ALBERT

Description: Activated leukocyte cell adhesion molecule (ALCAM/CD166) is a member of the immunoglobulin super-family. It is expressed on the surfaces of activated monocytes, dendritic cells and macrophages. These immune cells use ALCAM through homotypic and heterotypic adhesions to control multiple stages in the inflammatory response. Indeed, anti-ALCAM antibodies and recombinant soluble ALCAM significantly inhibit monocyte transendothelial migration, stabilization of the immunological synapse and dendritic cell-mediated T-lymphocyte proliferation. Despite this significance, there is currently no understanding of how the human ALCAM gene is regulated. In this study, we identified the mechanisms for transcription, basal transcriptional activation and immunosuppressive silencing of the ALCAM gene. A common site for transcription of the ALCAM gene was identified 350 base pairs (bp) upstream from the translational start site. Multiple truncated fragments of the ALCAM promoter was cloned from genomic DNA and sub-cloned upstream of a promoterless luciferase vector. A proximal 650-bp promoter sequence conferred tissue-independent activation in hematopoietic, epithelial and endothelial cells. A canonical Sp1 binding sequence at −550 upstream of the translational start site was mapped within this proximal positive regulatory promoter region. Site-directed mutagenesis revealed this sequence was essential for optimum ALCAM promoter activity. Importantly, Sp1 occupied the cognate sequence in vivo as determined by chromatin immunoprecipitation assays. Over-expression of Sp1 significantly increased ALCAM promoter activity whereas a control expression vector had no impact. DNA sequences in the interval −600 to −800 negatively influenced promoter activity in a tissue-specific manner. This region contained a putative binding sequence for the aryl hydrocarbon receptor (Ahr), which highlighted ALCAM as a potential target of the immunosuppressing ligand dioxin. This hypothesis was tested by examination of whether ALCAM activation is blocked by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) in monocytes differentiating into macrophages and dendritic cells. Expression of ALCAM was increased 3–5-fold in HL-60 and THP-1 monocytes treated with the differentiating agent phorbol 12-myristate 13-acetate. TCDD dose dependently blocked this activation, indeed, the highest concentration of TCDD (25 nM) used in this study completely blocked ALCAM activation in both monocytic cells. In conclusion, we have unveiled for the first time, the molecular basis for transcription and basal trans-activation of the human ALCAM gene, and identified the Ahr-pathway as a powerful silencer of ALCAM gene activation. Further studies of the ALCAM promoter, may clarify how this gene is up-regulated as part of the inflammatory response, and how it is silenced by immunotoxins. Heterologous expression of ALCAM may be a potential strategy to mitigate the immunosuppressive effects of dioxins and polycyclic aromatic hydrocarbons.

Description: The histone deacetylase inhibitors (HDA-CIs) butyrate and trichostatin A activate γ-globin expression via a p38 mitogen-activating protein kinase (MAPK)-dependent mechanism. We hypothesized that down-stream effectors of p38 MAPK, namely activating transcription factor-2 (ATF-2) and cyclic AMP response element (CRE) binding protein (CREB), are intimately involved in fetal hemoglobin induction by these agents. In this study, we observed increased ATF-2 and CREB1 phosphorylation mediated by the HDACIs in K562 cells, in conjunction with histone H4 hyperacetylation. Moreover, enhanced DNA-protein interactions occurred in the CRE in the Gγ-globin promoter (G-CRE) in vitro after drug treatments; subsequent chromatin immunoprecipitation assay confirmed ATF-2 and CREB1 binding to the G-CRE in vivo. Enforced expression of ATF-2 and CREB produced Gγ-promoter trans-activation which was abolished by a 2-base pair mutation in the putative G-CRE. The data presented herein demonstrate that γ-gene induction by butyrate and trichostatin A involves ATF-2 and CREB1 activation via p38 MAPK signaling.

Description: Migration of endothelial cells as a sheet in fully differentiated blood vessels is essential for reducing vascular permeability during wound healing. Indeed, loss of collective endothelial sheet migration contributes to increased vascular permeability in tumor angiogenesis and several vascular proliferative disorders. Despite this significance, mechanisms responsible for keeping migrating endothelial cells in a monolayer, sheet or tube are poorly understood. To unravel the basis for collective endothelial cell migration, we used time-lapse video microscopy to study early events of wound closure in confluent monolayers of primary microvascular endothelial cells in a live cell chamber. Immediately after wounding (0– 20 min), endothelial cells at the margin of the wound (marginal cells) retracted away from the wounded area and showed no visible lamellipodia extensions. The next phase of early wound healing (20 min – 6 hours) revealed extensive lamellipodia formation and migration of marginal cells into the wounded region. Remarkably, sub-marginal endothelial cells that were several microns away from the wound edge protruded lamellipodia that formed dynamic cell-cell contacts with the substratum of marginal cells at the wound edge. In several instances sub-marginal cells physically and coordinately pulled back endothelial cells at wound edge to maintain regularity of the endothelial sheet front. Cell-tracking measurements revealed autonomous and yet coordinated migration of marginal and sub-marginal endothelial cells culminating in net protrusion of the endothelial sheet into the wound. This study provides in real-time evidence of retraction of endothelial cells at the wound edge by several microns prior to the initiation of forward migration. In addition, we show for the first time that endothelial cells several microns away from the wound edge actively participate in sheet migration through the extention of lamellipodia into the substratum of cells at the wound edge. These findings highlight an important role in endothelial sheet migration for the Rho family of GTPases given their intimate control of cell retraction and lamelipodia extensions. Future studies will directly evaluate the influence of Rac, Cdc42 and RhoA in retraction of marginal cells and formation of lamellipodia by sub-marginal cells in endothelial sheet migration.

Description: Activated leukocyte cell adhesion molecule (ALCAM/CD166) is a member of the immunoglobulin cell adhesion super family, which has been implicated in diverse physiological and pathophysiological events involving cell migration. Hitherto, ALCAM’s role in inflammation has not been determined. In this study, we show ALCAM is involved in controlling migration of mononuclear leukocytes across the pulmonary endothelium. We demonstrated that ALCAM is localized at intercellular junctions in pulmonary microvascular endothelial cells in vitro and in vivo. ALCAM co-localized with multiple adherens junction molecules including cadherins, catenins and Dlg, as determined by confocal microscopy, and these observations were confirmed by co-immunoprecipitation and co-distribution assays. Treatment of endothelial cultures with EGTA and cytochalasin D translocated ALCAM from intercellular junctions to the cytosol indicating a requirement for homotypic cadherin adhesion and an intact endothelial cytoskeleton for maintaining ALCAM at endothelial cell junctions. Collectively, these data supports the conclusion that ALCAM contributes to the adherens junction complex in endothelial cells. To determine ALCAM’s role in leukocyte-endothelial cell interactions, adult Sprague Dawley rats were intratracheally instilled with macrophage inflammatory protein-1, and this treatment caused acute expression of ALCAM exclusively in newly recruited mononuclear but not polymorphonuclear leukocytes in the alveolar airway. Given that no ALCAM reactivity was observed in peripheral blood leukocytes, we concluded ALCAM is activated as part of the phenotypic switch by mononuclear leukocytes transitioning from circulation to interstitial tissue compartments. To determine the physiological relevance of this finding we examined whether ALCAM was required for transendothelial migration using monocyte chemoattractant protein 1 (MCP-1). MCP-1 dose- and time-dependently increased the number of transmigrated THP-1 monocytes across pulmonary microvascular endothelial monolayers. Recombinant soluble ALCAM dose-dependently reduced the number of transmigrated THP-1 monocytes, whereas in control experiments recombinant soluble vascular endothelial cadherin had no effect on transmigration. This study shows for the first time that ALCAM is located at endothelial cell junctions where it is intimately involved in controlling the number of monocytes that pass through endothelial barriers. ALCAM may therefore play an essential role in the response to inflammation by enhancing recruitment of mononuclear leukocytes by inflamed tissues.

Description: Abstract 1537 Poster Board I-560 Sickle cell disease (SCD) is characterized by intravascular hemolysis generating cell-free hemoglobin at concentrations that exceed the scavenging capabilities of heme-binding plasma proteins. Heme is a major source of oxidative stress, which is widely known to increase vascular permeability and cause tissue edema. Barrier disruptive effects of oxidative stress can however be counterbalanced by adaptive antioxidant defenses. Hitherto, the identity of specific antioxidant enzymes and cognate mechanisms protecting individual organs from oxidative stress in SCD remains poorly defined. In this study, microarray analysis was performed using non-toxic concentrations of hemin to analyze mechanisms of antioxidant defense by the endothelium. Multiple candidate antioxidant enzymes were identified each differentially elevated in several major organs in anemic SCD mice compared to non-anemic heterozygote and hemizygote littermates. Remarkably, none of the antioxidants was elevated in the brain of sickle mice. Moreover, the antioxidant phenotype in the kidney, spleen and liver of sickle mice were predominantly acute while the sickle lung was characterized by a predominantly chronic antioxidant phenotype. This latter finding was confirmed in SCD patients with chronic lung disease. Antioxidant enzyme activity was significantly higher in the lungs of adult sickle mice aged 3-6 months than in younger mice aged 4-6 weeks (p=0.004). However, this enhanced antioxidant activity declined significantly in middle-age mice 11-13 months old (p=0.005). Vascular permeability assessed by extravsasation of Evans blue dye was normal in the brain of sickle mice of all ages in agreement with our data indicating absence of oxidative stress in this organ. On the contrary, vascular permeability in the lung, kidney and heart of adult sickle mice was abnormally high. This abnormality deteriorated significantly exclusively in the lung (p= 0.04) but not in the heart or kidney in middle-age mice. Increased lung permeability in middle-age sickle mice was confirmed by overt tissue edema determined by lung wet/dry weight ratios. Our study has shown for the first time that the antioxidant response to the systemic chronic hemolysis of SCD is organ-specific. Furthermore, we have identified decline of antioxidant reserve concomitant with tissue edema as potential age-dependant risk factors for fatal lung complications in SCD. Finally, our data provide a framework to develop targeted antioxidant therapies to preserve organ function in SCD. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 1538 Poster Board I-561 Circulating plasma hemoglobin contributes to major vasculopathies including pulmonary hypertension in patients who have sickle cell disease (SCD). There is an emerging concept that such vasculopathies are relatively mild because of activation of several cytoprotective pathways in SCD. The biochemical profile of plasma and the transcriptome of peripheral blood cells in patients who have SCD offer indirect support for this concept. Indeed, heme oxygenase-1 (HO-1), an acute phase enzyme that degrades heme into intermediates and byproducts with vasculoprotective properties is markedly elevated in mononuclear leukocytes of patients who have SCD. Nonetheless, the scope of the cytoprotective mechanisms of the lung and other organs impacted directly by sickle vasculopathies remain poorly appreciated. We previously identified an array of cytoprotective enzymes in lung endothelial cells chronically exposed to non-toxic concentrations of hemin in vitro. In this study, we examined the expression of NAD(P)H oxidase and candidate cytoprotective enzymes in two models of transgenic mice with SCD, and examined HO-1 expression in sickle chronic lung disease. Although NAD(P)H oxidase catalyzes reactive oxygen species generation by heme and is responsible for increased adhesion of leukocytes to the endothelium in SCD mice, there was no elevation of any of its subunits (gp91Phox and p22Phox, p47Phox, p67Phox and p40 Phox) in sickle mice lungs compared to hemizygote control mice lungs. Quantitative RT-PCR analysis revealed unexpectedly no difference in HO-1 mRNA level in sickle and non-sickle control lungs. On the contrary, analysis of the same tissues showed significantly higher NAD(P)H quinone oxidoreductase-1 (NQO1) mRNA level in both Berkeley and Townes knock-in sickle mice compared to controls (p