SCN2β Functions as a Cell Adhesion Molecule in Prostate Cancer Metastasis

Lepori-Bui, Nadia
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University of Delaware
Prostate cancer (PCa) is a silent disease treatable during its early stages but hard to diagnose due to the absence of symptoms and reliable disease markers. The five year survival rates of men with advanced stage and grade PCa are less than 30% and virtually all of these men have metastases to bone, predominantly in the lumbar and sacral regions of the spine. In over 85% of these cases, perineural invasion (PNI) is also observed. PNI is characterized by the close association of cancer cells along, around, and through nerve tissue. The currently accepted pathway of PCa metastasis is through the bloodstream or lymphatic system. However, these mechanisms do not account for the specific localization of PCa cells to the lumbar and sacral spine. This observation, combined with the frequency of PNI found in PCa cases and the abundance of nerves connecting the prostate and the spine, suggests that the cancer cells could be taking a more direct route of metastasis to these destinations by migrating along nerve cells. A protein complex believed to be involved in the migration of PCa cells is SCN2β, a subunit of voltage-gated sodium channels (VGSC). These channels are made up of one pore-forming α-subunit and two auxiliary β-subunits. The β-subunits have extracellular V-set Ig-loop domains that are highly conserved when compared to neural cell adhesion molecules like Myelin Protein Zero Like protein 2 (MPZL2). The subunit SCN2β, which functions both to traffic α-subunits to the cell surface and as a cellular adhesion molecule capable of forming both homotypic and heterotypic associations with other V-set Ig-loop domain containing proteins, is of particular interest. The expression of SCN2β has been correlated to an increased metastatic phenotype in PCa cells. I hypothesize that SCN2β is required for PCa cell adhesion to and migration along peripheral nerve cells. To test this hypothesis, I had two aims. For my first aim, I cloned various proteins and protein domains associated with SCN2β (both binding partners and repulsive domains). These proteins, when overexpressed in human PCa cancer cells, could be used in migration assays to determine their functions and interactions as well as purified to assay their binding strength directly. For my second aim, I performed several migration assays on cells overexpressing SCN2β, with various conditions to inhibit or modify its function, to compare their migration with that of normal PCa cells. I have several protein cDNA sequences successfully ligated into mammalian expression vectors and ready for transfection into cancer cells. In my migration assays, I observed that overexpression of SCN2β does increase migration in all cell types, and that inhibition of its normal function decreases migration.