3\', 5\'-cyclic adenosine monophosphate (cAMP) mediates the effects of sympathetic stimulation on the rate and strength of cardiac contraction. Beyond this pivotal role, in cardiac myocytes cAMP also orchestrates a diverse array of reactions to various stimuli. To ensure specificity of response, the cAMP signaling pathway is intricately organized into multiple, spatially confined, subcellular domains, each governing a distinct cellular function. In this review, we describe the molecular components of the cAMP signalling pathway, how they organized are inside the intracellular space and how they achieve exquisite regulation of signalling within nanometer-size domains. We delineate the key experimental findings that lead to the current model of compartmentalised cAMP signaling and we offer an overview of our present understanding of how cAMP nanodomains are structured and regulated within cardiac myocytes. Furthermore, we discuss how compartmentalized cAMP signaling is affected in cardiac disease and consider the potential therapeutic opportunities arising from understanding such organization. By exploiting the nuances of compartmentalized cAMP signaling, novel and more effective therapeutic strategies for managing cardiac conditions may emerge. Finally, we highlight the unresolved questions and hurdles that must be addressed to translate these insights into interventions that may benefit patients.

The complex interactome crucial for successful pregnancy is constituted by the intricate network of endocrine and paracrine signaling pathways, involving gametes, embryos, and the female reproductive tract. Specifically, the oviduct exhibits distinct responses to gametes and early embryos during particular phases of the estrus cycle, a process tightly regulated by reproductive hormones. Moreover, these hormones play a pivotal role in orchestrating cyclical changes within oviductal epithelial cells. To unravel the molecular mechanisms underlying these dynamic changes, our study aimed to investigate the involvement of protein kinase A (PKA) in oviductal epithelial cells throughout the estrus cycle and in advanced pregnancy, extending our studies to oviductal epithelial cell in primary culture. By a combination of 2D-gel electrophoresis, Western blotting, and mass spectrometry, we identified 17 proteins exhibiting differential phosphorylation status mediated by PKA. Among these proteins, we successfully validated the phosphorylation status of heat shock 70 kDa protein (HSP70), aconitase 2 (ACO2), and lamin B1 (LMNB1). Our findings unequivocally demonstrate the dynamic regulation of PKA throughout the estrus cycle in oviductal epithelial cells. Also, analysis by bioinformatics tools suggest its pivotal role in mediating cyclical changes possibly through modulation of apoptotic pathways. This research sheds light on the intricate molecular mechanisms underlying reproductive processes, with implications for understanding fertility and reproductive health.

Acute nociceptive pain in mice caused by subcutaneous (intraplantar) injection of TRPV1 ion channel agonist capsaicin (1.6 μg/mouse) and the effects of protein kinase A inhibitor H-89 (0.05 mg/mouse, intraplantar injection) and NMDA receptor channel antagonists MK-801 (7.5 and 15 μg/mouse, topical application) and hemantane (0.5 mg/mouse, topical application) on the pain were assessed. MK-801 and hemantane were found to reduce the duration of the pain response. H-89 did not significantly affect the pain in animals, but preliminary administration of this drug abolished the antinociceptive effect of MK-801 (7.5 μg/mouse) and weakens the effect of hemantane (0.5 mg/mouse).

Vasopressin controls water permeability in the renal collecting duct by regulating the water channel protein, aquaporin-2 (AQP2). Phosphoproteomic studies have identified multiple proteins that undergo phosphorylation changes in response to vasopressin. The kinases responsible for phosphorylation of most of these sites have not been identified. Here, we use large-scale Bayesian data integration methods to predict the responsible kinases for 51 phospho-proteomically identified vasopressin-regulated phosphorylation sites in the renal collecting duct. To do this, we applied Bayes\' Rule to rank the 515 known mammalian protein kinases for each site. Bayes\' rule was applied recursively to integrate each of seven independent data sets, each time using the posterior probability vector of a given step as the prior probability vector of the next step. 30 of the 33 phosphorylation sites that increase with vasopressin were predicted to be phosphorylated by protein kinase A catalytic subunit-a (PKA), consistent with prior studies implicating PKA in vasopressin signaling. Eighteen of the vasopressin-regulated phosphorylation sites were decreased in response to vasopressin and all but three of these sites were predicted to be targets of extracellular signal-regulated kinases, ERK1 and ERK2. This result implies that ERK1 and ERK2 are inhibited in response to vasopressin V2 receptor occupation, secondary to PKA activation. The six phosphorylation sites not predicted to be phosphorylated by PKA or ERK1/2 are potential targets of other protein kinases previously implicated in aquaporin-2 regulation, including cyclin-dependent kinase 18 (CDK18), calmodulin-dependent kinase 2d (CAMK2D). AMP-activated kinase catalytic subunit a-1 (PRKAA1) and CDC42 binding protein kinase beta (CDC42BPB).

Members of the phosphodiesterase 4 (PDE4) enzyme family regulate the availability of the secondary messenger cyclic adenosine monophosphate (cAMP) and, by doing so, control cellular processes in health and disease. In particular, PDE4D has been associated with Alzheimer\'s disease and the intellectual disability seen in fragile X syndrome. Furthermore, single point mutations in critical PDE4D regions cause acrodysostosis type 2(ACRDYS2, also referred to as inactivating PTH/PTHrP signalling disorder 5 or iPPSD5), where intellectual disability is seen in ∼90% of patients alongside the skeletal dysmorphologies that are characteristic of acrodysostosis type 1 (ACRDYS1/iPPSD4) and ACRDYS2. Two contrasting mechanisms have been proposed to explain how mutations in PDE4D cause iPPSD5. The first mechanism, the \'over-activation hypothesis\', suggests that cAMP/PKA (cyclic adenosine monophosphate/protein kinase A) signalling is reduced by the overactivity of mutant PDE4D, whilst the second, the \'over-compensation hypothesis\' suggests that mutations reduce PDE4D activity. That reduction in activity is proposed to cause an increase in cellular cAMP, triggering the overexpression of other PDE isoforms. The resulting over-compensation then reduces cellular cAMP and the levels of cAMP/PKA signalling. However, neither of these proposed mechanisms accounts for the fine control of PDE activation and localization, which are likely to play a role in the development of iPPSD5. This review will draw together our understanding of the role of PDE4D in iPPSD5 and present a novel perspective on possible mechanisms of disease.

The bidirectional long-distance transport of organelles is crucial for cell body-synapse communication. However, the mechanisms by which this transport is modulated for synapse formation, maintenance, and plasticity are not fully understood. Here, we demonstrate through quantitative analyses that maintaining sensory neuron-motor neuron synapses in the Aplysia gill-siphon withdrawal reflex is linked to a sustained reduction in the retrograde transport of lysosomal vesicles in sensory neurons. Interestingly, while mitochondrial transport in the anterograde direction increases within 12 hours of synapse formation, the reduction in lysosomal vesicle retrograde transport appears three days after synapse formation. Moreover, we find that formation of new synapses during learning induced by neuromodulatory neurotransmitter serotonin further reduces lysosomal vesicle transport within 24 hours, whereas mitochondrial transport increases in the anterograde direction within one hour of exposure. Pharmacological inhibition of several signaling pathways pinpoints PKA as a key regulator of retrograde transport of lysosomal vesicles during synapse maintenance. These results demonstrate that synapse formation leads to organelle-specific and direction specific enduring changes in long-distance transport, offering insights into the mechanisms underlying synapse maintenance and plasticity.

Glucagon-like peptide-1 (GLP-1) is a multifunctional incretin hormone with various physiological effects beyond its well-characterized effect of stimulating glucose-dependent insulin secretion in the pancreas. An emerging role for GLP-1 and its receptor, GLP-1R, in brain neuroprotection and in the suppression of inflammation, has been documented in recent years. GLP-1R is a G protein-coupled receptor (GPCR) that couples to Gs proteins that stimulate the production of the second messenger cyclic 3\',5\'-adenosine monophosphate (cAMP). cAMP, acting through its two main effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), exerts several anti-inflammatory (and some pro-inflammatory) effects in cells, depending on the cell type. The present review discusses the cAMP-dependent molecular signaling pathways elicited by the GLP-1R in cardiomyocytes, cardiac fibroblasts, central neurons, and even in adrenal chromaffin cells, with a particular focus on those that lead to anti-inflammatory effects by the GLP-1R. Fully elucidating the role cAMP plays in GLP-1R\'s anti-inflammatory properties can lead to new and more precise targets for drug development and/or provide the foundation for novel therapeutic combinations of the GLP-1R agonist medications currently on the market with other classes of drugs for additive anti-inflammatory effect.

Ablation of the immune-specific catalytic subunit Cβ2 of protein kinase A is associated with a proinflammatory phenotype and increased sensitivity to autoimmunity in mice. Here we show that tumour growth of the adenocarcinoma cell line EO771 in the breast and in the lung after injection into the mammary fat pad and tail vein, respectively, was significantly reduced in mice ablated for Cβ2 compared to wild-type mice. In both cases, the breast and lung tumours showed increased infiltration of immune cells in the mice lacking Cβ2 compared to wild-type mice. Despite this, it appeared that solid tissue- versus intravenously injected EO771 cells evoked different immune responses. This was reflected by significantly increased levels of splenic proinflammatory immune cells and circulating cytokines in Cβ2 ablated mice carrying breast- but not the lung tumours. Moreover, Cβ2 ablated mice injected with EO771 cells showed increased overall survival compared to wild-type mice. Taken together, our results suggest for a role for immune cell-specific Cβ2 in protecting against tumour growth induced by EO771 cells in mice that is reflected in improved overall survival.

OBJECTIVE: Apigenin, a natural bioflavonoid, is reported as an anti-diabetic agent since it possesses the ability to inhibit α-glucosidase activity, cause stimulation of insulin action and secretion, manage ROS, and prevent diabetes complications. Apigenin was identified as a new insulin secretagogue that enhances glucose-stimulated insulin secretion and seems like a better antidiabetic drug candidate. Here we explored the insulinotropic mechanism(s) of apigenin in vitro in mice islets and in vivo in diabetic rats.
METHODS: Size-matched pancreatic islets were divided into groups and incubated in the presence or absence of apigenin and agonists or antagonists of major insulin signaling pathways. The secreted insulin was measured by ELISA. The intracellular cAMP was estimated by cAMP acetylation assay. The acute and chronic effects of apigenin were evaluated in diabetic rats.
RESULTS: apigenin dose-dependently enhanced insulin secretion in isolated mice islets, and its insulinotropic effect was exerted at high glucose concentrations distinctly different from glibenclamide. Furthermore, apigenin amplified glucose-induced insulin secretion in depolarized and glibenclamide-treated islets. Apigenin showed no effect on intracellular cAMP concentration; however, an additive effect was observed by apigenin in both forskolin and IBMX-induced insulin secretion. Interestingly, H89, a PKA inhibitor, and U0126, a MEK kinase inhibitor, significantly inhibited apigenin-induced insulin secretion; however, no significant effect was observed by using ESI-05, an epac2 inhibitor. Apigenin improved glucose tolerance and increased glucose-stimulated plasma insulin levels in diabetic rats. Apigenin also lowered blood glucose in diabetic rats upon chronic treatment.
CONCLUSIONS: Apigenin exerts glucose-stimulated insulin secretion by modulating the PKA-MEK kinase signaling cascade independent of K-ATP channels.

Protein kinase A (PKA) is a conserved kinase crucial for fundamental biological processes linked to growth, development, and metabolism. The PKA catalytic subunit is expressed as multiple isoforms in diverse eukaryotes; however, their contribution to ensuring signaling specificity in response to environmental cues remains poorly defined. Catalytic subunit activity is classically moderated via interaction with an inhibitory regulatory subunit. Here, a quantitative mass spectrometry approach is used to examine heat-stress-induced changes in the binding of yeast Tpk1-3 catalytic subunits to the Bcy1 regulatory subunit. We show that Tpk3 is not regulated by Bcy1 binding but, instead, is deactivated upon heat stress via reversible sequestration into cytoplasmic granules. These \"Tpk3 granules\" are enriched for multiple PKA substrates involved in various metabolic processes, with the Hsp42 sequestrase required for their formation. Hence, regulated sequestration of Tpk3 provides a mechanism to control isoform-specific kinase signaling activity during stress conditions.