Prostaglandin biosynthesis and subcellular localization of prostaglandin H synthase activity in the lone star tick, Amblyomma americanum

Abstract

We report on prostaglandin (PG) biosynthesis in the lone star tick, Amblyomma americanum. In vitro preparations of whole female ticks and internal tissues were competent to biosynthesize four PGs: PGA2/PGB2, PGD2, PGE2, PGF2 alpha. PGA2/PGB2 was the major product under optimal conditions. PG biosynthesis by whole tick and internal tissues were sensitive to incubation conditions including, protein concentration, time, temperature, pH, and presence of a co-factor cocktail composed of reduced glutathione, hydroquinone, and hemoglobin. Under standard assay conditions, 2 mg/ml protein were incubated at pH 8.0 for 2 min at 32 degrees C. PG biosynthesis was inhibited by indomethacin, a potent cyclooxygenase inhibitor in mammalian systems. Internal tissue preparations were fractionated into cytosolic and microsomal preparations by ultracentrifugation. PG biosynthetic activity was detected in both fractions. The subcellular distribution of PG biosynthetic activity in ticks is similar to other invertebrates, but quite different from mammals, in which PG biosynthetic activity is almost exclusively localized in the microsomal fractions. PGH synthase-2 was detected in the microsomal fraction on western blot analysis. These results suggest that the lone star tick is competent to biosynthesize PGs. These compounds may contribute to the success of tick feeding ecology by attenuating the defense responses of vertebrate hosts during lengthy feeding periods.