2011 Vol. 2, No. 5

News and views
EphB2: a signature of colorectal cancer stem cells to predict relapse
Xiaoxue Zhang
2011, 2(5): 347-348. doi: 10.1007/s13238-011-1058-6
“A friend to man,” Dr. Feifan Tang: a story of causative agent of trachoma, from “Tang's virus” to Chlamydia trachomatis, to “Phylum Chlamydiae”
Guangsheng Cheng, Ming Li, George F. Gao
2011, 2(5): 349-350. doi: 10.1007/s13238-011-1050-1
Retinoic acid inducible gene-I, more than a virus sensor
Feng Liu, Jun Gu
2011, 2(5): 351-357. doi: 10.1007/s13238-011-1045-y
Retinoic acid inducible gene-I (RIG-I) is a caspase recruitment domain (CARD) containing protein that acts as an intracellular RNA receptor and senses virus infection. After binding to double stranded RNA (dsRNA) or 5'-triphosphate single stranded RNA (ssRNA), RIG-I transforms into an open conformation, translocates onto mitochondria, and interacts with the downstream adaptor mitochondrial antiviral signaling (MAVS) to induce the production of type I interferon and inflammatory factors via IRF3/7 and NF-κB pathways, respectively. Recently, accumulating evidence suggests that RIG-I could function in non-viral systems and participate in a series of biological events, such as inflammation and inflammation related diseases, cell proliferation, apoptosis and even senescence. Here we review recent advances in antiviral study of RIG-I as well as the functions of RIG-I in other fields.
Thyroid hormone action in metabolic regulation
Yiyun Song, Xuan Yao, Hao Ying
2011, 2(5): 358-368. doi: 10.1007/s13238-011-1046-x
Thyroid hormone plays pivotal roles in growth, differentiation, development and metabolic homeostasis via thyroid hormone receptors (TRs) by controlling the expression of TR target genes. The transcriptional activity of TRs is modulated by multiple factors including various TR isoforms, diverse thyroid hormone response elements, different heterodimeric partners, coregulators, and the cellular location of TRs. In the present review, we summarize recent advance in understanding the molecular mechanisms of thyroid hormone action obtained from human subject research, thyroid hormone mimetics application, TR isoform-specific knock-in mouse models, and mitochondrion study with highlights in metabolic regulations. Finally, as future perspectives, we share our thoughts about current challenges and possible approaches to promote our knowledge of thyroid hormone action in metabolism.
Conserved arginine residue in the membrane-spanning domain of HIV-1 gp41 is required for efficient membrane fusion
Yufei Long, Fanxia Meng, Naoyuki Kondo, Aikichi Iwamoto, Zene Matsuda
2011, 2(5): 369-376. doi: 10.1007/s13238-011-1051-0
Despite the high mutation rate of HIV-1, the amino acid sequences of the membrane-spanning domain (MSD) of HIV-1 gp41 are well conserved. Arginine residues are rarely found in single membrane-spanning domains, yet an arginine residue, R696 (the numbering is based on that of HXB2), is highly conserved in HIV-1 gp41. To examine the role of R696, it was mutated to K, A, I, L, D, E, N, and Q. Most of these substitutions did not affect the expression, processing or surface distribution of the envelope protein (Env). However, a syncytia formation assay showed that the substitution of R696 with amino acid residues other than K, a naturally observed mutation in the gp41 MSD, decreased fusion activity. Substitution with hydrophobic amino acid residues (A, I, and L) resulted in a modest decrease, while substitution with D or E, potentially negatively-charged residues, almost abolished the syncytia formation. All the fusion-defective mutants showed slower kinetics with the cell-based dual split protein (DSP) assay that scores the degree of membrane fusion based on pore formation between fusing cells. Interestingly, the D and E substitutions did show some fusion activity in the DSP assays, suggesting that proteins containing D or E substitutions retained some fusion pore-forming capability. However, nascent pores failed to develop, due probably to impaired activity in the pore enlargement process. Our data show the importance of this conserved arginine residue for efficient membrane fusion.
APP and APLP1 are degraded through autophagy in response to proteasome inhibition in neuronal cells
Fangfang Zhou, Theo van Laar, Huizhe Huang, Long Zhang
2011, 2(5): 377-383. doi: 10.1007/s13238-011-1047-9
rotein in the pathogenesis of Alzheimer's disease (AD). Both APP and its paralogue APLP1 (amyloid beta precursor-like protein 1) have multiple functions in cell adhesion and proliferation. Previously it was thought that autophagy is a novel beta-amyloid peptide (Aβ)-generating pathway activated in AD. However, the protein proteolysis of APLP1 is still largely unknown. The present study shows that APLP1 is rapidly degraded in neuronal cells in response to stresses, such as proteasome inhibition. Activation of the endoplasmic reticulum (ER) stress by proteasome inhibitors induces autophagy, causing reduction of mature APLP1/APP. Blocking autophagy or JNK stress kinase rescues the protein expression for both APP and APLP1. Therefore, our results suggest that APP/APLP1 is degraded through autophagy and the APLP1 proteolysis is mainly mediated by autophagy-lysosome pathway.
Research articles
A structural view of the antibiotic degradation enzyme NDM-1 from a superbug
Yu Guo, Jing Wang, Guojun Niu, Wenqing Shui, Yuna Sun, Honggang Zhou, Yaozhou Zhang, Cheng Yang, Zhiyong Lou, Zihe Rao
2011, 2(5): 384-394. doi: 10.1007/s13238-011-1055-9
Gram-negative Enterobacteriaceae with resistance to carbapenem conferred by New Delhi metallo-β-lactamase 1 (NDM-1) are a type of newly discovered antibioticresistant bacteria. The rapid pandemic spread of NDM-1 bacteria worldwide (spreading to India, Pakistan, Europe, America, and Chinese Taiwan) in less than 2 months characterizes these microbes as a potentially major global health problem. The drug resistance of NDM-1 bacteria is largely due to plasmids containing the blaNDM-1 gene shuttling through bacterial populations. The NDM-1 enzyme encoded by the blaNDM-1 gene hydrolyzes β-lactam antibiotics, allowing the bacteria to escape the action of antibiotics. Although the biological functions and structural features of NDM-1 have been proposed according to results from functional and structural investigation of its homologues, the precise molecular characteristics and mechanism of action of NDM-1 have not been clarified. Here, we report the threedimensional structure of NDM-1 with two catalytic zinc ions in its active site. Biological and mass spectroscopy results revealed that D-captopril can effectively inhibit the enzymatic activity of NDM-1 by binding to its active site with high binding affinity. The unique features concerning the primary sequence and structural conformation of the active site distinguish NDM-1 from other reported metallo-β-lactamases (MBLs) and implicate its role in wide spectrum drug resistance. We also discuss the molecular mechanism of NDM-1 action and its essential role in the pandemic of drug-resistant NDM-1 bacteria. Our results will provide helpful information for future drug discovery targeting drug resistance caused by NDM-1 and related metallo-β-lactamases.
Spliceosomal genes in the D. discoideum genome: a comparison with those in H. sapiens, D. melanogaster, A. thaliana and S. cerevisiae
Bing Yu, Petra Fey, Karen E. Kestin-Pilcher, Alexei Fedorov, Ashwin Prakash, Rex L. Chisholm, Jane Y. Wu
2011, 2(5): 395-409. doi: 10.1007/s13238-011-1052-z
Little is known about pre-mRNA splicing in Dictyostelium discoideum although its genome has been completely sequenced. Our analysis suggests that pre-mRNA splicing plays an important role in D. discoideum gene expression as two thirds of its genes contain at least one intron. Ongoing curation of the genome to date has revealed 40 genes in D. discoideum with clear evidence of alternative splicing, supporting the existence of alternative splicing in this unicellular organism. We identified 160 candidate U2-type spliceosomal proteins and related factors in D. discoideum based on 264 known human genes involved in splicing. Spliceosomal small ribonucleoproteins (snRNPs), PRP19 complex proteins and late-acting proteins are highly conserved in D. discoideum and throughout the metazoa. In non-snRNP and hnRNP families, D. discoideum orthologs are closer to those in A. thaliana, D. melanogaster and H. sapiens than to their counterparts in S. cerevisiae. Several splicing regulators, including SR proteins and CUGbinding proteins, were found in D. discoideum, but not in yeast. Our comprehensive catalog of spliceosomal proteins provides useful information for future studies of splicing in D. discoideum where the efficient genetic and biochemical manipulation will also further our general understanding of pre-mRNA splicing.
Targeted deletion of mouse Rad1 leads to deficient cellular DNA damage responses
Chunbo Zhang, Yuheng Liu, Zhishang Hu, Lili An, Yikun He, Haiying Hang
2011, 2(5): 410-422. doi: 10.1007/s13238-011-1049-7
The Rad1 gene is evolutionarily conserved from yeast to human. The fission yeast Schizosaccharomyces pombe Rad1 ortholog promotes cell survival against DNA damage and is required for G2/M checkpoint activation. In this study, mouse embryonic stem (ES) cells with a targeted deletion of MRad1, the mouse ortholog of this gene, were created to evaluate its function in mammalian cells. MRad1-/- ES cells were highly sensitive to ultraviolet-light (UV light), hydroxyurea (HU) and gamma rays, and were defective in G2/M as well as S/M checkpoints. These data indicate that MRad1 is required for repairing DNA lesions induced by UV-light, HU and gamma rays, and for mediating G2/M and S/M checkpoint controls. We further demonstrated that MRad1 plays an important role in homologous recombination repair (HRR) in ES cells, but a minor HRR role in differentiated mouse cells.
CSN1 inhibits c-Jun phosphorylation and down-regulates ectopic expression of JNK1
Tomohiko Tsuge, Suchithra Menon, Yingchun Tong, Ning Wei
2011, 2(5): 423-432. doi: 10.1007/s13238-011-1043-0
CSN1 is a component of the COP9 signalosome (CSN), a conserved protein complex with pleiotropic functions in many organs and cell types. CSN regulates ubiquitinproteasome dependent protein degradation via the deneddylation and the associated deubiquitination activities. In addition, CSN associates with protein kinases and modulates cell signaling, particularly the activator protein 1 (AP-1) pathway. We have shown previously that CSN1 suppresses AP-1 transcription activity and inhibits ultraviolet (UV) and serum activation of c-fos expression. Here we show that CSN1 can inhibit phosphorylation of proto-oncogene c-Jun product and repress c-Jun dependent transcription. Further, CSN1 dramatically downregulates ectopic expression of c-Jun N-terminal kinase 1 (JNK1) in cultured cells. The decline in JNK1 is not caused by excessive proteolysis or by 3' UTR-dependent mRNA instability, but by CSN1-dependent repression of one or multiple steps in transcriptional and posttranscriptional mechanisms. Thus, in contrast to CSN5/Jab1, which promotes AP-1 activity, CSN1 displays a negative effect on the AP-1 pathway. Finally, we discuss about the dynamic equilibrium of the CSN complexes in regulation of the AP-1 pathway.