The Yeast Tor Signaling Pathway Is Involved in G2/M Transition via Polo-Kinase

Abstract

The target of rapamycin (Tor) protein plays central roles in cell growth. Rapamycin inhibits cell growth and promotes cell cycle arrest at G1 (G0). However, little is known about whether Tor is involved in other stages of the cell division cycle. Here we report that the rapamycin-sensitive Tor complex 1 (TORC1) is involved in G2/M transition in S. cerevisiae. Strains carrying a temperature-sensitive allele of KOG1 (kog1-105) encoding an essential component of TORC1, as well as yeast cell treated with rapamycin show mitotic delay with prolonged G2. Overexpression of Cdc5, the yeast polo-like kinase, rescues the growth defect of kog1-105, and in turn, Cdc5 activity is attenuated in kog1-105 cells. The TORC1-Type2A phosphatase pathway mediates nucleocytoplasmic transport of Cdc5, which is prerequisite for its proper localization and function. The C-terminal polo-box domain of Cdc5 has an inhibitory role in nuclear translocation. Taken together, our results indicate a novel function of Tor in the regulation of cell cycle and proliferation.

Tor Directly Controls the Atg1 Kinase Complex To Regulate Autophagy

“…Using these criteria, we chose four Ser residues (S348, VOL. 30,2010 Tor DIRECTLY CONTROLS THE Atg1 KINASE COMPLEX 1051 S496, S535, and S541) in addition to the identified serines (Fig. 1C).…”

“…The yeast strains and plasmids used in this study are listed in Tables 1 and 2, respectively. Standard techniques were used for yeast manipulation (30). The replacement of Ser residues with Ala to generate the ATG13-SA alleles was performed by PCR-mediated mutagenesis using QuikChange (Stratagene, La Jolla, CA).…”

“…Immunoprecipitation and kinase assay for TORC1 were performed as described previously with some modifications (18,30).…”

Recovery from Rapamycin

“…Haploid cells containing kog1 ts as the sole allele were created by transforming kog1⌬/KOG1 diploids with pRS313(kog1-105) (21). After sporulation, haploid kog1⌬ pRS313(kog1-105) transformants were isolated by tetrad dissection using a standard protocol.…”

TOR under stress: Targeting TORC1 by Rho1 GTPase

“…To determine whether TORC1 also mediates the effect of nitrogen starvation on Rho1 activity, we employed a temperature-sensitive mutant of KOG1. 39 After inactivation of TORC1 by shifting the mutant cells to the nonpermissive temperature, we found that the Rho1-mediated CWI pathway was no longer responsive to nitrogen starvation, indicating that TORC1 mediates the effect of nitrogen starvation on the pathway.…”