Silencing the expression of mitochondrial acyl-CoA thioesterase I and acyl-CoA synthetase 4 inhibits hormone-induced steroidogenesis

Tyrosine phosphatases in steroidogenic cells: regulation and function

In adrenocortical and Leydig cells PKA activation by trophic hormones increases the activity of protein tyrosine phosphatases and also induces the expression of MAP kinase phosphatase 1 (MKP-1), a dual activity protein phosphatase (serine/threonine and tyrosine). This work summarizes the knowledge on the regulation and the role played by cAMP-activated tyrosine phosphatases as well as MKP-1 in the hormonal activation of the acute and chronic phases of steroidogenesis.

cAMP increases mitochondrial cholesterol transport through the induction of arachidonic acid release inside this organelle in Leydig cells

We have investigated the direct effect of arachidonic acid on cholesterol transport in intact cells or isolated mitochondria from steroidogenic cells and the effect of cyclic-AMP on the specific release of this fatty acid inside the mitochondria. We show for the first time that cyclic-AMP can regulate the release of arachidonic acid in a specialized compartment of MA-10 Leydig cells, e.g. the mitochondria, and that the fatty acid induces cholesterol transport through a mechanism different from the classical pathway. Arachidonic acid and arachidonoyl-CoA can stimulate cholesterol transport in isolated mitochondria from nonstimulated cells. The effect of arachidonoyl-CoA is inhibited by the reduction in the expression or in the activity of a mitochondrial thioesterase that uses arachidonoyl-CoA as a substrate to release arachidonic acid. cAMP-induced arachidonic acid accumulation into the mitochondria is also reduced when the mitochondrial thioesterase activity or expression is blocked. This new feature in the regulation of cholesterol transport by arachidonic acid and the release of arachidonic acid in specialized compartment of the cells could offer novel means for understanding the regulation of steroid synthesis but also would be important in other situations such as neuropathological disorders or oncology disorders, where cholesterol transport plays an important role.

Protein tyrosine phosphatases regulate arachidonic acid release, StAR induction and steroidogenesis acting on a hormone-dependent arachidonic acid-preferring acyl-CoA synthetase

The activation of the rate-limiting step in steroid biosynthesis, that is the transport of cholesterol into the mitochondria, is dependent on PKA-mediated events triggered by hormones like ACTH and LH. Two of such events are the protein tyrosine dephosphorylation mediated by protein tyrosine phosphatases (PTPs) and the release of arachidonic acid (AA) mediated by two enzymes, ACS4 (acyl-CoA synthetase 4) and Acot2 (mitochondrial thioesterase). ACTH and LH regulate the activity of PTPs and Acot2 and promote the induction of ACS4. Here we analyzed the involvement of PTPs on the expression of ACS4. We found that two PTP inhibitors, acting through different mechanisms, are both able to abrogate the hormonal effect on ACS4 induction. PTP inhibitors also reduce the effect of cAMP on steroidogenesis and on the level of StAR protein, which facilitates the access of cholesterol into the mitochondria. Moreover, our results indicate that exogenous AA is able to overcome the inhibition produced by PTP inhibitors on StAR protein level and steroidogenesis. Then, here we describe a link between PTP activity and AA release, since ACS4 induction is under the control of PTP activity, being a key event for AA release, StAR induction and steroidogenesis.

A revised nomenclature for mammalian acyl-CoA thioesterases/hydrolases

Acyl-CoA thioesterases, also known as acyl-CoA hydrolases, are a group of enzymes that hydrolyze CoA esters such as acyl-CoAs (saturated, unsaturated, branched-chain), bile acid-CoAs, CoA esters of prostaglandins, etc., to the corresponding free acid and CoA. However, there is significant confusion regarding the nomenclature of these genes. In agreement with the HUGO Gene Nomenclature Committee and the Mouse Genomic Nomenclature Committee, a revised nomenclature for mammalian acyl-CoA thioesterases/hydrolases has been suggested for the 12 member family. The family root symbol is ACOT, with human genes named ACOT1-ACOT12, and rat and mouse genes named Acot1-Acot12. Several of the ACOT genes are the result of splicing events, and these splice variants are cataloged.