Inhibition of interleukin-3-andinterferon-α-induced JAK/STAT signaling by the synthetic α-X-2′,3,4,4′-tetramethoxychalcones α-Br-TMC and α-CF3-TMC

The JAK/STAT pathway is an essential mediator of cytokine signaling, often upregulated in human diseases and therefore recognized as a relevant therapeutic target. We previously identified the synthetic chalcone-alpha-bromo-2',3,4,4'-tetramethoxychalcone (alpha-Br-TMC) as a novel JAK2/STAT5 inhibitor. We also found that treatment with alpha-Br-TMC resulted in a downward shift of STAT5 proteins in SDS-PAGE, suggesting a post-translational modification that might affect STAT5 function. In the present study, we show that a single cysteine within STAT5 is responsible for the alpha-Br-TMC-induced protein shift, and that this modification does not alter STAT5 transcriptional activity. We also compared the inhibitory activity of alpha-Br-TMC to that of another synthetic - chalcone, alpha-trifluoromethyl-2',3,4,4'-tetramethoxychalcone (alpha-CF3-TMC). We found that, like alpha-Br-TMC, alpha-CF3-TMC inhibits JAK2 and STAT5 phosphorylation in response to interleukin-3, however without altering STAT5 mobility in SDS-PAGE. Moreover, we demonstrate that both alpha-Br-TMC and alpha-CF3-TMC inhibit interferon-alpha-induced activation of STAT1 and STAT2, by inhibiting their phosphorylation and the expression of downstream interferon-stimulated genes. Together with the previous finding that alpha-Br-TMC and alpha-CF3-TMC inhibit the response to inflammation by inducing Nrf2 and blocking NF-kappa B activities, our data suggest that synthetic chalcones might be useful as anti-inflammatory, anti-cancer and immunomodulatory agents in the treatment of human diseases.