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SignificanceUnlike other single-component intramembrane proteases such as rhomboid and S2P, γ-secretase contains four components: presenilin, Pen-2, Aph-1, and nicastrin. Previous electron cryomicroscopy (cryo-EM) analysis of human γ-secretase in amphipols revealed its overall architecture and 19 distinct transmembrane segments (TMs). However, the lack of side-chain density in the TMs, together with disordered inter-TM loops, disallowed TM assignment. Our current cryo-EM structure of human γ-secretase at 4.32-Å resolution allows specific assignment of all TMs and reveals principles of subunit packing. Our results also suggest that different detergents, as exemplified by amphipols and digitonin, may have little impact on the core conformation of γ-secretase.

These authors are equally contributed.Keywords: AtHDG11, drought stress, salt stress, transgenic cotton, transgenic poplar, cotton yield. SummaryDrought and salinity are two major environmental factors limiting crop production worldwide. Improvement of drought and salt tolerance of crops with transgenic approach is an effective strategy to meet the demand of the ever-growing world population. Arabidopsis ENHANCED DROUGHT TOLERANCE1/HOMEODOMAIN GLABROUS11 (AtEDT1/HDG11), a homeodomain-START transcription factor, has been demonstrated to significantly improve drought tolerance in Arabidopsis, tobacco, tall fescue and rice. Here we report that AtHDG11 also confers drought and salt tolerance in upland cotton (Gossypium hirsutum) and woody plant poplar (Populus tomentosa Carr.). Our results showed that both the transgenic cotton and poplar exhibited significantly enhanced tolerance to drought and salt stress with well-developed root system. In the leaves of the transgenic cotton plants, proline content, soluble sugar content and activities of reactive oxygen species-scavenging enzymes were significantly increased after drought and salt stress compared with wild type. Leaf stomatal density was significantly reduced, whereas stomatal and leaf epidermal cell size were significantly increased in both the transgenic cotton and poplar plants. More importantly, the transgenic cotton showed significantly improved drought tolerance and better agronomic performance with higher cotton yield in the field both under normal and drought conditions. These results demonstrate that AtHDG11 is not only a promising candidate for crops improvement but also for woody plants.

Overexpression of the epidermal growth factor (EGF) receptor (EGFR) is associated with enhanced invasion and metastasis in head and neck squamous cell carcinoma (HNSCC). Long Pentraxin PTX3 is involved in immune escape in cancer cells. Here, we identified PTX3 as a promoting factor that mediates EGF-induced HNSCC metastasis. EGF-induced PTX3 transcriptional activation is via the binding of c-Jun to the activator protein (AP)-1 binding site of the PTX3 promoter. PI3K/Akt and NF-κB were essential for the PTX3 activation. EGF-induced PTX3 expression was blocked in c-Jun- and NF-κB-knockdown cells. EGF-mediated PTX3 secretion resulted in the enhancement of cell migration and invasion, and interactions between cancer and endothelial cells. The tail-vein injection animal model revealed that depletion of PTX3 decreased EGF-primed tumor cell metastatic seeding of the lungs. In addition, fibronectin, matrix metalloproteinase-9 (MMP9) and E-cadherin were essential components in EGFR/PTX3-mediated cancer metastasis. In conclusion, PI3K/Akt and NF-κB-dependent regulation of AP-1 mediates PTX3 transcriptional responses to EGF. Autocrine production of EGF-induced PTX3 in turn induces metastatic molecules, activating inflammatory cascades and metastasis.

Cotton fiber elongation, largely achieved by cell wall loosening, is an important stage during cotton fiber development. In this present research, a fiber preferential cDNA encoding a pectate lyase (PEL) which could exclusively degrade the de-esterified pectin was isolated from a cotton (Gossypium hirsutum) fiber cDNA library. Subsequently, the corresponding PEL genes were isolated from four different cotton species and characterized. In vitro enzyme assays indicated that GhPEL really exhibited cleavage-activity against de-esterified pectin. The temporal-spatial expression analyses revealed that the GhPEL gene was preferentially expressed in fibers at 10 days-post anthesis (DPA). Antisense GhPEL transgenic cotton plants were generated by Agrobacterium-mediated transformation. Six homozygous lines, each with one or two copies of the transgene inserted as determined by southern blot analysis of the NPTII gene, were selected for further functional analysis. The GhPEL expression during fiber elongation in these transgenic lines was significantly suppressed in various degrees. Furthermore, the reduction of GhPEL enzymatic activity by decreasing GhPEL transcripts severely affected the degradation of de-esterified pectin in primary cell walls of transgenic cotton fibers, which consequently blocked cell wall loosening in early fiber development. Ultimately, the fiber elongation of all these transgenic lines was repressed. These results suggested that GhPEL may play an important role in the process of normal fiber elongation in cotton.

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Aberrant cleavage of amyloid precursor protein (APP) by γ-secretase contributes to the development of Alzheimer's disease. More than 200 disease-derived mutations have been identified in presenilin (the catalytic subunit of γ-secretase), making modulation of γ-secretase activity a potentially attractive therapeutic opportunity. Unfortunately, the technical challenges in dealing with intact γ-secretase have hindered discovery of modulators and demand a convenient substitute approach. Here we report that, similar to γ-secretase, the archaeal presenilin homolog PSH faithfully processes the substrate APP C99 into Aβ42, Aβ40, and Aβ38. The molar ratio of the cleavage products Aβ42 over Aβ40 by PSH is nearly identical to that by γ-secretase. The proteolytic activity of PSH is specifically suppressed by presenilin-specific inhibitors. Known modulators of γ-secretase also modulate PSH similarly in terms of the Aβ42/Aβ40 ratio. Structural analysis reveals association of a known γ-secretase inhibitor with PSH between its two catalytic aspartate residues. These findings identify PSH as a surrogate protease for the screening of agents that may regulate the protease activity and the cleavage preference of γ-secretase.A myloid precursor protein (APP) is initially cleaved by β-secretase in the extracellular space, producing a membrane-tethered, 99-residue carboxyl-terminal fragment known as APP C99 (1). APP C99 then undergoes sequential cleavages by γ-secretase, first at the e sites, yielding Aβ49/Aβ48, and eventually at the γ-sites, generating Aβ42/Aβ40/Aβ38 (2-4) (Fig. 1A). The 230-kDa γ-secretase contains four components: presenilin (PS), Pen-2, Aph-1, and nicastrin (NCT), of which PS1 is the target of most mutations derived from early-onset familial Alzheimer's disease (FAD) patients. Rather than abolishing the protease activity of γ-secretase, these mutations are thought to increase the molar ratio of Aβ42 over Aβ40 (2).Among the cleavage products of γ-secretase, Aβ42 is particularly prone to aggregation, leading to formation of β-amyloid plaque in the brain and presumably causing Alzheimer's disease (3). Other FAD-derived mutations map to APP and PS2, lending support to the causal relationship between formation of β-amyloid plaque and Alzheimer's disease (5). Therapeutic intervention of Alzheimer's disease may directly benefit from in vitro investigation of γ-secretase and discovery of its potential modulators (6). Unfortunately, such effort has been hampered by the difficulty in expression, purification, and manipulation of the complex protease. This problem persists despite recent breakthroughs in structural elucidation of γ-secretase and nicastrin (7,8).The intramembrane aspartate protease PSH from the archaeon Methanoculleus marisnigri JR1 shares 19% sequence identity and 53% sequence similarity with human PS1 (hPS1). The signature motifs for catalysis, ΦYDΦΦ (Φ for a hydrophobic residue) on transmembrane segment 6 (TM6) and ΦGΦGD on TM7, are identical between PSH and hPS1. PSH can be readily overexpressed in Escheri...

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