AKAP signaling complexes: pointing towards the next generation of therapeutic targets?

Biological processes and signal transduction pathways regulated by the protein methyltransferase SETD7 and their significance in cancer

Protein methyltransferases have been shown to methylate histone and non-histone proteins, leading to regulation of several biological processes that control cell homeostasis. Over the past few years, the histone-lysine N-methyltransferase SETD7 (SETD7; also known as SET7/9, KIAA1717, KMT7, SET7, SET9) has emerged as an important regulator of at least 30 non-histone proteins and a potential target for the treatment of several human diseases. This review discusses current knowledge of the structure and subcellular localization of SETD7, as well as its function as a histone and non-histone methyltransferase. This work also underlines the putative contribution of SETD7 to the regulation of gene expression, control of cell proliferation, differentiation and endoplasmic reticulum stress, which indicate that SETD7 is a candidate for novel targeted therapies with the aim of either stimulating or inhibiting its activity, depending on the cell signaling context.

Astroglial cAMP signalling in space and time

To maintain a high level of specificity and normal cell function, the cyclic adenosine monophosphate (cAMP) pathway is tightly regulated in space and time. Recent advances in cAMP reporter technology have provided insights into spatio-temporal characteristics of cAMP signalling in individual living cells, including astrocytes. Astrocytes are glial cells in the central nervous system with many homeostatic functions. In contrast to neurons, astrocytes are electrically silent, but, in response to extracellular stimuli through activation of surface receptors, they can increase intracellular levels of secondary messengers, e.g. Ca²⁺ and cAMP. This enables them to communicate with neighbouring cells, such as neurons and endothelial cells of blood vessels. The dynamics of receptor-mediated Ca²⁺ signalling in astrocytes has been extensively studied in the past in contrast to cAMP signalling. Here, we present the first insights into the temporal dynamics of cAMP signalling in living astrocytes, which revealed that cAMP signals in astrocytes exhibit tonic dynamics and are slower than Ca²⁺ signals with phasic dynamics. We debate on the heterogeneity of basal cAMP levels in astrocytes and how hypotonicity-induced astrocyte swelling affects temporal dynamics of cAMP signalling. Understanding the spatio-temporal characteristics of cAMP signalling in astrocytes is of extreme importance because cAMP governs many important cellular processes and any malfunctions may lead to pathology.

The DUF1669 domain of FAM83 family proteins anchor casein kinase 1 isoforms

Members of the casein kinase 1 (CK1) family of serine-threonine protein kinases are implicated in the regulation of many cellular processes, including the cell cycle, circadian rhythms, and Wnt and Hedgehog signaling. Because these kinases exhibit constitutive activity in biochemical assays, it is likely that their activity in cells is controlled by subcellular localization, interactions with inhibitory proteins, targeted degradation, or combinations of these mechanisms. We identified members of the FAM83 family of proteins as partners of CK1 in cells. All eight members of the FAM83 family (FAM83A to FAM83H) interacted with the α and α-like isoforms of CK1; FAM83A, FAM83B, FAM83E, and FAM83H also interacted with the δ and ε isoforms of CK1. We detected no interaction between any FAM83 member and the related CK1γ1, CK1γ2, and CK1γ3 isoforms. Each FAM83 protein exhibited a distinct pattern of subcellular distribution and colocalized with the CK1 isoform(s) to which it bound. The interaction of FAM83 proteins with CK1 isoforms was mediated by the conserved domain of unknown function 1669 (DUF1669) that characterizes the FAM83 family. Mutations in FAM83 proteins that prevented them from binding to CK1 interfered with the proper subcellular localization and cellular functions of both the FAM83 proteins and their CK1 binding partners. On the basis of its function, we propose that DUF1669 be renamed the polypeptide anchor of CK1 domain.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Counterregulation of cAMP-directed kinase activities controls ciliogenesis

The primary cilium emanates from the cell surface of growth-arrested cells and plays a central role in vertebrate development and tissue homeostasis. The mechanisms that control ciliogenesis have been extensively explored. However, the intersection between GPCR signaling and the ubiquitin pathway in the control of cilium stability are unknown. Here we observe that cAMP elevation promotes cilia resorption. At centriolar satellites, we identify a multimeric complex nucleated by PCM1 that includes two kinases, NEK10 and PKA, and the E3 ubiquitin ligase CHIP. We show that NEK10 is essential for ciliogenesis in mammals and for the development of medaka fish. PKA phosphorylation primes NEK10 for CHIP-mediated ubiquitination and proteolysis resulting in cilia resorption. Disarrangement of this control mechanism occurs in proliferative and genetic disorders. These findings unveil a pericentriolar kinase signalosome that efficiently links the cAMP cascade with the ubiquitin-proteasome system, thereby controlling essential aspects of ciliogenesis.

Blockage of AKAP12 accelerates angiotensin II (Ang II)-induced cardiac injury in mice by regulating the transforming growth factor β1 (TGF-β1) pathway

Hypertension is a multifactorial chronic inflammatory disease that leads to cardiac remodeling. A-kinase anchor protein 12 (AKAP12) is a scaffolding protein that has multiple functions in various biological events, including the regulation of vessel integrity and differentiation of neural barriers in blood. However, the role of AKAP12 in angiotensin II (Ang II)-induced cardiac injury remains unclear. In the present study, Ang II infusion reduced AKAP12 expressions in the hearts of wild-type (WT) mice, and AKAP12 knockout (KO) enhanced the infiltration of inflammatory cells. In addition, AKAP12 deletion accelerated Ang II-induced cardiac histologic alterations and dysfunction. Further, AKAP12^-/- aggravated heart failure by promoting the inflammation, oxidative stress, cellular apoptosis, and autophagy induced by Ang II. Furthermore, AKAP12 KO elevated Ang II-induced cardiac fibrosis, as indicated by the following: (1) Masson trichrome staining showed that Ang II infusion markedly increased fibrotic areas of the WT mouse heart, which was greatly accelerated in AKAP12^-/- mice; (2) immunohistochemistry analysis showed increased expression of transforming growth factor β1 (TGF-β1) and α-smooth muscle actin (α-SMA) in the AKAP12^-/- mouse heart; (3) reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) analysis showed increased expression of fibrosis-related molecules in the AKAP12-deficient mouse heart; and (4) Western blot analysis indicated significantly higher upregulation of p-SMAD2/3 in the AKAP12^-/- mouse heart. In vitro, AKAP12 knockdown in HL-1 cells was responsible for TGF-β1-induced inflammation, the generation of reactive oxygen species (ROS), apoptosis, autophagy, and fibrosis. Furthermore, overexpression of AKAP12 reduced fibrosis triggered by TGF-β1 in cells. Overall, our study suggests that fibrosis induced by Ang II may be alleviated by AKAP12 expression through inactivation of the TGF-β1 pathway.

Investigating PKA-RII specificity using analogs of the PKA:AKAP peptide inhibitor STAD-2

Generation of the second messenger molecule cAMP mediates a variety of cellular responses which are essential for critical cellular processes. In response to elevated cAMP levels, cAMP dependent protein kinase (PKA) phosphorylates serine and threonine residues on a wide variety of target substrates. In order to enhance the precision and directionality of these signaling events, PKA is localized to discrete locations within the cell by A-kinase anchoring proteins (AKAPs). The interaction between PKA and AKAPs is mediated via an amphipathic α-helix derived from AKAPs which binds to a stable hydrophobic groove formed in the dimerization/docking (D/D) domain of PKA-R in an isoform-specific fashion. Although numerous AKAP disruptors have previously been identified that can inhibit either RI- or RII-selective AKAPs, no AKAP disruptors have been identified that have isoform specificity for RIα versus RIβ or RIIα versus RIIβ. As a strategy to identify isoform-specific AKAP inhibitors, a library of chemically stapled protein-protein interaction (PPI) disruptors was developed based on the RII-selective AKAP disruptor, STAD-2. An alanine was substituted at each position in the sequence, and from this library it was possible to delineate the importance of longer aliphatic residues in the formation of a region which complements the hydrophobic cleft formed by the D/D domain. Interestingly, lysine residues that were added to both terminal ends of the peptide sequence to facilitate water solubility appear to contribute to isoform specificity for RIIα over RIIβ while having only weak interaction with RI. This work supports current hypotheses on the mechanisms of AKAP binding and highlights the significance of particular residue positions that aid in distinguishing between the RII isoforms and may provide insight into future design of isoform-selective AKAP disruptors.

A-Kinase Anchoring Protein-Lbc: A Molecular Scaffold Involved in Cardiac Protection

Heart failure is a lethal disease that can develop after myocardial infarction, hypertension, or anticancer therapy. In the damaged heart, loss of function is mainly due to cardiomyocyte death and associated cardiac remodeling and fibrosis. In this context, A-kinase anchoring proteins (AKAPs) constitute a family of scaffolding proteins that facilitate the spatiotemporal activation of the cyclic adenosine monophosphate (AMP)-dependent protein kinase (PKA) and other transduction enzymes involved in cardiac remodeling. AKAP-Lbc, a cardiac enriched anchoring protein, has been shown to act as a key coordinator of the activity of signaling pathways involved in cardiac protection and remodeling. This review will summarize and discuss recent advances highlighting the role of the AKAP-Lbc signalosome in orchestrating adaptive responses in the stressed heart.

Characterisation of peptide interactions that regulate PKCε activation

Targeting the interaction between PKC isoforms and their anchoring proteins can specifically regulate kinase activity. εV1-2 and pseudoεRACK peptides, derived from the PKCε C2 domain, modulate its association with receptor for activated C-kinase 2 (RACK2) and thus its function. Details of these interactions remain obscure, and we therefore investigated binding of these peptides using biophysical techniques. Surface plasmon resonance (SPR) indicated that the inhibitory εV1-2 peptide bound to RACK2, and inhibited PKCε binding as expected. In contrast, SPR and NMR demonstrated that the activating pseudoεRACK peptide and related sequences did not bind to PKCε, indicating that their mechanisms of action do not involve binding to the kinase as previously proposed. Our results clarify which interactions could be targeted in developing new therapeutics that inhibit PKCε-RACK2 interaction.

Role of A-kinase anchoring protein 95 in the regulation of cytochrome P450 family 19 subfamily A member 1 (CYP19A1) in human ovarian granulosa cells

Irregular expression of cytochrome P450 family 19 subfamily A member 1 (CYP19A1) is involved in the development of polycystic ovary syndrome (PCOS). Activation of the cAMP/protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway plays a crucial role in FSH regulation of CYP19A1 in human ovarian granulosa cells. A-Kinase anchor protein 95 (AKAP95) is known to confine PKA to the nucleus. However, it is unclear whether anchoring PKA to the nucleus is essential for the induction of CYP19A1 by FSH in human ovarian granulosa cells. Using the human granulosa cell line KGN and primary cultured human luteinised granulosa cells (hLGCs), we found that knockdown of AKAP8, the gene encoding AKAP95, or inhibition of AKAP95 reduced the amount of PKA anchored in the nucleus and attenuated the phosphorylation of CREB by either FSH or activation of the cAMP/PKA pathway. Moreover, knockdown of AKAP8 or inhibition of AKAP95 also significantly attenuated FSH-induced CYP19A1 expression and oestrogen synthesis. Furthermore, significant decreases in AKAP95 and CYP19A1 were observed in hLGCs obtained from PCOS patients. The results of the present study demonstrate a crucial role for AKAP95 in CYP19A1 expression and oestrogen synthesis in hLGCs, which implies that AKAP95 may be involved in the pathogenesis of PCOS.

Single cell whole genome sequencing reveals that NFKB1 mutation affects radiotherapy sensitivity in cervical cancer

Cervical cancer is the third most common cancer in women. Radiotherapy resistance remains a major obstacle for patients with cervical cancer. Somatic alterations in human genomes are responsible for radiotherapy resistance. Here, we performed single cell whole genome sequencing on 13 cells before radiotherapy and 12 cells after radiotherapy from a Chinese woman patient with cervical carcinoma. We identified one damaging mutation in NFKB1 (G430E), which showed significantly increased mutant allele frequency after radiotherapy than that before radiotherapy. Further functional assays showed that NFKB1 was a tumour suppressor in cervical cancer by inhibiting cell proliferation, colony formation and migration, while the mutation in NFKB1 could weaken the tumour suppressing functions of NFKB1. NFKB1 enhanced the sensitivity of cervical cancer cells to the effects of irradiation, and the mutation in NFKB1 weakened this effect. These results suggested that NFKB1 may be a potential molecular target in cervical cancer radiation therapy in the future.

AKAP95-mediated nuclear anchoring of PKA mediates cortisol-induced PTGS2 expression in human amnion fibroblasts

Phosphorylation of the transcription factors cyclic adenosine monophosphate response element-binding protein (CREB) and signal transducer and activator of transcription 3 (STAT3) by protein kinase A (PKA) is required for the cortisol-induced production of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) in human amnion fibroblasts, which critically mediates human parturition (labor). We found that PKA was confined in the nucleus by A-kinase-anchoring protein 95 (AKAP95) in amnion fibroblasts and that this localization was key to the cortisol-induced expression of PTGS2, the gene encoding COX-2. Cortisol increased the abundance of nuclear PKA by stimulating the expression of the gene encoding AKAP95. Knockdown of AKAP95 not only reduced the amounts of nuclear PKA and phosphorylated CREB but also attenuated the induction of PTGS2 expression in primary human amnion fibroblasts treated with cortisol, whereas the phosphorylation of STAT3 in response to cortisol was not affected. The abundances of AKAP95, phosphorylated CREB, and COX-2 were markedly increased in human amnion tissue after labor compared to those in amnion tissues from cesarean sections without labor. These results highlight an essential role for PKA that is anchored in the nucleus by AKAP95 in the phosphorylation of CREB and the consequent induction of COX-2 expression by cortisol in amnion fibroblasts, which may be important in human parturition.

Cardiac Phosphodiesterases and Their Modulation for Treating Heart Disease

An important hallmark of cardiac failure is abnormal second messenger signaling due to impaired synthesis and catabolism of cyclic adenosine 3',5'- monophosphate (cAMP) and cyclic guanosine 3',5'- monophosphate (cGMP). Their dysregulation, altered intracellular targeting, and blunted responsiveness to stimulating pathways all contribute to pathological remodeling, muscle dysfunction, reduced cell survival and metabolism, and other abnormalities. Therapeutic enhancement of either cyclic nucleotides can be achieved by stimulating their synthesis and/or by suppressing members of the family of cyclic nucleotide phosphodiesterases (PDEs). The heart expresses seven of the eleven major PDE subtypes - PDE1, 2, 3, 4, 5, 8, and 9. Their differential control over cAMP and cGMP signaling in various cell types, including cardiomyocytes, provides intriguing therapeutic opportunities to counter heart disease. This review examines the roles of these PDEs in the failing and hypertrophied heart and summarizes experimental and clinical data that have explored the utility of targeted PDE inhibition.

Functions of intrinsic disorder in transmembrane proteins

Intrinsic disorder is common in integral membrane proteins, particularly in the intracellular domains. Despite this observation, these domains are not always recognized as being disordered. In this review, we will discuss the biological functions of intrinsically disordered regions of membrane proteins, and address why the flexibility afforded by disorder is mechanistically important. Intrinsically disordered regions are present in many common classes of membrane proteins including ion channels and transporters; G-protein coupled receptors (GPCRs), receptor tyrosine kinases and cytokine receptors. The functions of the disordered regions are many and varied. We will discuss selected examples including: (1) Organization of receptors, kinases, phosphatases and second messenger sources into signaling complexes. (2) Modulation of the membrane-embedded domain function by ball-and-chain like mechanisms. (3) Trafficking of membrane proteins. (4) Transient membrane associations. (5) Post-translational modifications most notably phosphorylation and (6) disorder-linked isoform dependent function. We finish the review by discussing the future challenges facing the membrane protein community regarding protein disorder.

PKA Regulates PINK1 Stability and Parkin Recruitment to Damaged Mitochondria through Phosphorylation of MIC60

A mitochondrial kinase, PTEN-induced putative kinase 1 (PINK1), selectively recruits the ubiquitin ligase Parkin to damaged mitochondria, which modifies mitochondria by polyubiquitination, leading to mitochondrial autophagy. Here, we report that treatment with an adenylate cyclase agonist or expression of protein kinase A (PKA) impairs Parkin recruitment to damaged mitochondria and decreases PINK1 protein levels. We identified a mitochondrial membrane protein, MIC60 (also known as mitofilin), as a PKA substrate. Mutational and mass spectrometric analyses revealed that the Ser528 residue of MIC60 undergoes PKA-dependent phosphorylation. MIC60 transiently interacts with PINK1, and MIC60 downregulation leads to a reduction in PINK1 and mislocalization of Parkin. Phosphorylation-mimic mutants of MIC60 fail to restore the defect in Parkin recruitment in MIC60-knocked down cells, whereas a phosphorylation-deficient MIC60 mutant facilitates the mitochondrial localization of Parkin. Our findings indicate that PKA-mediated phosphorylation of MIC60 negatively regulates mitochondrial clearance that is initiated by PINK1 and Parkin.

The many faces of compartmentalized PKA signalosomes

Cellular signal transmission requires the dynamic formation of spatiotemporally controlled molecular interactions. At the cell surface information is received by receptor complexes and relayed through intracellular signaling platforms which organize the actions of functionally interacting signaling enzymes and substrates. The list of hormone or neurotransmitter pathways that utilize the ubiquitous cAMP-sensing protein kinase A (PKA) system is expansive. This requires that the specificity, duration, and intensity of PKA responses are spatially and temporally restricted. Hereby, scaffolding proteins take the center stage for ensuring proper signal transmission. They unite second messenger sensors, activators, effectors, and kinase substrates within cellular micro-domains to precisely control and route signal propagation. A-kinase anchoring proteins (AKAPs) organize such subcellular signalosomes by tethering the PKA holoenzyme to distinct cell compartments. AKAPs differ in their modular organization showing pathway specific arrangements of interaction motifs or domains. This enables the cell- and compartment- guided assembly of signalosomes with unique enzyme composition and function. The AKAP-mediated clustering of cAMP and other second messenger sensing and interacting signaling components along with functional successive enzymes facilitates the rapid and precise dissemination of incoming signals. This review article delineates examples for different means of PKA regulation and for snapshots of compartmentalized PKA signalosomes.

Distinct phosphodiesterase 5A-containing compartments allow selective regulation of cGMP-dependent signalling in human arterial smooth muscle cells

Cyclic GMP (cGMP) translates and integrates much of the information encoded by nitric oxide (NO^·) and several natriuretic peptides, including the atrial natriuretic peptide (ANP). Previously, we reported that integration of a cGMP-specific cyclic nucleotide phosphodiesterase, namely phosphodiesterase 5A (PDE5A), into a protein kinase G (PKG)- and inositol-1,4,5-trisphosphate receptor (IP₃R)-containing endoplasmic reticulum (ER) signalosome allows localized control of PDE5A activity and of PKG-dependent inhibition of IP₃-mediated release of ER Ca²⁺ in human platelets. Herein, we report that PDE5A integrates into an analogous signalosome in human arterial smooth muscle cells (HASMC), wherein it regulates muscarinic agonist-dependent Ca²⁺ release and is activated selectively by PKG-dependent phosphorylation. In addition, we report that PDE5A also regulates HASMC functions via events independent of PKG, but rather through actions coordinated by competitive cGMP-mediated inhibition of cAMP hydrolysis by the so-called cGMP-inhibited cAMP PDE, namely phosphodiesterase 3A (PDE3A). Indeed, we show that ANP increases both cGMP and cAMP levels in HASMC and promotes phosphorylation of vasodilator-stimulated phospho-protein (VASP) at each the PKG and PKA phospho-acceptor sites. Since selective inhibition of PDE5 decreased DNA synthesis and chemotaxis of HASMC, and that PDE3A knockdown obviated these effects, our findings are consistent with a role for a PDE5A-PDE3A-PKA axis in their regulation. Our findings provide insight into the existence of distinct "pools" of PDE5A in HASMC and support the idea that these discrete compartments regulate distinct cGMP-dependent events. As a corollary, we suggest that it may be possible to target these distinct PDE5A-regulated pools and in so-doing differentially impact selected cGMP-regulated functions in these cells.

Shaping mitochondrial dynamics: The role of cAMP signalling

In recent years, our idea of mitochondria evolved from "mere" energy and metabolite producers to key regulators of many cellular functions. In order to preserve and protect their functional status, these organelles engage a number of dynamic processes that allow them to decrease accumulated burden and maintain their homeostasis. Indeed, mitochondria can unite (fusion), divide (fission), position themselves strategically in the cell (motility/trafficking) and if irreversibly damaged or dysfunctional eliminated (mitophagy). These dynamic processes can be controlled both by mitochondrial and cellular signalling pathways, hence allowing mitochondria to tune their function to the cellular needs. Among the regulatory mechanisms, reversible phosphorylation downstream the cyclic AMP (cAMP) signalling cascade was shown to deeply influence mitochondrial dynamics. This review explores the emerging evidence suggesting that cAMP is a key player in the orchestration of mitochondrial fusion/fission, motility and mitophagy, extending the repertoire of this second messenger, which is now recognised as a major regulator of mitochondrial homeostasis.

Ca2+ tunnelling through the ER lumen as a mechanism for delivering Ca2+ entering via store-operated Ca2+ channels to specific target sites

Ca²⁺ signalling is perhaps the most universal and versatile mechanism regulating a wide range of cellular processes. Because of the many different calcium‐binding proteins distributed throughout cells, signalling precision requires localized rises in the cytosolic Ca²⁺ concentration. In electrically non‐excitable cells, for example epithelial cells, this is achieved by primary release of Ca²⁺ from the endoplasmic reticulum via Ca²⁺ release channels placed close to the physiological target. Because any rise in the cytosolic Ca²⁺ concentration activates Ca²⁺ extrusion, and in order for cells not to run out of Ca²⁺, there is a need for compensatory Ca²⁺ uptake from the extracellular fluid. This Ca²⁺ uptake occurs through a process known as store‐operated Ca²⁺ entry. Ideally Ca²⁺ entering the cell should not diffuse to the target site through the cytosol, as this would potentially activate undesirable processes. Ca²⁺ tunnelling through the lumen of the endoplasmic reticulum is a mechanism for delivering Ca²⁺ entering via store‐operated Ca²⁺ channels to specific target sites, and this process has been described in considerable detail in pancreatic acinar cells and oocytes. Here we review the most important evidence and present a generalized concept.

AKAP-mediated feedback control of cAMP gradients in developing hippocampal neurons

Cyclic AMP (cAMP) and protein kinase A (PKA), classical examples of spatially compartmentalized signaling molecules, are critical axon determinants that regulate neuronal polarity and axon formation, yet little is known about micro-compartmentalization of cAMP and PKA signaling and its role in developing neurons. Here, we revealed that cAMP forms a gradient in developing hippocampal neurons, with higher cAMP levels in more distal regions of the axon compared to other regions of the cell. Interestingly, this cAMP gradient changed according to the developmental stage and depended on proper anchoring of PKA by A-kinase anchoring proteins (AKAPs). Disrupting PKA anchoring to AKAPs increased the cAMP gradient in early-stage neurons and led to enhanced axon elongation. Our results provide new evidence for a local negative feedback loop, assembled by AKAPs, for the precise control of a growth-stage-dependent cAMP gradient to ensure proper axon growth.

Clustering and Functional Coupling of Diverse Ion Channels and Signaling Proteins Revealed by Super-resolution STORM Microscopy in Neurons

The fidelity of neuronal signaling requires organization of signaling molecules into macromolecular complexes, whose components are in intimate proximity. The intrinsic diffraction limit of light makes visualization of individual signaling complexes using visible light extremely difficult. However, using super-resolution stochastic optical reconstruction microscopy (STORM), we observed intimate association of individual molecules within signaling complexes containing ion channels (M-type K⁺, L-type Ca²⁺, or TRPV1 channels) and G protein-coupled receptors coupled by the scaffolding protein A-kinase-anchoring protein (AKAP)79/150. Some channels assembled as multi-channel supercomplexes. Surprisingly, we identified novel layers of interplay within macromolecular complexes containing diverse channel types at the single-complex level in sensory neurons, dependent on AKAP79/150. Electrophysiological studies revealed that such ion channels are functionally coupled as well. Our findings illustrate the novel role of AKAP79/150 as a molecular coupler of different channels that conveys crosstalk between channel activities within single microdomains in tuning the physiological response of neurons.

Deficiency of the intermediate filament synemin reduces bone mass in vivo

While the type IV intermediate filament protein, synemin, has been shown to play a role in striated muscle and neuronal tissue, its presence and function have not been described in skeletal tissue. Here, we report that genetic ablation of synemin in 14-wk-old male mice results in osteopenia that includes a more than 2-fold reduction in the trabecular bone fraction in the distal femur and a reduction in the cross-sectional area at the femoral middiaphysis due to an attendant reduction in both the periosteal and endosteal perimeter. Analysis of serum markers of bone formation and static histomorphometry revealed a statistically significant defect in osteoblast activity and osteoblast number in vivo. Interestingly, primary osteoblasts isolated from synemin-null mice demonstrate markedly enhanced osteogenic capacity with a concomitant reduction in cyclin D1 mRNA expression, which may explain the loss of osteoblast number observed in vivo. In total, these data suggest an important, previously unknown role for synemin in bone physiology.

The A-Kinase Anchoring Protein (AKAP) Glycogen Synthase Kinase 3β Interaction Protein (GSKIP) Regulates β-Catenin through Its Interactions with Both Protein Kinase A (PKA) and GSK3β

The A-kinase anchoring protein (AKAP) GSK3β interaction protein (GSKIP) is a cytosolic scaffolding protein binding protein kinase A (PKA) and glycogen synthase kinase 3β (GSK3β). Here we show that both the AKAP function of GSKIP, i.e. its direct interaction with PKA, and its direct interaction with GSK3β are required for the regulation of β-catenin and thus Wnt signaling. A cytoplasmic destruction complex targets β-catenin for degradation and thus prevents Wnt signaling. Wnt signals cause β-catenin accumulation and translocation into the nucleus, where it induces Wnt target gene expression. GSKIP facilitates control of the β-catenin stabilizing phosphorylation at Ser-675 by PKA. Its interaction with GSK3β facilitates control of the destabilizing phosphorylation of β-catenin at Ser-33/Ser-37/Thr-41. The influence of GSKIP on β-catenin is explained by its scavenger function; it recruits the kinases away from the destruction complex without forming a complex with β-catenin. The regulation of β-catenin by GSKIP is specific for this AKAP as AKAP220, which also binds PKA and GSK3β, did not affect Wnt signaling. We find that the binding domain of AKAP220 for GSK3β is a conserved GSK3β interaction domain (GID), which is also present in GSKIP. Our findings highlight an essential compartmentalization of both PKA and GSK3β by GSKIP, and ascribe a function to a cytosolic AKAP-PKA interaction as a regulatory factor in the control of canonical Wnt signaling. Wnt signaling controls different biological processes, including embryonic development, cell cycle progression, glycogen metabolism, and immune regulation; deregulation is associated with diseases such as cancer, type 2 diabetes, inflammatory, and Alzheimer's and Parkinson's diseases.

Targeting cAMP/PKA pathway for glycemic control and type 2 diabetes therapy

In mammals, cyclic adenosine monophosphate (cAMP) is an intracellular second messenger that is usually elicited by binding of hormones and neurotransmitters to G protein-coupled receptors (GPCRs). cAMP exerts many of its physiological effects by activating cAMP-dependent protein kinase (PKA), which in turn phosphorylates and regulates the functions of downstream protein targets including ion channels, enzymes, and transcription factors. cAMP/PKA signaling pathway regulates glucose homeostasis at multiple levels including insulin and glucagon secretion, glucose uptake, glycogen synthesis and breakdown, gluconeogenesis, and neural control of glucose homeostasis. This review summarizes recent genetic and pharmacological studies concerning the regulation of glucose homeostasis by cAMP/PKA in pancreas, liver, skeletal muscle, adipose tissues, and brain. We also discuss the strategies for targeting cAMP/PKA pathway for research and potential therapeutic treatment of type 2 diabetes mellitus (T2D).

Fibrolamellar Hepatocellular Carcinoma: Mechanistic Distinction From Adult Hepatocellular Carcinoma

Fibrolamellar hepatocellular carcinoma (FL-HCC) has historically been classified as a rare subtype of HCC. However, unlike "classic" HCC, it occurs in children and young adults without underlying liver disease. The recent discovery of a deletion mutation in all FL-HCCs represented a major advancement in understanding the pathogenesis of this disease. This deletion results in the fusion of the genes encoding a heat shock protein (DNAJB1) and the catalytic subunit of protein kinase A (PKA, PRKACA), and overexpression of PRKACA and enhanced cAMP-dependent PKA activity. This review summarizes recent advancements in FL-HCC pathogenesis and characteristics of the HSP40-PKA C protein.

Anchoring of both PKA-RIIα and 14-3-3θ regulates retinoic acid induced 16 mediated phosphorylation of heat shock protein 70

Our previous study reported that retinoic acid induced 16 (RAI16) could enhance tumorigenesis in hepatocellular carcinoma (HCC). However, the cellular functions of RAI16 are still unclear. In this study, by immunoprecipitation and tandem (MS/MS) mass spectrometry analysis, we identified that RAI16 interacted with the type II regulatory subunit of PKA (PKA-RIIα), acting as a novel protein kinase A anchoring protein (AKAP). In addition, RAI16 also interacted with heat shock protein 70 (HSP70) and 14-3-3θ. Further studies indicated that RAI16 mediated PKA phosphorylation of HSP70 at serine 486, resulting in anti-apoptosis events. RAI16 was also phosphorylated by the anchored PKA at serine 325, which promoted the recruitment of 14-3-3θ, which, in turn, inhibited RAI16 mediated PKA phosphorylation of HSP70. These findings offer mechanism insight into RAI16 mediated anti-apoptosis signaling in HCC.

MRP4 (ABCC4) as a potential pharmacologic target for cardiovascular disease

This review focuses on multidrug resistance protein 4 (MRP4 or ABCC4) that has recently been shown to play a role in cAMP homeostasis, a key-pathway in vascular biology and in platelet functions. In vascular system, recent data provide evidence that inhibition of MRP4 prevents human coronary artery smooth muscle cell proliferation in vitro and in vivo, as well as human pulmonary artery smooth muscle cell proliferation in vitro and pulmonary hypertension in mice in vivo. In the heart, MRP4 silencing in adult rat ventricular myocytes results in an increase in intracellular cAMP levels leading to enhanced cardiomyocyte contractility. However, a prolonged inhibition of MRP4 can promote cardiac hypertrophy. In addition, secreted cAMP, through its metabolite adenosine, prevents adrenergically induced cardiac hypertrophy and fibrosis. Finally, MRP4 inhibition in platelets induces a moderate thrombopathy. The localization of MRP4 underlines the emerging concept of cAMP compartmentalization in platelets, which is a major regulatory mechanism in other cells. cAMP storage in platelet dense granules might limit the cAMP cytosolic concentration upon adenylate cyclase activation, a necessary step to induce platelet activation. In this review, we discuss the therapeutic potential of direct pharmacological inhibition of MRP4 in atherothrombotic disease, via its vasodilating and antiplatelet effects.

Revisiting protein kinase-substrate interactions: Toward therapeutic development

Despite the efforts of pharmaceutical companies to develop specific kinase modulators, few drugs targeting kinases have been completely successful in the clinic. This is primarily due to the conserved nature of kinases, especially in the catalytic domains. Consequently, many currently available inhibitors lack sufficient selectivity for effective clinical application. Kinases phosphorylate their substrates to modulate their activity. One of the important steps in the catalytic reaction of protein phosphorylation is the correct positioning of the target residue within the catalytic site. This positioning is mediated by several regions in the substrate binding site, which is typically a shallow crevice that has critical subpockets that anchor and orient the substrate. The structural characterization of this protein-protein interaction can aid in the elucidation of the roles of distinct kinases in different cellular processes, the identification of substrates, and the development of specific inhibitors. Because the region of the substrate that is recognized by the kinase can be part of a linear consensus motif or a nonlinear motif, advances in technology beyond simple linear sequence scanning for consensus motifs were needed. Cost-effective bioinformatics tools are already frequently used to predict kinase-substrate interactions for linear consensus motifs, and new tools based on the structural data of these interactions improve the accuracy of these predictions and enable the identification of phosphorylation sites within nonlinear motifs. In this Review, we revisit kinase-substrate interactions and discuss the various approaches that can be used to identify them and analyze their binding structures for targeted drug development.

Lithocholic bile acid accumulated in yeast mitochondria orchestrates a development of an anti-aging cellular pattern by causing age-related changes in cellular proteome

We have previously revealed that exogenously added lithocholic bile acid (LCA) extends the chronological lifespan of the yeast Saccharomyces cerevisiae, accumulates in mitochondria and alters mitochondrial membrane lipidome. Here, we use quantitative mass spectrometry to show that LCA alters the age-related dynamics of changes in levels of many mitochondrial proteins, as well as numerous proteins in cellular locations outside of mitochondria. These proteins belong to 2 regulons, each modulated by a different mitochondrial dysfunction; we call them a partial mitochondrial dysfunction regulon and an oxidative stress regulon. We found that proteins constituting these regulons (1) can be divided into several "clusters", each of which denotes a distinct type of partial mitochondrial dysfunction that elicits a different signaling pathway mediated by a discrete set of transcription factors; (2) exhibit 3 different patterns of the age-related dynamics of changes in their cellular levels; and (3) are encoded by genes whose expression is regulated by the transcription factors Rtg1p/Rtg2p/Rtg3p, Sfp1p, Aft1p, Yap1p, Msn2p/Msn4p, Skn7p and Hog1p, each of which is essential for longevity extension by LCA. Our findings suggest that LCA-driven changes in mitochondrial lipidome alter mitochondrial proteome and functionality, thereby enabling mitochondria to operate as signaling organelles that orchestrate an establishment of an anti-aging transcriptional program for many longevity-defining nuclear genes. Based on these findings, we propose a model for how such LCA-driven changes early and late in life of chronologically aging yeast cause a stepwise development of an anti-aging cellular pattern and its maintenance throughout lifespan.

Screening for small molecule disruptors of AKAP-PKA interactions

Protein-protein interactions (PPIs) are highly specific and diverse. Their selective inhibition with peptides, peptidomimetics, or small molecules allows determination of functions of individual PPIs. Moreover, inhibition of disease-associated PPIs may lead to new concepts for the treatment of diseases with an unmet medical need. Protein kinase A (PKA) is an ubiquitously expressed protein kinase that controls a plethora of cellular functions. A-kinase anchoring proteins (AKAPs) are multivalent scaffolding proteins that directly interact with PKA. AKAPs spatially and temporally restrict PKA activity to defined cellular compartments and thereby contribute to the specificity of PKA signaling. However, it is largely unknown which of the plethora of PKA-dependent signaling events involve interactions of PKA with AKAPs. Moreover, AKAP-PKA interactions appear to play a role in a variety of cardiovascular, neuronal, and inflammatory diseases, but it is unclear whether these interactions are suitable drug targets. Here we describe an enzyme-linked immunosorbent assay (ELISA) for the screening of small molecule libraries for inhibitors of AKAP-PKA interactions. In addition, we describe a homogenous time-resolved fluorescence (HTRF) assay for use in secondary validation screens. Small molecule inhibitors are invaluable molecular tools for elucidating the functions of AKAP-PKA interactions and may eventually lead to new concepts for the treatment of diseases where AKAP-PKA interactions represent potential drug targets.

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.

Emerging roles of A-kinase anchoring proteins in cardiovascular pathophysiology

Heart and blood vessels ensure adequate perfusion of peripheral organs with blood and nutrients. Alteration of the homeostatic functions of the cardiovascular system can cause hypertension, atherosclerosis, and coronary artery disease leading to heart injury and failure. A-kinase anchoring proteins (AKAPs) constitute a family of scaffolding proteins that are crucially involved in modulating the function of the cardiovascular system both under physiological and pathological conditions. AKAPs assemble multifunctional signaling complexes that ensure correct targeting of the cAMP-dependent protein kinase (PKA) as well as other signaling enzymes to precise subcellular compartments. This allows local regulation of specific effector proteins that control the function of vascular and cardiac cells. This review will focus on recent advances illustrating the role of AKAPs in cardiovascular pathophysiology. The accent will be mainly placed on the molecular events linked to the control of vascular integrity and blood pressure as well as on the cardiac remodeling process associated with heart failure. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca²⁺ -release channels, as well as signalling by cyclic nucleotides and Ca²⁺ . Ca²⁺ -binding proteins (calmodulin, centrin) and Ca²⁺ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H⁺ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca²⁺ -channels, exocyst complexes and Ca²⁺ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.

Pharmacological targeting of AKAP-directed compartmentalized cAMP signalling

The second messenger cyclic adenosine monophosphate (cAMP) can bind and activate protein kinase A (PKA). The cAMP/PKA system is ubiquitous and involved in a wide array of biological processes and therefore requires tight spatial and temporal regulation. Important components of the safeguard system are the A-kinase anchoring proteins (AKAPs), a heterogeneous family of scaffolding proteins defined by its ability to directly bind PKA. AKAPs tether PKA to specific subcellular compartments, and they bind further interaction partners to create local signalling hubs. The recent discovery of new AKAPs and advances in the field that shed light on the relevance of these hubs for human disease highlight unique opportunities for pharmacological modulation. This review exemplifies how interference with signalling, particularly cAMP signalling, at such hubs can reshape signalling responses and discusses how this could lead to novel pharmacological concepts for the treatment of disease with an unmet medical need such as cardiovascular disease and cancer.

Targeting protein-protein interactions in complexes organized by A kinase anchoring proteins

Cyclic AMP is a ubiquitous intracellular second messenger involved in the regulation of a wide variety of cellular processes, a majority of which act through the cAMP – protein kinase A (PKA) signaling pathway and involve PKA phosphorylation of specific substrates. PKA phosphorylation events are typically spatially restricted and temporally well controlled. A-kinase anchoring proteins (AKAPs) directly bind PKA and recruit it to specific subcellular loci targeting the kinase activity toward particular substrates, and thereby provide discrete spatiotemporal control of downstream phosphorylation events. AKAPs also scaffold other signaling molecules into multi-protein complexes that function as crossroads between different signaling pathways. Targeting AKAP coordinated protein complexes with high-affinity peptidomimetics or small molecules to tease apart distinct protein–protein interactions (PPIs) therefore offers important means to disrupt binding of specific components of the complex to better understand the molecular mechanisms involved in the function of individual signalosomes and their pathophysiological role. Furthermore, development of novel classes of small molecules involved in displacement of AKAP-bound signal molecules is now emerging. Here, we will focus on mechanisms for targeting PPI, disruptors that modulate downstream cAMP signaling and their role, especially in the heart.

Scaffolding during the cell cycle by A-kinase anchoring proteins

Cell division relies on coordinated regulation of the cell cycle. A process including a well-defined series of strictly regulated molecular mechanisms involving cyclin-dependent kinases, retinoblastoma protein, and polo-like kinases. Dysfunctions in cell cycle regulation are associated with disease such as cancer, diabetes, and neurodegeneration. Compartmentalization of cellular signaling is a common strategy used to ensure the accuracy and efficiency of cellular responses. Compartmentalization of intracellular signaling is maintained by scaffolding proteins, such as A-kinase anchoring proteins (AKAPs). AKAPs are characterized by their ability to anchor the regulatory subunits of protein kinase A (PKA), and thereby achieve guidance to different cellular locations via various targeting domains. Next to PKA, AKAPs also associate with several other signaling elements including receptors, ion channels, protein kinases, phosphatases, small GTPases, and phosphodiesterases. Taking the amount of possible AKAP signaling complexes and their diverse localization into account, it is rational to believe that such AKAP-based complexes regulate several critical cellular events of the cell cycle. In fact, several AKAPs are assigned as tumor suppressors due to their vital roles in cell cycle regulation. Here, we first briefly discuss the most important players of cell cycle progression. After that, we will review our recent knowledge of AKAPs linked to the regulation and progression of the cell cycle, with special focus on AKAP12, AKAP8, and Ezrin. At last, we will discuss this specific AKAP subset in relation to diseases with focus on a diverse subset of cancer.

PKA-type I selective constrained peptide disruptors of AKAP complexes

A-Kinase Anchoring Proteins (AKAPs) coordinate complex signaling events by serving as spatiotemporal modulators of cAMP-dependent protein kinase activity in cells. Although AKAPs organize a plethora of diverse pathways, their cellular roles are often elusive due to the dynamic nature of these signaling complexes. AKAPs can interact with the type I or type II PKA holoenzymes by virtue of high-affinity interactions with the R-subunits. As a means to delineate AKAP-mediated PKA signaling in cells, we sought to develop isoform-selective disruptors of AKAP signaling. Here, we report the development of conformationally constrained peptides named RI-STapled Anchoring Disruptors (RI-STADs) that target the docking/dimerization domain of the type 1 regulatory subunit of PKA. These high-affinity peptides are isoform-selective for the RI isoforms, can outcompete binding by the classical AKAP disruptor Ht31, and can selectively displace RIα, but not RIIα, from binding the dual-specific AKAP149 complex. Importantly, these peptides are cell-permeable and disrupt Type I PKA-mediated phosphorylation events in the context of live cells. Hence, RI-STAD peptides are versatile cellular tools to selectively probe anchored type I PKA signaling events.

Epac proteins: specific ligands and role in cardiac remodelling

Epacs (exchange proteins directly activated by cAMP) act as guanine-nucleotide-exchange factors for the Ras-like small G-proteins Rap1 and Rap2, and are now recognized as incontrovertible factors leading to complex and diversified cAMP signalling pathways. Given the critical role of cAMP in the regulation of cardiac function, several studies have investigated the functional role of Epacs in the heart, providing evidence that Epacs modulate intracellular Ca2+ and are involved in several cardiac pathologies such as cardiac hypertrophy and arrhythmia. The present review summarizes recent data on the Epac signalling pathway and its role in cardiac pathophysiology. We also discuss recent advances in the discovery of novel pharmacological modulators of Epacs that were identified by high-throughput screening and their therapeutic potential for the treatment of cardiac disorders.

Neurobeachin Regulates Glutamate- and GABA-Receptor Targeting to Synapses via Distinct Pathways

Neurotransmission and synaptic strength depend on expression of post-synaptic receptors on the cell surface. Post-translational modification of receptors, trafficking to the synapse through the secretory pathway, and subsequent insertion into the synapse involves interaction of the receptor with A-kinase anchor proteins (AKAPs) and scaffolding proteins. Neurobeachin (Nbea), a brain specific AKAP, is required for synaptic surface expression of both glutamate and GABA receptors. Here, we investigated the role of Nbea-dependent targeting of postsynaptic receptors by studying Nbea interaction with synapse-associated protein 102 (SAP102/Dlg3) and protein kinase A subunit II (PKA II). A Nbea mutant lacking the PKA binding domain showed a similar distribution as wild-type Nbea in Nbea null neurons and partially restored GABA receptor surface expression. To understand the relevance of Nbea interaction with SAP102, we analysed SAP102 null mutant mice. Nbea levels were reduced by ~80 % in SAP102 null mice, but glutamatergic receptor expression was normal. A single-point mutation in the pleckstrin homology domain of Nbea (E2218R) resulted in loss of binding with SAP102. When expressed in Nbea null neurons, this mutant fully restored GABA receptor surface expression, but not glutamate receptor expression. Our results suggest that the PKA-binding domain is not essential for Nbea’s role in receptor targeting and that Nbea targets glutamate and GABA receptors to the synapse via distinct molecular pathways by interacting with specific effector proteins.

Mechanisms and dynamics of AKAP79/150-orchestrated multi-protein signalling complexes in brain and peripheral nerve

A-kinase anchoring proteins (AKAPs) have emerged as a converging point of diverse signals to achieve spatiotemporal resolution of directed cellular regulation. With the extensive studies of AKAP79/150 in regulation of ion channel activity, the major questions to be posed centre on the mechanism and functional role of synergistic regulation of ion channels by such signalling proteins. In this review, we summarize recent discoveries of AKAP79/150-mediated modulation of voltage-gated neuronal M-type (KCNQ, Kv7) K(+) channels and L-type CaV 1 Ca(2+) channels, on both short- and longer-term time scales, highlighting the dynamics of the macromolecular signalling complexes in brain and peripheral nerve We also discuss several models for the possible mechanisms of these multi-protein assemblies and how they serve the agenda of the neurons in which they occur.

Mechanisms by which different functional states of mitochondria define yeast longevity

Mitochondrial functionality is vital to organismal physiology. A body of evidence supports the notion that an age-related progressive decline in mitochondrial function is a hallmark of cellular and organismal aging in evolutionarily distant eukaryotes. Studies of the baker’s yeast Saccharomyces cerevisiae, a unicellular eukaryote, have led to discoveries of genes, signaling pathways and chemical compounds that modulate longevity-defining cellular processes in eukaryotic organisms across phyla. These studies have provided deep insights into mechanistic links that exist between different traits of mitochondrial functionality and cellular aging. The molecular mechanisms underlying the essential role of mitochondria as signaling organelles in yeast aging have begun to emerge. In this review, we discuss recent progress in understanding mechanisms by which different functional states of mitochondria define yeast longevity, outline the most important unanswered questions and suggest directions for future research.

Pharmacological regulation of the cholesterol transport machinery in steroidogenic cells of the testis

Reduced serum testosterone (T), or hypogonadism, is estimated to affect about 5 million American men, including both aging and young men. Low serum T has been linked to mood changes, worsening cognition, fatigue, depression, decreased lean body mass and bone mineral density, increased visceral fat, metabolic syndrome, decreased libido, and sexual dysfunction. Administering exogenous T, known as T-replacement therapy (TRT), reverses many of the symptoms of low T levels. However, this treatment can result in luteinizing hormone suppression which, in turn, can lead to reduced sperm numbers and infertility, making TRT inappropriate for men who wish to father children. Additionally, TRT may result in supraphysiologic T levels, skin irritation, and T transfer to others upon contact; and there may be increased risk of prostate cancer and cardiovascular disease, particularly in aging men. Therefore, the development of alternate therapies for treating hypogonadism would be highly desirable. To do so requires greater understanding of the series of steps leading to T formation and how they are regulated, and the identification of key steps that are amenable to pharmacological modulation so as to induce T production. We review herein our current understanding of mechanisms underlying the pharmacological induction of T formation in hypogonadal testis.

A-kinase-anchoring proteins coordinate inflammatory responses to cigarette smoke in airway smooth muscle

β2-Agonist inhibitors can relieve chronic obstructive pulmonary disease (COPD) symptoms by stimulating cyclic AMP (cAMP) signaling. A-kinase-anchoring proteins (AKAPs) compartmentalize cAMP signaling by establishing protein complexes. We previously reported that the β2-agonist fenoterol, direct activation of protein kinase A (PKA), and exchange factor directly activated by cAMP decrease cigarette smoke extract (CSE)-induced release of neutrophil attractant interleukin-8 (IL-8) from human airway smooth muscle (ASM) cells. In the present study, we tested the role of AKAPs in CSE-induced IL-8 release from ASM cells and assessed the effect of CSE on the expression levels of different AKAPs. We also studied mRNA and protein expression of AKAPs in lung tissue from patients with COPD. Our data show that CSE exposure of ASM cells decreases AKAP5 and AKAP12, both capable of interacting with β2-adrenoceptors. In lung tissue of patients with COPD, mRNA levels of AKAP5 and AKAP12 were decreased compared with lung tissue from controls. Using immunohistochemistry, we detected less AKAP5 protein in ASM of patients with COPD Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage II compared with control subjects. St-Ht31, which disrupts AKAP-PKA interactions, augmented CSE-induced IL-8 release from ASM cells and diminished its suppression by fenoterol, an effect mediated by disturbed ERK signaling. The modulatory role of AKAP-PKA interactions in the anti-inflammatory effects of fenoterol in ASM cells and the decrease in expression of AKAP5 and AKAP12 in response to cigarette smoke and in lungs of patients with COPD suggest that cigarette smoke-induced changes in AKAP5 and AKAP12 in patients with COPD may affect efficacy of pharmacotherapy.