title: Reduction of TLR4 mRNA stability and protein expressions through inhibiting cytoplasmic translocation of HuR transcription factor by E₂ and/or ERα in LPS-treated H9c2 cardiomyoblast cells.
abstract: Our previous results have indicated that Akt mediates 17β-estradiol (E₂) and/or estrogen receptor α (ERα) to inhibit lipopolysaccharide (LPS)-induced JNK activity, tumor necrosis factor α (TNFα) protein expression, and exhibits cardioprotective effects. Toll-like receptor 4 (TLR4) mRNAs often contain AU-rich elements (AREs) in their 3'-untranslated regions (3'UTR) which have a high affinity for RNA-binding proteins. It is not known whether E₂ and ERα affect TLR4 mRNA stability and TLR4 protein expression through regulating the RNA-binding proteins, human antigen R (HuR), tristetraprolin (TTP) and AU-binding factor 1 (AUF-1) in myocardial cells. Therefore, we investigated if the LPS in- duces these RNA-binding proteins to regulate TLR4 mRNAs of cardiomyocytes, and whether the E₂/ERα reduces the TLR4 mRNA stability induced by LPS through the inhibition of RNA-binding protein expression. Using a doxycycline (Dox)-induced Tet-On ERα H9c2 myocardic cell model, we also aimed to identify whether E₂ and/or ERα regulate LPS-induced TLR4 mRNA stability. The results of Western blotting and reverse transcription-PCR assays demonstrated that LPS significantly in- creased the level of cytoplasmic HuR protein and the stability of TLR4 mRNA, and farther induced TLR4 protein expression in H9c2 cells, an effect mediated through the JNK pathway. Interestingly, E₂ and/or ERα decreased the cytoplasmic HuR protein level and TLR4 mRNA stability, and farther decreased the level of TLR4 protein induced by LPS in H9c2 cardiomyoblast cells. Therefore, LPS triggered HuR expression which led to enhanced TLR4 mRNA and upregulated TLR4 expression through JNK1/2 in myocardial cells.
authors.affiliation: Department of Biotechnology, Asia University, Taichung 41354, Taiwan, Republic of China.
authors.forename: Ming-Jen
authors.initials: MJ
authors.lastname: Fan
authors.forename: Rosa
authors.initials: R
authors.lastname: Huang-Liu
authors.forename: Chia-Yao
authors.initials: CY
authors.lastname: Shen
authors.forename: Da-Tong
authors.initials: DT
authors.lastname: Ju
authors.forename: Yueh-Min
authors.initials: YM
authors.lastname: Lin
authors.forename: Peiying
authors.initials: P
authors.lastname: Pai
authors.forename: Pi-Yu
authors.initials: PY
authors.lastname: Huang
authors.forename: Tsung-Jung
authors.initials: TJ
authors.lastname: Ho
authors.forename: Fuu-Jen
authors.initials: FJ
authors.lastname: Tsai
authors.forename: Chang-Hai
authors.initials: CH
authors.lastname: Tsai
authors.forename: Chih-Yang
authors.initials: CY
authors.lastname: Huang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D051959:ELAV Proteins / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D048055:Mitogen-Activated Protein Kinase 8 / Q000502:physiology; D048056:Mitogen-Activated Protein Kinase 9 / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D020871:RNA Stability; D051381:Rats; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000235:genetics*
chemical_list: D051959:ELAV Proteins; D047628:Estrogen Receptor alpha; D008070:Lipopolysaccharides; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D004958:Estradiol; D048056:Mitogen-Activated Protein Kinase 9; D048055:Mitogen-Activated Protein Kinase 8