title: TRAM1 protect HepG2 cells from palmitate induced insulin resistance through ER stress-JNK pathway.
abstract: Excess serum free fatty acids (FFAs) are fundamental to the pathogenesis of insulin resistance. Chronic endoplasmic reticulum (ER) stress is a major contributor to obesity-induced insulin resistance in the liver. With high-fat feeding (HFD), FFAs can activate chronic endoplasmic reticulum (ER) stress in target tissues, initiating negative crosstalk between FFAs and insulin signaling. However, the molecular link between insulin resistance and ER stress remains to be identified. We here reported that translocating chain-associated membrane protein 1 (TRAM1), an ER-resident membrane protein, was involved in the onset of insulin resistance in hepatocytes. TRAM1 was significantly up-regulated in insulin-resistant liver tissues and palmitate (PA)-treated HepG2 cells. In addition, we showed that depletion of TRAM1 led to hyperactivation of CHOP and GRP78, and the activation of downstream JNK pathway. Given the fact that the activation of ER stress played a facilitating role in insulin resistance, the phosphorylation of Akt and GSK-3β was also analyzed. We found that depletion of TRAM1 markedly attenuated the phosphorylation of Akt and GSK-3β in the cells. Moreover, application with JNK inhibitor SP600125 reversed the effect of TRAM1 interference on Akt phosphorylation. The accumulation of lipid droplets and expression of two key gluconeogenic enzymes, PEPCK and G6Pase, were also determined and found to display a similar tendency with the phosphorylation of Akt. Glucose uptake assay indicated that knocking down TRAM1 augmented PA-induced down-regulation of glucose uptake, and inhibition of JNK using SP600125 could block the effect of TRAM1 on glucose uptake. These data implicated that TRAM1 might protect HepG2 cells against PA-induced insulin resistance through alleviating ER stress.
authors.affiliation: Department of Endocrinology, Affiliated Hospital of Nantong University, 20 Xisi Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Zhuqi
authors.initials: Z
authors.lastname: Tang
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Wanlu
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Chunhua
authors.initials: C
authors.lastname: Wan
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Guangfei
authors.initials: G
authors.lastname: Xu
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Xiaoke
authors.initials: X
authors.lastname: Nie
authors.affiliation: Department of Endocrinology, Affiliated Hospital of Nantong University, 20 Xisi Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Nana
authors.initials: N
authors.lastname: Xia
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Pathogen Biology, Medical College, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China; Jiangsu Province Key Laboratory for Inflammation and Molecular Drug Target, Nantong University, 19 Qixiu Road, Nantong 226001, Jiangsu Province, People's Republic of China.
authors.forename: Suxin
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Endocrinology, Affiliated Hospital of Nantong University, 20 Xisi Road, Nantong 226001, Jiangsu Province, People's Republic of China. Electronic address: neifenmicui@163.com.
authors.forename: Shiwei
authors.initials: S
authors.lastname: Cui
authors.affiliation: Department of Endocrinology, Affiliated Hospital of Nantong University, 20 Xisi Road, Nantong 226001, Jiangsu Province, People's Republic of China. Electronic address: binghuodinghuo@163.com.
authors.forename: Cuifang
authors.initials: C
authors.lastname: Wang
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D005947:Glucose / Q000378:metabolism; D056945:Hep G2 Cells / Q000378:metabolism*; D006801:Humans; D007333:Insulin Resistance; D020935:MAP Kinase Signaling System; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D010168:Palmitates; C486174:TRAM1 protein, human; D005947:Glucose
keywords: ER stress; Insulin resistance; JNK; TRAM1; Type 2 diabetes