Phagocytosis of Candida albicans induces apoptosis of human neutrophils

Neutrophil-mediated inflammation is terminated through the programmed cell death or apoptosis of the neutrophil, a process that can be inhibited by soluble mediators released during an inflammatory response. It has been reported, however, that the phagocytosis of intact bacteria can accelerate apoptosis. We evaluated the effects of the phagocytosis of a common nosocomial pathogen, Candida albicans, on the expression of apoptosis. Phagocytosis of killed Candida induced a dose-dependent increase in the apoptosis of normal neutrophils after 18 h of in vitro culture, from 40.7+/-9.1% to 81.7+/-4.5%, while supernatants from neutrophil:Candida co-cultures actually inhibited apoptosis. Induction of apoptosis was not dependent on phagocytosis, since opsonization of yeast with serum failed to increase apoptosis, while inhibition of phagocytosis with latrunculin B resulted in a slightly increased apoptotic rate. Increased apoptosis induced by Candida was associated with increased activity of the membrane-associated apoptotic enzyme, caspase 8, and with increased expression of the active form of the key executioner caspase, caspase 3. Increased apoptosis was associated with depletion of intracellular glutathione (GSH), and could be inhibited by the addition of exogenous GSH. These data demonstrate an important physiologic role for host-pathogen interactions in the resolution of inflammation and suggest that the response to an invading pathogen is an important stimulus to the restoration of normal immunologic homeostasis.

The AF-1 and AF-2 activating domains of retinoic acid receptor-alpha (RARalpha) and their phosphorylation are differentially involved in parietal endodermal differentiation of F9 cells and retinoid-induced expression of target genes

Retinoic acid (RA) induces the differentiation of F9 cells cultured as monolayers into primitive endodermal-like cells, whereas a combination of RA and cAMP leads to parietal endodermal differentiation. In RA receptor alpha-null F9 cells (RARalpha-/- cells), RA still efficiently triggers RARgamma-mediated primitive endodermal differentiation, but parietal endodermal differentiation is markedly delayed. To investigate the role of RARalpha1 activation functions AF-1 and AF-2 and of their phosphorylation sites during RA- and cAMP-induced parietal differentiation, cell lines reexpressing WT or mutated RARalpha1 were established in RARalpha-/- cells. We have found that the protein kinase A (PKA) phosphorylation site and the AF-2AD core (helix 12) of RARalpha1 are required for efficient parietal endodermal differentiation, whereas the AF-1 proline-directed kinase phosphorylation site is dispensible. Interestingly, deletion of the AF-1 activating domain (the A/B region), but not of the AF-2AD core, generates a dominant negative mutant that abrogates primitive endodermal differentiation when expressed in RARalpha-/- cells. We also show that the RARalpha AF-1 and AF-2 activation functions, but not their phosphorylation sites, are involved in the induction of RA-responsive genes in a differential promoter context-dependent manner.

Effects of hypoxia on granulocytic-monocytic progenitors in rats. Role of bone marrow stroma

Hemorrhagic shock leads to hypoxia and is associated with bone marrow (BM) failure. Hemorrhagic shock is also a predisposing factor in immune dysregulation. Since the BM is the major organ of immune cells in the adult, its failure following hemorrhagic shock may explain the increased susceptibility to infection. The in vitro evidence indicates that hypoxia mediates altered functions in BM stroma. Since similar hematopoietic alterations are reported in hypoxia and hemorrhagic shock, hypoxia alone could be a representative model to study BM responses during hemorrhagic shock. In this study, we use an animal model to dissect the hematopoietic effects of hypoxia. We subjected rats to hypoxia, and at days 1 and 5 post-hypoxia we determined the numbers of granulocytic-monocytic progenitors (CFU-GM) in the BM. We found significant increase (P < 0.05) in CFU-GM at day 1 and a downward trend by day 5. Enhanced BM cellularity could not explain the increase in CFU-GM by day 1. BM stromal cells mediated most of the stimulatory effects by hypoxia. CFU-GM was inversely proportional to bioactive TGF-beta and directly proportional to IL-1. Compared to normoxic rats, IL-6 production was suppressed in BM cells from hypoxic rats. The results show that hypoxia alone initiate a stimulatory response in CFU-GM progenitors. These effects are at least partially mediated through the BM stroma. In the absence of a second insult, CFU-GM reverts to baseline. The data also suggest that hypoxia mediates complex responses that include cytokine production. These results add to the current understanding of hematopoietic responses by hypoxia and adds to the mechanisms of immune dysfunctions following hemorrhagic shock.

Stra13 expression is associated with growth arrest and represses transcription through histone deacetylase (HDAC)-dependent and HDAC-independent mechanisms

Stra13 is a transcriptional repressor related within its basic helix-loop-helix domain with the Drosophila Hairy, Enhancer of Split, and the mouse Hes1 proteins that interact with the corepressor Groucho. Because Stra13 lacks the conserved WRPW motif for interaction with Groucho, we examined the function and mechanism of transcriptional repression mediated by Stra13 that exhibits several distinctive features. Here, we report that Stra13 expression is closely associated with cell growth arrest induced by several triggers such as retinoic acid and trichostatin A (TSA; a specific histone deacetylase inhibitor) as well as by serum starvation. Stra13 expression is transcriptionally repressed and maintained at a low level in cells through a negative autoregulatory mechanism that is brought about by its interaction with the corepressor histone deacetylase (HDAC1). This interaction requires the Stra13 C-terminal domain containing three alpha-helices, which are also functionally critical to its repressive activity. Thus, inhibition of HDAC activity by TSA abrogates Stra13-mediated repression of its promoter, resulting in induction of Stra13 expression that is coincident with TSA-induced growth arrest. Further, once induced, Stra13 strongly represses the expression of the cell proliferation-associated gene c-Myc through an HDAC1-independent pathway that involves its interaction with the basal transcription factor TFIIB. Our studies indicate that Stra13 may play a key role in signaling pathways that lead to growth arrest and terminal differentiation by repression of target genes via HDAC-dependent and HDAC-independent mechanisms.

Phosphorylation of activation functions AF-1 and AF-2 of RAR alpha and RAR gamma is indispensable for differentiation of F9 cells upon retinoic acid and cAMP treatment

The role of RAR alpha 1 and RAR gamma 2 AF-1 and AF-2 activation functions and of their phosphorylation was investigated during RA-induced primitive and parietal differentiation of F9 cells. We found that: (i) primitive endodermal differentiation requires RAR gamma 2, whereas parietal endodermal differentiation requires both RAR gamma 2 and RAR alpha 1, and in all cases AF-1 and AF-2 must synergize; (ii) primitive endodermal differentiation requires the proline-directed kinase site of RAR gamma 2-AF-1, whereas parietal endodermal differentiation additionally requires that of RAR alpha 1-AF-1; (iii) the cAMP-induced parietal endodermal differentiation also requires the protein kinase A site of RAR alpha-AF-2, but not that of RAR gamma; and (iv) the AF-1-AF-2 synergism and AF-1 phosphorylation site requirements for RA-responsive gene induction are promoter context-dependent. Thus, AF-1 and AF-2 of distinct RARs exert specific cellular and molecular functions in a cell-autonomous system mimicking physiological situations, and their phosphorylation by kinases belonging to two main signalling pathways is required to enable RARs to transduce the RA signal during F9 cell differentiation.

Overexpression of Stra13, a novel retinoic acid-inducible gene of the basic helix-loop-helix family, inhibits mesodermal and promotes neuronal differentiation of P19 cells

We report the cDNA cloning of Stra13, a novel retinoic acid (RA)-inducible gene from P19 embryonal carcinoma cells that encodes a basic helix-loop-helix (bHLH) protein that shows the highest sequence similarities to the Drosophila Hairy and Enhancer of split and mouse Hes proteins. Stra13 does not bind to the known consensus motifs (E-box and N-box) for bHLH proteins, but can repress activated transcription (through an alpha-helix rich domain) in part by interaction with general factors of the basal transcription machinery. During mouse embryogenesis, Stra13 RNA is expressed in the neuroectoderm, and also in a number of mesodermal and endodermal derivatives. Remarkably, overexpression of Stra13 in P19 cells results in neuronal differentiation in monolayer culture, under conditions where wild-type P19 cells only undergo mesodermal/endodermal differentiation. This neuronal differentiation is accompanied by an altered expression of mesodermal and neuronal markers, indicating that Stra13 could be one of the earliest RA target genes whose expression is required for repression of mesodermal/endodermal differentiation and/or induction of neuronal differentiation when P19 cell aggregates are exposed to RA. Our results raise the possibility that Stra13 could be involved as a repressor in a number of decision events occurring during differentiation of various cell lineages.

Differential effects of acute hypoxia and endotoxin on the secretion and expression of bone marrow interleukin-1 and interleukin-6

Hemorrhagic shock induces tissue hypoxia and has been demonstrated to alter the myelopoietic response to bacterial lipopolysaccharide (LPS). Interleukin-1 and interleukin-6 are important mediators of immunologic events after hemorrhagic shock. Bone marrow stroma release inflammatory cytokines, which may play a role in the regulation of myelopoiesis after injury. The aim of this study was to correlate cytokine gene expression with protein release and myelopoiesis by total bone marrow cells. The role of bone marrow stroma after exposure to hypoxia and lipopolysaccharide was also examined. BALB/c mice were designated as normoxia or hypoxia and total bone marrow cells were harvested. Hypoxia mice were exposed to 2 h of 5% O2/95% N2, and then returned to room air. Additional groups of mice were given LPS intraperitoneally. Bone marrow stroma, from BALB/c mice, was similarly designated. Myelopoiesis was assessed by growth of granulocyte-macrophage progenitor cells (CFU-GM). Interleukin-1 and interleukin-6 protein activity was assessed by bioassay. RNA was extracted from both total bone marrow cells and bone marrow stroma. By day 5, LPS alone resulted in a 93% increase in CFU-GM versus normoxia. Hypoxia and LPS exposure significantly decreased CFU-GM on days 1, 3, and 5. LPS alone induced an increase in interleukin-6. At 2, 6, and 24 h, hypoxia blunted interleukin-6 release in response to LPS. Hypoxia alone could not induce interleukin-6. However, hypoxia did induce interleukin-1 mRNA without the release of bioactive protein. In the remainder of groups, interleukin-1 protein levels and mRNA levels were correlated. Bone marrow stroma interleukin-1 and interleukin-6 protein activity was consistently correlated with that of total bone marrow. These data demonstrate that bone marrow cytokine production is differentially regulated by hypoxia. Hypoxia impairs interleukin-6 protein and mRNA in response to LPS, which may play a role in the suppression of myelopoiesis after shock. Also, bone marrow stroma plays an integral role in regulating myelopoiesis.

The expression pattern of the mouse receptor tyrosine kinase gene MDK1 is conserved through evolution and requires Hoxa-2 for rhombomere-specific expression in mouse embryos

Segmentation of the hindbrain has been conserved throughout the vertebrate species and results in the transient formation of rhombomeres, which are lineage-restricted compartments. Studies on the molecular mechanisms underlying the segmentation process have revealed that rhombomeric boundaries coincide with the expression limits of several evolutionary conserved genes such as the zinc-finger transcription factor Krox-20 and homeobox genes which are expressed in a specific spatial and temporal order and have been shown to be important regulators of segmental identity. In addition to Krox-20 and Hox genes, several members of the Eph subfamily of receptor protein tyrosine kinase (RTK) genes are also expressed in a segment-restricted manner in the hindbrain, suggesting that these receptors may act in concert with Hox genes to establish regional identity. In the cascade of regulatory interactions leading to segmental identity, Krox-20 appears to act "upstream" of Hox genes, but the identity of the "downstream" effectors has not yet been identified. We report here the isolation of the zebrafish orthologue of the mouse RTK gene MDK1 which belongs to the Eph receptor subfamily and show that the major expression domains of the mouse and the zebrafish genes have been conserved through evolution. Since the coincident spatial and temporal expression of Hoxa-2 and MDK1 in the mouse hindbrain suggested a possible regulatory link between them, we analyzed the expression of the MDK1 in Hoxa-2 null mutant embryos. A selective lack of MDK1 expression in rhombomere 3 of Hoxa-2 mutant hindbrains together with an overall altered expression pattern in the other rhombomeres was observed, thus demonstrating that MDK1 lies downstream of Hoxa-2 in the morphogenetic signaling cascade.

Cell-type and promoter-context dependent retinoic acid receptor (RAR) redundancies for RAR beta 2 and Hoxa-1 activation in F9 and P19 cells can be artefactually generated by gene knockouts

By using RAR type (alpha, beta, or gamma)-specific synthetic retinoids and a pan-retinoic X receptor (RXR)-specific ligand, we have investigated the contribution of RARs and RXRs in the activation of RA target genes and the differentiation of embryonal carcinoma cells. We demonstrate cell-type- and promoter context-dependent functional redundancies that differ between the three RAR types for mediating the induction of RARbeta2 and Hoxa-1 in wild-type, RARgamma-/- and RARalpha-/- F9 cells and in P19 cells. The extent of redundancy between RARs is further modulated by the synergistic activation of RXRs with a pan-RXR agonist. We also demonstrate that the expression of RARbeta2 is auto-inducible in RARgamma-/- but not in wild-type F9 cells, indicating that the functional redundancies observed between RARs in gene disruption studies can be artefactually generated. Thus, even though all three RARs can functionally substitute each other for inducing the expression of RA target genes and cell differentiation, one RAR can cell-specifically override the activity of the other RARs. Interestingly, only RARgamma can mediate the retinoic acid-induced differentiation of wild-type F9 cells, whereas the differentiation of P19 cells can be mediated by either RARalpha or RARgamma.

Synergistic activation of retinoic acid (RA)-responsive genes and induction of embryonal carcinoma cell differentiation by an RA receptor alpha (RAR alpha)-, RAR beta-, or RAR gamma-selective ligand in combination with a retinoid X receptor-specific ligand

Retinoic acid receptor (RAR)-retinoid X receptor (RXR) heterodimers bind to cognate response elements in vitro more efficiently than do RAR or RXR homodimers, and both RAR and RXR partners have been shown to activate various promoters in transiently transfected cells. We have now investigated whether ligand-dependent activation of both heterodimeric partners is involved in induced expression of endogenous RA-responsive genes and in P19 and F9 cell differentiation. On their own, low concentrations of retinoids selective for either RAR alpha, RAR beta, or RAR gamma did not induce or very inefficiently induced the expression of several RA target genes or triggered differentiation. An RXR-specific synthetic retinoid was similarly inefficient at any concentration. In contrast, at the same concentrations, various combinations of RAR (RAR alpha, RAR beta, or RAR gamma) and RXR selective retinoids resulted in synergistic induction of all retinoic acid (RA) target genes examined, as well as in cell differentiation. However, the magnitude of this synergistic activation varied depending on both the RAR-RXR combination and the promoter context of the responsive genes. Promiscuous activation of the three RARs, or concomitant activation of RAR alpha and RAR gamma, at selective retinoid concentrations also resulted in induction of gene expression and cell differentiation. Taken together, our results are consistent with the conclusion that the RAR and RXR partners of RAR-RXR heterodimers can synergistically activate transcription of RA-responsive genes and can induce differentiation of P19 and F9 cells. Our results also indicate that there is a significant degree of functional redundancy between the three RAR types which, however, varies with the nature of the RA target genes.

Tuberculin screening of trauma admissions at a university hospital. A preventive strategy

OBJECTIVE

To determine the prevalence of tuberculosis (TB) infection in our trauma service population, namely, those patients who had positive Mantoux (purified protein derivative [PPD] [tuberculin]) tests.

DESIGN

Prospective study.

SETTING

Trauma service at a university hospital in Newark, NJ.

PATIENTS AND METHODS

During a 9-month period, 110 admitted trauma patients underwent screening for TB. Of these patients, 20 had undergone recent PPD tests in the last 6 months, of which nine were positive. The remaining 90 patients underwent PPD and delayed-type hypersensitivity skin tests (anergy panel); five patients were unavailable for follow-up. The patients also answered questions regarding human immunodeficiency virus status, risk factors for TB infection, and clinical symptoms.

RESULTS

The mean age of the study group was 34 years (age range, 13 to 69 years). Eighty-four percent of these patients were males who belonged to the high-risk socioeconomic, racial, and ethnic groups (poor, non-white). The tests for 15 patients (17%) were newly discovered to be positive for PPD. Eleven percent of the patients with negative PPD tests were anergic, thus raising the percentage of patients with positive PPD tests to 20%. The human immunodeficiency virus status was known in only 41% of the total patients. All patients with positive PPD tests had a chest x-ray film performed; of these patients, positive findings for TB were determined for one patient. Another patient had evidence of abdominal TB at laparotomy. All patients with positive PPD tests were given appointments in the pulmonary clinic for follow-up, and only three of 15 patients kept their appointments.

CONCLUSIONS

Patients who were admitted to the trauma service were predominantly young males from high-risk groups with a high incidence of TB infection. Their admission to the trauma service was a unique opportunity for screening and implementing existing preventive programs.

Reexpression of retinoic acid receptor (RAR) gamma or overexpression of RAR alpha or RAR beta in RAR gamma-null F9 cells reveals a partial functional redundancy between the three RAR types

Disruption of retinoic acid receptor (RAR) gamma in F9 embryonal carcinoma cells leads to aberrent differentiation and reduced activation of expression of several all-trans-retinoic acid (RA)-induced genes. We have analyzed the expression of several additional RA-responsive genes in RAR alpha- and RAR gamma-null F9 cells. The RA-induced activation of Cdx1, Gap43, Stra4, and Stra6 was specifically impaired in RAR gamma-null cells, supporting the idea that each RAR may regulate distinct subsets of target genes. To further investigate the role of RAR gamma in F9 cell differentiation, "rescue" cell lines reexpressing RAR gamma 2 or overexpressing either RAR alpha 1 or RAR beta 2 were established in RAR gamma-null cells. Reexpression of RAR gamma or overexpression of RAR alpha restored both target-gene activation and the differentiation potential. In contrast, over-expression of RAR beta only poorly restored differentiation, although it could replace RAR gamma for the activation of target genes. Functional redundancy between the various RARs is discussed.

Repair of a massive ventral hernia in a morbidly obese patient

Aggressive perioperative management, with progressive preoperative pneumoperitoneum, is a worthy method of repairing massive ventral hernias with associated loss of domain in morbidly obese patients. The authors present a case and its successful outcome.

Targeted disruption of retinoic acid receptor alpha (RAR alpha) and RAR gamma results in receptor-specific alterations in retinoic acid-mediated differentiation and retinoic acid metabolism

F9 embryonic teratocarcinoma stem cells differentiate into an epithelial cell type called extraembryonic endoderm when treated with retinoic acid (RA), a derivative of retinol (vitamin A). This differentiation is presumably mediated through the actions of retinoid receptors, the RARs and RXRs. To delineate the functions of each of the different retinoid receptors in this model system, we have generated F9 cell lines in which both copies of either the RAR alpha gene or the RAR gamma gene are disrupted by homologous recombination. The absence of RAR alpha is associated with a reduction in the RA-induced expression of both the CRABP-II and Hoxb-1 (formerly 2.9) genes. The absence of RAR gamma is associated with a loss of the RA-inducible expression of the Hoxa-1 (formerly Hox-1.6), Hoxa-3 (formerly Hox-1.5), laminin B1, collagen IV (alpha 1), GATA-4, and BMP-2 genes. Furthermore, the loss of RAR gamma is associated with a reduction in the metabolism of all-trans-RA to more polar derivatives, while the loss of RAR alpha is associated with an increase in metabolism of RA relative to wild-type F9 cells. Thus, each of these RARs exhibits some specificity with respect to the regulation of differentiation-specific gene expression. These results provide an explanation for the expression of multiple RAR types within one cell type and suggest that each RAR has specific functions.

Differential transcription of multiple copies of a silk worm gene encoding tRNA(Gly1)

Ten different tRNA(Gly1) genes from the silk worm, Bombyx mori, have been cloned and characterized. These genes were transcribed in vitro in homologous nuclear extracts from the posterior silk gland (PSG) or nuclear extracts derived from the middle silk gland or ovarian tissues. Although the transcription levels were much higher in the PSG nuclear extracts, the transcriptional efficiency of the individual genes followed a similar pattern in all the extracts. Based on the levels of in vitro transcription, the ten tRNA(Gly1) genes could be divided into three groups, viz., those which were transcribed at very high levels (e.g., clone pR8), high to medium levels (e.g., pBmi1, pBmp1, pBmh1, pBmt1) and low to barely detectable levels (e.g., pBms1, pBmj1 and pBmk1). The coding sequences of all these tRNA genes being identical, the differential transcription suggested that the flanking sequences modulate their transcriptional efficiency. The presence of positive and negative regulatory elements in the 5' flanking regions of these genes was confirmed by transcription competition experiments. A positive element was present in the immediate upstream A+T-rich sequences in all the genes, but no consensus sequences correlating to the transcriptional status could be generated. The presence of negative elements on the other hand was indicated only in some of the genes and therefore may have a role in the differential transcription of these tRNA(Gly1) genes in vivo.

Loss of retinoic acid receptor gamma function in F9 cells by gene disruption results in aberrant Hoxa-1 expression and differentiation upon retinoic acid treatment

Retinoic acid (RA) signal transduction is believed to be mediated through several high-affinity nuclear receptors [RA receptors (RARs) and retinoid X receptors], which are members of the steroid/thyroid/vitamin D superfamily and function as transcription factors. Why multiple RARs exist and what gene targets are regulated by each of the three receptors remain compelling questions in developmental biology. Through targeted disruption of both RAR gamma alleles, we have identified several differentiation-specific genes that are regulated either directly or indirectly by RAR gamma in F9 embryonal carcinoma cells. These include genes encoding Hoxa-1 (Hox-1.6) and the extracellular matrix proteins laminin B1 and collagen type IV (alpha 1), all of which are RA inducible in wild-type F9 embryonal carcinoma cells but are not significantly induced in the RAR gamma-/- lines. In contrast, transcripts encoding Hoxb-1 (Hox-2.9) and cellular RA binding protein II (CRABPII) are activated by RA for a longer period of time in the RAR gamma-/- lines compared to the wild-type F9 line. Not all RA-responsive genes are aberrantly expressed; Rex-1, RAR beta, and SPARC transcripts are regulated in the RAR gamma-/- lines as they are in F9 wild-type cells. Our results support the idea that each RAR may regulate different subsets of RA-responsive genes, which may explain, in part, the complex regulation of developmental processes by retinoids.