Hypoxia upregulates hypoxia inducible factor (HIF)-3alpha expression in lung epithelial cells: characterization and comparison with HIF-1alpha.
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.
Li
Qi Fang
QF
Department of Anesthesiology, Renji Hospital, Shanghai Second Medical University, 1630 Dongfang Road, Shanghai 200127, China.
Wang
Xiang Rui
XR
Yang
Yue Wu
YW
Lin
Han
H
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
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