Inhibition of the Mitotic Kinesin Eg5 Up-regulates Hsp70 through the Phosphatidylinositol 3-Kinase/Akt Pathway in Multiple Myeloma Cells

Min Liu,Ritu Aneja,Chunyong Liu,Lei Sun,Jinmin Gao,Hongxia Wang,Jin-Tang Dong,Vasiliki Sarli,Athanassios Giannis,Harish C Joshi,Jun Zhou

doi:10.1074/jbc.m601324200

Min Liu, Ritu Aneja + Show 9 more

Open Access

https://doi.org/10.1074/jbc.m601324200

Copy DOI

Abstract

The microtubule-dependent motor protein Eg5 plays a critical role in spindle assembly and maintenance in mitosis. Herein we show that the suppression of Eg5 by a specific inhibitor arrested mitosis, induced apoptosis, and up-regulated Hsp70 in human multiple myeloma cells. Mechanistically, Hsp70 induction occurred at the transcriptional level via a cis-regulatory DNA element in Hsp70 promoter and was mediated by the phosphatidylinositol 3-kinase/Akt pathway. Eg5 inhibitor-mediated Hsp70 up-regulation is cytoprotective because blocking Hsp70 induction directly by antisense or small interfering RNA or indirectly by inhibiting the phosphatidylinositol 3-kinase/Akt pathway significantly increased Eg5 inhibitor-induced apoptosis. Furthermore, a farnesyltransferase inhibitor interacted synergistically with the Eg5 inhibitor in inducing apoptosis through disrupting the Akt/Hsp70 signaling axis. These findings provide the first evidence for Eg5 inhibitor activity in hematologic malignancy and identify Hsp70 up-regulation as a critical mechanism responsible for modulating myeloma cell sensitivity to Eg5 inhibitors. In addition, these findings suggest that a combination of Eg5 inhibitors with agents abrogating Hsp70 induction would be useful for myeloma therapy in the clinic.

Highlights

Inhibitors of Eg5 have emerged as a new class of agents that interfere with the mitotic spindle [7]
Eg5 Inhibitor Dimethylenastron Induces Mitotic Arrest and Apoptosis in Human Multiple Myeloma Cells—Using a sulforhodamine B-based cytotoxicity assay, we found that dimethylenastron was highly potent against RPMI8226 human multiple myeloma cells with an LD50 of 0.48 ␮M (Fig. 1A)
We show for the first time that dimethylenastron, an Eg5-specific cell-permeable inhibitor, potently inhibited cell proliferation and induced apoptosis in myeloma cells

Summary

Introduction

Inhibitors of Eg5 ( named kinesin spindle protein or kinesin-5) have emerged as a new class of agents that interfere with the mitotic spindle [7]. Dimethylenastron activated the PI3K/Akt pathway, which in turn caused a remarkable transcriptional up-regulation of heat shock protein 70 (Hsp70).2 Dimethylenastron-induced apoptosis was enhanced by blocking Hsp70 induction directly with antisense or small interfering RNA or indirectly by inhibiting the phosphatidylinositol 3-kinase (PI3K)/Akt pathway with pharmacological or dominant-negative approaches. We found that FTI277, a specific small-molecule inhibitor of farnesyltransferase, synergized with dimethylenastron in inducing apoptosis by interrupting the PI3K/Akt/Hsp70 cascade.

Results

Conclusion