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Soil carbon (C) and nitrogen (N) availability depend on the breakdown of soil polymers such as lignin, chitin, and protein that represent the major fraction of soil C and N but are too large for immediate uptake by plants and microorganisms. Microorganisms may adjust the production of enzymes targeting different polymers to optimize the balance between C and N availability and demand, and for instance increase the depolymerization of N-rich compounds when C availability is high and N availability low (microbial N mining). Such a mechanism could mitigate plant N limitation but also lie behind a stimulation of soil respiration frequently observed in the vicinity of plant roots (priming effect). We here compared the effect of increased C and N availability on the depolymerization of native bulk soil organic matter (SOM), and of C-13-enriched lignin, chitin, and protein added to the same soil in two complementary ten day microcosm incubation experiments. A significant reduction of chitin depolymerization (described by the recovery of chitin-derived C in the sum of dissolved organic, microbial and respired C) upon N addition indicated that chitin was degraded to serve as a microbial N source under low-N conditions and replaced in the presence of an immediately available alternative. Protein and lignin depolymerization in contrast were not affected by N addition. Carbon addition enhanced microbial N demand and SOM decomposition rates, but significantly reduced lignin, chitin, and protein depolymerization. Our findings contrast the hypothesis of increased microbial N mining as a key driver behind the priming effect and rather suggest that C addition promoted the mobilization of other soil C pools that replaced lignin, chitin, and protein as microbial C sources, for instance by releasing soil compounds from mineral bonds. We conclude that SOM decomposition is interactively controlled by multiple mechanisms including the balance between C vs N availability. Disentangling the

Rising atmospheric CO2 concentrations accompanied by global warming and altered precipitation patterns calls for assessment of long-term effects of these global changes on carbon (C) dynamics in terrestrial ecosystems, as changes in net C exchange between soil and atmosphere will impact the atmospheric CO2 concentration profoundly. In many ecosystems, including the heath/grassland system studied here, increased plant production at elevated CO2 increase fresh C input from litter and root exudates to the soil and concurrently decrease soil N availability. Supply of labile C to the soil may accelerate the decomposition of soil organic C (SOC), a phenomenon termed ‘the priming effect’, and the priming effect is most pronounced at low soil N availability. Hence, we hypothesized that priming of SOC decomposition in response to labile C addition would increase in soil exposed to long-term elevated CO2 exposure. Further, we hypothesized that long-term warming would enhance SOC priming rates, whereas drought would decrease the priming response. We incubated soil from a long-term, full-factorial climate change field experiment, with the factors elevated atmospheric CO2 concentration, warming and prolonged summer drought with either labile C (sucrose) or water to assess the impact of labile C on SOC dynamics. We used sucrose with a 13C/12C signature that is distinct from that of the native SOC, which allowed us to assess the contribution of these two C sources to the CO2 evolved. Sucrose induced priming of SOC, and the priming response was higher in soil exposed to long-term elevated CO2 treatment. Drought tended to decrease the priming response, whereas long-term warming did not affect the level of priming significantly. We were also able to assess whether SOC-derived primed C in elevated CO2 soil was assimilated before or after the initiation of the CO2 treatment 8 years prior to sampling, because CO2 concentrations were raised by fumigating the experimental plots with pure

Transferrin internalization via clathrin-mediated endocytosis and subsequent recycling after iron delivery has been extensively studied. Here we demonstrate a previously unrecognized parameter regulating this recycling -the binding of galectin-3 to particular glycoforms of transferrin. Two fractions of transferrin, separated by affinity chromatography based on their binding or not to galectin-3, are targeted to kinetically different endocytic pathways in HFL-1 cells expressing galectin-3 but not in SKBR3 cells lacking galectin-3; the SKBR3 cells, however can acquire the ability to target these transferrin glycoforms differently after preloading with exogenously added galectin-3. In all, this study provides the first evidence of a functional role for transferrin glycans, in intracellular trafficking after uptake. Moreover, the galectin-3 bound glycoform increased in cancer, suggesting a pathophysiological regulation. These are novel aspects of transferrin cell biology, which has previously considered only degree of iron loading, but not other forms of heterogeneity.

The α1,3-fucosyltransferase VII (Fuc-TVII) is involved in the biosynthesis of E- and P-selectin ligands such as sialyl Lewis x (SLex) on human leukocytes. Recently, individuals were characterized carrying a missense mutation (G329A; Arg110-Gln) in the FUT7 gene encoding this enzyme. The mutated FUT7 construct produced a Fuc-TVII enzyme with impaired activity compared with the wildtype enzyme. Polymorphonuclear granulocytes from an individual carrying this mutation homozygously also showed a reduced expression of SLex. In the present study, we have established Epstein–Barr virus-transformed B-cell lines from this individual (SIGN) and from an individual not carrying the mutation (IWO). The cell lines were confirmed to be of B-cell origin by flow cytometry analysis. IWO cells interacted with E-selectin in an in vitro flow chamber analysis whereas SIGN cell did not. However, when SIGN cell was transiently transfected with wildtype FUT7 cDNA, interaction with E-selectin could be restored. Cell surface expression of the SLex-related epitopes recognized by antibodies CSLEX-1, KM-93 and HECA-452 was elevated on IWO cells compared with that on SIGN cells, consistent with a role of these antigens in E-selectin recognition. These cell lines will be useful in further characterization of E-selectin ligands and encourage further studies on the consequences of the FUT7-G329A mutation in vivo.

Galectins, E-and P-selectins are carbohydrate-binding proteins that are up regulated at inflammatory lesions. Selectins expressed ou the activated endothelium mediate transient binding to leukocyte ligands that require sequential action of α 2,3-sialyltransferases and a 1,3-fucosyltransferases. ln leukocytes α1,3 fucosyltransferase VII adds fucose to α 2,3- sialylated lactosarnine acceptors in the final step of the biosynthesis of the selectin binding epitope sialyl Lewis x. The finding of low sialyl Lewis x expression in polymorphonuclear leukocytes from a patient with ulcerative colitis led to the discovery of a missense mutation (G329A) in the human gene coding for α1,3 fucosyltransferase VII, FUT7. Studies including enzymatic and immunochemical analysis oftransfected cell lines and isolated polymorphonuclear leukocytes from patients confirmed that this mutation impair the ability of α1,3 fucosyltransferase VII to synthesize sialyl Lewis x. The frequency of the mutation were measured in a mixed Swedish population and found to be -1 %. One individual carrying the FUT7-G329A mutation homozygously was identified. This individual suffered from ulcer disease, noninsulin-dependent diabetes, osteoporosis, spondyloarthrosis, and Sjögren's syndrome, but the relationship between disease and the mutation is not established. Studies using an in vitro flow chamber assay showed that transfected B-lymphoma cells and Epstein-Barr virus transformed B cells only transcribing FUT7-G329A were not able to interact with E-selectin during flow whereas polymorphonuclear leukocytes from the FUT7-G329A homozygous individual interacted well with both P- and E selectin during flow. The mRNA level of the fucosyltransferase IV coding gene, FUT4, was found to be elevated in the homozygous individual, which resulted in elevated levels ofthe CD65s epitope. However, transfected B-lymphoma cells and Epstein- Barr virus transformed cells did not show a similar elevation of FUT4 mRNA. In in vitro st

We recently identified several individuals carrying a missense mutation (G329A; Arg110-Gln) in the FUT7 gene encoding fucosyltransferase VII. This enzyme is involved in the biosynthesis of the sialyl Lewis x (Lex) epitope on human leukocytes, which has been identified as an important component of leukocyte ligands for E- and P-selectin. No enzyme activity was measurable in expression studies in COS-7 cells using the mutated FUT7 construct. One of the identified individuals carried this mutation homozygously. Flow cytometry analysis of polymorphonuclear leukocytes (PMN) from this individual showed a nearly complete absence of staining with mAbs directed against sialyl Lex and a diminished staining with an E-selectin IgG chimera. However, staining with P-selectin IgG chimera and Abs directed against P-selectin glycoprotein ligand-1 was not affected by the mutation. PMN from the homozygously mutated individual was further analyzed in an in vitro flow chamber assay. The number of rolling PMN and the rolling velocities on both E- and P-selectin were in the range of PMN from nonmutated individuals. FUT4 and FUT7 mRNA was quantified in PMN isolated from individuals carrying the FUT7 mutation. It was found that PMN from both FUT7 homozygously and heterozygously mutated individuals exhibited an elevated expression of FUT4 mRNA compared with PMN from FUT7 nonmutated individuals. The elevated expression of fucosyltransferase IV was reflected as an increased expression of the Lex and CD65s Ags on PMN from these individuals. The significance of the mutation was supported by transfection of BJAB cells.