KIT and gastrointestinal stromal tumor: To examine whether ER export of RTKs other than KIT was blocked by M-COPA, we used GIST-T1 cells (a human GIST cell line expressing mutant KIT (KITΔ560–578) and wild-type platelet-derived growth factor receptor A (PDGFRA)) (27) and PC-9 cells (a human LAD cell line expressing mutant EGFR (EGFRΔ746–750) and wild-type hepatocyte growth factor receptor (MET)) (28).