Ribosomal Stress Couples the Unfolded Protein Response to p53-dependent Cell Cycle Arrest

Fang Zhang,Robert B Hamanaka,Ekaterina Bobrovnikova-Marjon,John D Gordan,Mu-Shui Dai,Hua Lu,M Celeste Simon,J Alan Diehl

doi:10.1074/jbc.m604674200

Abstract

Protein misfolding in the endoplasmic reticulum (ER) triggers a signaling pathway termed the unfolded protein response path-way (UPR). UPR signaling is transduced through the transmembrane ER effectors PKR-like ER kinase (PERK), inositol requiring kinase-1 (IRE-1), and activating transcription factor 6 (ATF6). PERK activation triggers phosphorylation of eIF2alpha leading to repression of protein synthesis, thereby relieving ER protein load and directly inhibiting cyclin D1 translation thereby contributing to cell cycle arrest. However, PERK(-/-) murine embryonic fibroblasts have an attenuated G(1)/S arrest that is not attributable to cyclin D1 loss, suggesting a cyclin D1-independent mechanism. Here we show that the UPR triggers p53 accumulation and activation. UPR induction promotes enhanced interaction between the ribosome proteins (rpL5, rpL11, and rpL23) and Hdm2 in a PERK-dependent manner. Interaction with ribosomal proteins results in inhibition of Hdm2-mediated ubiquitination and degradation of p53. Our data demonstrate that ribosomal subunit:Hdm2 association couples the unfolded protein response to p53-dependent cell cycle arrest.

Highlights

endoplasmic reticulum (ER) Stress Triggers p53 Activation and p21Cip1 Induction—To evaluate the impact of ER stress on p53 accumulation and induction of downstream targets, p53-proficient HCT116 cells were cultured in glucose-free media or in complete media supplemented with 5 ␮g/ml tunicamycin and analyzed by immunoblot
The cyclin D1/CDK4 kinase is one of two kinases that promote G1 to S-phase transition; the cyclin E/CDK2 kinase participates in this process
Cyclin E levels are maintained following ER stress suggesting that inhibition of CDK2 likely results from increased association with inhibitors such as p21Cip1 or p27Kip1

Summary

Introduction

Our data reveal that UPR induction by glucose deprivation or tunicamycin treatment triggers p53 accumulation and activation in a PERK-dependent manner. Glucose Deprivation Activates p53 in a PERK-dependent Manner—We have previously demonstrated that the ER-associated kinase, PERK, plays a critical role in the regulation of cell cycle progression following ER stress (17, 18). Dominant negative PERK (DN PERK) was expressed in p53ϩ/ϩ HCT116 cells, and p53 and p21Cip1 protein levels were assessed by immunoblot following a time course of tunicamycin treatment (data not shown) or glucose starvation.

Results

Conclusion