Unexpected Phenotype of Mice Lacking Shcbp1, a Protein Induced during T Cell Proliferation

T cell development and activation are highly regulated processes, and their proper execution is important for a competent immune system. Shc SH2-domain binding protein-1 (Shcbp1) is an evolutionarily conserved protein that binds to the adaptor protein ShcA. Studies in Drosophila and in cell lines have strongly linked Shcbp1 to cell proliferation, embryonic development, growth factor signaling, and tumorigenesis. Here we show that Shcbp1 expression is strikingly upregulated during the β-selection checkpoint in thymocytes, and that its expression tightly correlates with proliferative stages of T cell development. To evaluate the role for Shcbp1 during thymic selection and T cell function in vivo, we generated mice with global and conditional deletion of Shcbp1. Surprisingly, the loss of Shcbp1 expression did not have an obvious effect during T cell development. However, in a mouse model of experimental autoimmune encephalomyelitis (EAE), which depends on CD4⁺ T cell function and mimics multiple features of the human disease multiple sclerosis, Shcbp1 deficient mice had reduced disease severity and improved survival, and this effect was T cell intrinsic. These data suggest that despite the striking upregulation of Shcbp1 during T cell proliferation, loss of Shcbp1 does not directly affect T cell development, but regulates CD4⁺ T cell effector function in vivo.     

Chemical-induced formation of BZ-junction with base extrusion

The crystal structure of BZ-junction reveals that left-handed Z-DNA stabilized by Z-DNA binding domain (Zα) is continuously stacked to right-handed B-DNA with AT bases’ extrusion in the junction site. However, this structure might not fully represent the BZ-junction in solution due to the possibility of the junction formation either by crystal packing or Zα interaction. Therefore, we investigated BZ-junction in solution with chemical Z-DNA inducers using CD and 2-aminopurine base-extrusion assay. We confirmed the formation of Z-DNA and BZ-junction with base-extrusion by chemical Z-DNA inducers. However, neither typical Z-DNA nor base-extrusion could be detected with some inducers such as spermine, suggesting that the energy barrier for the formation of the BZ junction might vary depending on the Z-DNA induction conditions.     

Receptor for AGE (RAGE): weaving tangled webs within the inflammatory response

The family of RAGE ligands, including Advanced Glycation Endproducts (AGEs), S100/calgranulins, High Mobility Group Box-1 (HMGB1) and amyloid beta peptide (Abeta) and beta-sheet fibrils are highly enriched in immune and inflammatory foci. In parallel, upregulation of Receptor for AGE (RAGE) is noted in diverse forms of inflammation and autoimmunity, based on experiments examining human tissues as well as animal models. Indeed, prior to the demonstration that S100/calgranulins were signal transduction ligands of RAGE, these molecules were considered "biomarkers" of disease and disease activity in disorders such as colitis and arthritis. Premiere roles for RAGE in advancing cellular migration implicate this receptor in targeting immune cells to vulnerable foci. Once engaged, ligand-RAGE interaction in inflammatory and vascular cells amplifies upregulation of inflammatory cytokines, adhesion molecules and matrix metalloproteinases (MMPs). Discerning the primal versus chronic injury-provoking roles for this ligand-receptor interaction is a challenge in delineating the functions of the ligand/RAGE axis. As RAGE is expressed by many of the key cell types linked integrally to the immune response, we propose that the sites and time course of ligand-RAGE stimulation determine the phenotype produced by this axis. Ultimately, drawing the fine line between antagonism versus stimulation of the receptor in health and disease will depend on the full characterization of RAGE in repair versus injury.     

Transbuccal delivery of 5-aza-2 -deoxycytidine: effects of drug concentration, buffer solution, and bile salts on permeation

Delivery of 5-aza-2 -deoxycytidine (decitabine) across porcine buccal mucosa was evaluated as an alternative to the complex intravenous infusion regimen currently used to administer the drug. A reproducible high-performance liquid chromatography method was developed and optimized for the quantitative determination of this drug. Decitabine showed a concentration-dependent passive diffusion process across porcine buccal mucosa. An increase in the ionic strength of the phosphate buffer from 100 to 400 mM decreased the flux from 3.57 +/- 0.65 to 1.89 +/- 0.61 microg/h/cm2. Trihydroxy bile salts significantly enhanced the flux of decitabine at a 100 mM concentration (P > .05). The steady-state flux of decitabine in the presence of 100 mM of sodium taurocholate and sodium glycocholate was 52.65 +/- 9.48 and 85.22 +/- 7.61 microg/cm2/h, respectively. Two dihydroxy bile salts, sodium deoxytaurocholate and sodium deoxyglycocholate, showed better enhancement effect than did trihydroxy bile salts. A 38-fold enhancement in flux was achieved with 10 mM of sodium deoxyglycocholate.     

Opposing roles of RAGE and Myd88 signaling in extensive liver resection

In extensive liver resection secondary to primary or metastatic liver tumors, or in living donor liver transplantation, strategies to quell deleterious inflammatory responses and facilitate regeneration are essential. The receptor for advanced glycation endproducts (RAGE) and myeloid differentiating factor 88 (Myd88) are implicated in the inflammatory response. To establish the contributions of RAGE vs. Myd88 signaling in extensive liver resection, we probed the effect of RAGE and/or Myd88, the latter primarily a key transducer of major toll-like receptors and also implicated in interleukin-1 (Il1) signaling, in a murine model of extensive (85%) hepatectomy. We report that, although Myd88 is thoroughly essential for survival via regulation of NF-κB and TNF-α, deletion of RAGE significantly improved survival compared to wild-type, Myd88-null, or RAGE-null/Myd88-null mice. RAGE opposes Myd88 signaling at multiple levels: by suppression of p65 levels, thereby reducing activation of NF-κB and consequent production of cyclin D1, and by suppression of Il6-mediated phosphorylation of Stat3, thereby down-regulating Pim1 and suppressing the hyperplastic response. Further, RAGE-dependent suppression of glyoxalase1, a detoxification pathway for pre-AGEs, enhances AGE levels and suppresses Il6 action. We conclude that blockade of RAGE may rescue liver remnants from the multiple signals that preclude adaptive proliferation triggered primarily by Myd88 signaling pathways.     

CCL5 modulates pneumococcal immunity and carriage

Understanding the requirements for protection against pneumococcal carriage and pneumonia will greatly benefit efforts in controlling these diseases. Recently, it has been shown that genetic polymorphisms can result in diminished expression of CCL5, which results in increased susceptibility to and progression of infectious diseases. We show that CCL5, together with Th cytokine mRNA expression, is temporally up-regulated during pneumococcal carriage. To determine the contribution of CCL5 to pneumococcal surface antigen A-specific humoral and cellular pneumococcal immunity, mice were treated with anti-CCL5 or control Abs before and during Streptococcus pneumoniae strain EF3030-challenge for the initiation of carriage. CCL5 blockade resulted in a decrease of CD4(+) and CD8(+) T cells as well as CD11b(+) cells in the spleen, cervical lymph node, lung, and nasopharyngeal associated lymphoid tissue during the recognition phase of the pneumococcal adaptive immune response. CCL5 blockade significantly reduced the Ag-specific IgG2a and IgG1 Abs in serum and IgA Ab levels in nasal washes. These decreases also corresponded to reductions in Ag-specific T cell (mucosal and systemic) responses. CCL5 inhibition resulted in decreasing the quantity of IL-4- and IFN-gamma-secreting CD4(+) T cells and increasing the number of Ag-specific IL-10-producing CD4(+) T cells; these changes combined also corresponded with the transition from pneumococcal carriage to lethal pneumonia. These data suggest that CCL5 is an essential factor for the induction and maintenance of protective pneumococcal immunity.     

Characterization of a novel interaction between ELMO1 and ERM proteins

ERMs are closely related proteins involved in cell migration, cell adhesion, maintenance of cell shape, and formation of microvilli through their ability to cross-link the plasma membrane with the actin cytoskeleton. ELMO proteins are also known to regulate actin cytoskeleton reorganization through activation of the small GTPbinding protein Rac via the ELMO-Dock180 complex. Here we showed that ERM proteins associate directly with ELMO1 as purified recombinant proteins in vitro and at endogenous levels in intact cells. We mapped ERM binding on ELMO1 to the N-terminal 280 amino acids, which overlaps with the region required for binding to the GTPase RhoG, but is distinct from the C-terminal Dock180 binding region. Consistent with this, ELMO1 could simultaneously bind both radixin and Dock180, although radixin did not alter Rac activation via the Dock180-ELMO complex. Most interestingly, radixin binding did not affect ELMO binding to active RhoG and a trimeric complex of active RhoG-ELMO-radixin could be detected. Moreover, the three proteins colocalized at the plasma membrane. Finally, in contrast to most other ERM-binding proteins, ELMO1 binding occurred independently of the state of radixin C-terminal phosphorylation, suggesting an ELMO1 interaction with both the active and inactive forms of ERM proteins and implying a possible role of ELMO in localizing or retaining ERM proteins in certain cellular sites. Together these data suggest that ELMO1-mediated cytoskeletal changes may be coordinated with ERM protein crosslinking activity during dynamic cellular functions.     

Integrin-linked Kinase Interactions with ELMO2 Modulate Cell Polarity

Cell polarization is a key prerequisite for directed migration during development, tissue regeneration, and metastasis. Integrin-linked kinase (ILK) is a scaffold protein essential for cell polarization, but very little is known about the precise mechanisms whereby ILK modulates polarization in normal epithelia. Elucidating these mechanisms is essential to understand tissue morphogenesis, transformation, and repair. Here we identify a novel ILK protein complex that includes Engulfment and Cell Motility 2 (ELMO2). We also demonstrate the presence of RhoG in ILK–ELMO2 complexes, and the localization of this multiprotein species specifically to the leading lamellipodia of polarized cells. Significantly, the ability of RhoG to bind ELMO is crucial for ILK induction of cell polarization, and the joint expression of ILK and ELMO2 synergistically promotes the induction of front-rear polarity and haptotactic migration. This places RhoG–ELMO2–ILK complexes in a key position for the development of cell polarity and forward movement. Although ILK is a component of many diverse multiprotein species that may contribute to cell polarization, expression of dominant-negative ELMO2 mutants is sufficient to abolish the ability of ILK to promote cell polarization. Thus, its interaction with ELMO2 and RhoG is essential for the ability of ILK to induce front-rear cell polarity.