Giardia lamblia aurora kinase: a regulator of mitosis in a binucleate parasite.
Giardia lamblia is a major cause of diarrhoeal disease worldwide. Since it has no known toxin, the ability of trophozoites to colonise the human small intestine is required for its pathogenesis. Mitosis in this protozoan parasite is a unique challenge because its two equivalent nuclei and complex cytoskeleton must be duplicated and segregated accurately. Giardial mitosis is a complex and rapid event that is poorly understood at the cellular and molecular levels. Higher eukaryotes have one to three members of the highly conserved Ser/Thr aurora kinase (AK) family that regulate key aspects of mitosis and cytokinesis. Giardia has a single AK orthologue (gAK) with 61% similarity to human AK A. In addition to the conserved active site residues, activation loop and destruction-box motifs characteristic of AKs, gAK contains a unique insert near the active site region. We epitope-tagged gAK at its C-terminus and expressed it under its own promoter. During interphase, gAK localises exclusively to the nuclei, but is not phosphorylated as shown by lack of staining with an antibody specific to phosphorylated AK A (pAK). In contrast, during mitosis pAK localises to the basal bodies/centrosomes and co-localises with tubulin to the spindle. During specific stages of mitosis, giardial pAK also localised dynamically to cytoskeletal structures unique to Giardia: the paraflagellar dense rods of the anterior flagella and the median body, whose functions are unknown, as well as to the parent attachment disc. Two AK inhibitors significantly decreased giardial growth and increased the numbers of cells arrested in cytokinesis. These inhibitors appeared to increase microtubule nucleation and cell-ploidy. Our data show that gAK is phosphorylated in mitosis and suggest that it plays an important role in the Giardia cell cycle. The pleiotropic localisation of AK suggests that it may co-ordinate the reorganisation and segregation of tubulin-containing structures in mitosis. We believe this is the first report of a signalling protein regulating cell division in Giardia.
Davids
Barbara J
BJ
Department of Pathology, Division of Infectious Diseases, University of California at San Diego, 214 Dickinson Street, San Diego, CA 92103-8416, USA. Bdavids@ucsd.edu
Williams
Sarah
S
Lauwaet
Tineke
T
Palanca
Tiffany
T
Gillin
Frances D
FD
D000818:Animals; D000953:Antigens, Protozoan / Q000032:analysis / Q000235:genetics*; D064096:Aurora Kinase A; D064127:Aurora Kinases; D001483:Base Sequence; D018385:Centrosome / Q000201:enzymology; D003967:Diarrhea / Q000469:parasitology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D016829:Giardia lamblia / Q000201:enzymology*; D006790:Host-Parasite Interactions; D006801:Humans; D007411:Intestinal Diseases, Parasitic / Q000276:immunology; D008870:Microtubules / Q000201:enzymology; D008938:Mitosis / Q000502:physiology*; D008969:Molecular Sequence Data; D010274:Parasitology / Q000379:methods; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment
D000953:Antigens, Protozoan; D004791:Enzyme Inhibitors; C576917:AURKA protein, human; D064096:Aurora Kinase A; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases