J Biol Chem. 2006 Apr 20; [Epub ahead of print] J Biol Chem. 2005 Oct 21;280(42):35684-95.
Epub 2005 Aug 22.
Inhibition of the mitotic kinesin Eg5 upregulates Hsp70 through the PI3K/Akt pathway in multiple myeloma cells.
Liu M, Aneja R, Liu C, Sun L, Gao J, Wang H, Dong JT, Sarli V, Giannis A, Joshi HC, Zhou J.
Department of Genetics and Cell Biology,
The microtubule-dependent motor protein Eg5 plays a critical role in spindle assembly and maintenance in mitosis. Herein we show that suppression of Eg5 by a specific inhibitor arrests mitosis, induces apoptosis, and upregulates Hsp70 in human multiple myeloma cells. Mechanistically, Hsp70 induction occurs at the transcriptional level via a cis-regulatory DNA element in Hsp70 promoter and is mediated by the PI3K/Akt pathway. Eg5 inhibitor-mediated Hsp70 upregulation is cytoprotective, because blocking Hsp70 induction directly by antisense or small interfering RNA or indirectly by inhibiting the PI3K/Akt pathway significantly increases Eg5 inhibitor-induced apoptosis. Furthermore, a farnesyltransferase inhibitor interacts 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 upregulation as a critical mechanism responsible for modulating myeloma cell sensitivity to Eg5 inhibitors. In addition, these findings suggest that combination of Eg5 inhibitors with agents abrogating Hsp70 induction is more useful for myeloma therapy in the clinic.
PMID: 16627469 [PubMed - as supplied by publisher]
Docking and rolling, a model of how the mitotic motor Eg5 works.
Rosenfeld SS, Xing J, Jefferson GM, King PH.
Department of Neurology,
Whereas kinesin I is designed to transport cargoes long distances in isolation, a closely related kinesin motor, Eg5, is designed to generate a sustained opposing force necessary for proper mitotic spindle formation. Do the very different roles for these evolutionarily related motors translate into differences in how they generate movement? We have addressed this question by examining when in the ATPase cycle the Eg5 motor domain and neck linker move through the use of a series of novel spectroscopic probes utilizing fluorescence resonance energy transfer, and we have compared our results to kinesin I. Our results are consistent with a model in which movement in Eg5 occurs in two sequential steps, an ATP-dependent docking of the neck linker, followed by a rotation or "rolling" of the entire motor domain on the microtubule surface that occurs with ATP hydrolysis. These two forms of movement are consistent with the functions of a motor designed to generate sustained opposing force, and hence, our findings support the argument that the mechanochemical features of a molecular motor are shaped more by the demands placed on it than by its particular family of origin.
J Biol Chem. 2006 Apr 20; [Epub ahead of print]
J Biol Chem. 2005 Oct 21;280(42):35684-95. Epub 2005 Aug 22.