MEK5 promotes lung adenocarcinoma

Abstract

[EN]Lung cancer represents the leading cause of cancer death worldwide [1]. Because of that, intense efforts are being devoted to the development of novel therapeutic strategies to fight the disease [2]. In this respect, identification of new oncogenic drivers offers therapeutic opportunities in tumours in which those molecules or other cooperating elements play a pathophysiological role. Here, we show that the MEK5 mitogen-activated protein kinase kinase has a pivotal role in lung cancer. Originally, this study was initiated with the purpose of evaluating the potential oncogenic role of the MEK5 pathway. In fact, while the MEK5 pathway has been found to be deregulated in several neoplasias [3–6], whether exclusive activation of that pathway promotes tumorigenesis has not previously been addressed. To explore that possibility, we generated transgenic mice engineered to express a constitutively active form of MEK5 by site-directed mutagenesis of the MEK5 Ser311 and Thr315 residues to aspartic acid (MEK5DD) (figure 1a). These acidic amino acid changes result in a MEK5 form in which the aspartic acid substitutions function as phosphomimetic residues [7, 8]. As a consequence, MEK5DD acts as a constitutively active kinase that is able to phosphorylate its downstream target, the ERK5 mitogen-activated protein kinase. Phosphorylation of ERK5 by constitutively active MEK5DD results in sustained activation of ERK5. Such ERK5 phosphorylation ( pERK5) provokes a change in its electrophoretic mobility with respect to unphosphorylated ERK5, a characteristic that can be used to differentiate ERK5 from pERK5 by Western blotting [9]. The MEK5DD cDNA was subcloned into the pCEFL mammalian expression vector, which contains an N-terminal Flag tag sequence that serves to differentiate MEK5DD from endogenous MEK5. Increasing amounts of the cDNA coding for Flag-tagged MEK5DD were transfected in HeLa cells and its expression was analysed by Western blotting with an anti-Flag antibody. As shown in figure 1b, expression of Flag-MEK5DD caused the appearance of pERK5, indicative of pathway activation