Non-melanoma skin cancers (NMSC) are the most common malignancies in the United States. These malignancies vary from indolent lesions to those which are clinically aggressive. At present the molecular biologic correlates predictive of clinical aggressiveness are poorly characterized. Patients with these cancers are most often treated surgically. However, some patients require non-surgical intervention. Systemic interferon-alpha (IFN) plus 13 cis-retinoic acid (RA) is effective in the treatment of these patients. However, it is not possible to determine a priori which patients will benefit from this therapy. A reasonable hypothesis is that cell death deregulation contributes to the development of these tumors. This hypothesis provides the conceptual framework for examining the molecular genetic alterations commonly associated with NMSC in the context of cell death regulation. In fact, the most common mutations in NMSC occur in genes known to regulate cell death, p53 and Ha=-ras. Additionally, we have recently shown high levels of bcl-2 expression in certain types of NMSC. Our preliminary studies also suggest that altered expression of bax and bcl-x may contribute to the pathogenesis of NMSC. Tissue samples will be obtained from patients receiving protocol IFN plus RA and/or surgical treatment at the University of Texas M.D. Anderson Cancer Center. Samples will be assessed for expression of bcl-2 and related gene family members known to regulate cell death including bcl-x and bax using Western blotting and immunohistochemistry. In addition, the apoptotic index will be directly assessed using in situ labeling techniques. The results will be correlated with clinical pathologic parameters and patient response to therapy. The effects of apoptosis deregulation on the development of skin cancer will be studied prospectively in a transgenic mouse model that has been established using a keratin promoter-bcl-2 cDNA minigene (HK1-bcl-2). The HK1-bcl-2 mice will be examined for the effects of bcl-2 overexpression on epidermal differentiation by using immunofluorescence techniques for specific differentiation markers. Transgenic mice will be observed for spontaneous development of cutaneous neoplasms. These mice will also be treated topically with DMBA followed by serial applications of TPA as well as tested for susceptibility for UV induced skin carcinogenesis. Collaborative genetic complementation studies will assess the ability of overexpressed bcl-2 to cooperate with Ha-ras during in vivo skin carcinogenesis using HK1-ras transgenic mice. Finally, a series of established murine and human squamous cell skin cancer cell lines will be used to examine the influence of specific molecular genetic events on susceptibility to apoptosis induction by IFN and RA. These studies are intended to lead to a better understanding of the biologic basis of NMSC and to facilitate the transfer of the translational implications of these studies to the clinical setting.
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