Abstract 316: Triggering receptor expressed on myeloid cell-like transcript 2 (TLT-2) and TLR-4 contribute to activation of human dendritic cells via ERK signaling pathway
Authors: Chao-Yang Lai, Hsin-Hung Lin, Alice L. Yu, Huan-Chieh Cho, Shu-Hwa Chen, Kuo-I Lin, Wen-Bin Yang, Yi-Kai Chiu, John Yu
Journal: Cancer Research (2010)

Abstract Triggering receptor expressed on myeloid cell (TREM) proteins are a family of receptors that regulate many different cell processes. TREM-like transcript 2 (TLT-2) is one of these TREM proteins. It have been reported that TLT-2 plays important roles in inflammation and T cell activation, but it is still elusive in its signal transduction in the cell. In an attempt to identify the active ingredient of Reishi (Ganoderma lucidum) for potential drug development, we isolated a high molecular weight polysaccharide fraction, F3, and performed a comprehensive analysis of its immunomodulatory and adjuvant activities. It was found that this polysaccharide extract had potent immunomodulatory and adjuvant activities in vivo and in vitro. F3-treated mice showed an increase in the number of dendritic cells as well as CD4, CD8, regulatory T, B, plasma, NK, and NKT cells in the spleen. F3 also elevated the levels of twelve cytokines and chemokines in the blood of mice. F3 displayed potent adjuvant activity for tetanus toxoid in the absence of alum and potentiated antibody responses to alum-containing tetanus toxoid in mice. In addition, F3 also boosted Th1 and Th2 response in vivo. In vitro, F3 induced the maturation of dendritic cells derived from human monocytes by upregulating CD40, CD54, CD80, CD83, CD86, and HLA-DR, enhanced mixed lymphocyte reaction and increased the production of sixteen cytokines and chemokines. In microarray analysis, expressions of 7,688 genes were modulated in dendritic cells after treatment with F3, including cytokine and chemokine genes. To ascertain the possible receptors of F3 on human DCs, neutralizing antibodies against TLR-4 and TREM-like transcript 2 (TLT-2), but not TLR-2 and DC-SIGN, partially blocked F3-induced cytokine and chemokine release. TLT-2 and TLR-4 neutralizing antibodies or siRNA of TLT-2 also suppressed F3-induced phosphorylation of ERK1/2 in DCs. Moreover, inhibitors of NF-κB, p38 MAPK and Akt, but not JNK, suppressed F3-induced upregulation of surface markers and reduced F3-induced cytokine production in DCs. F3 and LPS also enhanced phosphorylation of ERK1/2 and TNF-α expression through Raf-MEK signaling cascade and involvement of signaling pathway was validated through the use of specific inhibitors for Raf-MEK- ERK pathway in TLT-2 transfected U937, confirming our observations in DCs. We further demonstrated the expression of Blimp-1 in dendritic cells and its upregulation by F3. The latter could be blocked by TLT-2 antibody. These results provide insight into the TLT-2 mediated signal transduction and immunomodulatory mechanisms of F3 polysaccharide. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 316.