To examine whether expression of interleukin-6 (IL-6) and interleukin-8 (IL-8) in human carcinoma cells can be influenced by host fibroblasts, we investigated the expression of IL-6 and IL-8 mRNA in carcinoma cells cocultured with fibroblasts. Four human cancer cell lines, NUGC3 and GaCa gastric carcinoma cells, RERF-LCOK lung carcinoma cells, and GBK-1 gallbladder carcinoma cells, which constitutively express large amounts of both IL-6 and IL-8, were cocultured with murine 3T3 fibroblasts, in which IL-6 and IL-8 were not detected, under the same conditions. By Northern blot analysis, the expression of IL-6 mRNA was significantly decreased in NUGC3, GBK-1, and RERF-LCOK cells but was increased in GaCa cells. The expression of IL-8 mRNA was significantly increased in GaCa and GBK-1 cells but decreased in RERF-LCOK cells. Using cell-free conditioned medium, only the NUGC3-3T3 culture supernatant showed little effect on IL-6 and IL-8 mRNA expression in the NUGC3 cells, thereby suggesting that changes in IL-6 and IL-8 mRNA expression observed in the coculture experiment depended mainly on 3T3-NUGC3 contact and not on soluble factors. Similar changes in IL-6 and IL-8 mRNA expression were noted when NUGC3 cells were cultured with paraformaldehyde-fixed 3T3 cells or the 3T3 membrane fraction, thereby supporting this notion. Northern blot analysis of transplanted NUGC3 tumors in nude mice showed a decrease in IL-6 mRNA expression and augmentation of IL-8 mRNA expression. Sera from the NUGC3-bearing mice showed only small differences in IL-6 and IL-8. The downregulation of IL-6 mRNA was reversed 20 hours after NUGC3 cancer cells were separated from the in vivo grown NUGC3 tumors and cultured in vitro. These results suggest that tumors producing IL-6 or IL-8 can be differently modulated by the host cell-mediated pathways, such as contact between fibroblast and tumor cells.

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