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Recent studies suggested that co-expression of the two β3 integrins, αvβ3 and αIIbβ3, in human melanoma cells enhanced cell survival and promoted growth in vivo. To reveal the underlying mechanisms we have investigated the angiogenic phenotype of αIIbβ3 integrin-transduced human melanoma cells expressing integrin αvβ3. Upon hetero- or orthotopic injections into SCID mice the αIIbβ3 integrin-overexpressing clones (ESL, ESH, 19L and 19H) grew more rapidly than the mock transfectant one (3.1P). Investigating the tumor-induced angiogenesis of the implanted tumors, it became clear that transfected tumors have a higher microvessel density compared to 3.1P. Furthermore, flow cytometry indicated that vascular endothelial growth factor (VEGF) is constitutively expressed by the cells of both the mock and the transfected clones. However, the mock transfectant clone, 3.1P, did not express basic fibroblast growth factor (bFGF) at protein level (<1%), unlike the αIIbβ3 integrin-transfected clones, 19L and 19H, (33.9 and 84.1 %, respectively). Quantitative PCR analysis of 6 related human melanoma clones with various levels of αIIbβ3 integrin expressions revealed a correlation between the αIIb protein and bFGF mRNA expressions, suggesting that the increased bFGF protein expression is due to transcriptional regulation. The altered bFGF expression may be regulated by integrin-linked signaling, since β3-endonexin is upregulated in transfected 19H cells and kinase inhibitors downregulate bFGF. In summary, the illegitimate expression of αIIbβ3 integrin in human melanoma cells already expressing αvβ3 integrin may alter their in vivo growth properties due to the modulation of their angiogenic phenotype.
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J. Vasc. Biol. 42, Sup:2 (2005) p44