PRKACA: the catalytic subunit of protein kinase A and adrenocortical tumors

Overexpression of olfactory receptor 78 ameliorates brain injury in cerebral ischaemia-reperfusion rats by activating Prkaca-mediated cAMP/PKA-MAPK pathway

Ischemic stroke is one of the main causes of disability and death. However, recanalization of occluded cerebral arteries is effective only within a very narrow time window. Therefore, it is particularly important to find neuroprotective biological targets for cerebral artery recanalization. Here, gene expression profiles of datasets GSE160500 and GSE97537 were downloaded from the GEO database, which were related to ischemic stroke in rats. Olfactory receptor 78 (Olfr78) was screened, and which highly associated with Calcium signalling pathway and MAPK pathway. Interacting protein of Olfr78, Prkaca, was predicted by STRING, and their interaction was validated by Co-IP analysis. Then, a rat model of middle cerebral artery occlusion/reperfusion (MCAO/R) and a neuronal cell model stimulated by oxygen-glucose deprivation/reoxygenation (OGD/R) were constructed, and the results showed that expression of Olfr78 and Prkaca was downregulated in MCAO rats and OGD/R-stimulated neurons. Overexpression of Olfr78 or Prkaca inhibited the secretion of inflammatory factors, Ca2+ overload, and OGD/R-induced neuronal apoptosis. Moreover, Overexpression of Prkaca increased protein levels of cAMP, PKA and phosphorylated p38 in OGD/R-stimulated neurons, while SB203580, a p38 inhibitor, treatment inhibited activation of the cAMP/PKA-MAPK pathway and counteracted the effect of Olfr78 overexpression on improvement of neuronal functions. Meanwhile, overexpression of Olfr78 or Prkaca markedly inhibited neuronal apoptosis and improved brain injury in MCAO/R rats. In conclusion, overexpression of Olfr78 inhibited Ca2+ overload and reduced neuronal apoptosis in MCAO/R rats by promoting Prkaca-mediated activation of the cAMP/PKA-MAPK pathway, thereby improving brain injury in cerebral ischaemia-reperfusion.

Comparative proteomic analysis of three major extracellular vesicle classes secreted from human primary and metastatic colorectal cancer cells: Exosomes, microparticles, and shed midbody remnants

Cell-derived extracellular vesicles (EVs) are evolutionary-conserved secretory organelles that, based on their molecular composition, are important intercellular signaling regulators. At least three classes of circulating EVs are known based on mechanism of biogenesis: exosomes (sEVs/Exos), microparticles (lEVs/MPs), and shed midbody remnants (lEVs/sMB-Rs). sEVs/Exos are of endosomal pathway origin, microparticles (lEVs/MPs) from plasma membrane blebbing and shed midbody remnants (lEVs/sMB-Rs) arise from symmetric cytokinetic abscission. Here, we isolate sEVs/Exos, lEVs/MPs, and lEVs/sMB-Rs secreted from human isogenic primary (SW480) and metastatic (SW620) colorectal cancer (CRC) cell lines in milligram quantities for label-free MS/MS-based proteomic profiling. Purified EVs revealed selective composition packaging of exosomal protein markers in SW480/SW620-sEVs/Exos, metabolic enzymes in SW480/SW620-lEVs/MPs, while centralspindlin complex proteins, nucleoproteins, splicing factors, RNA granule proteins, translation-initiation factors, and mitochondrial proteins selectively traffic to SW480/SW620- lEVs/sMB-Rs. Collectively, we identify 39 human cancer-associated genes in EVs; 17 associated with SW480-EVs, 22 with SW620-EVs. We highlight oncogenic receptors/transporters selectively enriched in sEVs/Exos (EGFR/FAS in SW480-sEVs/Exos and MET, TGFBR2, ABCB1 in SW620-sEVs/Exos). Interestingly, MDK, STAT1, and TGM2 are selectively enriched in SW480-lEVs/sMB-Rs, and ADAM15 to SW620-lEVs/sMB-Rs. Our study reveals sEVs/Exos, lEVs/MPs, and lEVs/sMB-Rs have distinct protein signatures that open potential diagnostic avenues of distinct types of EVs for clinical utility.

Downregulated RBM5 Enhances CARM1 Expression and Activates the PRKACA/GSK3β Signaling Pathway through Alternative Splicing-Coupled Nonsense-Mediated Decay

Downregulated RNA-binding motif protein 5 (RBM5) promotes the development and progression of various tumors, including bladder cancer (BC). Alternative splicing (AS) plays a crucial role in the progression of cancer by producing protein isomers with different functions or by promoting nonsense-mediated mRNA decay (NMD). However, whether RBM5 modulates the progression of BC through AS-NMD remains unexplored. In this study, we revealed that the downregulation of RBM5 expression promoted the expression of coactivator-associated arginine methyltransferase 1 (CARM1) in BC cells and tissues. Increased expression of CARM1 facilitated the activation of the Wnt/β-catenin axis and cell proliferation, which then contributed to the poor prognosis of patients with BC. Interestingly, RBM5 bound directly to CARM1 mRNA and participated in AS-NMD, downregulating the expression of CARM1. In addition, we revealed that protein kinase catalytic subunit alpha (PRKACA) functioned as a phosphorylated kinase of GSK3β, was regulated by CARM1 at the transcription level, and promoted the growth and progression of BC cells. Furthermore, in this study, we demonstrated a regulatory mechanism of Wnt/β-catenin activation through the RBM5/CARM1/PRKACA axis and identified a novel potential target for treating BC.

Fatty acid desaturase 2 determines the lipidomic landscape and steroidogenic function of the adrenal gland

Corticosteroids regulate vital processes, including stress responses, systemic metabolism, and blood pressure. Here, we show that corticosteroid synthesis is related to the polyunsaturated fatty acid (PUFA) content of mitochondrial phospholipids in adrenocortical cells. Inhibition of the rate-limiting enzyme of PUFA synthesis, fatty acid desaturase 2 (FADS2), leads to perturbations in the mitochondrial lipidome and diminishes steroidogenesis. Consistently, the adrenocortical mitochondria of Fads2-/- mice fed a diet with low PUFA concentration are structurally impaired and corticoid levels are decreased. On the contrary, FADS2 expression is elevated in the adrenal cortex of obese mice, and plasma corticosterone is increased, which can be counteracted by dietary supplementation with the FADS2 inhibitor SC-26192 or icosapent ethyl, an eicosapentaenoic acid ethyl ester. In humans, FADS2 expression is elevated in aldosterone-producing adenomas compared to non-active adenomas or nontumorous adrenocortical tissue and correlates with expression of steroidogenic genes. Our data demonstrate that FADS2-mediated PUFA synthesis determines adrenocortical steroidogenesis in health and disease.

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.

Oncogenic PKA signaling increases c-MYC protein expression through multiple targetable mechanisms

Genetic alterations that activate protein kinase A (PKA) are found in many tumor types. Yet, their downstream oncogenic signaling mechanisms are poorly understood. We used global phosphoproteomics and kinase activity profiling to map conserved signaling outputs driven by a range of genetic changes that activate PKA in human cancer. Two signaling networks were identified downstream of PKA: RAS/MAPK components and an Aurora Kinase A (AURKA)/glycogen synthase kinase (GSK3) sub-network with activity toward MYC oncoproteins. Findings were validated in two PKA-dependent cancer models: a novel, patient-derived fibrolamellar carcinoma (FLC) line that expresses a DNAJ-PKAc fusion and a PKA-addicted melanoma model with a mutant type I PKA regulatory subunit. We identify PKA signals that can influence both de novo translation and stability of the proto-oncogene c-MYC. However, the primary mechanism of PKA effects on MYC in our cell models was translation and could be blocked with the eIF4A inhibitor zotatifin. This compound dramatically reduced c-MYC expression and inhibited FLC cell line growth in vitro. Thus, targeting PKA effects on translation is a potential treatment strategy for FLC and other PKA-driven cancers.

The signature of pyroptosis-related gene prognostic and immune microenvironment in adrenocortical carcinoma

Adrenocortical carcinoma (ACC) has a low incidence but a poor prognosis. And ACC has complex clinical manifestations and limited treatment. Pyroptosis has a dual character and has both positive and negative effects on cancer. However, the role of pyroptosis-related genes (PRGs) in ACC and the impact on ACC progression remains unelucidated. This study performed systematic bioinformatics analysis and basic experimental validation to enable the establishment of prognostic models and demonstrate levels of immune infiltration. Pearson's correlation analysis was used to assess the association of PRGs with tumor immune infiltration, tumor mutation burden (TMB), microsatellite instability (MSI), and immune checkpoints. There 4 PRGs were upregulated, and 25 PRGs were downregulated in ACC. At the same time, we analyzed and reviewed the genetic mutation variation landscape of PRGs. Functional enrichment analysis was also performed to clarify the function of PRGs. Pyroptosis, the inflammatory response, the Toll-like receptor signaling pathway, and the NOD-like receptor signaling pathway are the functions and pathways mainly involved and exerted effects by these 33 PRGs. The results of the prognosis analysis revealed high expression of CASP3, CASP9, GSDMB, GSDMD, NLRC4, PRKACA, and SCAF11 caused a poor survival rate for ACC patients. The above seven PRGs were screened by the optimal λ value of LASSO Cox analysis, and the five selected genes (CASP3, CASP9, GSDMB, GSDMD, NLRC4) were involved in constructing a prognostic PRGs model which enables the overall survival in ACC patients can be predicted with moderate to high accuracy. Prognostic PRGs, especially CASP9, which is the independent factor of ACC prognosis, may be closely correlated with immune-cell infiltration, tumor mutation burden, microsatellite instability, and immune checkpoints. Quantitative Real-Time PCR (qRT-PCR), Western blot and immunohistochemical were performed to validate the mRNA expression levels of CASP9 in adjacent normal tissues and ACC tissues. According to the result of immune checkpoints analysis, NLRC4 and GSDMB may be identified as potential therapeutic targets. In conclusion, we established a prognostic model of PRG characteristics in ACC and analyzed the relationship between PRGs and immune infiltration. Through our study, it may be helpful to find the mechanism of pyroptosis in ACC.

Mosaic PRKACA duplication causing a novel and distinct phenotype of early-onset Cushing's syndrome and acral cutaneous mucinosis

SIGNIFICANCE STATEMENT

We describe a mosaic PRKACA duplication in a young infant who presented with a Carney-like complex: bilateral non-pigmented micronodular adrenal hyperplasia, severe early-onset Cushing's syndrome, and distinct acral soft tissue overgrowth due to cutaneous mucinosis. This represents a novel manifestation of PRKACA disruption and broadens the extra-adrenal phenotype of PRKACA-associated Cushing's syndrome. Our data suggest that Cushing's syndrome phenotypes arising from somatic and germline PRKACA abnormalities can exist on a spectrum. We emphasise the value of ascertaining a genetic diagnosis for PRKACA-mediated adrenal and extra-adrenal disease to guide individualised and targeted care.

Association between genome-wide epigenetic and genetic alterations in breast cancer tissue and response to HER2-targeted therapies in HER2-positive breast cancer patients: new findings and a systematic review

Recent evidence suggests that genetic and epigenetic mechanisms might be associated with acquired resistance to cancer therapies. The aim of this study was to assess the association of genome-wide genetic and epigenetic alterations with the response to anti-HER2 agents in HER2-positive breast cancer patients. PubMed was screened for articles published until March 2021 on observational studies investigating the association of genome-wide genetic and epigenetic alterations, measured in breast cancer tissues or blood, with the response to targeted treatment in HER2-positive breast cancer patients. Sixteen studies were included in the review along with ours, in which we compared the genome-wide DNA methylation pattern in breast tumor tissues of patients who acquired resistance to treatment (case group, n = 6) to that of patients who did not develop resistance (control group, n = 6). Among genes identified as differentially methylated between the breast cancer tissue of cases and controls, one of them, PRKACA, was also reported as differentially expressed in two studies included in the review. Although included studies were heterogeneous in terms of methodology and study population, our review suggests that genes of the PI3K pathway may play an important role in developing resistance to anti-HER2 agents in breast cancer patients. Genome-wide genetic and epigenetic alterations measured in breast cancer tissue or blood might be promising markers of resistance to anti-HER2 agents in HER2-positive breast cancer patients. Further studies are needed to confirm these data.

Treatment of Primary Pigmented Nodular Adrenocortical Disease

Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of adrenocorticotropin hormone (ACTH)-independent Cushing's syndrome (CS), which mainly occurs in children and young adults. Treatment options with proven clinical efficacy for PPNAD include adrenalectomy (bilateral or unilateral adrenalectomy) and drug treatment to control hypercortisolemia. Previously, the main treatment of PPNAD is bilateral adrenal resection and long-term hormone replacement after surgery. In recent years, cases reports suggest that unilateral or subtotal adrenal resection can also lead to long-term remission in some patients without the need for long-term hormone replacement therapy. Medications for hypercortisolemia, such as Ketoconazole, Metyrapone and Mitotane et.al, have been reported as a preoperative transition for in some patients with severe hypercortisolism. In addition, tryptophan hydroxylase inhibitor, COX2 inhibitor Celecoxib, somatostatin and other drugs targeting the possible pathogenic mechanisms of the disease are under study, which are expected to be applied to the clinical treatment of PPNAD in the future. In this review, we summarize the recent progress on treatment of PPNAD, in which options of surgical methods, research results of drugs acting on possible pathogenic mechanisms, and the management during gestation are described in order to provide new ideas for clinical treatment.

Novel protein kinase cAMP-Activated Catalytic Subunit Alpha (PRKACA) inhibitor shows anti-tumor activity in a fibrolamellar hepatocellular carcinoma model

Fibrolamellar hepatocellular carcinoma (FL-HCC) is known as a highly aggressive liver cancer that typically affects young adults without virus infection. Since this type of cancer does not respond to chemotherapy, surgery is the only known effective therapeutic option. Most FL-HCC patients express the fusion gene DNAJB1-PRKACA, which has been recognized as the signature of FL-HCC. It has also been reported that PRKACA kinase activity is essential for its oncogenic activity, suggesting that PRKACA kinase inhibition could be considered as an useful therapeutic target. In this study, we established an evaluation system for PRKACA kinase inhibitors and synthesized DS89002333, a novel PRKACA inhibitor. DS89002333 showed potent PRKACA inhibitory activity and inhibited fusion protein-dependent cell growth both in vitro and in vivo. Furthermore, this compound showed anti-tumor activity in an FL-HCC patient-derived xenograft model expressing the DNAJB1-PRKACA fusion gene. Our data suggest that DS89002333 could be considered as a potential therapeutic agent for FL-HCC.

Structural and Enzymological Evidence for an Altered Substrate Specificity in Okur-Chung Neurodevelopmental Syndrome Mutant CK2αLys198Arg

Specific de novo mutations in the CSNK2A1 gene, which encodes CK2α, the catalytic subunit of protein kinase CK2, are considered as causative for the Okur-Chung neurodevelopmental syndrome (OCNDS). OCNDS is a rare congenital disease with a high phenotypic diversity ranging from neurodevelopmental disabilities to multi-systemic problems and characteristic facial features. A frequent OCNDS mutation is the exchange of Lys198 to Arg at the center of CK2α′s P+1 loop, a key element of substrate recognition. According to preliminary data recently made available, this mutation causes a significant shift of the substrate specificity of the enzyme. We expressed the CK2α^Lys198Arg recombinantly and characterized it biophysically and structurally. Using isothermal titration calorimetry (ITC), fluorescence quenching and differential scanning fluorimetry (Thermofluor), we found that the mutation does not affect the interaction with CK2β, the non-catalytic CK2 subunit, and that the thermal stability of the protein is even slightly increased. However, a CK2α^Lys198Arg crystal structure and its comparison with wild-type structures revealed a significant shift of the anion binding site harboured by the P+1 loop. This observation supports the notion that the Lys198Arg mutation causes an alteration of substrate specificity which we underpinned here with enzymological data.

An Overview of the Heterogeneous Causes of Cushing’s Syndrome due to Primary Macronodular Adrenal Hyperplasia (PMAH)

Primary macronodular adrenal hyperplasia (PMAH) is considered a rare cause of adrenal Cushing syndrome, is pituitary ACTH-independent, generally results from bilateral adrenal macronodules (>1 cm), and is often associated with variable cortisol secretion, resulting in a heterogeneous clinical presentation. Recent advances in the molecular pathogenesis of PMAH have offered new insights into the comprehension of this heterogeneous and complex adrenal disorder. Different molecular mechanisms involving the actors of the cAMP/protein kinase A pathway have been implicated in the development of PMAH, including germline and/or somatic molecular defects such as hyperexpression of the G-protein aberrant receptors and pathogenic variants of MC2R, GNAS, PRKAR1A, and PDE11A. Nevertheless, since 2013, the ARMC5 gene is believed to be a major genetic cause of PMAH, accounting for more than 80% of the familial forms of PMAH and 30% of apparently sporadic cases, except in food-dependent Cushing syndrome in which ARMC5 is not involved. Recently, 2 independent groups have identified that the tumor suppressor gene KDM1A is responsible for PMAH associated specifically with food-dependent Cushing syndrome. Consequently, PMAH has been more frequently genetically associated than previously assumed. This review summarizes the most important aspects, including hormone secretion, clinical presentation, radiological imaging, and molecular mechanisms, involved in familial Cushing syndrome associated with PMAH.

Protein Kinase A Downregulation Delays the Development and Progression of Polycystic Kidney Disease

Background: Upregulation of cAMP-dependent and -independent PKA signaling is thought to promote cystogenesis in polycystic kidney disease (PKD). PKA-I regulatory subunit RIα is increased in kidneys of orthologous mouse models. Kidney-specific knockout of RIα upregulates PKA activity, induces cystic disease in wild-type mice, and aggravates it in Pkd1 ^RC/RC mice. Methods: PKA-I activation or inhibition was compared to EPAC activation or PKA-II inhibition using Pkd1 ^RC/RC metanephric organ cultures. The effect of constitutive PKA (preferentially PKA-I) downregulation in vivo was ascertained by kidney-specific expression of a dominant negative RIαB allele in Pkd1 ^RC/RC mice obtained by crossing Prkar1α ^R1αB/WT, Pkd1 ^RC/RC, and Pkhd1-Cre mice (C57BL/6 background). The effect of pharmacologic PKA inhibition using a novel, selective PRKACA inhibitor (BLU2864) was tested in mIMCD3 3D cultures, metanephric organ cultures, and Pkd1 ^RC/RC mice on a C57BL/6 x 129S6/Sv F1 background. Mice were sacrificed at 16 weeks of age. Results: PKA-I activation promoted and inhibition prevented ex vivo P-Ser133 CREB expression and cystogenesis. EPAC activation or PKA-II inhibition had no or only minor effects. BLU2864 inhibited in vitro mIMCD3 cystogenesis and ex vivo P-Ser133 CREB expression and cystogenesis. Genetic downregulation of PKA activity and BLU2864 directly and/or indirectly inhibited many pro-proliferative pathways and were both protective in vivo BLU2864 had no detectable on- or off-target adverse effects. Conclusions: PKA-I is the main PKA isozyme promoting cystogenesis. Direct PKA inhibition may be an effective strategy to treat PKD and other conditions where PKA signaling is upregulated. By acting directly on PKA, the inhibition may be more effective than or substantially increase the efficacy of treatments that only affect PKA activity by lowering cAMP.

Developing Biliary Atresia-like Model by Treating Human Liver Organoids with Polyinosinic:Polycytidylic Acid (Poly (I:C))

Background: We explored the feasibility of creating BA-like organoids by treating human liver organoids with Polyinosinic:Polycytidylic acid (Poly I:C). Methods: Organoids were developed from the liver parenchyma collected during Kasai portoenterostomy (BA) and surgery for other liver disorders (non-BA). The non-BA organoids were co-cultured with poly I:C (40 µg/mL). The organoid morphology from both samples was compared on day 17. RNA-sequencing was performed to examine the transcriptomic differences. Results: Non-BA liver organoids developed into well-expanded spherical organoids with a single-cell layer of epithelial cells and a single vacuole inside. After poly I:C treatment, the majority of these organoids developed into an aberrant morphology with a high index of similarity to BA organoids which are multi-vacuoled and/or unexpanded. RNA-sequencing analysis revealed that 19 inflammatory genes were commonly expressed in both groups. Conditional cluster analysis revealed several genes (SOCS6, SOCS6.1, ARAF, CAMK2G, GNA1C, ITGA2, PRKACA, PTEN) that are involved in immune-mediated signaling pathway had a distinct pattern of expression in the poly I:C treated organoids. This resembled the expression pattern in BA organoids (p < 0.05). Conclusions: Poly I:C treated human liver organoids exhibit morphology and genetic signature highly compatible to organoids developed from BA liver samples. They are potential research materials to study immune-mediated inflammation in BA.

Prokaryotic expression of human-sourced and zebrafish-sourced protein kinase A alpha catalytic subunits combined with in vitro and in silico assay

The extensively studied cAMP-dependent protein kinase A (PKA) is involved in the regulation of critical cell processes, including metabolism, gene expression, and cell proliferation. Therefore, PKA has been viewed increasingly as potential target for variety of drugs and environmental endocrine disruptors. Consequentially, the preparation of PKA protein became an important initial step for the subsequent exploration of PKA's character in endocrine disrupting effects of pesticides. To investigate PKA protein, which is potential to be the environmental endocrine toxicity target of triazole fungicides, a strategy to heterologously express protein kinase A catalytic alpha subunit of human (hPKAcα) and zebrafish (zPKAcα) in Escherichia coli (E. coli) BL21(DE3) host cells was demonstrated. After optimizing conditions and protein purification, we successfully obtained enzymatically active hPKAcα and zPKAcα. Western blot analysis indicated that the recombinant hPKAcα and zPKAcα still retained their characteristic antigenicity and binding activity, while in vitro kinase activity assays revealed that the recombinant hPKAcα and zPKAcα maintained enzyme activity. By in silico methods including homology modelling and molecular docking, the affinity of ligands and the models of hPKAcα and zPKAcα were further tested. The present study offered a valuable method to achieve the prokaryotic expression of a eukaryotic protein kinase and laid a foundation to facilitate further investigation of toxicological target of triazole pesticides.

The Dynamic Change of Gene-Regulated Networks in Cashmere Goat Skin with Seasonal Variation

The Cashmere goat (Capra hircus) is renowned for its high-quality fiber production trait. The hair cycle in Cashmere goat has an annual rhythm. To deepen the understanding of the molecular foundation of annual rhythm in the skin of Cashmere goat, we did a comparative analysis of the Cashmere goat skin transcriptome all year round. 4002 Differentially expressed genes (DEGs) were identified with seasonal variations. 12 months transcriptome were divided into four developmental stages: Jan-Mar, Apr-Jul, Aug-Oct, and Nov-Dec based on gene expression patterns. 13 modules of highly correlated genes in skin were identified using WGCNA. Ten of these modules were consistent with the development stages. The gene function of those genes in each module was analyzed by functional enrichment. The results indicated that Wnt and Hedgehog signaling pathways were inhibited from January to March and activated from April to July. The cutaneous immune system of Cashmere goats has high activity from August to October. Fatty acid metabolism dominates goat skin from November to December. This study provides new information related to the annual skin development cycle, which could provide molecular biological significance for understanding the seasonal development and response to the annual rhythm of skin.

Boolean model for melanogenesis

Melanogenesis is a highly regulated process through which the pigment melanin is produced in skin cells. Irregularities in the molecular events that govern the process of skin pigmentation can cause disorders like vitiligo. In order to understand the biology of disease progression, it is important to have an in depth understanding of intracellular events. Mathematical models provide an integrated view of intracellular signalling. There are very few models to date that incorporate intracellular processes relevant to melanogenesis and only one to our knowledge that simulates the dynamics of response to varying levels of input. Here, we report the formulation of the largest Boolean model (265 nodes) for melanogenesis to date. The model was built on the basis of a detailed interaction network graph published by Raghunath et al. Through additional manual curation of the reported interactions, we converted the graph into a set of Boolean rules, following the procedure of the first Boolean model (62 nodes) for melanogenesis published by Lee et al. Simulations show that the predicted response to varying UV levels for most of the nodes is similar to the predictions of the existing model. The greater complexity allows investigation of the sensitivity of melanin to additional nodes. We carried out perturbation analysis of the network through node deletion and constitutive activation to identify sensitivity of outcomes, and compared the nodes identified as sensitive to previous reports.

Sequence and Structure-Based Analysis of Specificity Determinants in Eukaryotic Protein Kinases

Protein kinases lie at the heart of cell-signaling processes and are often mutated in disease. Kinase target recognition at the active site is in part determined by a few amino acids around the phosphoacceptor residue. However, relatively little is known about how most preferences are encoded in the kinase sequence or how these preferences evolved. Here, we used alignment-based approaches to predict 30 specificity-determining residues (SDRs) for 16 preferences. These were studied with structural models and were validated by activity assays of mutant kinases. Cancer mutation data revealed that kinase SDRs are mutated more frequently than catalytic residues. We have observed that, throughout evolution, kinase specificity has been strongly conserved across orthologs but can diverge after gene duplication, as illustrated by the G protein-coupled receptor kinase family. The identified SDRs can be used to predict kinase specificity from sequence and aid in the interpretation of evolutionary or disease-related genomic variants.

Modulation of polycystic kidney disease by G-protein coupled receptors and cyclic AMP signaling

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a systemic disorder associated with polycystic liver disease (PLD) and other extrarenal manifestations, the most common monogenic cause of end-stage kidney disease, and a major burden for public health. Many studies have shown that alterations in G-protein and cAMP signaling play a central role in its pathogenesis. As for many other diseases (35% of all approved drugs target G-protein coupled receptors (GPCRs) or proteins functioning upstream or downstream from GPCRs), treatments targeting GPCR have shown effectiveness in slowing the rate of progression of ADPKD. Tolvaptan, a vasopressin V2 receptor antagonist is the first drug approved by regulatory agencies to treat rapidly progressive ADPKD. Long-acting somatostatin analogs have also been effective in slowing the rates of growth of polycystic kidneys and liver. Although no treatment has so far been able to prevent the development or stop the progression of the disease, these encouraging advances point to G-protein and cAMP signaling as a promising avenue of investigation that may lead to more effective and safe treatments. This will require a better understanding of the relevant GPCRs, G-proteins, cAMP effectors, and of the enzymes and A-kinase anchoring proteins controlling the compartmentalization of cAMP signaling. The purpose of this review is to provide an overview of general GPCR signaling; the function of polycystin-1 (PC1) as a putative atypical adhesion GPCR (aGPCR); the roles of PC1, polycystin-2 (PC2) and the PC1-PC2 complex in the regulation of calcium and cAMP signaling; the cross-talk of calcium and cAMP signaling in PKD; and GPCRs, adenylyl cyclases, cyclic nucleotide phosphodiesterases, and protein kinase A as therapeutic targets in ADPKD.

A Pilot Study Using a Multistaged Integrated Analysis of Gene Expression and Methylation to Evaluate Mechanisms for Evening Fatigue in Women Who Received Chemotherapy for Breast Cancer

CONTEXT

Fatigue is the most common symptom associated with cancer and its treatment. Investigation of molecular mechanisms associated with fatigue may identify new therapeutic targets.

OBJECTIVE

The objective of this pilot study was to evaluate the relationships between gene expression and methylation status and evening fatigue severity in women with breast cancer who received chemotherapy.

METHODS

Latent class analysis (LCA) was used to identify evening fatigue phenotypes. In this analysis, the lowest (i.e., moderate, n = 7) and highest (i.e., very high, n = 29) fatigue-severity classes identified using LCA were analyzed via two stages. First, a total of 32,609 transcripts from whole blood were evaluated for differences in expression levels between the classes. Next, 637 methylation sites located within the putative transcription factor binding sites for those genes demonstrating differential expression were evaluated for differential methylation state between the classes.

RESULTS

A total of 89 transcripts in 75 unique genes were differentially expressed between the moderate (the lowest fatigue-severity class identified) and very high evening fatigue classes. In addition, 23 differentially methylated probes and three differentially methylated regions were found between the moderate and very high evening fatigue classes.

CONCLUSIONS

Using a multistaged integrated analysis of gene expression and methylation, differential methylation was identified in the regulatory regions of genes associated with previously hypothesized mechanisms for fatigue, including inflammation, immune function, neurotransmission, circadian rhythm, skeletal muscle energy, carbohydrate metabolism, and renal function as well as core biological processes including gene transcription and the cell-cycle regulation.

A distinct epigenetic profile distinguishes stenotic from non-inflamed fibroblasts in the ileal mucosa of Crohn's disease patients

BACKGROUND

The chronic remitting and relapsing intestinal inflammation characteristic of Crohn's disease frequently leads to fibrosis and subsequent stenosis of the inflamed region. Approximately a third of all Crohn's disease patients require resection at some stage in their disease course. As the pathogenesis of Crohn's disease associated fibrosis is largely unknown, a strong necessity exists to better understand the pathophysiology thereof.

METHODS

In this study, we investigated changes of the DNA methylome and transcriptome of ileum-derived fibroblasts associated to the occurrence of Crohn's disease associated fibrosis. Eighteen samples were included in a DNA methylation array and twenty-one samples were used for RNA sequencing.

RESULTS

Most differentially methylated regions and differentially expressed genes were observed when comparing stenotic with non-inflamed samples. By contrast, few differences were observed when comparing Crohn's disease with non-Crohn's disease, or inflamed with non-inflamed tissue. Integrative methylation and gene expression analyses revealed dysregulation of genes associated to the PRKACA and E2F1 network, which is involved in cell cycle progression, angiogenesis, epithelial to mesenchymal transition, and bile metabolism.

CONCLUSION

Our research provides evidence that the methylome and the transcriptome are systematically dysregulated in stenosis-associated fibroblasts.

Single nucleotide polymorphisms alter kinase anchoring and the subcellular targeting of A-kinase anchoring proteins

A-kinase anchoring proteins (AKAPs) shape second-messenger signaling responses by constraining protein kinase A (PKA) at precise intracellular locations. A defining feature of AKAPs is a helical region that binds to regulatory subunits (RII) of PKA. Mining patient-derived databases has identified 42 nonsynonymous SNPs in the PKA-anchoring helices of five AKAPs. Solid-phase RII binding assays confirmed that 21 of these amino acid substitutions disrupt PKA anchoring. The most deleterious side-chain modifications are situated toward C-termini of AKAP helices. More extensive analysis was conducted on a valine-to-methionine variant in the PKA-anchoring helix of AKAP18. Molecular modeling indicates that additional density provided by methionine at position 282 in the AKAP18γ isoform deflects the pitch of the helical anchoring surface outward by 6.6°. Fluorescence polarization measurements show that this subtle topological change reduces RII-binding affinity 8.8-fold and impairs cAMP responsive potentiation of L-type Ca²⁺ currents in situ. Live-cell imaging of AKAP18γ V282M-GFP adducts led to the unexpected discovery that loss of PKA anchoring promotes nuclear accumulation of this polymorphic variant. Targeting proceeds via a mechanism whereby association with the PKA holoenzyme masks a polybasic nuclear localization signal on the anchoring protein. This led to the discovery of AKAP18ε: an exclusively nuclear isoform that lacks a PKA-anchoring helix. Enzyme-mediated proximity-proteomics reveal that compartment-selective variants of AKAP18 associate with distinct binding partners. Thus, naturally occurring PKA-anchoring-defective AKAP variants not only perturb dissemination of local second-messenger responses, but also may influence the intracellular distribution of certain AKAP18 isoforms.

Pathogenesis of benign unilateral adrenocortical tumors: focus on cAMP/PKA pathway

Somatic mutations affecting genes in the cAMP/PKA (protein kinase A) signaling pathway have been described as causative for the pathogenesis of benign unilateral adrenocortical adenomas associated with cortisol over secretion. These include predominantly somatic mutations in the PRKACA gene which encodes the catalytic subunit α of PKA. In addition, mutations in the GNAS gene, coding for the stimulatory G protein α, have been observed in approximately 10% of cortisol producing adenomas (CPA). The mutations render PKA signaling constitutively active and are therefore involved in cortisol over secretion of these tumors. Despite the prominent role of the cAMP/PKA pathway in the pathogenesis of unilateral CPA, also mutations in the CTNNB1 gene, encoding β-catenin, were identified in CPA. However, mutations in β-catenin are not limited to CPA and are not associated with cortisol secretion since they were predominantly found in endocrine-inactive adenomas (EIA) and might hence contribute to tumorigenesis in adrenocortical tissues. In this review, recent findings in the pathogenesis of benign adrenocortical tumors with a particular focus on the cAMP/PKA signaling pathway are summarized.

miR-503 suppresses the proliferation and metastasis of esophageal squamous cell carcinoma by triggering autophagy via PKA/mTOR signaling

MicroRNA (miR)-503 is involved in the regulation of the malignant phenotype in multiple tumor types, and has been proven to be a novel diagnostic and therapeutic target; however, its function and mechanisms of action have not yet been fully elucidated in esophageal squamous cell carcinoma (ESCC). In the current study, we detected miR‑503 expression by RT‑qPCR and found that miR‑503 expression was increased in ESCC, but negatively correlated with lymph node metastasis, TNM stage and tumor differentiation. Functionally, we confirmed that miR‑503 inhibited the proliferation and metastasis of ESCC cells by triggering cellular autophagy. Mechanistically, we confirmed that miR‑503 exerted its biological effects by targeting protein kinase CAMP‑activated catalytic subunit alpha (PRKACA) in ESCC by dual luciferase reporter assay. Moreover, miR‑503 was found to trigger autophagy in ESCC cells through the protein kinase A (PKA)/mammalian target of rapamycin (mTOR) pathway. Taken together, our results demonstrate that miR‑503 suppresses the proliferation and metastasis of ESCC via the activation of autophagy, mediated by the PKA/mTOR signaling pathway.

The Many Faces of Primary Aldosteronism and Cushing Syndrome: A Reflection of Adrenocortical Tumor Heterogeneity

Adrenal cortical tumors constitute a heterogeneous group of neoplasms with distinct clinical, morphological, and molecular features. Recent discoveries of specific genotype–phenotype correlations in adrenal cortical adenomas have transformed our understanding of their respective endocrine syndromes. Indeed, a proportion of patients with primary aldosteronism are now known to harbor adrenal cortical adenomas with heterogeneous molecular alterations (KCNJ5, ATP1A1, ATP2B3, and CACNA1D) involving the calcium/calmodulin kinase signaling pathway. Several lines of evidence suggest that KCNJ5-mutant aldosterone-producing adenomas have distinct clinicopathological phenotype compared to those harboring ATP1A1, ATP2B3, and CACNA1D mutations. Benign adrenal cortical tumors presenting with Cushing syndrome often have diverse mutations (PRKACA, PRKAR1A, GNAS, PDE11A, and PDE8B) involving the cyclic AMP signaling pathway. In addition to cortisol-producing adenomas, bilateral micronodular adrenocortical disease and primary bilateral macronodular adrenal hyperplasia (PBMAH) have also expanded the spectrum of benign neoplasms causing adrenal Cushing disease. The recent discovery of inactivating ARMC5 germline mutations in PBMAH has challenged the old belief that this disorder is mainly a sporadic disease. Emerging evidence suggests that PBMAH harbors multiple distinct clonal proliferations, reflecting the heterogeneous genomic landscape of this disease. Although most solitary adrenal cortical tumors are sporadic, there is an increasing recognition that inherited susceptibility syndromes may also play a role in their pathogenesis. This review highlights the molecular and morphological heterogeneity of benign adrenal cortical neoplasms, reflected in the diverse presentations of primary aldosteronism and adrenal Cushing syndrome.

The Many Faces of Primary Aldosteronism and Cushing Syndrome: A Reflection of Adrenocortical Tumor Heterogeneity

Adrenal cortical tumors constitute a heterogeneous group of neoplasms with distinct clinical, morphological, and molecular features. Recent discoveries of specific genotype-phenotype correlations in adrenal cortical adenomas have transformed our understanding of their respective endocrine syndromes. Indeed, a proportion of patients with primary aldosteronism are now known to harbor adrenal cortical adenomas with heterogeneous molecular alterations (KCNJ5, ATP1A1, ATP2B3, and CACNA1D) involving the calcium/calmodulin kinase signaling pathway. Several lines of evidence suggest that KCNJ5-mutant aldosterone-producing adenomas have distinct clinicopathological phenotype compared to those harboring ATP1A1, ATP2B3, and CACNA1D mutations. Benign adrenal cortical tumors presenting with Cushing syndrome often have diverse mutations (PRKACA, PRKAR1A, GNAS, PDE11A, and PDE8B) involving the cyclic AMP signaling pathway. In addition to cortisol-producing adenomas, bilateral micronodular adrenocortical disease and primary bilateral macronodular adrenal hyperplasia (PBMAH) have also expanded the spectrum of benign neoplasms causing adrenal Cushing disease. The recent discovery of inactivating ARMC5 germline mutations in PBMAH has challenged the old belief that this disorder is mainly a sporadic disease. Emerging evidence suggests that PBMAH harbors multiple distinct clonal proliferations, reflecting the heterogeneous genomic landscape of this disease. Although most solitary adrenal cortical tumors are sporadic, there is an increasing recognition that inherited susceptibility syndromes may also play a role in their pathogenesis. This review highlights the molecular and morphological heterogeneity of benign adrenal cortical neoplasms, reflected in the diverse presentations of primary aldosteronism and adrenal Cushing syndrome.

Histopathological and genetic characterization of aldosterone-producing adenomas with concurrent subclinical cortisol hypersecretion: a case series

PURPOSE

Aldosterone-producing adenomas with concurrent subclinical cortisol hypersecretion are reported in an increasing number of patients. Five aldosterone-producing adenomas from patients with primary aldosteronism and subclinical hypercortisolism were examined.

THE AIMS OF OUR STUDY WERE

(1) to analyze pathological features and immunohistochemical expression of CYP11B1 (11β-hydroxylase) and CYP11B2 (aldosterone synthase) in these tumors; (2) to investigate somatic mutations involved in adrenal steroid hypersecretion and/or tumor growth.

METHODS

Archival micro-dissected paraffin-embedded slides from tumor specimens were used for histological and molecular studies. Immunohistochemistry was performed using monoclonal anti-CYP11B1 and anti-CYP11B2 antibodies. Cellular composition was determined by examining for known features of zona fasciculata and zona glomerulosa, and immunoreactivity for CYP11B1 and CYP11B2 by McCarty H-score. Spot regions for mutations in KCNJ5, ATP1A1, ATP2B3, CACNA1D, PRKACA, and CTNNB1 gene sequences were evaluated.

RESULTS

Four APAs showed a predominant (≥50%) zona fasciculata-like cell pattern: one tumor had CYP11B1 H-score = 150, no detectable CYP11B2 expression, and harbored a PRKACA p.Leu206Arg mutation (that we have reported previously elsewhere), one had no CYP11B1 expression, CYP11B2 H-score = 40, and no mutations; the remaining two adenomas had high CYP11B1 H-score (160 and 240, respectively) and low CYP11B2 H-score (30 and 15, respectively), with the latter harboring a CTNNB1 p.Ser45Phe activating mutation. One of five aldosterone-producing adenomas had a predominant zona glomerulosa-like pattern, CYP11B1 H-score = 15, CYP11B2 H-score = 180, and no mutations.

CONCLUSIONS

The majority of aldosterone-producing adenomas with concurrent subclinical cortisol hypersecretion were composed mainly of zona fasciculata-like cells, while CYP11B1 and CYP11B2 immunostaining demonstrated clear heterogeneity. In a subset of cases, different somatic mutations may be involved in hormone excess and tumor formation.

Carney complex review: Genetic features

Carney complex is a multiple neoplasia syndrome having endocrine and non-endocrine manifestations. Diagnostic criteria include myxoma, lentigines, and primary pigmented nodular adrenocortical disease, amongst other signs/symptoms. In most cases it is an autosomal dominant disease, and diagnosis therefore requires study and follow-up of the family members. Inactivating mutations of the PRKAR1A gene were identified as the main cause of the disease, although since 2015 other disease-related genes, including PRKACA and PRKACB activating mutations, have also been related with Carney complex. This review will address the genetic aspects related to Carney complex.

Targeting the Architecture of Deregulated Protein Complexes in Cancer

The architectures of central signaling hubs are precisely organized by static and dynamic protein-protein interactions (PPIs). Upon deregulation, these PPI platforms are capable to propagate or initiate pathophysiological signaling events. This causes the acquisition of molecular features contributing to the etiology or progression of many diseases, including cancer, where deregulated molecular interactions of signaling proteins have been best studied. The reasons for PPI-dependent reprogramming of cancer-initiating cells are manifold; in many cases, mutations perturb PPIs, enzyme activities, protein abundance, or protein localization. Consequently, the pharmaceutical targeting of PPIs promises to be of remarkable therapeutic value. For this review we have selected three key players of oncogenic signaling which are differently affected by PPI deregulation: two (the small G proteins of the RAS family and the transcription factor MYC) are considered "undruggable" using classical drug discovery approaches and in the case of the third protein discussed here, PKA, standard kinase inhibitors, may be unsuitable in the clinic. These circumstances require alternative strategies, which may lie in pharmaceutical drug interference of critical PPIs accountable for oncogenic signaling.

Channeling of cAMP in PDE-PKA Complexes Promotes Signal Adaptation

Spatiotemporal control of the cAMP signaling pathway is governed by both hormonal stimulation of cAMP generation by adenylyl cyclases (activation phase) and cAMP hydrolysis by phosphodiesterases (PDEs) (termination phase). The termination phase is initiated by PDEs actively targeting the protein kinase A (PKA) R-subunit through formation of a PDE-PKAR-cyclic adenosine monophosphate (cAMP) complex (the termination complex). Our results using PDE8 as a model PDE, reveal that PDEs mediate active hydrolysis of cAMP bound to its receptor RIα by enhancing the enzymatic activity. This accelerated cAMP turnover occurs via formation of a stable PDE8-RIα complex, where the protein-protein interface forms peripheral contacts and the central ligand cements this ternary interaction. The basis for enhanced catalysis is active translocation of cAMP from its binding site on RIα to the hydrolysis site on PDE8 through direct "channeling." Our results reveal cAMP channeling in the PDE8-RIα complex and a molecular description of how this channel facilitates processive hydrolysis of unbound cAMP. Thus, unbound cAMP maintains the PDE8-RIα complex while being hydrolyzed, revealing an undiscovered mode for amplification of PKA activity by cAMP-mediated sequestration of the R-subunit by PDEs. This novel regulatory mode explains the paradox of cAMP signal amplification by accelerated PDE-mediated cAMP turnover. This highlights how target effector proteins of small-molecule ligands can promote enzyme-mediated ligand hydrolysis by scaffolding effects. Enhanced activity of the PDE8-RIα complex facilitates robust desensitization, allowing the cell to respond to dynamic levels of cAMP rather than steady-state levels. The PDE8-RIα complex represents a new class of PDE-based complexes for specific drug discovery targeting the cAMP signaling pathway.

Cell signaling pathways in the adrenal cortex: Links to stem/progenitor biology and neoplasia

The adrenal cortex is a dynamic tissue responsible for the synthesis of steroid hormones, including mineralocorticoids, glucocorticoids, and androgens in humans. Advances have been made in understanding the role of adrenocortical stem/progenitor cell populations in cortex homeostasis and self-renewal. Recently, large molecular profiling studies of adrenocortical carcinoma (ACC) have given insights into proteins and signaling pathways involved in normal tissue homeostasis that become dysregulated in cancer. These data provide an impetus to examine the cellular pathways implicated in adrenocortical disease and study connections, or lack thereof, between adrenal homeostasis and tumorigenesis, with a particular focus on stem and progenitor cell pathways. In this review, we discuss evidence for stem/progenitor cells in the adrenal cortex, proteins and signaling pathways that may regulate these cells, and the role these proteins play in pathologic and neoplastic conditions. In turn, we also examine common perturbations in adrenocortical tumors (ACT) and how these proteins and pathways may be involved in adrenal homeostasis.

Comprehensive Molecular Characterization of Pheochromocytoma and Paraganglioma

We report a comprehensive molecular characterization of pheochromocytomas and paragangliomas (PCCs/PGLs), a rare tumor type. Multi-platform integration revealed that PCCs/PGLs are driven by diverse alterations affecting multiple genes and pathways. Pathogenic germline mutations occurred in eight PCC/PGL susceptibility genes. We identified CSDE1 as a somatically mutated driver gene, complementing four known drivers (HRAS, RET, EPAS1, and NF1). We also discovered fusion genes in PCCs/PGLs, involving MAML3, BRAF, NGFR, and NF1. Integrated analysis classified PCCs/PGLs into four molecularly defined groups: a kinase signaling subtype, a pseudohypoxia subtype, a Wnt-altered subtype, driven by MAML3 and CSDE1, and a cortical admixture subtype. Correlates of metastatic PCCs/PGLs included the MAML3 fusion gene. This integrated molecular characterization provides a comprehensive foundation for developing PCC/PGL precision medicine.

Regulation of zonation and homeostasis in the adrenal cortex

The adult adrenal cortex is organized into concentric zones, each specialized to produce distinct steroid hormones. Cellular composition of the cortex is highly dynamic and subject to diverse signaling controls. Cortical homeostasis and regeneration rely on centripetal migration of steroidogenic cells from the outer to the inner cortex, which is accompanied by direct conversion of zona glomerulosa (zG) into zona fasciculata (zF) cells. Given the important impact of tissue structure and growth on steroidogenic function, it is essential to understand the mechanisms governing adrenal zonation and homeostasis. Towards this end, we review the distinctions between each zone by highlighting their morphological and ultra-structural features, discuss key signaling pathways influencing zonal identity, and evaluate current evidence for long-term self-renewing stem cells in the adult cortex. Finally, we review data supporting zG-to-zF transdifferentiation/direct conversion as a major mechanism of adult cortical renewal.

Cushing's syndrome mutant PKAL205R exhibits altered substrate specificity

The PKA^L205R hotspot mutation has been implicated in Cushing's syndrome through hyperactive gain-of-function PKA signaling; however, its influence on substrate specificity has not been investigated. Here, we employ the Proteomic Peptide Library (ProPeL) approach to create high-resolution models for PKA^WT and PKA^L205R substrate specificity. We reveal that the L205R mutation reduces canonical hydrophobic preference at the substrate P + 1 position, and increases acidic preference in downstream positions. Using these models, we designed peptide substrates that exhibit altered selectivity for specific PKA variants, and demonstrate the feasibility of selective PKA^L205R loss-of-function signaling. Through these results, we suggest that substrate rewiring may contribute to Cushing's syndrome disease etiology, and introduce a powerful new paradigm for investigating mutation-induced kinase substrate rewiring in human disease.

60 YEARS OF POMC: Adrenal and extra-adrenal functions of ACTH

The pituitary adrenocorticotropic hormone (ACTH) plays a pivotal role in homeostasis and stress response and is thus the major component of the hypothalamo-pituitary-adrenal axis. After a brief summary of ACTH production from proopiomelanocortin (POMC) and on ACTH receptor properties, the first part of the review covers the role of ACTH in steroidogenesis and steroid secretion. We highlight the mechanisms explaining the differential acute vs chronic effects of ACTH on aldosterone and glucocorticoid secretion. The second part summarizes the effects of ACTH on adrenal growth, addressing its role as either a mitogenic or a differentiating factor. We then review the mechanisms involved in steroid secretion, from the classical Cyclic adenosine monophosphate second messenger system to various signaling cascades. We also consider how the interaction between the extracellular matrix and the cytoskeleton may trigger activation of signaling platforms potentially stimulating or repressing the steroidogenic potency of ACTH. Finally, we consider the extra-adrenal actions of ACTH, in particular its role in differentiation in a variety of cell types, in addition to its known lipolytic effects on adipocytes. In each section, we endeavor to correlate basic mechanisms of ACTH function with the pathological consequences of ACTH signaling deficiency and of overproduction of ACTH.

Role of phospholipases in adrenal steroidogenesis

Phospholipases are lipid-metabolizing enzymes that hydrolyze phospholipids. In some cases, their activity results in remodeling of lipids and/or allows the synthesis of other lipids. In other cases, however, and of interest to the topic of adrenal steroidogenesis, phospholipases produce second messengers that modify the function of a cell. In this review, the enzymatic reactions, products, and effectors of three phospholipases, phospholipase C, phospholipase D, and phospholipase A2, are discussed. Although much data have been obtained concerning the role of phospholipases C and D in regulating adrenal steroid hormone production, there are still many gaps in our knowledge. Furthermore, little is known about the involvement of phospholipase A2, perhaps, in part, because this enzyme comprises a large family of related enzymes that are differentially regulated and with different functions. This review presents the evidence supporting the role of each of these phospholipases in steroidogenesis in the adrenal cortex.

Protein kinase A catalytic subunit isoform PRKACA; History, function and physiology

Our appreciation of the scope and influence of second messenger signaling has its origins in pioneering work on the cAMP-dependent protein kinase. Also called protein kinase A (PKA), this holoenzyme exists as a tetramer comprised of a regulatory (R) subunit dimer and two catalytic (C) subunits. Upon binding of two molecules of the second messenger cAMP to each R subunit, a conformational change in the PKA holoenzyme occurs to release the C subunits. These active kinases phosphorylate downstream targets to propagate cAMP responsive cell signaling events. This article focuses on the discovery, structure, cellular location and physiological effects of the catalytic subunit alpha of protein kinase A (encoded by the gene PRKACA). We also explore the potential role of this essential gene as a molecular mediator of certain disease states.

Haploinsufficiency for either one of the type-II regulatory subunits of protein kinase A improves the bone phenotype of Prkar1a+/- mice

Carney Complex (CNC), a human genetic syndrome predisposing to multiple neoplasias, is associated with bone lesions such as osteochondromyxomas (OMX). The most frequent cause for CNC is PRKAR1A deficiency; PRKAR1A codes for type-I regulatory subunit of protein kinase A (PKA). Prkar1a(+/-) mice developed OMX, fibrous dysplasia-like lesions (FDL) and other tumors. Tumor tissues in these animals had increased PKA activity due to an unregulated PKA catalytic subunit and increased PKA type II (PKA-II) activity mediated by the PRKAR2A and PRKAR2B subunits. To better understand the effect of altered PKA activity on bone, we studied Prkar2a and Prkar2b knock out (KO) and heterozygous mice; none of these mice developed bone lesions. When Prkar2a(+/-) and Prkar2b(+/-) mice were used to generate Prkar1a(+/-)Prkar2a(+/-) and Prkar1a(+/-)Prkar2b(+/-) animals, bone lesions formed that looked like those of the Prkar1a(+/-) mice. However, better overall bone organization and mineralization and fewer FDL lesions were found in both double heterozygote groups, indicating a partial restoration of the immature bone structure observed in Prkar1a(+/-) mice. Further investigation indicated increased osteogenesis and higher new bone formation rates in both Prkar1a(+/-)Prkar2a(+/-) and Prkar1a(+/-)Prkar2b(+/-) mice with some minor differences between them. The observations were confirmed with a variety of markers and studies. PKA activity measurements showed the expected PKA-II decrease in both double heterozygote groups. Thus, haploinsufficiency for either of PKA-II regulatory subunits improved bone phenotype of mice haploinsufficient for Prkar1a, in support of the hypothesis that the PRKAR2A and PRKAR2B regulatory subunits were in part responsible for the bone phenotype of Prkar1a(+/-) mice.