Low level, long-term inorganic arsenite exposure causes generalized resistance to apoptosis in cultured human keratinocytes: potential role in skin co-carcinogenesis.
Inorganic arsenic is a human carcinogen that targets the skin. Carcinogenesis is a multistep process in which acquired apoptotic resistance is a common event and prior work in non-skin cells shows acquired resistance to apoptosis occurs with chronic arsenite exposure. In the present study, when HaCaT cells, an immortalized, non-tumorigenic human keratinocyte cell line, were continuously exposed to low-level inorganic arsenite (as sodium arsenite; 100 nM) for 28 weeks, the cells acquired a generalized resistance to apoptosis. This included resistance to apoptosis induced by acute high concentrations of arsenite, ultraviolet A (UVA) irradiation, and several chemotherapeutic compounds (cisplatin, etoposide and doxorubicin). These arsenite-tolerant (As-TL) cells showed similar levels of UVA-induced reactive oxygen species (ROS) and oxidative DNA damage when compared to passage match control cells. Because cellular apoptosis is dependent on the balance between proapoptotic and survival pathways, the roles of protein kinase B (PKB), a key antiapoptotic molecule, in this acquired apoptotic resistance were investigated. Stimulation of apoptosis markedly decreased nuclear phosphorylated PKB (P-PKB) levels in control cells, but As-TL cells showed greatly increased stability of nuclear P-PKB. Pretreatment of the As-TL cells with LY294002 or Wortmannin, which specifically inhibit PKB phosphorylation, completely blocked apoptotic resistance in As-TL cells, indicating acquired apoptotic resistance is associated with increased stability of nuclear P-PKB. Because arsenic and UV irradiation are co-carcinogenic in mouse skin, resistance to UV-induced apoptosis in As-TL cells may allow UV-damaged cells to escape normal cell population controls and initiate the carcinogenic cascade. The observation that As-TL cells show no lessening of UV-induced genotoxicity supports this possibility.
Pi
Jingbo
J
Laboratory of Comparative Carcinogenesis, National Cancer Institute at the National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
He
Yuying
Y
Bortner
Carl
C
Huang
Jianli
J
Liu
Jie
J
Zhou
Tong
T
Qu
Wei
W
North
Susan L
SL
Kasprzak
Kazimierz S
KS
Diwan
Bhalchandra A
BA
Chignell
Colin F
CF
Waalkes
Michael P
MP
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D018053:Arsenites / Q000008:administration & dosage / Q000494:pharmacology*; D002460:Cell Line; D003043:Cocarcinogenesis; D004249:DNA Damage; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D012878:Skin Neoplasms / Q000139:chemically induced; D017670:Sodium Compounds / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D014466:Ultraviolet Rays
D018053:Arsenites; D017382:Reactive Oxygen Species; D017670:Sodium Compounds; C017947:sodium arsenite