TGF-β/Smad signaling inhibits IFN-γ and TNF-α-induced TARC (CCL17) production in HaCaT cells

Abstract

Background: A Th2 chemokine, thymus and activation regulated chemokine (TARC/CCL17), produced by keratinocytes, is implicated in the development of atopic dermatitis by recruiting CLA +CCR4 + lymphocytes into lesional skin and its expression was induced by proinflammatory cytokines such as interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). However, it remains unknown how TARC expression is negatively regulated in keratinocytes. Objective: We sought to determine whether transforming growth factor-β1 (TGF-β1) regulated TARC expression in keratinocytes. Methods: The effect of TGF-β1 on mRNA and protein expression of IFN-γ and TNF-α-induced TARC in a human keratinocyte cell line, HaCaT cells, was evaluated by using RT-PCR and ELISA. Adenovector-mediated gene transfer was used to determine the effect of Smad proteins on TARC expression in HaCaT cells. Results: TGF-β1 inhibited mRNA and protein expression of IFN-γ and TNF-α-induced TARC in HaCaT cells. The inhibitory effect of TGF-β1 on the TARC expression was suppressed by overexpression of Smad7, a major inhibitory regulator of Smad pathway for transforming growth factor-β (TGF-β) signaling, but not by PD98059, an inhibitor for ERK/mitogen-activated protein kinase (MAPK) pathway. In addition, overexpression of Smad2 or Smad3, major signal transducing Smads, was sufficient to inhibite the IFN-γ and TNF-α-induced TARC production in HaCaT cells. Conclusion: TGF-β1 inhibited IFN-γ and TNF-α-induced TARC production in HaCaT cells via Smad2/3, suggesting that modulation of TGF-β/Smad signaling pathway may be beneficial for the treatment of atopic dermatitis.