Figure 3c shows that pKit[Tyr721] co-localized with golgin97 (trans-Golgi marker) rather than with GM130 (cis-Golgi marker), indicating that more activation occurs on trans-Golgi than on cis-Golgi. Also, tyrosine phosphorylation signals are concentrated in the Golgi (Supplementary Figures S3b and c), indicating that Golgi apparatus serves as a platform for tyrosine phosphorylation signaling in GISTs. In GIST-T1 and HeLa cells transfected with a mastocytoma-type mutant Kit(D814Y),14, 34, 38 autophosphorylation of the mutant mainly occurs on the Golgi (Supplementary Figure S3d). Here, GOLGA1 is linked to mastocytoma.