Constitutive Expression of the α4 Integrin Correlates with Tumorigenicity and Lymph Node Metastasis of the B16 Murine Melanoma

Abstract

The lymphatic system plays a critical role in melanoma metastasis, and yet, virtually no information exists regarding the cellular and molecular mechanisms that take place between melanoma cells and the lymphatic vasculature. Here, we generated B16-F1 melanoma cells that expressed high (B16α4+) and negligible (B16α4-) levels of α4 integrin to determine how the expression of α4 integrins affects tumor cell interactions with lymphatic endothelial cells in vitro and how it impacts lymphatic metastasis in vivo. We found a direct correlation between α4 integrin expression on B16-F1 melanoma cells and their ability to form adhesive interactions with monolayers of lymphatic endothelial cells. Adhesion of B16-F1 melanoma cells to lymphatic endothelial cells was mediated by the melanoma cell α4 integrin binding to its counterreceptor, vascular cell adhesion molecule 1 (VCAM-1), that was constitutively expressed on the lymphatic endothelial cells. VCAM-1 was also expressed on the tumor-associated lymphatic vessels of B16-F1 and B16α4+ tumors growing in the subcutaneous space of C57BL/6J mice. B16-F1 tumors metastasized to lymph nodes in 30% of mice, whereas B16α4+ tumors generated lymph node metastases in 80% of mice. B16-F1 melanoma cells that were deficient in α4 integrins (B16α4-) were nontumorigenic. Collectively, these data show that the α4 integrin expressed by melanoma cells contributes to tumorigenesis and may also facilitate metastasis to regional lymph nodes by promoting stable adhesion of melanoma cells to the lymphatic vasculature.