Characterization of various types of mast cells derived from model mice of familial gastrointestinal stromal tumors with KIT-Asp818Tyr mutation.

Sporadic mast cell neoplasms and gastrointestinal stromal tumors (GISTs) often have various types of somatic gain-of-function mutations of the c-kit gene which encodes a receptor tyrosine kinase, KIT. Several types of germline gain-of-function mutations of the c-kit gene have been detected in families with multiple GISTs. All three types of model mice for the familial GISTs with germline c-kit gene mutations at exon 11, 13 or 17 show development of GIST, while they are different from each other in skin mast cell number. Skin mast cell number in the model mice with exon 17 mutation was unchanged compared to the corresponding wild-type mice. In the present study, we characterized various types of mast cells derived from the model mice with exon 17 mutation (KIT-Asp818Tyr) corresponding to human familial GIST case with human KIT-Asp820Tyr to clarify the role of the c-kit gene mutation in mast cells. Bone marrow-derived cultured mast cells (BMMCs) derived from wild-type mice, heterozygotes and homozygotes were used for the experiments. Immortalized BMMCs, designated as IMC-G4 cells, derived from BMMCs of a homozygote during long-term culture were also used. Ultrastructure, histamine contents, proliferation profiles and phosphorylation of various signaling molecules in those cells were examined. In IMC-G4 cells, presence of additional mutation(s) of the c-kit gene and effect of KIT inhibitors on both KIT autophosphorylation and cell proliferation were also analyzed. We demonstrated that KIT-Asp818Tyr did not affect ultrastructure and proliferation profiles but did histamine contents in BMMCs. IMC-G4 cells had an additional novel c-kit gene mutation of KIT-Tyr421Cys which is considered to induce neoplastic transformation of mouse mast cells and the mutation appeared to be resistant to a KIT inhibitor of imatinib but sensitive to another KIT inhibitor of nilotinib. IMC-G4 cells might be a useful mast cell line to investigate mast cell biology.