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A diverse array of cellular stresses can lead to accumulation of misfolded or unfolded proteins in endoplasmic reticulum (ER), which subsequently elicits ER stress. Inositol-requiring enzyme 1a (IRE1α) is the most sensitive of the three unfolded protein response (UPR) branches which are triggered to cope with ER stress in mammalian cells. IRE1α signaling is quite contextspecific on account of many adaptor and modulator proteins that directly interact with it, including heat shock proteins (HSPs), RING finger protein 13 (RNF13), poly (ADP-ribose) polymerase 16 (PARP16), Bax/Bak, and Bax inhibitor-1 (BI-1). The activated IRE1α triggers different downstream pathways depending on the UPRosome formed by distinct modulator proteins. At the initial phase of ER stress, IRE1α-XBP1 axis functions as an adaptive response. While ER stress sustains or intensifies, signals shift to apoptotic responses. Furthermore, IRE1α signaling can be exploited to the development of a wide range of prevalent human diseases, with cancer the most characterized. Here we provide an overview of recent insights into the complex IRE1α signaling network which makes IRE1α an intriguing cell fate switch. Besides, the functional relevance is presented since IRE1α activation also participates in some other physiological processes beyond protein-folding status. [ABSTRACT FROM AUTHOR]

A diverse array of cellular stresses can lead to accumulation of misfolded or unfolded proteins in endoplasmic reticulum (ER), which subsequently elicits ER stress. Inositol-requiring enzyme 1α (IRE1α) is the most sensitive of the three unfolded protein response (UPR) branches which are triggered to cope with ER stress in mammalian cells. IRE1α signaling is quite contextspecific on account of many adaptor and modulator proteins that directly interact with it, including heat shock proteins (HSPs), RING finger protein 13 (RNF13), poly (ADP-ribose) polymerase 16 (PARP16), Bax/Bak, and Bax inhibitor-1 (BI-1). The activated IRE1α triggers different downstream pathways depending on the UPRosome formed by distinct modulator proteins. At the initial phase of ER stress, IRE1α-XBP1 axis functions as an adaptive response. While ER stress sustains or intensifies, signals shift to apoptotic responses. Furthermore, IRE1α signaling can be exploited to the development of a wide range of prevalent human diseases, with cancer the most characterized. Here we provide an overview of recent insights into the complex IRE1α signaling network which makes IRE1α an intriguing cell fate switch. Besides, the functional relevance is presented since IRE1α activation also participates in some other physiological processes beyond protein-folding status. [ABSTRACT FROM AUTHOR]

Background/Aims: Activated hepatic stellate cells (HSCs) are the major source of extracellular matrix (ECM). Therefore inhibiting HSC activation is considered as an effective strategy to inhibit the process of liver fibrosis. This study aimed to investigate the underlying mechanism of methyl helicterate (MH) isolated from Helicteres angustifolia on the activation of HSCs. Methods: HSC-T6 cells were treated with various concentration of MH and autophagy was inhibited by 3-Methyl adenine (3-MA) or RNA interference. Cell viability was observed by MTT assay and cell colony assay. Cell cycle and apoptosis were analyzed using flow cytometry. Autophagic vacuoles were observed by transmission electron microscopy and monodansyl cadaverine (MDC) staining. Moreover, autophagy-related genes and proteins were detected using real-time PCR and Western blot assays, respectively. Results: MH significantly inhibited HSC activation, as evidenced by the inhibition of cell viability, colony formation and the expression of α-SMA and collagen I. MH caused cell cycle arrest in G2/M phase. Moreover, MH significantly induced apoptosis through regulating the mitochondria-dependent pathway and the activity of caspases. MH treatment significantly increased lysosomes and autophagosomes, and enhanced the formation of autophagic vacuoles and autophagic flux. Interestingly, inhibiting autophagy by 3-MA or RNA interference abolished the ability of MH in inhibiting HSC activation. On the other hand, induction of autophagy promoted MH-induced HSC apoptosis. Further study showed that MH-induced HSC apoptosis and autophagy was mediated by the JNK and PI3K/Akt/mTOR pathways. Conclusion: Our results demonstrate that MH-induced HSC apoptosis and autophagy may be one of the important mechanisms for its anti-fibrosis effect. [ABSTRACT FROM AUTHOR]