土地退化过程、机制与影响——以土地退化与恢复专题评估报告为基础

土地退化已成为威胁32亿人口福祉的全球性重大环境问题之一,近年来受到UN、IPBES、IPCC等组织的广泛关注。然而,当前的土地退化研究中,还存在概念不清、过程和机理不明、影响认识不彻底等问题,因此,厘清土地退化的概念、过程和机制是防止土地退化和恢复退化土地的关键。以生物多样性和生态系统服务政府间科学-政策平台（IPBES）土地退化与恢复专题评估报告为基础,剖析了土地退化的概念、过程、机制及影响：土地退化过程受自然环境和人类活动两大因素驱动,退化过程包括疑似退化、历史退化、敏感退化、弹性退化、持续退化和永久退化6种状态;土地退化类型可根据土地利用类型分为城市土地退化、农田退化、森林与草地退化、湿地退化等;土地退化具有多重影响,包括威胁食物和水安全,影响生物多样性及生态系统服务,引发地区冲突、大规模人口迁徙和疾病传播,加剧贫困及全球气候变化。土地退化过程、机制及影响的审视将为我国沙漠化、石漠化等土地退化的进一步研究提供理论指导,并为我国"山水林田湖草"土地系统的统筹治理和"美丽中国"、"生态文明"建设提供决策支持。     

Regulated degradation of HMG-CoA reductase, an integral membrane protein of the endoplasmic reticulum, in yeast

Numerous integral membrane proteins are degraded in the mammalian ER. HMG-CoA reductase (HMG-R), a key enzyme in the mevalonate pathway by which isoprenoids and sterols are synthesized, is one substrate of ER degradation. The degradation of HMG-R is modulated by feedback signals from the mevalonate pathway. We investigated the role of regulated degradation of the two isozymes of HMG-R, Hmg1p and Hmg2p, in the physiology of Saccharomyces cerevisiae. Hmg1p was quite stable, whereas Hmg2p was rapidly degraded. Degradation of Hmg2p proceeded independently of vacuolar proteases or secretory traffic, indicating that Hmg2p degradation occurred at the ER. Hmg2p stability was strongly affected by modulation of the mevalonate pathway through pharmacological or genetic means. Decreased mevalonate pathway flux resulted in decreased degradation of Hmg2p. One signal for degradation of Hmg2p was a nonsterol, mevalonate-derived molecule produced before the synthesis of squalene. Genetic evidence indicated that a farnesylated protein may also be necessary for Hmg2p degradation. Studies with reporter genes demonstrated that the stability of each isozyme was determined by its noncatalytic NH2-terminal domain. Our data show that ER protein degradation is widely conserved among eukaryotes, and that feedback control of HMG-R degradation is an ancient paradigm of regulation.     

Uptake, degradation, and release of fibrillar and soluble forms of Alzheimer's amyloid beta-peptide by microglial cells.

Microglia are phagocytic cells that are the main inflammatory response cells of the central nervous system. In Alzheimer's disease brain, activated microglia are concentrated in regions of compact amyloid deposits that contain the 39-43-amino acid Abeta peptide. We examined the uptake, degradation, and release of small aggregates of fibrillar Abeta (fAbeta) or soluble Abeta (sAbeta) by microglia. We found that although some degradation of fAbeta was observed over 3 days, no further degradation was observed over the next 9 days. Instead, there was a slow release of intact Abeta. The poor degradation was not due to inhibition of lysosomal function, since the rate of alpha2-macroglobulin degradation was not affected by the presence of fAbeta in the late endosomes/lysosomes. In contrast to fAbeta, internalization of sAbeta was not saturable. After internalization, sAbeta was released rapidly from microglia, and very little was degraded. These data show that fAbeta and sAbeta interact differently with microglia but that after internalization a large fraction of both are released without degradation.     

Purification, characterization, and cDNA cloning of an AU-rich element RNA-binding protein, AUF1.

The degradation of some proto-oncogene and lymphokine mRNAs is controlled in part by an AU-rich element (ARE) in the 3' untranslated region. It was shown previously (G. Brewer, Mol. Cell. Biol. 11:2460-2466, 1991) that two polypeptides (37 and 40 kDa) copurified with fractions of a 130,000 x g postribosomal supernatant (S130) from K562 cells that selectively accelerated degradation of c-myc mRNA in a cell-free decay system. These polypeptides bound specifically to the c-myc and granulocyte-macrophage colony-stimulating factor 3' UTRs, suggesting they are in part responsible for selective mRNA degradation. In the present work, we have purified the RNA-binding component of this mRNA degradation activity, which we refer to as AUF1. Using antisera specific for these polypeptides, we demonstrate that the 37- and 40-kDa polypeptides are immunologically cross-reactive and that both polypeptides are phosphorylated and can be found in a complex(s) with other polypeptides. Immunologically related polypeptides are found in both the nucleus and the cytoplasm. The antibodies were also used to clone a cDNA for the 37-kDa polypeptide. This cDNA contains an open reading frame predicted to produce a protein with several features, including two RNA recognition motifs and domains that potentially mediate protein-protein interactions. These results provide further support for a role of this protein in mediating ARE-directed mRNA degradation.     

Degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) by the lignin-degrading basidiomycete Phanerochaete chrysosporium.

Degradation of the BTEX (benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes) group of organopollutants by the white-rot fungus Phanerochaete chrysosporium was studied. Our results show that the organism efficiently degrades all the BTEX components when these compounds are added either individually or as a composite mixture. Degradation was favored under nonligninolytic culture conditions in malt extract medium, in which extracellular lignin peroxidases (LIPs) and manganese-dependent peroxidases (MNPs) are not produced. The noninvolvement of LIPs and MNPs in BTEX degradation was also evident from in vitro studies using concentrated extracellular fluid containing LIPs and MNPs and from a comparison of the extents of BTEX degradation by the wild type and the per mutant, which lacks LIPs and MNPs. A substantially greater extent of degradation of all the BTEX compounds was observed in static than in shaken liquid cultures. Furthermore, the level of degradation was relatively higher at 25 than at 37 degrees C, but pH variations between 4.5 and 7.0 had little effect on the extent of degradation. Studies with uniformly ring-labeled [14C]benzene and [14C]toluene showed substantial mineralization of these compounds to 14CO2.     

Regulation of protein degradation in normal and transformed human cells. Effects of growth state, medium composition, and viral transformation.

In WI-38, a normal human fibroblast, the rates of degradation of short lived and long lived proteins are identical whether the cultures are growing exponentially or are density-inhibited. Replacement of the growth medium with fresh medium does not alter these rates. In VA-13, an SV-40 transformed derivative of WI-38, the rates of protein degradation are also independent of growth rate and fresh medium. However, in both WI-38 and VA-13 the rate of long lived protein degradation increases as the serum concentration is reduced below 5%. After complete serum withdrawal, the rate increases by 60 to 100% in both cell types. Withdrawal of arginine and phenylalanine triples the rate of long lived protein degradation, while addition of 10% dialyzed serum to this amino acid-deficient medium reduces the effect to twice that of the controls. Incubation of both types of cells in phosphate-buffered saline also increases protein degradation. This effect is reduced by glucose, albumin, and dialyzed serum. Therefore, the rate of protein degradation is independent of growth rate in normal and transformed human cells. However, the rate of degradation is closely coupled to certain medium alterations.     

内蒙古呼伦贝尔草甸草原的草地退化等级数量分析

采用样方取样方法实地调查内蒙古呼伦贝尔草甸草原的植物群落特征,利用植被和土壤数据,应用系统聚类分析方法对其草地退化等级进行定量划分.结果表明:(1)植被指标聚类可将草地划分为3个等级,即轻度退化、中度退化和重度退化草地,而利用土壤指标聚类则划分为2个等级,其中轻度退化和中度退化草地的土壤状况相似合为一个等级,重度退化草地为另一个等级;(2)随着放牧梯度的变化,植被和土壤都发生了变化,中度退化草地植被变化大,而土壤变化不大;(3)内蒙古呼伦贝尔草甸草原为同一草地利用单元,所划分的草地退化等级系列是由放牧引起的.     

Insulin receptor substrate (IRS)-2, not IRS-1, protects human neuroblastoma cells against apoptosis

Insulin receptor substrates (IRS)-1 and -2 are major substrates of insulin and type I insulin-like growth factor (IGF-I) receptor (IGF-IR) signaling. In this study, SH-EP human neuroblastoma cells are used as a model system to examine the differential roles of IRS-1 and IRS-2 on glucose-mediated apoptosis. In the presence of high glucose, IRS-1 underwent caspase-mediated degradation, followed by focal adhesion kinase (FAK) and Akt degradation and apoptosis. IRS-2 expression blocked all these changes whereas IRS-1 overexpression had no effect. In parallel, IRS-2, but not IRS-1, overexpression enhanced IGF-I-mediated Akt activation without affecting extracellular regulated kinase signaling. While IRS-1 was readily degraded by caspases, hyperglycemia-mediated IRS-2 degradation was unaffected by caspase inhibitors but blocked by proteasome and calpain inhibitors. Our data suggest that the differential degradation of IRS-1 and IRS-2 contributes to their distinct modes of action and the increased neuroprotective effects of IRS-2 in this report are due, in part, to its resistance to caspase-mediated degradation.     

Microbial degradation of furanic compounds: biochemistry,genetics, and impact

Microbial metabolism of furanic compounds, especially furfural and 5-hydroxymethylfurfural (HMF), is rapidly gaining interest in the scientific community. This interest can largely be attributed to the occurrence of toxic furanic aldehydes in lignocellulosic hydrolysates. However, these compounds are also widespread in nature and in human processed foods, and are produced in industry. Although several microorganisms are known to degrade furanic compounds, the variety of species is limited mostly to Gram-negative aerobic bacteria, with a few notable exceptions. Furanic aldehydes are highly toxic to microorganisms, which have evolved a wide variety of defense mechanisms, such as the oxidation and/or reduction to the furanic alcohol and acid forms. These oxidation/reduction reactions constitute the initial steps of the biological pathways for furfural and HMF degradation. Furfural degradation proceeds via 2-furoic acid, which is metabolized to the primary intermediate 2-oxoglutarate. HMF is converted, via 2,5-furandicarboxylic acid, into 2-furoic acid. The enzymes in these HMF/furfural degradation pathways are encoded by eight hmf genes, organized in two distinct clusters in Cupriavidus basilensis HMF14. The organization of the five genes of the furfural degradation cluster is highly conserved among microorganisms capable of degrading furfural, while the three genes constituting the initial HMF degradation route are organized in a highly diverse manner. The genetic and biochemical characterization of the microbial metabolism of furanic compounds holds great promises for industrial applications such as the biodetoxifcation of lignocellulosic hydrolysates and the production of value-added compounds such as 2,5-furandicarboxylic acid.     

Autophagy, heterophagy, microautophagy and crinophagy as the means for intracellular degradation

It is generally accepted that the lysosomal compartment plays an important role in the degradation of cellular components. In this communication we discuss various experimental models which have been used to study mechanisms of intralysosomal degradation and also discuss the evidence obtained in support of the following proposals: 1. The autophagosomes can be isolated into high purity and are the subcellular locus of induced protein degradation. 2. Different membrane components such as proteins and lipids are degraded at different rates inside the lysosomes. Intralysosomal hydrolysis is not the rate limiting step in degradation. 3. Lysosomes take up soluble material in vitro by invagination and pinching off of their membranes (microautophagy). 4. Secretory vesicles can degrade their secretory contents by fusing with the lysosomes.     

myc Boxes, Which Are Conserved in myc Family Proteins, Are Signals for Protein Degradation via the Proteasome

Cellular levels of the rapidly degraded c-myc protein play an important role in determining the proliferation status of cells. Increased levels of c-myc are frequently associated with rapidly proliferating tumor cells. We show here that myc boxes I and II, found in the N termini of all members of the myc protein family, function to direct the degradation of the c-myc protein. Both myc boxes I and II contain sufficient information to independently direct the degradation of otherwise stably expressed proteins to which they are fused. At least part of the myc box-directed degradation occurs via the proteasome. The mechanism of myc box-directed degradation appears to be conserved between yeast and mammalian cells. Our results suggest that the myc boxes may play an important role in regulating the level and activity of the c-myc protein.     

Trafficking, ubiquitination, and down-regulation of the human platelet-activating factor receptor

Platelet-activating factor (PAF) is a potent phospholipid mediator involved in various disease states such as allergic asthma, atherosclerosis and psoriasis. The human PAF receptor (PAFR) is a member of the G protein-coupled receptor family. Following PAF stimulation, cells become rapidly desensitized; this refractory state can be maintained for hours and is dependent on PAFR phosphorylation, internalization, and down-regulation. In this report, we characterized ligand-induced, long term PAFR desensitization, and pathways leading to its degradation. Some GPCRs are known to be targeted to proteasomes for degradation while others traffic via the early/late endosomes toward lysosomes. Specific inhibitors of lysosomal proteases and inhibitors of the proteasome were effective in reducing the ligand-induced PAFR down-regulation by 40 and 25%, respectively, indicating the importance of receptor targeting to both lysosomes and proteasomes in long term cell desensitization to PAF. The effects of the proteasome and lysosomal protease inhibitors were additive and, together, completely blocked ligand-induced degradation of PAFR. Using dominant-negative Rab5 and 7 and colocalization of the PAFR with the early endosome autoantigen I (EEAI) or transferrin, we confirmed that ligand-induced PAFR down-regulation was Rab5/7-dependent and involved lysosomal degradation. In addition, we also demonstrated that PAFR was ubiquitinated in an agonist-independent manner. However, a dominant negative ubiquitin ligase (NCbl) reduced PAFR ubiquitination and inhibited ligand-induced but not basal receptor degradation. Our results indicate that PAFR degradation can occur via both the proteasome and lysosomal pathways and ligand-stimulated degradation is ubiquitin-dependent.     

Htm1p, a mannosidase-like protein, is involved in glycoprotein degradation in yeast

Misfolded proteins are recognized in the endoplasmic reticulum (ER), transported back to the cytoplasm and degraded by the proteasome. Processing intermediates of N-linked oligosaccharides on incompletely folded glycoproteins have an important role in their folding/refolding, and also in their targeting to proteolytic degradation. In Saccharomyces cerevisiae, we have identified a gene coding for a non-essential protein that is homologous to mannosidase I (HTM1) and that is required for degradation of glycoproteins. Deletion of the HTM1 gene does not affect oligosaccharide trimming. However, deletion of HTM1 does reduce the rate of degradation of the mutant glycoproteins such as carboxypeptidase Y, ABC-transporter Pdr5-26p and oligosaccharyltransferase subunit Stt3-7p, but not of mutant Sec61-2p, a non-glycoprotein. Our results indicate that although Htm1p is not involved in processing of N-linked oligosaccharides, it is required for their proteolytic degradation. We propose that this mannosidase homolog is a lectin that recognizes Man8GlcNAc2 oligosaccharides that serve as signals in the degradation pathway.     

Secretory pathway quality control operating in Golgi,plasmalemmal, and endosomal systems

Exportable proteins that have significant defects in nascent polypeptide folding or subunit assembly are frequently retained in the endoplasmic reticulum and subject to endoplasmic reticulum-associated degradation by the ubiquitin-proteasome system. In addition to this, however, there is growing evidence for post-endoplasmic reticulum quality control mechanisms in which mutant or non-native exportable proteins may undergo anterograde transport to the Golgi complex and post-Golgi compartments before intracellular disposal. In some instances, these proteins may undergo retrograde transport back to the endoplasmic reticulum with re-targeting to the endoplasmic reticulum-associated degradation pathway; in other typical cases, they are targeted into the endosomal system for degradation by vacuolar/lysosomal proteases. Such quality control targeting is likely to involve recognition of features more commonly expressed in mutant proteins, but may also be expressed by wild-type proteins, especially in cells with perturbation of local environments that are essential for normal protein trafficking and stability in the secretory pathway and at the cell surface .     

Eco-cultural health,global health,and sustainability

Anthropogenic stress on the earth’s ecosystems has resulted in widespread prevalence of ecosystem distress syndrome, a quantifiable set of signs of ecosystem degradation. At the same time, the planet is witnessing rapid declines in global cultural diversity and in the vitality of the world’s cultures, which closely mirror, and are interrelated with, ecological degradation. As a consequence of this converging crisis of loss of ecosystem and cultural health, global health and sustainability are increasingly under threat. An eco-cultural health perspective based on understanding the linkages between human activities, ecological and cultural disruption, and public health is essential for addressing these threats and achieving global sustainability.     

Diffuse PAH contamination of surface soils: environmental occurrence,bioavailability, and microbial degradation

The purpose of this review is to recognize the scientific and environmental importance of diffuse pollution with polycyclic aromatic hydrocarbons (PAHs). Diffuse PAH pollution of surface soil is characterized by large area extents, low PAH concentrations, and the lack of point sources. Urban and pristine topsoils receive a continuous input of pyrogenic PAHs, which induces a microbial potential for PAH degradation. The significance of this potential in relation to black carbon particles, PAH bioaccessibility, microbial PAH degradation, and the fate of diffuse PAHs in soil is discussed. Finally, the state-of-the-art methods for future investigations of the microbial degradation of diffuse PAH pollution are reviewed.     

Polyamines,ribonucleases, and the stability of RNA

Summary The polyamines influence the activity of many enzymes involved in the synthesis and degradation of RNA. These organic cations (putrescine, spermidine, spermine) stimulate, for example, many DNA-dependent RNA polymerases and affect both RNA chain elongation and initiation. The polyamines also bind to polynucleotides, forming complexes having, in many cases, physical properties quite distinct from the parent polymer. Some of these complexes are resistent to ribonuclease mediated hydrolysis. However, polyamines alter the activity, as well as the specificity of some RNases, so the actual rate of breakdown of RNA is dependent on the interaction of polyamine with both RNA and enzyme. The hydrolytic rate may also be controlled by the presence of purine homopolymer, which acts to strongly inhibit RNase activity. The addition of polyadenylic acid tracts to the 3 terminus of the RNA substrate, for example, protects the unpolyadenylated portion of the RNA molecule from degradation. Longer segments of poly(A) are more effective in this respect; however, regardless of poly(A) length, low concentrations of spermidine reverse the inhibition of RNase activity, with concomitant rapid degradation of the unpolyadenylated portion of the RNA molecule. Thus, RNA degradation depends not only on the presence of RNase, but on poly(A) length and spermidine concentration as well. Although the relative importance, within the cell, of each of these interactions is not known, the above mechanisms illustrate certain of the complexities and interrelations that may exist for the synthesis and, in particular, the RNase mediated degradation of RNA.A submitted article     

Chemical C-terminal protein sequence analysis: improved sensitivity, length of degradation, proline passage, and combination with edman degradation

Use of a C-terminal sequencer with modified solvents, reagent concentrations, chromatographic parameters, temperatures, and reaction cartridge geometry yields four sets of improvements in chemical degradations. They are increased sensitivity, longer runs, passage of Pro residues, and practical combination with N-terminal degradation. Over 200 proteins and protein fragments with sizes between 20 and 600 residues were analyzed. C-terminal sequences could be interpreted for more than 10 residues at high picomole sample levels, while the 10-pmol level gave 4-5 residues. The average initial yield was 15% but up to 30% could be achieved. The improved performance allowed combination of C- and N-terminal degradations from the same sample application. After initial Edman degradation, the sample is moved to the C-terminal instrument for continued sequencing. Proteins available in limited amount are thereby efficiently analyzed. Lys, modified from the N-terminal degradation, may be detected as the alkylated thiohydantoin-phenylthiocarbamyl-Lys derivative in the C-terminal degradation. Notably, C-terminal sequence analysis could be proceeded through Pro residues which unexpectedly were no absolute hindrance. The improved technique provides characterization of truncation patterns and microheterogeneities in proteins down to the 10-pmol level and is a useful approach for analysis of N-terminally blocked polypeptides.