Human keratinocytes lack the components to produce leukotriene B4.
The cellular origin of leukotriene B4 (LTB4), a potent pro-inflammatory molecule present in psoriatic lesions, has yet to be determined. In the present study, cultured human keratinocytes were evaluated for their ability to produce LTB4. Keratinocytes stimulated under a variety of conditions did not produce detectable amounts of LTB4, as measured by enzyme immunoassay and liquid chromatographic techniques. Prostaglandin E2 and 15-hydroxyeicosatetraenoic acid were the only eicosanoids detected. The capacity of keratinocytes to synthesize 5-lipoxygenase (5-LO) products, or lack thereof, was further evaluated by preparing subcellular fractions and examining them for the presence of 5-LO activity and the proteins responsible for LTB4 production. Using Western blot analysis, we detected no bands that migrated with the 78-kDa 5-LO enzyme. Subcellular fractions were also examined for the presence of the 5-LO-activating protein (FLAP). This protein, which is essential to 5-LO activity, could not be detected in any keratinocyte preparation examined. Consistent with the absence of proteins, the mRNAs for 5-LO and FLAP were undetectable by reverse transcriptase polymerase chain reactions analysis. These results demonstrate that human keratinocytes lack the crucial proteins necessary for LTB4 production.
Breton
J
J
Department of Inflammation Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406-0939, USA.
Woolf
D
D
Young
P
P
Chabot-Fletcher
M
M
D058927:5-Lipoxygenase-Activating Proteins; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D015777:Eicosanoids / Q000096:biosynthesis; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism*; D007975:Leukotriene B4 / Q000096:biosynthesis* / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic
D058927:5-Lipoxygenase-Activating Proteins; C548592:ALOX5AP protein, human; D002352:Carrier Proteins; D015777:Eicosanoids; D008565:Membrane Proteins; D012333:RNA, Messenger; D007975:Leukotriene B4; D001094:Arachidonate 5-Lipoxygenase