This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Estimates indicate that about one million new cases of skin cancer are reported in the United States annually. Initiation of skin tumorigenesis by exposure to ultraviolet (UV) radiation or environmental chemicals involves the acquisition of DNA lesions. Subsequent clonal expansion of preneoplastic or "initiated" cells depends not only on increased cell proliferation but also on a decreased rate of cells undergoing apoptosis. The broad objective of this proposal is to determine whether caspase-2 plays a role in the elimination of cells with genetic lesions in a mouse model of skin carcinogenesis. The rationale for this line of investigation is based on exciting new evidence indicating that DNA damage-induced apoptosis of transformed or tumor-derived human cell lines depends to a large extent upon caspase-2 activation. In particular, the applicant's findings demonstrated that caspase-2 activation occurs upstream of mitochondrial cytochrome c release and formation of the Apaf-1 apoptosome in response to the DNA-damaging antineoplastic drug etoposide. These observations, combined with the knowledge that caspase-2 knockout mice lack a dramatic phenotype, suggest that while caspase-2 is dispensable for normal developmental cell killing, it may play a fundamental role in pathological cell killing. The hypothesis to be tested is that caspase-2 is critical for the disposal of cells with damaged DNA to prevent the accumulation of mutations and/or the clonal expansion of preneoplastic cells. Caspase-2 knockout and wild-type mice will be used for these studies and their response to carcinogenic agents, both chemical and physical, will be analyzed at the histopathological and molecular levels. The following specific aims are proposed to test the hypothesis: 1) Determine whether a deficiency of caspase-2 alters the susceptibility of keratinocytes in vivo to undergo apoptosis following exposure to either UV radiation or the initiating agent 7,12- dimethylbenz(a)anthracene (DMBA); 2) Determine whether UV or DMBA [unreadable] the tumor promoter 12- Otetradecanoylphorbol- 13-acetate (TPA) treatment results in tumor formation and whether this coincides with increased cell proliferation and/or a suppression of apoptosis in the epidermis of caspase-2 knockout versus wild-type mice; and 3) Determine the susceptibility of cultured neonatal keratinocytes from wild-type or caspase-2-deficient mice to DNA damage-induced apoptosis. Combined, these studies will provide critical new information about caspase-2?s ability to modulate tumor development in vivo by promoting apoptosis of keratinocytes after mutagen exposure.