Adenylyl cyclase--A-kinase anchoring protein complexes: the next dimension in cAMP signaling.
ABSTRACT The formation of multiprotein complexes is a repeated theme in biology ranging from the regulation of the extracellular signal-regulated kinase and cAMP signaling pathways to the formation of postsynaptic density complexes or tight junctions. A-kinase anchoring proteins (AKAPs) are well known for their ability to scaffold protein kinase A and components upstream and downstream of cAMP production, including G protein-coupled receptors, cAMP-dependent Rap-exchange factors, and phosphodiesterases. Specific adenylyl cyclase (AC) isoforms have also been identified as components of AKAP complexes, namely AKAP79, Yotiao, and mAKAP. In this review, we summarize recent evidence for AC-AKAP complexes and requirements for compartmentalization of cAMP signaling. The ability of AKAPs to assemble intricate feedback loops to control spatiotemporal aspects of cAMP signaling adds yet another dimension to the classic cAMP pathway.
Article: Adenylyl cyclase type 6 overexpression selectively enhances beta-adrenergic and prostacyclin receptor-mediated inhibition of cardiac fibroblast function because of colocalization in lipid rafts.[show abstract] [hide abstract]
ABSTRACT: Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Fibroblasts are activated by factors such as transforming growth factor beta and inhibited by agents that elevate 3',5'-cyclic adenosine monophosphate (cAMP) levels. cAMP signal generation and response is known to be compartmentalized in many cell types in part through the colocalization of receptors and specific adenylyl cyclase isoforms in lipid rafts and caveolae. The present study sought to define the localization of key G protein-coupled receptors with adenylyl cyclase type 6 (AC6) in lipid rafts of rat cardiac fibroblasts and to determine if this colocalization was functionally relevant. We found that cardiac fibroblasts produce cAMP in response to agonists for beta-adrenergic (isoproterenol), prostaglandin EP2 (butaprost), adenosine (adenosine-5'-N-ethylcarboxamide, NECA), and prostacyclin (beraprost) receptors. Overexpression of AC6 increased cAMP production stimulated by isoproterenol and beraprost but not by butaprost or NECA. A key function of fibroblasts is the production of collagen. Isoproterenol- and beraprostmediated inhibition of collagen synthesis was also enhanced by AC6 overexpression, while inhibition by butaprost and NECA were unaltered. Lipid raft fractions from cardiac fibroblasts contain the preponderance of beta-adrenergic receptors and AC6 but exclude EP2 receptors. While we could not determine the localization of native prostacyclin receptors, we were able to determine that epitope-tagged prostanoid IP receptors (IPR) expressed in COS7 cells did localize, in part, in lipid raft fractions. These findings indicate that IP receptors are expressed in lipid rafts and can activate raft-localized AC isoforms. AC6 is completely compartmentized in lipid raft domains where it is activated solely by coresident G protein-coupled receptors to regulate cardiac fibroblast function.Archiv für Experimentelle Pathologie und Pharmakologie 07/2008; 377(4-6):359-69. · 2.65 Impact Factor
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ABSTRACT: The AKAP gravin is a scaffold for protein kinases, phosphatases, and adaptor molecules obligate for resensitization and recycling of beta2-adrenergic receptors. Gravin binds to the receptor through well characterized protein-protein interactions. These interactions are facilitated approximately 1000-fold when gravin is anchored to the cytoplasmic leaflet of the plasma membrane. Although the N-terminal region (approximately 550 residues) is highly negatively charged and probably natively unfolded, it could anchor gravin to the inner leaflet through hydrophobic insertion of its N-terminal myristate and electrostatic binding of three short positively charged domains (PCDs). Loss of the site of N-myristoylation was found to affect neither AKAP macroscopic localization nor AKAP function. Synthetic peptides corresponding to PCD1-3 bound in vitro to unilamellar phospholipid vesicles with high affinity, a binding reversed by calmodulin in the presence of Ca2+. In vivo gravin localization is regulated by intracellular Ca2+, a function mapping to the N terminus of the protein harboring PCD1, PCD2, and PCD3. Mutation of any two PCDs eliminates membrane association of the non-myristoylated gravin, the sensitivity to Ca2+/calmodulin, and the ability of this scaffold to catalyze receptor resensitization and recycling.Journal of Biological Chemistry 09/2006; 281(33):23932-44. · 4.77 Impact Factor
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ABSTRACT: Recurrent vaginal candidiasis (RVC) is an important health problem with unknown pathogenesis. Although impairment of the T-cell response is associated with persistent or recurrent candidiasis, data on immunologic responses in patients with RVC are controversial. To evaluate the T-cell response in patients with RVC and the ability of cytokines and cytokine antagonists to modulate IFN-gamma production in cultures stimulated with Candida albicans antigens. Participants in the study included 13 patients with RVC and 7 control women with sporadic candidiasis. Cytokines were determined by ELISA in supernatants of mononuclear cells with C albicans, purified protein derivative, or tetanus toxoid antigen. IFN-gamma production was absent or low in 11 of 13 women (84.6%) with RVC. Absent or low IFN-gamma production was specific to C albicans antigens (189 +/- 389 pg/mL), because high IFN-gamma levels were found in cultures stimulated with purified protein derivative (739 +/- 774 pg/mL) or tetanus toxoid antigens (1085 +/- 546 pg/mL). Monoclonal antibody anti-IL-10 enhanced IFN-gamma levels (750 +/- 753 pg/mL), and IL-10 suppressed this cytokine production in patients with sporadic candidiasis. Mononuclear cells from patients with RVC stimulated with C albicans antigen have low or absent IFN-gamma production. IL-10 plays an important role in downregulation of the T-cell response in these patients.Journal of Allergy and Clinical Immunology 02/2002; 109(1):102-5. · 11.00 Impact Factor