Human bronchial epithelial cells express an active and inducible biosynthetic pathway for leukotrienes B4 and C4.
BACKGROUND
Human bronchial epithelial cells synthesize cyclooxygenase and 15-lipoxygenase products, but the 5-lipoxygenase (5-LO) pathway that generates the leukotriene (LT) family of bronchoconstrictor and pro-inflammatory mediators is thought to be restricted to leucocytes.


OBJECTIVE
We hypothesized that human bronchial epithelial cells (HBECs) express a complete and active 5-LO pathway for the synthesis of LTB4 and LTC4, either constitutively or after stimulation.


METHODS
Flow cytometry, RT-PCR, Western blotting, enzyme immunoassays and reverse-phase high-performance liquid chromatography were used to investigate constitutive and stimulated expression of 5-LO pathway enzymes and the synthesis of LTs B4 and C4 in primary HBECs and in the 16-HBE 14o- cell line.


RESULTS
Constitutive mRNA and protein expression for 5-LO, 5-LO-activating protein (FLAP), LTA4 hydrolase and LTC4 synthase were demonstrated in primary HBECs and in the 16-HBE 14o- cell line. In 16-HBE 14o- cells, treatment with calcium ionophore A23187, bradykinin or LPS up-regulated the expression of these enzymes. The up-regulation of 5-LO was blocked by the anti-inflammatory glucocorticoid dexamethasone. Human bronchial epithelial cells were shown to generate bioactive LTs, with primary HBECs generating 11-fold more LTC4 and five-fold more LTB4 than 16-HBE 14o- cells. LT production was enhanced by ionophore treatment and blocked by the FLAP inhibitor MK-886.


CONCLUSIONS
Expression of an active and inducible 5-LO pathway in HBEC suggests that damaged or inflamed bronchial epithelium may synthesize LTs that contribute directly to bronchoconstriction and leucocytosis in airway inflammation.
Jame
A J
AJ
Division of Infection, University of Southampton School of Medicine, Southampton General Hospital, Southampton, UK.
Lackie
P M
PM
Cazaly
A M
AM
Sayers
I
I
Penrose
J F
JF
Holgate
S T
ST
Sampson
A P
AP
D058927:5-Lipoxygenase-Activating Proteins; D001093:Arachidonate 15-Lipoxygenase / Q000096:biosynthesis* / Q000276:immunology; D001094:Arachidonate 5-Lipoxygenase / Q000096:biosynthesis* / Q000276:immunology; D001920:Bradykinin / Q000494:pharmacology; D001980:Bronchi / Q000201:enzymology* / Q000276:immunology / Q000473:pathology; D016084:Bronchoconstriction / Q000187:drug effects / Q000276:immunology; D016085:Bronchoconstrictor Agents / Q000276:immunology / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000276:immunology; D002460:Cell Line; D004847:Epithelial Cells / Q000201:enzymology* / Q000276:immunology / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000276:immunology; D005982:Glutathione Transferase / Q000096:biosynthesis / Q000276:immunology; D006801:Humans; D007249:Inflammation / Q000201:enzymology / Q000276:immunology / Q000473:pathology; D018836:Inflammation Mediators / Q000276:immunology / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D007975:Leukotriene B4 / Q000096:biosynthesis* / Q000276:immunology; D017997:Leukotriene C4 / Q000096:biosynthesis* / Q000276:immunology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008565:Membrane Proteins / Q000096:biosynthesis / Q000276:immunology; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000276:immunology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000276:immunology; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology; D014665:Vasodilator Agents / Q000494:pharmacology
D058927:5-Lipoxygenase-Activating Proteins; C548592:ALOX5AP protein, human; D016085:Bronchoconstrictor Agents; D002352:Carrier Proteins; D018836:Inflammation Mediators; D007476:Ionophores; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D012333:RNA, Messenger; D014665:Vasodilator Agents; D007975:Leukotriene B4; D017997:Leukotriene C4; D000001:Calcimycin; D001093:Arachidonate 15-Lipoxygenase; D001094:Arachidonate 5-Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases; D005982:Glutathione Transferase; C041116:leukotriene-C4 synthase; D001920:Bradykinin