Tumor suppressor WARTS ensures genomic integrity by regulating both mitotic progression and G1 tetraploidy checkpoint function.
Defects in chromosomes or mitotic spindles activate the spindle checkpoint, resulting in cell cycle arrest at prometaphase. The prolonged activation of spindle checkpoint generally leads to mitotic exit without segregation after a transient mitotic arrest and the consequent formation of tetraploid G(1) cells. These tetraploid cells are usually blocked to enter the subsequent S phase by the activation of p53/pRb pathway, which is referred to as the G(1) tetraploidy checkpoint. A human homologue of the Drosophila warts tumor suppressor, WARTS, is an evolutionarily conserved serine-threonine kinase and implicated in development of human tumors. We previously showed that WARTS plays a crucial role in controlling mitotic progression by forming a regulatory complex with zyxin, a regulator of actin filament assembly, on mitotic apparatus. However, when WARTS is activated during cell cycle and how the loss of WARTS function leads to tumorigenesis have not been elucidated. Here we show that WARTS is activated during mitosis in mammalian cells, and that overexpression of a kinase-inactive WARTS in Rat1 fibroblasts significantly induced mitotic delay. This delay resulted from prolonged activation of the spindle assembly checkpoint and was frequently followed by mitotic slippage and the development of tetraploidy. The resulting tetraploid cells then abrogated the G(1) tetraploidy checkpoint and entered S phase to achieve a DNA content of 8N. This impairment of G(1) tetraploidy checkpoint was caused as a consequence of failure to induce p53 expression by expressing a kinase-inactive WARTS. WARTS thus plays a critical role in maintenance of ploidy through its actions in both mitotic progression and the G(1) tetraploidy checkpoint.
Iida
Shin-Ichi
S
Department of Tumor Genetics and Biology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
Hirota
Toru
T
Morisaki
Tetsuro
T
Marumoto
Tomotoshi
T
Hara
Toshihiro
T
Kuninaka
Shinji
S
Honda
Shinobu
S
Kosai
Ken-Ichiro
K
Kawasuji
Michio
M
Pallas
David C
DC
Saya
Hideyuki
H
D000199:Actins / Q000378:metabolism; D000818:Animals; D002453:Cell Cycle; D004247:DNA / Q000096:biosynthesis; D004330:Drosophila; D029721:Drosophila Proteins; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D016193:G1 Phase; D016678:Genome; D006367:HeLa Cells; D006801:Humans; D008856:Microscopy, Fluorescence; D008938:Mitosis; D011003:Ploidies; D011123:Polyploidy; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D051381:Rats; D016196:S Phase; D008941:Spindle Apparatus; D013997:Time Factors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000199:Actins; D029721:Drosophila Proteins; D016159:Tumor Suppressor Protein p53; D004247:DNA; D011494:Protein Kinases; C092745:LATS1 protein, human; C093503:wts protein, Drosophila; D017346:Protein Serine-Threonine Kinases