MCM Proteins Are Negative Regulators of Hypoxia-Inducible Factor 1

MCM proteins are components of a DNA helicase that plays an essential role in DNA replication and cell proliferation. However, MCM proteins are present in excess relative to origins of replication, suggesting they may serve other functions. Decreased proliferation is a fundamental physiological response to hypoxia in many cell types, and hypoxia-inducible factor 1 (HIF-1) has been implicated in this process. Here, we demonstrate that multiple MCM proteins bind directly to the HIF-1 alpha subunit and synergistically inhibit HIF-1 transcriptional activity via distinct O(2)-dependent mechanisms. MCM3 inhibits transactivation domain function, whereas MCM7 enhances HIF-1 alpha ubiquitination and proteasomal degradation. HIF-1 activity decreases when quiescent cells re-enter the cell cycle, and this effect is MCM dependent. Exposure to hypoxia leads to MCM2-7 down-regulation in diverse cell types. These studies reveal a function of MCM proteins apart from their DNA helicase activity and establish a direct link between HIF-1 and the cell-cycle machinery.