Received for publication June 30, 2006.
Revised August 29, 2006.
Accepted for publication August 29, 2006.

DISSECTING THE ROLES OF CHK1/CDC2 AND MEK1/2/ERK1/2 IN RELATION TO UCN-01-INDUCED APOPTOSIS IN HUMAN MULTIPLE MYELOMA CELLS

Abstract

The functional roles of Cdc2 and Chk1 in synergistic interactions between UCN-01 and MEK1/2 inhibitors (e.g., PD184352) were examined in human multiple myeloma cells in relation to MEK1/2/ERK1/2 activation and lethality. Time course studies revealed that MEK1/2/ERK1/2 phosphorylation preceded Cdc2 dephosphorylation (Tyr15) following UCN-01 exposure. Furthermore, enforced expression of Cdc2 or siRNA-mediated Cdc2 knockdown failed to modify ERK1/2 activation status in either the presence or absence of UCN-01, arguing against a causal relationship between these events. However, ectopic expression of Cdc2 sensitized cells to the lethality of UCN-01/MEK inhibitor regimen, while Cdc2 knockdown by siRNA significantly diminished the lethal effects of this combination. Conversely, Chk1 knockdown by siRNA enhanced lethality mediated by UCN-01/PD184352. Interestingly, Chk1 knockdown reduced basal ERK1/2 activation and antagonized the ability of UCN-01 to activate ERK1/2. Finally, ectopic expression of constitutively active MEK1 significantly protected cells from the UCN-01/MEK1/2 inhibitor regimen without modifying Cdc2 activation status. Together, these findings indicate that while UCN-01-mediated Chk1 inhibition and Cdc2 activation are unlikely to be responsible for MEK1/2/ERK1/2 activation, both of these events contribute functionally to enhanced lethality in cells co-exposed to MEK inhibitors. They also suggest a role for Chk1 in UCN-01-induced ERK1/2 activation, implying the existence of a heretofore unrecognized link between Chk1 and ERK1/2 signaling.

Key words: MAP Kinase, Mechanisms of cell killing/apoptosis

This article has been cited by other articles:

				H. Hamed, W. Hawkins, C. Mitchell, D. Gilfor, G. Zhang, X.-Y. Pei, Y. Dai, M. P. Hagan, J. D. Roberts, A. Yacoub, et al. Transient exposure of carcinoma cells to RAS/MEK inhibitors and UCN-01 causes cell death in vitro and in vivo Mol. Cancer Ther., March 1, 2008; 7(3): 616 - 629. [Abstract] [Full Text] [PDF]

				X.-Y. Pei, Y. Dai, S. Tenorio, J. Lu, H. Harada, P. Dent, and S. Grant MEK1/2 inhibitors potentiate UCN-01 lethality in human multiple myeloma cells through a Bim-dependent mechanism Blood, September 15, 2007; 110(6): 2092 - 2101. [Abstract] [Full Text] [PDF]

				Y. Dai, P. Khanna, S. Chen, X.-Y. Pei, P. Dent, and S. Grant Statins synergistically potentiate 7-hydroxystaurosporine (UCN-01) lethality in human leukemia and myeloma cells by disrupting Ras farnesylation and activation Blood, May 15, 2007; 109(10): 4415 - 4423. [Abstract] [Full Text] [PDF]