STK11 and cancer: Conversely, Lkb1 deletion is associated with a transient hyper-proliferative HSC response that is followed by an AMPK/mTOR independent catastrophic HSC depletion, pancytopenia and animal death.36, 37, 38 Ionizing radiation regulates AMPK activation in endothelial cells,39 mouse embryonic fibroblasts (MEFs)40 and cancer cells.41, 42 However, the effect of radiation on AMPK in HSPC is poorly understood and the predominant upstream kinase responsible for radiation-induced AMPK activation is unknown.