title: Hypoxia upregulates hypoxia inducible factor (HIF)-3alpha expression in lung epithelial cells: characterization and comparison with HIF-1alpha.
abstract: The role of the hypoxia-inducible factor (HIF) subunits 1alpha and 2alpha in response to hypoxia is well established in lung epithelial cells, whereas little is known about HIF-3alpha with respect to transcriptional and translational regulation by hypoxia. HIF-3alpha and HIF-1alpha are two similar but distinct basic helix-loop-helix-PAS proteins, which have been postulated to activate hypoxia responsive genes in response to hypoxia. Here, we used quantitative real time RT-PCR and immunoblotting to determine the activation of HIF-3alpha vs. HIF-1alpha by hypoxia. HIF-3alpha was strongly induced by hypoxia (1% O2) both at the level of protein and mRNA due to an increase in protein stability and transcriptional activation, whereas HIF-1alpha protein and mRNA levels enhanced transiently and then decreased because of a reduction in its mRNA stability in A549 cells, as measured on mRNA and protein levels. Interestingly, HIF-3alpha and HIF-1alpha exhibited strikingly similar responses to a variety of activating or inhibitory pharmacological agents. These results demonstrate that HIF-3alpha is expressed abundantly in lung epithelial cells, and that the transcriptional induction of HIF-3alpha plays an important role in the response to hypoxia in vitro. Our findings suggest that HIF-3alpha, as a member of the HIF system, is complementary rather than redundant to HIF-1alpha induction in protection against hypoxic damage in alveolar epithelial cells.
authors.affiliation: Department of Anesthesiology, Renji Hospital, Shanghai Second Medical University, 1630 Dongfang Road, Shanghai 200127, China.
authors.forename: Qi Fang
authors.initials: QF
authors.lastname: Li
authors.forename: Xiang Rui
authors.initials: XR
authors.lastname: Wang
authors.forename: Yue Wu
authors.initials: YW
authors.lastname: Yang
authors.forename: Han
authors.initials: H
authors.lastname: Lin
mesh_terms: D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D003035:Cobalt / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis* / Q000235:genetics; D011650:Pulmonary Alveoli / Q000166:cytology; D020871:RNA Stability; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors / Q000378:metabolism; D012097:Repressor Proteins; D020545:Respiratory Mucosa / Q000166:cytology; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D051017:Apoptosis Regulatory Proteins; D051792:Basic Helix-Loop-Helix Proteins; D003035:Cobalt; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D012097:Repressor Proteins; D014157:Transcription Factors; D014475:Uncoupling Agents; C497442:HIF1A protein, human; C116973:HIF3A protein, human; C018021:cobaltous chloride