Heat shock protein 70-mediated sensitization of cells to apoptosis by Carboxyl-Terminal Modulator Protein

Longzhen Piao,Jongsun Park,Brian A Hemmings,Ragna Sack,Gang Min Hur,Janghee Hong,Derek P Brazil,Daniel Hess,Jeong-Lan Kim,Kyeong Ah Park,Jeong Ho Seok,Taehoon Chun,Yuwen Li,Gi Ryang Kweon,Hee Sun Byun,Sauveur-Michel Maira,Keum-Jin Yang,Jae Youl Cho,Minho Won

doi:10.1186/1471-2121-10-53

Abstract

BackgroundThe serine/threonine protein kinase B (PKB/Akt) is involved in insulin signaling, cellular survival, and transformation. Carboxyl-terminal modulator protein (CTMP) has been identified as a novel PKB binding partner in a yeast two-hybrid screen, and appears to be a negative PKB regulator with tumor suppressor-like properties. In the present study we investigate novel mechanisms by which CTMP plays a role in apoptosis process.ResultsCTMP is localized to mitochondria. Furthermore, CTMP becomes phosphorylated following the treatment of cells with pervanadate, an insulin-mimetic. Two serine residues (Ser37 and Ser38) were identified as novel in vivo phosphorylation sites of CTMP. Association of CTMP and heat shock protein 70 (Hsp70) inhibits the formation of complexes containing apoptotic protease activating factor 1 and Hsp70. Overexpression of CTMP increased the sensitivity of cells to apoptosis, most likely due to the inhibition of Hsp70 function.ConclusionOur data suggest that phosphorylation on Ser37/Ser38 of CTMP is important for the prevention of mitochondrial localization of CTMP, eventually leading to cell death by binding to Hsp70. In addition to its role in PKB inhibition, CTMP may therefore play a key role in mitochondria-mediated apoptosis by localizing to mitochondria.

Highlights

The serine/threonine protein kinase B (PKB/Akt) is involved in insulin signaling, cellular survival, and transformation
Carboxyl-terminal modulator protein (CTMP) is localized to the mitochondrial intermembrane space and/or matrix We previously reported that CTMP localized to the plasma membrane, leading to PKB inhibition [10]
We provide the first evidence that CTMP, a negative regulator of PKB, localizes to the mitochondria in a MTSdependent manner (Figure 3A and 3B)

Summary

Introduction

The serine/threonine protein kinase B (PKB/Akt) is involved in insulin signaling, cellular survival, and transformation. Carboxyl-terminal modulator protein (CTMP) has been identified as a novel PKB binding partner in a yeast two-hybrid screen, and appears to be a negative PKB regulator with tumor suppressor-like properties. Protein kinase B (PKB/Akt) is activated by receptor tyrosine kinases and regulates cell proliferation, survival, and motility [1,2]. Phosphorylation of two amino acids (Thr308 and Ser473) is required for full PKB activation [3,4]. Phosphorylation on a second regulatory site at the carboxyl terminus (Ser473; termed the hydrophobic motif) by rictor-mTOR and DNA-PK can further activate PKB seven- to ten-fold The crystal structure of PKB suggests that Ser473 phosphorylation is important for kinase activation and stabilization [8,9]

Methods

Results

Discussion

Conclusion