UVB induces a biphasic response of HIF-1alpha in cultured human keratinocytes.
Hypoxia in the skin is important in chronic degenerative dermo-epidermal changes, inflammation, photoageing and carcinogenesis. In these processes, vascular endothelial growth factor (VEGF) plays a crucial role and is known to be affected by ultraviolet radiation (UVR). Hypoxia-inducible factor-1 (HIF-1) closely regulates the expression of VEGF in several experimental settings. We set out to study the impact of acute UVB irradiation on the level of HIF-1 as a major regulator of hypoxia-induced genes. Effects of UVB exposure on HIF-1alpha expression were investigated in HaCaT cells after a single irradiation by Western blots. Downstream target gene expression was measured by quantitative real-time polymerace chair reaction (PCR). UVB treatment resulted in an initial decrease of the HIF-1alpha protein level followed by a subsequent prolonged increase. If cells were exposed to additional UVB irradiation, another decrease in HIF-1alpha was provoked, similar to the original effect. The observed changes followed a strict timeline and were dose-dependent. The role of the PI3K/AKT pathway was examined. No change in the total level of AKT after UVB treatment was seen; however, its phosphorylation level was found to be markedly higher. In accordance with these observations, wortmannin, an inhibitor of PI3-kinase effectively blocked the UVB-induced increase in HIF-1alpha. In agreement with previous findings, UVB irradiation increased VEGF and haem oxygenase-1 mRNA levels determined by quantitative real-time PCR. It is concluded that changes in HIF-1alpha expression underlie the alterations in expression of VEGF upon UVB irradiation. Our findings indicate the involvement of PI3K in UVB-mediated HIF-1alpha upregulation.
Wunderlich
Livius
L
Department of Medical Chemistry, Semmelweis University, Budapest, Hungary.
Paragh
György
G
Wikonkál
Norbert M
NM
Bánhegyi
Gábor
G
Kárpáti
Sarolta
S
Mandl
József
J
D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000528:radiation effects; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D015870:Gene Expression / Q000528:radiation effects*; D051547:Heme Oxygenase-1 / Q000235:genetics; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000378:metabolism / Q000528:radiation effects*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011829:Radiation Dosage; D015398:Signal Transduction / Q000528:radiation effects*; D014466:Ultraviolet Rays; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D051547:Heme Oxygenase-1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D000077191:Wortmannin; C497442:HIF1A protein, human; C467484:VEGFA protein, human; C496541:HMOX1 protein, human