Phosphorylation by aurora kinase A induces Mdm2-mediated destabilization and inhibition of p53

Abstract

Aurora kinase A is a member of a new family of serine/threonine kinases that includes Drosophila melanogaster Aurora and Saccharomyces cerevisiae Ipl1 kinase, both of which are essential for controlling normal chromosome segregation and centrosome functions [1][2][3] . Aurora kinase A has been implicated in regulating centrosome function, spindle assembly, spindle maintenance and mitotic commitment in cells [4][5][6][7] . AURKA, encoding aurora kinase A, is a putative oncogene that is amplified and overexpressed in many human cancers [8][9][10][11][12][13] . The molecular targets of aurora kinase A have not been well characterized. We previously reported that phosphorylationmediated feedback between aurora kinase A and protein phosphatase 1 operates through mitosis and that disruption of this interaction results in defects in chromosome segregation 14 .Overexpression of aurora kinase A 8 and loss of wild-type p53 function induce similar phenotypes of centrosome amplification and aneuploidy in cells 15,16 . These observations suggest that gain of aurora kinase A function and loss of wild-type p53 function may be interdependent in common pathways. The finding that human tumors with elevated expression of aurora kinase A have wild-type TRP53 (encoding p53) also suggests that gain of aurora kinase A function may cause loss of wild-type p53 function, contributing to malignant transformation. p53 induces growth arrest or apoptosis in cells exposed to stress and is frequently mutated or deleted in human cancers. Expression of p53 is controlled by Mdm2, which promotes ubiquitination by E3 ubiquitin ligase activity and degradation of p53 by the cytoplasmic 26S proteasome 17 . Stability and activity of p53 are also regulated by post-translational modifications 18-23 including phosphorylation, acetylation, glycosylation and attachment of a small ubiquitin-related modifier protein. Phosphorylation at multiple sites is the predominant mechanism known to stabilize and abrogate Mdm2-mediated ubiquitination and activates p53. In contrast, phosphorylation of the core domain at Thr155 by the COP9 signalosome has been reported to target p53 for degradation 24 . The present study investigated whether phosphorylation by aurora kinase A also regulates p53 activity. RESULTS Aurora kinase A phosphorylates and interacts with p53We first investigated the ability of aurora kinase A to phosphorylate p53 in an in vitro kinase assay. We incubated bacterially expressed glutathione S-transferase (GST) and a GST-p53 fusion protein with aurora kinase A immunoprecipitated from mitotic HeLa cells and γ 32 P ATP. The aurora kinase A immunocomplex clearly phosphorylated GST-p53 (Fig. 1a). To confirm the specificity of aurora kinase A in phosphorylating p53, we used immunoprecipitated wild-type and kinase-inactive aurora kinase A (K162R) in an in vitro kinase assay with GST-p53. Wild-type aurora kinase A phosphorylated p53 but the kinase-inactive mutant did not (Fig. 1b), confirming that aurora A R T I C L E S

BimEL is phosphorylated at mitosis by Aurora A and targeted for degradation by βTrCP1

“…The p53 tumor suppressor was shown to be phosphorylated by Aurora A leading to destabilization and degradation of the p53 protein in a mechanism reminiscent of what we have observed for BimEL. 47,48 Similarly, Aurora A was shown to phosphorylate BRCA1 and promote G2/M cell cycle progression. 49 Thus, in addition to the wide range of substrates targeted by Aurora A regulating chromosome and spindle dynamics during mitosis, it can also phosphorylate and deactivate tumor-suppressor pathways including Bim.…”

Overexpression of Aurora-A kinase promotes tumor cell proliferation and inhibits apoptosis in esophageal squamous cell carcinoma cell line

“…However, the molecular mechanism(s) by which Aurora-A increases expression of Bcl-2 protein remains to be elucidated in the future study. Recently, several targets that are phosphorylated by Aurora-A kinase have been identified, including the tumor suppressor protein p53 and HURP (hepatoma upregulated protein) [13,21]. Aurora-A overexpression leads to increased degradation of p53 and stabilization of HURP, causing facilitating oncogenic transformation of cells.…”

“…Ectopic expression of Aurora-A in murine fibroblasts as well as mammary epithelia induces centrosome amplification, aneuploidy, and oncogenic phenotype [11], suggesting that when overexpressed, Aurora-A is a potential oncogene. Recent study indicates that Aurora-A overexpression induces a striking increase in resistance to Taxol-induced apoptosis in HeLa cells [12], also, cells depleted of Aurora-A are sensitive to cisplatin-induced apoptosis in MCF-7 cells, and elevated expression of Aurora-A abolishes this response [13]. Although Aurora-A overexpression has been shown to prevent apoptosis by anti-cancer drugs, however, the molecular mechanisms mediating these effects are largely unknown.…”

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

“…13 As a consequence, the phosphorylation status of p53 Ser315 is periodic and regulated throughout cell cycle. Interestingly, the expression of E2F1-3 and cyclin A are precisely regulated during the cell cycle (reviewed in Loughan and La Thangue 6 ).…”