Selective induction of interleukin-8 expression in metastatic melanoma cells by transforming growth factor-beta 1

Interleukin (IL)-8 and transforming growth factor (TGF)-beta1 are proangiogenic factors overexpressed in advanced human melanoma. We investigated the effects of TGF-beta1 on IL-8 expression in the well-characterized A375 human melanoma system. We demonstrated by enzyme-linked immunoassay and Northern blot analysis that TGF-beta1 selectively induced IL-8 expression, at both protein and mRNA levels, in highly metastatic A375SM cells but not cells of their poorly metastatic parental line A375P. Transient transfection with luciferase reporter gene constructs revealed that TGF-beta1 activated IL-8 promoter activity in A375SM cells but not A375P cells. Studies with progressive 5' deletion constructs and site-specific mutations demonstrated that a construct containing -133 to +44 of the 5'-flanking sequence was necessary and sufficient for maximal TGF-beta1-induced transcription response and that TGF-beta1-induced activation of IL-8 promoter depended on AP-1 (-126 to -120 bp), NF-kappaB (-94 to -71 bp), and C/EBP-like factor NF-IL6 (-94 to -81 bp) in this region. Interestingly, both A375P and A375SM cells expressed type I and type II TGF-beta receptors and TGF-beta1 induced the nuclear translocation of Smad3 protein in both A375P and A375SM cells. Moreover, both A375P and A375SM cells were susceptible to TGF-beta1-induced growth inhibition. Our data thus demonstrated that TGF-beta1 selectively induced IL-8 expression in highly metastatic A375SM melanoma cells. This TGF-beta1-induced IL-8 expression could be an amplification cascade responsible for overexpression of IL-8 in human melanoma and one of potential mechanisms by which TGF-beta1 promotes angiogenesis, growth, and metastasis of human melanoma.