Delayed Release of Prostaglandins from Arachidonic Acid and Kinetic Changes in Prostaglandin H Synthase Activity on the Induction of Prostaglandin H Synthase-2 after Lipopolysaccharide-Treatment of RAW264.7 Macrophage-Like Cells.

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Abstract
In a mouse macrophage-like cell line, RAW264.7, arachidonic acid was cleaved within 30 min of lipopolysaccharide (LPS)-treatment. However, prostaglandin (PG) synthesis did not accompany this cleavage, being delayed by 4 h, although significant PGH synthase (PGHS) activity was detected in the lysate of LPS-nontreated cells. The K(m) value of this basal PGHS activity toward arachidonic acid was more than one hundred-fold higher than that for the lysate of cells treated with LPS for 4 h. Changes in the sensitivity of the PGHS activity to nonsteroidal antinflammatory drugs after LPS-treatment also suggested induction of PGHS with different properties from that in the case of basal PGHS. The concomitant increase in PGH synthase (PGHS) activity with the induction of PGHS-2 protein after LPS-treatment suggested a contribution by PGHS-2 to the delayed synthesis of PGs in LPS-treated macrophage cells. As for PGHS in the control cells without LPS-treatment, a different K(m) value from that of PGHS-1 and the lack of cross-reactivity to anti-PGHS-1 antibodies suggested that this basal PGHS was different from the typical PGHS-1. The lower affinity of this enzyme for arachidonic acid might be the reason for the failure to release PGs by the cells without LPS-treatment.

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