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Cellular Oncology
Volume 32 (2010), Issue 4, Pages 245-257
http://dx.doi.org/10.3233/CLO-2010-0521

Oncogenic K-Ras Activates p38 to Maintain Colorectal Cancer Cell Proliferation during MEK Inhibition

Winan J. van Houdt, Menno T. de Bruijn, Benjamin L. Emmink, Danielle Raats, Frederik J. H. Hoogwater, Inne H. M. Borel Rinkes, and Onno Kranenburg

Department of Surgery, University Medical Center Utrecht, Heidelberglaan, Utrecht, The Netherlands

Copyright © 2010 Hindawi Publishing Corporation and the authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Colon carcinomas frequently contain activating mutations in the K-ras proto-oncogene. K-ras itself is a poor drug target and drug development efforts have mostly focused on components of the classical Ras-activated MEK/ERK pathway. Here we have studied whether endogenous oncogenic K-ras affects the dependency of colorectal tumor cells on MEK/ERK signaling.

Methods: K-ras mutant colorectal tumor cell lines C26, HCT116 and L169 were used. K-ras or components of the MEK/ERK and p38 pathway were suppressed by RNA interference (RNAi). MEK was inhibited by U0126. p38 was inhibited by SB203850.

Results: MEK inhibition, or suppression of MEK1/2 or ERK1/2 by RNA interference, reduced the proliferation rate of all colorectal cancer cell lines. However, cell proliferation returned to normal after two weeks of chronic inhibition, despite the continued suppression of MEK or ERK. In contrast, K-ras-suppressed tumor cells entered an irreversible senescent-like state following ERK pathway inhibition. MEK inhibition or ERK1/2 suppression caused activation of p38α in a K-ras-dependent manner. Inhibition or suppression of p38α prevented the recovery of K-ras mutant tumor cells during prolonged MEK inhibition.

Conclusions: Oncogenic K-ras activates p38α to maintain cell proliferation during MEK inhibition. MEK-targeting therapeutics can create an acquired tumor cell dependency on p38α.