A New Role of the Complement System: C3 Provides Protection in a Mouse Model of Lung Infection with Intracellular Chlamydia psittaci

The complement system modulates the intensity of innate and specific immunity. While it protects against infections by extracellular bacteria its role in infection with obligate intracellular bacteria, such as the avian and human pathogen Chlamydia (C.) psittaci, is still unknown. In the present study, knockout mice lacking C3 and thus all main complement effector functions were intranasally infected with C. psittaci strain DC15. Clinical parameters, lung histology, and cytokine levels were determined. A subset of infections was additionally performed with mice lacking C5 or C5a receptors. Complement activation occurred before symptoms of pneumonia appeared. Mice lacking C3 were ∼100 times more susceptible to the intracellular bacteria compared to wild-type mice, with all C3^−/− mice succumbing to infection after day 9. At a low infective dose, C3^−/− mice became severely ill after an even longer delay, the kinetics suggesting a so far unknown link of complement to the adaptive, protective immune response against chlamydiae. The lethal phenotype of C3^−/− mice is not based on differences in the anti-chlamydial IgG response (which is slightly delayed) as demonstrated by serum transfer experiments. In addition, during the first week of infection, the absence of C3 was associated with partial protection characterized by reduced weight loss, better clinical score and lower bacterial burden, which might be explained by a different mechanism. Lack of complement functions downstream of C5 had little effect. This study demonstrates for the first time a strong and complex influence of complement effector functions, downstream of C3 and upstream of C5, on the outcome of an infection with intracellular bacteria, such as C. psittaci.     

On the mechanism of sequence-specific DNA-dependent acetylation of p53: the acetylation motif is exposed upon DNA binding

P53 acetylation requires p300-docking to two contiguous sites in the activation domain that in turn mediates DNA-dependent acetylation of the tetramer. In an attempt to further define the mechanism of DNA-dependent acetylation of p53, an in vitro system has been reconstituted with distinct p53 isoforms and has been used to reveal conformational constraints on p53 acetylation. Two native p53 tetrameric isoforms purified from Sf9 cells differing by the extent of phosphorylation within the C-terminal acetylation site are both acetylated in a sequence-specific DNA-dependent manner. By contrast, p53 purified from an Escherichia coli expression system is in a largely denatured conformation and its acetylation is DNA-independent. Heating native p53 to destroy the folded structure restores DNA-independent acetylation similar to that seen with bacterially expressed p53. There are at least two sites of conformational flexibility in the p53 tetramer: the first in the flexible S10 beta-sheet within the MDM2 ubiquitination sequence and the second in the C-terminal regulatory domain. We analysed therefore whether DNA-dependent acetylation correlated with conformational changes in either of these two regions. DNA-dependent acetylation of p53 is maintained in a dose-dependent manner by low concentrations of consensus site DNA under conditions where flexibility in the S10 beta-sheet region is maintained. Oligonucleotide DNAs that promote acetylation stimulate the binding of monoclonal antibodies PAb421 and ICA-9; two antibodies whose contiguous epitopes overlap the C-terminal acetylation motif. By contrast, bent oligonucleotide DNAs that conceal both the S10 beta-sheet from binding of the monoclonal antibody DO-12 and attenuate binding of the monoclonal antibody PAb421 can preclude acetylation. These data suggest that, in the absence of DNA, the acetylation motif of p53 is in a cryptic state, but after DNA binding, allosteric effects mediate an exposure of the acetylation motif to allow DNA-dependent acetylation of the tetramer.     

An alternative transcript from the death-associated protein kinase 1 locus encoding a small protein selectively mediates membrane blebbing

Death-associated protein kinase 1 (DAPK-1) is a multidomain protein kinase with diverse roles in autophagic, apoptotic and survival pathways. Bioinformatic screens were used to identify a small internal mRNA from the DAPK-1 locus (named s-DAPK-1). This encodes a 295 amino acid polypeptide encompassing part of the ankyrin-repeat domain, the P-loop motifs, part of the cytoskeletal binding domain of DAPK-1, and a unique C-terminal 'tail' extension not present in DAPK-1. Expression of s-DAPK-1 mRNA was detected in a panel of normal human tissues as well as primary colorectal cancers, indicating that its expression occurs in vivo. s-DAPK-1 gene transfection into cells produces two protein products: one with a denatured mass of 44 kDa, and a smaller product of 40 kDa. Double alanine mutation of the C-terminal tail extension of s-DAPK-1 (Gly296/Arg297) prevented production of the 40 kDa fragment, suggesting that the smaller product is generated by in vivo proteolytic processing. The s-DAPK-1 gene cannot substitute for full-length DAPK-1 in an mitogen-activated protein kinase kinase/extracellular signal-regulated kinase-dependent apoptotic transfection assay. However, the transfection of s-DAPK-1 was able to mimic full-length DAPK-1 in the induction of membrane blebbing. The 44 kDa protease-resistant mutant s-DAPK-1G296A/R297A had very low activity in membrane blebbing, whereas the 40 kDa s-DAPK-1Deltatail protein exhibited the highest levels of membrane blebbing. Deletion of the tail extension of s-DAPK-1 increased its half-life, shifted the equilibrium of the protein from cytoskeletal to soluble cytosolic pools, and altered green fluorescent protein-tagged s-DAPK-1 protein localization as observed by confocal microscopy. These data highlight the existence of an alternative product of the DAPK-1 locus, and suggest that proteolytic removal of the C-terminal tail of s-DAPK-1 is required to stimulate maximally its membrane-blebbing function.     

Superantigen-induced CD4 memory T cell anergy. I. Staphylococcal enterotoxin B induces Fyn-mediated negative signaling

Memory CD4 T cells must provide robust protection for an organism while still maintaining self-tolerance. Superantigens reveal a memory cell-specific regulatory pathway, by which signaling through the TCR can lead to clonal tolerance (anergy). Here we show that the src kinase Fyn is a critical regulator of anergy in murine memory CD4 T cells induced by the bacterial superantigen staphylococcal enterotoxin B (SEB). Exposure to SEB results in impaired TCR signaling due to failed CD3/ZAP-70 complex formation. Further, signal transduction through the TCR remains similarly blocked when anergic memory cells are subsequently exposed to agonist peptide antigen. Pharmacological inhibition or genetic elimination of Fyn kinase reverses memory cell anergy, resulting in SEB-induced cell proliferation. The mechanism underlying impaired TCR signaling and subsequent memory cell anergy must involve a Fyn signaling pathway given that the suppression of Fyn activity restores CD3/ZAP-70 complex formation and TCR proximal signaling.     

Effects of immobilization stress on tuberoinfundibular dopaminergic (TIDA) neuronal activity and prolactin levels in lactating and non-lactating female rats.

The effects of immobilization stress on the prolactin secretory response and on the activity of the tuberoinfundibular dopaminergic (TIDA) neurons were determined in intact, virgin female rats on the morning of diestrus or proestrus and in post-partum, lactating female rats. The virgin females exhibited a significant increase in circulating levels of prolactin which was evident by 1 minute and persisted during the immobilization (5 minutes). In contrast, the prolactin secretory response in lactating females was significantly attenuated compared to non-lactating animals. The activity of the TIDA neurons was not altered by the 5 minutes of stress. Even after 30 minutes of immobilization, TIDA neuronal activity was not affected in either the lactating or cycling females. These data suggest that the cycling female rat is capable of a prolactin secretory response to the stressor without inhibition of TIDA neuronal activity. It seems likely that prolactin releasing factors mediate this response. In contrast, stress did not produce a similar prolactin increase during lactation. It seems likely that, during lactation, the pituitary is not sensitive to releasing factors unless the TIDA neurons are inhibited. There appear to be differences in the sensitivity of the pituitary depending on the physiological state of the model employed.     

Protein-cationic detergent interaction. Interaction of bovine serum albumin and other proteins with alkylpyridinium bromides studied by viscosity, gel filtration and spin-label methods.

Viscosity, gel filtration and spin-labelling methods have been used to study the influence of alkylpyridinium bromides on the conformation of bovine serum albumin and other proteins. Cationic detergents cause partial unfolding of the native protein molecules. The magnitude of these changes increases with increasing length of the detergent hydrocarbon chain. When cationic detergents are added to reduced and carboxymethylated bovine serum albumin the observed changes are opposite to those found in native protein.     

Lack of involvement of dopamine and serotonin during the orphanin FQ/Nociceptin (OFQ/N)-induced prolactin secretory response

The purpose of these studies was to examine possible mechanisms of Orphanin FQ/Nociceptin (OFQ/N)-induced prolactin release. We investigated the involvement of the dopaminergic neurons by quantifying DOPAC:DA levels in the median eminence and neurointermediate lobe following central administration of OFQ/N to female Sprague-Dawley rats. To specifically determine the involvement of the tuberoinfundibular dopaminergic neurons, immunocytochemical studies were conducted to visualize c-fos protein expression in the arcuate nucleus following central administration of OFQ/N. In addition, the role of serotonergic activation was examined in dose response studies using the selective serotonin antagonist ritansarin and the nonselective antagonist metergoline. Finally, the pharmacological specificity of the prolactin response was examined by pretreating animals with [Nphe1] NC (1-13)NH2, a drug reported to antagonize OFQ/N effects. The results of these studies indicate that the increase in prolactin release following central administration of OFQ/N does not inhibit tuberoinfundibular, tuberohypophyseal or periventricular hypophysial dopaminergic neuronal activity at 10 min after drug administration, a time when prolactin levels were significantly elevated. Furthermore, serotonergic activation is not involved since pharmacological blockade of serotonergic receptors did not alter the prolactin secretory response to OFQ/N. NC (1-13)NH2 did not antagonize the stimulatory effects of OFQ/N on prolactin secretion. The neural effects of OFQ/N on dopaminergic neuronal activity may occur following a different time course than that of the prolactin increase.     

[35S]Thiosulphate oxidation by rat liver mitochondria in the presence of glutathione

1. Rat liver mitochondria incubated in oxygen with glutathione and [(35)S]-thiosulphate produced labelled sulphate. 2. Inner-labelled thiosulphate (S.(35)SO(3))(2-) was converted into [(35)S]sulphate more rapidly than outer-labelled thiosulphate ((35)S.SO(3))(2-). 3. Thiosulphate labelled in both sulphur atoms was formed during ((35)S.SO(3))(2-) oxidation; the outer sulphur atom before oxidation to sulphate was incorporated into the inner position. 4. A thiosulphate cycle in the metabolic pathway of sulphate formation in animal tissues is discussed.