αV integrin promotes in vitro and in vivo survival of cells in metastatic melanoma

Abstract

The expression of integrin ␣V subunit on 4 melanomaderived cell lines (A2058, SK-mel-5, WM-115 and WM-266-4) was analyzed. WM-115 cells, which originate from a primary tumor, were negative, whereas all 3 metastasis-derived lines had high levels of ␣V. To study ␣V integrins in the survival of melanoma cells, we developed a novel strategy that is exempt from extracellular inhibitors of ligand binding, which can activate integrin signaling and have integrin-independent effects on apoptosis. A recombinant adenovirus was used to transfer cDNA coding for a single-chain intracellular anti-␣V integrin antibody into the melanoma cells. Anti-␣V integrin adenovirus effectively inhibited the cell surface expression of ␣V integrins. In cell culture experiments, the depletion of ␣V integrins detached cells from extracellular matrix and induced apoptosis. Moreover, it prevented WM-266-4 cells from forming tumors in severe combined immunodeficiency mice but it could not prevent the growth of tumors that were formed by ␣V-negative WM-115 cells. Our results indicate that in primary melanomas there are cells that survive without ␣V integrins, whereas during the progression of disease cells can develop a dependency on these receptors. Furthermore, the data oppose the possibility that in melanoma cells apoptosis could occur due to direct activation of caspases by ligand-free ␣V integrins on the cell surface. © 2004 Wiley-Liss, Inc. Key words: integrin; melanoma; intracellular single-chain antibody; adenovirusThe ␣V integrin can form a heterodimeric adhesion receptor with 5 different integrin ␤ subunits, namely, ␤1, ␤3, ␤5, ␤6 and ␤8. These receptors bind to various extracellular matrix proteins such as fibronectin, vitronectin and osteopontin. In adult individuals, relatively few cell types express significant amounts of ␣V, and genetic data from mouse experiments indicate that most organs develop properly even in the absence of all ␣V integrins. 1 In human melanoma, the expression of ␣V together with its partner ␤3 has been connected to tumor growth, disease progression and poor prognosis. 2-8 Additionally, ␣V integrins may play a role in the progression of ovarian carcinoma, cervical tumors, breast cancer and squamous cell carcinoma, 9 -13 and it has also been connected to the formation of bone metastasis in prostate cancer. 14 Based on the analysis of knockout mice, it is obvious that in vivo, most normal cell types can survive without ␣V integrins. 1 In cancer cells, the inhibition of ␣V function has been associated with apoptosis, and appropriate ligand binding may be essential for the function of ␣V integrins during cancer progression. For example, the secretion of osteopontin, a ligand for ␣V␤3, by melanocytes has been reported to promote antiapoptotic signaling. 15 Furthermore, after disruption of cell-matrix contacts, unbound ␣V integrins may promote apoptosis in human melanoma and human intestinal carcinoma cells. 16,17 It has also been reported that in T24-E carcinoma cells, death is stimulated by attachment to the extrac...

Integrins as therapeutic targets: lessons and opportunities

“…One of the most important is α V β 3 56 which is known to act as a trigger for cell survival 57 and this may be important in angiogenesis where endothelial cell survival is critical. It also plays a key role in metastasis where its expression in melanoma is associated with highly metastatic disease 58 . Etaracizumab is a monoclonal antibody to α V β 3 that is undergoing early clinical development for treatment of melanoma [59][60] and solid tumours 61 .…”

Extracellular matrix proteins, neural differentiation and melanoma progression

“…Integrin α5β1 promotes in vitro and in vivo survival of cells in metastatic melanoma [68,70] and correlates with migratory behavior of malignant cells as well as the normal human melanocytes to adhere, spread and migrate in skin wounds. In tumor cells, it is of advantage to have more integrin α5β1 and less integrin v3 to facilitate rapid binding to blood clots and other matrix components.…”

“…Highly invasive melanoma cells express relatively high levels of α5β1 and low levels of α5β3. The switch in integrin expression leads to even higher MMP-2 production, which correlates with higher invasion capacity of these cells [40,68] . Thus high integrin expression at the invasive front leads to higher proteolysis related activities, which in turn leads to the alteration of Ln5 towards a motility inducing structure.…”

Quantitative expression of the homeobox and integrin genes in human gastric carcinoma

“…This integrin is essential to cellular migration (40,41), and it may contribute to angiogenesis (42) and survival in metastatic cells (43). On the other hand, the αVß1 integrin mediates the effects of the fibronectin, a matrix glycoprotein that regulates important cellular pathways such as proliferation and adhesion (44).…”