IL-11 and its receptor, IL-11Ra, are expressed in human cancers; however, the functional role of IL-11 in tumor progression is not known. We found that IL11 is a hypoxia-inducible, VHL-regulated gene in human cancer cells and that expression of IL11 mRNA was dependent, at least in part, on HIF-1. A cooperative interaction between HIF-1 and AP-1 mediated transcriptional activation of the IL11 promoter. Additionally, we found that human cancer cells expressed a functional IL-11Ra subunit, which triggered signal transduction either by exogenous recombinant human IL-11 or by autocrine production of IL-11 in cells cultured under hypoxic conditions. Silencing of IL11 dramatically abrogated the ability of hypoxia to increase anchorage-independent growth and significantly reduced tumor growth in xenograft models. Notably, these results were phenocopied by partial knockdown of STAT1 in a human prostate cancer cell line (PC3), suggesting that this pathway may play an important role in mediating the effects of IL-11 under hypoxic conditions. In conclusion, these results identify IL11 as an oxygen- and VHL-regulated gene and provide evidence of a pathway “hijacked” by hypoxic cancer cells that may contribute to tumor progression.
Barbara Onnis, Nicole Fer, Annamaria Rapisarda, Victor S. Perez, Giovanni Melillo
(A) HCT116 cells were serum starved for 24 hours, cultured under normoxia or hypoxia for an additional 72 hours, and then plated in soft agar (mean ± SEM of 3 independent experiments; t test). (B) HCT116 cells were cultured as described above and then plated for clonogenic assay. Colonies were stained after 10 days (mean ± SEM of 2 independent experiments). (C) Levels of ERK protein phosphorylation and HIF-1α protein were measured using Western blot analysis in HCT116 cells cultured as described above. Results are representative of 2 independent experiments. (D) HCT116 cells were cultured under normoxia or hypoxia for 24, 48, and 72 hours. IL11 mRNA expression was analyzed using quantitative RT-PCR, and results are presented as the mean ± SEM of 2 independent experiments (t test). (E) PC3 cells were cultured under normoxia or hypoxia for 24, 48, and 72 hours. Results are presented as mean fold change relative to the normoxia sample ± SEM of 4 different quantitative RT-PCR experiments (t test). (F) Levels of IL-11 protein were measured in supernatant from PC3 cells cultured under normoxia or hypoxia for 24, 48, and 72 hours using a commercially available ELISA kit. Results represent the mean ± SEM of 3 separate experiments (t test). *P < 0.01; **P < 0.001; ***P < 0.0001.