Fission yeast Any1, β-arrestin-like protein, is involved in TSC-Rheb signaling and the regulation of amino acid transporters

Abstract

SummaryRheb GTPase and the Tsc1-Tsc2 protein complex, which serves as a GTPase-activating protein for Rheb, have crucial roles in the regulation of cell growth in response to extracellular conditions. In Schizosaccharomyces pombe, Rheb and Tsc1-Tsc2 regulate cell cycle progression, the onset of meiosis and the uptake of amino acids. In cells lacking Tsc2 (Dtsc2), the amino acid transporter Aat1, which is normally expressed on the plasma membrane under starvation conditions, is confined to the Golgi. Here, we show that the loss of either pub1 + , encoding an E3 ubiquitin ligase, or any1 + , encoding a b-arrestin-like protein, allows constitutive expression of Aat1 on the plasma membrane in Dtsc2 cells, suggesting that Pub1 and Any1 are required for localization of Aat1 to the Golgi. Subsequent analysis revealed that, in the Golgi, Pub1 and Any1 form a complex that ubiquitylates Aat1. Physical interaction of Pub1 and Any1 is more stable in Dtsc2 cells than in wild-type cells and is independent of Tor2 activity. These results indicate that the TSC-Rheb signaling pathway regulates the localization of amino acid transporters via Pub1 and Any1 in a Tor2-independent manner. Our study demonstrates that, unlike in budding yeast (in which Rsp5 and ARTs, a pair of proteins analogous to Pub1 and Any1, respectively, primarily act to reduce expression of the transporters on plasma membrane when nutrients are abundant), the primary role of fission yeast Pub1 and Any1 is to store the transporter in the Golgi under nutrient-rich conditions.

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

“…TSC (Tsc2) is also required for proline uptake. Thus, with respect to amino acid uptake, TORC1 and TSC play a positive role irrespective of the nature of the amino acid, suggesting that TORC1 and TSC regulate amino acid uptake at a posttranscriptional and/or subcellular localization level, in accord with recent findings (53,60).…”

Fission yeast arrestin-related trafficking adaptor, Arn1/Any1, is ubiquitinated by Pub1 E3 ligase and regulates endocytosis of Cat1 amino acid transporter

“…We therefore named SPBC18H10.20c arn1 + ( ar resti n 1) and carried out the following experiments. While we were preparing this manuscript, Nakase et al have independently identified SPBC18H10.20c as a gene whose mutation suppressed a growth defect of tsc2 Δ caused by a failure of leucine uptake and referred to this gene product as Any1 (Nakase et al, 2013; see Discussion). S. pombe possesses one homologous protein to Arn1, which is encoded by SPAC1F12.05, and it shares 38% identity and 57% similarity to Arn1.…”

“…As described above, Nakase et al independently reported that Arn1/Any1 (they named SPBC18H10.20c Any1) regulates subcellular distribution of some transporters including Aat1, an S. pombe homolog of S. cerevisiae general amino acid transporter Gap1 (Nakase et al, 2010; Nakase et al, 2013). However, Cat1 was not characterized.…”

“…We identified arn1 + as a gene whose high-copy expression confers canavanine resistance on wild-type cells using a S. pombe genomic library (Fig. 1), whereas any1 + was isolated in a screening for mutations that restore a growth defect of tsc2 Δ owing to a failure of leucine uptake (Nakase et al, 2013). 2) We demonstrated that Arn1 is ubiquitinated probably at Lys263 by Pub1 E3 ubiquitin ligase and that its ubiquitination is important for regulation of Cat1 endocytosis (Fig.…”

“…5B,C). 3) Nakase et al concluded that Any1 is required to store Aat1 in the Golgi and that deletion of any1 + mislocalizes the transporter to the PM (Nakase et al, 2013). By contrast, our findings revealed that Arn1 is required for Cat1 endocytosis in response to environmental conditions.…”