A Centrosomal Localization Signal in Cyclin E Required for Cdk2-Independent S Phase Entry

Abstract

Excess cyclin E-Cdk2 accelerates entry into S phase of the cell cycle and promotes polyploidy, which may contribute to genomic instability in cancer cells. We identified 20 amino acids in cyclin E as a centrosomal localization signal (CLS) essential for both centrosomal targeting and promoting DNA synthesis. Expressed wild-type, but not mutant, CLS peptides localized on the centrosome, prevented endogenous cyclin E and cyclin A from localizing to the centrosome, and inhibited DNA synthesis. Ectopic cyclin E localized to the centrosome and accelerated S phase entry even with mutations that abolish Cdk2 binding, but not with a mutation in the CLS. These results suggest that cyclin E has a modular centrosomal-targeting domain essential for promoting S phase entry in a Cdk2-independent manner.

A small molecule based on the pRb2/p130 spacer domain leads to inhibition of cdk2 activity, cell cycle arrest and tumor growth reduction in vivo

“…Although it has been described that cdk2 is not an essential gene in the mouse, (Berthet et al, 2003;Geng et al, 2003;Ortega et al, 2003;Tetsu and McCormick, 2003) an overexpression of cdk2 with associated cyclins has been shown in several tumors (Al-Aynati et al, 2004;Olofsson et al, 2004). Furthermore, cdk2 has been recently found to be required for centrosome duplication in mammalian cells (Matsumoto et al, 1999;Matsumoto and Maller, 2004) suggesting that inhibition of cdk2 activity would be an effective anticancer approach. In addition, cdk2 has rapidly emerged as a potential inhibition target by small molecule drugs that will hopefully lead to the development of effective therapies for proliferative disorders (Gibbs and Oliff, 1994;Senderowicz, 2003 We were therefore led to generate a molecular tool that provides a mechanism-based model for the inhibition of cdk2 activity.…”

Steroidogenic Factor 1 (NR5A1) resides in centrosomes and maintains genomic stability by controlling centrosome homeostasis

“…This CLS has similar properties as other centrosome-targeting domains from proteins like AKAP450, Cyclin A, Cyclin E, which displace their endogenous proteins from centrosomes when overexpressed. [27][28][29][30] These CLS domains interact with scaffold proteins important for centrosome localization and functions of their endogenous proteins.…”

Expression of a cyclin E1 isoform in mice is correlated with the quiescent cell cycle status of hepatocytesin vivo

“…45 However, the localization of cyclin E1 to the centrosome is controlled by the CLS encoded in exon 9, which has a critical effect on S phase entry and DNA synthesis independently of cdk2. 37 As in the ⌬3/8 isoform lacking the NLS but still containing an intact CLS, we speculated that ⌬3/8 should be restrained to the cytoplasm. In fact, our experiments clearly demonstrated that ⌬3/8 was exclusively located in the cytoplasm and failed to undergo nuclear import in parallel with cdk2 in quiescent cells.…”