Chronic
inflammation of the urinary tract is a significant risk factor for the development of
bladder cancer. We have shown that acute and chronic
inflammation induced by
intravesical instillations of killed Escherichia coli strikingly enhances
N-methyl-N-nitrosourea (MNU)-initiated rat bladder
carcinogenesis. To test the hypothesis that
cytokines released during
inflammation may be involved in the enhancement of bladder
carcinogenesis, we conducted an in vitro experiment. Using soft
agar growth as an index of transformation, we examined the effect of
inflammation-associated
cytokines on the enhancement of MNU-initiated transformation of
MYP3 cells, an anchorage-dependent nontumorigenic rat bladder epithelial cell line. In the first experiment, after 1-h exposure to MNU (50 micrograms/ml), cells (5 x 10(4)) were grown in soft
agar in the presence of
interleukin (IL)-1 alpha,
IL-6,
IL-8, or
tumor necrosis factor-alpha (10 to 100 ng/ml). Colonies consisting of more than 20 cells were counted 4 weeks later. Among the
cytokines tested,
IL-6 (100 ng/ml) significantly increased colony counts over those for the untreated controls (P < 0.001). In the second experiment, the cells treated with MNU similarly as in the first experiment were cultured with or without
IL-6 (100 ng/ml) for 1 week before the cells (5 x 10(4)) were grown in soft
agar in the presence or absence of
IL-6.
IL-6 pretreatment increased colony counts irrespective of subsequent
IL-6 treatment (P < 0.05). Moreover, IL-6-stimulated anchorage-dependent growth of MNU transformants far exceeded that of the parental
MYP3. However, among the transformants, there was no parallel relationship in response to
IL-6 between anchorage-dependent and -independent growth. Our results suggest that
IL-6 may provide a selective growth advantage to MNU-initiated bladder epithelial cells in vitro and that it may be
a factor accounting for the marked enhancement of
inflammation-associated rat bladder
carcinogenesis.