Mutations in the intracellular juxtamembrane domain of the c-kit gene in 32 dogs with different grades of histologically confirmed mastocytoma were studied. Transcript RNAs extracted from neoplastic tissue surgically collected from dogs of different breeds and from a negative control were reverse transcribed into complementary DNA and amplified by polymerase chain reaction. The region corresponding to the c-kit juxtamembrane domain was sequenced and compared with GenBank sequences. Two different types of mutations were identified within exon 11: a previously underscribed single-nucleotide substitution and a 6-bp deletion. The c-kit juxtamembrane domain sequences of all dogs were grouped in 3 clusters. No mutations were detected in tissues constitutively expressing c-kit (cerebellum and spleen), obtained from dogs not affected by mastocytoma (controls). All the substitutions were found in dogs bearing grade I or II mast cell tumors; the deletion was detected in 1 dog with grade II mastocytoma.
Abstract. KIT receptor, the c-kit gene product, is thought to play a major role in canine mastocytoma, one of the most common neoplastic diseases in dogs. In the present study, the expression of c-kit proto-oncogene in blood and in tumor biopsies from 41 dogs with histologically confirmed mastocytoma at different grades of cellular differentiation and 5 negative control dogs was investigated using real-time (quantitative) reverse transcription-polymerase chain reaction (RRT-PCR). The animals were followed up for over 1 year after surgery in order to characterize the kinetics of c-kit expression in blood. Transcript mRNAs extracted from blood at different time points after surgery and from tumor tissue surgically removed from each dog were used in a quantitative RRT-PCR assay targeting the extracellular coding region of the c-kit gene. Tissues constitutively expressing c-kit (brain and spleen) were used as positive controls. Levels of expression of c-kit were higher in tumor biopsies than in blood; the blood level decreased in the patients between 1 and 3 months after surgery. No KIT expression was detected in blood from the 5 dogs not affected by mastocytoma (negative controls). The RRT-PCR appears to be a suitable method for sensitive and quantitative detection of c-kit gene expression in canine blood and neoplastic tissues. Although c-kit expression levels measured by RRT-PCR do not correlate with prognosis, they confirm that surgery remains the main treatment to reduce circulating mastocytes and that circulating mast cells can be detected even in benign highly differentiated forms of mastocytoma such as grade I.
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