Mechanisms of prostaglandin E2 release by intact cells expressing cyclooxigenase2: evidence for a ‘two-component’ model

Prostaglandin (PG) release in cells expressing constitutive cy-clooxygenase-1 is known to be regulated by liberation of ara-chidonic acid by phospholipase A2 followed by metabolism by cyclooxygenase. However, the relative contribution of phos-pholipase A2 to the release of PGs in cells expressing cyclo-oxygenase-2 is not clear. We addressed this question by using radioimmunoassay to measure PGE2 release by human cells (A549) induced to express cyclooxygenase-2 (measured by Western blot analysis) by interleukin-1b. Cells were either un-stimulated or stimulated with agents known to activate phos-pholipase A2 (bradykinin, Des-Arg 10-kallidin, or the calcium ionophore A23187) or treated with exogenous arachidonic acid. When cells were treated to express cyclooxygenase-2, th