2010 Vol. 1, No. 2

News and views
Revival of gene therapy
Xiaoxue Zhang, George F. Gao
2010, 1(2): 107-108. doi: 10.1007/s13238-010-0026-x
Bat and virus
Zhengli Shi
2010, 1(2): 109-114. doi: 10.1007/s13238-010-0029-7
“Light” of the spinach major light-harvester structure
Min-Ze Jia
2010, 1(2): 115-116. doi: 10.1007/s13238-010-0023-0
The role of BRCA1 in DNA damage response
Jiaxue Wu, Lin-Yu Lu, Xiaochun Yu
2010, 1(2): 117-123. doi: 10.1007/s13238-010-0010-5
BRCA1 is a well-established tumor suppressor gene, which is frequently mutated in familial breast and ovarian cancers. The gene product of BRCA1 functions in a number of cellular pathways that maintain genomic stability, including DNA damage-induced cell cycle checkpoint activation, DNA damage repair, protein ubiquitination, chromatin remodeling, as well as transcriptional regulation and apoptosis. In this review, we discuss recent advances regarding our understanding of the role of BRCA1 in tumor suppression and DNA damage response, including DNA damage-induced cell cycle checkpoint activation and DNA damage repair.
Molecular and cellular bases of chronic myeloid leukemia
Yaoyu Chen, Cong Peng, Dongguang Li, Shaoguang Li
2010, 1(2): 124-132. doi: 10.1007/s13238-010-0016-z
Chronic myeloid leukemia (CML) is a myeloproliferative disease characterized by the overproduction of granulocytes, which leads to high white blood cell counts and splenomegaly in patients. Based on clinical symptoms and laboratory findings, CML is classified into three clinical phases, often starting with a chronic phase, progressing to an accelerated phase and ultimately ending in a terminal phase called blast crisis. Blast crisis phase of CML is clinically similar to an acute leukemia; in particular, B-cell acute lymphoblastic leukemia (B-ALL) is a severe form of acute leukemia in blast crisis, and there is no effective therapy for it yet. CML is induced by the BCR-ABL oncogene, whose gene product is a BCR-ABL tyrosine kinase. Currently, inhibition of BCR-ABL kinase activity by its kinase inhibitor such as imatinib mesylate (Gleevec) is a major therapeutic strategy for CML. However, the inability of BCR-ABL kinase inhibitors to completely kill leukemia stem cells (LSCs) indicates that these kinase inhibitors are unlikely to cure CML. In addition, drug resistance due to the development of BCRABL mutations occurs before and during treatment of CML with kinase inhibitors. A critical issue to resolve this problem is to fully understand the biology of LSCs, and to identify key genes that play significant roles in survival and self-renewal of LSCs. In this review, we will focus on LSCs in CML by summarizing and discussing available experimental results, including the original studies from our own laboratory.
Nitric oxide: promoter or suppressor of programmed cell death?
Yiqin Wang, Chen Chen, Gary J. Loake, Chengcai Chu
2010, 1(2): 133-142. doi: 10.1007/s13238-010-0018-x
Nitric oxide (NO) is a short-lived gaseous free radical that predominantly functions as a messenger and effector molecule. It affects a variety of physiological processes, including programmed cell death (PCD) through cyclic guanosine monophosphate (cGMP)-dependent and-independent pathways. In this field, dominant discoveries are the diverse apoptosis networks in mammalian cells, which involve signals primarily via death receptors (extrinsic pathway) or the mitochondria (intrinsic pathway) that recruit caspases as effector molecules. In plants, PCD shares some similarities with animal cells, but NO is involved in PCD induction via interacting with pathways of phytohormones. NO has both promoting and suppressing effects on cell death, depending on a variety of factors, such as cell type, cellular redox status, and the flux and dose of local NO. In this article, we focus on how NO regulates the apoptotic signal cascade through protein S-nitrosylation and review the recent progress on mechanisms of PCD in both mammalian and plant cells.
Alpha-helical cationic antimicrobial peptides: relationships of structure and function
Yibing Huang, Jinfeng Huang, Yuxin Chen
2010, 1(2): 143-152. doi: 10.1007/s13238-010-0004-3
Antimicrobial peptides (AMPs), with their extraordinary properties, such as broad-spectrum activity, rapid action and difficult development of resistance, have become promising molecules as new antibiotics. Despite their various mechanisms of action, the interaction of AMPs with the bacterial cell membrane is the key step for their mode of action. Moreover, it is generally accepted that the membrane is the primary target of most AMPs, and the interaction between AMPs and eukaryotic cell membranes (causing toxicity to host cells) limits their clinical application. Therefore, researchers are engaged in reforming or de novo designing AMPs as a ‘singleedged sword’ that contains high antimicrobial activity yet low cytotoxicity against eukaryotic cells. To improve the antimicrobial activity of AMPs, the relationship between the structure and function of AMPs has been rigorously pursued. In this review, we focus on the current knowledge of α-helical cationic antimicrobial peptides, one of the most common types of AMPs in nature.
Research articles
A dimeric structure of PD-L1: functional units or evolutionary relics?
Yong Chen, Peipei Liu, Feng Gao, Hao Cheng, Jianxun Qi, George F. Gao
2010, 1(2): 153-160. doi: 10.1007/s13238-010-0022-1
PD-L1 is a member of the B7 protein family, most of whose members so far were identified as dimers in a solution and crystalline state, either complexed or uncomplexed with their ligand(s). The binding of PD-L1 with its receptor PD-1 (CD279) delivers an inhibitory signal regulating the T cell function. Simultaneously with the Garboczi group, we successfully solved another structure of human PD-L1 (hPD-L1). Our protein crystallized in the space group of C2221 with two hPD-L1 molecules per asymmetric unit. After comparison of reported B7 structures, we have found some intrinsic factors involved in the interaction of these two molecules. Based on these results, we tend to believe this uncomplexed hPD-L1 structure demonstrated its potential dimeric state in solution, althougt it could just be an evolutionary relic, too weak to be detected under present technology, or still a functional unit deserved our attentions.
Metaxin deficiency alters mitochondrial membrane permeability and leads to resistance to TNF-induced cell killing
Koh Ono, Xiaofei Wang, Sung Ouk Kim, Lucas C. Armstrong, Paul Bornstein, Jiahuai Han
2010, 1(2): 161-173. doi: 10.1007/s13238-010-0017-y
Metaxin, a mitochondrial outer membrane protein, is critical for TNF-induced cell death in L929 cells. Its deficiency, caused by retroviral insertion-mediated mutagenesis, renders L929 cells resistance to TNF killing. In this study, we further characterized metaxin deficiency-caused TNF resistance in parallel with Bcl-XL overexpressionmediated death resistance. We did not find obvious change in mitochondria membrane potential in metaxindeficient (Metmut) and Bcl-XL-overexpressing cells, but we did find an increase in the release rate of the mitochondrial membrane potential probe rhodamine 123 (Rh123) that was preloaded into mitochondria. In addition, overexpression of a function-interfering mutant of metaxin (MetaΔTM/C) or Bcl-XL in MCF-7.3.28 cells also resulted in an acquired resistance to TNF killing and a faster rate of Rh123 release, indicating a close correlation between TNF resistance and higher rates of the dye release from the mitochondria. The release of Rh123 can be controlled by the mitochondrial membrane permeability transition (PT) pore, as targeting an inner membrane component of the PT pore by cyclosporin A (CsA) inhibited Rh123 release. However, metaxin deficiency and Bcl-XL overexpression apparently affect Rh123 release from a site(s) different from that of CsA, as CsA can overcome their effect. Though both metaxin and Bcl-XL appear to function on the outer mitochondrial membrane, they do not interact with each other. They may use different mechanisms to increase the permeability of Rh123, since previous studies have suggested that metaxin may influence certain outer membrane porins while Bcl-XL may form pores on the outer membrane. The alteration of the mitochondrial outer membrane properties by metaxin deficiency and Bcl-XL overespression, as indicated by a quicker Rh123 release, may be helpful in maintaining mitochondrial integrity.
The class A macrophage scavenger receptor type I (SR-AI) recognizes complement iC3b and mediates NF-κB activation
Jason W. K. Goh, Yen Seah Tan, Alister W. Dodds, Kenneth B. M. Reid, Jinhua Lu
2010, 1(2): 174-187. doi: 10.1007/s13238-010-0020-3
The macrophage scavenger receptor SR-AI binds to host tissue debris to perform clearance and it binds to bacteria for phagocytosis. In addition, SR-AI modulates macrophage activation through cell signaling. However, investigation of SR-AI signaling on macrophages is complicated due to its promiscuous ligand specificity that overlaps with other macrophage receptors. Therefore, we expressed SR-AI on HEK 293T cells to investigate its ligand binding and signaling. On 293Tcells, SR-AI could respond to E. coli DH5α, leading to NF-κB activation and IL-8 production. However, this requires E. coli DH5α to be sensitized by fresh serum that is treated with heat-inactivation or complement C3 depletion. Anti-C3 antibody inhibits the binding of SR-AI to serum-sensitized DH5α and blocks DH5α stimulation of SR-AI signaling. Further analysis showed that SR-AI can directly bind to purified iC3b but not C3 or C3b. By mutagenesis, The SRCR domain of SR-AI was found to be essential in SR-AI binding to serum-sensitized DH5α. These results revealed a novel property of SR-AI as a complement receptor for iC3b-opsonized bacteria that can elicit cell signaling.
Surfactant protein A (SP-A) binds to phosphatidylserine and competes with annexin V binding on late apoptotic cells
Anne Jäkel, Kenneth B. M. Reid, Howard Clark
2010, 1(2): 188-197. doi: 10.1007/s13238-010-0024-z
The role of surfactant protein A (SP-A) in the recognition and clearance of apoptotic cells is well established, but to date, it is still not clear which surface molecules of apoptotic cells are involved in the process. Here we present evidence that phosphatidylserine (PS) is a relevant binding molecule for human SP-A. The binding is Ca2+-dependent and is not inhibited by mannose, suggesting that the sugar-binding site of the carbohydrate recognition domain (CRD) of SP-A is not involved. Flow cytometry studies on apoptotic Jurkat cells revealed apparent inhibition of annexin V binding by increasing concentrations of SP-A in late apoptotic but not early apoptotic cells, and this was consistent for Jurkat cells and neutrophils. Supporting these data, confocal microscopy results show a co-localisation of annexin V and SP-A in late apoptotic but not early apoptotic cells. However, we cannot conclude that this inhibition is exclusively due to the binding of SP-A to PS on the cell surface, as annexin V is not wholly specific for PS and SP-A also interacts with other phospholipids that might become exposed on the apoptotic cell surface.
New nsp8 isoform suggests mechanism for tuning viral RNA synthesis
Shuang Li, Qi Zhao, Yinjie Zhang, Yang Zhang, Mark Bartlam, Xuemei Li, Zihe Rao
2010, 1(2): 198-204. doi: 10.1007/s13238-010-0028-8
During severe acute respiratory syndrome coronavirus (SARS-CoV) infection, the activity of the replication/transcription complexes (RTC) quickly peaks at 6 hours post infection (h.p.i) and then diminishes significantly in the late post-infection stages. This "down-up-down" regulation of RNA synthesis distinguishes different viral stages:primary translation, genome replication, and finally viron assembly. Regarding the nsp8 as the primase in RNA synthesis, we confirmed that the proteolysis product of the primase (nsp8) contains the globular domain (nsp8C), and indentified the resectioning site that is notably conserved in all the three groups of coronavirus. We subsequently crystallized the complex of SARS-CoV nsp8C and nsp7, and the 3-D structure of this domain revealed its capability to interfuse into the hexadecamer super-complex. This specific proteolysis may indicate one possible mechanism by which coronaviruses to switch from viral infection to genome replication and viral assembly stages.