The purpose of this research is to develop the mouse skin carcinogenesis model as a paradigm for the study of tumor modifiers: their numbers and locations within the genome, their genetic interactions, biological functions and effects on the somatic genetic events of tumor development. Our ultimate goal is to clone tumor modifiers in the mouse for testing in human populations, with a view to improving the prospects for prediction of risk, prevention and therapy of human cancers. To achieve the broad aims set out in this proposal, we have set up an international consortium of groups and consultants with complementary expertise in the study of mouse tumor modifiers (P.Demant, Holland and T.Dragani,Italy), generation of novel models through germline manipulation, (T.Jacks, Boston; D.Hanahan and E.Epstein, San Francisco), physical induction of germline deletions for functional studies of modifier genes (T.Sato and M.Kusakabe, Japan), and the search for tumor modifiers in human populations (B.Ponder, UK). Our initial aim is to determine the number and chromosomal locations of skin tumor modifier loci in a variety of mouse strains, using a combination of genetic approaches including interspecific backcrosses between mus spretus and mus musculus. Since the detection of human modifiers of complex traits directly using human material involves approaches such as linkage disequilibrium with single nucleotide polymorphisms, we will pursue a parallel strategy in the mouse by investigating animals selected from a mixture of genetic backgrounds by virtue of sensitivity or resistance to skin carcinogenesis. This will be carried out using chemical carcinogenesis in skin as a method of tumor induction, and will provide us with information on the degree of overlap of these different approaches to the detection and analysis of tumor modifiers. A number of transgenic/knock out models for skin tumor induction will also be investigated. These include keratin promoter-driven ras or HPV transgenic mice, which develop multiple squamous carcinomas, and patched (Ptc) knock-out mice, which provide a model for the development of basal cell carcinomas after UV treatment. Modifiers of these transgene/knockout induced phenotypes will be analyzed using genetic mapping approaches in mus musculus and mus spretus crosses. In the same crosses, DNA repair capacity will be assessed (with J.Cleaver, San Francisco) in individual mice and the relationship between loci that control DNA repair and the tumor predisposition loci will be investigated. These studies may identify subsets of tumor modifiers which operate in skin independent of the mode of tumor induction, or which may be specific for a particular genetic insult or target cell within the skin. Together with Drs.Kusakabe and Sato in Japan, we will induce germline deletions in regions of the mouse genome that harbor potential tumor modifier or tumor suppressor genes as a prelude to functional studies in vivo. The relationship between these germline tumor modifiers and the somatic genetic alterations which take place during tumorigenesis will be investigated using microsatellite-based LOH, CGH and genomic arrays (with J.Gray, D.Pinkel and D.Albertson, San Francisco) to study patterns of gene loss or gain in tumors representing different stages of carcinogenesis. Finally, candidate modifiers identified using mouse approaches will be studied in humans to determine their relevance to the development of human skin or other tumor types.