Silencing of VEGF-A translation in monocytic cells inhibits angiogenic activity. ( A ) EC proliferation was measured in presence of medium conditioned by IFN-γ-treated U937 cells. U937 cells were pre-treated with IFN-γ for up to 24 h, and then fresh medium was added for an additional 2 h. The conditioned medium was added to 50% confluent ECs, and proliferation measured by MTT assay. Cells were treated with recombinant VEGF-A (rVEGF-A, 10 ng/ml) as a positive control. Stimulation of proliferation was expressed as fold-increase compared to cells treated with medium alone (gray bars). Parallel wells contained conditioned medium pre-incubated with anti-VEGF-A antibody (black bars). Shown are the mean and standard deviation from three independent experiments. ( B ) Tube-formation by ECs on growth factor-depleted matrigel was determined after 12 h in presence of conditioned medium from U937 cells treated with IFN-γ for 8, 16, or 24 h, or with recombinant human VEGF-A (10 ng/ml). ( C ) EC tube formation was quantitated by computer-assisted tracing. Shown are the mean and standard deviation from three representative fields, for three independent experiments. ( D ) IFN-γ activates the transcription of VEGF-A, Cp, and other pro-inflammatory genes in macrophages at the site of chronic inflammation. Subsequently, IFN-γ activates the GAIT complex that binds to the GAIT element in the 3′UTR of VEGF-A, Cp, and possibly other transcripts, and silences their translation. This mechanism prevents persistent expression of these inflammatory proteins and reduces or resolves chronic inflammation and tissue injury.
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