Direct evidence for the role of centrosomally localized p53 in the regulation of centrosome duplication.

Abnormalampliﬁcationofcentrosomesisthemajorcauseof mitotic defects and chromosome instability in cancercells. Centrosomes duplicate oncein each cell cycle, andabrogation of the regulatory mechanism underlyingcentrosomeduplicationleadstocentrosomeampliﬁcation.p53tumorsuppressorproteinisinvolvedintheregulationof centrosome duplication: loss of p53as well asexpression of certain p53mutants result in deregulatedcentrosomeduplicationandcentrosomeampliﬁcation.p53atleastinpartdependsonitstransactivationfunctiontocontrolcentrosomeduplication,primarilyviaupregulationof p21 cyclin-dependent kinase (CDK) inhibitor, whichprevents untimely activation of CDK2/cyclin E, a keyinitiator of centrosome duplication. However, numerousstudieshaveshownthepresenceofp53atcentrosomes,yetthe role of the centrosomally localized p53in theregulationofcentrosomeduplicationhadbeenenigmatic.Here, we comparatively examined wild-type p53andp53mutants that are transactivation(þ)/centrosome-binding( ), transactivation( )/centrosome-binding(þ)and transactivation( )/centrosome-binding( ) for theirabilitiestocontrolcentrosomeduplication.Wefoundthatthetransactivation(þ)/centrosome-binding( )andtrans-activation( )/centrosome-binding(þ) mutants suppresscentrosome duplication only partially compared withwild-type p53. Moreover, the transactivation( )/centro-some-binding( )mutantalmostcompletelylosttheabilityto suppress centrosome duplication. These observationsprovidedirectevidenceforthecentrosomallylocalizedp53toparticipateintheregulationofcentrosomeduplicationin a manner independent of its transactivation functionin addition to its transactivation-dependent regulation ofcentrosomeduplication.Oncogene(2007)26,2939–2944.doi:10.1038/sj.onc.1210085;publishedonline30October2006Keywords: p53;centrosome;centrosomeduplicationIntroductionThecentrosomesplayakeyroleintheestablishmentofbipolar spindles during mitosis as core components ofspindlepoles.Aschromosomesarepulledtowardeachspindle pole, the formation of bipolar spindles isessential for accurate chromosome segregation. Uponcytokinesis,eachdaughtercellreceivesonlyonecentro-some,andthuscentrosomes,likeDNA,duplicateonceineachcellcycle.Therefore,atanygiventimepoint,acell has either one or two centrosomes, and numeralhomeostasis of centrosomes must be maintained. Thepresence of more than two centrosomes (centrosomeampliﬁcation) increases the frequency of mitotic defectand unbalanced chromosome segregation. Indeed,centrosome ampliﬁcation is frequently found in cancercells, and occurrence of centrosome ampliﬁcation isstrongly associated with chromosome instability (re-viewed by D’Assoro et al., 2002; Fukasawa, 2005).Generationofampliﬁedcentrosomesisprimarilycausedbyderegulatedduplicationofcentrosomes.Centrosomeduplication proceeds in coordination with other cellcycleevents(i.e.,DNAreplication),normallystartingatthe time of Sphase entry and being completed in lateG2phase (Mazia, 1987). Thus, it is not surprising thatthe pathways controlling initiation of DNA synthesisare also involved in the regulation of centrosomeduplication. For instance, cyclin-dependent kinase 2(CDK2)/cyclin E, a key initiator of DNA replication(reviewedbyHeichmanandRoberts,1994;Sherr,1994),triggerscentrosomeduplication(reviewedbyHinchcliffeandSluder,2002).Accordingly,p53isalsoinvolvedinthe regulation of centrosome duplication (reviewed byTarapore and Fukasawa, 2002). p21