Protein Kinase A Inhibitor Research Articles

Sympathetic Neurons Promote Small Cell Lung Cancer Through the Beta-2 Adrenergic Receptor.

The vagal nerve is linked to tumorigenesis in multiple tissues including small cell lung cancer (SCLC). However, the role of sympathetic neuron in SCLC development remains unknown. Here, we observed a significant reduction in tumor growth following chemical denervation of local sympathetic nerves in a mouse model of SCLC. Further study identified that β2-adrenergic receptor (ADRB2) on cancer cells mediated the crosstalk with nerve fibers. Genetic deletion or pharmacological inhibition of ADRB2 led to reduced tumor growth and improved survival. Moreover, blocking ADRB2 also reduced the growth of human SCLC organoids and xenografts. Further studies revealed that ADRB2 promoted cancer cell expansion through activating Protein Kinase A (PKA) signaling. Consistently, inhibition of PKA also reduced the growth of SCLC cells. These findings offer the initial insight into the role played by sympathetic neurons in the development of SCLC and may open a new therapeutic avenue to treat this deadly malignancy.

Taste receptor T1R3 regulates testosterone synthesis via the cAMP-PKA-SP1 pathway in testicular Leydig cells

Taste receptor type 1 subunit 3 (T1R3) is a G protein-coupled receptor encoded by the TAS1R3 gene that can be specifically activated by certain sweeteners or umami agents for sweet/umami recognition. T1R3 is a potential target for regulating male reproduction. However, studies on the impact of non-nutritive sweeteners on reproduction are limited. In the present study, we evaluated the impact of the non-nutritive sweeteners (saccharin sodium, sucralose and acesulfame-K) on testosterone synthesis in testicular Leydig cells of Xiang pigs by comparing the relative abundance of mRNA transcripts and protein expression of T1R3, steroidogenic related factors, and intracellular cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), as well as testosterone levels using Western blotting, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA). To clarify the specific mechanism, a dual luciferase assay was used to uncover the relationship between the transcription factors and steroidogenic enzyme. The acute intratesticular injection of a typical non-nutritive sweeteners was conducted to verify this impact in mouse. The results showed that saccharin sodium not only enhanced T1R3 expression in Leydig cells of Xiang pigs, but also caused significant increases in testosterone, cAMP, PKA, phosphorylation of specificity protein 1 (p-SP1), total protein of specificity protein 1 (SP1), steroidogenic acute regulatory protein (StAR), and 3β-hydroxysteroid dehydrogenase type 1 (3β-HSD1) (P<0.05). Similarly, treatment of Leydig cells with sucralose and acesulfame-K also increased testosterone level, protein expression of T1R3, 17-α-hydroxylase/17, 20-lyase (CYP17A1), and 3β-HSD1 (P<0.05). Treatment with SQ22536 (an adenylate cyclas inhibitor) or H89 (a PKA inhibitor) significantly reduced saccharin sodium-induced protein levels of p-SP1, StAR, CYP17A1, and 3β-HSD1 (P<0.05). In addition, a dual luciferase assay further demonstrated that SP1 significantly increased the promoter activity of CYP17A1 (P<0.05). When mouse testes were injected with saccharin sodium, T1R3, p-SP1, CYP17A1, and 3β-HSD1 were upregulated, leading to a significant testicular increase in testosterone and cAMP levels (P<0.05). These results suggest a mechanism by which the taste receptor T1R3 regulates testosterone production, and this mechanism may be linked to the cAMP-PKA pathway. Understanding the interrelationship between T1R3 and the cAMP-PKA-SP1 pathway contributes to clarify the regulatory mechanisms of male reproduction.

Phosphopeptide-bridged NH2-TiO2-mediated carbon dots self-enhancing and electrochemiluminescence microsensors for label-free protein kinase A detection.

A novel electrochemiluminescence (ECL) method was developed for determination of protein kinase A (PKA) ultra-sensitively based on amidated nano-titanium (NH2-TiO2) embellished carbon dots (Mg@N-CDs) fluorescent probe, which integrated the target recognition and ECL signal enhancement. The Cys-labeled kemptides were employed to build a serine-rich synthetic substrate-heptapeptide (Cys-kemptide) on the Au-electrode surface. Then, the PKA-induced biosensor was triggered as a signal switch to introduce the large amounts of TiO2 decorated Mg@N-CD nanohybrid (Ti@NMg-CDs) into AuE/Cys-phosphopeptides for signal output. In particular, the presence of PKA could induce the formation of Cys-phosphopeptides by the catalytic reaction between specific substrate (kemptide) and PKA, which acts as an initiator to link the Ti@NMg-CDs according to the bridge interactions Ti-O-P. In this way, multiple Cys-phosphopeptides were adsorbed onto a single Ti@NMg-CDs, and the Ti@NMg-CDs not only provided high specific selectivity but also large surface area, as well as unprecedented high ECL efficiency. Using this PKA-induced enhanced sensor, the limit of detection of the PKA was 4.89 × 10-4 U/mL (S/N = 3). The proposed ECL biosensor was also universally applicable for the screening of PKA inhibitors and determining of other kinases activity. Our sensing system has excellent performance of specificity and the screening of kinase inhibitors, as well as it will inspire future effort in clinical diagnostics and new drug discovery.

Cyclic adenosine monophosphate critically modulates cardiac GLP-1 receptor's anti-inflammatory effects.

Glucagon-like peptide (GLP)-1 receptor (GLP1R) agonists exert a multitude of beneficial cardiovascular effects beyond control of blood glucose levels and obesity reduction. They also have anti-inflammatory actions through both central and peripheral mechanisms. GLP1R is a G protein-coupled receptor (GPCR), coupling to adenylyl cyclase (AC)-stimulatory Gs proteins to raise cyclic 3`-5`-adenosine monophosphate (cAMP) levels in cells. cAMP exerts various anti-apoptotic and anti-inflammatory effects via its effectors protein kinase A (PKA) and Exchange protein directly activated by cAMP (Epac). However, the precise role and importance of cAMP in mediating GLP1R`s anti-inflammatory actions, at least in the heart, remains to be determined. To this end, we tested the effects of the GLP1R agonist liraglutide on lipopolysaccharide (LPS)-induced acute inflammatory injury in H9c2 cardiac cells, either in the absence of cAMP production (AC inhibition) or upon enhancement of cAMP levels via phosphodiesterase (PDE)-4 inhibition with roflumilast. Liraglutide dose-dependently inhibited LPS-induced apoptosis and increased cAMP levels in H9c2 cells, with roflumilast but also PDE8 inhibition further enhancing cAMP production by liraglutide. GLP1R-stimulated cAMP markedly suppressed the LPS-dependent induction of pro-inflammatory tumor necrosis factor (TNF)-a, interleukin (IL)-1b, and IL-6 cytokine expression, of inducible nitric oxide synthase (iNOS) expression and nuclear factor (NF)-kB activity, of matrix metalloproteinases (MMP)-2 and MMP-9 levels and activities, and of myocardial injury markers in H9c2 cardiac cells. The effects of liraglutide were mediated by the GLP1R since they were abolished by the GLP1R antagonist exendin(9-39). Importantly, AC inhibition completely abrogated liraglutide`s suppression of LPS-dependent inflammatory injury, whereas roflumilast significantly enhanced the protective effects of liraglutide against LPS-induced inflammation. Finally, PKA inhibition or Epac1/2 inhibition alone only partially blocked liraglutide`s suppression of LPS-induced inflammation in H9c2 cardiac cells, but, together, PKA and Epac1/2 inhibition fully prevented liraglutide from reducing LPS-dependent inflammation. cAMP, via activation of both PKA and Epac, is essential for GLP1R`s anti-inflammatory signaling in cardiac cells and that cAMP levels crucially regulate the anti-inflammatory efficacy of GLP1R agonists in the heart. Strategies that elevate cardiac cAMP levels, such as PDE4 inhibition, may potentiate the cardiovascular, including anti-inflammatory, benefits of GLP1R agonist drugs.

Inhibition of Renin Expression Is Regulated by an Epigenetic Switch From an Active to a Poised State.

Renin-expressing cells are myoendocrine cells crucial for the maintenance of homeostasis. Renin is regulated by cAMP, p300 (histone acetyltransferase p300)/CBP (CREB-binding protein), and Brd4 (bromodomain-containing protein 4) proteins and associated pathways. However, the specific regulatory changes that occur following inhibition of these pathways are not clear. We treated As4.1 cells (tumoral cells derived from mouse juxtaglomerular cells that constitutively express renin) with 3 inhibitors that target different factors required for renin transcription: H-89-dihydrochloride, PKA (protein kinase A) inhibitor; JQ1, Brd4 bromodomain inhibitor; and A-485, p300/CBP inhibitor. We performed assay for transposase-accessible chromatin with sequencing (ATAC-seq), single-cell RNA sequencing, cleavage under targets and tagmentation (CUT&Tag), and chromatin immunoprecipitation sequencing for H3K27ac (acetylation of lysine 27 of the histone H3 protein) and p300 binding on biological replicates of treated and control As4.1 cells. In response to each inhibitor, Ren1 expression was significantly reduced and reversible upon washout. Chromatin accessibility at the Ren1 locus did not markedly change but was globally reduced at distal elements. Inhibition of PKA led to significant reductions in H3K27ac and p300 binding specifically within the Ren1 super-enhancer region. Further, we identified enriched TF (transcription factor) motifs shared across each inhibitory treatment. Finally, we identified a set of 9 genes with putative roles across each of the 3 renin regulatory pathways and observed that each displayed differentially accessible chromatin, gene expression, H3K27ac, and p300 binding at their respective loci. Inhibition of renin expression in cells that constitutively synthesize and release renin is regulated by an epigenetic switch from an active to poised state associated with decreased cell-cell communication and an epithelial-mesenchymal transition. This work highlights and helps define the factors necessary for renin cells to alternate between myoendocrine and contractile phenotypes.

Phosphorylation of Insig-2 mediates inhibition of fatty acid synthesis by polyunsaturated fatty acids

Insig-1 and Insig-2 are endoplasmic reticulum (ER) proteins that inhibit lipid synthesis by blocking transport of sterol regulatory element-binding proteins (SREBP-1 and SREBP-2) from ER to Golgi. In the Golgi, SREBPs are processed proteolytically to release their transcription-activating domains, which enhance the synthesis of fatty acids, triglycerides, and cholesterol. Heretofore, the two Insigs have redundant functions, and there is no rationale for two isoforms. The current data identify a specific function for Insig-2. We show that eicosapentaenoic acid (EPA), a polyunsaturated fatty acid, inhibits fatty acid synthesis in human fibroblasts and rat hepatocytes by activating adenylate cyclase, which induces protein kinase A (PKA) to phosphorylate serine-106 in Insig-2. Phosphorylated Insig-2 inhibits the proteolytic processing of SREBP-1, thereby blocking fatty acid synthesis. Phosphorylated Insig-2 does not block the processing of SREBP-2, which activates cholesterol synthesis. Insig-1 lacks serine-106 and is not phosphorylated at this site. EPA inhibition of SREBP-1 processing was reduced by the replacement of serine-106 in Insig-2 with alanine or by treatment with KT5720, a PKA inhibitor. Inhibition did not occur in mutant human fibroblasts that possess Insig-1 but lack Insig-2. These data provide an Insig-2-specific mechanism for the long-known inhibition of fatty acid synthesis by polyunsaturated fatty acids.

Purinergic agonists increase [Ca2+]i in rat conjunctival goblet cells through ryanodine receptor type 3.

ATP and benzoylbenzoyl-ATP (BzATP) increase free cytosolic Ca2+ concentration ([Ca2+]i) in conjunctival goblet cells (CGCs) resulting in mucin secretion. The purpose of this study was to investigate the source of the Ca2+i mobilized by ATP and BzATP. First-passage cultured rat CGCs were incubated with Fura-2/AM, and [Ca2+]i was measured under several conditions with ATP and BzATP stimulation. The following conditions were used: 1) preincubation with the Ca2+ chelator EGTA, 2) preincubation with the SERCA inhibitor thapsigargin (10-6 M), which depletes ER Ca2+ stores, 3) preincubation with phospholipase C (PLC) or protein kinase A (PKA) inhibitor, or 4) preincubation with the voltage-gated calcium channel antagonist nifedipine (10-5 M) and the ryanodine receptor (RyR) antagonist dantrolene (10-5 M). Immunofluorescence microscopy (IF) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to investigate RyR presence in rat and human CGCs. ATP-stimulated peak [Ca2+]i was significantly lower after chelating Ca2+i with 2 mM EGTA in Ca2+-free buffer. The peak [Ca2+]i increase in CGCs preincubated with thapsigargin, the PKA inhibitor H89, nifedipine, and dantrolene, but not the PLC inhibitor, was reduced for ATP at 10-5 M and BzATP at 10-4 M. Incubating CGCs with dantrolene alone decreased [Ca2+]i and induced CGC cell death at a high concentration. RyR3 was detected in rat and human CGCs with IF and RT-qPCR. We conclude that ATP- and BzATP-induced Ca2+i increases originate from the ER and that RyR3 may be an essential regulator of CGC [Ca2+]i. This study contributes to the understanding of diseases arising from defective Ca2+ signaling in nonexcitable cells.NEW & NOTEWORTHY ATP and benzoylbenzoyl-ATP (BzATP) induce mucin secretion through an increase in free cytosolic calcium concentration ([Ca2+]i) in conjunctival goblet cells (CGCs). The mechanisms through which ATP and BzATP increase [Ca2+]i in CGCs are unclear. Ryanodine receptors (RyRs) are fundamental in [Ca2+]i regulation in excitable cells. Herein, we find that ATP and BzATP increase [Ca2+]i through the activation of protein kinase A, voltage-gated calcium channels, and RyRs, and that RyRs are crucial for nonexcitable CGCs' Ca2+i homeostasis.

Abstract Mo070: Metabolic Syndrome Alters cAMP Homeostasis and Contractile Function of Cardiomyocytes

Approximately one third of the population in the US has metabolic syndrome (MetS), a condition associated with increased risk for coronary artery disease and myocardial infarction. But whether MetS alters properties of the myocardium before the occurrence of ischemic insults remains to be fully elucidated. For this purpose, MetS was induced in C57Bl/6 female mice with a dietary paradigm recapitulating Western-style alimentary habits in humans. Animals on regular chow were used as control (Ctrl). Cardiac function was assessed by echocardiography and myocytes were studied under field stimulation, following enzymatic dissociation. From 3-12 months on the diet, MetS mice had increased body weight, impaired glucose metabolism, augmented left ventricular (LV) mass, but preserved cardiac function, with respect to Ctrl mice. Using ECGs, heart rate variability was attenuated in MetS mice, suggesting that metabolic disorders alter cardiac sympathovagal balance. At the cellular level, LV myocytes from MetS mice had increased volume (+24%), enhanced fractional cell shortening (+42%), and faster kinetics of relaxation (-27%), with respect to Ctrl myocytes. Because cAMP and protein Kinase A (PKA) modulates myocardial contractility upon activation of G-protein coupled receptors, including beta-adrenergic receptors (B-AR), levels of these molecules were assessed by ELISA assay. Consistent with enhanced cell shortening and faster relaxation, levels of cAMP and PKA activity were, respectively, 1.8-fold and 1.9-fold larger in MetS myocytes, in comparison to Ctrl cells. Interestingly, inhibition of PKA with H-89 reduced cell shortening (-30%) and delayed kinetics of relaxation (+50%) in MetS myocytes but had no major effects on Ctrl cells. To establish the contribution of the cAMP/PKA signaling in the functional behavior of the heart with MetS, mice were treated with the B-AR blocker propranolol. Under this condition, MetS mice had reduced ejection fraction and impaired indices of diastolic function, with respect to Ctrl animals. Interestingly, myocytes obtained from Ctrl and MetS mice treated with the B-AR blocker had comparable cell shortening and kinetics of relaxation. Collectively, these results indicate that metabolic syndrome alters the functional properties of the myocytes and heart by affecting cAMP homeostasis. These properties may increase myocardial oxygen demand predisposing the heart to ischemic insults.

Deciphering the role of protein kinase A in the control of FoxP3 expression in regulatory T cells in health and autoimmunity

The molecular mechanisms that govern differential T cell development from CD4+CD25-conventional T (Tconv) into CD4+CD25+ forkhead-box-P3+ (FoxP3+) inducible regulatory T (iTreg) cells remain unclear. Herein, we investigated the relative contribution of protein kinase A (PKA) in this process. Mechanistically, we found that PKA controlled the efficiency of human iTreg cell generation through the expression of different FoxP3 splicing variants containing or not the exon 2. We found that transient PKA inhibition reduced the recruitment of cAMP-responsive element-binding protein (CREB) on regulatory regions of the FoxP3 gene, a condition that is associated with an impaired acquisition of their suppressive capacity in vitro. To corroborate our findings in a human model of autoimmunity, we measured CREB phosphorylation and FoxP3 levels in iTreg cells from treatment-naïve relapsing–remitting (RR)-multiple sclerosis (MS) subjects. Interestingly, both phospho-CREB and FoxP3 induction directly correlated and were significantly reduced in RR-MS patients, suggesting a previously unknown mechanism involved in the induction and function of human iTreg cells.

Nonylphenol releases arachidonic acid in rat Sertoli cells via activation of PKA and PLA2.

The endocrine disruptor, nonylphenol (NP) increases 20:4n-6 release in Sertoli cells via PKA/cPLA2 activation. Our data show that lipid metabolism could be a target of NP-induced abnormal reproductive outcomes. Nonylphenol (NP), an endocrine-disrupting chemical, is an environmental contaminant, and many notorious effects on male fertility have been reported in animal models and wild-type species. Here, we evaluated the effects of NP in follicle-stimulating hormone (FSH) signal transduction pathways and lipid metabolism using an in vitro model of rat Sertoli cell (SC) primary culture. Results show that an acute (1 h) SC exposure to NP (10 µM) increased the intra- and extra-cellular concentrations of free fatty acids (FFAs), mainly arachidonic acid (20:4n-6). Phosphatidylinositol seemed to be the major phospholipid source of this 20:4n-6 release by activation of the protein kinase A (PKA)/cytoplasmic phospholipase A2 (cPLA2) pathway. NP also increased diacylglycerols (DAG) levels and the expression (mRNA) of cyclooxygenase 2 (Cox2) and prostaglandin E2 (PGE2) levels. It is noteworthy that accumulation of lipid droplets took place after 24 h NP exposition, which was prevented by both a PKA inhibitor and a PLA2 inhibitor. Like FSH, NP triggers the release of 20:4n-6, which is a substrate for PGE2 synthesis via PKA/PLA2 activation. In addition, NP induces the formation of DAG, which could be required as a cofactor of the PKC-mediated activation of the COX2 inflammatory pathway. Our findings suggest that NP alters lipid homeostasis in SCs by inducing the activation of pro-inflammatory pathways that may trigger adverse effects in testis physiology over time. Concomitantly, the SC enhances the acylation of surplus FFAs (including 20:4n-6) in neutral lipids as a protective mechanism to shield itself from lipotoxicity and pro-inflammatory signals.

The PDE4 inhibitor apremilast modulates ethanol responses in Gabrb1-S409A knock-in mice via PKA-dependent and independent mechanisms

We previously showed that the PDE4 inhibitor apremilast reduces ethanol consumption in mice by protein kinase A (PKA) and GABAergic mechanisms. Preventing PKA phosphorylation of GABAA β3 subunits partially blocked apremilast-mediated decreases in drinking. Here, we produced Gabrb1-S409A mice to render GABAA β1 subunits resistant to PKA-mediated phosphorylation. Mass spectrometry confirmed the presence of the S409A mutation and lack of changes in β1 subunit expression or phosphorylation at other residues. β1-S409A male and female mice did not differ from wild-type C57BL/6J mice in expression of Gabrb1, Gabrb2, or Gabrb3 subunits or in behavioral characteristics. Apremilast prolonged recovery from ethanol ataxia to a greater extent in Gabrb1-S409A mice but prolonged recovery from zolpidem and propofol to a similar extent in both genotypes. Apremilast shortened recovery from diazepam ataxia in wild-type but prolonged recovery in Gabrb1-S409A mice. In wild-type mice, the PKA inhibitor H89 prevented apremilast modulation of ataxia by ethanol and diazepam, but not by zolpidem. In Gabrb1-S409A mice, inhibiting PKA or EPAC2 (exchange protein directly activated by cAMP) partially reversed apremilast potentiation of ethanol, diazepam, and zolpidem ataxia. Apremilast prevented acute tolerance to ethanol ataxia in both genotypes, but there were no genotype differences in ethanol consumption before or after apremilast. In contrast to results in Gabrb3-S408A/S409A mice, PKA phosphorylation of β1-containing GABAA receptors is not required for apremilast's effects on acute tolerance or on ethanol consumption but is required for its ability to decrease diazepam intoxication. Besides PKA we identified EPAC2 as an additional cAMP-dependent mechanism by which apremilast regulates responses to GABAergic drugs.

PGE2-PKA Control of Mitochondrial Membrane Potential Dictates Macrophages Proliferation and Efferocytic Function During Lung Injury

In the lungs, phenotypically different alveolar macrophages (AMs) co-exist with interstitial monocyte-derived macrophages (Mo-Macs) to regulate lung homeostasis. We have shown that airspace-recruited Mo-Macs resolve inflammation, restoring lung-fluid homeostasis. Analyzing publicly available datasets (Immgen Consortium), we found that compared to Mo-Macs, AMs are also enriched with pathways regulating mitochondria function, but their significance remain elusive. During development, AMs are generated by differentiation of lung-recruited fetal liver monocytes by granulocyte macrophage-colony stimulating factor (GM-CSF). In contrast, Mo-Macs require macrophage colony-stimulating factor (M-CSF) to differentiate from monocytes. Here, we mimic the developmental program of AM versus Mo-Macs by differentiating bone marrow monocytes towards AM-like cells (G-BMDM) or Mo-Mac-like cells (M-BMDM) to understand the role of mitochondrial activity in regulating macrophage functions. We confirmed that G-BMDMs highly express canonical AM-like genes on the cell surface, such as Itgax, Siglecf, Chil3, Ear2, Egr2, and Car4. M-BMDM mimics Mo-Macs as they show higher C1q, Mmp9, Folr2, and Cx3cr1 expression. G-BMDM and M-BMDM showed similar mitochondrial mass. However, G-BMDM showed higher mitochondrial membrane potential (ΔΨm) than M-BMDM, which was associated with compromised efferocytic capacity. These findings were recapitulated in vivo at homeostasis where ΔΨm was higher in AM than Mo-Macs or monocytes. AM compared to other tissue resident macrophages expresses very low level of Ptgs1 &amp; 2 the rete limiting enzymes for PGE2 production. Prostaglandin E2 (PGE2) is a potent lipid mediator and modulator of immune cell function and activates protein kinase A (PKA) through generating cAMP. We, therefore, assessed if PGE2 was a factor in diversifying ΔΨm between G-BMDM and M-BMDM. Using the COX2 sensor (COXFLuor), we found that M-BMDM generated more PGE2 than G-BMDM. PGE2 reduced ΔΨm in G-BMDM to the level of M-BMDM. However, this response was not seen in G-BMDM upon inhibiting EP2 receptor (TG4-155; 10μm) or PKA (H89; 5μm), indicating PGE2 functioned by ligating its receptor and elevating PKA activity. During infection or injury many cell types upregulate Ptgs2 expression and activity to produce local PGE2. Further studies showed that during endotoxin induced acute lung injury, Mo-Macs have high COX2 activity and are the major source of PGE2 in the alveolar milieu to promote AM proliferation and efferocytic function, and help resolve edema. However, inhibition of PKA (H89; 1mg/Kg, i.t), impaired AM proliferation and efferocytosis, leading to unresolved injury. These findings indicate that the PGE2-PKA axis stabilizes mitochondrial function in Mo-Macs to maintain the AM-proliferative-efferocytotic niche for resolving edema. This study is funded by NIH grant 5R01-HL155941-03 and P01 HL151327-03. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Epidermal Growth Factor Reduces Collecting Duct Water Permeability by Inhibiting Aquaporin-2 Phosphorylation at Ser269

Prior studies showed that epidermal growth factor (EGF) inhibits vasopressin-stimulated osmotic water permeability in the renal collecting duct. Here, we investigated the underlying mechanism of this response. Using the Burg isolated perfused tubule technique in microdissected rat inner medullary collecting ducts (IMCDs), we found that addition of 0.1 μM EGF to the peritubular bath significantly decreased 0.1 nM 1‐deamino‐8‐D‐arginine vasopressin (dDAVP)-stimulated water permeability, confirming prior observations. The inhibitory effect of EGF on dDAVP-stimulated water permeability was associated with a reduction in intracellular cyclic AMP levels and protein kinase A (PKA) activity. Using phospho-specific antibodies and immunoblotting in IMCD suspensions, we showed that EGF significantly reduces dDAVP-stimulated aquaporin-2 (AQP2) phosphorylation at S264 and S269. This effect was absent when membrane-permeable 8-cpt-cAMP (0.1 mM) was used to stimulate AQP2 phosphorylation, suggesting that EGF’s effect was on a pre-cAMP step. Immunofluorescence labeling of microdissected IMCDs showed that EGF significantly reduced apical AQP2 abundance in the presence of dDAVP. To address what protein kinase might be responsible for S269 phosphorylation, we used Bayesian analysis to integrate multiple -omic datasets. Thirteen top ranked protein kinases were subsequently tested by in vitro phosphorylation experiments for their ability to phosphorylate AQP2 peptides using a mass spectrometry readout. The results show that the PKA catalytic-α subunit increased phosphorylation at S256, S264, and S269. None of the other kinases phosphorylated S269. Additionally, PKA inhibitors, H-89 and PKI, strongly inhibited dDAVP-stimulated AQP2 phosphorylation at S269. These results indicate that EGF decreases the water permeability of the collecting duct by inhibiting cAMP production, thereby inhibiting PKA and decreasing AQP2 phosphorylation at S269, a site previously shown to regulate AQP2 endocytosis. This work was funded by NHLBI project ZIA-HL001285 and ZIA-HL006129, M.A.K. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

PKIB, a Novel Target for Cancer Therapy.

The serine-threonine kinase protein kinase A (PKA) is a cyclic AMP (cAMP)-dependent intracellular protein with multiple roles in cellular biology including metabolic and transcription regulation functions. The cAMP-dependent protein kinase inhibitor β (PKIB) is one of three known endogenous protein kinase inhibitors of PKA. The role of PKIB is not yet fully understood. Hormonal signaling is correlated with increased PKIB expression through genetic regulation, and increasing PKIB expression is associated with decreased cancer patient prognosis. Additionally, PKIB impacts cancer cell behavior through two mechanisms; the first is the nuclear modulation of transcriptional activation and the second is the regulation of oncogenic AKT signaling. The limited research into PKIB indicates the oncogenic potential of PKIB in various cancers. However, some studies suggest a role of PKIB in non-cancerous disease states. This review aims to summarize the current literature and background of PKIB regarding cancer and related issues. In particular, we will focus on cancer development and therapeutic possibilities, which are of paramount interest in PKIB oncology research.

Abstract LB009: Unveiling the significance of DARPP-32 and its partners, including GRB7 and DKK1, in breast cancer: Integrative insights from patient data and cell line transcriptomics

Abstract DARPP-32 plays a crucial role in regulating both protein-phosphatase-1 (PP-1) and protein kinase A (PKA), its function being reliant on its phosphorylation status. We have previously demonstrated that low DARPP-32 expression is associated with adverse survival of breast cancer patients, particularly those with oestrogen receptor (ER) positive disease; however, there is limited information on how DARPP-32 may alter breast cancer cell behaviour. We have recently published an integrative approach using patient data and cell line transcriptomics to understand the role of DARPP-32 in breast cancer. We analysed the transcriptome of T47D ER positive breast cancer cells following DARPP-32 knockdown, including treatments in combination with 17β-estradiol or PKA inhibitor fragment (6-22) amide. 202 differentially expressed transcripts were identified in DARPP-32 knock down cells and treatment of these cells with 17β-estradiol or PKA inhibitor fragment (6-22) amide led to the differential expression of 193 and 181 transcripts respectively. Differentially expressed transcripts were compared with genes identified as associated with DARPP-32 expression in 1980 breast cancer patients within the METABRIC cohort using an Artificial Neural Network approach (ANN). Several genes overlapped with those identified from cell line transcriptomics, including PTK7, TRAF5, and KLK6. Both DKK1 and GRB7 were identified as genes associated with DARPP-32 expression in patients using ANN, therefore protein expression was determined in a large cohort of early-stage breast cancer patients (n&amp;gt;1000). We demonstrated that DKK1 and GRB7 protein expression was significantly correlated with DARPP-32 Threonine-34 phosphorylation levels within the same samples (all P&amp;lt;0.05). We have now applied an ANN-based integrative data mining approach to identify genes with the largest effect on other genes resulting in an interactome map, which was based on genes identified within the cell line transcriptomics and original ANN. 1878 genes were identified for inclusion within an interactome map in the total patient cohort, whereas 1003 were identified in ER negative disease alone and 2144 in ER positive disease alone. Pathway enrichment analysis identified the ubiquitin proteosome pathway, the insulin pathway-protein kinase B signalling cascade and the RAS pathway. This study underscores the significance of DARPP-32, a central molecular switch, in breast cancer, elucidating its impact on patient prognosis and highlighting potential molecular targets for therapeutic intervention. The integrative approach combining patient data with cell line transcriptomics provides insights into the complex mechanisms underlying breast cancer progression and opens avenues for further research and targeted interventions. Citation Format: Behnaz Saidy, Richa Vasan, Megan-Rose Greener, Rosie Durrant, Adelynn Immanuel, Andrew Green, Emad Rakha, Ian Ellis, Graham Ball, Stewart Martin, Sarah J. Storr. Unveiling the significance of DARPP-32 and its partners, including GRB7 and DKK1, in breast cancer: Integrative insights from patient data and cell line transcriptomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB009.

Ghrelin enhances tubular magnesium absorption in the kidney.

Osteoporosis after bariatric surgery is an increasing health concern as the rate of bariatric surgery has risen. In animal studies mimicking bariatric procedures, bone disease, together with decreased serum levels of Ca2+, Mg2+ and the gastric hormone Ghrelin were described. Ghrelin regulates metabolism by binding to and activating the growth hormone secretagogue receptor (GHSR) which is also expressed in the kidney. As calcium and magnesium are key components of bone, we tested the hypothesis that Ghrelin-deficiency contributes to osteoporosis via reduced upregulation of the renal calcium channel TRPV5 and the heteromeric magnesium channel TRPM6/7. We expressed GHSR with TRPV5 or TRPM6/7 channel in HEK293 cells and treated them with purified Ghrelin. Whole-cell current density was analyzed by patch-clamp recording. Nephron-specific gene expression was performed by tubular microdissection followed by qPCR in wild-type (WT) mice, and immunofluorescent imaging of GHSR-eGFP mice. Tubular magnesium homeostasis was analyzed in GHSR-null and WT mice at baseline and after caloric restriction. After Ghrelin exposure, whole-cell current density did not change for TRPV5 but increased for TRPM6/7 in a dose-dependent fashion. Applying the Ghrelin-mimetic (D-Trp7, Ala8,D-Phe10)-α-MSH (6-11) amide without and with the GHSR antagonist (D-Lys3)-GHRP6, we confirmed the stimulatory role of Ghrelin towards TRPM6/7. As GHSR initiates downstream signaling via protein kinase A (PKA), we found that the PKA inhibitor H89 abrogated TRPM6/7 stimulation by Ghrelin. Similarly, transfected Gαs, but not the Gαs mutant Q227L, nor Gαi2, Gαq, or Gα13 upregulated TRPM6/7 current density. In microdissected TALs and DCTs similar levels of GHSR mRNA were detected. In contrast, TRPM6 mRNA was expressed in the DCT and also detected in the TAL at 25% expression compared to DCT. Immunofluorescent studies using reporter GHSR-eGFP mice showed a strong eGFP signal in the TAL but surprisingly displayed no eGFP signal in the DCT. In 3-, 6-, and 9-month-old GHSR-null and WT mice, baseline serum magnesium was not significantly different, but 24-h urinary magnesium excretion was elevated in 9-month-old GHSR-null mice. In calorically restricted GHSR-null mice, we detected excess urinary magnesium excretion and reduced serum magnesium levels compared to WT mice. The kidneys from calorically restricted WT mice showed upregulated gene expression of magnesiotropic genes Hnf1b, Cldn-16, Cldn-19, Fxyd-2b, and Parvalbumin compared to GHSR-null mice. Our in vitro studies show that Ghrelin stimulates TRPM6/7 via GHSR and Gαs-PKA signaling. The murine studies are consistent with Ghrelin-GHSR signaling inducing reduced urinary magnesium excretion, particularly in calorically restricted mice when Ghrelin levels are elevated. This effect may be mediated by Ghrelin-upregulation of TRPM6 in the TAL and/or upregulation of other magnesiotropic genes. We postulate that rising Ghrelin levels with hunger contribute to increased renal Mg2+ reabsorption to compensate for lack of enteral Mg2+ uptake.

Abstract 3064: Unmasking the deadly tango: PKA and lipid genes in prostate cancer's bone invasion

Abstract About 88% of metastatic prostate cancer (PCa) cases involve bone metastasis. When PCa cells spread to the bone, a metabolic adaptation to the new environment takes place, partly influenced by factors secreted by the homing organ. Thus, we hypothesize that metabolic reprogramming, both in the tumor and bone niche drive PCa bone metastasis. In this work, we carried out an integrative in vitro, in vivo, and bioinformatics approach to identify key regulators governing the metabolic behavior of PCa cells. We performed an indirect co-culture between PCa (PC3) and bone progenitor (MC3T3 or Raw264.7) cells. PCa cells displayed a strong transcriptional (RNA-seq) activation of lipid metabolism, including PPAR-signaling, fat digestion, and PI3K-Akt pathway. Accordingly, treatment with the conditioned media (CM) of the co-culture promoted lipid accumulation in PC3 cells (Bodipy 493/503 staining). To assess the clinical relevance of the in vitro model, we performed an unsupervised clustering analysis using transcriptomics data from human PCa and bone metastatic samples (GSE74685). Results showed that the metabolic genes deregulated in PC3 by the co-culture, could accurately cluster samples in primary tumor or bone metastasis. We next performed a multivariable Cox regression analysis and built a prognostic model, identifying a novel signature of 5 lipid-associated genes, PPARA, VDR, SLC16A1, PAPSS2 and GPX1, associated with a 23-fold higher risk of death in PCa patients (SU2C-PCF dataset). The expression of this signature was validated in a PDX pre-clinical model (MDA PCa PDX series) when comparing MDA-PCa-183 growing intrafemorally vs. subcutaneously. In order to identify the central hubs regulating this transcriptional phenotype, we performed an Ingenuity Pathway Analysis (QIAGEN), showcasing that the lipid-related signature deregulated by the bone niche is indeed modulated by the Protein Kinase A (PKA). Accordingly, the expression of these signature was downregulated by PKA inhibition (H89; PKA inhibitor). Moreover, secretome analyses (ESI MS/MS) revealed that bone secreted type I collagen (Col1a1) and fibronectin (Fn1) regulate PKA activity in PCa cells. Further, we investigated whether PKA could modulate critical mechanisms for bone progression, focusing on osteopontin (SPP1), a secreted protein involved in the adhesion and invasion of PCa cells, whose regulatory mechanism in tumor cells is yet to be elucidated. Strikingly, we observed not only that the activation of PKA using Forskolin in PCa cells activated SPP1 expression, but also that PKA inhibition led to a significant impairment of the SPP1 induction triggered by bone soluble factors secreted during the PC3/MC3T3 co-culture. Altogether, we showcase PKA as a central hub of PCa energetic metabolism during bone progression and outline a lipid-associated gene signature that can be targeted to halt metastatic PCa. Citation Format: Pablo Sanchis, Nicolas Anselmino, Estefania Labanca, Agustina Sabater, Juan Bizzotto, Gaston Pascual, Rocio Seniuk, Sofia Lage-Vickers, Antonina Mitrofanova, Pia Valacco, Ayelen Toro, Javier Cotignola, Nora Navone, Elba Vazquez, Geraldine Gueron. Unmasking the deadly tango: PKA and lipid genes in prostate cancer's bone invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3064.

Attenuation of propofol-induced hippocampal neuron damage in developing rats by dexmedetomidine

This study explored the mechanism of dexmedetomidine attenuating propofol damage to hippocampal neurons in rats. By constructing rat hippocampal neuron model and carrying out targeted intervention; enzyme linked immunosorbent assay (ELISA) detected IL-1β and IL-18 levels; while Nissl staining observed hippocampus Histopathology; flow cytometry quantitatively analyzed the number of hippocampal neuron cells and apoptosis rate. Moreover, levels of PKA, Caspase-1 and NOD-like receptor thermal protein domain associated protein 3(NLRP3) and corresponding proteins were measured. Results showed that, there were more Nissl bodies in cytoplasm of hippocampal neurons in control group, and distribution in the cytoplasm was relatively uniform. Moreover, IL-1β and IL-18 in model group continued to increase; while dexmedetomidine effectively inhibited apoptosis of hippocampal neurons, which may be related to decreased expression of protein kinase A (PKA). After using PKA inhibitors, apoptosis was significantly inhibited, and when the expression of PKA was reduced, Caspase-1 was down-regulated along with reduced NLRP3 level, which improved the injury of hippocampal neurons. Dexmedetomidine can therefore down-regulate the level of Caspase-1 in hippocampal neurons by inhibiting the PKA signaling pathway, improving apoptosis, reducing the genetic and protein expressions of NLRP3, and slowing down the damage of hippocampal neurons.

Role of M4 -receptor cholinergic signaling in direct pathway striatal projection neurons during dopamine depletion.

Direct pathway striatal projection neurons (dSPNs) are characterized by the expression of dopamine (DA) class 1 receptors (D1 R), as well as cholinergic muscarinic M1 and M4 receptors (M1 R, M4 R). D1 R enhances neuronal firing through phosphorylation of voltage-gate calcium channels (CaV 1 Ca2+ channels) activating Gs proteins and protein kinase A (PKA). Concurrently, PKA suppresses phosphatase PP-1 through DARPP-32, thus extending this facilitatory modulation. M1 R also influences Ca2+ channels in SPNs through Gq proteins and protein kinase C. However, the signaling mechanisms of M4 R in dSPNs are less understood. Two pathways are attributed to M4 R: an inhibitory one through Gi/o proteins, and a facilitatory one via the cyclin Cdk5. Our study reveals that a previously observed facilitatory modulation via CaV 1 Ca2+ channels is linked to the Cdk5 pathway in dSPNs. This result could be significant in treating parkinsonism. Therefore, we questioned whether this effect persists post DA-depletion in experimental parkinsonism. Our findings indicate that in such conditions, M4 R activation leads to a decrease in Ca2+ current and an increased M4 R protein level, contrasting with the control response. Nevertheless, parkinsonian and control actions are inhibited by the Cdk5 inhibitor roscovitine, suggesting Cdk5's role in both conditions. Cdk5 may activate PP-1 via PKA inhibition in DA depletion. Indeed, we found that inhibiting PP-1 restores control M4 R actions, implying that PP-1 is overly active via M4 Rs in DA-depleted condition. These insights contribute to understanding how DA-depletion alters modulatory signaling in striatal neurons. Additional working hypotheses are discussed.

Protein Kinase A Is a Master Regulator of Physiological and Pathological Cardiac Hypertrophy.

The sympathoadrenergic system and its major effector PKA (protein kinase A) are activated to maintain cardiac output coping with physiological or pathological stressors. If and how PKA plays a role in physiological cardiac hypertrophy (PhCH) and pathological CH (PaCH) are not clear. Transgenic mouse models expressing the PKA inhibition domain (PKAi) of PKA inhibition peptide alpha (PKIalpha)-green fluorescence protein (GFP) fusion protein (PKAi-GFP) in a cardiac-specific and inducible manner (cPKAi) were used to determine the roles of PKA in physiological CH during postnatal growth or induced by swimming, and in PaCH induced by transaortic constriction (TAC) or augmented Ca2+ influx. Kinase profiling was used to determine cPKAi specificity. Echocardiography was used to determine cardiac morphology and function. Western blotting and immunostaining were used to measure protein abundance and phosphorylation. Protein synthesis was assessed by puromycin incorporation and protein degradation by measuring protein ubiquitination and proteasome activity. Neonatal rat cardiomyocytes (NRCMs) infected with AdGFP (GFP adenovirus) or AdPKAi-GFP (PKAi-GFP adenovirus) were used to determine the effects and mechanisms of cPKAi on myocyte hypertrophy. rAAV9.PKAi-GFP was used to treat TAC mice. (1) cPKAi delayed postnatal cardiac growth and blunted exercise-induced PhCH; (2) PKA was activated in hearts after TAC due to activated sympathoadrenergic system, the loss of endogenous PKIα (PKA inhibition peptide α), and the stimulation by noncanonical PKA activators; (3) cPKAi ameliorated PaCH induced by TAC and increased Ca2+ influxes and blunted neonatal rat cardiomyocyte hypertrophy by isoproterenol and phenylephrine; (4) cPKAi prevented TAC-induced protein synthesis by inhibiting mTOR (mammalian target of rapamycin) signaling through reducing Akt (protein kinase B) activity, but enhancing inhibitory GSK-3α (glycogen synthase kinase-3α) and GSK-3β signals; (5) cPKAi reduced protein degradation by the ubiquitin-proteasome system via decreasing RPN6 phosphorylation; (6) cPKAi increased the expression of antihypertrophic atrial natriuretic peptide (ANP); (7) cPKAi ameliorated established PaCH and improved animal survival. Cardiomyocyte PKA is a master regulator of PhCH and PaCH through regulating protein synthesis and degradation. cPKAi can be a novel approach to treat PaCH.