Cyclin D/Cdk4: new insights from Drosophila

The Drosophila cyclin-dependent protein kinase complex CycD/Cdk4 has been known to drive cellular growth (accumulation of mass) as well as proliferation (cell cycle progression). Recent data demonstrate that Hif prolyl hydroxylase (Hph) is required for the induction of growth, but not for the induction of proliferation. Normal levels of Hph are required for cellular growth, demonstrating that Hph, in addition to its known function in the cellular response low oxygen levels, regulates growth. Since Hph's hydroxylation activity depends on oxygen and possibly the mitochondrial activity, these data provide a link between CycD/Cdk4 and oxygen/energy homeostasis.