One day after plating, DCDML cultures were transfected in M199 medium without BOTS or antibiotics using Lipofectamine 2000 (Invitrogen, Waltham, MA, USA). following the manufacturer's suggested protocol. Control experiments confirmed that the efficiency of transient transfection of DCDMLs is consistently ∼70%.43 (link) The SBE4-Luc reporter construct was provided by Bert Vogelstein (Johns Hopkins University; Addgene plasmid #16495). pcDNA3 plasmids encoding the following ErbB species were obtained from Addgene (Watertown, MA, USA): ErbB2-EGFP (#39321), originally from Martin Offterdinger; EGFR-GFP (#32751) from Alexander Sorkin; and ErbB4 (#29527) from Yardena Samuels.