The central theme of our laboratory is to understand molecular mechanisms underlying the development and progression of skin cancers. Skin cancer is the most common form of cancer in humans, and can arise from melanocytes (melanoma) or keratinocytes (basal and squamous cell carcinoma). There is considerable evidence that resistance to apoptosis is a common feature of melanoma and represents a significant obstacle in treating metastatic disease. There is also evidence that dysfunctional apoptosis is involved in the development of ultraviolet (UV)-induced nonmelanoma skin cancers. Our initial work has focused on Survivin, a newly recognized inhibitor of apoptosis, as a model paradigm to address the role of apoptosis in both melanoma and nonmelanoma skin cancer.

Our research efforts have been channeled along the following projects.

1. Regulation of apoptosis in melanocytic cells

How is apoptosis regulated in normal melanocytes? Melanocytic cells are relatively resistant to most apoptotic stimuli, and we have begun to elucidate the pathways involved. Melanocytic cells express a multitude of apoptosis inhibitors but Survivin appears to be the only apoptotic inhibitor routinely expressed in melanoma cells but not normal melanocytes. We have used adenoviral delivery to express Survivin in melanocytes and study its function. We have also prepared a transgenic mouse with constitutive expression of Survivin in melanocytes, which exhibits increased susceptibility to UV-induced melanoma. Finally, we are studying mechanisms of transcriptional suppression of Survivin in melanocytes, and transcriptional activation in melanoma.

How is apoptosis dysregulated in melanoma? In melanoma cells, blocking Survivin triggers translocation of mitochondrial apoptosis-inducing factor (AIF) to the nucleus, initiating both caspase-dependent and caspase-independent apoptosis. We are investigating the role of AIF in apoptotic responses in melanoma cell lines. To identify other potential protein partners that Survivin may interact with, we carried out a high throughput screen based on yeast 2-hybrid strategy and are currently studying several interesting candidate molecules and how they may affect Survivin localization and function.

Can apoptosis-based therapies be developed? We have designed a cell-permeable Survivin antagonist that slows melanoma tumor growth in vivo. We plan to modify this system using a peptide-based analog in a novel animal model of UV-induced melanoma.

2. Role of apoptosis in multi-step skin carcinogenesis

The conventional notion is that apoptosis serves as a barrier to tumor formation, but its impact on early steps in tumorigenesis has not been well studied. We are using Survivin and Survivin antagonists as tools to modulate keratinocyte apoptosis in transgenic mice to address this question. Squamous cell carcinoma can be induced in mice via topical application of carcinogen and tumor promoter (DMBA,PMA), or chronic UV radiation. The advantage of using UV is that microscopic tumor precursors (p53-mutant clones) can be visualized and quantitated. Initial studies using a transgenic mouse with keratinocyte expression of Survivin revealed that while tumor regression was averted and conversion to carcinoma was enhanced, there was a paradoxical reduction in tumor formation. We have shown that apoptosis is required initially in this model to create space for keratinocyte clones to expand into, that if Survivin is expressed too early, the transition from small to large clones is impaired. We have developed inducible transgenic systems that will allow us to dissect out the role of Survivin and apoptosis at each step in tumorigenesis.

3. Targeting oxidative stress pathways in melanocytes

We are studying oxidative responses in melanocytes, and using antioxidants to modulate UV-induced oxidative damage in these cells and human nevi (moles). Preclinical studies will involve modulating UV-induced melanoma in a mouse model. Ultimately we hope to perform a clinical trial in patients at increased risk for melanoma, to see if we can protect their nevi from UV-induced oxidative stress/damage by pretreating with an oral antioxidant.