Visinin-like Protein-1 is a Potent Inhibitor of Cell Adhesion and Migration in Squamous Carcinoma Cells

Tumor cell invasion is a highly integrated and complex process comprising several biologically distinct functions such as cell adhesion, motility, proteolysis, etc. Visinin-like protein-1 (VILIP-1), a member of the neuronal EF-hand calcium-sensor protein family, plays a role in regulating tumor cell invasiveness of mouse squamous cell carcinoma (SCC). VILIP-1 enhances cyclic adenosine monophosphate levels through PKA induction. However, the mechanism by which VILIP-1 reduces cell invasiveness is not well understood. In this study, we show that VILIP-1 decreased cell adhesion and migration/invasiveness of highly invasive mouse SCC cells. Forced expression of VILIP-1 reduced cell adhesion to fibronectin in parallel to downregulating alphav and alpha5 integrin subunit levels. VILIP-1 overexpression also led to decreased migration ability. Conversely, short hairpin RNA-mediated VILIP-1 knock-down of SCC cells' characterized by little or no invasiveness, correlated with increased adhesion to fibronectin and enhanced expression of alphav and alpha5 integrin subunits together with increased cell migration. Function-blocking assays with inhibitory anti-alpha5 and anti-alphav integrin antibodies showed that both subunits contributed to cell adhesion, migration, and invasiveness of highly invasive SCC cell lines. These results point to a critical role of VILIP-1 in regulating cell adhesion and migration by downregulation of fibronectin receptor expression. Decreased or absent VILIP-1 expression in SCC cell subpopulations may lead to a more advanced malignant phenotype characterized by changes in adhesive ability and increased cell motility, suggestive of a tumor suppressor function.