Independent [Ca2+]i increases and cell proliferation induced by the carcinogen safrole in human oral cancer cells.
The effect of the carcinogen safrole on intracellular Ca2+ movement and cell proliferation has not been explored previously. The present study examined whether safrole could alter Ca2+ handling and growth in human oral cancer OC2 cells. Cytosolic free Ca2+ levels ([Ca2+]i) in populations of cells were measured using fura-2 as a fluorescent Ca2+ probe. Safrole at a concentration of 325 microM started to increase [Ca2+]i in a concentration-dependent manner. The Ca2+ signal was reduced by 40% by removing extracellular Ca2+, and was decreased by 39% by nifedipine but not by verapamil or diltiazem. In Ca2+-free medium, after pretreatment with 650 microM safrole, 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) barely induced a [Ca2+]i rise; in contrast, addition of safrole after thapsigargin treatment induced a small [Ca2+]i rise. Neither inhibition of phospholipase C with 2 microM U73122 nor modulation of protein kinase C activity affected safrole-induced Ca2+ release. Overnight incubation with 1 microM safrole did not alter cell proliferation, but incubation with 10-1000 microM safrole increased cell proliferation by 60+/-10%. This increase was not reversed by pre-chelating Ca2+ with 10 microM of the Ca2+ chelator BAPTA. Collectively, the data suggest that in human oral cancer cells, safrole induced a [Ca2+]i rise by causing release of stored Ca2+ from the endoplasmic reticulum in a phospholipase C- and protein kinase C-independent fashion and by inducing Ca2+ influx via nifedipine-sensitive Ca2+ entry. Furthermore, safrole can enhance cell growth in a Ca2+-independent manner.
Huang
Jong-Khing
JK
Department of Surgery, Kaohsiung Veterans General Hospital, Kaohsiung, 813, Taiwan.
Huang
Chun-Jen
CJ
Chen
Wei-Chuan
WC
Liu
Shiuh-Inn
SI
Hsu
Shu-Shong
SS
Chang
Hong-Tai
HT
Tseng
Li-Ling
LL
Chou
Chiang-Ting
CT
Chang
Chih-Hung
CH
Jan
Chung-Ren
CR
D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002273:Carcinogens; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D009543:Nifedipine / Q000494:pharmacology; D012451:Safrole; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
D002121:Calcium Channel Blockers; D002273:Carcinogens; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D012451:Safrole; D002118:Calcium