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These findings uncover an unexpected mechanism that couples changes in extracellular hormonal signals to hepatic lipid homeostasis; disrupting CREBZF function may have the therapeutic potential for treating fatty liver disease and insulin resistance. (Hepatology 2018).

Aims/hypothesis Liver X receptors (LXRs) are important transcriptional regulators of lipid homeostasis and proliferation in several cell types. However, the roles of LXRs in pancreatic beta cells have not been fully established. The aim of this study was to investigate the effects of LXRs on pancreatic beta cell proliferation. Methods Gene expression was analysed using real-time RT-PCR. Transient transfection and reporter gene assays were used to determine the transcriptional activity of LXRs in pancreatic beta cells. Cell viability and proliferation were analysed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), DNA fluorometric, BrdU labelling and [3 H]thymidine incorporation assays. Cell cycle distribution was investigated by flow cytometry analysis. Adenovirus-based RNA interference was used to knockdown LXRα, LXRβ and p27 in MIN6 cells and mouse islets.Results We found that both Lxrα (also known as Nr1h3) and Lxrβ (also known as Nr1h2) were expressed and transactivated the LXR response element in HIT-T15 and MIN6 cells. Activation of LXRs dose-dependently inhibited pancreatic beta cell viability and proliferation. This was accompanied by beta cell cycle arrest at the G1 phase. Furthermore, LXR activation increased levels of the p27 protein by inhibiting its degradation. Knockdown of p27 reversed these effects of LXR activation on growth inhibition and cell cycle arrest. Conclusions/interpretation Our observations indicate that LXR activation inhibits pancreatic beta cell proliferation through cell cycle arrest. A well-known regulator of pancreatic beta cell cycle progression, p27, is upregulated and mediates the effects of LXRs on growth inhibition in beta cells. These observations suggest the involvement of aberrant activation of LXR in beta cell mass inadequacy, which is an important step in the development of type 2 diabetes.Keywords Beta cell . Cell cycle . Islet . LXR . p27 . Proliferation Abbreviations CMV cytomegalovirus GFP green fluorescent protein LXR liver X receptor LXRE liver X receptor response element MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide RNAi RNA interference SKP2 S-phase kinase-associated protein 2 siRNA small interfering RNA

The cytoplasmic coat protein complex-II (COPII) is 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 the nutritional state remains largely unexplored, however. Here, we show that dynamic changes of COPII vesicle trafficking parallel the activation of transcription factor X-box binding protein 1 (XBP1s), a critical transcription factor in handling cellular endoplasmic reticulum (ER) stress in both live cells and mouse livers upon physiological fluctuations of nutrient availability. Using live-cell imaging approaches, we demonstrate that XBP1s is sufficient to promote COPII-dependent trafficking, mediating the nutrient stimulatory effects. Chromatin immunoprecipitation (ChIP) coupled with high-throughput DNA sequencing (ChIP-seq) and RNA-sequencing analyses reveal that nutritional signals induce dynamic XBP1s occupancy of promoters of COPII traffic-related genes, thereby driving the COPII-mediated trafficking process. Liver-specific disruption of the inositol-requiring enzyme 1α (IRE1α)-XBP1s signaling branch results in diminished COPII vesicle trafficking. Reactivation of XBP1s in mice lacking hepatic IRE1α 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 trafficking: The IRE1α-XBP1s axis functions as a nutrient-sensing regulatory nexus that integrates nutritional states and the COPII vesicle trafficking. COPII | metabolic sensing | XBP1s | nutrient availability | liver steatosis T he cytoplasmic coat protein complex-II (COPII) is evolutionarily conserved secretory machinery that is essential for cellular protein and lipid trafficking through cargo sorting and vesicle formation at the endoplasmic reticulum (ER) (1-4). The vast majority of proteins and lipids exported from the ER require the COPII secretory machinery. The assembly of COPII-coated vesicles for facilitating the transport of cellular cargos has been demonstrated to be a highly complex process (1-6). Activated small GTPase SAR1 localizes to the specialized ER exit sites and initiates the COPII coat assembly, by first recruiting the inner coat formed by the heterodimer SEC23/SEC24, followed by the outer coat heterotetramer SEC13/SEC31, to deform the ER membrane and eventually produce carrier vesicles (2, 4, 7-9). Mutations in COPII components or accessory factors have been implicated in several human genetic diseases, including chylomicron retention disease, congenital dyserythropoietic anemia type II, and cranio-lenticulosutural dysplasia (10-14). However, it remains largely unexplored how the COPII machinery is regulated to meet the cellular secretory demand in response to various physiological stimuli.As a metabolically active tissue, the liver possesses a remarkable adaptive capacity to secrete lipids and proteins according to...

Long-range communication between intestinal symbiotic bacteria and extra-intestinal organs can occur through circulating bacterial signal molecules, through neural circuits, or through cytokines or hormones from host cells. Here we report that Nod1 ligands derived from intestinal bacteria act as signal molecules and directly modulate insulin trafficking in pancreatic beta cells. The cytosolic peptidoglycan receptor Nod1 and its downstream adapter Rip2 are required for insulin trafficking in beta cells in a cellautonomous manner. Mechanistically, upon recognizing cognate ligands, Nod1 and Rip2 localize to insulin vesicles, recruiting Rab1a to direct insulin trafficking through the cytoplasm. Importantly, intestinal lysozyme liberates Nod1 ligands into the circulation, thus enabling long-range communication between intestinal microbes and islets. The intestine-islet crosstalk bridged by Nod1 ligands modulates host glucose tolerance. Our study defines a new type of inter-organ communication based on circulating bacterial signal molecules, which has broad implications for understanding the mutualistic relationship between microbes and host.

Background and Aims STAT3, a member of the signal transducer and activator of transcription (STAT) family, is strongly associated with liver injury, inflammation, regeneration, and hepatocellular carcinoma development. However, the signals that regulate STAT3 activity are not completely understood. Approach and Results Here we characterize CREB/ATF bZIP transcription factor CREBZF as a critical regulator of STAT3 in the hepatocyte to repress liver regeneration. We show that CREBZF deficiency stimulates the expression of the cyclin gene family and enhances liver regeneration after partial hepatectomy. Flow cytometry analysis reveals that CREBZF regulates cell cycle progression during liver regeneration in a hepatocyte‐autonomous manner. Similar results were observed in another model of liver regeneration induced by intraperitoneal injection of carbon tetrachloride (CCl4). Mechanistically, CREBZF potently associates with the linker domain of STAT3 and represses its dimerization and transcriptional activity in vivo and in vitro. Importantly, hepatectomy‐induced hyperactivation of cyclin D1 and liver regeneration in CREBZF liver‐specific knockout mice was reversed by selective STAT3 inhibitor cucurbitacin I. In contrast, adeno‐associated virus–mediated overexpression of CREBZF in the liver inhibits the expression of the cyclin gene family and attenuates liver regeneration in CCl4‐treated mice. Conclusions These results characterize CREBZF as a coregulator of STAT3 to inhibit regenerative capacity, which may represent an essential cellular signal to maintain liver mass homeostasis. Therapeutic approaches to inhibit CREBZF may benefit the compromised liver during liver transplantation.

Prostaglandin E 2 (PGE 2 ) is a well-known mediator of ␤-cell dysfunction in both type 1 and type 2 diabetes. We recently reported that down-regulation of the Akt pathway activity is implicated in PGE 2 -induced pancreatic ␤-cell dysfunction. The aim of this study was to further dissect the signaling pathway of this process in pancreatic ␤-cell line HIT-T15 cells and primary mouse islets. We found that PGE 2 time-dependently increased the c-Jun N-terminal kinase (JNK) pathway activity. JNK inhibition by the JNK-specific inhibitor SP600125 reversed PGE 2 -inhibited glucose-stimulated insulin secretion (GSIS). PGE 2 induced dephosphorylation of Akt and FOXO1, leading to nuclear localization and transactivation of FOXO1. Activation of FOXO1 induced nuclear exclusion but had no obvious effect on the whole-cell protein level of pancreatic and duodenal homeobox 1 (PDX1). However, these effects were all attenuated by JNK inhibition. Furthermore, adenovirus-mediated overexpression of dominant-negative (DN)-FOXO1 abolished whereas constitutively active (CA)-FOXO1 mimicked the effects of PGE 2 on GSIS in isolated mouse islets. In addition, we demonstrated that DN-JNK1 but not DN-JNK2 or CA-Akt abolished the PGE 2 -induced AP-1 luciferase reporter activity, whereas DN-JNK1 and CA-Akt but not DN-JNK2 reversed the effect of PGE 2 on FOXO1 transcriptional activity, and overexpression of DN-JNK1 rescued PGE 2 -impaired GSIS in mouse islets. Our results revealed that activation of the JNK is involved in PGE 2 -induced ␤-cell dysfunction. PGE 2 -mediated JNK1 activation, through dephosphorylation of Akt and FOXO1, leads to nuclear accumulation of FOXO1 and nucleocytoplasmic shuttling of PDX1, finally resulting in defective GSIS in pancreatic ␤-cells. (Endocrinology 150: 5284 -5293, 2009)

The initiation and development of diabetes are mainly ascribed to the loss of functional ␤-cells. Therapies designed to regenerate ␤-cells provide great potential for controlling glucose levels and thereby preventing the devastating complications associated with diabetes. This requires detailed knowledge of the molecular events and underlying mechanisms in this disorder. Here, we report that expression of microRNA-223 (miR-223) is up-regulated in islets from diabetic mice and humans, as well as in murine Min6 ␤-cells exposed to tumor necrosis factor ␣ (TNF␣) or high glucose. Interestingly, miR-223 knockout (KO) mice exhibit impaired glucose tolerance and insulin resistance. Further analysis reveals that miR-223 deficiency dramatically suppresses ␤-cell proliferation and insulin secretion. Mechanistically, using luciferase reporter gene assays, histological analysis, and immunoblotting, we demonstrate that miR-223 inhibits both forkhead box O1 (FOXO1) and SRY-box 6 (SOX6) signaling, a unique bipartite mechanism that modulates expression of several ␤-cell markers (pancreatic and duodenal homeobox 1 (PDX1), NK6 homeobox 1 (NKX6.1), and urocortin 3 (UCN3)) and cell cycle-related genes (cyclin D1, cyclin E1, and cyclin-dependent kinase inhibitor P27 (P27)). Importantly, miR-223 overexpression in ␤-cells could promote ␤-cell proliferation and improve ␤-cell function. Taken together, our results suggest that miR-223 is a critical factor for maintaining functional ␤-cell mass and adaptation during metabolic stress.