Cutaneous melanoma is thought to progress through a series of distinct phases that include a non-invasive or minimally invasive radial growth phase and a vertical growth phase that acquires metastatic capacity. According to the widely accepted staging system, vertical thickness of primary tumor is the best predictor of the aggressiveness of melanoma. However, tumor thickness is not always a reliable parameter. Although a number of other clinical and biological parameters that influence melanoma progression have been identified, to date there are no molecular markers that can reliably predict aggressiveness of melanoma. Malignant melanoma is also known to exhibit molecular plasticity and transdifferentiate along several cellular pathways, including endothelial and neural cell types. Melanoma transdifferentiation seems to have biological and prognostic significance. We have investigated the effects of neuronal differentiation on melanoma tumor progression. We showed that the neuron-specific microtubule associated protein 2 (MAP2), a protein found primarily in the dendrites of post-mitotic, terminally differentiated neurons, is expressed abundantly in early invasive cutaneous primary melanoma lesions but present only less frequently or absent in metastatic lesions. MAP2 expression appears to be inversely correlated with tumor progression. The primary function of MAP2 is to stabilize microtubules. MAP2 alters the 'dynamic instability'of microtubules, a property critical for mitotic spindle formation and chromosome segregation. Therefore, we hypothesized that neuronal differentiation and activation of MAP2 gene expression in neoplastic melanocytes that are destined to divide rapidly, disrupts mitotic apparatus, inhibits cell proliferation and tumor progression. Retrospective immuno-histochemical and survival analysis of a small cohort showed that patients whose primary tumors were MAP2-positive had significantly longer disease-free survival than those with MAP2-negative melanoma. Investigation of the mechanisms that underlie the effects of MAP2 showed that overexpression of MAP2 in metastatic melanoma cells leads to stabilization of microtubules, G2-M arrest, growth inhibition followed by apoptosis. MAP2 expressing cells show mitotic spindle and cytokinesis defects similar to those seen in cells treated with microtubule-disrupting agents. Thus, ectopic activation of a neuronal differentiation gene in melanoma during early progression inhibits cell division and correlates with inhibition or delay of metastasis. The goal of this study is to test the hypothesis that expression of neuronal markers in cutaneous primary melanoma reduces tumor cell proliferative potential, increases the frequency of cell death and is associated with longer disease-free survival of patients. We propose to test and validate neuronal markers nestin, NEDD9 and MAP2 as a melanoma prognostics marker by investigating the association between MAP2 expression and a) markers for melanoma cell proliferation and apoptosis, and b) clinical outcome in patients diagnosed with melanoma.
Cutaneous melanoma is the deadliest form of skin cancer. If diagnosed early and treated appropriately before the cancer becomes aggressive, melanoma is often curable. However, there are no biological markers to reliably assess the aggressiveness of melanoma. The goal of this project is to assess the value of novel markers in predicting melanoma tumor aggressiveness.
