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1 Pediatric Pulmonary Division, Case Western Reserve University, Cleveland, Ohio 44106; and 2 Department of Pharmacology, Pennsylvania State University, Hershey, Pennsylvania 17033
Human tracheal epithelial (TE) cells selectively
incorporate their major lipoxygenase product,
15-hydroxyeicosatetraenoic acid (15-HETE), into the
sn-2 position of phosphatidylinositol (PI) (S. E. Alpert and R. W. Walenga. Am. J. Respir.
Cell Mol. Biol. 8: 273-281, 1993). Here we
investigated whether 15-HETE-PI is a substrate for receptor-mediated
generation of 15-HETE-substituted diglycerides (DGs) and whether these
15-HETE-DGs directly activate and/or alter conventional
diacylglycerol-induced activation of protein kinase C (PKC) isotypes in
these cells. Primary human TE monolayers incubated with 0.5 µM
15-[3H]-HETE or
15-[14C]HETE for
1-2 h were stimulated with 1 nM to 1 µM platelet-activating factor (PAF) for 30 s to 6 min, and the radiolabel in the medium, cellular phospholipids, and neutral lipids was assessed by
high-performance liquid and thin-layer chromatography. PAF mobilized
radiolabel from PI in a dose-dependent manner (22 ± 5% decrease
after 1 µM PAF) without a concomitant release of free intra- or
extracellular 15-HETE. 14C-labeled
DGs were present in unstimulated TE monolayers incubated with
15-[14C]HETE, and the
major 14C band, identified as
sn-1,2-15-[14C]HETE-DG,
increased transiently in response to PAF. Western blots of freshly
isolated and cultured human TE cells revealed PKC isotypes
,
I,
II,
,
, and
. In
vitro, cell-generated
sn-1,2-15-[14C]HETE-DG
selectively activated immunoprecipitated PKC-
and inhibited diacylglycerol-induced activation of PKC-
, -
, -
I,
and -
II. Our observations indicate that 15-HETE-DGs can
modulate the activity of PKC isotypes in human TE cells and suggest an
intracellular autocrine role for 15-HETE in human airway epithelia.
15-hydroxyeicosatetraenoic acid; protein kinase C; human airway epithelial cells; signal transduction; monohydroxy-substituted diacylglycerols
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