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.

ABSTRACT

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.