of prolyl hydroxylases, to accumulate HIF-1alpha protein under normoxia. Treatment with EDHB (250-500 microM) increased HIF-1alpha protein levels in HeLa and D407 cells, but not in ARPE-19 cells, whereas EDHB at lower concentrations (50-100 microM) consistently induced HO-1 mRNA expression (about 20-fold) in these three cell lines. Moreover, EDHB increased the HO-1 gene promoter activity via the enhancer that lacks a HIF-1-binding site. In conclusion, the signals evoked by hypoxia and after EDHB treatment differentially regulate HO-1 mRNA expression through HIF-1alpha-independent mechanisms.
Li
Bin
B
Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai 980-8575, Japan.
Takeda
Kazuhisa
K
Yokoyama
Satoru
S
Shibahara
Shigeki
S
D001565:Benzoates / Q000737:chemistry*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D011393:Procollagen-Proline Dioxygenase / Q000037:antagonists & inhibitors*; D011401:Promoter Regions, Genetic; D055213:Retinal Pigment Epithelium / Q000166:cytology
D001565:Benzoates; D004791:Enzyme Inhibitors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011393:Procollagen-Proline Dioxygenase; D051547:Heme Oxygenase-1