Cell-cycle dependent shuttling of myotonic dystrophy protein kinase between cytoplasmic organelles and the mitotic apparatus

Purpose. Myotonic dystrophy (DM) is inherited as an autosomal dominant disorder in which cataracts of the eye lens, in addition to skeletal muscle weakness and myotonia are characteristic findings. The gene responsible for the disease is a member of a new family of serine/threonine protein kinases. The goal of this research is to test the hypothesis that DM kinase is directly or indirectly associated with the cytoskeleton. Methods. Immunofluorescence microscopy was used to determine the subcellular localization of DM kinase in the B3 human lens epithelial cell line using an antibody specific for the helical domain of the enzyme. Results. We found a perinuclear staining pattern in interphase cells consistent with endoplasmic reticulum (ER) or Golgi localization. This distribution was disrupted when cells were treated with colcemed, but was not affected when treated with cytochalasin B. In metaphase cells, the antibody reacted specifically at the spindle poles and to a lesser degree with spindle microtubules. In cells undergoing cytokinesis the antibody labelled a pair of immunoreactive bands perpendicular to residual microtubules at the construction separating the two daughter cells. Conclusion. DM protein kinase is associated with ER/Golgi during interphase, but is redistributed to spindle poles and specific midbody structures in cells undergoing mitosis and cytokinesis.