Dab2-E-cadherin Duo: A New Role in Squamous Cell Carcinoma Development

Objectives: Disabled2 (Dab2) is an adaptor protein involved in cellular endocytosis and recycling machinery, and its down-regulation has been associated with progression of epithelial cancers. However, Dab2 involvement in the early stages of squamous cell carcinoma (SCC) has not been elucidated. We previously reported that transient loss of Dab2 is associated with decreased E-cadherin-mediated cell-cell contact, which led to increased SCC cell spread. Here, we investigated whether the effect of a permanent Dab2 depletion on these cells is dependent on their malignant potential.
Methods: The immortalized HaCaT and ras-transformed HaCaT keratinocytes (II-4) were transfected with lentiviral-mediated sh-Dab2 sequences, which down-regulated Dab2 at the mRNA level. The levels of Dab2, E-cadherin and other proteins were investigated by Western Blot and immunofluorescent analyses, and cell morphology was analyzed by bright field microscopy.
Results: 3-fold and 2-fold decrease of Dab2 expression were achieved in the II-4 SCC cells and HaCaT cells, respectively. E-cadherin, EEA1, and Caveolin-1 proteins were moderately decreased in HaCaT cells. In contrast, these proteins were markedly down-regulated in II-4 cells. Increased cell spread was confirmed in both cell cultures, and immunofluorescent staining of HaCaT cells, and moreover of II-4 cells, showed the propensity of Dab2 to remain at the perinculear area instead of being diffused throughout the cells cytoplasm.
Conclusions: Dab2 depletion in HaCaT and II-4 SCC cells is associated with downregulation and altered cellular localization of E-cadherin and other endocytic proteins. Importantly, the extent to which the characteristics of these cells are changed is dependent on their malignant potential. Our study sheds light on the reciprocal relationship between Dab2 and E-cadherin, as affecting the expression of one influences the level of the other. These data demonstrate that E-cadherin and Dab2 work in concert during SCC development, and further elucidates their role in the progression of epithelial cancer.