Influence of silencing TRAF6 with shRNA on LPS/TLR4 signaling in vitro

This study investigated the influence of silencing TRAF6 with shRNA on lipopolysaccharide (LPS)/toll-like receptor (TLR)-4 signaling pathway in vitro. Four plasmids (pGCsi-TRAF6-shRNA1, 2, 3, 4) containing different shRNA sequences were designed and synthesized. The proliferation of RAW264.7 cells after transfected with these plasmids was measured by MTT assay. Inflammatory cellular models were established by LPS stimulation. Levels of TNF-alpha, IL-1beta and TGF-beta1 in the supernatants, mRNA expressions of TRAF6, IL-6 and COX-2, protein expression of TRAF6 and translocation of NF-kappaB were assayed by ELISA, real-time quantitative PCR and Western blotting, respectively. The results showed that the TRAF6 gene knockdown by RNAi hardly inhibited the proliferation of RAW264.7 cells within 72 h. The mRNA and protein expression of TRAF6 was lower in the TRAF6-shRNA1, 2 groups than in the TRAF6-shRNA3, 4 groups. Therefore, pGCsi-TRAF6-shRNA1, 2 were selected for the subsequent experiments. Our results still showed that pGCsi-TRAF6-shRNA1, 2 could significantly reduce the production of pro-inflammatory cytokines and mediators including TNF-alpha, IL-1beta, IL-6 and COX-2, and inhibit NF-kappaB nuclear translocation. Moreover, pGCsi-TRAF6-shRNA1, 2 could suppress the release of TGF-beta1 at the protein level. It was concluded that the recombinant plasmid pTRAF6-shRNA can, to some extent, inhibit inflammatory response stimulated by LPS at the initial phase. TRAF6 may become the potential therapeutic target of many inflammation-related diseases.