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Front. Cell Dev. Biol. | doi: 10.3389/fcell.2019.00244

Subcellular targeting of the Euplotes raikovi kinase Er-MAPK1, as revealed by expression in different cell systems

  • 1University of Camerino, Italy
  • 2Advanced ICT Research Institute, National Institute of Information and Communications Technology (Japan), Japan

In the ciliate Euplotes raikovi, a 631-amino acid Er-MAPK1 protein kinase was found to localize in nucleoli of the transcriptionally active nucleus (macronucleus) and act as a key component of an autocrine, cell-growth promoting self-signaling mechanism. While its 283-amino acid N-terminal domain includes all the structural specificities of the mitogen-activated protein kinases required for a catalytic function, the 348-amino acid C-terminal domain is structurally unique with undetermined functions. By expressing the two Er-MAPK1 domains tagged with the green fluorescent protein in mammalian fibroblasts, the yeast Schizosaccharomyces pombe and the ciliate Tetrahymena thermophila, evidence was obtained that the C-terminal domain contains all the sequence information responsible for the Er-MAPK1 subcellular localization. However, in fibroblasts and S. pombe this information determined a nucleolar localization of the GFP-tagged C-terminal domain, and a ciliary localization in T. thermophila. In the light of these findings, the Er-MAPK1 localization in E. raikovi was re-examined via immunoreactions and shown to be ciliary besides that nuclear, as is the case for the mammalian intestinal cell kinase with which the Er-MAPK1 N-terminal domain shares a strong sequence identity and a catalytic function.

Keywords: Ciliated protozoa, protein kinase, Heterologous gene expression, GFP-fusion proteins, nuclear and ciliary protein kinase, ICK-related kinase, MAK-related kinase

Received: 24 Jun 2019; Accepted: 04 Oct 2019.

Copyright: © 2019 Candelori, Yamamoto, Iwamoto, Montani, Amici and Vallesi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Adriana Vallesi, University of Camerino, Camerino, 62032, Marche, Italy, adriana.vallesi@unicam.it