Cutaneous melanoma, the deadliest form of skin cancer, arises from neural crest derived melanocytes. Much progress has been made in delineating molecular events that initiate the cascade of malignant changes leading to metastatic melanoma. These advances have led to some remarkable improvements in treatment of melanoma. However, the notorious intrinsic resistance to conventional therapies and development of treatment resistance to targeted therapies continue to be vexing problems highlighting the need to explore additional avenues for preventing melanoma development and progression. In this context, the role for Notch signaling in melanoma remains to be fully understood and exploited. Notch signaling, an important cell signaling mechanism, is known to play a role in melanocyte development. However, molecular mechanisms and the specific roles Notch plays in melanoma development and progression are not completely understood. Preliminary data obtained in my laboratory showed a possible biphasic role for Notch signaling in melanoma tumor progression. In skin resident benign neo-plastic melanocytes and early primary melanoma, a downregulation of Notch signaling and its effector HES1, a transcriptional repressor, allows elaboration of neuronal differentiation. This is indicated by the expression of a protein, MAP2 that is normally present only in terminally differentiated neurons that lack ability to divide. A retrospective survival analysis showed that patients whose primary skin tumors were MAP2-positive survived significantly longer without melanoma recurrence than those diagnosed with MAP2-negative melanoma. MAP2 is absent or found less frequently in metastatic melanoma. In agreement with its primary function of binding to and stabilizing microtubules, MAP2 alters the dynamic instability of microtubules and induces mitotic spindle defects in melanoma. Preliminary data also showed that molecular players that initiate the malignant changes in melanocytes also play a role in activation of this neuronal differentiation marker. Thus, activation of a neuron-specific gene in melanocytes at early stages of malignant transformation correlates with inhibition of proliferation in vitro and tumor growth and progression in vivo. Based on these data, we hypothesized that Notch signaling, has a dual or biphasic role in melanoma. First, Notch signaling is downregulated during early steps in malignant transformation by sustained oncogenic signaling to promote neuronal differentiation as a fail-safe mechanism against melanoma tumorigenesis, and additional genetic events such as loss of PTEN then lead to upregulation of Notch signaling to support melanoma tumor progression. To test this hypothesis, we will use a combination of in vitro and in vivo approaches to accomplish the following Aims:
In Aim 1, we will study mechanisms of transdifferentiation in melanocytes and patient-derived melanoma using primary melanocytes and a panel of well-characterized melanoma cell lines, we will investigate the molecular mechanisms.
In Aim 2, we will investigate the role of Notch signaling and neuronal differentiation in melanomagenesis using metastatic melanoma cells with stable knockdown of HES1and/or treated with inhibitors of Notch signaling in immunocompromised mice, and a genetic cross between transgenic mice with inducible MPA2 expression in melanocytes and BrafCa/Pten-/- mice.
In Aim 3, we will evaluate the prognostic significance of Notch in melanoma employing quantitative immunohistochemical method to analyze an in- house created melanoma tissue microarray consisting of 225 stage I-III primary melanoma specimens with complete clinical history. The hypothesis on the dual role of Notch in transdifferentiation and use of combination of mouse genetic model and a fully annotated melanoma tissue microarray are the innovative aspects of the proposed research. Data obtained from these studies have the potential to uncover more reliable prognostic markers for melanoma aggressiveness and impact the management of aggressive cutaneous melanoma.
Melanoma of the skin is one of the deadliest cancers and it occurrence is steadily increasing in the United States. Melanoma develops from cells in the skin that normally produce skin pigment melanin. Excessive exposure to sun rays can lead to damage that can result in skin cancer including melanoma. Many US military Veterans, who served outdoors and on high seas in tropical and subtropical zones are exposed to ultraviolet radiation for prolonged periods and may have a significant risk of developing melanoma. Melanoma can often be cured if diagnosed early, but advanced cancer that has spread beyond skin is often deadly because there are not many effective treatments. Steady progress is being made in understanding the biology of melanoma with the hope that such understanding can lead to its prevention and treatment. The objective of this research is to better understand and exploit an intrinsic feature of melanoma that allows conversion of the rapidly dividing tumor cells into non-dividing 'brain cell-like' cell as potential new treatment for melanoma.