Loss of human Greatwall results in G2 arrest and multiple mitotic defects due to deregulation of the cyclin B-Cdc2/PP2A balance.
Here we show that the functional human ortholog of Greatwall protein kinase (Gwl) is the microtubule-associated serine/threonine kinase-like protein, MAST-L. This kinase promotes mitotic entry and maintenance in human cells by inhibiting protein phosphatase 2A (PP2A), a phosphatase that dephosphorylates cyclin B-Cdc2 substrates. The complete depletion of Gwl by siRNA arrests human cells in G2. When the levels of this kinase are only partially depleted, however, cells enter into mitosis with multiple defects and fail to inactivate the spindle assembly checkpoint (SAC). The ability of cells to remain arrested in mitosis by the SAC appears to be directly proportional to the amount of Gwl remaining. Thus, when Gwl is only slightly reduced, cells arrest at prometaphase. More complete depletion correlates with the premature dephosphorylation of cyclin B-Cdc2 substrates, inactivation of the SAC, and subsequent exit from mitosis with severe cytokinesis defects. These phenotypes appear to be mediated by PP2A, as they could be rescued by either a double Gwl/PP2A knockdown or by the inhibition of this phosphatase with okadaic acid. These results suggest that the balance between cyclin B-Cdc2 and PP2A must be tightly regulated for correct mitotic entry and exit and that Gwl is crucial for mediating this regulation in somatic human cells.
Universités Montpellier 2 et 1, Centre de Recherche de Biochimie Macromoléculaire, Centre National de la Recherche Scientifique UMR 5237, 34293 Montpellier Cedex 5, France.
Andrew
A
Burgess
Suzanne
S
Vigneron
Estelle
E
Brioudes
Jean-Claude
JC
Labbé
Thierry
T
Lorca
Anna
A
Castro
D002453:Cell Cycle / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D006801:Humans; D008938:Mitosis / Q000187:drug effects; D019319:Okadaic Acid / Q000378:metabolism / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism
D019926:Cyclin B; D056744:Cyclin B1; D011506:Proteins; D034741:RNA, Small Interfering; D019319:Okadaic Acid; D017346:Protein Serine-Threonine Kinases; D054648:Protein Phosphatase 2; D010744:Phosphoric Monoester Hydrolases