The mechanism of Akt activation in TLR4 signaling

• Main Authors: Wan-Ching Hsu, 徐婉晴
• Other Authors: Ping-Hui Tseng
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/14118003628333623370

碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 100 === Toll-like receptors (TLRs) are important in innate immune to regulate inflammatory responses and cytokines secretion. TLR4, the most-studied TLRs, recognizes lipopolysaccharide (LPS) from Gram-negative bacteria to activate NF-B, MAPKs and type I interferon by MyD88-dependent and TRIF-dependent pathway. Besides, it has been reported that TLR4 also triggered Akt activation. Akt, also called protein kinase B (PKB), is a serine/threonine kinase that regulates glucose homeostasis, proliferation, protein synthesis and survival. During growth factors stimulation, Akt is activated by phosphatidylinositol 3-kinase (PI3K). However by what mechanism TLR4 activates Akt is still unclear. First of all, by knocking down specific protein with short hairpin RNA (shRNA), we defined Akt activation in TLR4 signal pathway depended on MyD88 and TRIF. Meanwhile, in line with reported data that Akt activation is associated with ubiquitinaiton by TRAF6, an E3 ligase downstream of TLR4, our data showed that Akt phosphorylation was downregulated in TRAF6-scilencing RAW264.7 upon LPS treatment. Furthermore, recent studies that focused on TLR4-mediated PI3K activation have conflicted results. From our results, Akt activation with LPS depended on PI3K and PI3K. In cells knocked-down different subtypes of PI3K, we find that PI3K is more important than PI3K in Akt activation of TLR4 signal pathway, and negatively regulated TLR4-induced autophagy. In TLR4-induced cytokines production, our results indicated that IL-6 mRNA expression is decreased but there was no difference in TNF mRNA expression in PI3K and PI3K knocked-down cells. In conclusion, LPS-induced Akt activation is associated with MyD88 and TRIF in TLR4 signal pathwa. Akt activation is accompanied with ubiquitination which mediated by TRAF6 and pjosphorylation which is regulated by PI3K upon LPS treatment. Moreover, the activated Akt is able to control critical immune responses, such as autophagy and cytokines production.