2013 Vol. 4, No. 4

Selective secretion of microRNA in CNS system
Qipeng Zhang, Jie Xu, Qun Chen, Xi Chen, Ke Zen, Chen-Yu Zhang
2013, 4(4): 243-247. doi: 10.1007/s13238-013-3006-0
The newly emerged SARS-Like coronavirus HCoV-EMC also has an "Achilles' heel": current effective inhibitor targeting a 3C-like protease
Zhilin Ren, Liming Yan, Ning Zhang, Yu Guo, Cheng Yang, Zhiyong Lou, Zihe Rao
2013, 4(4): 248-250. doi: 10.1007/s13238-013-2841-3
Negative regulation of NLRP3 inflammasome signaling
Shuzhen Chen, Bing Sun
2013, 4(4): 251-258. doi: 10.1007/s13238-013-2128-8
Inflammasomes are multiprotein complexes that serve as a platform for caspase-1 activation and interleukin-1β (IL-1β) maturation as well as pyroptosis. Though a number of inflammasomes have been described, the NLRP3 inflammasome is the most extensively studied. NLRP3 inflammasome is triggered by a variety of stimuli, including infection, tissue damage and metabolic dysregulation, and then activated through an integrated cellular signal. Many regulatory mechanisms have been identified to attenuate NLRP3 inflammasome signaling at multiple steps. Here, we review the developments in the negative regulation of NLRP3 inflammasome that protect host from inflammatory damage.
Pannexin-1 influences peritoneal cavity cell population but is not involved in NLRP3 inflammasome activation
Hongbin Wang, Yue Xing, Liming Mao, Yi Luo, Lishan Kang, Guangxun Meng
2013, 4(4): 259-265. doi: 10.1007/s13238-013-2114-1
Pannexin-1 (Panx1) forms nonselective large channel in cell plasma membrane and has been shown to be associated with NLRP3 inflammasome activation, ATP release and phagocytes recruitment. In the current study, by manipulation of Panx1 expression in human myeloid cells and application of Panx1 deficient mice, we failed to find a correlation between Panx1 and NLRP3 inflammasome activation, although an interaction between these two proteins was evident. However, in thioglycollate induced peritonitis, Panx1 deficient mice showed much more phagocytes infiltration. Further analyses showed that mice deficient for Panx1 exhibited enlarged F4/80lowGr1-Ly6C- cell population in the peritonea. Our study thus reveals an important role for Panx1 in regulation of peritoneal cell population and peritonitis development.
Research article
Regulation of tumor angiogenesis by the microtubule-binding protein CLIP-170
Xiaodong Sun, Fang Li, Bin Dong, Shaojun Suo, Min Liu, Dengwen Li, Jun Zhou
2013, 4(4): 266-276. doi: 10.1007/s13238-013-3007-z
Angiogenesis, the expansion of preexisting blood vessels, is a complex process required for tumor growth and metastasis. Although current antiangiogenic strategies have shown promising results in several cancer types, identification of additional antiangiogenic targets is required to improve the therapeutic response. Herein, we show that the microtubule-binding protein CLIP-170 (cytoplasmic linker protein of 170 kDa) is highly expressed in breast tumor samples and correlates positively with blood vessel density. Depletion of CLIP-170 significantly impaired vascular endothelial tube formation and sprouting in vitro and inhibited breast tumor growth in mice by decreasing tumor vascularization. Our data further show that CLIP-170 is important for the migration but not the proliferation of vascular endothelial cells. In addition, CLIP-170 promotes the polarization of endothelial cells in response to the angiogenic stimulus. These findings thus demonstrate a critical role for CLIP-170 in tumor angiogenesis and suggest its potential as a novel antiangiogenic target.
Structures of SdrD from Staphylococcus aureus reveal the molecular mechanism of how the cell surface receptors recognize their ligands
Xiao Wang, Jingpeng Ge, Bao Liu, Yulin Hu, Maojun Yang
2013, 4(4): 277-285. doi: 10.1007/s13238-013-3009-x
Staphylococcus aureus is the most important Gram-positive colonizer of human skin and nasal passage, causing high morbidity and mortality. SD-repeat containing protein D (SdrD), an MSCRAMM (Microbial Surface Components Recognizing Adhesive Matrix Molecules) family surface protein, plays an important role in S. aureus adhesion and pathogenesis, while its binding target and molecular mechanism remain largely unknown. Here we solved the crystal structures of SdrD N2-N3 domain and N2-N3-B1 domain. Through structural analysis and comparisons, we characterized the ligand binding site of SdrD, and proposed a featured sequence motif of its potential ligands. In addition, the structures revealed for the first time the interactions between B1 domain and N2-N3 domain among B domain-containing MSCRAMMs. Our results may help in understanding the roles SdrD plays in S. aureus adhesion and shed light on the development of novel antibiotics.
Plasma membrane calcium ATPase 4b inhibits nitric oxide generation through calcium-induced dynamic interaction with neuronal nitric oxide synthase
Wenjuan Duan, Juefei Zhou, Wei Li, Teng Zhou, Qianqian Chen, Fuyu Yang, Taotao Wei
2013, 4(4): 286-298. doi: 10.1007/s13238-013-2116-z
The activation and deactivation of Ca2+-and calmodulindependent neuronal nitric oxide synthase (nNOS) in the central nervous system must be tightly controlled to prevent excessive nitric oxide (NO) generation. Considering plasma membrane calcium ATPase (PMCA) is a key deactivator of nNOS, the present investigation aims to determine the key events involved in nNOS deactivation of by PMCA in living cells to maintain its cellular context. Using time-resolved Förster resonance energy transfer (FRET), we determined the occurrence of Ca2+-induced protein-protein interactions between plasma membrane calcium ATPase 4b (PMCA4b) and nNOS in living cells. PMCA activation significantly decreased the intracellular Ca2+ concentrations ([Ca2+]i), which deactivates nNOS and slowdowns NO synthesis. Under the basal[Ca2+]i caused by PMCA activation, no protein-protein interactions were observed between PMCA4b and nNOS. Furthermore, both the PDZ domain of nNOS and the PDZ-binding motif of PMCA4b were essential for the protein-protein interaction. The involvement of lipid raft microdomains on the activity of PMCA4b and nNOS was also investigated. Unlike other PMCA isoforms, PMCA4 was relatively more concentrated in the raft fractions. Disruption of lipid rafts altered the intracellular localization of PMCA4b and affected the interaction between PMCA4b and nNOS, which suggest that the unique lipid raft distribution of PMCA4 may be responsible for its regulation of nNOS activity. In summary, lipid rafts may act as platforms for the PMCA4b regulation of nNOS activity and the transient tethering of nNOS to PMCA4b is responsible for rapid nNOS deactivation.
Structural insight into enhanced calcium indicator GCaMP3 and GCaMPJ to promote further improvement
Yingxiao Chen, Xianqiang Song, Sheng Ye, Lin Miao, Yun Zhu, Rong-Guang Zhang, Guangju Ji
2013, 4(4): 299-309. doi: 10.1007/s13238-013-2103-4
Genetically encoded Ca2+ indicators (GECI) are important for the measurement of Ca2+ in vivo. GCaMP2, a widelyused GECI, has recently been iteratively improved. Among the improved variants, GCaMP3 exhibits significantly better fluorescent intensity. In this study, we developed a new GECI called GCaMPJ and determined the crystal structures of GCaMP3 and GCaMPJ. GCaMPJ has a 1.5-fold increase in fluorescence and 1.3-fold increase in calcium affinity over GCaMP3. Upon Ca2+ binding, GCaMP3 exhibits both monomeric and dimeric forms. The structural superposition of these two forms reveals the role of Arg-376 in improving monomer performance. However, GCaMPJ seldom forms dimers under conditions similar to GCaMP3. Structural and mutagenesis studies on Tyr-380 confirmed its importance in blocking the cpEGFP β-barrel holes. Our study proposes an efficient tool for mapping Ca2+ signals in intact organs to facilitate the further improvement of GCaMP sensors.
Upregulation of SIRT1 by 17β-estradiol depends on ubiquitin-proteasome degradation of PPAR-γ mediated by NEDD4-1
Limin Han, Pan Wang, Ganye Zhao, Hui Wang, Meng Wang, Jun Chen, Tanjun Tong
2013, 4(4): 310-321. doi: 10.1007/s13238-013-2124-z
17β-estradiol (E2) treatment of cells results in an upregulation of SIRT1 and a down-regulation of PPARγ. The decrease in PPARγ expression is mediated by increased degradation of PPARγ. Here we report that PPARγ is ubiquitinated by HECT E3 ubiquitin ligase NEDD4-1 and degraded, along with PPARγ, in response to E2 stimulation. The PPARγ interacts with ubiquitin ligase NEDD4-1 through a conserved PPXY-WW binding motif. The WW3 domain in NEDD4-1 is critical for binding to PPARγ. NEDD4-1 overexpression leads to PPARγ ubiquitination and reduced expression of PPARγ. Conversely, knockdown of NEDD4-1 by specific siRNAs abolishes PPARγ ubiquitination. These data indicate that NEDD4-1 is the E3 ubiquitin ligase responsible for PPARγ ubiquitination. Here, we show that NEDD4-1 delays cellular senescence by degrading PPARγ expression. Taken together, our data show that E2 could upregulate SIRT1 expression via promoting the PPARγ ubiquitination-proteasome degradation pathway to delay the process of cell senescence.