Influx of extracellular calcium is required for the membrane translocation of 5-lipoxygenase and leukotriene synthesis.
Our studies assessed the effects of increases in intracellular calcium concentrations [( Ca2+]i) on leukotriene synthesis and membrane translocation of 5-lipoxygenase (5LO). The calcium ionophore ionomycin and the tumor promoter thapsigargin stimulated leukotriene production and translocation of 5-lipoxygenase to the membrane. Both agents elicited prolonged rises in [Ca2+]i. Leukotriene C4 production associated with [Ca2+]i in cells stimulated with various concentrations of ionomycin and thapsigargin suggests that a threshold [Ca2+]i level of approximately 300-400 nM is required. In the absence of extracellular Ca2+, both the ionomycin- and thapsigargin-induced rises in [Ca2+]i were transient, indicating that the prolonged [Ca2+]i elevation is due to an influx of extracellular Ca2+. Addition of EGTA to the external medium before, or at different times during, the treatment with ionomycin or thapsigargin instantaneously inhibited 5LO translocation and leukotriene synthesis, indicating that Ca2+ influx plays an essential role in 5LO membrane translocation and leukotriene synthesis. No leukotriene production was detected when cells were stimulated by a physiological stimulus of leukotriene D4. The addition of 100 nM leukotriene D4 triggered peak rises in [Ca2+]i that were comparable to those achieved by the ionomycin and thapsigargin. However, the leukotriene D4 induced rise was transient and rapidly declined to a lower but still elevated steady-state level, which was attributed to Ca2+ influx. Stimulation with 100 nM leukotriene D4 for 15 s increased the cellular levels of 1,4,5-inositol triphosphate (IP3), 1,3,4-IP3, and 1,3,4,5-inositol tetraphosphate (IP4).(ABSTRACT TRUNCATED AT 250 WORDS)
Wong
A
A
Department of Cell Sciences, SmithKline Beecham, King of Prussia, Pennsylvania 19406.
Cook
M N
MN
Foley
J J
JJ
Sarau
H M
HM
Marshall
P
P
Hwang
S M
SM
D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism*; D001491:Basophils / Q000502:physiology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D015471:Leukemia, Basophilic, Acute; D015289:Leukotrienes / Q000096:biosynthesis*; D051381:Rats; D011971:Receptors, Immunologic / Q000378:metabolism; D018077:Receptors, Leukotriene; D013189:SRS-A / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014407:Tumor Cells, Cultured
D007295:Inositol Phosphates; D015289:Leukotrienes; D011971:Receptors, Immunologic; D018077:Receptors, Leukotriene; D013189:SRS-A; D013729:Terpenes; D000001:Calcimycin; D004533:Egtazic Acid; D015759:Ionomycin; D019284:Thapsigargin; D001094:Arachidonate 5-Lipoxygenase; D000252:Calcium-Transporting ATPases; D002118:Calcium