Abstract
Drosophila cyclinD (CycD) is the single fly ortholog of the mammalian cyclin D1 and promotes both cell cycle progression and cellular growth. However, little is known about how CycD promotes cell growth. We show here that CycD/Cdk4 hyperactivity leads to increased mitochondrial biogenesis (mitobiogenesis), mitochondrial mass, NRF-1 activity (Tfam transcript levels) and metabolic activity in Drosophila, whereas loss of CycD/Cdk4 activity has the opposite effects. Surprisingly, both CycD/Cdk4 addition and loss of function increase mitochondrial superoxide production and decrease lifespan, indicating that an imbalance in mitobiogenesis may lead to oxidative stress and aging. In addition, we provide multiple lines of evidence indicating that CycD/Cdk4 activity affects the hypoxic status of cells and sensitizes animals to hypoxia. Both mitochondrial and hypoxia-related effects can be detected at the global transcriptional level. We propose that mitobiogenesis and the hypoxic stress response have an antagonistic relationship, and that CycD/Cdk4 levels regulate mitobiogenesis contemporaneous to the cell cycle, such that only when cells are sufficiently oxygenated can they proliferate.