Jaewang Ghim

Mind Bomb 1-Expressing Intermediate Progenitors Generate Notch Signaling to Maintain Radial Glial Cells

Notch signaling is critical for the stemness of radial glial cells (RGCs) during embryonic neurogenesis. Although Notch-signal-receiving events in RGCs have been well characterized, the signal-sending mechanism by the adjacent cells is poorly understood. Here, we report that conditional inactivation of mind bomb-1 (mib1), an essential component for Notch ligand endocytosis, in mice using the nestin and hGFAP promoters resulted in complete loss of Notch activation, which leads to depletion of RGCs, and premature differentiation into intermediate progenitors (IPs) and finally neurons, which were reverted by the introduction of active Notch1. Interestingly, Mib1 expression is restricted in the migrating IPs and newborn neurons, but not in RGCs. Moreover, sorted Mib1+ IPs and neurons can send the Notch signal to neighboring cells. Our results reveal that not only newborn neurons but also IPs are essential Notch-ligand-presenting cells for maintaining RGC stemness during both symmetric and asymmetric divisions.

O‐GlcNAcase is essential for embryonic development and maintenance of genomic stability

Dysregulation of O‐GlcNAc modification catalyzed by O‐GlcNAc transferase (OGT) and O‐GlcNAcase (OGA) contributes to the etiology of chronic diseases of aging, including cancer, cardiovascular disease, type 2 diabetes, and Alzheimer’s disease. Here we found that natural aging in wild‐type mice was marked by a decrease in OGA and OGT protein levels and an increase in O‐GlcNAcylation in various tissues. Genetic disruption of OGA resulted in constitutively elevated O‐GlcNAcylation in embryos and led to neonatal lethality with developmental delay. Importantly, we observed that serum‐stimulated cell cycle entry induced increased O‐GlcNAcylation and decreased its level after release from G2/M arrest, indicating that O‐GlcNAc cycling by OGT and OGA is required for precise cell cycle control. Constitutively, elevated O‐GlcNAcylation by OGA disruption impaired cell proliferation and resulted in mitotic defects with downregulation of mitotic regulators. OGA loss led to mitotic defects including cytokinesis failure and binucleation, increased lagging chromosomes, and micronuclei formation. These findings suggest an important role for O‐GlcNAc cycling by OGA in embryonic development and the regulation of the maintenance of genomic stability linked to the aging process.

Phospholipase signalling networks in cancer

Phospholipases (PLC, PLD and PLA) are essential mediators of intracellular and intercellular signalling. They can function as phospholipid-hydrolysing enzymes that can generate many bioactive lipid mediators, such as diacylglycerol, phosphatidic acid, lysophosphatidic acid and arachidonic acid. Lipid mediators generated by phospholipases regulate multiple cellular processes that can promote tumorigenesis, including proliferation, migration, invasion and angiogenesis. Although many individual phospholipases have been extensively studied, how phospholipases regulate diverse cancer-associated cellular processes and the interplay between different phospholipases have yet to be fully elucidated. A thorough understanding of the cancer-associated signalling networks of phospholipases is necessary to determine whether these enzymes can be targeted therapeutically.

Jab1 Induces the Cytoplasmic Localization and Degradation of p53 in Coordination with Hdm2

The biological mechanisms for maintaining the basal level of p53 in normal cells require nuclear exclusion and cytoplasmic degradation. Here, we showed that Jab1 facilitates p53 nuclear exclusion and its subsequent degradation in coordination with Hdm2. p53 was excluded from the nucleus in the presence of Jab1; this exclusion was prevented by leptomycin B treatment. Nuclear export of p53 was accompanied by a decrease in the levels of p53, as well as of its target proteins, which include p21 and Bax. Domain analyses of Jab1 showed that the N-terminal domain, 1-110, was capable of inducing cytoplasmic translocation of p53. Furthermore, 110-191 was required to facilitate the degradation of p53. Neither of these mutants incorporated into the CSN complex, indicating that Jab1 could affect the levels of p53 independent of intact CSN complex. Conversely, Jab1 was incapable of translocating and degrading two p53 mutants, W23S and 6KR, neither of which could be modified by Hdm2. Moreover, Jab1 did not affect the cellular localization or protein levels of p53 in p53 and Hdm2 double-null mouse embryo fibroblasts. We further observed that the ablation of endogenous Jab1 by small interfering RNA prevented Hdm2-mediated p53 nuclear exclusion. Under stressed conditions, which could sequester Hdm2 in its inactive state, Jab1 did not affect p53. Our studies implicate that Jab1 is required to remove post-translationally modified p53 and provide a novel target for p53-related cancer therapies.

CXCL12 secreted from adipose tissue recruits macrophages and induces insulin resistance in mice

Aims/hypothesisObesity-induced inflammation is initiated by the recruitment of macrophages into adipose tissue. The recruited macrophages, called adipose tissue macrophages, secrete several proinflammatory cytokines that cause low-grade systemic inflammation and insulin resistance. The aim of this study was to find macrophage-recruiting factors that are thought to provide a crucial connection between obesity and insulin resistance.MethodsWe used chemotaxis assay, reverse phase HPLC and tandem MS analysis to find chemotactic factors from adipocytes. The expression of chemokines and macrophage markers was evaluated by quantitative RT-PCR, immunohistochemistry and FACS analysis.ResultsWe report our finding that the chemokine (C-X-C motif) ligand 12 (CXCL12, also known as stromal cell-derived factor 1), identified from 3T3-L1 adipocyte conditioned medium, induces monocyte migration via its receptor chemokine (C-X-C motif) receptor 4 (CXCR4). Diet-induced obese mice demonstrated a robust increase of CXCL12 expression in white adipose tissue (WAT). Treatment of obese mice with a CXCR4 antagonist reduced macrophage accumulation and production of proinflammatory cytokines in WAT, and improved systemic insulin sensitivity.Conclusions/interpretationIn this study we found that CXCL12 is an adipocyte-derived chemotactic factor that recruits macrophages, and that it is a required factor for the establishment of obesity-induced adipose tissue inflammation and systemic insulin resistance.

Crif1 is a novel transcriptional coactivator of STAT3

Signal transducer and activator of transcription 3 (STAT3) is a transcriptional factor that performs a broad spectrum of biological functions in response to various stimuli. However, no specific coactivator that regulates the transcriptional activity of STAT3 has been identified. Here we report that CR6‐interacting factor 1 (Crif1) is a specific transcriptional coactivator of STAT3, but not of STAT1 or STAT5a. Crif1 interacts with STAT3 and positively regulates its transcriptional activity. Crif1−/− embryos were lethal around embryonic day 6.5, and manifested developmental arrest accompanied with defective proliferation and massive apoptosis. The expression of STAT3 target genes was markedly reduced in a Crif1−/− blastocyst culture and in Oncostatin M‐stimulated Crif1‐deficient MEFs. Importantly, the key activities of constitutively active STAT3‐C, such as transcription, DNA binding, and cellular transformation, were abolished in the Crif1‐null MEFs, suggesting the essential role of Crif1 in the transcriptional activity of STAT3. Our results reveal that Crif1 is a novel and essential transcriptional coactivator of STAT3 that modulates its DNA binding ability, and shed light on the regulation of oncogenic STAT3.

Emodin Regulates Glucose Utilization by Activating AMP-activated Protein Kinase

Background: AMPK activation improves glucose tolerance and insulin sensitivity. Results: Emodin increases glucose uptake in skeletal muscle and lowers blood glucose levels via AMPK activation. Conclusion: Administration of emodin leads to increased glucose tolerance and insulin sensitivity in vivo. Significance: Our results highlight the potential value of emodin as a drug for the treatment of diabetes. AMP-activated protein kinase has been described as a key signaling protein that can regulate energy homeostasis. Here, we aimed to characterize novel AMP-activated kinase (AMPK)-activating compounds that have a much lower effective concentration than metformin. As a result, emodin, a natural anthraquinone derivative, was shown to stimulate AMPK activity in skeletal muscle and liver cells. Emodin enhanced GLUT4 translocation and [14C]glucose uptake into the myotube in an AMPK-dependent manner. Also, emodin inhibited glucose production by suppressing the expression of key gluconeogenic genes, such as phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, in hepatocytes. Furthermore, we found that emodin can activate AMPK by inhibiting mitochondrial respiratory complex I activity, leading to increased reactive oxygen species and Ca2+/calmodulin-dependent protein kinase kinase activity. Finally, we confirmed that a single dose administration of emodin significantly decreased the fasting plasma glucose levels and improved glucose tolerance in C57Bl/6J mice. Increased insulin sensitivity was also confirmed after daily injection of emodin for 8 days using an insulin tolerance test and insulin-stimulated PI3K phosphorylation in wild type and high fat diet-induced diabetic mouse models. Our study suggests that emodin regulates glucose homeostasis in vivo by AMPK activation and that this may represent a novel therapeutic principle in the treatment of type 2 diabetic models.

Proteomic analysis of tumor necrosis factor-alpha (TNF-α)-induced L6 myotube secretome reveals novel TNF-α-dependent myokines in diabetic skeletal muscle.

There is a strong possibility that skeletal muscle can respond to irregular metabolic states by secreting specific cytokines. Obesity-related chronic inflammation, mediated by pro-inflammatory cytokines, is believed to be one of the causes of insulin resistance that results in type 2 diabetes. Here, we attempted to identify and characterize the members of the skeletal muscle secretome in response to tumor necrosis factor-alpha (TNF-α)-induced insulin resistance. To conduct this study, we comparatively analyzed the media levels of proteins released from L6 skeletal muscle cells. We found 28 TNF-α modulated secretory proteins by using separate filtering methods: Gene Ontology, SignalP, and SecretomeP, as well as the normalized Spectral Index for label-free quantification. Ten of these secretory proteins were increased and 18 secretory proteins were decreased by TNF-α treatment. Using microarray analysis of Zuker diabetic rat skeletal muscle combined with bioinformatics and Q-PCR, we found a correlation between TNF-α-mediated insulin resistance and type 2 diabetes. This novel approach combining analysis of the conditioned secretome and transcriptome has identified several previously unknown, TNF-α-dependent secretory proteins, which establish a foothold for research on the different causes of insulin resistance and their relationships with each other.

PML-IV functions as a negative regulator of telomerase by interacting with TERT.

Maintaining proper telomere length requires the presence of the telomerase enzyme. Here we show that telomerase reverse transcriptase (TERT), a catalytic component of telomerase, is recruited to promyelocytic leukemia (PML) nuclear bodies through its interaction with PML-IV. Treatment of interferon-α (IFNα) in H1299 cells resulted in the increase of PML proteins with a concurrent decrease of telomerase activity, as previously reported. PML depletion, however, stimulated telomerase activity that had been inhibited by IFNα with no changes in TERT mRNA levels. Upon treatment with IFNα, exogenous TERT localized to PML nuclear bodies and binding between TERT and PML increased. Immunoprecipitation and immunofluorescence analyses showed that TERT specifically bound to PML-IV. Residues 553-633 of the C-terminal region of PML-IV were required for its interaction with the TERT region spanning residues 1-350 and 595-946. The expression of PML-IV and its deletion mutant, 553-633, suppressed intrinsic telomerase activity in H1299. TERT-mediated immunoprecipitation of PML or the 553-633 fragment demonstrated that these interactions inhibited telomerase activity. H1299 cell lines stably expressing PML-IV displayed decreased telomerase activity with no change of TERT mRNA levels. Accordingly, telomere length of PML-IV stable cell lines was shortened. These results indicate that PML-IV is a negative regulator of telomerase in the post-translational state.

Phospholipase D2 drives mortality in sepsis by inhibiting neutrophil extracellular trap formation and down-regulating CXCR2

Lee et al. find that phospholipase D2 deficiency increases survival and decreases organ damage during experimental sepsis in mice which could be reversed with a CXCR2 antagonist. Thus, targeting PLD2 may offer therapeutics for septic patients.