Overexpression of the VSSC‐associated CAM, beta‐2, enhances LNCaP cell metastasis associated behavior

BACKGROUND Prostate cancer (PCa) is the second‐leading cause of cancer death in American men. This is due largely to the “silent” nature of the disease until it has progressed to a highly metastatic and castrate resistant state. Voltage sensitive sodium channels (VSSCs) are multimeric transmembrane protein complexes comprised of a pore‐forming α subunit and one or two β subunits. The β‐subunits modulate surface expression and gating kinetics of the channels but also have inherent cell adhesion molecule (CAM) functions. We hypothesize that PCa cells use VSSC β‐subunits as CAMs during PCa progression and metastasis. METHODS We overexpressed the beta‐2 isoform as a C‐terminal fusion protein with enhanced cyan fluorescence protein (ECFP) in the weakly metastatic LNCaP cells. The effect of beta‐2 overexpression on cell morphology was examined using confocal microscopy while metastasis‐associated behavior was tested by performing several in vitro metastatic functional assays and in vivo subcutaneous tumor studies. RESULTS We found that cells overexpressing beta‐2 (2BECFP) converted to a bipolar fibroblastic morphology. 2BECFP cells were more adhesive than control (ECFP) to vitronectin (twofold) and Matrigel® (1.3‐fold), more invasive through Matrigel® (3.6‐fold in 72 hr), and had enhanced migration (2.1‐fold in 96 hr) independent of proliferation in wound‐healing assays. In contrast, 2BECFP cells have a reduced tumor‐take and tumor volume in vivo even though the overexpression of beta‐2 was maintained. CONCLUSIONS Functional overexpression of VSSC β‐subunits in PCa may be one mechanism leading to increased metastatic behavior while decreasing the ability to form localized tumor masses. Prostate 72:1080–1092, 2012. © 2011 Wiley Periodicals, Inc.