AXL and neoplasm: To determine whether Axl mediates tumor cell-induced angiogenesis, human breast cancer cells (MDA-MB-231) were transduced with lentiviral shRNA against scrambled sequence (shScramble) or Axl (shAxl) to generate stable cell lines and reductions in the level of the Axl protein in knockdown cells was confirmed by immunoblot (Figure 1A).