Tumor cells with KRAS or BRAF mutations orERK5/MAPK7 amplification are not addicted to ERK5 activity for cell proliferation

Lochhead, P. A., Clark, J., Wang, L.-Z., Gilmour, L., Squires, M., Gilley, R., Foxton, C., Newell, D. R., Wedge, S. R. and Cook, S. J. (2016) Tumor cells with KRAS or BRAF mutations orERK5/MAPK7 amplification are not addicted to ERK5 activity for cell proliferation. Cell Cycle, 15(4), pp. 506-518. (doi: 10.1080/15384101.2015.1120915) (PMID:26959608)

Abstract

ERK5, encoded by MAPK7, has been proposed to play a role in cell proliferation, thus attracting interest as a cancer therapeutic target. While oncogenic RAS or BRAF cause sustained activation of the MEK1/2-ERK1/2 pathway, ERK5 is directly activated by MEK5. It has been proposed that RAS and RAF proteins can also promote ERK5 activation. Here we investigated the interplay between RAS-RAF-MEK-ERK and ERK5 signaling and studied the role of ERK5 in tumor cell proliferation in 2 disease-relevant cell models. We demonstrate that although an inducible form of CRAF (CRAF:ER*) can activate ERK5 in fibroblasts, the response is delayed and reflects feed-forward signaling. Additionally, oncogenic KRAS and BRAF do not activate ERK5 in epithelial cells. Although KRAS and BRAF do not couple directly to MEK5-ERK5, ERK5 signaling might still be permissive for proliferation. However, neither the selective MEK5 inhibitor BIX02189 or ERK5 siRNA inhibited proliferation of colorectal cancer cells harbouring KRASG12C/G13D or BRAFV600E. Furthermore, there was no additive or synergistic effect observed when BIX02189 was combined with the MEK1/2 inhibitor Selumetinib (AZD6244), suggesting that ERK5 was neither required for proliferation nor a driver of innate resistance to MEK1/2 inhibitors. Finally, even cancer cells with MAPK7 amplification were resistant to BIX02189 and ERK5 siRNA, showing that ERK5 amplification does not confer addiction to ERK5 for cell proliferation. Thus ERK5 signaling is unlikely to play a role in tumor cell proliferation downstream of KRAS or BRAF or in tumor cells with ERK5 amplification. These results have important implications for the role of ERK5 as an anti-cancer drug target.

• Item Type: Articles
• Additional Information: This work was funded by a project grant from the Association of International Cancer Research, a program grant from Cancer Research UK and an MRC DPFS Industry Collaboration Agreement. The Cook lab receives strategic support from the BBSRC in the form of an Institute Strategic Program grant.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Gilmour, Dr Lesley
• Authors: Lochhead, P. A., Clark, J., Wang, L.-Z., Gilmour, L., Squires, M., Gilley, R., Foxton, C., Newell, D. R., Wedge, S. R., and Cook, S. J.
• College/School: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Journal Name: Cell Cycle
• Publisher: Taylor & Francis
• ISSN: 1538-4101
• ISSN (Online): 1551-4005
• Published Online: 09 March 2016
• Copyright Holders: Copyright © 2016 The Authors
• First Published: First published in Cell Cycle 15(4): 506-518
• Publisher Policy: Reproduced under a Creative Commons License