Chloroquine Inhibits Ca(2+) Signaling in Murine CD4(+) Thymocytes.
OBJECTIVE
Bitter-tasting chloroquine can suppress T cell activation by inhibiting Ca(2+) signaling. However, the mechanism of inhibition remains largely unclear.


METHODS
In this study, CD4(+) T cells were isolated from the thymus, and the calcium content of CD4(+) thymocytes was measured using fura-2 AM and a TILL imaging system. Pyrazole-3 (Pyr3), thapsigargin (TG), and caffeine were used to assess the effects of chloroquine on the intracellular Ca(2+) content of CD4(+) T cells.


RESULTS
In murine CD4(+) thymocytes, chloroquine decreased the TG-triggered intracellular Ca(2+) increase in a dose-dependent manner. In the absence of chloroquine under Ca(2+)-free conditions (0 mM Ca(2+) and 0.5 mM EGTA), TG induced a transient Ca(2+) increase. After restoration of the extracellular Ca(2+) concentration to 2 mM, a dramatic Ca(2+) increase occurred. This elevation was completely blocked by chloroquine and was markedly inhibited by Pyr3, a selective antagonist of transient receptor potential C3 (TRPC3) channel and stromal interaction molecule (STIM)/Orai channel. Furthermore, the TG-induced transient Ca(2+) increase under Ca(2+)-free conditions was eliminated in the presence of chloroquine. Chloroquine also blocked the dialyzed inositol-1,4,5-trisphosphate (IP3)-induced intracellular Ca(2+) increase. However, chloroquine was not able to decrease the caffeine-induced Ca(2+) increase.


CONCLUSIONS
These data indicate that chloroquine inhibits the elevation of intracellular Ca(2+) in thymic CD4(+) T cells by inhibiting IP3 receptor-mediated Ca(2+) release from intracellular stores and TRPC3 channel-mediated and/or STIM/Orai channel-mediated Ca(2+) influx.
Institute for Medical Biology & Hubei Provincial Key Laboratory for Protection and Application of Special Plants in the Wuling Area of China, College of Life Sciences, South-Central University for Nationalities, Wuhan, China.
Jin-Chao
JC
Xu
Yong-Bo
YB
Peng
Ming-Yu
MY
Wei
Yi-Fan
YF
Wu
Donglin
D
Guo
Gangjian
G
Qin
Guangju
G
Ji
Jinhua
J
Shen
Qing-Hua
QH
Liu
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D008297:Male; D051379:Mice; D011720:Pyrazoles / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D060168:Thymocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D011720:Pyrazoles; C559943:ethyl-1-(4-(2*3*3-trichloroacrylamide)phenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylate; D002110:Caffeine; D019284:Thapsigargin; D002738:Chloroquine; D002118:Calcium