Hypoxia-inducible Factor-1α, a Key Factor in the Keratinocyte Response to UVB Exposure

Abstract

Hypoxia-inducible factor-1 (HIF-1) is a major transcription factor sensitive to oxygen levels, which responds to stress factors under both hypoxic and nonhypoxic conditions. UV irradiation being a common stressor of skin, we looked at the effect of UVB on HIF-1␣ expression in keratinocytes. We found that UVB induces a biphasic HIF-1␣ variation through reactive oxygen species (ROS) generation. Whereas rapid production of cytoplasmic ROS down-regulates HIF-1␣ expression, delayed mitochondrial ROS generation results in its up-regulation. Indeed, activation of p38 MAPK and JNK1 mediated by mitochondrial ROS were required for HIF-1␣ phosphorylation and accumulation after UVB irradiation. Our experiments also revealed a key role of HIF-1␣ in mediating UVB-induced apoptosis. We conclude that the broad impact of the HIF-1 transcription factor on gene expression could make it a key regulator of UV-responsive genes and photocarcinogenesis. Solar UV radiation is the major risk factor for the development of skin cancer, the most common malignancy in the world. Several factors participate in the human natural photoprotective barrier, including constitutive and UV-induced pigmentation, stratum corneum thickness, UV-induced immune responses, UV-induced apoptosis, antioxidant defense, and DNA repair systems (1, 2). To develop a strategy for the prevention and the therapy of skin cancer, relationships between the various cellular signaling pathways that modulate cellular responses to UV irradiation in skin cells require a more indepth understanding. Within this complex group of UV-induced cellular responses, the role of ROS 3 appears central with dual effects (3). On one hand, an increase in ROS concentrations following UVB irradiation leads to cytotoxicity through protein, lipid, and DNA oxidation both in vitro and in vivo (4 -7). Reduction of the deleterious effects of UV-induced ROS by reinforcement of the antioxidant defense supports this notion (8 -10). On the other hand, ROS can also act as second messenger molecules mediating the response of cells to UVB (11)(12)(13)(14). We have recently demonstrated that UVB induces ROS production in two distinct waves. Whereas the second peak in ROS concentration has a direct effect on apoptosis, the first peak could mediate signal transduction (10). In this study, we addressed the possible role of ROS as second messengers after UVB irradiation and their potential relationship with a stress-inducible transcription factor, HIF-1. This factor, so named for its exquisite sensitivity to oxygen levels in the cell environment, participates in the regulation of numerous genes involved in angiogenesis, glycolysis, apoptosis, migration, and metastasis (15-18). We decided to look at HIF-1␣ expression within the context of ROS production in keratinocytes, in response to UVB irradiation, because ROS were already known to influence HIF-1␣ regulation and hypoxia-induced apoptosis (19). Moreover, involvement of HIF in the modulation of cell responses to growth factors under normoxia in a ROS-dependen...

Oxidized glycerophosphocholines as biologically active mediators for ultraviolet radiation-mediated effects

“…UVR mediated changes to phospholipids is therefore thought to occur as a result of photo-oxidation reactions 80 . Recent studies by photobiologists indicate that UVB generates ROS through a series of sequential steps involving: EGFR activation, ROS generation by cytosolic NADPH oxidase, ras/ERK & p38MAPK activation, p53 activation, and finally apoptotic signaling leading to mitochondrial ROS generation [81][82][83][84][85][86][87][88] . Thus, UVBmediated ROS are likely involved in the generation of ox-GPCs.…”

Catalase overexpression reduces UVB-induced apoptosis in a human xeroderma pigmentosum reconstructed epidermis

“…High efficiency of lentiviral vector-mediated gene transfer in normal and XPC keratinocytes As previously shown, lentiviral vectors provide high efficiency and sustained transgene expression in normal human keratinocytes. [22][23][24] In this study, the same type of lentivectors was used for the transduction of XPC keratinocytes to overexpress either the marker gene EGFP (TPEW) or the 'therapeutic' gene catalase (TPCATW) (Figure 2a). The percentage of EGFPpositive cells assessed by cytofluometry 5 days post-transduction reached 85-95% both in normal and XPC cells (Figure 2b).…”

“…[16][17][18][19][20] Several studies have shown that keratinocyte exposure to UVB irradiation generates ROS in excessive quantities that quickly overwhelm various antioxidant defense systems including non-enzymatic (a-tocopherol and vitamin C) and enzymatic antioxidants (catalase and superoxide dismutase). [21][22][23][24] UVB-induced ROS production leads to cytotoxicity through proteins, lipids and DNA oxidation both in vitro and in vivo. 21,[25][26][27] Unlike lipids and proteins, damaged DNA molecules cannot be replaced and need to be repaired.…”

Low Dose Ultraviolet B Irradiation Increases Hyaluronan Synthesis in Epidermal Keratinocytes via Sequential Induction of Hyaluronan Synthases Has1–3 Mediated by p38 and Ca2+/Calmodulin-dependent Protein Kinase II (CaMKII) Signaling*

“…For example, a key role has been demonstrated for epidermal growth factor receptor (EGFR), a prominent receptor tyrosine kinase in keratinocytes (39), in relaying UVB-induced responses (40). It is also important to distinguish between immediate and delayed effects (41). This versatility in responses and the multitude of pathways potentially activated could account for the dynamic temporal patterns previously observed in hyaluronan secretion and HAS expression.…”