Hypoxia-mediated control of HIF/ARNT machinery in epidermal keratinocytes.
Transcriptional activity of hypoxia-induced factor 1 (HIF1) - a heterodimer of HIF1α and ARNT (HIF1β) - is essential for cellular adaptation to environmental stress and plays an important role in skin development, wound healing, tumorigenesis and barrier function. Using primary mouse and human epidermal keratinocytes at ambient or hypoxic (1% O(2)) conditions we studied effects of hypoxia upon HIF protein expression. Significant nuclear levels of ARNT and HIF1α along with high HIF1 activity in normoxic keratinocytes suggest an as yet uncharacterised oxygen-independent role for HIF pathway in the epidermis. Acute hypoxia results in an instant but transient increase of HIF1α protein accompanied by a gradual decrease in its mRNA, while ARNT expression remains unchanged. In prolonged (chronic) hypoxia both HIF1α and Arnt are downregulated along with decline of HIF1 activity. However, expression of classical HIF1 targets such as Selenbp1 and Vegfa remains high. Thus, keratinocytes respond to acute hypoxia with immediate block of HIF1α protein degradation and concomitant increase of HIF activity, while under chronic hypoxia pro-angiogenic signalling is maintained through HIF1-independent pathway(s). Decline of HIF1α during chronic exposure is controlled at both mRNA and protein levels, while Arnt is downregulated post-translationally. Distinct transcription levels of Hif1α and Hif3α splice variants under normoxia and their differential response to hypoxia suggest functional diversity of Hif-α isoforms and highlight the complexity of HIF machinery control in epidermal keratinocytes.
College of Medicine, Dentistry and Nursing, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, UK.
Lynda
L
Weir
Douglas
D
Robertson
Irene M
IM
Leigh
J Keith
JK
Vass
Andrey A
AA
Panteleyev
D017398:Alternative Splicing; D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D004817:Epidermis / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D000860:Hypoxia; D015603:Keratinocytes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
D051017:Apoptosis Regulatory Proteins; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D015415:Biomarkers; D012333:RNA, Messenger; D012097:Repressor Proteins; D042461:Vascular Endothelial Growth Factor A; D000099162:Endothelial PAS Domain-Containing Protein 1; C497396:ARNT protein, human; C116973:HIF3A protein, human; C467484:VEGFA protein, human