Purpose: Interleukin (IL)-8 is an important mediator of angiogenesis, tumorigenicity, and metastasis in transitional cell carcinoma (TCC) of the bladder. Nuclear factor kappaB (NF-kappaB)/relA regulates IL-8 expression in several neoplasms. The purpose of this study was to determine whether the organ microenvironment (hypoxia, acidosis) regulates the expression of IL-8 in TCC via NF-kappaB, and whether inhibition of NF-kappaB function by mutant IkappaB-alpha prevents induction of IL-8 expression.
Experimental design: IL-8 mRNA expression and protein production by human TCC cell lines (UM-UC-14, HTB-9, RT-4, KU-7 and 253J B-V) were measured by Northern blot analysis and ELISA under acidic (pH 7.35-6.0) and hypoxic (1.0% O(2)) conditions. The involvement of NF-kappaB and activator protein 1 in the regulation of IL-8 production was evaluated by electrophoretic mobility shift assay. Furthermore, the tumorigenicity and metastatic potential of UM-UC-14 cells were determined after transfection with mutant IkappaB-alpha.
Results: We found that acidic and hypoxic conditions increased IL-8 mRNA expression and protein production by several, but not all, TCC cell lines evaluated. NF-kappaB, but not activator protein 1, was inducibly activated in UM-UC-14 under both acidic and hypoxic conditions, but not in UM-UC-14 mutant IkappaB-alpha transfectants. Tumor growth and lymph node metastasis were inhibited in UM-UC-14 mutant IkappaB-alpha transfectants compared with UM-UC-14 controls. This effect was associated with the inhibition of IL-8 production, cellular proliferation, and angiogenesis.
Conclusions: These results suggest that TCCs of the bladder have heterogenic responses to physicochemical changes in the microenvironment and identify NF-kappaB as a potential molecular target for therapy.