A Measurable Activation of the bZIP Transcription Factor Atf1 in a Fission Yeast Strain Devoid of Stress-activated and Cell Integrity Mitogen-activated Protein Kinase (MAPK) Activities

Xin Zhou,Yan Ma,Toshiaki Kato,Takayoshi Kuno

doi:10.1074/jbc.c111.338715

Abstract

In Schizosaccharomyces pombe, the stress-activated Sty1 MAPK pathway is essential for cell survival under stress conditions. The Sty1 MAPK regulates Atf1 transcription factor to elicit stress responses in extreme conditions of osmolarity and reactive oxygen species-generating agents such as hydrogen peroxide, heat, low glucose, and heavy metal. Herein, using a newly developed Renilla luciferase reporter assay with enhanced detection sensitivity and accuracy, we show that distinct signaling pathways respond to cadmium and other reactive oxygen species-generating agents for the activation of Atf1. Also, surprisingly, a measurable activation of Atf1 transcription factor was still observed devoid of Sty1 MAPK activity. Further genetic and biological analyses revealed that the residual activation is caused by the activation of the cell wall integrity Pmk1 MAPK pathway and a redox-mediated activation of Atf1.

Highlights

Activation of Atf1 is regulated by the Sty1 mitogen-activated protein kinase (MAPK) under multiple stresses, and the Pmk1 MAPK is suggested to regulate the activity of Atf1
The results show that distinct signaling pathways respond to cadmium and other ROS-generating agents for the activation of Atf1 and, surprisingly, that Atf1 transcription factor can still be activated by different extracellular stress agents independently of the activation of the Sty1 MAPK pathway
Our previous data obtained by using the firefly luciferase reporter assay suggest that the protein tyrosine phosphatase Pyp1 is responsible for sensing and transmitting the signals to Sty1 MAPK upon treatment with CdCl2 or LG [13]

Summary

Introduction

Activation of Atf1 is regulated by the Sty1 MAPK under multiple stresses, and the Pmk1 MAPK is suggested to regulate the activity of Atf1. In wild-type cells, various kinds of stresses caused various patterns of increase in response, and in ⌬atf1 cells, there was no response upon any treatment (Fig. 1B), indicating that the 3xCRE::Renilla reporter assay reflects the Atf1 activity.

Results

Conclusion