2015 Vol. 6, No. 2

News and views
Hepatitis A virus exhibits a structure unique among picornaviruses
Ling Zhu, Xiaoxue Zhang
2015, 6(2): 79-80. doi: 10.1007/s13238-014-0103-7
Recent progress in studies of factors that elicit pancreatic β-cell expansion
Qiu Li, Zhi-Chun Lai
2015, 6(2): 81-87. doi: 10.1007/s13238-014-0123-3
The loss of or decreased functional pancreatic β-cell is a major cause of type 1 and type 2 diabetes. Previous studies have shown that adult β-cells can maintain their ability for a low level of turnover through replication and neogenesis. Thus, a strategy to prevent and treat diabetes would be to enhance the ability of β-cells to increase the mass of functional β-cells. Consequently, much effort has been devoted to identify factors that can effectively induce β-cell expansion. This review focuses on recent reports on small molecules and protein factors that have been shown to promote β-cell expansion.
Iron homeostasis and tumorigenesis: molecular mechanisms and therapeutic opportunities
Caiguo Zhang, Fan Zhang
2015, 6(2): 88-100. doi: 10.1007/s13238-014-0119-z
Excess iron is tightly associated with tumorigenesis in multiple human cancer types through a variety of mechanisms including catalyzing the formation of mutagenic hydroxyl radicals, regulating DNA replication, repair and cell cycle progression, affecting signal transduction in cancer cells, and acting as an essential nutrient for proliferating tumor cells. Thus, multiple therapeutic strategies based on iron deprivation have been developed in cancer therapy. During the past few years, our understanding of genetic association and molecular mechanisms between iron and tumorigenesis has expanded enormously. In this review, we briefly summarize iron homeostasis in mammals, and discuss recent progresses in understanding the aberrant iron metabolism in numerous cancer types, with a focus on studies revealing altered signal transduction in cancer cells.
Research articles
Crystal structures of GI.8 Boxer virus P dimers in complex with HBGAs, a novel evolutionary path selected by the Lewis epitope
Ning Hao, Yutao Chen, Ming Xia, Ming Tan, Wu Liu, Xiaotao Guan, Xi Jiang, Xuemei Li, Zihe Rao
2015, 6(2): 101-116. doi: 10.1007/s13238-014-0126-0
Human noroviruses (huNoVs) recognize histo-blood group antigens (HBGAs) as attachment factors, in which genogroup (G) I and GⅡ huNoVs use distinct binding interfaces. The genetic and evolutionary relationships of GⅡ huNoVs under selection by the host HBGAs have been well elucidated via a number of structural studies; however, such relationships among GI NoVs remain less clear due to the fact that the structures of HBGA-binding interfaces of only three GI NoVs with similar binding profiles are known. In this study the crystal structures of the P dimers of a Lewis-binding strain, the GI.8 Boxer virus (BV) that does not bind the A and H antigens, in complex with the Lewis b (Leb) and Ley antigens, respectively, were determined and compared with those of the three previously known GI huNoVs, i.e. GI.1 Norwalk virus (NV), GI.2 FUV258 (FUV) and GI.7 TCH060 (TCH) that bind the A/H/Le antigens. The HBGA binding interface of BV is composed of a conserved central binding pocket (CBP) that interacts with the β-galactose of the precursor, and a well-developed Le epitope-binding site formed by five amino acids, including three consecutive residues from the long P-loop and one from the S-loop of the P1 subdomain, a feature that was not seen in the other GI NoVs. On the other hand, the H epitope/acetamido binding site observed in the other GI NoVs is greatly degenerated in BV. These data explain the evolutionary path of GI NoVs selected by the polymorphic human HBGAs. While the CBP is conserved, the regions surrounding the CBP are flexible, providing freedom for changes. The loss or degeneration of the H epitope/acetamido binding site and the reinforcement of the Le binding site of the GI.8 BV is a typical example of such change selected by the host Lewis epitope.
Characterization of a novel mouse model with genetic deletion of CD177
Qing Xie, Julia Klesney-Tait, Kathy Keck, Corey Parlet, Nicholas Borcherding, Ryan Kolb, Wei Li, Lorraine Tygrett, Thomas Waldschmidt, Alicia Olivier, Songhai Chen, Guang-Hui Liu, Xiangrui Li, Weizhou Zhang
2015, 6(2): 117-126. doi: 10.1007/s13238-014-0109-1
Neutrophils play an essential role in the innate immune response to infection. Neutrophils migrate from the vasculature into the tissue in response to infection. Recently, a neutrophil cell surface receptor, CD177, was shown to help mediate neutrophil migration across the endothelium through interactions with PECAM1. We examined a publicly available gene array dataset of CD177 expression from human neutrophils following pulmonary endotoxin instillation. Among all 22,214 genes examined, CD177 mRNA was the most upregulated following endotoxin exposure. The high level of CD177 expression is also maintained in airspace neutrophils, suggesting a potential involvement of CD177 in neutrophil infiltration under infectious diseases. To determine the role of CD177 in neutrophils in vivo, we constructed a CD177-genetic knockout mouse model. The mice with homozygous deletion of CD177 have no discernible phenotype and no significant change in immune cells, other than decreased neutrophil counts in peripheral blood. We examined the role of CD177 in neutrophil accumulation using a skin infection model with Staphylococcus aureus. CD177 deletion reduced neutrophil counts in inflammatory skin caused by S. aureus. Mechanistically we found that CD177 deletion in mouse neutrophils has no significant impact in CXCL1/KC-or fMLP-induced migration, but led to significant cell death. Herein we established a novel genetic mouse model to study the role of CD177 and found that CD177 plays an important role in neutrophils.
Threonine 32 (Thr32) of FoxO3 is critical for TGF-β-induced apoptosis via Bim in hepatocarcinoma cells
Xiangxuan Zhao, Yong Liu, Lei Du, Leya He, Biyun Ni, Junbo Hu, Dahai Zhu, Quan Chen
2015, 6(2): 127-138. doi: 10.1007/s13238-014-0121-5
Transforming growth factor-β (TGF-β) exerts apoptotic effects on various types of malignant cells, including liver cancer cells. However, the precise mechanisms by which TGF-β induces apoptosis remain poorly known. In the present study, we have showed that threonine 32 (Thr32) residue of FoxO3 is critical for TGF-β to induce apoptosis via Bim in hepatocarcinoma Hep3B cells. Our data demonstrated that TGF-β induced FoxO3 activation through specific de-phosphorylation at Thr32. TGF-β-activated FoxO3 cooperated with Smad2/3 to mediate Bim up-regulation and apoptosis. FoxO3 (de)phosphorylation at Thr32 was regulated by casein kinase I-ε (CKI-ε). CKI inhibition by small molecule D4476 could abrogate TGF-β-induced FoxO/Smad activation, reverse Bim up-regulation, and block the sequential apoptosis. More importantly, the deregulated levels of CKI-ε and p32FoxO3 were found in human malignant liver tissues. Taken together, our findings suggest that there might be a CKI-FoxO/Smad-Bim engine in which Thr32 of FoxO3 is pivotal for TGF-β-induced apoptosis, making it a potential therapeutic target for liver cancer treatment.
Comparison of human and Drosophila atlastin GTPases
Fuyun Wu, Xiaoyu Hu, Xin Bian, Xinqi Liu, Junjie Hu
2015, 6(2): 139-146. doi: 10.1007/s13238-014-0118-0
Formation of the endoplasmic reticulum (ER) network requires homotypic membrane fusion, which involves a class of atlastin (ATL) GTPases. Purified Drosophila ATL is capable of mediating vesicle fusion in vitro, but such activity has not been reported for any other ATLs. Here, we determined the preliminary crystal structure of the cytosolic segment of Drosophila ATL in a GDP-bound state. The structure reveals a GTPase domain dimer with the subsequent three-helix bundles associating with their own GTPase domains and pointing in opposite directions. This conformation is similar to that of human ATL1, to which GDP and high concentrations of inorganic phosphate, but not GDP only, were included. Drosophila ATL restored ER morphology defects in mammalian cells lacking ATLs, and measurements of nucleotide-dependent dimerization and GTPase activity were comparable for Drosophila ATL and human ATL1. However, purified and reconstituted human ATL1 exhibited no in vitro fusion activity. When the cytosolic segment of human ATL1 was connected to the transmembrane (TM) region and C-terminal tail (CT) of Drosophila ATL, the chimera still exhibited no fusion activity, though its GTPase activity was normal. These results suggest that GDP-bound ATLs may adopt multiple conformations and the in vitro fusion activity of ATL cannot be achieved by a simple collection of functional domains.
Structural implications of Dpy30 oligomerization for MLL/SET1 COMPASS H3K4 trimethylation
Hongmei Zhang, Mei Li, Yu Gao, Chenjun Jia, Xiaowei Pan, Peng Cao, Xuelin Zhao, Jiping Zhang, Wenrui Chang
2015, 6(2): 147-151. doi: 10.1007/s13238-014-0127-z
Overexpression of Hdac6 enhances resistance to virus infection in embryonic stem cells and in mice
Dekun Wang, Qingwen Meng, Lihong Huo, Meng Yang, Lingling Wang, Xinyu Chen, Jianchao Wang, Zhiguo Li, Xiaoying Ye, Na Liu, Qiuyan Li, Zhen Dai, Hongsheng Ouyang, Ning Li, Jun Zhou, Lingyi Chen, Lin Liu
2015, 6(2): 152-156. doi: 10.1007/s13238-014-0120-6