Mitochondrial coupling factor 6 as an endogenous inhibitor of prostacyclin synthesis and an endogenous vasoconstrictor

Abstract

The possible presence of an unknown prostacyclin-synthesis inhibitory substance has been reported in some strains of rats. We purified the inhibitory substance from the heart of spontaneously hypertensive rats by collecting active fractions after gel-filtration column chromatography and reverse-phase high performance liquid chromatography. The automated gas-phase sequencing indicated that the prostacyclin-inhibitory peptide was identical to coupling factor 6. Recombinant rat coupling factor 6, which was synthesized using a cleavable fusion protein strategy, attenuated baseline and bradykinin (10 −6 M)-induced prostacyclin synthesis and [ 3H] arachidonic acid (AA) release in human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. Exogenous AA- and prostaglandin H2-induced prostacyclin synthesis were unchanged even after treatment with 10 −7 M recombinant coupling factor 6. Baseline and bradykinin-induced [ 3H] AA release were suppressed by arachidonyl trifluoromethyl ketone, a relatively specific inhibitor of cytosolic phospholipase A 2 (PLA 2), and simultaneous administration of coupling factor 6 showed no further effect. Neither oleyloxyethyl phosphorylcholine nor bromoenol lactone affected AA release. Intravenous injection of recombinant coupling factor 6 increased arterial blood pressure in rats, whereas a specific antibody to coupling factor 6 decreased systemic blood pressure. We conclude that coupling factor 6 possesses a novel function of prostacyclin synthesis inhibition in endothelial cells via suppression of Ca 2+-dependent cytosolic PLA 2 and functions as an endogenous vasoconstrictor.