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Keywords:

  • β3 integrins;
  • bFGF;
  • vascularization;
  • human melanoma;
  • xenograft

Abstract

Previous studies indicated that transfection of the platelet integrin αIIbβ3 into human melanoma cells expressing integrin αvβ3 promoted their in vivo (but not in vitro) growth and cell survival. To reveal the underlying pathomechanism, we have analyzed the angiogenic phenotype of αIIbβ3 integrin-transduced human melanoma cells expressing integrin αvβ3. Upon heterotopic or orthotopic (intracutaneous) injections into SCID mice, the αIIbβ3 integrin-overexpressing clones, ESL, ESH, 19L and 19H, grew more rapidly than the mock transfectant (αvβ3 expressing) clone, 3.1P. Morphometry demonstrated an increased intratumoral microvessel density in 19L and 19H tumors compared to 3.1P. Immunocytochemistry and flow cytometry indicated that vascular endothelial growth factor (VEGF) is constitutively expressed in the majority of the cells of both the mock and the αIIbβ3 integrin-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. Furthermore, cDNA microarray analysis of the 19H cells revealed 12 downregulated and 36 upregulated genes [among them 3 upregulated vasculogenic mimicry-genes (CD34, endothelin receptor B, Prostaglandin I-2 synthase)] when compared to 3.1P cells. The altered bFGF expression may be influenced by integrin-linked signaling, since bβ3-endonexin is upregulated in αIIbβ3-transfected cells and tyrosine kinase inhibitors downregulate bFGF both at mRNA and protein levels. We propose here that 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. © 2005 Wiley-Liss, Inc.