Effects of arsenic and UVB on normal human cultured keratinocytes: impact on apoptosis and implication on photocarcinogenesis.
Inorganic arsenic is an environmental toxin and a human carcinogen. Being a co-mutagen, arsenic enhances carcinogenesis of ultraviolet irradiation on the mouse skin. Apoptosis, a well-regulated cell death process, is essential for cell development and tissue homeostasis. Dysregulation of apoptosis will lead to various kinds of pathological conditions, such as cancers. The purpose of this study is to investigate the apoptotic effect induced by the interactions of arsenic and UVB on cultured human keratinocytes. Cultured keratinocytes were treated with sodium arsenite (1 microM) and/or UVB 50 mJ/cm2 irradiation in different combinations, including arsenic alone (As group), UVB alone (UVB group), arsenic followed by UVB (As/UVB group), and UVB followed by As (UVB/As group) treatments. Our results revealed that a low concentration of sodium arsenite did not induce keratinocytes apoptosis. The UVB group showed obvious elevation of caspase-8, -9, and -3 activities in addition to strong induction of apoptosis as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine nick-end labeling (TUNEL) assay. Similar pro-apoptotic effects were observed in the UVB/As group. In contrast, only subtle changes of cell morphology and survival rate were noticed in the As/UVB group. In addition, the results of Western blot and activity assay of caspase-8, -9, and -3 revealed that neither the receptor nor the mitochondrial apoptotic signaling pathway was activated in the As/UVB group. Therefore, we conclude that the pretreatment of keratinocytes with sodium arsenite decreased the pro-apoptotic effects induced by UVB. This finding corroborated with the animal model studying the effects of arsenic and UVB on carcinogenesis. The molecular mechanisms by which arsenic decreased UVB-induced apoptosis remain to be elucidated.
Chen
Po-Hung
PH
Department of Dermatology, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan, Republic of China.
Lan
Cheng-Che E
CC
Chiou
Min-Hsi
MH
Hsieh
Ming-Chu
MC
Chen
Gwo-Shing
GS
D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D018053:Arsenites / Q000633:toxicity*; D015153:Blotting, Western; D002273:Carcinogens / Q000633:toxicity; D020169:Caspases / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D002478:Cells, Cultured; D003043:Cocarcinogenesis; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D020287:In Situ Nick-End Labeling; D015603:Keratinocytes / Q000187:drug effects / Q000528:radiation effects; D017670:Sodium Compounds / Q000633:toxicity*; D014466:Ultraviolet Rays
D018053:Arsenites; D002273:Carcinogens; D017670:Sodium Compounds; C017947:sodium arsenite; D020169:Caspases