M-COPA markedly increased the colocalization of KIT/PDGFRA with an ER marker, protein disulfide isomerase (PDI), suggesting that ER export of KIT and PDGFRA is blocked in M-COPA-treated GIST-T1 cells (Fig. 1, B and C). The gene discussed is PDGFRA; the disease is gastrointestinal stromal tumor.