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

Abstract

c TOR proteins reside in two distinct complexes, TOR complexes 1 and 2 (TORC1 and TORC2), that are central for the regulation of cellular growth, proliferation, and survival. TOR is also the target for the immunosuppressive and anticancer drug rapamycin. In Schizosaccharomyces pombe, disruption of the TSC complex, mutations in which can lead to the tuberous sclerosis syndrome in humans, results in a rapamycin-sensitive phenotype under poor nitrogen conditions. We show here that the sensitivity to rapamycin is mediated via inhibition of TORC1 and suppressed by overexpression of isp7 ؉ , a member of the family of 2-oxoglutarate-Fe(II)-dependent oxygenase genes. The transcript level of isp7 ؉ is negatively regulated by TORC1 but positively regulated by TORC2. Yet we find extensive similarity between the transcriptome of cells disrupted for isp7؉ and cells mutated in the catalytic subunit of TORC1. Moreover, Isp7 regulates amino acid permease expression in a fashion similar to that of TORC1 and opposite that of TORC2. Overexpression of isp7 ؉ induces TORC1-dependent phosphorylation of ribosomal protein Rps6 while inhibiting TORC2-dependent phosphorylation and activation of the AGC-like kinase Gad8. Taken together, our findings suggest a central role for Isp7 in amino acid homeostasis and the presence of isp7 ؉ -dependent regulatory loops that affect both TORC1 and TORC2.

TORC1 Regulates Developmental Responses to Nitrogen Stress via Regulation of the GATA Transcription Factor Gaf1

“…Isp7 is a member of the family of 2-oxoglutarate-Fe(II)-dependent oxygenases. Isp7 regulates amino acid uptake through transcription regulation of general and specific amino acid permeases ( 27 ). The transcript of isp7 + is strongly upregulated following inactivation of TORC1 or in response to nitrogen stress (complete withdrawal of nitrogen from the growth medium or its replacement with a poor nitrogen source) ( 27 ).…”

“…Isp7 regulates amino acid uptake through transcription regulation of general and specific amino acid permeases ( 27 ). The transcript of isp7 + is strongly upregulated following inactivation of TORC1 or in response to nitrogen stress (complete withdrawal of nitrogen from the growth medium or its replacement with a poor nitrogen source) ( 27 ). However, isp7 + suppresses the induction of many nitrogen stress-induced genes, similarly to TORC1 ( 27 ).…”

“…The transcript of isp7 + is strongly upregulated following inactivation of TORC1 or in response to nitrogen stress (complete withdrawal of nitrogen from the growth medium or its replacement with a poor nitrogen source) ( 27 ). However, isp7 + suppresses the induction of many nitrogen stress-induced genes, similarly to TORC1 ( 27 ). Consistently, isp7 + positively regulates TORC1 activity, and its overexpression results in activation of TORC1 under nitrogen stress conditions.…”

Rapid regulation of nuclear proteins by rapamycin‐induced translocation in fission yeast

“…pombe is not sensitive to rapamycin (Otsubo and Yamamato, 2008; Figure 2A). However, to eliminate competition from the endogenous TOR signalling system, we used a strain with a deletion of fkh1 + (eliminating the native FKBP12 domain) and combined this with tor1-S1834E (tor1SE) (Laor et al, 2014;Weisman et al, 2005). Mutation of the conserved serine (S) residue in the FRB domain of Tor1 to glutamic acid (E) residue dramatically reduces the interaction with Fkh1 in the presence of rapamycin (Weisman et al, 2005).…”

Genetic Analysis of Four Sexual Differentiation Process Proteins (isp4/SDPs) in Chaetomium thermophilum and Thermomyces lanuginosus Reveals Their Distinct Roles in Development

“…In S. pombe, five isp genes (isp3-isp7) were identified and they were preferentially expressed during sporogensis. Further study revealed that they were involved in diverse biological/biochemical functions (Yanagida, 2009;Shimanuki et al, 2010;Laor et al, 2014). Isp4 has been found up-regulated by nitrogen starvationinduced meiosis and found to encode an oligopeptide transporter (OPT).…”