Transcriptional Control of BubR1 by p53 and Suppression of Centrosome Amplification by BubR1

Abstract

Elimination of the regulatory mechanism underlying numeral homeostasis of centrosomes, as seen in cells lacking p53, results in abnormal amplification of centrosomes, which increases the frequency of chromosome segregation errors, and thus contributes to the chromosome instability frequently observed in cancer cells. We have previously reported that p53^−/− mouse cells in prolonged culture undergo genomic convergence similar to that observed during tumor progression; early-passage p53^−/− cells are karyotypically heterogeneous due to extensive chromosome instability associated with centrosome amplification, while late-passage p53^−/− cells are aneuploid yet karyotypically homogeneous and chromosomally stable. Moreover, they contain numerically normal centrosomes. Through the microarray analysis of early- and late-passage p53^−/− cells, we identified the BubR1 spindle checkpoint protein, which plays a critical role in suppression of centrosome amplification and stabilization of chromosomes in late-passage p53^−/− cells. Up-regulation of BubR1 augments the checkpoint function, which effectively senses the spindle/chromosome aberrations associated with centrosome amplification. We further found that BubR1 transcription is largely controlled by p53. In early-passage p53^−/− cells, BubR1 expression is low and the checkpoint function in response to microtubule toxin is considerably compromised. In late-passage cells, however, regaining of BubR1 expression restores the checkpoint function to mitotic aberrations caused by microtubule toxin. Our studies demonstrate the molecular aspect of genomic convergence in cultured cells, providing critical information for understanding the stepwise progression of tumors.

ACKNOWLEDGMENTS

We thank J. Salisbury for anticentrin antibody, G. Wahl for an H2B-GFP plasmid, M. Oren for mouse p53 plasmids, W. Dai for anti-BubR1 antibody, and P. Rao for anti-MPM2 antibody. We also thank Sandy Schwemberger and George Babcock for FACS analysis. We also thank A. Staubach, E. Hunter, and I. Wenker for technical assistance.

This research was supported by grants-in-aid from the Naito Foundation and the Ministry of Education, Sports and Culture, Japan (13760221 and 1590492 to M.O.), the Japan Society for the Promotion of Science (to T.O.), and the National Institutes of Health (CA90522 and CA95925 to K.F.).