Polycomb proteins and skin cancer prevention

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DESCRIPTION (provided by applicant): Epidermal squamous cell carcinoma is one of the most common forms of human cancer and the incidence is increasing. Thus, skin cancer is an important health concern and advanced disease recurs and is life- threatening and disfiguring. Because skin cancer development involves multiple events over a long period of time, prevention is an important and preferred option. For this reason there is a major ongoing effort to identify preventive agents that can be taken orally or applied on the skin surface. In particula, we have focused on the impact of sulforaphane (SFN), derived from broccoli, on function of the Ezh2 Polycomb Group (PcG) protein. PcG proteins are important epigenetic regulators that methylate and ubiquitinate specific histones to produce closed chromatin and silence tumor suppressor gene expression. Key polycomb group proteins, including Ezh2, are overexpressed in skin cancer and this drives silencing of p21Cip1 and other tumor suppressors leading to enhanced tumor cell survival. We have shown that SFN suppresses Ezh2 which leads to increased p21Cip1 expression. These changes ultimately lead to cessation of skin cancer cell proliferation and increased cancer cell death. Our exciting unpublished preliminary studies suggest that a pathway that includes two master regulators of keratinocyte survival and stem cell fate, DNp63a and KLF4, regulates Ezh2 level. These proteins have not been previously considered as important prevention targets. We hypothesize that in cancer cells a DNp63a, KLF4 pathway stimulates Ezh2 gene expression which, in turn, acts to reduce p21Cip1 expression leading to increased cancer cell survival. We further propose that SFN inhibits events in this pathway to reduce Ezh2 expression and increase tumor suppressor expression. Experiments in this proposal revolve around well-defined translation-relevant goals. Specific Aim 1 studies how DNp63a and KLF4 regulate Ezh2 level. Specific Aims 2 examines SFN regulation of this pathway. Specific Aim 3 examines Ezh2 regulation of p21Cip1 expression, and Specific Aim 4 address the impact of Ezh2 and SFN treatment on tumor formation in vivo. These studies are highly relevant to understanding the biological role of SFN in preventing skin cancer formation.