Protein kinase Cµ plays an essential role in hypertonicity-induced heat shock protein 70 expression

Yun-Sook Lim,Jae-Seon Lee,Tai-Qin Huang,Jeong-Sun Seo

doi:10.3858/emm.2008.40.6.596

Yun-Sook Lim, Jae-Seon Lee + Show 2 more

Open Access

https://doi.org/10.3858/emm.2008.40.6.596

Copy DOI

Abstract

Heat shock protein 70 (HSP70), which evidences important functions as a molecular chaperone and anti-apoptotic molecule, is substantially induced in cells exposed to a variety of stresses, including hypertonic stress, heavy metals, heat shock, and oxidative stress, and prevents cellular damage under these conditions. However, the molecular mechanism underlying the induction of HSP70 in response to hypertonicity has been characterized to a far lesser extent. In this study, we have investigated the cellular signaling pathway of HSP70 induction under hypertonic conditions. Initially, we applied a variety of kinase inhibitors to NIH3T3 cells that had been exposed to hypertonicity. The induction of HSP70 was suppressed specifically by treatment with protein kinase C (PKC) inhibitors (Gö6976 and GF109203X). As hypertonicity dramatically increased the phosphorylation of PKCmu, we then evaluated the role of PKCmu in hypertonicity-induced HSP70 expression and cell viability. The depletion of PKCmu with siRNA or the inhibition of PKCmu activity with inhibitors resulted in a reduction in HSP70 induction and cell viability. Tonicity-responsive enhancer binding protein (TonEBP), a transcription factor for hypertonicity-induced HSP70 expression, was translocated rapidly into the nucleus and was modified gradually in the nucleus under hypertonic conditions. When we administered treatment with PKC inhibitors, the mobility shift of TonEBP was affected in the nucleus. However, PKCmu evidenced no subcellular co-localization with TonEBP during hypertonic exposure. From our results, we have concluded that PKCmu performs a critical function in hypertonicity-induced HSP70 induction, and finally cellular protection, via the indirect regulation of TonEBP modification.

Highlights

Because all organisms face environmental and pathophysiological stresses, they need to develop appropriate protective mechanisms
As ERK and p38 were activated in cells exposed to hypertonic conditions (Figure 1B), we attempted to determine whether ERK or p38 were involved in hypertonicity-induced Heat shock protein 70 (HSP70) expression
When cells were treated with a broad range of protein kinase C (PKC) inhibitor (GF109203X), hypertonicity-induced HSP70 expression was inhibited completely (Figure 1E)

Summary

Introduction

Because all organisms face environmental and pathophysiological stresses, they need to develop appropriate protective mechanisms. HSP70 synthesis has been identified in response to a broad range of chemicals and biological signals, including hypertonic stress, amino acid analogues, energy metabolism inhibitors, radiation, oxidative stress, and heavy metals (Williams and Morimoto, 1990; Hatayama et al, 1993; Abe et al, 1995; Wagner et al, 1999). This means that HSP70 is involved in a general cellular defense mechanism. The cytoprotective roles of HSP70 were clearly identified and the molecular mechanisms inherent to the anti-apoptotic function of HSP70 were clearly elucidated (Beere et al, 2000; Li et al, 2000; Ravagnan et al, 2001; Lee et al, 2005)

Objectives

Methods

Results

Conclusion