Characterization of VLA-3 integrin-mediated adhesion and its expre ision in cancer cells

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Cell adhesion molecules play a crucial role in the initial process of cancer metastasis through the cell-matrix interaction. In this study, we investigated the role of VLA-3 (α3β1 integrin) in invasion and metastasis of cancer cells and the regulation mechanism of its expression.1. Role of VLA-3 integrin in the motility of melanoma cells: We evaluated the role of soluble factors produced by epidermal cells in A375 melanoma cell motility by using the Boyden chamber chemoinvasion system. The motility-stimulating activity was associated with the α3 integrin-dependent adhesion-promoting activity and identified as laminin-5. Purified laminin-5 was capable of potentiating melanoma cell migration as measured in either the chemotaxis assay or the haptotaxis assay. Furthermore, immobilized laminin-5 induced A375 melanoma cells to secrete matrix metalloproteinase-9 (type IV collagenase) into the culture medium. These results strongly suggest that the interaction of laminin-5 produced in the epidermis with the α3β1 integrin on melanoma cells is involved in cell migration, invasion, and degradation of extracellular matrix proteins.2. Regulatory mechanism of the α3 integrin expression: We have cloned an approximately 4 kb DNA fragment of the 5'-flanking region of the murine α3 integrin gene and analyzed its promoter activity. Transfection of MKN1 gastric carcinoma cells with serially truncated segments of this region linked to a luciferase gene indicated that the sequence between positions -260 and -119 bp is required for efficient transcription in the cells. The sequence analysis of this segment showed the presence of several consensus sequences for transcription factors. The introduction of mutation in one of the Ets-binding sequences greatly decreased its promoter activity, suggesting that the transcription of the α3 integrin gene in these cells is regulated by the Ets-family of transcription factors.