Hsp90 is a core centrosomal component and is required at different stages of the centrosome cycle in Drosophila and vertebrates

To determine the molecular composition of the centrosome of a higher eukary ote, we carried out a systematic nano-electrospray tandem or MALDI mass spe ctrometry analysis of the polypeptides present in highly enriched preparati ons of immunoisolated Drosophila centrosomes. One of the proteins identifie d is Hsp83, a member of the highly conserved Hsp90 family including chapero nes known to maintain the activity of many proteins but suspected to have o ther essential, unidentified functions. We have found that a fraction of th e total Hsp90 pool is localized at the centrosome throughout the cell cycle at different stages of development in Drosophila and vertebrates. This ass ociation between Hsp90 and the centrosome can be observed in purified centr osomes and after treatment with microtubule depolymerizing drugs, two crite ria normally used to define core centrosomal components. Disruption of Hsp9 0 function by mutations in the Drosophila gene or treatment of mammalian ce lls with the Hsp90 inhibitor geldanamycin, results in abnormal centrosome s eparation and maturation, aberrant spindles and impaired chromosome segrega tion. This suggests that another role of Hsp90 might be to ensure proper ce ntrosome function.