Somatic p16^INK4a loss accelerates melanomagenesis

Loss of p16 INK4a-RB and ARF-p53 tumor suppressor pathways, as well as activation of RAS-RAF signaling, is seen in a majority of human melanomas. Although heterozygous germline mutations of p16 INK4a are associated with familial melanoma, most melanomas result from somatic genetic events: often p16 INK4a loss and N-RAS or B-RAF mutational activation, with a minority possessing alternative genetic alterations such as activating mutations in K-RAS and/or p53 inactivation. To generate a murine model of melanoma featuring some of these somatic genetic events, we engineered a novel conditional p16 INK4a-null allele and combined this allele with a melanocyte-specific, inducible CRE recombinase strain, a conditional p53-null allele and a loxP-stop-loxP activatable oncogenic K-Ras allele. We found potent synergy between melanocyte-specific activation of K-Ras and loss of p16 INK4a and/or p53 in melanomagenesis. Mice harboring melanocyte-specific activated K-Ras and loss of p16 INK4a and/or p53 developed invasive, unpigmented and nonmetastatic melanomas with short latency and high penetrance. In addition, the capacity of these somatic genetic events to rapidly induce melanomas in adult mice suggests that melanocytes remain susceptible to transformation throughout adulthood.