Lipoxygenase products as common intermediates in cyclic AMP-dependent and -independent adrenal steroidogenesis in rats

Abstract

Aldosterone secretion from adrenal glomerulosa cells can be stimulated by angiotensin II (AII), extracellular potassium and ACTH. Mitochondria from these cells respond to intracellular factors generated by AII (cyclic AMP (cAMP)-independent steroidogenesis) and ACTH (cAMP-dependent steroidogenesis), suggesting that the two-signal-transduction mechanisms are linked by a common intermediate. We have evaluated this hypothesis by stimulating mitochondria from the unstimulated zona glomerulosa with a subcellular post-mitochondrial fraction (PMF) obtained from the zona glomerulosa after stimulation with AII or from the fasciculata gland after stimulation with ACTH; the subcellular fractions were also tested on mitochondria from fasciculata cells. PMFs obtained after incubation of adrenal zona glomerulosa with or without AII (0.1 microM) or ACTH (0.1 nM) were able to increase net progesterone synthesis 4.5-fold in mitochondria isolated from unstimulated rat zona glomerulosa. AII-pretreated PMFs from the zona glomerulosa also stimulated steroidogenesis by mitochondria from zona fasciculata cells. Separate experiments showed that inhibitors of arachidonic acid release and metabolism (bromophenacyl bromide, nordihydroguaiaretic acid, caffeic acid or esculetin) blocked corticosterone production in fasciculata cells stimulated with ACTH, suggesting that arachidonic acid could be the common intermediate in the actions of AII and ACTH on steroid synthesis. Evidence to support this concept was obtained from experiments in which the formation of an activated PMF by treatment of zona fasciculata with ACTH was blocked by the presence of the same inhibitors. Moreover, the inhibitory effects of these substances on PMF activation by ACTH were overcome by exogenous arachidonic acid and, in addition, arachidonic acid release was stimulated by ACTH.(ABSTRACT TRUNCATED AT 250 WORDS)

An adrenocorticotropin‐regulated phosphoprotein intermediary in steroid synthesis is similar to an acyl‐CoA thioesterase enzyme

“…This coincides also with the observation that the activity of ARTISt is hormone-dependent and operates under several different signaltransduction mechanisms [9,19]. So far, there is no description to our knowledge of a possible regulation of acyl-CoA thioesterase activity by protein phosphorylation.…”

“…The steroidogenic activity of the soluble partially purified protein was blocked by the use of inhibitors of AA release. This inhibition could be overcome by addition of exogenous AA [17], thereby concluding that this protein regulates steroid synthesis through the activation of AA release [9,17]. The activity of the protein was dependent on cAMP and cAMP-dependent protein kinase [17].…”

Purification of a Novel 43‐kDa Protein (p43) Intermediary in the Activation of Steroidogenesis from Rat Adrenal Gland

“…Still we cannot conclude that this protein is a direct stimulator of phospholipase A,; however, the fact that inhibitors of arachidonic acid release can block the effect of the purified protein would suggest that it may be an activator of an adrenocorticotropin-dependent phospholipase in the in vitro recombination assay. This concept is supported by recent publications reporting that inhibitors of arachidonic acid release cause a potent inhibition of adrenocorticotropin-stimulated, and dibutyryl-CAMP-stimulated steroidogenesis in rat adrenal cells at a point between cAMP production and the metabolism from cholesterol to pregnenolone [17,18]. Exogenous arachidonic acid can overcome this inhibition and adrenocorticotropin is also able to stimulate the release of arachidonic acid from isolated adrenal fasciculata cells [17].…”

“…As we previously described, the soluble, adrenocorticotropin-and CAMP-dependent steroidogenic factor requires the presence of the particulate fraction (105000Xg pellet) to stimulate mitochondrial steroidogenesis [17]. p43 could correspond with that steroidogenic factor, as its activity proved to be dependent on adrenocorticotropin, required addition of the 105000Xg pellet, and was blocked by the use of a phospholipase A, inhibitor.…”

“…This protein is cycloheximide sensitive and shares some properties with the family of phospholipid-transport proteins [19]. The role of arachidonic acid and the lipoxygenase products as intermediaries occurs at a point between CAMP-dependent protein phosphorylation and the metabolism of cholesterol to pregnenolone [17]. Protein phosphorylation is a universal event in the mechanism of action of peptide hormones.…”