Restricted diffusion of a freely diffusible second messenger: mechanisms underlying compartmentalized cAMP signalling

145

143

Cyclic di-GMP (c-di-GMP) is a second messenger molecule that regulates the transition between sessile and motile lifestyles in bacteria. Bacteria often encode multiple diguanylate cyclase (DGC) and phosphodiesterase (PDE) enzymes that produce and degrade c-di-GMP, respectively. Because of multiple inputs into the c-di-GMP-signaling network, it is unclear whether this system functions via high or low specificity. High-specificity signaling is characterized by individual DGCs or PDEs that are specifically associated with downstream c-di-GMP-mediated responses. In contrast, low-specificity signaling is characterized by DGCs or PDEs that modulate a general signal pool, which, in turn, controls a global c-di-GMPmediated response. To determine whether c-di-GMP functions via high or low specificity in Vibrio cholerae, we correlated the in vivo c-di-GMP concentration generated by seven DGCs, each expressed at eight different levels, to the c-di-GMP-mediated induction of biofilm formation and transcription. There was no correlation between total intracellular c-di-GMP levels and biofilm formation or gene expression when considering all states. However, individual DGCs showed a significant correlation between c-di-GMP production and c-di-GMP-mediated responses. Moreover, the rate of phenotypic change versus c-di-GMP concentration was significantly different between DGCs, suggesting that bacteria can optimize phenotypic output to c-di-GMP levels via expression or activation of specific DGCs. Our results conclusively demonstrate that c-di-GMP does not function via a simple, low-specificity signaling pathway in V. cholerae.signaling specificity | systems biology

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Quantification of high-specificity cyclic diguanylate signaling

Massie¹,

Reynolds²,

Koestler³

et al. 2012

145

143

“…PDE-catalyzed cyclic nucleotide degradation provides an important mechanism for regulating signaling. Indeed, the PDE component of cAMP pathways ensures the proper intensity and spatiotemporal distribution of the signal (4,5), as illustrated by many studies on different endocrine tissues (6)(7)(8).…”

mentioning

confidence: 99%

Modulation of Leydig cell function by cyclic nucleotide phosphodiesterase 8A

Vasta

Shimizu‐Albergine

Beavo

2006

Leydig cells produce testosterone in the testes under the pulsatile control of pituitary luteinizing hormone (LH). cAMP is the intracellular messenger for LH action on steroidogenesis, and pharmacological evidence indicates that the response to LH can be modulated by cyclic nucleotide phosphodiesterases (PDEs). However the types and roles of the PDEs present in Leydig cells have not been fully defined. We report here that PDE8A is expressed in Leydig cells, and using PDE8A knockout mice we provide evidence that PDE8A is a key regulator of LH signaling and steroidogenesis. A 4-fold increase in the sensitivity to LH for testosterone production was detected in Leydig cells isolated from PDE8A knockout mice. In Leydig cells from wild-type mice, 3-isobutyl-1-methylxanthine, a compound that inhibits all cAMP PDEs except PDE8A, elicited only a small increase in the sensitivity of testosterone production to LH. However, in the PDE8-null mice, the effect of this inhibitor is much more pronounced. These observations indicate that PDE8A and at least one other PDE control the same or a complementary pool of cAMP that mediates LH-regulated steroidogenesis. Overall, these results suggest that pharmacological manipulation of PDE8A, alone or in combination with other PDEs present in Leydig cells, may be exploited to modulate testosterone synthesis and possibly to treat various conditions where the local levels of this androgen need to be altered.cAMP ͉ testosterone ͉ PDE8A ͉ testis ͉ steroidogenesis T he second messenger cAMP plays important roles in mediating the biological effects of a wide variety of first messengers. Increases in intracellular cAMP lead to activation of cAMP-dependent protein kinases, guanine nucleotide exchange factors, and cyclic nucleotide-gated channels, which in turn can regulate the activity of other signaling and metabolic pathways (1). cAMP signaling pathways are controlled through regulation of the synthesis of cAMP by adenylyl cyclases and degradation by phosphodiesterases (PDEs) (1, 2). The cyclic nucleotidePDEs are now recognized to form a superfamily of 11 different, but homologous, gene-families that all contain highly homologous catalytic domains near their C termini (3). PDE-catalyzed cyclic nucleotide degradation provides an important mechanism for regulating signaling. Indeed, the PDE component of cAMP pathways ensures the proper intensity and spatiotemporal distribution of the signal (4, 5), as illustrated by many studies on different endocrine tissues (6-8).Leydig cells are interstitial cells located adjacent to the seminiferous tubules in the testes. The best-established function of Leydig cells is to produce the androgen, testosterone, under the pulsatile control of pituitary luteinizing hormone (LH) (9). It has been demonstrated that cAMP is the major intracellular messenger for LH action on steroidogenesis and that most, if not all, of the signaling action of cAMP is due to cAMP-dependent protein kinase (PKA)-mediated effects on proteins regulating the steroid biosynthetic pathway (9...

“…To assure specificity of the cellular output to different ligands, spatiotemporal compartmentation of the cAMP/PKA pathway into distinct PKA microdomains is thought to be essential (28). Inactive PKA is an heterotetramer consisting of two regulatory (PKA R) and two catalytic subunits, but the catalytic subunits dissociate from the regulatory peptides upon activation by cAMP and phosphorylate target molecules.…”

mentioning

confidence: 99%

Myosin Va cooperates with PKA RIα to mediate maintenance of the endplate in vivo

Röder¹,

Choi²,

Reischl

et al. 2010

108

Myosin V motor proteins facilitate recycling of synaptic receptors, including AMPA and acetylcholine receptors, in central and peripheral synapses, respectively. To shed light on the regulation of receptor recycling, we employed in vivo imaging of mouse neuromuscular synapses. We found that myosin Va cooperates with PKA on the postsynapse to maintain size and integrity of the synapse; this cooperation also regulated the lifetime of acetylcholine receptors. Myosin Va and PKA colocalized in subsynaptic enrichments. These accumulations were crucial for synaptic integrity and proper cAMP signaling, and were dependent on AKAP function, myosin Va, and an intact actin cytoskeleton. The neuropeptide and cAMP agonist, calcitonin-gene related peptide, rescued fragmentation of synapses upon denervation. We hypothesize that neuronal ligands trigger local activation of PKA, which in turn controls synaptic integrity and turnover of receptors. To this end, myosin Va mediates correct positioning of PKA in a postsynaptic microdomain, presumably by tethering PKA to the actin cytoskeleton.cAMP | muscle | neuromuscular junction | microdomain | synaptic plasticity R ecently, myosin V motor proteins were found to be crucial for the plasticity of central and peripheral synapses by facilitating, respectively, the recycling of AMPA (1-3) and acetylcholine receptors (AChRs) (4). The neuromuscular junction (NMJ) is the synapse between motor neurons and skeletal muscle fibers. Even though it is formed during ontogenesis and then maintained over the years (5), half-lives (t 1/2 ) of a few days are typical for its protein constituents, such as the AChR (6). The high enrichment of AChRs in the postsynapse is regulated by accurate targeting and turnover of this receptor. Vesicular transport is employed for this purpose, using different routes of exocytosis, endocytosis, and recycling (7-9). We identified myosin Va as the first motor protein involved in AChR trafficking and have found it to facilitate its recycling (4). Down-regulation of myosin Va led to a reduced t 1/2 of AChRs (4) similar to pathological conditions, such as denervation (6, 10-13) or dystrophy (14). A shortened t 1/2 of AChRs accompanies morphological changes of the NMJ: while NMJs in mouse muscles are normally elliptic and pretzel-shaped (15), they elongate and fragment under pathological conditions (16,17).Previous studies have revealed a major role of cAMP signaling in controlling the t 1/2 of AChRs (12, 18). cAMP is formed upon activation of G protein-coupled receptors and mediates its effects mainly through protein kinase A (PKA). Notably, stimulation of cAMP synthesis rescued AChR lifetime in denervated (12,19) and dystrophic muscles (14). Several groups have described antagonistic functions of protein kinase C and PKA on AChR persistence and synaptic strength (18,20,21): although activation of protein kinase C destabilizes AChRs, PKA activity protects this receptor from such destabilization (18). In this context, the neuropeptide and cAMP agonist, α-calcitonin gene-rel...