SIRT1 is a member of a highly conserved gene family (sirtuins) encoding nicotinamide adenine dinucleotide (NAD)+-dependent deacetylases, originally found to deacetylate histones leading to increased DNA stability and prolonged survival in yeast and higher organisms, including mammals. SIRT1 has been found to function as a deacetylase for numerous protein targets involved in various cellular pathways, including stress responses, apoptosis and axonal degeneration. However, the role of SIRT1 in ultraviolet (UV) signalling pathways remains unknown. Using cell culture and Western blot analysis in this study we found that SIRT1 is expressed in cultured human skin keratinocytes. Both UV radiation and H2O2, two major inducers of skin cell damage, down-regulate SIRT1 in a time- and dose-dependent manner. We observed that reactive oxygen species-mediated JNK activation is involved in this SIRT1 down-regulation. SIRT1 activator, resveratrol, which has been considered as an important antioxidant, protects against UV- and H2O2-induced cell death, whereas SIRT inhibitors such as sirtinol and nicotinamide enhance cell death. Activation of SIRT1 negatively regulates UV- and H2O2-induced p53 acetylation, because nicotinamide and sirtinol as well as SIRT1 siRNA enhance UV- and H2O2-induced p53 acetylation, whereas SIRT1 activator resveratrol inhibits it. We also found that SIRT1 is involved in UV-induced AMP-activated protein kinase (AMPK) and downstream acetyl-CoA carboxylase (ACC), phosphofructose kinase-2 (PFK-2) phosphorylation. Collectively, our data provide new insights into understanding of the molecular mechanisms of UV-induced skin aging, suggesting that SIRT1 activators such as resveratrol could serve as new anti-skin aging agents.

Collectively, our results provide evidence for AQP3-facilitated ovarian cancer cell migration, suggesting a novel function for AQP3 expression in high-grade tumors. The results that curcumin inhibits EGF-induced up-regulation of AQP3 and cell migration, provide a new explanation for the anticancer potential of curcumin.

AMP-activated protein kinase or AMPK is an evolutionarily conserved sensor of cellular energy status, activated by a variety of cellular stresses that deplete ATP. However, the possible involvement of AMPK in UV-and H 2 O 2 -induced oxidative stresses that lead to skin aging or skin cancer has not been fully studied. We demonstrated for the first time that UV and H 2 O 2 induce AMPK activation (Thr 172 phosphorylation) in cultured human skin keratinocytes. UV and H 2 O 2 also phosphorylate LKB1, an upstream signal of AMPK, in an epidermal growth factor receptor-dependent manner. Using compound C, a specific inhibitor of AMPK and AMPK-specific small interfering RNA knockdown as well as AMPK activator, we found that AMPK serves as a positive regulator for p38 and p53 (Ser 15 ) phosphorylation induced by UV radiation and H 2 O 2 treatment. We also observed that AMPK serves as a negative feedback signal against UV-induced mTOR (mammalian target of rapamycin) activation in a TSC2-dependent manner. Inhibiting mTOR and positively regulating p53 and p38 might contribute to the pro-apoptotic effect of AMPK on UV-or H 2 O 2 -treated cells. Furthermore, activation of AMPK also phosphorylates acetylCoA carboxylase or ACC, the pivotal enzyme of fatty acid synthesis, and PFK2, the key protein of glycolysis in UV-radiated cells. Collectively, we conclude that AMPK contributes to UVand H 2 O 2 -induced apoptosis via multiple mechanisms in human skin keratinocytes and AMPK plays important roles in UV-induced signal transduction ultimately leading to skin photoaging and even skin cancer.Ultraviolet (UV) spectrum is divided into UVC (200 -280 nm), UVB (280 -320 nm), and UVA (320 -400 nm). UVB and UVA are of environmental significance and social concern, because UVC is filtered through the ozone layer. UV penetrates into the papillary area of the dermis (ϳ0.2 mm) and induces DNA damages of residing keratinocytes and dendritic cells. They are perturbed both phenotypically and functionally undergoing apoptosis upon UV radiation (1, 2). Previous studies in human keratinocytes in vitro and in human skin in vivo have demonstrated that UV response comprises trans-activation of cell surface growth factor receptors, such as EGFR, 3 and their attendant downstream signal transduction machinery such as MAPK and phosphatidylinositol 3-kinase/AKT (2-6). Although MAPK, including JNK and p38, is responsible for UV-induced cell apoptosis and skin aging, other cellular signals such as AKT (also known as protein kinase B) serve as survival signals in skin cells to fight against UV-induced widespread cell death (1-4). However, the possible involvement of other signals, AMP-activated protein kinase or AMPK, for example, in UV-induced cell apoptosis leading to skin aging or cancer has not been fully studied.AMPK is a heterotrimeric serine-threonine kinase that senses depletion of intracellular energy and responds by stimulating catabolic pathways that generate ATP (5, 6). One mechanism for sensing cellular energy levels involves allosteric activation o...

Abstract. Aquaporins (AQPs) are a family of 13 small (~30 kDa/monomer), hydrophobic, integral membrane proteins. AQPs are expressed in various epithelial and endothelial cells involved in fluid transport. Here, we demonstrated for the first time that AQP1 is expressed in cultured human retinal pigment epithelial (RPE) cells (ARPE-19 cell line). Ultraviolet radiation (UVB) and H 2 O 2 , two major factors causing RPE cell damage, induced AQP1 downregulation which was mediated by MEK/ERK activation. UV and H 2 O 2 as well as AQP1-specific siRNA knockdown impaired water permeability of ARPE-19 cells. Notably, pretreatment with all-trans retinoic acid attenuated UV-and H 2 O 2 -induced AQP1 downregulation and water permeability impairment. Considering that water permeability is involved in multiple functions of RPE cells such as cellular junction formation, fluid or protein exchange and barrier formation, our data elucidated a novel mechanism through which UV radiation and oxidative stress induce eye cell damage. Our results further support the notion that all-trans retinoic acid might be useful for protection against UV or oxidative stress-induced eye cell damage.

Abstract.Vitiligo is an acquired and progressive disorder manifested by the selective destruction of melanocytes in the skin. An extremely high level of hydrogen peroxide (H 2 O 2 ) in plasma as well as in lesional skin has been reported in vitiligo patients. High H 2 O 2 level has been suggested to be responsible for the disappearance of melanocytes in vitiligo. JNK and p38 MAPK are strongly induced by oxidative stress and related to neuron loss in neurodegenerative disorders. Minocycline, an antibiotic possessing antioxidant activity, is capable of attenuating oxidative stress-induced neurotoxicity. To investigate whether minocycline rescues melanocytes from H 2 O 2 -induced apoptosis, cultured mouse melanocytes (B10BR) were treated with H 2 O 2 in the presence or absence of minocycline. Our data showed that H 2 O 2 decreases cell viability in a concentration-dependent manner which is attenuated by minocycline. Also, H 2 O 2 treatment activates JNK and p38 MAPK, and executive caspase 3 in B10BR cells. Minocycline significantly inhibits H 2 O 2 -induced activation of JNK, p38 MAPK and caspase 3. Collectively, we concluded that minocycline protects melanocytes against H2O2-induced apoptosis in vitro. Its protective effect is associated with the inhibition of JNK and p38 MAPK. Our findings suggest that minocycline, a clinically well-tolerated, safe antibiotic, may be used to prevent melanocyte loss in the early stage of vitiligo.