Polo-like Kinase 1-mediated Phosphorylation Stabilizes Pin1 by Inhibiting Its Ubiquitination in Human Cells

Abstract

The Polo-like kinase 1 (Plk1) is a key regulator of mitosis. It is reported that the human peptidyl-prolyl cis/trans-isomerase Pin1 binds to Plk1 from mitotic cell extracts in vitro. Here we demonstrate that Ser-65 in Pin1 is the major site for Plk1-specific phosphorylation, and the polo-box domain of Plk1 is required for this phosphorylation. Interestingly, the phosphorylation of Pin1 by Plk1 does not affect its isomerase activity but rather is linked to its protein stability. Pin1 is ubiquitinated in HeLa S3 cells, and substitution of Glu for Ser-65 reduces the ubiquitination of Pin1. Furthermore, inhibition of Plk1 activity by expression of a dominant negative form of Plk1 or by transfection of small interfering RNA targeted to Plk1 enhances the ubiquitination of Pin1 and subsequently reduces the amount of Pin1 in human cancer cells. Since previous reports suggested that Plk1 is a substrate of Pin1, our work adds a new dimension to this interaction of two important mitotic regulators.

Some p53-binding proteins that can function as arbiters of life and death

“…76,77 Moreover, phosphorylation events regulate both its nuclear localization and substrate binding capability (reviewed in Wulf et al 59 ), while recently its ubiquitin-mediated degradation has been found to be inhibited by mitotic signals through Polo-like Kinase1 (Plk1). 78 Plk1 is overexpressed in many tumors and this may contribute to the increased levels of Pin1 observed in several cancers. Deregulation of Pin1 can therefore contribute to cancer progression, but this must be reconciled with its role as a regulator of p53 and p73.…”

EEL-1, a Hect E3 ubiquitin ligase, controls asymmetry and persistence of the SKN-1 transcription factor in the earlyC. elegansembryo

“…For example, the E3 ligase activity of EEL-1 could be controlled by phosphorylation, as in case of the Hect E3 ligase Itch (Gao et al, 2004). Alternatively, ubiquitin-dependent degradation of a protein can be enhanced or suppressed by its phosphorylation (Musti et al, 1997;Deng et al, 2004;Eckerdt et al, 2005;Nishi and Lin, 2005;Stitzel et al, 2006). Either of these hypotheses could explain spatially restricted activity at one stage, but uniform activity at a slightly later stage.…”

Pin1 : une peptidyl-prolylcis-transisomérase multifonctionnelle et une cible anticancéreuse prometteuse

“…Cette phosphorylation ne régule pas l'activité de Pin1, mais sa stabilité, en inhibant son ubiquitination et sa dégradation par le protéasome. En effet, la déplétion de PLK1 dans des cellules cancéreuses humaines entraîne l'ubiquitination et la dégradation de Pin1 [29]. Les études citées précédemment ont permis d'identifier plusieurs mécanismes de régulation de Pin1, mais il reste primordial de continuer ces investigations pour comprendre plus finement comment Pin1 est régulée afin d'identifier de nouvelles pistes thérapeutiques pour inhiber Pin1 dans les cancers humains.…”