The Polycomb group (PcG) protein, enhancer of zeste homologue 2 (EZH2), has an essential role in promoting histone H3 lysine 27 trimethylation (H3K27me3) and epigenetic gene silencing1–4. This function of EZH2 is important for cell proliferation and inhibition of cell differentiation, and is implicated in cancer progression5–10. Here, we demonstrate that under physiological conditions, cyclin-dependent kinase 1 (CDK1) and cyclin-dependent kinase 2 (CDK2) phosphorylate EZH2 at Thr 350 in an evolutionarily conserved motif. Phosphorylation of Thr 350 is important for recruitment of EZH2 and maintenance of H3K27me3 levels at EZH2-target loci. Blockage of Thr 350 phosphorylation not only diminishes the global effect of EZH2 on gene silencing, it also mitigates EZH2-mediated cell proliferation and migration. These results demonstrate that CDK-mediated phosphorylation is a key mechanism governing EZH2 function and that there is a link between the cell-cycle machinery and epigenetic gene silencing.

Prostate cancer (PCa) patients with regional lymph node involvement at radical prostatectomy often experience disease progression to other organs, with the bone as the predominant site. The transcription factor Runx2 plays an important role in bone formation and PCa cell migration, invasion and metastasis. Here we demonstrated that the forkhead protein FOXO1, a key downstream effector of the tumor suppressor PTEN, inhibits the transcriptional activity of Runx2 in PCa cells. This inhibition was enhanced by PTEN but diminished by active Akt. FOXO1 bound to Runx2 in vitro and in vivo and suppressed Runx2’s activity independent of its transcriptional function. FOXO1 inhibited Runx2-promoted migration of PCa cells while silencing of endogenous FOXO1 enhanced PCa cell migration in a Runx2-dependent manner. Forced expression of FOXO1 also inhibited Runx2-promoted PCa cell invasion. Finally, we found that expression of PTEN and the level of FOXO1 in the nucleus is inversely correlated with expression of Runx2 in a cohort of PCa specimens from patients with lymph node and bone metastasis. These data reveal FOXO1 as a critical negative regulator of Runx2 in PCa cells. Inactivation of FOXO1 due to frequent loss of PTEN in PCa cells may leave the oncogenic activities of Runx2 unchecked, thereby driving promiscuous expression of Runx2 target genes involved in cell migration and invasion and favoring PCa progression.