A positive feedback loop between the p53 and Lats2 tumor suppressors prevents tetraploidization

Abstract

Damage to the mitotic spindle and centrosome dysfunction can lead to cancer. To prevent this, cells trigger a succession of checkpoint responses, where an initial mitotic delay is followed by slippage without cytokinesis, spawning tetraploid G1 cells that undergo a p53-dependent G1/S arrest. We describe the importance of Lats2 (Large Tumor Suppressor 2) in this checkpoint response. Lats2 binds Mdm2, inhibits its E3 ligase activity, and activates p53. Nocodazole, a microtubule poison that provokes centrosome/mitotic apparatus dysfunction, induces Lats2 translocation from centrosomes to the nucleus and p53 accumulation. In turn, p53 rapidly and selectively up-regulates Lats2 expression in G2/M cells, thereby defining a positive feedback loop. Abrogation of Lats2 promotes accumulation of polyploid cells upon exposure to nocodazole, which can be prevented by direct activation of p53. The Lats2-Mdm2-p53 axis thus constitutes a novel checkpoint pathway critical for the maintenance of proper chromosome number.[Keywords: Lats2; Mdm2; p53; tetraploidy checkpoint] Supplemental material is available at http://www.genesdev.org.

Fbw7 regulates the activity of endoreduplication mediators and the p53 pathway to prevent drug-induced polyploidy

“…(Waldman et al, 1996). Since p53 responds to oncogenic stresses such as cyclin E deregulation (Deffie et al, 1995;Stewart et al, 1999), unscheduled DNA replication (Bartkova et al, 2005) or microtubule disruption (Doxsey et al, 2005), and has an essential role in the prevention of polyploidy (Di Leonardo et al, 1997;Aylon et al, 2006), it was important to verify the functionality of p53 in HCT116 Fbw7 À/À cells. We measured the level and activity of p53 by determining its own level and the levels of its target gene product, Mdm2, in Fbw7 À/À and Fbw7 þ / þ cells before and after treatment with vinblastine.…”

“…To support this notion, we also examined the induction of two additional p53 target-gene products, Lats2 and p21 cip1 . Lats2 is activated by mitotic apparatus damage, upon which it translocates from the centrosome to the nucleus, where Fbw7 activity prevents drug-induced polyploidy S Finkin et al it interacts with and inhibits Mdm2 to induce p53 (Aylon et al, 2006). p21 cip1 is a well-characterized inhibitor of cell cycle progression.…”

“…For that end, Lats2 was stably overexpressed in Fbw7 À/À and Fbw7 þ / þ cells, and their responses to taxol were monitored. Lats2 was chosen since it specifically regulates the p53 response to mitotic stress (Aylon et al, 2006), and Fbw7 affects its induction (Figure 6a). The levels of ectopic Lats2 in the transfected cells were approximately fourfold higher than the endogenous levels (Figure 6c).…”

“…These phosphorylations reduce p53 levels and transcriptional activity (Katayama et al, 2004;Liu et al, 2004). Aurora A also phosphorylates Lats2, a serine/threonine kinase considered to be a tumor suppressor which controls M phase transit and activation of the p53-dependent tetraploidy checkpoint (Toji et al, 2004;Aylon et al, 2006).…”

Reactivation of epigenetically silenced miR-512 and miR-373 sensitizes lung cancer cells to cisplatin and restricts tumor growth

“…Western blot analysis was performed as described. 53 For detection of pAkt and total Akt, cells were incubated for 20 h with medium supplemented with 0.5% serum, and then treated with 10 ng/ml insulin (Sigma Aldrich), harvested in sample buffer, boiled and sonicated for 5 min.…”