Dab2-Dependent Modulation of the Tumor Microenvironment can Promote Cancer Development

Objectives: In many epithelial cancers, such as esophageal carcinoma, the adaptor protein Disabled-2 (Dab2), which is crucial for intact cellular endocytosis and recycling, is down-regulated. However, Dab2’s role in the development of skin squamous cell carcinoma (SCC) has not been investigated. To elucidate the potential involvement of Dab2 in altering the tumor microenvironment to support SCC progression, we investigated the consequences of Dab2 depletion on the characteristics and growth of human dermal fibroblasts.
Methods: Human dermal fibroblasts were transfected with a control sh-scrambled sequence or different lentiviral-mediated shDab2 sequences in order to down-regulate Dab2 at its mRNA level. The expression of Dab2, Eps15, EEA1 and Caveolin-1 in these cells were analyzed by Western Blot and immunofluorescent analyses. Cell counts were performed daily to analyze cell proliferation rate.
Results: Using Western Blot analysis, we observed a 5-fold decrease in Dab2 level, as well as down-regulation of the associated proteins Eps15, EEA1 and Caveolin-1 in shDab2-fibroblasts when compared to control fibroblasts. Immunofluorescence analysis revealed faint cytoplasmic Dab2 staining in shDab2-fibroblasts that further confirmed the depletion of this protein in these cells, in comparison to strong Dab2 staining in control fibroblasts. Importantly, Dab2 depletion significantly increased fibroblast proliferation.
Conclusions: The tumor microenvironment is composed of neoplastic epithelial cells that coexist with a variety of stromal cell types and supportive stromal components. Whereas other work from our lab showed that Dab2 depletion in SCC tumor cells can promote SCC progression, the results of this study demonstrate that decreased Dab2 expression in dermal fibroblasts can profoundly affect the behavior and growth of these quiescent cells. These results suggest that not only that Dab2 loss in neoplastic keratinocytes can support cancer development, but Dab2 loss in dermal fibroblasts can potentially affect the tumor microenvironment and further support the growth of tumor cells to enhance SCC progression.