cAMP-dependent Kinase Research Articles

Anti-thrombotic effects of ginsenoside Rk3 by regulating cAMP and PI3K/MAPK pathway on human platelets

Background and objectiveThe ability to inhibit aggregation has been demonstrated with synthetically derived ginsenoside compounds G-Rp (1, 3, and 4) and ginsenosides naturally found in Panax ginseng 20(S)-Rg3, Rg6, F4, and Ro. Among these compounds, Rk3 (G-Rk3) from Panax ginseng needs to be further explored in order to reveal the mechanisms of action during inhibition. MethodologyOur study focused to investigate the action of G-Rk3 on agonist-stimulated human platelet aggregation, inhibition of platelet signaling molecules such as fibrinogen binding with integrin αIIbβ3 using flow cytometry, intracellular calcium mobilization, dense granule secretion, and thromboxane B2 secretion. In addition, we checked the regulation of phosphorylation on PI3K/MAPK pathway, and thrombin-induced clot retraction was also observed in platelets rich plasma. Key ResultsG-Rk3 significantly increased amounts of cyclic adenosine monophosphate (cAMP) and led to significant phosphorylation of cAMP-dependent kinase substrates vasodilator-stimulated phosphoprotein (VASP) and inositol 1,4,5-trisphosphate receptor (IP3R). In the presence of G-Rk3, dense tubular system Ca2+ was inhibited, and platelet activity was lowered by inactivating the integrin αIIb/β3 and reducing the binding of fibrinogen. Furthermore, the effect of G-Rk3 extended to the inhibition of MAPK and PI3K/Akt phosphorylation resulting in the reduced secretion of intracellular granules and reduced production of TXA2. Lastly, G-Rk3 inhibited platelet aggregation and thrombus formation via fibrin clot. Conclusions and implicationsThese results suggest that when dealing with cardiovascular diseases brought upon by faulty aggregation among platelets or through the formation of a thrombus, the G-Rk3 compound can play a role as an effective prophylactic or therapeutic agent.

A 7-Hydroxy 4-Methylcoumarin Enhances Melanogenesis in B16-F10 Melanoma Cells.

The objectives of this study were to investigate the melanogenetic potentials of the naturally occurring 7-hydroxy coumarin derivatives 7-hydroxy 5,6-dimethoxycoumarin (7H-5,6DM), 7-hydroxy 6,8-dimethoxycoumarin (7H-6,8DM), 7-hydroxy 6-methoxycoumarin (7H-6M), and 7-hydroxy 4-methylcoumarin (7H-4M) in the melanogenic cells model for murine B16F10 melanoma cells. The initial results indicated that melanin production and intracellular tyrosinase activity were significantly stimulated by 7H-4M but not by 7H-5,6DM, 7H-6,8DM, or 7H-6M. Therefore, our present study further investigated the melanogenic effects of 7H-4M in B16-F10 cells, as well as its mechanisms of action. In a concentration-dependent manner, 7H-4M increased intracellular tyrosinase activity, leading to the accumulation of melanin without affecting the viability of B16-F10 cells. Our study further investigated the effects of 7H-4M on melanogenesis, including its ability to promote tyrosinase activity, increase melanin content, and activate molecular signaling pathways. The results indicate that 7H-4M effectively stimulated tyrosinase activity and significantly increased the expression of melanin synthesis-associated proteins, such as microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP1), and TRP2. Based on our findings, we can conclude that 7H-4M has the ability to activate the melanogenesis process through the upregulation of cAMP-dependent protein kinase (PKA) and the cAMP response element-binding protein (CREB). Additionally, our study showed that 7H-4M induced melanogenic effects by downregulating the extracellular signal-regulated kinase (ERK) and the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt)/glycogen synthesis kinase-3β (GSK-3β) cascades, while upregulating the JNK and p38 signaling pathways. Finally, the potential of using 7H-4M in topical applications was tested through primary human skin irritation tests. During these tests, no adverse reactions were induced by 7H-4M. In summary, our results indicate that 7H-4M regulates melanogenesis through various signaling pathways such as GSK3β/β-catenin, AKT, PKA/CREB, and MAPK. These findings suggest that 7H-4M has the potential to prevent the development of pigmentation diseases.

Differential changes in cyclic adenosine 3'-5' monophosphate (cAMP) effectors and major Ca2+ handling proteins during diabetic cardiomyopathy.

Diabetic cardiomyopathy (DCM) is associated with differential and time-specific regulation of β-adrenergic receptors and cardiac cyclic nucleotide phosphodiesterases with consequences for total cyclic adenosine 3'-5' monophosphate (cAMP) levels. We aimed to investigate whether these changes are associated with downstream impairments in cAMP and Ca2+ signalling in a type 1 diabetes (T1D)-induced DCM model. T1D was induced in adult male rats by streptozotocin (65 mg/kg) injection. DCM was assessed by cardiac structural and molecular remodelling. We delineated sequential changes affecting the exchange protein (Epac1/2), cAMP-dependent protein kinase A (PKA) and Ca2+ /Calmodulin-dependent kinase II (CaMKII) at 4, 8 and 12 weeks following diabetes, by real-time quantitative PCR and western blot. Expression of Ca2+ ATPase pump (SERCA2a), phospholamban (PLB) and Troponin I (TnI) was also examined. Early upregulation of Epac1 transcripts was noted in diabetic hearts at Week 4, followed by increases in Epac2 mRNA, but not protein levels, at Week 12. Expression of PKA subunits (RI, RIIα and Cα) remained unchanged regardless of the disease stage, whereas CaMKII increased at Week 12 in DCM. Moreover, PLB transcripts were upregulated in diabetic hearts, whereas SERCA2a and TnI gene expression was unchanged irrespective of the disease evolution. PLB phosphorylation at threonine-17 was increased in DCM, whereas phosphorylation of both PLB at serine-16 and TnI at serine-23/24 was unchanged. We show for the first time differential and time-specific regulations in cardiac cAMP effectors and Ca2+ handling proteins, data that may prove useful in proposing new therapeutic approaches in T1D-induced DCM.

An NMR portrait of functional and dysfunctional allosteric cooperativity in cAMP-dependent protein kinase A.

The cAMP-dependent protein kinase A (PKA) is the archetypical eukaryotic kinase. The catalytic subunit (PKA-C) structure is highly conserved among the AGC-kinase family. PKA-C is a bilobal enzyme with a dynamic N-lobe, harbouring the Adenosine-5'-triphosphate (ATP) binding site and a more rigid helical C-lobe. The substrate-binding groove resides at the interface of the two lobes. A distinct feature of PKA-C is the positive binding cooperativity between nucleotide and substrate. Several PKA-C mutations lead to the development of adenocarcinomas, myxomas, and other rare forms of liver tumours. Nuclear magnetic resonance (NMR) spectroscopy shows that these mutations disrupt the allosteric communication between the two lobes, causing a drastic decrease in binding cooperativity. The loss of cooperativity correlates with changes in substrate fidelity and reduced kinase affinity for the endogenous protein kinase inhibitor (PKI). The similarity between PKI and the inhibitory sequence of the kinase regulatory subunits suggests that the overall mechanism of regulation of the kinase may be disrupted. We surmise that a reduced or obliterated cooperativity may constitute a common trait for both orthosteric and allosteric mutations of PKA-C that may lead to dysregulation and disease.

Radiofrequency Irradiation Attenuated UVB-Induced Skin Pigmentation by Modulating ATP Release and CD39 Expression.

Hyperpigmentation stimulated by ultraviolet (UV)-induced melanin overproduction causes various cosmetic problems. UV radiation's activation of the cyclic adenosine monophosphate (cAMP)-mediated cAMP-dependent protein kinase (PKA)/cAMP response element-binding protein (CREB)/microphthalmia-associated transcription factor (MITF) pathway is the main pathway for melanogenesis. However, the secretion of adenosine triphosphate (ATP) from keratinocytes due to UV radiation also leads to melanogenesis. Adenosine, converted from ATP by CD39 and CD73, can activate adenylate cyclase (AC) activity and increase intracellular cAMP expression. cAMP-mediated PKA activation results in dynamic mitochondrial changes that affect melanogenesis via ERK. We evaluated whether radiofrequency (RF) irradiation could decrease ATP release from keratinocytes and suppress the expression of CD39, CD73, and A2A/A2B adenosine receptors (ARs) and the activity of AC and downregulate the PKA/CREB/MITF pathway, which would eventually decrease melanogenesis in vitro in UV-irradiated cells and animal skin. Our results indicate that RF decreased ATP release from UVB-irradiated keratinocytes. When conditioned media (CM) from UVB-irradiated keratinocytes (CM-UVB) were administered to melanocytes, the expressions of CD39, CD73, A2A/A2BARs, cAMP, and PKA increased. However, the expression of these factors decreased when CM from UVB and RF-irradiated keratinocytes (CM-UVB/RF) was administered to melanocytes. The phosphorylation of DRP1 at Ser637, which inhibits mitochondrial fission, increased in UVB-irradiated animal skin and was decreased by RF irradiation. The expression of ERK1/2, which can degrade MITF, was increased using RF treatment in UVB-irradiated animal skin. Tyrosinase activity and melanin levels in melanocytes increased following CM-UVB administration, and these increases were reversed after CD39 silencing. Tyrosinase activity and melanin levels in melanocytes were decreased by CM-UVB/RF irradiation. In conclusion, RF irradiation decreased ATP release from keratinocytes and the expressions of CD39, CD73, and A2A/A2BARs, which decreased AC activity in melanocytes. RF irradiation downregulated the cAMP-mediated PKA/CREB/MITF pathway and tyrosinase activity, and these inhibitory effects can be mediated via CD39 inhibition.

A research on the expression of Nucb2/ cAMP / PKA in the hippocampus of alcohol-dependent rats

To probe into the expression of Nucb2/cAMP/PKA signaling in the hippocampus of alcohol-dependent rats. Male SD rats were first divided into control (n = 8) and model groups (n = 8) at random. Subsequently, alcohol dependence model was prepared by double bottles of intermittent drinking 20% alcohol. Apart from that, the changes of body weight, alcohol intake and alcohol preference were recorded during the modeling period; the behavioral changes of rats were recorded by elevated plus maze and water maze; Followed by model establishment, qRT-PCR was being applied to detect mRNA levels and protein expression levels of nucleobindin-2 (Nucb2), adenylate cyclase (AC), cAMP-dependent protein kinase A (PKA) and cAMP-responsive element binding protein (CREB) etc. There was no remarkable distinction between the weight of rats in both control and model groups throughout the experiment (P＞0.05); after the alcohol consumption of rats in the drinking group exceeded 28d, the alcohol intake finally reached the plateau (16.65 ± 1.31) g/(kg.24 h). What's more, the alcohol preference (61.77 ± 2.81) % reached the stable baseline, which means that the rat alcohol dependence model was established; in comparison with those of the control group (P < 0.01), the number of open arm entries and the retention time of open arm in the model group were remarkably decreased in the elevated plus maze assay; in the water maze assay, the memory ability of the model group was reduced in comparison with the control group (P < 0.05); In comparison with the control group, the relative expression levels of Nucb2, AC, PKA and CREB were noticeably decreased in the model group. Nucb2 is not only bound up with alcohol dependence,but also may conduct a pivotal role in alcohol dependence by regulating the cAMP/PKA signaling pathway.

Activity of cAMP-Dependent Protein Kinase is Reduced in Protein-Energy Malnourished Rats

Glucagon decreases glutathione synthesis in hepatocytes from well-nourished rats. However, in hepatocytes from malnourished rats, glucagon does not inhibit glutathione synthesis, suggesting a desensitization of cAMP-mediated signal transduction. We investigated the mechanism for this desensitization of cAMP-mediated responsiveness in malnourished rats by comparing the signal transduction pathways in rats fed very low protein diets (0.5 g protein/100 g diet) with those of rats fed diets adequate in protein (15 g protein/100 g diet) for 2 wk. Glucagon receptor and forskolin-stimulated cAMP production were greater in hepatocytes from malnourished rats. Stimulation of adenylyl cyclase with forskolin, guanine nucleotides or manganese in hepatic membranes was also enhanced after malnutrition. Moreover, quantity of the stimulatory guanine nucleotide regulatory protein was 70–80% greater in hepatocytes from malnourished rats but the inhibitory guanine nucleotide regulatory protein was not different. These results suggested that desensitization of cAMP-mediated signal transduction after malnutrition occurred at a site distal to cAMP production. Maximal activity of cAMP-dependent protein kinase was 60% lower in liver homogenates from malnourished rats compared with controls. This difference in activity was confined to the cytosolic compartment, with no difference in activity observed in the particulate fraction. Lower activity of cAMP-dependent protein kinase in the cytosol of malnourished rats was associated with a 43% reduction in the quantity of regulatory subunit type I, with no difference in the regulatory subunit type II. These data indicate that desensitization of cAMP signal transduction in rat liver after malnutrition is due to a decrease in the quantity and activity of cAMP-dependent protein kinase.

Edmond Fischer's kinase legacy: History of the protein kinase inhibitor and protein kinaseA.

Although Fischer's extraordinary career came to focus mostly on the protein phosphatases, after his co-discovery of Phosphorylase Kinase with Ed Krebs he was clearly intrigued not only by cAMP-dependent protein kinase (PKA), but also by the heat-stable, high-affinity protein kinase inhibitor (PKI). PKI is an intrinsically disordered protein that contains at its N-terminus a pseudo-substrate motif that binds synergistically and with high-affinity to the PKA catalytic (C) subunit. The sequencing and characterization of this inhibitor peptide (IP20) were validated by the structure of the PKA C-subunit solved first as a binary complex with IP20 and then as a ternary complex with ATP and two magnesium ions. A second motif, nuclear export signal (NES), was later discovered in PKI. Both motifs correspond to amphipathic helices that convey high-affinity binding. The dynamic features of full-length PKI, recently captured by NMR, confirmed that the IP20 motif becomes dynamically and sequentially ordered only in the presence of the C-subunit. The type I PKA regulatory (R) subunits also contain a pseudo-substrate ATPMg2-dependent high-affinity inhibitor sequence. PKI and PKA, especially the Cβ subunit, are highly expressed in the brain, and PKI expression is also cell cycle-dependent. In addition, PKI is now linked to several cancers. The full biological importance of PKI and PKA signaling in the brain, and their importance in cancer thus remains to be elucidated.

Mitoguardin2 Is Associated With Hyperandrogenism and Regulates Steroidogenesis in Human Ovarian Granulosa Cells.

Polycystic ovary syndrome (PCOS) is an endocrinopathy characterized by hyperandrogenism, anovulation, and polycystic ovaries, in which hyperandrogenism manifests by excess androgen and other steroid hormone abnormalities. Mitochondrial fusion is essential in steroidogenesis, while the role of mitochondrial fusion in granulosa cells of hyperandrogenic PCOS patients remains unclear. In this study, mRNA expression of mitochondrial fusion genes mitoguardin1, -2 (MIGA 1, -2) was significantly increased in granulosa cells of hyperandrogenic PCOS but not PCOS with normal androgen levels, their mRNA expression positively correlated with testosterone levels. Dihydrotestosterone (DHT) treatment in mice led to high expression of MIGA2 in granulosa cells of ovulating follicles. Testosterone or forskolin/ phorbol 12-myristate 13-acetate treatments increased expression of MIGA2 and the steroidogenic acute regulatory protein (StAR) in KGN cells. MIGA2 interacted with StAR and induced StAR localization on mitochondria. Furthermore, MIGA2 overexpression significantly increased cAMP-activated protein kinase A (PKA) and phosphorylation of AMP-activated protein kinase (pAMPK) at T172 but inhibited StAR protein expression. However, MIGA2 overexpression increased CYP11A1, HSD3B2, and CYP19A1 mRNA expression. As a result, MIGA2 overexpression decreased progesterone but increased estradiol synthesis. Besides the androgen receptor, testosterone or DHT might also regulate MIGA2 and pAMPK (T172) through LH/choriogonadotropin receptor-mediated PKA signaling. Taken together, these findings indicate that testosterone regulates MIGA2 via PKA/AMP-activated protein kinase signaling in ovarian granulosa cells. It is suggested mitochondrial fusion in ovarian granulosa cells is associated with hyperandrogenism and potentially leads to abnormal steroidogenesis in PCOS.

MiR-34c-3p Regulates Protein Kinase A Activity Independent of cAMP by Dicing prkar2b Transcripts in Theileria annulata-Infected Leukocytes.

MicroRNAs (miRNAs) are small noncoding RNAs that can play critical roles in regulating various cellular processes, including during many parasitic infections. Here, we report a regulatory role for miR-34c-3p in cAMP-independent regulation of host cell protein kinase A (PKA) activity in Theileria annulata-infected bovine leukocytes. We identified prkar2b (cAMP-dependent protein kinase A type II-beta regulatory subunit) as a novel miR-34c-3p target gene and demonstrate how infection-induced upregulation of miR-34c-3p repressed PRKAR2B expression to increase PKA activity. As a result, the disseminating tumorlike phenotype of T. annulata-transformed macrophages is enhanced. Finally, we extend our observations to Plasmodium falciparum-parasitized red blood cells, where infection-induced augmentation in miR-34c-3p levels led to a drop in the amount of prkar2b mRNA and increased PKA activity. Collectively, our findings represent a novel cAMP-independent way of regulating host cell PKA activity in infections by Theileria and Plasmodium parasites. IMPORTANCE Small microRNA levels are altered in many diseases, including those caused by parasites. Here, we describe how infection by two important animal and human parasites, Theileria annulata and Plasmodium falciparum, induce changes in infected host cell miR-34c-3p levels to regulate host cell PKA kinase activity by targeting mammalian prkar2b. Infection-induced changes in miR-34c-3p levels provide a novel epigenetic mechanism for regulating host cell PKA activity independent of fluxes in cAMP to both aggravate tumor dissemination and improve parasite fitness.

Comparative and integrative analysis of transcriptomic and epigenomic-wide DNA methylation changes in African American prostate cancer

ABSTRACT African American (AA) men have the highest incidence and mortality rate from Prostate cancer (PCa) than any other racial/ethnic group. To date, PCa genomic studies have largely under-represented tumour samples from AA men. We measured genome-wide DNA methylation in benign and tumor prostate tissues from AA men using the Illumina Infunium 850 K EPIC array. mRNA expression database from a subset of the AA biospecimen were used to assess correlation of transcriptome and methylation datasets. Genome-wide methylation analysis identified 11,460 probes that were significant (p < 0.01) and differentially methylated in AA PCa compared to normal prostate tissues and showed significant (p < 0.01) inverse-correlation with mRNA expression. Ingenuity pathway analysis and Gene Ontology analysis in our AA dataset compared with TCGA dataset showed similarities in methylation patterns: top candidate genes with significant hypermethylation and corresponding down-regulated gene expression were associated with biological pathways in hemidesmosome assembly, mammary gland development, epidermis development, hormone biosynthesis, and cell communication. In addition, top candidate genes with significant hypomethylation and corresponding up-regulated gene expression were associated with biological pathways in macrophage differentiation, cAMP-dependent protein kinase activity, protein destabilization, transcription co-repression, and fatty acid biosynthesis. In contrast, differences in genome-wide methylation in our AA dataset compared with TCGA dataset were enriched for genes in steroid signalling, immune signalling, chromatin structure remodelling and RNA processing. Overall, differential methylation of AMIGO3, IER3, UPB1, GRM7, TFAP2C, TOX2, PLSCR2, ZNF292, ESR2, MIXL1, BOLL, and FGF6 were significant and uniquely associated with PCa progression in our AA cohort.

Metabolism-based approaches for autosomal dominant polycystic kidney disease.

Autosomal Dominant Polycystic Kidney Disease (ADPKD) leads to end stage kidney disease (ESKD) through the development and expansion of multiple cysts throughout the kidney parenchyma. An increase in cyclic adenosine monophosphate (cAMP) plays an important role in generating and maintaining fluid-filled cysts because cAMP activates protein kinase A (PKA) and stimulates epithelial chloride secretion through the cystic fibrosis transmembrane conductance regulator (CFTR). A vasopressin V2 receptor antagonist, Tolvaptan, was recently approved for the treatment of ADPKD patients at high risk of progression. However additional treatments are urgently needed due to the poor tolerability, the unfavorable safety profile, and the high cost of Tolvaptan. In ADPKD kidneys, alterations of multiple metabolic pathways termed metabolic reprogramming has been consistently reported to support the growth of rapidly proliferating cystic cells. Published data suggest that upregulated mTOR and c-Myc repress oxidative metabolism while enhancing glycolytic flux and lactic acid production. mTOR and c-Myc are activated by PKA/MEK/ERK signaling so it is possible that cAMPK/PKA signaling will be upstream regulators of metabolic reprogramming. Novel therapeutics opportunities targeting metabolic reprogramming may avoid or minimize the side effects that are dose limiting in the clinic and improve on the efficacy observed in human ADPKD with Tolvaptan.

Very Low Protein Diets Induce a Rapid Decrease in Hepatic cAMP-Dependent Protein Kinase Followed by a Slower Increase in Adenylyl Cyclase Activity in Rats

Recent evidence indicates that cAMP-mediated responses are desensitized in liver during malnutrition. While receptor-stimulated production of cAMP is increased in hepatocytes from rats fed very low protein diets for 14 d, activity of cAMP-dependent protein kinase (PKA) is decreased in liver cytosol. The present study investigated the time course for this desensitization. Weanling rats were fed either a 0.5 (malnourished) or 15% protein (control) diet for 1, 3, 7 or 14 d. Total PKA activity decreased after only 3 d of feeding the low protein diet. This decrease was confined to the cytosolic compartment and was associated with a lower quantity of immunoreactive RI regulatory subunit of PKA, with no difference in the quantity of immunoreactive RII regulatory subunit. In contrast, basal-, MnCl2- and guanine nucleotide regulatory protein-stimulated adenylyl cyclase activities were not greater in liver membranes of malnourished rats than in those of the control rats until the 2nd wk of feeding. Greater activity was paralleled by an increase in the quantity of the stimulatory guanine nucleotide regulatory protein at d 14. The inhibitory guanine nucleotide regulatory protein quantity did not differ between dietary groups. Greater cAMP production was not mediated by changes in PKA phosphorylation of adenylyl cyclase because preincubation of membranes with purified PKA catalytic subunit decreased MnCl2-stimulated cAMP production equally in liver membranes of both control and malnourished rats. Similarly, treatment with alkaline phosphatase decreased adenylyl cyclase activity but did not eliminate the difference in adenylyl cyclase activity between control and malnourished rats. These data demonstrate that loss of PKA activity is an early response to a low protein diet and that, subsequently, a number of molecular adaptations occur which increase cAMP production. These changes may be adaptive responses to malnutrition that maintain essential cAMP-dependent functions.

Acacetin alleviates energy metabolism disorder through promoting white fat browning mediated by AC-cAMP pathway.

Acacetin (ACA), a flavone isolated from Chinese traditional medical herbs, has numerous pharmacological activities. However, little is known about the roles in white fat browning and energy metabolism. In the present study, we investigated whether and how ACA would improve energy metabolism in vivo and in vitro. ACA (20 mg/kg) was intraperitoneally injected to the mice with obesity induced by HFD for 14 consecutive days (in vivo); differentiated 3T3-L1 adipocytes were treated with ACA (20 µmol/L and 40 µmol/L) for 24 h (in vitro). The metabolic profile, lipid accumulation, fat-browning and mitochondrial contents, and so on were respectively detected. The results in vivo showed that ACA significantly reduced the body weight and visceral adipose tissue weight, alleviated the energy metabolism disorder, and enhanced the browning-related protein expressions in adipose tissue of rats. Besides, the data in vitro revealed that ACA significantly reduced the lipid accumulation, induced the expressions of the browning-related proteins and cAMP-dependent protein kinase A (PKA), and increased the mitochondrium contents, especially enhanced the energy metabolism of adipocytes; however, treatment with beta-adrenergic receptor blocker (propranolol, Pro) or adenyl cyclase (AC) inhibitor (SQ22536, SQ) abrogated the ACA-mediated effects. The data demonstrate that ACA alleviates the energy metabolism disorder through the pro-browning effects mediated by the AC-cAMP pathway. The findings would provide the experimental foundation for ACA to prevent and treat obesity and related metabolism disorders.

Gamma-aminobutyric acid (GABA) suppresses hemocyte phagocytosis by binding to GABA receptors and modulating corresponding downstream pathways in blood clam, Tegillarca granosa

Although accumulating data demonstrated that gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter, plays an important regulatory role in immunity of vertebrates, its immunomodulatory function and mechanisms of action remain poorly understood in invertebrates such as bivalve mollusks. In this study, the effect of GABA on phagocytic activity of hemocytes was evaluated in a commercial bivalve species, Tegillarca granosa. Furthermore, the potential regulatory mechanism underpinning was investigated by assessing potential downstream targets. Data obtained demonstrated that in vitro GABA incubation significantly constrained the phagocytic activity of hemocytes. In addition, the GABA-induced suppression of phagocytosis was markedly relieved by blocking of GABAA and GABAB receptors using corresponding antagonists. Hemocytes incubated with lipopolysaccharides (LPS) and GABA had significant higher K+-Cl- cotransporter 2 (KCC2) content compared to the control. In addition, GABA treatment led to an elevation in intracellular Cl−, which was shown to be leveled down to normal by blocking the ionotropic GABAA receptor. Treatment with GABAA receptor antagonist also rescued the suppression of GABAA receptor-associated protein (GABARAP), KCC, TNF receptor associated factor 6 (TRAF6), inhibitor of nuclear factor kappa-B kinase subunit alpha (IKKα), and nuclear factor kappa B subunit 1 (NFκB) caused by GABA incubation. Furthermore, incubation of hemocytes with GABA resulted in a decrease in cAMP content, an increase in intracellular Ca2+, and downregulation of cAMP-dependent protein kinase (PKA), calmodulin kinase II (CAMK2), calmodulin (CaM), calcineurin (CaN), TRAF6, IKKα, and NFκB. All these above-mentioned changes were found to be evidently relieved by blocking the metabotropic G-protein-coupled GABAB receptor. Our results suggest GABA may play an inhibitory role on phagocytosis through binding to both GABAA and GABAB receptors, and subsequently regulating corresponding downstream pathways in bivalve invertebrates.

Role of Protein Kinase A Activation in the Immune System with an Emphasis on Lipopolysaccharide-Responsive and Beige-like Anchor Protein in B Cells

Cyclic AMP-dependent protein kinase A (PKA) is a ubiquitous enzymatic complex that is involved in a broad spectrum of intracellular receptor signaling. The activity of PKA depends on A-kinase anchoring proteins (AKAPs) that attach to PKAs close to their substrates to control signaling. Although the relevance of PKA-AKAP signaling in the immune system is evident in T cells, its relevance in B and other immune cells remains relatively unclear. In the last decade, lipopolysaccharide-responsive and beige-like anchor protein (LRBA) has emerged as an AKAP that is ubiquitously expressed in B and T cells, specifically after activation. A deficiency of LRBA leads to immune dysregulation and immunodeficiency. The cellular mechanisms regulated by LRBA have not yet been investigated. Therefore, this review summarizes the functions of PKA in immunity and provides the most recent information regarding LRBA deficiency to deepen our understanding of immune regulation and immunological diseases.

Quercetin 3-O-Galactoside Isolated from Limonium tetragonum Inhibits Melanogenesis by Regulating PKA/MITF Signaling and ERK Activation.

Quercetin 3-O-galactoside (Q3G) is a common dietary flavanol that has been shown to possess several bioactivities, including anti-melanogenesis. However, how Q3G exerts its anti-melanogenic effect has not been studied. The current study, therefore aimed to investigate the anti-melanogenesis potential of Q3G and elucidate the underlying action mechanism in α-melanocyte-stimulating hormone (α-MSH)-induced hyperpigmentation model of B16F10 murine melanoma cells. Results showed that α-MSH stimulation significantly increased tyrosinase (TYR) and melanin production, which were significantly downregulated by Q3G treatment. The treatment with Q3G suppressed the transcriptional and protein expressions of melanogenesis-related enzymes TYR, tyrosinase related protein-1 (TRP-1), and TRP-2, along with the melanogenic transcription factor microphthalmia-associated transcription factor (MITF) in B16F10 cells. It was shown that Q3G downregulated MITF expression and suppressed its transcriptional activity by inhibiting the cAMP-dependent protein kinase A (PKA)-mediated activation of CREB and GSK3β. In addition, MAPK-regulated MITF activation signaling was also involved in the inhibition of melanin production by Q3G. The results suggest that the anti-melanogenic properties of Q3G rationalize further studies in vivo to confirm its action mechanism and consequent utilization as a cosmetic ingredient against hyperpigmentation.

Posttranslational modifications of cyclic AMP-dependent protein kinase a affect its binding to the CFTR anion channel.

CFTR is the only ion channel member in the ABC protein superfamily. Mutations of the protein cause malfunction of the pore or retention of the protein in the endoplasmic reticulum leading to the systemic disease cystic fibrosis, the most common lethal genetic disorder in the Caucasian population. CFTR activity relies on an irreversible gating mechanism which involves a cycle of ATP binding and hydrolysis at its cytosolic nucleotide binding domains (NBDs). Upon binding of two molecules of ATP the NBDs form a tight NBD dimer which triggers opening of the channel pore, while ATP hydrolysis closes the channel. ATP-dependent opening of the pore strongly depends on phosphorylation of the channel's regulatory (R) domain by cAMP-dependent protein kinase (PKA). At physiological ATP concentrations the NBDs of the channel are saturated by ligand, hence PKA phosphorylation plays the primary regulatory role. Our group has previously shown (PNAS 117:21740) that direct physical binding of PKA activates CFTR channels independently of, and additively to, phosphorylation. We hypothesized that PKA binding prevents its substrate, the R domain, from returning into an inhibitory position wedged in between the two NBDs, thereby shifting the closed-open equilibrium towards open. In contrast to the protein isolated from bovine heart, heterologously expressed PKA lacks such a binding effect. We therefore studied posttranslational modifications of PKA, and investigated their effects on CFTR activation by comparing the recombinant and tissue-isolated PKA isoforms. Results of the ongoing research will be presented at the meeting.

Cryo-EM investigation of the subconductance state of ryanodine receptor calcium release channels induced by scorpion toxins.

Ryanodine Receptors (RyRs) are ion channels that release Ca2+ from the endoplasmic or sarcoplasmic reticulum. They are known to undergo subconductance states, but such states have thus far remained elusive. Calcins are scorpion-derived peptides that can permeate the plasma membrane, thus gaining access to intracellular ion channels. They bind to RyRs with high potency and induce long-lived subconductance states. Using cryo-EM and functional assays, we describe the binding site of imperacalcin on RyR1, and show that binding of calcins results in extended ion conduction pathways with radii and electrostatic profiles that explain the subconductance. Calcin binding also results in large asymmetry throughout the RyR, including intersubunit breaks. Kinase assays show that calcins are excellent substrates for cAMP-dependent kinase, and our data show that this obliterates binding to the RyR, explaining how post-translational modifications can affect the fate of a cell-permeating peptide.

A-Kinase Anchoring Proteins in Cardiac Myocytes and Their Roles in Regulating Calcium Cycling.

The rate of calcium cycling and calcium transient amplitude are critical determinants for the efficient contraction and relaxation of the heart. Calcium-handling proteins in the cardiac myocyte are altered in heart failure, and restoring the proper function of those proteins is an effective potential therapeutic strategy. The calcium-handling proteins or their regulators are phosphorylated by a cAMP-dependent kinase (PKA), and thereby their activity is regulated. A-Kinase Anchoring Proteins (AKAPs) play a seminal role in orchestrating PKA and cAMP regulators in calcium handling and contractile machinery. This cAMP/PKA orchestration is crucial for the increased force and rate of contraction and relaxation of the heart in response to fight-or-flight. Knockout models and the few available preclinical models proved that the efficient targeting of AKAPs offers potential therapies tailor-made for improving defective calcium cycling. In this review, we highlight important studies that identified AKAPs and their regulatory roles in cardiac myocyte calcium cycling in health and disease.