Skin cancer is the most common human cancer and BCCs and SCCs make up a vast majority of these malignancies. In the case of BCCs a causal role of canonical Hedgehog (Hh) pathway activation has been well-established, and recent evidence further supports a role for canonical Hedgehog signaling in SCCs as well. Hh signaling is a key developmental pathway involved in cells proliferation and survival through downstream activation of Gli transcription factors. The Hh pathway can be regulated by other signaling cascades;including EGFR, Wnt/-catenin, IGFR and TGF. Key signaling molecules have been shown to be required for Gli activation including Gi proteins, PI3K and AKT;while PKA and GSK3? promote partial Gli degradation. Interestingly, BCCs and SCCs, among other cancer types, are also characterized by increased expression of the desmosomal cadherin Desmoglein 2 (Dsg2). Furthermore, overexpression of DSg2 in transgenic mice results in epidermal hyperproliferation, enhanced cell survival, and renders keratinocytes more susceptible to chemically induced carcinogenesis. Thus the goal of this project is to elucidate a potential crosstalk between Dsg2 and canonical Hh signaling. Using a transgenic mouse model overexpressing Dsg2, our preliminary results indicate a significant correlation between Dsg2 expression and Hh target gene transcription. Since these mice are more susceptible to chemically induced carcinogenesis, the potential for Dsg2 to mediate changes in cell growth and survival could be in part mediated by enhanced Gli activity. Gli-luciferase assays demonstrate that the expression of Dsg2 can enhance Gli activity in vitro. Finally, knockdown of Dsg2 in an SCC cell line results in decreased Gli expression. Taken together, these results suggest a role for Dsg2 as a positive regulator of canonical Hh signaling. The studies proposed here are designed to elucidate the mechanism by which Dsg2 enhances Gli activity, by both determining at what level of Hh signaling Dsg2 is acting and if Dsg2 processing by metalloproteases and/or caspases is necessary for this regulation. In vivo work using mice that overexpress Dsg2 and which are prone to Hh signaling activation (Ptc1+/lacZ) will provide insights into the consequences of simultaneous deregulation of both pathways in the skin. Finally, a translational study looking at the expression of Dsg2 and Hh proteins in human BCC and SCC samples will allow for the correlation of the deregulation of both pathways with tumor type and classification. Together these mechanistic studies will offer a clearer understanding of how canonical Hh signaling can be regulated by cell adhesion proteins;the ramifications of said deregulation with regards to cell proliferation, survival and oncogenic potential;and provide potential targets for novel cancer therapies.

Public Health Relevance

Skin cancer is the most common human cancer, with basal cell and squamous cell carcinomas (BCC, SCC) being diagnosed in more than 2.2 million people annually in the United States. This research focuses on better understanding the mechanism of pathogenic signaling for these and other epithelial-derived malignancies, with the goal of identifying molecular targets for disease treatment.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1-F09-A (08))
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Schmidt, Michael K
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Thomas Jefferson University
Schools of Medicine
United States
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Brennan-Crispi, Donna M; Hossain, Claudia; Sahu, Joya et al. (2015) Crosstalk between Desmoglein 2 and Patched 1 accelerates chemical-induced skin tumorigenesis. Oncotarget 6:8593-605