Steroidogenesis in isolated adrenal cells of rat. II. Effect of caffeine on ACTH and cyclic nucleotide-induced steroidogenesis and its relation to cyclic nucleotide phosphodiesterase (PDE)

Multilimbed membrane guanylate cyclase signaling system, evolutionary ladder

One monumental discovery in the field of cell biology is the establishment of the membrane guanylate cyclase signal transduction system. Decoding its fundamental, molecular, biochemical, and genetic features revolutionized the processes of developing therapies for diseases of endocrinology, cardio-vasculature, and sensory neurons; lastly, it has started to leave its imprints with the atmospheric carbon dioxide. The membrane guanylate cyclase does so via its multi-limbed structure. The inter-netted limbs throughout the central, sympathetic, and parasympathetic systems perform these functions. They generate their common second messenger, cyclic GMP to affect the physiology. This review describes an historical account of their sequential evolutionary development, their structural components and their mechanisms of interaction. The foundational principles were laid down by the discovery of its first limb, the ACTH modulated signaling pathway (the companion monograph). It challenged two general existing dogmas at the time. First, there was the question of the existence of a membrane guanylate cyclase independent from a soluble form that was heme-regulated. Second, the sole known cyclic AMP three-component-transduction system was modulated by GTP-binding proteins, so there was the question of whether a one-component transduction system could exclusively modulate cyclic GMP in response to the polypeptide hormone, ACTH. The present review moves past the first question and narrates the evolution and complexity of the cyclic GMP signaling pathway. Besides ACTH, there are at least five additional limbs. Each embodies a unique modular design to perform a specific physiological function; exemplified by ATP binding and phosphorylation, Ca²⁺-sensor proteins that either increase or decrease cyclic GMP synthesis, co-expression of antithetical Ca²⁺ sensors, GCAP1 and S100B, and modulation by atmospheric carbon dioxide and temperature. The complexity provided by these various manners of operation enables membrane guanylate cyclase to conduct diverse functions, exemplified by the control over cardiovasculature, sensory neurons and, endocrine systems.

ACTH-Modulated Membrane Guanylate Cyclase Signaling System: Origin and Creation

The membrane guanylate cyclase (MGC) cellular signaling pathway consists of seven signaling pathways and is critical for the survival of prokaryotes eukaryotes, and highly complex vertebrate organisms. A sequel to the author's earlier comprehensive reviews, covering the field of MGC from its origin to its establishment to the year 2014, this article exclusively deals with the history of its development from the year 1963 to 1987. It narrates the efforts involved in building on small projects, brick by brick, and its emergence from the chasm of disbelief, through steady, continuous work. To make the presentation simple and chronologically continuous, the subject matters of the earlier reviews and publication of these authors have been freely borrowed with appropriate citations.

Integrative Signaling Networks of Membrane Guanylate Cyclases: Biochemistry and Physiology

This monograph presents a historical perspective of cornerstone developments on the biochemistry and physiology of mammalian membrane guanylate cyclases (MGCs), highlighting contributions made by the authors and their collaborators. Upon resolution of early contentious studies, cyclic GMP emerged alongside cyclic AMP, as an important intracellular second messenger for hormonal signaling. However, the two signaling pathways differ in significant ways. In the cyclic AMP pathway, hormone binding to a G protein coupled receptor leads to stimulation or inhibition of an adenylate cyclase, whereas the cyclic GMP pathway dispenses with intermediaries; hormone binds to an MGC to affect its activity. Although the cyclic GMP pathway is direct, it is by no means simple. The modular design of the molecule incorporates regulation by ATP binding and phosphorylation. MGCs can form complexes with Ca²⁺-sensing subunits that either increase or decrease cyclic GMP synthesis, depending on subunit identity. In some systems, co-expression of two Ca²⁺ sensors, GCAP1 and S100B with ROS-GC1 confers bimodal signaling marked by increases in cyclic GMP synthesis when intracellular Ca²⁺ concentration rises or falls. Some MGCs monitor or are modulated by carbon dioxide via its conversion to bicarbonate. One MGC even functions as a thermosensor as well as a chemosensor; activity reaches a maximum with a mild drop in temperature. The complexity afforded by these multiple limbs of operation enables MGC networks to perform transductions traditionally reserved for G protein coupled receptors and Transient Receptor Potential (TRP) ion channels and to serve a diverse array of functions, including control over cardiac vasculature, smooth muscle relaxation, blood pressure regulation, cellular growth, sensory transductions, neural plasticity and memory.

Membrane guanylate cyclase is a beautiful signal transduction machine: overview

This article is a sequel to the four earlier comprehensive reviews which covered the field of membrane guanylate cyclase from its origin to the year 2002 (Sharma in Mol Cell Biochem 230:3-30, 2002) and then to the year 2004 (Duda et al. in Peptides 26:969-984, 2005); and of the Ca(2+)-modulated membrane guanylate cyclase to the year 1997 (Pugh et al. in Biosci Rep 17:429-473, 1997) and then to 2004 (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). This article contains three parts. The first part is "Historical"; it is brief, general, and freely borrowed from the earlier reviews, covering the field from its origin to the year 2004 (Sharma in Mol Cell Biochem, 230:3-30, 2002; Duda et al. in Peptides 26:969-984, 2005). The second part focuses on the "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily". It is divided into two sections. Section "Historical" and covers the area from its inception to the year 2004. It is also freely borrowed from an earlier review (Sharma et al. in Curr Top Biochem Res 6:111-144, 2004). Section "Ca(2+)-modulated ROS-GC membrane guanylate cyclase subfamily" covers the area from the year 2004 to May 2009. The objective is to focus on the chronological development, recognize major contributions of the original investigators, correct misplaced facts, and project on the future trend of the field of mammalian membrane guanylate cyclase. The third portion covers the present status and concludes with future directions in the field.

Atrial natriuretic factor regulation of cyclic GMP levels and steroidogenesis in isolated fasciculata cells of rat adrenal cortex

Isolated fasciculata cells of rat adrenal cortex, when incubated with atrial natriuretic factor (ANF), stimulated the levels of cyclic GMP and corticosterone production in a concentration-dependent manner without a rise in the levels of cyclic AMP. The ANF-dependent elevation of cyclic GMP was rapid, with a detectable increment in 30 s. ANF also stimulated the particulate guanylate cyclase. These results not only indicate the coupling of cyclic GMP and corticosterone production with ANF signal, but also demonstrate that, like the ACTH signal, cyclic AMP is not the mediator of ANF-induced adrenocortical steroidogenesis.

Regulatory role of guanosine 3',5'-monophosphate in adrenocorticotropin hormone-induced steroidogenesis

The relation between steroidogenesis induced by adrenocorticotropic hormone and the concentrations of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) was studied at different time intervals in isolated adrenal cells. Submaximal and supramaximal steroidogenic concentrations of the hormone did not cause detectable changes in cyclic AMP during the first 30 minutes, whereas there was an increase in the concentration of cyclic GMP that was accompanied by phosphorylation and steroidogenesis. It is therefore suggested that cyclic GMP, rather than cyclic AMP, is the physiological mediator of adrenocorticotropic hormone-induced adrenal steroidogenesis.

Rat pancreas adenylate cyclase V. Its presence in isolated rat pancreatic acinar cells

(1) In order to determine the cellular localization of the secretin- and pancreozymin-sensitive adenylate cyclase in rat pancreas, the occurence of this enzyme system has been investigated in isolated pancreatic cells. (2) Digestion of rat pancreatic lobules with collagenase yields a preparation of isolated cells which upon differential morphological analysis appears to consist for 97% of acinar cells and to contain for fewer centro-acinar and ductal cells than undissociated lobules. (3) Expressed per mg protein, the isolated cells contain the same amount of DNA, chymotrypsin and lactic dehydrogenase as the undissociated tissue. The stimulated adenylate cyclase activity is nearly entirely recovered in the isolated acinar cells, as is also the case for the low Km adenosine 3',5-cyclic monophosphate phosphodiesterase activity and the adenosine 3',5'-cyclic monophosphate (cyclic AMP) content. Marked losses are noted for the basal adenylate cyclase and the high Km cyclic AMP phosphodiesterase activities. (4) Washing the isolated acinar cells in Krebs-Ringer bicarbonate medium containing 10 mM 1-methyl-3-isobutylxanthine causes a cyclic AMP level 2.6 times that in cells washed in Krebs-Ringer bicarbonate alone. The cyclic AMP level is further increased by subsequently incubating the cells for 10 min in the presence of 3-10(-7) M pancreozymin-C-octapeptide or secretin to values 1.7 or 4.7 times the control level in cells incubated for 10 min with 1-methyl-3-isobutylxanthine alone. (5) It is suggested that the adenylate cyclase of the acinar cells may be involved, with another factor, in the stimulation of enzyme secretion, whereas a ductular cyclase would function in the regulation of the bicarbonate-dependent fluid secretion.

Metabolic regulation of steroidogenesis in isolated adrenal cells of rat. Relationship of adrenocorticotropin-, adenosine 3':5'-monophosphate-and guanosine 3':5'-monophosphate-stimulated steroidogenesis with the activation of protein kinase

The data presented with the isolated adrenal cells, in the present study, show that adrenocorticotropin in the physiological concentration range stimulates the synthesis of guanosine 3':5'-monophosphate(cyclic GMP), protein kinase activity, and steroidogenesis in a concentration-dependent manner without detectable rise in the levels of adenosine 3':5'-monophosphate (cyclic AMP). Millimolar concentrations of cyclic AMP and cyclic GMP, which stimulate corticosterone synthesis, also activate kinase activity and steroidogenesis in a sigmoid concentration-response manner. The process of phosphorylation activated by corticotropin, cyclic AMP and cyclic GMP is not inhibited by cycloheximide or actinomyin D. It is therefore proposed that the hormonal responses mediated by cyclic GMP and cyclic AMP are via the protein kinase enzymatic steps, and the inhibitory effect of cycloheximide and actinomycin D in corticotropin-stimulated steroidogenesis follows this step. In conjuction with our previous observations that the biosynthetic steps from (20S)-20-hydroxycholesterol to corticosterone are neither inhibited by cycloheximide nor affected by cyclic GMP, it is inferred that the rate-limiting step of adrenal steroidogenesis is the transformation of cholesterol to (20S)-20hydroxycholesterol and this very step is regulated by cyclic GMP and cyclic AMP. Of further significance are the findings that micromolar cincentrations of cyclic AMP and cyclic GMP, which do not stimulate steroidogenesis, effectively stimulate protein kinase activity in a concentration-dependent manner. It is therefore concluded that all cyclic-nucleotide-dependent protein kinase activities of the cell are not necessarily related to steroidogenesis.

Monolayer cultures of normal adult rat adrenocortical cells: steroidogenic responses to nucleotides, bacterial toxins and antimicrotubular agents

Monolayer cultures of normal rat adrenocortical cells were treated with agents which stimulate steroidogenesis by Y-1 adrenal tumour cells. Choleragen was active, whereas cyclic nucleotides other than cyclic AMP, bacterial endotoxins and antimicrotubular agents were inactive.

Effects of methylxanthines on gonadotropin-induced steroidogenesis and protein synthesis in isolated testis interstitial cells

The effects of 1-methyl 3-isobutyl xanthine (MIX) and theophylline on basal and gonadotropin-stimulated production of cyclic AMP and testosterone were evaluated in enzyme-dispersed testicular interstitial cells. The actions of these compounds upon precursor incorporation into RNA and protein were also examined in the same cell preparation. The considerable higher potency of MIX as a phosphodiesterase inhibitor was accompanied by a steeper dose-response curve for cyclic AMP recovery in incubation media of hormone-treated cells. Both inhibitors caused increases in basal and hormone-stimulated cyclic AMP levels. Although low concentrations of theophylline and MIX had no effect on the maximum levels of hCG-stimulated testosterone production, 10 mM theophylline and 1 mM MIX significantly inhibited steroidogenesis. Conversely, basal testosterone levels were increased by MIX and theophylline. The higher concentrations of MIX and theophylline also significantly inhibited precursor incorporation into RNA and protein. These actions of phosphodiesterase inhibitors upon RNA and protein synthesis could contribute to their inhibitory effects at high concentrations upon gonadotropin-induced steroidogenesis.

Effect of ascorbic acid on ACTH-induced cyclic AMP formation and steroidogenesis in isolated adrenal cells of vitamin E-deficient rats

Isolated adrenal cells from Vitamin E-deficient and control rats were prepared by a trypsin digestion method. Cyclic adenosine 3',5'-monophosphate (cyclic AMP) formation was studied in response to adrenocorticotropin (ACTH) in the presence and absence of ascorbate by measuring the conversion of prelabeled adenosine 5'-triphosphate [14C]ATP to cyclic [14C]AMP. Ascorbate (0.5 mM) inhibited ACTH-induced cyclic [14C]AMP formation in adrenal cells isolated from Vitamin E-deficient rats but had no effect in the control cells. The inhibitory effect of ascorbate on ACTH-induced cyclic AMP formation in Vitamin E-deficient rats decreased as the concentration of ACTH increased. In Vitamin E-deficient rats ascorbate inhibited ACTH-induced cyclic [14C]AMP formation after 30 min of incubation. There was no further significant accumulation of cyclic [14C]AMP at 60 min or 120 min although in the absence of ascorbate cyclic [14C]AMP continued to be formed. The in vitro addition of alpha-tocopherol reduced the inhibition of ACTH-induced cyclic [14C]AMP formation by ascorbate in Vitamin E-deficient rats. These studies suggest that alpha-tocopherol and ascorbate may affect ACTH-induced cyclic AMP formation through interaction with the membrane-bound enzyme adenylate cyclase.