Clustering of Activating Mutations in c-KIT’s Juxtamembrane Coding Region in Canine Mast Cell Neoplasms

Abstract

The proto-oncogene c-KIT encodes a growth factor receptor, KIT, with ligand-dependent tyrosine kinase activity that is expressed by several cell types including mast cells. c-KIT juxtamembrane coding region mutations causing constitutive activation of KIT are capable of transforming cell lines and have been identified in a human mast cell line and in situ in human gastrointestinal stromal tumors, but have not been demonstrated in situ in neoplastic mast cells from any species. To determine whether c-KIT juxtamembrane mutations occur in the development of mast cell neoplasms, we examined canine mastocytomas, which are among the most common tumors of dogs and which often behave in a malignant fashion, unlike human solitary mastocytomas. Sequencing of c-KIT cDNA generated from tumor tissues removed from seven dogs revealed that three of the tumors contained a total of four mutations in an intracellular juxtamembrane coding region that is completely conserved among vertebrates. In addition, two mutations were found in three mast cell lines derived from two additional dogs. One mutation from one line matched that found in situ in one of the tumors. The second was found in two lines derived from one dog at different times, indicating that the mutation was present in situ in the animal. All five mutations cause high spontaneous tyrosine phosphorylation of KIT. Our study provides in situ evidence that activating c-KIT juxtamembrane mutations are present in, and may therefore contribute to, the pathogenesis of mast cell neoplasia. Our data also suggest an inhibitory role for the KIT juxtamembrane region in controlling the receptor kinase activity.

Activate and resist: L576P-KIT in GIST

“…3A and B). Discussion L576P is a rare mutation located in the JMD of KIT described in GISTs (6-10), melanomas (11), and canine GISTs and mastocytomas (12,13). We observed three L576P mutations among 332 profiled GISTs, of which we report upon two cases here (the third being enrolled into the 62024 EORTC trial).…”

“…In particular, the COS-7 cells expressing the L576P/KIT c-DNA revealed spontaneous KIT phosphorylation (13), and in vitro sensitivity tests highlighted the need of a tenfold higher dose of imatinib to switch off activated L576P/KIT with respect to V599D/KIT (11).…”

Results of imatinib mesylate therapy in patients with refractory or recurrent acute myeloid leukemia, high‐risk myelodysplastic syndrome, and myeloproliferative disorders

“…23 Mastocytosis also frequently expresses mutated c-kit, which confers constitutive activation. However, this mutation occurs in codon 816, resulting in residue substitutions in the activation loop, 24 and is insensitive to imatinib in vitro. 25 Despite the frequent expression of c-kit in AML and MDS patients, mutations are reported rarely.…”

FLT3: ITDoes matter in leukemia

“…61 Internal tandem duplications are not unique to FLT3, as similar mutations have been reported to occur in the related receptor KIT (in canine mastocytomas) and in other (nonhuman) genes. 81,82 Partial tandem duplications of the mixed lineage leukemia (MLL) gene have been found in both AML and ALL, sometimes in conjunction with an FLT3/ITD mutation. [83][84][85][86] The cause of these duplication events has been speculated upon, but remains unknown.…”

“…[97][98][99] An activating tandem duplication within the juxtamembrane region of KIT was identified in a canine mastocytoma, and a variety of activating point mutations within this region of the receptor have been found in human gastrointestinal stromal tumors. 81,100 An activating juxtamembrane point mutation was also identified in the PDGF receptor. 97 …”