Genetic analysis of the formation of the Ysc-Yop translocation pore in macrophages by Yersinia enterocolitica: role of LcrV, YscF and YopN

The Ysc-Yop type III secretion (TTS) system allows extracellular Yersinia bacteria, adhering to eukaryotic target cells, to inject Yop effector proteins in the cytosol of these cells. The secretion apparatus, called the injectisome, ends up with a needle-like structure made of YscF. YopN, one of the proteins secreted by the injectisome is thought to act as a plug. YopB, YopD and LcrV, three other proteins secreted by the injectisome and called 'translocators' form a pore allowing translocation of the Yop effectors across the target cell plasma membrane. Here, we tested the role of LcrV, YscF and YopN in the formation of this pore in macrophages by monitoring the release of the low-molecular-weight fluorescent dye BCECF (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester, 623Da) and of the high-molecular-weight lactate dehydrogenase (LDH, 135 kDa). BCECF is released through the translocation pore itself provided no Yop effector is trafficking through the channel. In contrast, LDH is released by the osmotic lysis of the target cell that occurs after pore formation. This release is reduced by the GAP activity of YopE. In order to study the role of LcrV, one has to circumvent the regulatory effect of LcrV on the synthesis of YopB and YopD. We observed here that this regulatory role of LcrV is lost in a yopQ mutant and hence we studied the role of LcrV in a yopQ mutant background. A lcrV, yopQ double mutant was deficient in pore formation while able to produce YopB and YopD. Pore formation was restored by the introduction of lcrV(+) but not yopQ(+) confirming that LcrV itself is directly required for pore formation. Bacteria secreting only YopB, YopD and LcrV could form pores, showing that YopB, YopD and LcrV are sufficient for pore formation provided they are secreted by the same bacterium. LcrV is not involved in secretion of YopB and YopD as suggested previously. Bacteria producing normal Ysc injectisomes, including the YscF needle but no translocators did not form pores, indicating that the needle is not sufficient by itself for pore formation, as was also suggested. yopN mutant bacteria formed needles and released BCECF even if they secreted the effectors. This observation suggests that many translocation pores are not filled in the absence of YopN and thus that YopN might form a link between the needle and the pore, guiding the effectors.     

Early postnatal development of the mandibular permanent first molar in infants with isolated cleft palate

International Journal of Paediatric Dentistry 2012; 22: 280–285 Background. Based on measurements on dental casts, smaller permanent teeth in children with cleft palate have previously been reported in the literature; however, the early maturation of teeth and the size of the follicles and crowns have not been investigated. Hypothesis. The maturation of the mandibular permanent first molar (M1_inf) is delayed, and the mesiodistal diameters of the follicle and crown of M1_inf, respectively, are reduced in children with isolated cleft palate (ICP). Design. Retrospective, longitudinal. Cephalometric X‐rays were available for 2 and 22 months old children with clefts (64 children with ICP, and a control group of 38 children with unilateral incomplete cleft lip). The width of the follicle and the crown of M1_inf, and the maturation of M1_inf were assessed. Intra‐observer error was acceptable. Results. M1_inf maturation was delayed in children with ICP at both 2 and 22 months of age. The mesiodistal diameter of the crown of M1_inf in the ICP group was reduced. Thus, the two hypotheses could not be refuted. Conclusions. Children with ICP showed smaller dimensions of the M1_inf, and in addition, the maturation of M1_inf was delayed.     

Endogenous sex hormones and endometrial cancer risk in women in the European Prospective Investigation into Cancer and Nutrition (EPIC)

Epidemiological data show that reproductive and hormonal factors are involved in the etiology of endometrial cancer, but there is little data on the association with endogenous sex hormone levels. We analyzed the association between prediagnostic serum concentrations of sex steroids and endometrial cancer risk in the European Prospective Investigation into Cancer and Nutrition using a nested case-control design of 247 incident endometrial cancer cases and 481 controls, matched on center, menopausal status, age, variables relating to blood collection, and, for premenopausal women, phase of menstrual cycle. Using conditional regression analysis, endometrial cancer risk among postmenopausal women was positively associated with increasing levels of total testosterone, free testosterone, estrone, total estradiol, and free estradiol. The odds ratios (ORs) for the highest versus lowest tertile were 2.66 (95% confidence interval (CI) 1.50-4.72; P=0.002 for a continuous linear trend) for estrone, 2.07 (95% CI 1.20-3.60; P=0.001) for estradiol, and 1.66 (95% CI 0.98-2.82; P=0.001) for free estradiol. For total and free testosterone, ORs for the highest versus lowest tertile were 1.44 (95% CI 0.88-2.36; P=0.05) and 2.05 (95% CI 1.23-3.42; P=0.005) respectively. Androstenedione and dehydroepiandrosterone sulfate were not associated with risk. Sex hormone-binding globulin was significantly inversely associated with risk (OR for the highest versus lowest tertile was 0.57, 95% CI 0.34-0.95; P=0.004). In premenopausal women, serum sex hormone concentrations were not clearly associated with endometrial cancer risk, but numbers were too small to draw firm conclusions. In conclusion, relatively high blood concentrations of estrogens and free testosterone are associated with an increased endometrial cancer risk in postmenopausal women.     

Induction of anti-DNA autoanti-idiotypic antibodies in (NZB X NZW)F1 mice: possible role for specific immune suppression

(NZB X NZW)F1 (B/W) mice spontaneously produce anti-deoxyribonucleic (DNA) acid antibodies. PME77 anti-DNA monoclonal antibody (MoAb) is a syngeneic antibody bearing idiotype present in most B/W sera. In the present investigation the effect of immunization of B/W mice with the PME77 MoAb on the production of PME77 idiotypes and anti-DNA antibodies in B/W mouse sera was investigated. PME77 MoAb immunization regimen induced the production of autoanti-idiotypic antibodies and abrogated the expression of PME77 idiotype in B/W treated mice. In contrast, untreated mice and control B/W mice, receiving NZB polyclonal IgG2b which lacked detectable DNA binding capacity, expressed PME77 idiotopes. These results demonstrate that the expression of idiotype borne by autoantibodies may be modified through the induction of autoanti-idiotypic antibodies.     

Structural basis for activation of the complement system by component C4 cleavage

An essential aspect of innate immunity is recognition of molecular patterns on the surface of pathogens or altered self through the lectin and classical pathways, two of the three well-established activation pathways of the complement system. This recognition causes activation of the MASP-2 or the C1s serine proteases followed by cleavage of the protein C4. Here we present the crystal structures of the 203-kDa human C4 and the 245-kDa C4⋅MASP-2 substrate⋅enzyme complex. When C4 binds to MASP-2, substantial conformational changes in C4 are induced, and its scissile bond region becomes ordered and inserted into the protease catalytic site in a manner canonical to serine proteases. In MASP-2, an exosite located within the CCP domains recognizes the C4 C345C domain 60 Å from the scissile bond. Mutations in C4 and MASP-2 residues at the C345C–CCP interface inhibit the intermolecular interaction and C4 cleavage. The possible assembly of the huge in vivo enzyme–substrate complex consisting of glycan-bound mannan-binding lectin, MASP-2, and C4 is discussed. Our own and prior functional data suggest that C1s in the classical pathway of complement activated by, e.g., antigen–antibody complexes, also recognizes the C4 C345C domain through a CCP exosite. Our results provide a unified structural framework for understanding the early and essential step of C4 cleavage in the elimination of pathogens and altered self through two major pathways of complement activation.     

Replicative senescence of human dermal fibroblasts affects structural and functional aspects of the Golgi apparatus

It is well recognized that the world population is ageing rapidly. Therefore, it is important to understand ageing processes at the cellular and molecular levels to predict the onset of age‐related diseases and prevent them. Recent research has focused on the identification of ageing biomarkers, including those associated with the properties of the Golgi apparatus. In this context, Golgi‐mediated glycosylation of proteins has been well characterized. Additionally, other studies show that the secretion of many compounds, including pro‐inflammatory cytokines and extracellular matrix–degrading enzymes, is modified during ageing, resulting in physical and functional skin degradation. Since the Golgi apparatus is a central organelle of the secretory pathway, we investigated its structural organization in senescent primary human dermal fibroblasts using confocal and electron microscopy. In addition, we monitored the expression of Golgi‐related genes in the same cells. Our data showed a marked alteration in the Golgi morphology during replicative senescence. In contrast to its small and compact structure in non‐senescent cells, the Golgi apparatus exhibited a large and expanded morphology in senescent fibroblasts. Our data also demonstrated that the expression of many genes related to Golgi structural integrity and function was significantly modified in senescent cells, suggesting a relationship between Golgi apparatus function and ageing.     

p53-Regulated Apoptosis Is Differentiation Dependent in Ultraviolet B-Irradiated Mouse Keratinocytes

Previous studies from our laboratory, using p53 transgenic mice, have suggested that ultraviolet (UV) light-induced keratinocyte apoptosis in the skin is not affected by overexpression of mutant p53 protein. To further elucidate a possible role for p53 in UV-induced keratinocyte cell death, we now examine apoptosis in skin and isolated keratinocytes from p53 null (−/−) mice and assess the influence of cell differentiation on this process. In vivo, using this knockout model, epidermal keratinocytes in p53−/− mice exhibited only a 5.2-fold increase in apoptosis after 2000 J/m² UVB irradiation compared with a 26.3-fold increase in normal control animals. If this p53-dependent apoptosis is important in elimination of precancerous, UV-damaged keratinocytes, then it should be active in the undifferentiated cells of the epidermal basal layer. To test this hypothesis, we examined the effect of differentiation on UV-induced apoptosis in primary cultures of murine and human keratinocytes. Apoptosis was p53-independent in undifferentiated murine keratinocytes, which exhibited relative resistance to UVB-induced killing with only a 1.5-fold increase in apoptosis in p53+/+ cells and a 1.4-fold increase in p53−/− cells. Differentiated keratinocytes, in contrast, showed a 9.4-fold UVB induction of apoptosis in p53+/+ cells, almost three times the induction observed in p53−/− cells. This UV-induced difference in apoptosis was observed when keratinocytes were cultured on type IV collagen substrate, but not on plastic alone. Western blotting of UV-irradiated, differentiated keratinocytes did not support a role for either Bax or Bcl-2 in this process. In support of these findings in mice, cell death in human cultured keratinocytes also occurred in a differentiation-associated fashion. We conclude that p53-induced apoptosis eliminates damaged keratinocytes in the differentiated cell compartment, but this mechanism is not active in the basal, undifferentiated cells and is therefore of questionable significance in protection against skin cancer induction.     

Protein Content and Methyl Donors in Maternal Diet Interact to Influence the Proliferation Rate and Cell Fate of Neural Stem Cells in Rat Hippocampus

Maternal diet during pregnancy and early postnatal life influences the setting up of normal physiological functions in the offspring. Epigenetic mechanisms regulate cell differentiation during embryonic development and may mediate gene/environment interactions. We showed here that high methyl donors associated with normal protein content in maternal diet increased the in vitro proliferation rate of neural stem/progenitor cells isolated from rat E19 fetuses. Gene expression on whole hippocampi at weaning confirmed this effect as evidenced by the higher expression of the Nestin and Igf2 genes, suggesting a higher amount of undifferentiated precursor cells. Additionally, protein restriction reduced the expression of the insulin receptor gene, which is essential to the action of IGFII. Inhibition of DNA methylation in neural stem/progenitor cells in vitro increased the expression of the astrocyte-specific Gfap gene and decreased the expression of the neuron-specific Dcx gene, suggesting an impact on cell differentiation. Our data suggest a complex interaction between methyl donors and protein content in maternal diet that influence the expression of major growth factors and their receptors and therefore impact the proliferation and differentiation capacities of neural stem cells, either through external hormone signals or internal genomic regulation.     

Quality control despite mistranslation caused by an ambiguous genetic code

A high level of accuracy during protein synthesis is considered essential for life. Aminoacyl-tRNA synthetases (aaRSs) translate the genetic code by ensuring the correct pairing of amino acids with their cognate tRNAs. Because some aaRSs also produce misacylated aminoacyl-tRNA (aa-tRNA) in vivo, we addressed the question of protein quality within the context of missense suppression by Cys-tRNA(Pro), Ser-tRNA(Thr), Glu-tRNA(Gln), and Asp-tRNA(Asn). Suppression of an active-site missense mutation leads to a mixture of inactive mutant protein (from translation with correctly acylated aa-tRNA) and active enzyme indistinguishable from the wild-type protein (from translation with misacylated aa-tRNA). Here, we provide genetic and biochemical evidence that under selective pressure, Escherichia coli not only tolerates the presence of misacylated aa-tRNA, but can even require it for growth. Furthermore, by using mass spectrometry of a reporter protein not subject to selection, we show that E. coli can survive the ambiguous genetic code imposed by misacylated aa-tRNA tolerating up to 10% of mismade protein. The editing function of aaRSs to hydrolyze misacylated aa-tRNA is not essential for survival, and the EF-Tu barrier against misacylated aa-tRNA is not absolute. Rather, E. coli copes with mistranslation by triggering the heat shock response that stimulates nonoptimized polypeptides to achieve a native conformation or to be degraded. In this way, E. coli ensures the presence of sufficient functional protein albeit at a considerable energetic cost.