Overexpression of human myotonic dystrophy protein kinase in Schizosaccharomyces pombe induces an abnormal polarized and swollen cell morphology

We expressed human myotonic dystrophy protein kinase (DMPK) in the fission yeast Schizosaccharomyces pombe, in which the overexpression of human DMPK affects cell growth and cell shape. The human DMPK protein has a leucine-rich domain at the N-terminus, a serine/threonine kinase domain in the middle, and a hydrophobic region at the C-terminus. C-Terminus-deleted DMPK produced a middle-swollen phenotype (lemon-like shape), indicating an abnormality in cell division. On the other hand, when both the kinase domain and C-terminus were present, the expression of DMPK resulted in polarized cell growth and multinucleated/branched cells. The lemon-like phenotype seen with the C-terminus-deleted DMPK disappeared when the ATP binding site of DMPK was disrupted by replacing the lysine at amino acid 100 with arginine (K100R mutant). However, polarized and/or multinucleated cells lacking the DMPK N-terminus were not rescued by the K100R mutation. Therefore, we conclude that the N-terminus of DMPK plays an important role in DMPK kinase activity, and that the C-terminus of DMPK determines the intracellular localization of the protein.