全文获取类型
收费全文 | 7117篇 |
免费 | 675篇 |
国内免费 | 4篇 |
专业分类
7796篇 |
出版年
2023年 | 29篇 |
2022年 | 72篇 |
2021年 | 135篇 |
2020年 | 73篇 |
2019年 | 92篇 |
2018年 | 115篇 |
2017年 | 105篇 |
2016年 | 178篇 |
2015年 | 298篇 |
2014年 | 340篇 |
2013年 | 437篇 |
2012年 | 476篇 |
2011年 | 519篇 |
2010年 | 302篇 |
2009年 | 290篇 |
2008年 | 434篇 |
2007年 | 410篇 |
2006年 | 343篇 |
2005年 | 372篇 |
2004年 | 345篇 |
2003年 | 354篇 |
2002年 | 339篇 |
2001年 | 74篇 |
2000年 | 55篇 |
1999年 | 73篇 |
1998年 | 81篇 |
1997年 | 58篇 |
1996年 | 68篇 |
1995年 | 45篇 |
1994年 | 60篇 |
1993年 | 57篇 |
1992年 | 53篇 |
1991年 | 47篇 |
1990年 | 39篇 |
1989年 | 46篇 |
1988年 | 35篇 |
1987年 | 43篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 33篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 31篇 |
1980年 | 33篇 |
1979年 | 37篇 |
1978年 | 41篇 |
1976年 | 33篇 |
1974年 | 28篇 |
1972年 | 32篇 |
1967年 | 33篇 |
排序方式: 共有7796条查询结果,搜索用时 15 毫秒
81.
82.
Actions of Rho family small G proteins and p21-activated protein kinases on mitogen-activated protein kinase family members. 总被引:15,自引:7,他引:15 下载免费PDF全文
The mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that are regulated by distinct extracellular stimuli. The currently known members include extracellular signal-regulated protein kinase 1 (ERK1), ERK2, the c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPKs), and p38 MAP kinases. We find that overexpression of the Ste20-related enzymes p21-activated kinase 1 (PAK1) and PAK2 in 293 cells is sufficient to activate JNK/SAPK and to a lesser extent p38 MAP kinase but not ERK2. Rat MAP/ERK kinase kinase 1 can stimulate the activity of each of these MAP kinases. Although neither activated Rac nor the PAKs stimulate ERK2 activity, overexpression of either dominant negative Rac2 or the N-terminal regulatory domain of PAK1 inhibits Ras-mediated activation of ERK2, suggesting a permissive role for Rac in the control of the ERK pathway. Furthermore, constitutively active Rac2, Cdc42hs, and RhoA synergize with an activated form of Raf to increase ERK2 activity. These findings reveal a previously unrecognized connection between Rho family small G proteins and the ERK pathway. 相似文献
83.
84.
Andrew Reed Jon C. Pigage Helen K. Pigage Cody Glickman Jeremy M. Bono 《Ecology and evolution》2019,9(23):13344-13358
Microbiota inhabiting the gastrointestinal (GI) tract of animals has important impacts on many host physiological processes. Although host diet is a major factor influencing the composition of the gut micro‐organismal community, few comparative studies have considered how differences in diet influence community composition across the length of the GI tract. We used 16S sequencing to compare the microbiota along the length of the GI tract in Abert's (Sciurus aberti) and fox squirrels (S. niger) living in the same habitat. While fox squirrels are generalist omnivores, the diet of Abert's squirrels is unusually high in plant fiber, particularly in winter when they extensively consume fiber‐rich inner bark of ponderosa pine (Pinus ponderosa). Consistent with previous studies, microbiota of the upper GI tract of both species consisted primarily of facultative anaerobes and was less diverse than that of the lower GI tract, which included mainly obligate anaerobes. While we found relatively little differentiation between the species in the microbiota of the upper GI tract, the community composition of the lower GI tract was clearly delineated. Notably, the Abert's squirrel lower GI community was more stable in composition and enriched for microbes that play a role in the degradation of plant fiber. In contrast, overall microbial diversity was higher in fox squirrels. We hypothesize that these disparities reflect differences in diet quality and diet breadth between the species. 相似文献
85.
86.
Nicholas G.M. Davies Helen Browne Ben Davis Martin J. Drysdale Nicolas Foloppe Stephanie Geoffrey Ben Gibbons Terance Hart Roderick Hubbard Michael Rugaard Jensen Howard Mansell Andrew Massey Natalia Matassova Jonathan D. Moore James Murray Robert Pratt Stuart Ray Alan Robertson Stephen D. Roughley Joseph Schoepfer Paul Brough 《Bioorganic & medicinal chemistry》2012,20(22):6770-6789
Inhibitors of the Hsp90 molecular chaperone are showing promise as anti-cancer agents. Here we describe a series of 4-aryl-5-cyanopyrrolo[2,3-d]pyrimidine ATP competitive Hsp90 inhibitors that were identified following structure-driven optimization of purine hits revealed by NMR based screening of a proprietary fragment library. Ligand-Hsp90 X-ray structures combined with molecular modeling led to the rational displacement of a conserved water molecule leading to enhanced affinity for Hsp90 as measured by fluorescence polarization, isothermal titration calorimetry and surface plasmon resonance assays. This displacement was achieved with a nitrile group, presenting an example of efficient gain in binding affinity with minimal increase in molecular weight. Some compounds in this chemical series inhibit the proliferation of human cancer cell lines in vitro and cause depletion of oncogenic Hsp90 client proteins and concomitant elevation of the co-chaperone Hsp70. In addition, one compound was demonstrated to be orally bioavailable in the mouse. This work demonstrates the power of structure-based design for the rapid evolution of potent Hsp90 inhibitors and the importance of considering conserved water molecules in drug design. 相似文献
87.
Primary production of aquatic macrophytes and their epiphytes in two shallow lakes (Peipsi and Võrtsjärv) in Estonia 总被引:1,自引:0,他引:1
In shallow lakes with large littoral zones, epiphytes and submerged macrophytes can make an important contribution to the total annual primary production. We investigated the primary production (PP) of phytoplankton, submerged macrophytes, and their epiphytes, from June to August 2005, in two large shallow lakes. The production of pelagic and littoral phytoplankton and of the dominant submerged macrophytes in the littoral zone (Potamogeton perfoliatus in Lake Peipsi and P. perfoliatus and Myriopyllum spicatum in Lake Võrtsjärv) and of their epiphytes was measured using a modified 14C method. The total PP of the submerged macrophyte area was similar in both lakes: 12.4 g C m?2 day?1 in Peipsi and 12.0 g C m?2 day?1 in Võrtsjärv. In Peipsi, 84.2% of this production was accounted for by macrophytes, while the shares of phytoplankton and epiphytes were low (15.6 and 0.16%, respectively). In Võrtsjärv, macrophytes contributed 58%, phytoplankton 41.9% and epiphytes 0.1% of the PP in the submerged macrophyte area. Epiphyte production in both lakes was very low in comparison with that of phytoplankton and macrophytes: 0.01, 5.04, and 6.97 g C m?2 day?1, respectively, in Võrtsjärv, and 0.02, 1.93, and 10.5 g C m?2 day?1, respectively, in Peipsi. The PP of the littoral area contributed 10% of the total summer PP of Lake Peipsi sensu stricto and 35.5% of the total summer PP of Lake Võrtsjärv. 相似文献
88.
89.
Identification of Varicella-Zoster Virus-Specific CD8 T Cells in Patients after T-Cell-Depleted Allogeneic Stem Cell Transplantation 下载免费PDF全文
Pim L. J. van der Heiden Renate de Boer Dirk M. van der Steen Michel G. D. Kester Menno W. A. G. van der Hoorn Wilmy M. E. Haarman Helen E. Barnby-Porritt Jeremy W. Fry C. E. Napper Erik W. A. Marijt Roel Willemze J. H. Frederik Falkenburg Mirjam H. M. Heemskerk 《Journal of virology》2009,83(14):7361-7364
To study the role of CD8 T cells in the control of varicella-zoster virus (VZV) reactivation, we developed multimeric major histocompatibility complexes to identify VZV-specific CD8 T cells. Potential HLA-A2 binding peptides from the putative immediate-early 62 protein (IE62) of VZV were tested for binding, and peptides with sufficient binding capacity were used to generate pentamers. Patients with VZV reactivation following stem cell transplantation were screened with these pentamers, leading to the identification of the first validated class I-restricted epitope of VZV. In 42% of HLA-A2 patients following VZV reactivation, these IE62-ALW-A2 T cells could be detected ex vivo.Varicella-zoster virus (VZV) infects about 95% of the population, persists throughout life, and may lead to herpes zoster when the virus reactivates. After T-cell-depleted allogeneic stem cell transplantation (TCD alloSCT), reactivation of the virus leads to considerable morbidity (10). Primary infection elicits both humoral and cellular responses, but cellular immunity is essential for preventing herpes zoster. The VZV genome comprises more than 70 unique open reading frames that encode proteins that are coordinately expressed during replication. The product of open reading frame 62, the immediate-early 62 (IE62) protein, is required for the initiation of VZV replication (9) and is expressed at high levels before viral replication has occurred (8). Previous research has demonstrated that IE62-specific T cells were detected after primary VZV infection and in immune subjects (2, 4). In addition, T cells recognizing various other IE proteins and glycoproteins of VZV, as demonstrated by gamma interferon (IFN-γ) production upon stimulation with peptides or lysate derived from these proteins, have been described (1, 6, 13). The VZV-specific memory T cells found in these studies were predominantly CD4 T cells, while no VZV-specific CD8 T cells were demonstrated without prior in vitro expansion, possibly due to the low frequency of VZV-specific CD8 T cells or to the low sensitivity of the screening methods used to detect CD8 T cells by IFN-γ production upon stimulation. Frey et al. described CD8 epitopes of IE62 detected following in vitro restimulation. However, the HLA restriction and specificity of these T cells were not confirmed (4). Due to the lack of validated VZV-derived immunodominant peptides for major histocompatibility complex (MHC) class I, the analysis of VZV-specific CD8 T-cell responses is hampered (14). To be able to analyze the role of CD8 T cells in VZV reactivation, we therefore set out to identify epitopes for VZV by using VZV-IE62-specific MHC class I peptide complexes.The predictive algorithms BIMAS (11) and SYFPEITHI (12) were used to select potential HLA-A2 binding peptides from the IE62 protein. Peptides with a score of ≥3 (BIMAS) or ≥20 (SYFPEITHI) were considered to have potentially significant binding affinity. The 81 resulting 9-mer peptides were synthesized and tested for binding affinity with the REVEAL MHC-peptide binding assay (ProImmune, Oxford, United Kingdom). HLA-A2 binding affinity was determined by the ability of the peptides to stabilize the HLA-peptide complex. Based on the binding affinity measurements, 34 high- to medium-affinity HLA-A2 binding peptides were selected and used to generate ProVE MHC pentamers (ProImmune, Oxford, United Kingdom). To enable screening of this large number of pentamers, the pentamers were divided into five pools, each containing six or seven pentamers. In the initial screening with pooled pentamers, four HLA-A2-positive patients were screened after a clinical diagnosis of VZV reactivation after TCD alloSCT. The presence of viral DNA in plasma at the time of clinical observations of VZV reactivation was confirmed by real-time PCR on plasma samples as previously described (7). After informed consent was obtained, peripheral blood mononuclear cells (PBMCs) were cryopreserved and thawed and 0.5 × 106 cells were incubated with pentamers at a concentration of 0.03 mg/ml for 10 min at room temperature in RPMI medium supplemented with 2% fetal bovine serum. After the cells were washed twice, 8 μl of FluoroTag-phycoerythrin (PE) was added for 20 min of incubation at 4°C and the cells were counterstained with CD4, CD40, and CD19-fluorescein isothiocyanate (FITC). Flow cytometric analysis was performed on a FACScalibur fluorescence-activated cell sorter (FACS; Becton-Dickinson [BD], San Jose, CA). In one of four patients, pentamer pool 6, containing pentamers 61, 62, 64, 65, 66, and 67, was positive (0.06% of CD8 T cells); no other positive signals were observed. Staining with the individual pentamers revealed that pentamer 66, containing the epitope ALWALPHAA derived from the IE62 protein of VZV (IE62-ALW-A2) was responsible for the positive signal (0.06% of CD8 T cells, Fig. Fig.1B1B).Open in a separate windowFIG. 1.Screening with pentamers containing VZV-derived immunogenic epitopes. PBMCs of a patient after VZV reactivation following TCD alloSCT were incubated with pentamers and then stained with FluoroTag-PE to detect the pentamer-positive cells (A and B) and counterstained with CD4-, CD40-, and CD19-FITC. Pentamer staining of the CD4-, CD40-, and CD19-negative cells is shown. (A) PBMCs stained with pentamer 67 containing the epitope ALPHAAAAV, showing no specific staining. (B) PBMCs stained with pentamer 66 containing the epitope ALWALPHAA, showing specific staining. IE62-ALW-A2-specific T-cell clones were sorted into a single cell per well and expanded nonspecifically. The clones were stained with an irrelevant tetramer (C) and the IE62-ALW-A2 tetramer (D) in combination with CD8-FITC. Clones 1 and 2 were stained with a Vβ kit (BD) to demonstrate that clone 1 (E) and clone 2 (F) express different T-cell receptors. The results demonstrate that we isolated different T-cell clones that specifically stain with the IE62-ALW-A2 tetramer.To confirm the specificity of the IE62-ALW-A2-specific T cells, the pentamer-positive T cells were sorted into a single cell per well with a FACSDiva (BD) and expanded as previously described (5). The expanded T-cell clones were labeled specifically with the IE62-ALW-A2 PE-conjugated tetramer that was constructed as previously described (3) (Fig. (Fig.1D),1D), and Vβ analysis with the T-cell receptor Vβ repertoire kit (BD) showed that at least two different T-cell clones were isolated, demonstrating the oligoclonal origin of IE62-ALW-A2-positive T cells (Fig. 1E and F). To assess the cytolytic capacity of IE62-ALW-A2 T cells, chromium release assays were performed as described earlier (5). 51Cr-labeled Epstein-Barr virus (EBV) lymphoblastoid cell lines (LCLs) loaded with the IE62-ALW peptide were incubated with IE62-ALW-A2 T cells for 4 h. As demonstrated in Fig. Fig.2A,2A, HLA-A2-positive EBV LCLs loaded with the IE62-ALW-A2 peptide were lysed by both T-cell clones, whereas unloaded EBV LCLs were not lysed. To determine the avidity of the T-cell clones, the IE62-ALW-A2 peptide was titrated on EBV LCLs, and after 24 h of coculture, supernatants were harvested and used to determine the IFN-γ production of the stimulated T cells by standard enzyme-linked immunosorbent assay. Half-maximum IFN-γ production of the T-cell clones was observed when the stimulator cells were loaded with 10 ng/ml peptide, indicative of high-avidity T-cell clones (Fig. (Fig.2B).2B). To determine whether the T cells recognized cells endogenously expressing the IE-62-encoding gene, COS-A2 cells were transfected with Lipofectamine (Invitrogen, Carlsbad, CA) by using pcDNA vectors coding for different VZV genes, which were kindly provided by E. Wiertz (Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands). The transfected COS-A2 cells were used 24 h after transfection as stimulator cells in this assay. After 24 h of coculture, supernatants were harvested and used to determine the IFN-γ production of the stimulated T cells. IE62-ALW-A2 T-cell clones produced IFN-γ in response to COS-A2 cells endogenously expressing the IE62 protein, as well as COS-A2 cells pulsed with the IE62-ALW-A2 peptide. No IFN-γ was produced when the COS-A2 cells were transfected with the IE63-encoding gene of VZV or pulsed with an irrelevant peptide (Fig. (Fig.2C2C).Open in a separate windowFIG. 2.IE62-ALW-A2 T cells recognize IE62-ALW-A2 peptide-loaded target cells and target cells endogenously expressing IE62. (A) The cytolytic activity of IE62-ALW-A2-positive T-cell clones 1 and 2 was analyzed with the 51Cr release assay. T cells were incubated for 4 h with IE62-ALW-A2 peptide (pep)-loaded or unloaded, HLA-A2-positive EBV LCLs at an effector-to-target ratio of 10:1. (B) IE62-ALW-A2 T-cell clone 1 was stimulated with HLA-A2-positive EBV LCLs loaded with different concentrations of the IE62-ALW-A2 peptide. Release of IFN-γ (pg/ml) after 24 h of stimulation is shown. (C) IE62-ALW-A2 T-cell clones 1 and 2 were stimulated with HLA-A2-positive COS-A2 cells, left untreated, or loaded with the IE62-ALW-A2 peptide or with the IE4-ALR-B8 peptide as an irrelevant peptide or transfected with the IE63-encoding gene (COS-A2-IE63) or the IE62-encoding gene (COS-A2-IE62). Release of IFN-γ (picograms per milliliter) after 24 h of stimulation is shown.To determine whether IE62-ALW-A2-specific T cells were present in healthy individuals, cryopreserved PBMCs from 18 healthy, VZV-seropositive, HLA-A2-positive individuals were screened with the PE-conjugated VZV tetramer. PBMCs were labeled with tetramers for 15 min at 37°C in RPMI medium without phenol supplemented with 2% fetal bovine serum, washed, and analyzed with a FACScalibur. In 3 of these 18 serologically VZV-positive individuals, IE62-ALW-A2 tetramer-positive T cells could be detected (range, 0.01 to 0.02% of CD8 T cells). These data demonstrate that IE62-ALW-A2-specific T cells can be observed and that the frequency of these T cells is low under steady-state conditions in immunocompetent persons.To assess the frequency of IE62-ALW-A2-specific T cells in a cohort of patient who suffered from VZV reactivation following TCD alloSCT, 19 HLA-A2-positive patients after VZV reactivation following TCD alloSCT were screened by using the IE62-ALW-A2 tetramer. We screened these patients at a median of 47 days after the clinical diagnosis of VZV reactivation. In 8 of these 19 patients, IE62-ALW-A2-specific T cells could be directly detected ex vivo (mean, 0.04% [range, 0.01 to 0.11%] of CD8 T cells), indicating that this epitope is recognized in 42% of the HLA-A2-positive patients during VZV reactivation (Table (Table1).1). In VZV-seronegative patients (six screened), no IE62-ALW-A2 tetramer-positive cells could be detected.
Open in a separate windowaMean percentages of IE62-ALW-A2 tetramer-positive cells of CD8 T cells of three tetramer stainings performed on different days are shown.bPBMCs were in vitro stimulated (IVS) for 7 days with IE62-ALW-A2 peptide, and the mean percentages of tetramer-positive cells of three to six stimulations are shown. A negative result was defined as <0.01% of CD8+ T cells.cND, no PBMCs were available to do the analysis.To verify the presence of the IE62-ALW-A2-specific T cells in the patient and donor cohort and to investigate whether individuals negative for IE62-ALW-A2-specific T cells were unable to mount a response against the epitope or whether the frequency of IE62-ALW-A2-specific T cells was too low to detect by FACS, the presence of these T cells was further measured after in vitro stimulation. PBMCs were cultured at a concentration of 1 × 106/ml in 24-well plates in Iscove''s modified Dulbecco''s medium supplemented with 10% human serum in the presence of IE62-ALW peptide (1 μg/ml), interleukin-2 (IL-2; 50 IU/ml), and IL-15 (10 ng/ml). After stimulation for 7 days, the presence of IE62-ALW-A2-specific T cells was reassessed by tetramer labeling. These in vitro stimulations demonstrated that IE62-ALW-A2 CD8 T cells were detectable in another four patients and confirmed the presence of IE62-ALW-A2-specific T cells in eight patients and three healthy, VZV-seropositive individuals with ex vivo-detectable IE62-ALW-A2-specific T cells (Table (Table1;1; Fig. 3A to D). Thus, in 12 (63%) of 19 patients, IE62-ALW-A2 CD8 T cells could be detected either by direct tetramer labeling or after in vitro expansion, indicating that this HLA-A2-restricted epitope is commonly used in HLA-A2-positive individuals.Open in a separate windowFIG. 3.Detection and kinetics of IE62-ALW-A2-specific T cells. PBMCs with detectable IE62-ALW-A2 T cells (A, left side), a low level of detectable tetramer-positive cells (B, left side), or no detectable tetramer-positive cells (C and D, left side) were in vitro stimulated for 7 days with IE62-ALW-A2 peptide (I μg/ml) in the presence of IL-2 and IL-15 (A to D, right side). Cells were stained with CD4-FITC, CD40-FITC, and IE62-ALW-A2 tetramer, and the percentages of CD8+ T cells that were IE62-ALW-A2 tetramer positive are indicated. CD8+ T cells are defined as CD4− CD40− lymphocytes. (E) PBMCs of a patient during the course of VZV reactivation following TCD alloSCT were stained with the IE62-ALW-A2 tetramer in combination with CD8-FITC. The percentages of IE62-ALW-A2-specific CD8 T cells before, during, and after VZV reactivation are shown. In the box, the presence of viral DNA in peripheral blood is shown as measured by real-time PCR at various time points. The bold line illustrates the use of valaciclovir to treat the VZV reactivation.To study whether the immune response against the IE62-ALW-A2 epitope correlated with clinical reactivation, the percentage of IE62-ALW-A2-positive T cells was analyzed during the course of VZV reactivation in one patient. To determine the presence of viral DNA in plasma before and during the course of VZV reactivation, real-time PCR was performed on plasma samples derived at different time points. Six days prior to clinical signs of VZV reactivation, only 0.03% of the CD8 T cells were IE62-ALW-A2 specific. At 42 days after the onset of VZV reactivation, 0.23% of the CD8 T cells were IE62-ALW-A2 specific. After the VZV infection resolved, the percentage of IE62-ALW-A2-specific CD8 T cells declined to 0.09% at day 49 and 0.03% at day 145 after reactivation (Fig. (Fig.3D).3D). The T cells present at the peak of the response were predominantly HLA-DR positive, CD45RA negative, CCR7 negative, CD28 negative, and CD27 positive, consistent with an activated effector memory phenotype.In this study, we demonstrate that CD8 T cells specific for VZV are detectable without prior in vitro stimulation in patients with VZV reactivation following TCD alloSCT. We identified the ALWALPHAA peptide derived from the IE62-encoding gene of VZV as the first validated VZV-specific HLA class I-restricted immunogenic epitope by a pentamer-based epitope discovery method. The detection of the IE62-ALW peptide as an immunogenic peptide for VZV-specific CD8 T cells demonstrates the usefulness of this procedure for discovering new immunogenic virus- or tumor-specific epitopes. We demonstrated that, despite the low frequency, it is possible to detect VZV-specific CD8 T cells, allowing ex vivo analysis of the immune response to VZV infection, reactivation, and possibly VZV vaccination. 相似文献
TABLE 1.
Presence of IE62-ALW-A2-specific T cells in HLA-A2 patients after VZV reactivation following TCD alloSCTPatient | No. of days after:
| % IE62-ALW-A2+ T cells (SD)
| ||
---|---|---|---|---|
TCD alloSCT | VZV reactivation | Before IVSa | After IVSb | |
1 | 180 | 46 | Negative | 0.22 (0.15) |
2 | 190 | 38 | 0.03 (0.01) | 0.51 (0.21) |
3 | 545 | 31 | Negative | Negative |
4 | 294 | 52 | Negative | 0.12 (0.06) |
5 | 82 | 38 | Negative | Negative |
6 | 183 | 16 | Negative | 0.01 (0.01) |
7 | 176 | 81 | 0.02 (0.01) | 0.44 (0.06) |
8 | 99 | 35 | 0.11 (0.02) | 0.22 (0.04) |
9 | 601 | 88 | Negative | 0.01 (0.01) |
10 | 95 | 63 | Negative | Negative |
11 | 90 | 83 | Negative | Negative |
12 | 179 | 48 | Negative | Negative |
13 | 1,224 | 62 | Negative | Negative |
14 | 173 | 20 | 0.03 (0.01) | 0.22 (0.12) |
15 | 514 | 21 | 0.03 (0.01) | NDc |
16 | 635 | 40 | 0.02 (0.01) | ND |
17 | 161 | 8 | Negative | Negative |
18 | 174 | 48 | 0.01 (0.00) | 0.02 (0.01) |
19 | 92 | 49 | 0.04 (0.01) | 0.06 (0.02) |
90.
Lang CH Huber D Frost RA 《American journal of physiology. Regulatory, integrative and comparative physiology》2007,292(1):R328-R336
The present study determined whether thermal injury increases the expression of the ubiquitin (Ub) E3 ligases referred to as muscle ring finger (MuRF)-1 and muscle atrophy F-box (MAFbx; aka atrogin-1), which are muscle specific and responsible for the increased protein breakdown observed in other catabolic conditions. After 48 h of burn injury (40% total body surface area full-thickness scald burn) gastrocnemius weight was reduced, and this change was associated with an increased mRNA abundance for atrogin-1 and MuRF-1 (3.1- to 8-fold, respectively). Similarly, burn increased polyUb mRNA content in the gastrocnemius twofold. In contrast, there was no burn-induced atrophy of the soleus and no significant change in atrogin-1, MuRF-1, or polyUb mRNA. Burns also did not alter E3 ligase expression in heart. Four hours after administration of the anabolic agent insulin-like growth factor (IGF)-I to burned rats, the mRNA content of atrogin-1 and polyUb in gastrocnemius had returned to control values and the elevation in MuRF-1 was reduced 50%. In contrast, leucine did not alter E3 ligase expression. In a separate study, in vivo administration of the proteasome inhibitor Velcade prevented burn-induced loss of muscle mass determined at 48 h. Finally, administration of the glucocorticoid receptor antagonist RU-486 did not prevent burn-induced atrophy of the gastrocnemius or the associated elevation in atrogin-1, MuRF-1, or polyUb. In summary, the acute muscle wasting accompanying thermal injury is associated with a glucocorticoid-independent increase in the expression of several Ub E3 ligases that can be downregulated by IGF-I. 相似文献