Expression patterns of the metastasis suppressor NME1 in metastatic melanoma

Abstract

Localized melanoma is a curable form of skin cancer, with a 98% chance for survival. However, for individuals diagnosed with metastatic melanoma, the five-year survival rate is reduced down to 23%. To enhance patient survival, it remains imperative to fully differentiate melanoma metastasis mechanisms. Our motivation lies on depicting underlying patterns accompanying metastatic inhibition. Here, we examine inhibition of melanoma metastasis through analysis of the metastasis suppressor protein, NME1. NME1 is a known inhibitor of melanoma metastasis. Overall loss of NME1 protein in melanoma tumors is associated with reduced survival. Yet, not all melanoma tumors are the same. Melanomas are heterogenous and exhibit distinct differences across patients and across individual primary tumor cells. The prognostic implications of heterogenous NME1 expression within melanomas has not previously been defined. Our focus lies in characterizing how expression of NME1 across patients and across primary tumor cells may impact melanoma prognosis and overall metastatic incidence. We utilized a NME1-based approach to identify a mRNA expression signature associated with metastasis suppression in melanoma. Bioinformatic analysis of our metastasis suppression signature in a melanoma patient dataset exposed a subset of melanoma patients with altered survival. We were also interested in analyzing the heterogenous expression of NME1 protein within melanoma cells. Flow cytometry analysis revealed that melanoma cell lines contain a rare population of cells with low levels of NME1 protein. We utilized multiple methods to characterize the impact of NME1 loss on cell behavior. Experiments designed to mimic loss of NME1 through shNME1 produced results which suggest that NME1 is associated with melanoma spheroid formation. We further utilized an innovative approach, which relied on CRISPR technology, to study endogenous NME1 expression. Characterization of endogenous NME1 expression patterns lead to the identification of a previously unidentified group of cells, which have a neural crest-like phenotype and contain enhanced metastatic capacity. Overall, the expression pattern of NME1 within tumor cells and across patients provides an advantageous tool for identifying metastatic susceptibility.