Phytocomponent 4-hydroxy-3-methoxycinnamaldehyde ablates T-cell activation by targeting protein kinase C-θ and its downstream pathways.

Autoreactive T-cell responses have a crucial role in the pathology and clinical course of autoimmune diseases. Therefore, controlling the activation of these cells is an important strategy for developing therapies and therapeutics. Here, we identified that 4-hydroxy-3-methoxycinnamaldehyde (4H3MC) has a therapeutic potential for T-cell activation by modulating protein kinase C-θ (PKCθ) and its downstream pathways. Pre- and post-treatment with 4H3MC prevented IL-2 release from human transformed and untransformed T cells at the micromolar concentrations without any cytotoxic effects, in fact more efficiently than its structural analogue 4-hydroxycinnamic acid-a previously reported T-cell inhibitor. In silico analysis showed that 4H3MC is a potential inhibitor of PKC isotypes, including PKCθ-a crucial PKC isotype in T cells. Consistently, 4H3MC significantly blocked PKC activity in vitro and also inhibited the phosphorylation of PKCθ in T cells. 4H3MC had no effect on TCR-mediated membrane-proximal-signalling events such as phosphorylation of Zap70. Instead, it attenuated the phosphorylation of mitogen-activated protein kinases (ERK and p38) and promoter activities of NF-κB, AP-1 and NFAT. Taken together, our results provide the evidences that 4H3MC may have curative potential as a novel immune modulator in a broad range of immunopathological disorders by modulating PKCθ activity.