Regulation of arachidonic acid release in steroidogenesis: Role of a new acyl-CoA thioesterase (ARTISt).

It has been well established that arachidonic acid (AA) and its metabolism to leukotrienes plays an obligatory role in steroid production. The release of AA is regulated by hormone stimulation and protein phosphorylation. We have cloned a cDNA of a phosphoprotein with a molecular mass of 43 kDa (p43 ), purified from the cytosol of stimulated adrenal glands. This protein act s as intermediary in the stimulation of steroid synthesis through AA releas e, and has been found to be a member of a recently described acyl-CoA thioe sterase family. In view of the mandatory role of this protein in the activa tion of AA-mediated steroidogenesis, the term Arachidonic acid-Related Thio esterase Involved in Steroidogenesis (ARTISt), is proposed for p43. The pre sent study describes the production of the recombinant protein by cDNA expr ession in Escherichia coli and its functional characterization. Recombinant acyl-CoA thioesterase was capable to release AA from the respective acyl-C oA, and this activity was affected by well-recognized inhibitors of AA rele ase and metabolism: 4-bromophenacyl bromide (BPB) and nordihydroguariaretic acid (NDGA). In addition, the inhibition of acyl-CoA thioesterase activity by NDGA correlates with the inhibition of steroid synthesis produced by th is compound in adrenal cortex cells. Moreover, the recombinant protein was phosphorylated in vitro by PKA. These results provide the first evidence li nking acyl-CoA thioesterases with the regulation of steroidogenesis, and su pport a regulatory role for acyl-CoA thioesterases in steroidogenic tissues , suggesting an alternative pathway for AA release in signal transduction.