Nuclear translocation of Gln3 in response to nutrient signals requires Golgi-to-endosome trafficking in Saccharomyces cerevisiae

Abstract

The yeast Saccharomyces cerevisiae has developed specialized mechanisms that enable growth on suboptimal nitrogen sources. Exposure of yeast cells to poor nitrogen sources or treatment with the Tor kinase inhibitor rapamycin elicits activation of Gln3 and transcription of nitrogen catabolite-repressed (NCR) genes whose products function in scavenging and metabolizing nitrogen. Here, we show that mutations in class C and D Vps components, which mediate Golgi-to-endosome vesicle transport, impair nuclear translocation of Gln3, NCR gene activation, and growth in poor nitrogen sources. In nutrient-replete conditions, a significant fraction of Gln3 is peripherally associated with light membranes and partially colocalizes with Vps10-containing foci. These results reveal a role for Golgi-to-endosome vesicular trafficking in TORC1-controlled nuclear translocation of Gln3 and support a model in which Tor-mediated signaling in response to nutrient cues occurs in these compartments. These findings have important implications for nutrient sensing and growth control via mTor pathways in metazoans.rapamycin action ͉ Tor signaling

Distinct Phosphatase Requirements and GATA Factor Responses to Nitrogen Catabolite Repression and Rapamycin Treatment in Saccharomyces cerevisiae

“…(vii) Gln3-Myc 13 is not uniformly distributed in the cytoplasm of cells grown under repressive conditions but is associated with a cytoplasmic membrane system (49,50). Extending this observation, nuclear Gln3 localization in derepressive conditions was found to require several components that participate in Golgi-to-endosome vesicle transport (51).…”

Endolysosomal Membrane Trafficking Complexes Drive Nutrient-Dependent TORC1 Signaling to Control Cell Growth in Saccharomyces cerevisiae

“…The Vps-C complex is thought to promote amino acid homeostasis through several mechanisms. First, the Vps-C complex affects amino acid transporter expression and stability (Srivastava et al 2000;Puria et al 2008). Second, Vps-C complexes maintain vacuole integrity, and this organelle plays a key role in storage of amino acids that are acquired from the cytosol or produced directly at the vacuole by protein degradation during the normal recycling of proteins or autophagy (Wiemken and Durr 1974;Kitamoto et al 1988a;Onodera and Ohsumi 2005).…”

Vps Factors Are Required for Efficient Transcription Elongation in Budding Yeast

“…Like vps15D and vps34D, these other five vps mutants are also defective for vesicular protein transport from the Golgi to the vacuole (Bowers and Stevens 2005). Vps10 is an integral membrane protein that functions as the receptor for carboxypeptidase Y to mediate its trafficking from the late Golgi to late endosome (Bowers and Stevens 2005); and it was recently implicated in promoting nuclear entry of Gln3 (Puria et al 2008); however, eliminating the VPS10 gene conferred no sensitivity to 6-AU or MPA ( Figure 1C). Sensitivity to 6-AU and MPA does not necessarily indicate a transcription elongation defect; however, mutations in bona fide elongation factors have been found to reduce transcriptional induction of IMD2, encoding an MPA-resistant form of IMPDH (McPhillips et al 2004), in response to 6-AU or MPA treatment (Riles et al 2004).…”

“…The Ga subunit (Gpa1) of a heterotrimeric G protein activates the PI 3-kinase Vps34 (a class D Vps factor) at the endosomal membrane to promote the transcriptional response to mating factors (Slessareva et al 2006). Activation of genes for utilization of alternative nitrogen sources by Gln3 is enhanced by Vps factors, and it appears that Gln3 must traffic in vesicles containing Vps10 between Golgi and endosome for subsequent nuclear entry (Puria et al 2008). Recently, evidence was presented that the phosphoinositide PI(3,5)P 2 , produced at the late endosome promotes assembly of a transcriptional cofactor complex that enhances galactose induction of GAL gene transcription in the nucleus (Han and Emr 2011).…”