Subcellular Targeting of the Euplotes raikovi Kinase Er-MAPK1, as Revealed by Expression in Different Cell Systems

• Published in: Frontiers in cell and developmental biology 2019-10, Vol.7, p.244-244
• Main Authors: Candelori, Annalisa, Yamamoto, Takaharu G., Iwamoto, Masaaki, Montani, Maura, Amici, Augusto, Vallesi, Adriana
• Format: Article
• Language: English
• Subjects: Cell and Developmental Biology; ciliated protozoa; GFP-fusion proteins; heterologous gene expression; ICK-related kinase; nuclear and ciliary protein kinase; protein kinase
• ISSN: 2296-634X; 2296-634X
• DOI: 10.3389/fcell.2019.00244

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.