Cells grow abundantly when oxygen is available, and generally stop growing when it is scarce. Although this seems straightforward, no direct link has ever been established between the cellular machinery that senses oxygen and that which controls cell division. Now, in the June 10 issue of Molecular Cell, researchers at Johns Hopkins report that the mini-chromosome maintenance (MCM) proteins, which promote cell division, also directly control the oxygen-sensing hypoxia-inducible factor 1 (HIF-1) protein. "It's always been a mystery why a vast excess of MCM proteins is present in cells, but now we have discovered at least one reason," says Dr. Gregg Semenza, the C. Michael Armstrong Professor of Medicine, director of the vascular program in Hopkins' Institute for Cell Engineering and a member of the McKusick-Nathans Institute of Genetic Medicine. "Our data indicate that MCMs mediate crosstalk between the cell division machinery and proteins that help cells react to changes in their surroundings." Since discovering HIF-1 in the 1990s, Dr. Semenza's team has been studying how it works to sense oxygen levels and turn on genes that help cells survive when oxygen is low. To find proteins that HIF-1 physically interacts with, the team went on a biochemical fishing expedition and, using HIF-1 as bait, pulled out MCM7. MCM7 is a member of a larger group of related proteins that are known to bind to DNA and start its duplication when a cell gets ready to divide. Using a different protein-binding technique, the team then found that HIF-1 also binds to MCM3. When it senses low oxygen levels, HIF-1 turns on genes that enable cells to adapt, such as genes that stimulate the growth of new blood vessels and genes that alter a cell's metabolism to change how much oxygen it consumes for energy generation.Login Or Register To Read Full Story