GSK-3β-dependent destabilization of cyclin D1 mediates replicational stress-induced arrest of cell cycle

Chemotherapeutic agents are well known to induce growth arrest of cancerous cells by inducing DNA damage/replicational stress and engaging cellular apoptotic machinery. Our studies on hydroxyurea (HU) recognized cyclin D1 destabilization as the initiator of growth arrest at G1/S-phase independent of other cell cycle regulators. Cyclin D1 degradation was associated with its phosphorylation at Thr286 by glycogen synthase kinase-3β and inactivation of Akt kinase. Overexpression of the cyclin D1T286A mutant, or constitutively active Akt, conferred stability to cyclin D1 and helped bypass cell cycle arrest. Thus, growth arrest by HU seems to involve destabilization of cyclin D1 in addition to its well-established role as ribonucleotide reductase inhibitor.