LKB1 (STK11) is an essential human tumor suppressor, the key upstream activator of the AMP-activated protein kinase (AMPK). AMPK is a central metabolic switch found in all eukaryotes that govern glucose and lipid metabolism in response to alterations in nutrients and intracellular energy levels. LKB1 and AMPK control cell growth in response to environmental nutrient changes. One of the major growth regulatory pathways controlled by LKB1-AMPK is the mammalian target-of-rapamycin (mTOR) pathway. mTOR is a central integrator of nutrient and growth factors that control cell growth.