Characterization of the cDNA corresponding to a phosphoprotein (p43) intermediary in the action of ACTH

beta-Adrenergic stimulation controls the expression of a thioesterase specific for very-long-chain fatty acids in perfused hearts

Arachidonic acid is not freely stored in the cells. A number of different pathways for the mobilization of this compound have been proposed, including a novel mechanism that involves the release of arachidonic acid from arachidonoyl-CoA by a thioesterase with substrate specificity for very-long-chain fatty acids. In rat heart, the acyl-CoA thioesterase activity can be regulated by a mechanism that involves beta-adrenoceptors. In this paper we demonstrate that beta-adrenergic agonists also regulate the acyl-CoA thioesterase mRNA levels. Isoproterenol (10(-7)M)-a concentration known to exert physiological responses-increases in a time-dependent manner the acyl-CoA thioesterase mRNA levels, an effect blocked by a specific beta-adrenoceptor antagonist. In addition, our results show that cAMP is involved in this process. The acyl-CoA thioesterase mRNA levels are also increased by fasting, but not by di(2-ethylhexyl)phthalate, a peroxisome proliferator. These results may suggest the existence of a beta-adrenoceptor-activated regulatory pathway for arachidonic acid release in cardiac tissue.

Activation of a thioesterase specific for very-long-chain fatty acids by adrenergic agonists in perfused hearts

We have recently described an acyl-CoA thioesterase specific for very-long-chain fatty acids, named ARTISt, that regulates steroidogenesis through the release of arachidonic acid in adrenal zona fasciculata cells. In this paper we demonstrate the presence of the protein as a 43 kDa band and its mRNA in cardiac tissue. The activity of the protein was measured using an heterologous cell-free assay in which it is recombined with adrenal microsomes and mitochondria to activate mitochondrial steroidogenesis. Isoproterenol and phenylephrine activate the enzyme in a dose-dependent manner (10(-10)-10(-6) M). Both propranolol (10(-5) M) and prazosin (10(-5) M) block the action of isoproterenol and phenylephrine respectively. Antipeptide antibodies against the serine lipase motif of the protein and the Cys residue present in the catalytic domain also block the activity of the protein. Taken together, our results confirm the presence of ARTISt in heart and provide evidence for a catecholamine-activated regulatory pathway of the enzyme in that tissue.