Effect of interleukin-6 (IL-6) on vascular endothelial growth factor (VEGF) expression in myeloma cell lines.

(A) VEGF concentrations in culture supernatants. The myeloma cell lines U-266 (▴), OPM-2 (•), RPMI-8226 (▾), and IM-9 (▪) were exposed to 0, 1, and 10 ng/mL IL-6, respectively, for 72 hours. Data represent median values and interquartile ranges of five independent experiments performed in triplicates. Stars denote significant differences versus unstimulated controls (U-266, P < .005; OPM-2,P < .025; RPMI-8226, P < .005; multiple-comparisons' criterion). (B) RNase protection assays showing VEGF messenger RNA (mRNA) levels in U-266 and IM-9 cells after exposure to 0, 1, and 10 ng/mL IL-6, respectively, for 72 hours. Total RNA was hybridized against radioactively labeled complementary RNA probes for VEGF and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Sizes of protected fragments were 648 nucleotides for VEGF165, 438 nt for VEGF121, and 316/258 nt for GAPDH. Signals were analyzed by densitometric scanning and normalized against GAPDH. In contrast to U-266, VEGF mRNA levels were not upregulated in IM-9 cells lacking IL-6 receptor.