Research ArticleCancer

Activating mutations in MEK1 enhance homodimerization and promote tumorigenesis

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Sci. Signal.  30 Oct 2018:
Vol. 11, Issue 554, eaar6795
DOI: 10.1126/scisignal.aar6795

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Know thine enemy: Mutant MEK

Many cancers, notably melanomas, are driven by activation of the RAS-ERK signaling pathway, but tumors are often resistant to pathway-targeted therapies. Yuan et al. characterized cancer-related mutations in the pathway-mediating kinase MEK1 and found that deletion mutations in a loop portion of the protein promoted MEK1 homodimerization and autophosphorylation, enabling the activation of ERK with or without upstream pathway activity. These mutants transformed cells and differentially conferred resistance to MEK inhibitors. Understanding the precise functions of these mutants and detecting them at diagnosis may help devise more effective treatment strategies for patients.

Abstract

RAS-RAF-MEK-ERK signaling has a well-defined role in cancer biology. Although aberrant pathway activation occurs mostly upstream of the kinase MEK, mutations in MEK are prevalent in some cancer subsets. Here, we found that cancer-related, activating mutations in MEK can be classified into two groups: those that relieve inhibitory interactions with the helix A region and those that are in-frame deletions of the β3-αC loop, which enhance MEK1 homodimerization. The former, helix A–associated mutants, are inhibited by traditional MEK inhibitors. However, we found that the increased homodimerization associated with the loop-deletion mutants promoted intradimer cross-phosphorylation of the activation loop and conferred differential resistance to MEK inhibitors both in vitro and in vivo. MEK1 dimerization was required both for its activation by the kinase RAF and for its catalytic activity toward the kinase ERK. Our findings not only identify a previously unknown group of MEK mutants and provide insight into some key steps in RAF-MEK-ERK activation but also have implications for the design of therapies targeting RAS-ERK signaling in cancers.

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