Abrogation of c-kit/Steel factor-dependent tumorigenesis by kinase defective mutants of the c-kit receptor: c-kit kinase defective mutants as candidate tools for cancer gene therapy.

The growth and survival of many types of cancer cells are known to be supported by specific growth factor/cytokine systems. Among these, the activation of c-kit receptor and its ligand steel factor participates in several types of human carcinogenesis. W mutations of laboratory mouse strains are loss of functional mutations of the c-kit receptor. To examine the validity of these mutants in investigating c-kit-mediated carcinogenesis and in the treatment of c-kit-dependent tumors, we introduced various W mutations (W, Wv, and W42) into a transgenic mouse strain carrying human papillomavirus oncogenes, in which c-kit/Steel-mediated tumorigenesis occurs with a very high incidence. In all transgenic strains carrying a W mutation, the c-kit deficiency affected the tumorgenic process to various degrees. Tumor development was markedly suppressed in transgenic strains carrying kinase defective mutations (Wv and W42) in a heterozygous condition. In null-type (W) heterozygous transgenic mice, tumorigenesis was suppressed at a lower level. Moreover, minimal focal legions or, in some cases, no focal legions were found in the testes of W/Wv heterozygous transgenic mice, showing a close relationship between tumor cell growth and the degree of c-kit inactivation. These results indicated that c-kit activity is a pivotal determinant of testicular tumor development and that the kinase defective mutants of c-kit are valuable for treating c-kit-dependent cancer, as well as for clarifying the c-kit-mediated carcinogenesis.