Phosphorylation Status of Nuclear Ribosomal Protein S3 Is Reciprocally Regulated by Protein Kinase Cδ and Protein Phosphatase 2A

Tae-Sung Kim,Hag Dong Kim,Hyun-Seock Shin,Joon Kim

doi:10.1074/jbc.m109.018168

Abstract

It has been shown previously that ribosomal protein S3 (rpS3) has an endonuclease activity, which is increased by protein kinase Cdelta (PKCdelta)-dependent phosphorylation. However, the reciprocal mechanism for rpS3 dephosphorylation is not known. In this study, we examined phosphatases involved in rpS3 dephosphorylation, and we determined that rpS3 is specifically dephosphorylated by protein phosphatase 2A (PP2A). By immunoprecipitation assay, rpS3 only interacted with PP2Ac but not with protein phosphatase 1. The interaction between rpS3 and PP2Ac occurred only in the nuclear fraction. Moreover, the PP2Ac association with rpS3 was identified in cells transfected with wild-type rpS3 but not with mutant rpS3 lacking PKCdelta phosphorylation sites. PP2A inhibition using okadaic acid induced rpS3 phosphorylation. The level of phosphorylated rpS3 in cells was decreased by the overexpression of PP2Ac and was increased by the down-regulation of PP2Ac. Taken together, these results suggest that oxidative stress regulates the phosphorylation status of nonribosomal rpS3 by both activating PKCdelta and blocking the PP2A interaction with rpS3.

Highlights

Ribosomal protein S3 is a component of the 40 S small ribosomal subunit and is associated with protein synthesis
These results indicate that the level of (Fig. 7A, lane 3). These results suggest that phosphatase 2A (PP2A) interacts with phosphorylated Ribosomal protein S3 (rpS3) is regulated by PKC␦-dependent nonribosomal free rpS3 and that okadaic acid (OA) abrogates the interaction. phosphorylation and PP2A accessibility
We previously reported that PKC␦ phosphorylated two residues on rpS3, serine 6 and threonine 221, and that this phosphorylation was only detected in nonribosomal rpS3 and not in ribosome-associated rpS3 (22)

Summary

Introduction

Ribosomal protein S3 (rpS3) is a component of the 40 S small ribosomal subunit and is associated with protein synthesis. These results indicate that the phosphorylation status of rpS3 is regulated by both PKC␦ and PP2A. We obtained similar results using H2O2 and Ara-C treatments indicating that the interaction between rpS3 and PP2Ac decreases in a time-dependent manner (Fig. 3).

Results

Conclusion