Rosmarinic acid inhibits TCR‐induced T cell activation and proliferation in an Lck‐dependent manner

Abstract

Lck is a T cell-restricted Src family protein tyrosine kinase that plays pivotal roles in TCRmediated signaling. We aimed to identify novel agents that could disrupt the molecular interaction of the Src homology 2-domain of Lck (Lck SH2) with its binding partners, with the expectation that this would impair TCR signaling and generate immunosuppression. Largescale screening of plant extracts indicated that rosmarinic acid (RosA) in extracts of Prunella vulgaris consistently inhibits the interaction between Lck SH2 and a peptide containing its consensus binding sequence (pYEEI). The inhibitory effect of RosA was specific for SH2 domains of Src family protein tyrosine kinase. RosA inhibited TCR-induced-Ca 2+ mobilization and IL-2 promoter activation but not phorbol 12-myristate 13-acetate/ionomycininduced IL-2 promoter activation, indicating its point of inhibition at the membrane proximal site of TCR signaling. Furthermore, RosA inhibited TCR-induced splenocyte proliferation as well as one-way MLR at an IC 50 of 25-50 ? M and inhibited cytokine expression such as IL-2 and IFN-+ . Here, we first report RosA as an inhibitor of TCR-signaling and subsequent T cell proliferation.

Rosmarinic Acid Induces p56lck-Dependent Apoptosis in Jurkat and Peripheral T Cells via Mitochondrial Pathway Independent from Fas/Fas Ligand Interaction

“…2B). Previously we reported that RosA inhibits Lck SH2-pYEEI interaction and does not inhibit Lck kinase activity (25,26). Therefore, our current data are consistent with our previous reports, and RosA is not expected to inhibit AICD.…”

“…In our previous study we observed that RosA inhibits the proliferation of Jurkat cells, but not Lck-deficient J.CaM1.6 cells (25). As this Lck-dependent proliferation inhibition was observed in the absence of TCR stimulus, we assumed that another mechanism might be inhibiting Jurkat T cell proliferation besides blocking TCR-induced signaling (25,26).…”

“…As this Lck-dependent proliferation inhibition was observed in the absence of TCR stimulus, we assumed that another mechanism might be inhibiting Jurkat T cell proliferation besides blocking TCR-induced signaling (25,26). We looked for the possible participation of Lck in RosA-induced apoptosis by comparing RosAmediated apoptosis in Jurkat and J.CaM1.6 cells.…”

“…Previously, we demonstrated that RosA inhibited TCR-induced Ca 2ϩ flux and IL-2 promoter activation by inhibiting inducible T cell kinase and phospholipase C␥-1 activity (25,26). As 1) RosA was screened out as an Lck SH2 inhibitor in ELISA, and 2) RosA did not inhibit Lck kinase activity, we suggested that the inhibitory activity of RosA on TCR-induced signaling and subsequent proliferation is ascribed from its interaction with the Lck SH2 domain (25). Besides RosA-mediated inhibition of TCR signaling, RosA suppressed Jurkat T cell proliferation in the absence of TCR stimulus, and this prompted us to expect apoptosis to be another suppressive mechanism of T cell function.…”

Prolonged survival of islet allografts in mice treated with rosmarinic acid and anti-CD154 antibody

“…According to previous report, Ros A inhibits TCRinduced T cell activation and proliferation , perhaps by one or both of the following mechanisms: (1) Ros A might suppress T cell activation in response to the transplanted graft in vivo and/or (2) Ros A, a TCR-signaling inhibitor, may synergize with other immuosupressants that inhibit signaling cascades distinct from TCR signaling. Finally, Won et al (2003) demonstrated that a combined therapy of two differently functioning immunosuppressants synergistically inhibits T cell proliferation and, consequently, prolongs mouse skin graft survival; Won et al (2003) used Ros A, which inhibits TCR-induced IL-2 expression, and Rapa, which inhibits IL-2 receptor-mediated T-cell proliferation . Another known effect of Ros A is that it participates in the promotion of T cell apoptosis.…”