The MAP kinase-interacting kinases regulate cell migration, vimentin expression and eIF4E/CYFIP1 binding

Abstract

The MAP kinase-interacting kinases (Mnk1 and Mnk2) are activated by ERK and are best known for phosphorylating the translation initiation factor eIF4E. Genetic knockout of the Mnks impaired the migration of embryonic fibroblasts both in two-dimensional wound-healing experiments and in three-dimensional migration assays. Furthermore, a novel and selective Mnk inhibitor, Mnk-I1, which potently blocks eIF4E phosphorylation, blocked the migration of fibroblasts and cancer cells, without exerting 'off-target' effects on other signalling pathways such as Erk. Mnk-I1 or genetic knockout of the Mnks decreased the expression of vimentin, a marker of mesenchymal cells, without affecting vimentin mRNA levels. Vimentin protein levels were much lower in Mnk1/2-knockout cells than in controls, although mRNA levels were similar. Our data suggest that the Mnks regulate the translation of the vimentin mRNA and the stability of the vimentin protein. Inhibition or genetic knockout of the Mnks increased the binding of eIF4E to the cytoplasmic FMRP-interacting protein 1 (CYFIP1), which binds the fragile-X mental retardation protein, FMRP, a translational repressor. Since FMRP binds mRNAs for proteins involved in metastasis, the Mnk-dependent release of CYFIP1 from eIF4E is expected to release the repression of translation of FMRP-bound mRNAs, potentially providing a molecular mechanism for the control of cell migration by the Mnks. As Mnk1/2 are not essential for viability, inhibition of the Mnks may be a useful approach to tackling cancer metastasis, a key process contributing to mortality in cancer patients.

Dual Abrogation of Mnk and Mtor: A Novel Therapeutic Approach for the Treatment of Aggressive Cancers

“…Their catalytic domains share 78% sequence identity and the active sites are highly conserved [25,57]. MNK1 and MNK2 display the canonical bilobal arrangement of the ATP-binding cleft sandwiched in between the C-terminal and N-terminal lobes.…”

“…Recent studies have found that high levels of eIF4E-P coincided with poor clinical outcome in human cancers [22][23][24]. MNK1 and MNK2 are serine/threonine protein kinases responsible for the phosphorylation of S209 on eIF4E [25]. The phosphorylation of eIF4E correlates with the increase in mesenchymal markers such as N-cadherin, fibronectin and vimentin, along with the acquisition of invasive properties [26].…”

“…This variation is reflected in a single amino acid change in the MAPKbinding site and determines the difference observed in their regulation [47]. MNK1a has low basal activity, and is activated and tightly regulated by ERK and p38 kinases in response to mitogens and stress [25,48]. MNK2 displays high basal activity and is predominantly regulated by ERK1/2, although MNK2a is regulated by mTORC1 through at least one site in its C-terminal region [49,50].…”

“…The MNKs associate with the C-terminus of eIF4G, a vital interaction that brings the kinase into close enough proximity to phosphorylate eIF4E on Ser209 [5,39]. This phosphorylation enhances translation of specific mRNAs involved in cell survival [25]. Recent findings in a mouse lymphoma model demonstrate that the phosphorylated form of eIF4E is required for the translation of a subset of mRNAs that oppose apoptosis and favor tumorigenesis [13,21,30,[40][41][42].…”

Potential Anticancer Properties and Mechanisms of Action of Withanolides

“…Beside its structural role, vimentin is also involved with cellular migration and signal transduction [56]. Vimentin interacts with several kinases such as protein kinase A, protein kinase C, calcium calmodulin kinase, p21-activated kinase, Cdc2 kinase, Rho-kinase, Aurora-B polo-like kinase, Akt kinase, and Mnk1/2 which phosphorylate one or more of 41 sites on vimentin identified to date [57][58][59]. Higher expression of vimentin has been observed in cancer cells and correlates with induction of epithelial-to-mesenchymal transition, metastasis, and poor cancer prognosis.…”