2010 Vol. 1, No. 10

News and views
Chemotaxis: new role for Ras revealed
Jianshe Yan, Dale Hereld, Tian Jin
2010, 1(10): 879-880. doi: 10.1007/s13238-010-0119-6
Phosphorylation of Rictor at Thr1135 impairs the Rictor/Cullin-1 complex to ubiquitinate SGK1
Daming Gao, Lixin Wan, Wenyi Wei
2010, 1(10): 881-885. doi: 10.1007/s13238-010-0123-x
The Rictor/mTOR complex plays a pivotal role in a variety of cellular functions including cellular metabolism, cell proliferation and survival by phosphorylating Akt at Ser473 to fully activate the Akt kinase. However, its upstream regulatory pathways as well as whether it has additional function(s) remain largely unknown. We recently reported that Rictor contains a novel ubiquitin E3 ligase activity by forming a novel complex with Cullin-1, but not with other Cullin family members. Furthermore, we identified SGK1 as its downstream target. Interestingly, Rictor, but not Raptor or mTOR, promotes SGK1 ubiquitination. As a result, SGK1 expression is elevated in Rictor-/- MEFs. We further defined that as a feedback mechanism, Rictor can be phosphorylated by multiple AGC family kinases including Akt, S6K and SGK1. Phosphorylation of Rictor at the Thr1135 site did not affect its kinase activity towards phosphorylating its conventional substrates including Akt and SGK1. On the other hand, it disrupted the interaction between Rictor and Cullin-1. Consequently, T1135E Rictor was defective in promoting SGK1 ubiquitination and destruction. This finding further expands our knowledge of Rictor's function. Furthermore, our work also illustrates that Rictor E3 ligase activity could be governed by specific signaling kinase cascades, and that misregulation of this process might contribute to SGK overexpression which is frequently observed in various types of cancers.
Commitment and dedication of a Chinese plant physiologist
Tingyun Kuang, Ming Li, Le Kang
2010, 1(10): 886-887. doi: 10.1007/s13238-010-0122-y
Human catalase: looking for complete identity
Madhur M. Goyal, Anjan Basak
2010, 1(10): 888-897. doi: 10.1007/s13238-010-0113-z
Catalases are well studied enzymes that play critical roles in protecting cells against the toxic effects of hydrogen peroxide. The ubiquity of the enzyme and the availability of substrates made heme catalases the focus of many biochemical and molecular biology studies over 100 years. In human, this has been implicated in various physiological and pathological conditions. Advancement in proteomics revealed many of novel and previously unknown features of this mysterious enzyme, but some functional aspects are yet to be explained. Along with discussion on future research area, this mini-review compile the information available on the structure, function and mechanism of action of human catalase.
Wnt pathway antagonists and angiogenesis
Bin Zhang, Jian-xing Ma
2010, 1(10): 898-906. doi: 10.1007/s13238-010-0112-0
Dysregulation of the Wnt pathway has been extensively studied in multiple diseases, including some angiogenic disorders. Wnt signaling activation is a major stimulator in pathological angiogenesis and thus, Wnt antagonists are believed to have therapeutic potential for neovascular disorders. Actually, some Wnt antagonists have been identified directly from the anti-angiogenic factor family. This review summarizes the recent progress toward understanding of the roles of Wnt pathway antagonists in angiogenic regulation and their mechanism of action, and exploring their therapeutic potential.
The late stage of autophagy: cellular events and molecular regulation
Jingjing Tong, Xianghua Yan, Li Yu
2010, 1(10): 907-915. doi: 10.1007/s13238-010-0121-z
Autophagy is an intracellular degradation system that delivers cytoplasmic contents to the lysosome for degradation. It is a "self-eating" process and plays a "house-cleaner" role in cells. The complex process consists of several sequential steps-induction, autophagosome formation, fusion of lysosome and autophagosome, degradation, efflux transportation of degradation products, and autophagic lysosome reformation. In this review, the cellular and molecular regulations of late stage of autophagy, including cellular events after fusion step, are summarized.
microRNAs: tiny RNA molecules, huge driving forces to move the cell
Shenglin Huang, Xianghuo He
2010, 1(10): 916-926. doi: 10.1007/s13238-010-0116-9
Cell migration or movement is a highly dynamic cellular process, requiring precise regulation that is essential for a variety of biological processes. microRNAs (miRNAs) are a class of tiny non-coding RNA molecules that function as critical post-transcriptional regulators of gene expression. Emerging evidence demonstrates that miRNAs play important roles in cell migration and directly contribute to extracellular matrix (ECM) remodeling, cell adhesion, and cell signalling that controls cell migration by targeting a large number of protein-coding genes. Accordingly, the dysregulation of these miRNAs has been linked to several migration-related diseases. In this review, we summarize and highlight the recent advances concerning the roles and validated targets of miRNAs in the control of cell movement.
A transcription assay for EWS oncoproteins in Xenopus oocytes
King Pan Ng, Felix Cheung, Kevin A. W. Lee
2010, 1(10): 927-934. doi: 10.1007/s13238-010-0114-y
Aberrant chromosomal fusion of the Ewing's sarcoma oncogene (EWS) to several different cellular partners produces the Ewing's family of oncoproteins (EWSfusion-proteins, EFPs) and associated tumors (EFTs). EFPs are potent transcriptional activators, dependent on the N-terminal region of EWS (the EWS-activationdomain, EAD) and this function is thought to be central to EFT oncogenesis and maintenance. Thus EFPs are promising therapeutic targets, but detailed molecular studies will be pivotal for exploring this potential. Such studies have so far largely been restricted to intact mammalian cells while recent evidence has indicated that a mammalian cell-free transcription system may not support bona fide EAD function. Therefore, the lack of manipulatable assays for the EAD presents a significant barrier to progress. Using Xenopus laevis oocytes we describe a plasmid-based micro-injection assay that supports efficient, bona fide EAD transcriptional activity and hence provides a new vehicle for molecular dissection of the EAD.
Research articles
Trafficking abnormality and ER stress underlie functional deficiency of hearing impairmentassociated connexin-31 mutants
Kun Xia, Hong Ma, Hui Xiong, Qian Pan, Liangqun Huang, Danling Wang, Zhuohua Zhang
2010, 1(10): 935-943. doi: 10.1007/s13238-010-0118-7
Hearing impairment (HI) affects 1/1000 children and over 2% of the aged population. We have previously reported that mutations in the gene encoding gap junction protein connexin-31 (Cx31) are associated with HI. The pathological mechanism of the disease mutations remains unknown. Here, we show that expression of Cx31 in the mouse inner ear is developmentally regulated with a high level in adult inner hair cells and spiral ganglion neurons that are critical for the hearing process. In transfected cells, wild type Cx31 protein (Cx31wt) forms functional gap junction at cell-cell-contacts. In contrast, two HIassociated Cx31 mutants, Cx31R180X and Cx31E183K resided primarily in the ER and Golgi-like intracellular punctate structures, respectively, and failed to mediate lucifer yellow transfer. Expression of Cx31 mutants but not Cx31wt leads to upregulation of and increased association with the ER chaperone BiP indicating ER stress induction. Together, the HI-associated Cx31 mutants are impaired in trafficking, promote ER stress, and hence lose the ability to assemble functional gap junctions. The study reveals a potential pathological mechanism of HI-associated Cx31 mutations.
Interaction of Hsp40 with influenza virus M2 protein: implications for PKR signaling pathway
Zhenhong Guan, Di Liu, Shuofu Mi, Jie Zhang, Qinong Ye, Ming Wang, George F. Gao, Jinghua Yan
2010, 1(10): 944-955. doi: 10.1007/s13238-010-0115-x
Influenza virus contains three integral membrane proteins:haemagglutinin, neuraminidase, and matrix protein (M1 and M2). Among them, M2 protein functions as an ion channel, important for virus uncoating in endosomes of virus-infected cells and essential for virus replication. In an effort to explore potential new functions of M2 in the virus life cycle, we used yeast two-hybrid system to search for M2-associated cellular proteins. One of the positive clones was identified as human Hsp40/Hdj1, a DnaJ/Hsp40 family protein. Here, we report that both BM2 (M2 of influenza B virus) and A/M2 (M2 of influenza A virus) interacted with Hsp40 in vitro and in vivo. The region of M2-Hsp40 interaction has been mapped to the CTD1 domain of Hsp40. Hsp40 has been reported to be a regulator of PKR signaling pathway by interacting with p58IPK that is a cellular inhibitor of PKR. PKR is a crucial component of the host defense response against virus infection. We therefore attempted to understand the relationship among M2, Hsp40 and p58IPK by further experimentation. The results demonstrated that both A/M2 and BM2 are able to bind to p58IPK in vitro and in vivo and enhance PKR autophosphorylation probably via forming a stable complex with Hsp40 and P58IPK, and consequently induce cell death. These results suggest that influenza virus M2 protein is involved in p58IPK mediated PKR regulation during influenza virus infection, therefore affecting infected-cell life cycle and virus replication.
DEXH-Box protein DHX30 is required for optimal function of the zinc-finger antiviral protein
Peiying Ye, Shufeng Liu, Yiping Zhu, Guifang Chen, Guangxia Gao
2010, 1(10): 956-964. doi: 10.1007/s13238-010-0117-8
The zinc-finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses by eliminating viral mRNAs in the cytoplasm. In previous studies, we demonstrated that ZAP directly binds to the viral mRNAs and recruits the RNA exosome to degrade the target RNA. In this article, we provide evidence that a DEXH box RNA helicase, DHX30, is required for optimal antiviral activity of ZAP. Pull-down and co-immunoprecipitation assays demonstrated that DHX30 and ZAP interacted with each other via their N terminal domains. Downregulation of DHX30 with shRNAs reduced ZAP's antiviral activity. These data implicate that DHX30 is a cellular factor involved in the antiviral function of ZAP.