AXL and lung cancer: To determine whether endogenous AXL in cancer cells shares a common cleavage mechanism with exogenously expressed AXL, we treated 3 types of cancer cell lines—lung cancer cells (H1299 and A549; Fig. 3A), pancreatic cancer cells (AsPC-1, Panc-1, and Panc-28; Fig. 3B), and glioma cells (LN-18 and LN-229; Fig. 3C)—with PMA, as well as with various secretase/protease inhibitors.