Vol. 275, Issue 4, H1462-H1472, October 1998
Stimulation of different phospholipase
A2 isoforms by TNF-
and
IL-1
in adult rat ventricular myocytes
Shi J.
Liu1,2 and
Jane
McHowat3
1 Department of
Biopharmaceutical Sciences,
2 Department of Pharmacology and
Toxicology, and 3 Department of Pathology,
University of Arkansas for Medical Sciences, Little Rock, Arkansas
72205
We previously showed that in adult rat
ventricular myocytes interleukin (IL)-1
activates a
membrane-associated,
Ca2+-independent phospholipase
A2
(iPLA2). In this study, we
examined the possible existence of different
PLA2 isoforms and effects of tumor
necrosis factor (TNF)-
on iPLA2
activities. Western blot analysis identified
iPLA2 in both membrane (~82 kDa)
and cytosolic (~40 kDa) fractions and identified
Ca2+-dependent
PLA2
(cPLA2) only in cytosolic
fractions. With plasmenylcholine or alkylacyl glycerophosphorylcholine
as substrate, TNF- elicited a twofold transient increase in
cytosolic iPLA2 activity
accompanied by an increase in arachidonic acid release and decreased
membrane-associated iPLA2 activity
with plasmenylcholine. With phosphatidylcholine as substrate, TNF-
decreased both cytosolic and membrane-associated iPLA2 activities. TNF--induced
increases in cytosolic iPLA2
activity and arachidonic acid release were completely blocked by methyl arachidonyl fluorophosphonate (MAFP) but not by bromoenol lactone (BEL). TNF- and IL-1 together enhanced synergistically cytosolic and membrane PLA2 activities and
arachidonic acid release that were blocked differentially by MAFP and
BEL, respectively, and inhibited completely by MAFP plus BEL. These
results suggest that TNF- and IL-1 act on different
PLA2 isoforms in ventricular myocytes.
cytokines; signal transduction; arachidonic acid; methyl
arachidonyl fluorophosphonate; bromoenol lactone; Western blot; tumor
necrosis factor-; interleukin-1
