Cyclic AMP-Independent Regulation of Protein Kinase A Substrate Phosphorylation by Kelch Repeat Proteins

Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, Box 1603, 1 Gustave L. Levy Place, New York, NY 10029, USA.
Eukaryotic Cell (Impact Factor: 3.18). 12/2005; 4(11):1794-800. DOI: 10.1128/EC.4.11.1794-1800.2005
Source: PubMed

ABSTRACT Pseudohyphal and invasive growth in the yeast Saccharomyces cerevisiae is regulated by the kelch repeat-containing proteins Gpb1p and Gpb2p, which act downstream of the G protein alpha-subunit Gpa2p. Here we show that deletion of GPB1 and GPB2 causes increased haploid invasive growth in cells containing any one of the three protein kinase A (PKA) catalytic subunits, suggesting that Gpb1p and Gpb2p are able to inhibit each of these kinases. Cells containing gpb1Delta gpb2Delta mutations also display increased phosphorylation of the PKA substrates Sfl1p and Msn2p, indicating that Gpb1p and Gpb2p are negative regulators of PKA substrate phosphorylation. Stimulation of PKA-dependent signaling by gpb1Delta gpb2Delta mutations occurs in cells that lack both adenylyl cyclase and the high-affinity cyclic AMP (cAMP) phosphodiesterase. This effect is also seen in cells that lack the low-affinity cAMP phosphodiesterase. Given that these three enzymes control the synthesis and degradation of cAMP, these results indicate that the effect of Gpb1p and Gpb2p on PKA substrate phosphorylation does not occur by regulating the intracellular cAMP concentration. These findings suggest that Gpb1p and Gpb2p mediate their effects on the cAMP/PKA signaling pathway either by inhibiting the activity of PKA in a cAMP-independent manner or by activating phosphatases that act on PKA substrates.

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    • "proteins, Krh1 and Krh2, which were also called Gpb2 and Gpb1, referring to a possible role as Gβ subunit for Gpa2 (Harashima & Heitman, 2002). Later work, however, showed that these proteins function in an adenylate cyclase bypass pathway, allowing direct activation of PKA by activated Gpa2 (Lu & Hirsch, 2005, Peeters, et al., 2006). The kelch repeat proteins directly bind to the catalytic subunits of PKA and thereby stimulate association of the catalytic and regulatory subunits of PKA, lowering PKA activity. "
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    ABSTRACT: The yeast Saccharomyces cerevisiae has been a favorite organism for pioneering studies on nutrient-sensing and signaling mechanisms. Many specific nutrient responses have been elucidated in great detail. This has led to important new concepts and insight into nutrient-controlled cellular regulation. Major highlights include the central role of the Snf1 protein kinase in the glucose repression pathway, galactose induction, the discovery of a G-protein coupled receptor system and role of Ras in glucose-induced cAMP signaling, the role of the protein synthesis initiation machinery in general control of nitrogen metabolism, the cyclin-controlled protein kinase Pho85 in phosphate regulation, nitrogen catabolite repression and the nitrogen-sensing TOR pathway, and the discovery of transporter-like proteins acting as nutrient sensors. In addition, a number of cellular targets, like carbohydrate stores, stress tolerance and ribosomal gene expression, are controlled by the presence of multiple nutrients. The PKA signaling pathway plays a major role in this general nutrient response. It has led to the discovery of nutrient transceptors (transporter-receptors) as nutrient sensors. Major shortcomings in our knowledge are the relationship between rapid and steady-state nutrient signaling, the role of metabolic intermediates in intracellular nutrient sensing and the identity of the nutrient sensors controlling cellular growth. This article is protected by copyright. All rights reserved.
    FEMS microbiology reviews 02/2014; 38(2). DOI:10.1111/1574-6976.12065 · 13.24 Impact Factor
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    • "However, substantial evidence has accumulated discounting Gpb1/Gpb2 as b subunits (Peeters et al. 2007), including the fact that the site on Gpa2 at which the proteins bind does not correspond to the classic Gb-binding domain (Niranjan et al. 2007). Nonetheless , Gpb1 and Gpb2 play redundant roles in negatively regulating the activity of the Ras/PKA pathway, either by interference with the Gpr1/Gpa2 interaction (Harashima and Heitman 2005), or through stabilization of the Ras– GAP proteins, Ira1 and Ira2 (Harashima et al. 2006), or by stabilization of the interaction between the regulatory subunit, Bcy1, and the catalytic subunits, Tpk1–3, of protein kinase A (Lu and Hirsch 2005; Peeters et al. 2006; Budhwar et al. 2010), or by some combination of all three mechanisms. One should note that the studies on Gpr1, Gpa2, and Gpb1/2 have not examined the dynamic nature of these components in the context of signal transduction. "
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    ABSTRACT: Availability of key nutrients, such as sugars, amino acids, and nitrogen compounds, dictates the developmental programs and the growth rates of yeast cells. A number of overlapping signaling networks-those centered on Ras/protein kinase A, AMP-activated kinase, and target of rapamycin complex I, for instance-inform cells on nutrient availability and influence the cells' transcriptional, translational, posttranslational, and metabolic profiles as well as their developmental decisions. Here I review our current understanding of the structures of the networks responsible for assessing the quantity and quality of carbon and nitrogen sources. I review how these signaling pathways impinge on transcriptional, metabolic, and developmental programs to optimize survival of cells under different environmental conditions. I highlight the profound knowledge we have gained on the structure of these signaling networks but also emphasize the limits of our current understanding of the dynamics of these signaling networks. Moreover, the conservation of these pathways has allowed us to extrapolate our finding with yeast to address issues of lifespan, cancer metabolism, and growth control in more complex organisms.
    Genetics 09/2012; 192(1):73-105. DOI:10.1534/genetics.111.135731 · 5.96 Impact Factor
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    • "Further control on PKA is exerted by the kelch repeat proteins Gpb1 and Gpb2 that act via Ras2 or Gpa2 or that directly antagonize PKA ( Harashima & Heitman , 2002 ; Batlle et al . , 2003 ; Lu & Hirsch , 2005 ; Harashima et al . , 2006 ; Peeters et al . "
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    ABSTRACT: The budding yeast Saccharomyces cerevisiae is a eukaryotic microorganism that is able to choose between different unicellular and multicellular lifestyles. The potential of individual yeast cells to switch between different growth modes is advantageous for optimal dissemination, protection and substrate colonization at the population level. A crucial step in lifestyle adaptation is the control of self- and foreign adhesion. For this purpose, S. cerevisiae contains a set of cell wall-associated proteins, which confer adhesion to diverse biotic and abiotic surfaces. Here, we provide an overview of different aspects of S. cerevisiae adhesion, including a detailed description of known lifestyles, recent insights into adhesin structure and function and an outline of the complex regulatory network for adhesin gene regulation. Our review shows that S. cerevisiae is a model system suitable for studying not only the mechanisms and regulation of cell adhesion, but also the role of this process in microbial development, ecology and evolution.
    FEMS microbiology reviews 04/2011; 36(1):25-58. DOI:10.1111/j.1574-6976.2011.00275.x · 13.24 Impact Factor
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