PP2A Is Required for Centromeric Localization of Sgo1 and Proper Chromosome Segregation

Abstract

Loss of sister-chromatid cohesion triggers chromosome segregation in mitosis and occurs through two mechanisms in vertebrate cells: (1) phosphorylation and removal of cohesin from chromosome arms by mitotic kinases, including Plk1, during prophase, and (2) cleavage of centromeric cohesin by separase at the metaphase-anaphase transition. Bub1 and the MEI-S332/Shugoshin (Sgo1) family of proteins protect centromeric cohesin from mitotic kinases during prophase. We show that human Sgo1 binds to protein phosphatase 2A (PP2A). PP2A localizes to centromeres in a Bub1-dependent manner. The Sgo1-PP2A interaction is required for centromeric localization of Sgo1 and proper chromosome segregation in human cells. Depletion of Plk1 by RNA interference (RNAi) restores centromeric localization of Sgo1 and prevents chromosome missegregation in cells depleted of PP2A_Aalpha. Our findings suggest that Bub1 targets PP2A to centromeres, which in turn maintains Sgo1 at centromeres by counteracting Plk1-mediated chromosome removal of Sgo1.

Shugoshin regulates cohesion by driving relocalization of PP2A in Xenopus extracts

“…The role of Sgo in the regulation of mitotic cohesion has been addressed in a number of recent studies, mainly in yeast and human cells McGuinness et al 2005;Vaur et al 2005;Kitajima et al 2006;Tang et al 2006;Kawashima et al 2007;Vanoosthuyse et al 2007;Lee et al 2008). However, this is the first time that the Xenopus egg cell free system, in which vertebrate cohesin was initially characterized, is used.…”

“…Anomalous PP2A distribution in the absence of Sgo impairs cohesin release Sgo associates with PP2A in yeast and human cells, and this association is important for cohesin protection (Kitajima et al 2006;Riedel et al 2006;Tang et al 2006). In HeLa cells depleted of Sgo1 by siRNA, cohesion is completely lost even though the centromeric localization of PP2A is preserved, a result that led Kitajima et al (2006) to suggest that Sgo could have an additional role and provide protection by itself, maybe through physical association with cohesin.…”

Cantharidin-induced mitotic arrest is associated with the formation of aberrant mitotic spindles and lagging chromosomes resulting, in part, from the suppression of PP2Aα

“…Therefore, it is critical for cells to guard centromeric cohesion from the actions of mitotic kinases before the onset of anaphase. Recently, PP2A has been shown to associate with Shugosin (Sgo1; Drosophila, MEI-S332), one of the proteins that is needed for the protection of centromeric cohesion in animals (32,33). In addition, the association of PP2A with Sgo1 has been shown to be necessary for the centromeric localization of Sgo1 and proper chromosome segregation in human cells (32,33).…”

“…Recently, PP2A has been shown to associate with Shugosin (Sgo1; Drosophila, MEI-S332), one of the proteins that is needed for the protection of centromeric cohesion in animals (32,33). In addition, the association of PP2A with Sgo1 has been shown to be necessary for the centromeric localization of Sgo1 and proper chromosome segregation in human cells (32,33). The data shown here are consistent with the role of PP2A in the protection of chromosome segregation, for cantharidin treatment of mitotic cells at concentrations that inhibit the activity of PP2A results in the dissociation of the chromosomes aligned on the metaphase plate in a random and unorganized manner.…”

Insights into centromeric transcription in mitosis

“…1), to protect the centromeric cohesion in mitosis, thus preventing chromosome missegregation and chromosome instability. [16][17][18][19][20] Our recent immunofluorescence microscopy demonstrated that Sgo1 is sequentially recruited to kinetochores and inner centromeres. 10 The kinetochore and centromeric receptors for Sgo1 are histone H2A phosphor Thr120 (H2A pT120) and cohesin, respectively.…”