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RHBDL4-triggered downregulation of COPII adaptor protein TMED7 suppresses TLR4-mediated inflammatory signaling

ABSTRACT: The toll-like receptor 4 (TLR4) is a central regulator of innate immune signaling that primarily recognizes bacterial lipopolysaccharide (LPS) cell wall constituents to trigger cytokine secretion. We identify the intramembrane protease RHBDL4 as a negative regulator of TLR4 signaling. We show that RHBDL4-triggers the degradation of TLR4’s trafficking factor TMED7, a member of the p24 family of COPII adaptor proteins, which counteracts the transport of TLR4 to the cell surface. Besides TMED7, RHBDL4 cleaves a subset of related p24 cargo receptors, suggesting that this is a general protein abundance control mechanism to regulate the loading of specific secretory proteins into COPII vesicles. Notably, TLR4 activation by LPS mediates transcriptional upregulation of RHBDL4. Hence, TLR4 activation triggers an RHBDL4-dependent negative feedback loop to reduce the export of newly synthesized TLR4 molecules from the endoplasmic reticulum into COPII-coated vesicles. This secretory cargo tuning mechanism prevents the over-activation of TLR4-dependent signaling and consequently alleviates septic shock in a mouse model.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Thomas Ruppert

LAB HEAD: Thomas Ruppert

PROVIDER: PXD045934 | Pride | 2024-01-09

REPOSITORIES: Pride

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Project description:This experiment was conducted to identify mRNA transcripts alteration in liver of Ern1 liver specific knockout mice. The following abstract from the submitted manuscript describes the major findings of this work. The IRE1a-XBP1s axis regulates the COPII-mediated secretory program in response to nutrient availability. Lin Liu, Jie Cai, Xijun Liang, Qian Zhou, Huimin Wang, Chenyun Ding, Yuangang Zhu, Liwei Xiao, Tingting Fu, Zhisheng Xu, Jing Liu, Yujing Yin, Lei Fang, Bin Xue, Yan Wang, Aibin He, Yong Liu, Xiao-Wei Chen, and Zhenji Gan The cytoplasmic coat protein complex-II (COPII) is an evolutionarily conserved machinery that is essential for efficient trafficking of protein and lipid cargos. How the COPII machinery is regulated to meet the metabolic demand in response to alterations of nutritional state remains largely unexplored, however. Here, we show that dynamic changes of COPII-mediated secretion parallel the activation of XBP1s, the critical transcription factor in handling cellular ER stress, in both live cells and mouse liver upon physiological fluctuations of nutrient availability. Using live-cell imaging approaches, we demonstrate that XBP1s is sufficient to promote COPII-dependent secretion, mediating the nutrient stimulatory effects. ChIP-seq and RNA-seq analyses reveal that nutritional signals induce dynamic XBP1s occupancy of promoters of COPII secretion-related genes, thereby driving COPII-directed secretory process. Liver-specific disruption of the IRE1a-XBP1s signaling branch results in diminished COPII-mediated secretion. Reactivation of XBP1s in mice lacking hepatic IRE1a restores COPII-mediated lipoprotein secretion, and reverses the fatty liver and hypolipidemia phenotypes. Thus, our results demonstrate a previously unappreciated mechanism in the metabolic control of liver protein and lipid secretion: the IRE1a-XBP1s axis functions as a nutrient-sensing regulatory nexus that integrates nutritional states and the COPII secretory program.

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	X-14-524-01.raw	Raw

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RHBDL4-triggered downregulation of COPII adaptor protein TMED7 suppresses TLR4-mediated inflammatory signaling

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