Cell growth and proliferation are regulated by various intracellular and environmental cues, including nutrients, growth factors, energy, and stress. Recent studies have suggested that the mammalian target of rapamycin (mTOR) plays a key role in sensing and integrating these diverse signals, thus placing mTOR as a central regulator of cell growth and proliferation. Interest in mTOR is also spawned by clinical applications of mTOR inhibitors in transplantation, prevention of coronary restenosis (reconstriction or renarrowing of a coronary artery after it has been treated with angioplasty or stenting), and treatment of cancer.