Level of interleukin-8 expression by metastatic human melanoma cells directly correlates with constitutive NF-kappaB activity.

The purpose of this study was to determine whether constitutive NF-kappaB activity regulates the expression level of interleukin-8 (IL-8) in metastatic human melanoma cells. Cultures of metastatic human A375 melanoma cells expressed higher levels of IL-8 mRNA and protein than nonmetastatic A375 human melanoma cells. No discernible differences in IL-8 half-life were found between metastatic and nonmetastatic cells, but cells that overexpressed IL-8 had a higher transcription rate and increased IL-8 promoter activity. Analysis of the IL-8 promoter using deletion mutants revealed that the region within -133 was essential for constitutive IL-8 promoter activity and that mutation of NF-kappaB binding sites eliminated the constitutive IL-8 promoter activity. The activation of constitutive IL-8 transcription directly correlated with the level of constitutive NF-kappaB activity. Transfection of melanoma cells with a dominant-negative mutant IkappaBalpha expression vector (pLXSN-IkappaBalphaM) significantly decreased the level of constitutive NF-kappaB activity and expression of IL-8, demonstrating that constitutive NF-kappaB/relA activities contribute to overexpression of IL-8 in highly metastatic human melanoma cells.