Identification of the Human Mnk2 Gene (MKNK2) through Protein Interaction with Estrogen Receptor β

We have identified and characterized the human Mnk2 gene (HGMW-approved gene symbol MKNK2) through a yeast two-hybrid screen in which the Mnk2 protein interacted with the ligand-binding domain of estrogen receptor β (ERβ). Human Mnk2 is homologous to murine Mnk2 (∼94% identical) and human Mnk1 (71% identical), both of which encode MAP kinase interacting kinases that are phosphorylated and activated by ERK1 and 2. This report presents a thorough genomic sequence analysis revealing that the human Mnk2 gene has two C-terminal splice variants, designated here as Mnk2a and Mnk2b. These two isoforms are identical over the first 385 amino acids of the coding sequence and differ only in the final exon which encodes an additional 80 residues for Mnk2a and 29 residues for Mnk2b. A more detailed biological analysis in yeast showed that the Mnk2 interaction was selective for ERβ as opposed to ERα and that the interaction was specific to Mnk2b as opposed to Mnk2a or Mnk1. This pattern was reproduced in a mammalian two-hybrid system using a completely different set of fusion partners; and in both yeast and mammalian systems, the addition of estradiol decreased the interaction. While it remains unknown whether ERβ is a substrate of Mnk2, the interaction of these two proteins is reminiscent of ERα and ribosomal S6 kinase (p90-RSK), another MAP kinase-regulated kinase homologous to Mnk2 that is known to phosphorylate ERα.