Aneuploidy and Tetraploidy as Distinct Patterns During Melanomagenesis

Melanoma is characterized by a high degree of chromosome instability (CIN), the loss or gain of entire chromosomes or pieces of chromosomes. Also, CIN is likely to drive the progression of benign melanocytic lesions to malignant tumors, although very little is known about the acquisition of the mechanisms that promote CIN along this progression. Here, we describe the development of a model system to study the progression of melanomagenesis starting with normal human melanocytes followed by inactivation of the p53 and pRb tumor suppressors by addition of the E6/E7 proteins. The cells were then transduced with a growth-promoting, constitutionally-active mutant NRAS. The addition of E6/E7 and E6/E7 NRAS was found to give a growth advantage to the cells compared to normal melanocytes and a statistically significant gain of aneuploidy; aneuploidy was 24.7% in primary melanocytes, 33.8% in E6/E7 melanocytes, and 70.5% in E6/E7 NRAS melanocytes. Further, we found an increase in tetraploid cells in the cell model which was statistically significant between primary melanocytes and E6/E7, NRAS melanocytes. We also observed an increase in aneuploid cells between three population doublings in primary melanocytes, whereas this increase was not seen in the E6/E7 melanocytes. Together, these data demonstrate that this model system utilizing stepwise addition of genetic mutations driving melanomagenesis is a useful tool to study CIN and could even be used to study the mechanisms responsible for these alterations in genetic makeup.