Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.
1 Immunopathology Unit, Department of Experimental and Health Sciences, Pompeu Fabra University, Doctor Aiguader 88, 08003 Barcelona, Spain
2 Medical Oncology Research Program, Vall d’Hebron University Hospital Research Institute, Passeig Vall d’Hebron 119-129, 08035 Barcelona, Spain
3 Department of Biochemistry and Molecular Biology, Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia, Vancouver, V6T 1Z3, BC, Canada
*Author to whom correspondence should be addressed.
Abstract
The human MAP kinase-interacting kinases (or MAP kinase signal-integrating kinases), Mnks, comprise a group of four proteins derived from two genes (Gene symbols: MKNK1 and MKNK2) by alternative splicing. Mnk1a/b differ at their C-termini, as do Mnk2a/2b: in each case, the a-form possesses a longer C-terminal region than the b-form, which lacks the MAP kinase-binding region. The N-termini of all forms contain a polybasic region which binds importin α and the translation factor scaffold protein eukaryotic initiation factor (eIF) 4G. The catalytic domains of Mnk1a/b and Mnk2a/b share three unusual features: two short inserts and a DFD feature where other kinases have DFG. Mnk isoforms differ markedly in their activity and regulation, and in subcellular localization. The best-characterised Mnk substrate is eIF4E. The cellular role of eIF4E phosphorylation remains unclear: it may promote export of certain mRNAs from the nucleus. Other Mnk substrates bind to AU-rich elements that modulate the stability/translation of specific mRNAs. Mnks may also control production of inflammatory mediators and signaling from tyrosine kinase receptors, as well as cell proliferation or survival.