Shikonin inhibited mitogen-activated IL-4 and IL-5 production on EL-4 cells through downregulation of GATA-3 and c-Maf induction

Aim: To investigate the effects of shikonin on phorbol myristate acetate (PMA) plus cyclic adenosine monophosphate (cAMP)-induced T helper (T _H) 2 cell cytokine production, and the underlying mechanism. Main methods: We used activated EL-4 murine T-lymphoma cells, which produce interleukin (IL)-4 and IL-5, but not interferon (IFN)-γ, as T_H2 cell-like cells and treated them with PMA + cAMP to investigate the effects of shikonin on T_H2 cytokines, transcriptional factors, and the related mitogen-activated protein kinase (MAPK)/nuclear factor (NF)-κB signaling pathway. Key findings: The data show that shikonin inhibited the PMA + cAMP-induced mRNA and protein expression of IL-4 and IL-5 via the downregulation of GATA-binding protein-3 (GATA-3) and c-musculoaponeurotic fibrosarcoma (Maf) but not T-box expressed in T cells (T-bet). Moreover, shikonin suppressed the phosphorylation of p38, inhibitor of κB (IκB) kinase (IKK)-β and IκB-α, and the subsequent IκB-α degradation induced by PMA + cAMP; however, the PMA + cAMP-induced phosphorylation of extracellular signal-related kinase (ERK), which resulted in minor inhibition and phosphorylation of c-Jun N-terminal kinase (JNK), seemed to be unaffected by shikonin treatment. Significance: This study suggests that downregulation of GATA-3 and c-Maf via the suppression of p38, IKK-β and IκB-α phosphorylation might contribute to the inhibitory effect of shikonin on mitogen-induced IL-4 and IL-5 production in EL-4T cells. Furthermore, shikonin is a potential drug for treating allergic diseases.