On the mechanism of protective action of cold acclimatization against carbon tetrachloride - and ethionine-induced fatty liver

In this study the hepatic lipoprotein lipase (LPL), activity was evaluated in adult female mice acclimatized at 5-C and submitted to carbon tetrachloride (CCI) or ethionine, in order to determine the possible role of this enzuyme in the fatty liver. The results were compared with those obtained in mice kept at room temperature (27-C) that the same hepatoesteatosis inducing agent. In contrast to animals kept at room temperature, in cold aclimatized mice neither the enhancement of the LPL-liver activity by the action of CCI or ethionine occurred nor the development of fatty infiltration in the liver was observed. We conclude that the low temperature induced a protective effect against CCI or ethionine-induced fatty liver that was correlated with the no-increase of the hepatic LPL activity.

Disease-causing mutations improving the branch site and polypyrimidine tract: pseudoexon activation of LINE-2 and antisense Alu lacking the poly(T)-tail.

Cryptic exons or pseudoexons are typically activated by point mutations that create GT or AG dinucleotides of new 5' or 3' splice sites in introns, often in repetitive elements. Here we describe two cases of tetrahydrobiopterin deficiency caused by mutations improving the branch point sequence and polypyrimidine tracts of repeat-containing pseudoexons in the PTS gene. In the first case, we demonstrate a novel pathway of antisense Alu exonization, resulting from an intronic deletion that removed the poly(T)-tail of antisense AluSq. The deletion brought a favorable branch point sequence within proximity of the pseudoexon 3' splice site and removed an upstream AG dinucleotide required for the 3' splice site repression on normal alleles. New Alu exons can thus arise in the absence of poly(T)-tails that facilitated inclusion of most transposed elements in mRNAs by serving as polypyrimidine tracts, highlighting extraordinary flexibility of Alu repeats in shaping intron-exon structure. In the other case, a PTS pseudoexon was activated by an A>T substitution 9 nt upstream of its 3' splice site in a LINE-2 sequence, providing the first example of a disease-causing exonization of the most ancient interspersed repeat. These observations expand the spectrum of mutational mechanisms that introduce repetitive sequences in mature transcripts and illustrate the importance of intronic mutations in alternative splicing and phenotypic variability of hereditary disorders.

IL-13 induces expression of CD36 in human monocytes through PPARgamma activation.

The class B scavenger receptor CD36 is a component of the pattern recognition receptors on monocytes that recognizes a variety of molecules. CD36 expression in monocytes depends on exposure to soluble mediators. We demonstrate here that CD36 expression is induced in human monocytes following exposure to IL-13, a Th2 cytokine, via the peroxisome proliferator-activated receptor (PPAR)gamma pathway. Induction of CD36 protein was paralleled by an increase in CD36 mRNA. The PPARgamma pathway was demonstrated using transfection of a PPARgamma expression plasmid into the murine macrophage cell line RAW264.7, expressing very low levels of PPARgamma, and in peritoneal macrophages from PPARgamma-conditional null mice. We also show that CD36 induction by IL-13 via PPARgamma is dependent on phospholipase A2 activation and that IL-13 induces the production of endogenous 15-deoxy-Delta12,14-prostaglandin J2, an endogenous PPARgamma ligand, and its nuclear localization in human monocytes. Finally, we demonstrate that CD36 and PPARgamma are involved in IL-13-mediated phagocytosis of Plasmodium falciparum-parasitized erythrocytes. These results reveal a novel role for PPARgamma in the alternative activation of monocytes by IL-13, suggesting that endogenous PPARgamma ligands, produced by phospholipase A2 activation, could contribute to the biochemical and cellular functions of CD36.

Selective bystander proliferation of memory CD4+ and CD8+ T cells upon NK T or T cell activation.

Ag-experienced or memory T cells have increased reactivity to recall Ag, and can be distinguished from naive T cells by altered expression of surface markers such as CD44. Memory T cells have a high turnover rate, and CD8(+) memory T cells proliferate upon viral infection, in the presence of IFN-alphabeta and/or IL-15. In this study, we extend these findings by showing that activated NKT cells and superantigen-activated T cells induce extensive bystander proliferation of both CD8(+) and CD4(+) memory T cells. Moreover, proliferation of memory T cells can be induced by an IFN-alphabeta-independent, but IFN-gamma- or IL-12-dependent pathway. In these conditions of bystander activation, proliferating memory (CD44(high)) T cells do not derive from activation of naive (CD44(low)) T cells, but rather from bona fide memory CD44(high) T cells. Together, these data demonstrate that distinct pathways can induce bystander proliferation of memory T cells.

A new function of the Fas-FasL pathway in macrophage activation.

Upon infection with the protozoan parasite Leishmania major, susceptible BALB/c mice develop unhealing lesions associated with the maturation of CD4(+)Th2 cells secreting IL-4. In contrast, resistant C57BL/6 mice heal their lesions, because of expansion and secretion of IFN-gamma of CD4(+) Th1 cells. The Fas-FasL pathway, although not involved in Th cell differentiation, was reported to be necessary for complete resolution of lesions. We investigate here the role of IFN-gamma and IL-4 on Fas-FasL nonapoptotic signaling events leading to the modulation of macrophage activation. We show that addition of FasL and IFN-gamma to BMMø led to their increased activation, as reflected by enhanced secretion of TNF, IL-6, NO, and the induction of their microbicidal activity, resulting in the killing of intracellular L. major. In contrast, the presence of IL-4 decreased the synergy of IFN-gamma/FasL significantly on macrophage activation and the killing of intracellular L. major. These results show that FasL synergizes with IFN-gamma to activate macrophages and that the tight regulation by IFN-gamma and/or IL-4 of the nonapoptotic signaling events triggered by the Fas-FasL pathway affects significantly the activation of macrophages to a microbicidal state and may thus contribute to the pathogenesis of L. major infection.

Transcriptional activation of the utrophin promoter B by a constitutively active Ets-transcription factor.

Duchenne muscular dystrophy is an X-linked genetic disease caused by the absence of functional dystrophin. Pharmacological upregulation of utrophin, the autosomal homologue of dystrophin, offers a potential therapeutic approach to treat Duchenne patients. Full-length utrophin mRNA is transcribed from two alternative promoters, called A and B. In contrast to the utrophin promoter A, little is known about the factors regulating the activity of the utrophin promoter B. Computer analysis of this second promoter revealed the presence of several conserved binding motives for Ets-transcription factors. Using electrotransfer of cDNA into mouse muscles, we demonstrate that a genetically modified beta-subunit of the Ets-transcription factor GA-binding protein potently activates a utrophin promoter B reporter construct in innervated muscle fibers in vivo. These results make the GA-binding protein and the signaling cascade regulating its activity in muscle cells, potential targets for the pharmacological modulation of utrophin expression in Duchenne patients.

The Arabidopsis bHLH transcription factors MYC3 and MYC4 are targets of JAZ repressors and act additively with MYC2 in the activation of jasmonate responses.

Jasmonates (JAs) trigger an important transcriptional reprogramming of plant cells to modulate both basal development and stress responses. In spite of the importance of transcriptional regulation, only one transcription factor (TF), the Arabidopsis thaliana basic helix-loop-helix MYC2, has been described so far as a direct target of JAZ repressors. By means of yeast two-hybrid screening and tandem affinity purification strategies, we identified two previously unknown targets of JAZ repressors, the TFs MYC3 and MYC4, phylogenetically closely related to MYC2. We show that MYC3 and MYC4 interact in vitro and in vivo with JAZ repressors and also form homo- and heterodimers with MYC2 and among themselves. They both are nuclear proteins that bind DNA with sequence specificity similar to that of MYC2. Loss-of-function mutations in any of these two TFs impair full responsiveness to JA and enhance the JA insensitivity of myc2 mutants. Moreover, the triple mutant myc2 myc3 myc4 is as impaired as coi1-1 in the activation of several, but not all, JA-mediated responses such as the defense against bacterial pathogens and insect herbivory. Our results show that MYC3 and MYC4 are activators of JA-regulated programs that act additively with MYC2 to regulate specifically different subsets of the JA-dependent transcriptional response.

A role for the src family kinase Fyn in NK cell activation and the formation of the repertoire of Ly49 receptors.

NK cell function is regulated by a dual receptor system, which integrates signals from triggering receptors and MHC class I-specific inhibitory receptors. We show here that the src family kinase Fyn is required for efficient, NK cell-mediated lysis of target cells, which lack both self-MHC class I molecules and ligands for NKG2D, an activating NK cell receptor. In contrast, NK cell inhibition by the MHC class I-specific receptor Ly49A was independent of Fyn, suggesting that Fyn is specifically required for NK cell activation via non-MHC receptor(s). Compared to wild type, significantly fewer Fyn-deficient NK cells expressed the inhibitory Ly49A receptor. The presence of a transgenic Ly49A receptor together with its H-2(d) ligand strongly reduced the usage of endogenous Ly49 receptors in Fyn-deficient mice. These data suggest a model in which the repertoire of inhibitory Ly49 receptors is formed under the influenced of Fyn-dependent NK cell activation as well as the respective MHC class I environment. NK cells may acquire Ly49 receptors until they generate sufficient inhibitory signals to balance their activation levels. Such a process would ensure the induction of NK cell self-tolerance.

Why are slip lengths so large in carbon nanotubes?

The enhanced flow in carbon nanotubes is explained using a mathematical model that includes a depletion layer with reduced viscosity near the wall. In the limit of large tubes the model predicts no noticeable enhancement. For smaller tubes the model predicts enhancement that increases as the radius decreases. An analogy between the reduced viscosity and slip-length models shows that the term slip-length is misleading and that on surfaces which are smooth at the nanoscale it may be thought of as a length-scale associated with the size of the depletion region and viscosity ratio. The model therefore provides a physical interpretation of the classical Navier slip condition and explains why `slip-lengths' may be greater than the tube radius.

Caspase-8 and c-FLIPL associate in lipid rafts with NF-kappaB adaptors during T cell activation.

Humans and mice lacking functional caspase-8 in T cells manifest a profound immunodeficiency syndrome due to defective T cell antigen receptor (TCR)-induced NF-kappaB signaling and proliferation. It is unknown how caspase-8 is activated following T cell stimulation, and what is the caspase-8 substrate(s) that is necessary to initiate T cell cycling. We observe that following TCR ligation, a small portion of total cellular caspase-8 and c-FLIP(L) rapidly migrate to lipid rafts where they associate in an active caspase complex. Activation of caspase-8 in lipid rafts is followed by rapid cleavage of c-FLIP(L) at a known caspase-8 cleavage site. The active caspase.c-FLIP complex forms in the absence of Fas (CD95/APO1) and associates with the NF-kappaB signaling molecules RIP1, TRAF2, and TRAF6, as well as upstream NF-kappaB regulators PKC theta, CARMA1, Bcl-10, and MALT1, which connect to the TCR. The lack of caspase-8 results in the absence of MALT1 and Bcl-10 in the active caspase complex. Consistent with this observation, inhibition of caspase activity attenuates NF-kappaB activation. The current findings define a link among TCR, caspases, and the NF-kappaB pathway that occurs in a sequestered lipid raft environment in T cells.

Phenotypes of lung mononuclear phagocytes in HIV seronegative tuberculosis patients: evidence for new recruitment and cell activation

Mycobacterium tuberculosis preferentially resides in mononuclear phagocytes. The mechanisms by which mononuclear phagocytes keep M. tuberculosis in check or by which the microbe evades control to cause disease remain poorly understood. As an initial effort to delineate these mechanisms, we examined by immunostaining the phenotype of mononuclear phagocytes obtained from lungs of patients with active tuberculosis. From August 1994 to March 1995, consecutive patients who had an abnormal chest X-ray, no demostrable acid-fast bacilli in sputum specimens and required a diagnostic bronchoalveolar lavage (BAL) were enrolled. Of the 39 patients enrolled, 21 had microbiologically diagnosed tuberculosis. Thirteen of the 21 tuberculosis patients were either HIV seronegative (n = 12) or had no risk factor for HIV and constituted the tuberculosis group. For comparison, M. tuberculosis negative patients who had BAL samples taken during this time (n = 9) or normal healthy volunteers (n = 3) served as control group. Compared to the control group, the tuberculosis group had significantly higher proportion of cells expressing markers of young monocytes (UCHM1) and RFD7, a marker for phagocytic cells, and increased expression of HLA-DR, a marker of cell activation. In addition, tuberculosis group had significantly higher proportion of cells expressing dendritic cell marker (RFD1) and epithelioid cell marker (RFD9). These data suggest that despite recruitment of monocytes probably from the peripheral blood and local cell activation, host defense of the resident lung cells is insufficient to control M. tuberculosis.

The Role of Protein Kinases in Antigen-activation of Peripheral Blood Mononuclear Cells of Schistosoma mansoni Infected Individuals

T cell recognition of antigens displayed on the surface of antigen presenting cell results in rapid activation of protein tyrosine kinases and kinase C. This process leads to second messengers, such as inositol phosphates and diacylgycerol, and phosphorylation of multiple proteins. The role of different protein kinases in the activation of peripheral blood mononuclear cells (PBMC) from Schistosoma mansoni infected individuals was evaluated using genistein and H-7, specific inhibitors of protein tyrosine kinase and kinase C, respectively. Our results showed that proliferation in response to soluble egg antigen or adult worm antigen preparation of S. mansoni was reduced when PBMC were cultured in presence of protein kinase inhibitors. Using these inhibitors on in vitro granuloma reaction, we also observed a marked reduction of granuloma index. Taken together, our results suggest that S. mansoni antigen activation of PBMC involves protein kinases activity

An activation-independent role of transcription factors in insulator function.

Chromatin insulators are defined as transcriptionally neutral elements that prevent negative or positive influence from extending across chromatin to a promoter. Here we show that yeast subtelomeric anti-silencing regions behave as boundaries to telomere-driven silencing and also allow discontinuous propagation of silent chromatin. These two facets of insulator activity, boundary and silencing discontinuity, can be recapitulated by tethering various transcription activation domains to tandem sites on DNA. Importantly, we show that these insulator activities do not involve direct transcriptional activation of the reporter promoter. These findings predict that certain promoters behave as insulators and partition genomes in functionally independent domains.