Internal Amino Acids Promote Gap1 Permease Ubiquitylation via TORC1/Npr1/14-3-3-Dependent Control of the Bul Arrestin-Like Adaptors

Molecular Physiology of the Cell, Université Libre de Bruxelles, IBMM, Gosselies, Belgium.
Molecular and Cellular Biology (Impact Factor: 4.78). 09/2012; 32(22). DOI: 10.1128/MCB.00463-12
Source: PubMed


Ubiquitylation of many plasma membrane proteins promotes their endocytosis followed by degradation in the lysosome. The yeast general amino acid permease, Gap1, is ubiquitylated and down-regulated when a good nitrogen source like ammonium is provided to cells growing on a poor nitrogen source. This ubiquitylation requires the Rsp5 ubiquitin ligase and the redundant arrestin-like Bul1 and Bul2 adaptors. Previous studies have shown that Gap1 ubiquitylation involves the TORC1 kinase complex, which inhibits the Sit4 phosphatase. This causes inactivation of the protein kinase Npr1, which protects Gap1 against ubiquitylation. However, the mechanisms inducing Gap1 ubiquitylation after Npr1 inactivation remain unknown. We here show that on a poor nitrogen source, the Bul adaptors are phosphorylated in an Npr1-dependent manner and bound to 14-3-3 proteins that protect Gap1 against down-regulation. After ammonium is added and converted to amino acids, the Bul proteins are dephosphorylated, dissociate from the 14-3-3 proteins, and undergo ubiquitylation. Furthermore, dephosphorylation of Bul requires the Sit4 phosphatase, which is essential to Gap1 down-regulation. The data support the emerging concept that permease ubiquitylation results from activation of the arrestin-like adaptors of the Rsp5 ubiquitin ligase, this coinciding with their dephosphorylation, dissociation from the inhibitory 14-3-3 proteins, and ubiquitylation.

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Available from: Bruno André, Jan 29, 2014
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    • "Previous studies suggest that -arrestins are activated by dephosphorylation (Macgurn et al., 2011; Becuwe et al., 2012b; Merhi and Andre, 2012; O'Donnell et al., 2013). Therefore, we proceeded to examine whether pH-dependent activation of the RIM pathway correlates with changes in the phosphorylation status of Rim8. "
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    • "It has recently been demonstrated that arrestinrelated trafficking adaptors (ARTs) in S. cerevisiae containing structurally conserved features with the mammalian arrestin proteins interact with Rsp5 and act as adaptor molecules for the ubiquitination of the nutrient transporters by the ubiquitin ligase to regulate their intracellular trafficking. Moreover, the ARTs are themselves ubiquitinated by Rsp5 (Lin et al., 2008; Nikko et al., 2008; Nikko and Pelham, 2009; O'Donnell et al., 2010; Hatakeyama et al., 2010; Merhi and André, 2012). "
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    Biology Open 05/2014; 3(6). DOI:10.1242/bio.20148367 · 2.42 Impact Factor
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    • "It is known that inactivation of TORC1 leads to Tap42-Sit4 dependent dephosphorylation of Npr1 (Schmidt, et al., 1998, Jacinto, et al., 2001, Gander, et al., 2008). Most recent work links Tap42-Sit4 dependent Npr1 dephosphorylation to its activation and subsequent phosphorylation of arrestin-like Bul proteins, which in turn inhibits endocytosis of Gap1 under nitrogen-limitation (Merhi & Andre, 2012). Although being an attractive model fitting with several observations, this model still fails to explain how under similar conditions Bul1,2-dependent vacuolar sorting of Tat2 can take place (Abe & Iida, 2003). "
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