A precise balance between programmed cell death and proliferation is essential to maintain a healthy self renewing epidermis. Abnormalities in these processes characterize skin cancer and a wide array of inflammatory skin diseases. NF-KappaB/Rel proteins, a family of rapidly responsive transcription factors, are major regulators of epidermal cell growth. Recent genetic and biochemical studies identified the RelA NF-kappaB subunit as a non-redundant regulator in triggering epidermal cell growth arrest through down regulation of CDK4 and suppression of JNK signaling. In agreement with these observations, NF-KB blockade along with JNK activation and CDK4 up-regulation was detected in spontaneous human squamous cell carcinoma (SCC). These findings underscore the potential importance of CDK4 and JNK in epidermal growth regulation by RelA. The mechanisms by which RelA suppresses CDK4 levels and JNK activity, however, are not clear and a direct role for JNK cascade in diseases of abnormal epidermal growth, such as SCC, has not been established. The first goal of this proposal is to define mechanisms mediating CDK4 down regulation by RelA. To do this, we will investigate the nature and importance of the physical interactions that we have recently identified between RelA and CDK4. Systematic structure-functional studies will be performed to identify RelA domains involved in CDK4 regulation and epidermal cell growth. T he second goal is to define the role of the JNK signaling cascade in epidermal homeostasis and neoplasia in relation to NF-KappaB. Effects of gain- or loss-of-function in the JNK pathway on CDK4 levels and epidermal growth with or without NF-KappaB inhibition will be assessed. The potency of JNK activation in tumor promotion will be defined in human epidermal tissue through genetic interference approaches. By the end of this funding period, we hope to have defined the mechanisms through which NF-kappaB, CDK4 and JNK cascade regulate growth of both normal and neoplastic epidermal tissue and to provide insight into development of future molecular targets for diseases of abnormal cell growth, such as skin cancers.