The role of genetic susceptibility in melanoma development Abstract Our long-term goal is to identify new molecular targets for melanoma prevention and therapy. Current signaling therapy is restricted to very few targets. This program utilizes knowledge of combinations of environmental risk factors (UV radiation), inherited (germ-line) and somatic (acquired) mutations in genes that cooperate for melanoma development and progression to identify targets in a novel way. Even among susceptible individuals with sun exposure poor tanning, red hair, blue eyes, and multiple nevi, not all will develop melanoma and understanding the mechanisms of malignant transformation in the context of an inherited genetic background will provide insight for both prevention and therapy. The studies were initiated because of three major technological advances: 1. Identification of significantly greater numbers of inherited gene variants associated with risk for melanoma. Recent large-scale Genome Wide Association Studies (GWAS) studies have identified a series of novel gene variants which increase melanoma risk in pathways hitherto not known to be important in melanomagenesis. In this application, we are exploring the biological consequences of these inherited gene variants for melanoma development. 2. Identification of somatic mutations and gene variants as drivers and cooperating drivers in melanoma. We propose to study the effects of susceptibility genes in laboratory reconstructs of normal human skin in which we will investigate the modifying effects of somatic mutations. 3. Growth of melanocytes from older individuals. To achieve vigorous growth of melanocytes from donors over the age of 50, our laboratory has taken an indirect route: to isolate fibroblasts from 3mm punch biopsies of skin and reprogram these to induced pluripotent stem (iPS) cells that are immortal (similar to embryonic stem cells) and can differentiate into any human cell type including melanocytes. We have built an infrastructure to characterize the properties of melanocytes within the context of the normal human epidermis and dermis by producing reconstructed (synthetic) skin. In the first aim, we will characterize the biology of melanocytes derived through reprogramming of fibroblasts followed by differentiation from patients prone to melanoma. In the second aim, we will identify driver somatic mutant genes that cooperate with inherited risk genes for melanoma development and progression. We expect to develop models for melanoma development in the synthetic skin model that can then be validated in in vivo models of human melanoma. The environmental exposures, genes and gene combinations underlying transformation and progression will provide the ideal foundation for future studies in prevention in individuals susceptible to the disease. The same genes may also be targets for therapy.
Individuals with genetically determined phenotypes such as light skin color who poorly tan and have red hair, blue eyes and many moles are generally considered susceptible for melanoma compared to those with none of these attributes but only few contract the disease suggesting that additional genetic traits and environmental exposures play a major role. Recent research in single nucleotide polymorphisms (SNPs) associated with risk for melanoma has identified several risk associated SNPs but we do not know the biological basis of these as co-drivers for melanoma development. We will use normal cells from carriers of these SNPs to study the biological impact of this variation experimentally. One major reason for the lack of data on the biological significance of melanoma risk genes is that these patients are mainly identified at later stages of their life when melanocytes are very difficult to grow in tissue culture in high enough quantities for experimental studies. Therefore, our laboratories went an indirect route: we isolated normal fibroblasts from small punch biopsies of skin and reprogrammed them using four transcription factors in a technique that does not alter their genome structure. These so-called 'induced pluripotent stem cells'act similar to embryonic stem cells and can be differentiated into any of the >220 cell types of the human body. Fortuitous for us, those cells readily become melanocytes when stimulated with appropriate growth factor signals. We now want to stress the cells when they are embedded in artificial skin using ultraviolet light in the B and A range to determine whether they show any abnormalities when compared to cells without the gene variants. In the second aim we will hit the melanocytes from melanoma risk individuals with driver oncogenes that cannot transform on their own but need the currently unknown co-driver(s). We expect from these studies the identification of co-drivers that cooperate with driver genes and that will in the future prove to be the targets for melanoma prevention and therapy.