Identification and characterization of D-AKAP1 as a major adipocyte PKA and PP1 binding protein

Department of Biological Sciences, University of Calgary, Calgary, Alta., Canada T2N 4N1.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 08/2006; 346(1):351-7. DOI: 10.1016/j.bbrc.2006.05.138
Source: PubMed


Protein kinase A (PKA) plays an important role in the regulation of lipid metabolism in adipocytes. The activity of PKA is known to be modulated by its specific location in the cell, a process mediated by A-kinase anchoring proteins (AKAPs). In order to examine the subcellular localization of PKA in this tissue we performed a search for AKAP proteins in adipocytes. We purified a 120 kDa protein which can bind both the regulatory subunit of PKA as well as the catalytic subunit of protein phosphatase 1 (PP1). This protein was found to be enriched in the lipid droplet fraction of primary adipocytes and was identified as D-AKAP1. This protein may play an important role in the regulation of PKA in adipocytes.

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    • "PKA-mediated phosphorylation of PLIN1 in vertebrates113 and LSD1 in insects12 activates TG hydrolysis. In vertebrates, lipolysis is catalyzed by the concerted action of at least PLIN1 proteins, three lipases (ATGL, HSL, MGL), a co-lipase (CGI58), and two separate pools of PKA.24,114 PKA proximal to plasma membrane phosphorylates HSL triggering the translocation to the surface of LD.22,115 The second PKA seems to be on the surface of LD116,117 apparently recruited by the protein OPA1.118 "
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    ABSTRACT: The main cells of the adipose tissue of animals, adipocytes, are characterized by the presence of large cytosolic lipid droplets (LDs), which store triglyceride (TG) and cholesterol. However, most cells have LDs and the ability to store lipids. LDs have a well-known central role in storage and provision of fatty acids and cholesterol. However, the complexity of the regulation of lipid metabolism on the surface of the LDs is still a matter of intense study. Beyond this role, a number of recent studies have suggested that LDs have major functions in other cellular processes, such as protein storage and degradation, and infection and immunity. Thus, our perception of LDs, from simple globules of fat to highly dynamic organelles of unexpected complexity, has been radically transformed. Here we compiled some recent evidence supporting the emerging view that LDs act as platforms connecting a number of relevant metabolic and cellular functions.
    Lipid Insights 05/2014; 7(1):7-16. DOI:10.4137/LPI.S11128
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    • "All AKAPs contain an A-kinase-binding (AKB) domain and a unique targeting domain directing the PKA–AKAP complex to defined subcellular structures, membranes or organelles (Carr et al, 1992; Wong and Scott, 2004; Gold et al, 2006; Kinderman et al, 2006; Pidoux and Tasken, 2010). Some studies have suggested the presence of AKAPs associated with lipid droplets to trigger lipolysis by discrete control of perilipin phosphorylation (Zhang et al, 2005; Bridges et al, 2006). However, no AKAP targeting a pool of PKA to lipid droplets and controlling the induction of lipolysis via phosphorylation of perilipin has been identified to date. "
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    ABSTRACT: Adrenergic stimulation of adipocytes yields a cAMP signal that activates protein kinase A (PKA). PKA phosphorylates perilipin, a protein localized on the surface of lipid droplets that serves as a gatekeeper to regulate access of lipases converting stored triglycerides to free fatty acids and glycerol in a phosphorylation-dependent manner. Here, we report a new function for optic atrophy 1 (OPA1), a protein known to regulate mitochondrial dynamics, as a dual-specificity A-kinase anchoring protein associated with lipid droplets. By a variety of protein interaction assays, immunoprecipitation and immunolocalization experiments, we show that OPA1 organizes a supramolecular complex containing both PKA and perilipin. Furthermore, by a combination of siRNA-mediated knockdown, reconstitution experiments using full-length OPA1 with or without the ability to bind PKA or truncated OPA1 fused to a lipid droplet targeting domain and cellular delivery of PKA anchoring disruptor peptides, we demonstrate that OPA1 targeting of PKA to lipid droplets is necessary for hormonal control of perilipin phosphorylation and lipolysis.
    The EMBO Journal 11/2011; 30(21):4371-86. DOI:10.1038/emboj.2011.365 · 10.43 Impact Factor
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    • "PAP7 strongly enhances hormone-induced steroidogenesis, although its direct effects on StAR expression or phosphorylation have yet to be examined. Interestingly , several protein phosphatases have been reported in complex with AKAP121, such as protein phosphatase 1 and protein tyrosine phosphatase D1 (Steen et al., 2003; Cardone et al., 2004; Bridges et al., 2006). Multiple phosphatases have been implicated in StAR expression and steroidogenesis; thus, it may prove useful to revisit the function of these enzymes were they shown to be in complex at the mitochondria (Sayed et al., 1998; Castillo et al., 2004). "
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    ABSTRACT: Steroid hormones are synthesized in the adrenal gland, gonads, placenta and brain and are critical for normal reproductive function and bodily homeostasis. The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroid biosynthesis, i.e. the delivery of cholesterol from the outer to the inner mitochondrial membrane. The expression of the StAR protein is predominantly regulated by cAMP-dependent mechanisms in the adrenal and gonads. Whereas StAR plays an indispensable role in the regulation of steroid biosynthesis, a complete understanding of the regulation of its expression and function in steroidogenesis is not available. It has become clear that the regulation of StAR gene expression is a complex process that involves the interaction of a diversity of hormones and multiple signaling pathways that coordinate the cooperation and interaction of transcriptional machinery, as well as a number of post-transcriptional mechanisms that govern mRNA and protein expression. However, information is lacking on how the StAR gene is regulated in vivo such that it is expressed at appropriate times during development and is confined to the steroidogenic cells. Thus, it is not surprising that the precise mechanism involved in the regulation of StAR gene has not yet been established, which is the key to understanding the regulation of steroidogenesis in the context of both male and female development and function.
    Molecular Human Reproduction 04/2009; 15(6):321-33. DOI:10.1093/molehr/gap025 · 3.75 Impact Factor
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