Regulation of progranulin expression in myeloid cells

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All- trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34+progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-κB (NF-κB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cell-specific roles for NF-κB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-κB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.

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Abstract 112: Myeloid Mineralocorticoid Receptor Controls Inflammatory and Fibrotic Responses After Renal Ischemic Injury via Macrophage Interleukin-4 Receptor

Hypertension ◽

10.1161/hyp.70.suppl_1.112 ◽

2017 ◽

Vol 70 (suppl_1) ◽

Author(s):

Jonatan Barrera-Chimal ◽

Sebastian M Lechner ◽

Soumaya E Moghrabi ◽

Peter Kolkhof ◽

Frédéric Jaisser

Keyword(s):

Mineralocorticoid Receptor ◽

De Novo ◽

Interstitial Fibrosis ◽

Macrophage Polarization ◽

Peritoneal Macrophages ◽

Renal Ischemia ◽

Receptor Expression ◽

Interleukin 4 ◽

Mrna Levels ◽

Kidney Fibrosis

Introduction: Patients who survive an episode of acute kidney injury (AKI) are at high risk of de novo chronic kidney disease (CKD) development. Pharmacological mineralocorticoid receptor (MR) antagonism is useful to prevent CKD after a single episode of ischemic AKI in the rat. Objective: Test the involvement of myeloid MR in the development of kidney fibrosis after an ischemic AKI episode. Methods: We included 18 male C57/B6 mice that were divided in: sham, renal ischemia for 22.5 min and IR plus treatment with the non-steroidal MR antagonist finerenone (10 mg/kg) at -48, -24 and -1 h before IR. MR inactivation in myeloid cells (MR MyKO ) was achieved by crossing mice with the MR alleles flanked by loxP sites (MR f/f ) with mice expressing the Cre recombinase under the LysM promoter activity. In MR f/f and MR MyKO mice we induced renal IR of 22.5 min or sham surgery. The mice were followed-up during 4 weeks to test for AKI to CKD transition. In another set of mice, the macrophages were sorted from kidneys after 24 h of reperfusion and flow cytometry characterization or mRNA extraction was performed. Thyoglycolate elicited peritoneal macrophages were used for in vitro studies. Results: The progression of AKI to CKD after 4 weeks of renal ischemia in the untreated C57/B6 and MR f/f mice was characterized by a 50% increase in plasma creatinine, a 2-fold increase in the mRNA levels of TGF-β and fibronectin as well as by severe tubule-interstitial fibrosis. The mice that received finerenone or MR MyKO mice were protected against these alterations. Increased expression of M2-anti-inflamatory markers in kidney-isolated macrophages from finerenone-treated or MR MyKO mice was observed. The inflammatory population of Ly6C high macrophages was reduced by 50%. In peritoneal macrophages in culture, MR inhibition promoted increased IL-4 receptor expression and activation, facilitating macrophage polarization to an M2 phenotype. Conclusion: MR antagonism or myeloid MR deficiency facilitates macrophage polarization to a M2, anti-inflammatory phenotype after kidney IR, preventing maladaptive repair and chronic kidney fibrosis and dysfunction. MR inhibition acts through the modulation of IL-4 receptor signaling to facilitate macrophage phenotype switching.

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A novel function of Tis11b/BRF1 as a regulator of Dll4 mRNA 3′-end processing

Molecular Biology of the Cell ◽

10.1091/mbc.e11-02-0149 ◽

2011 ◽

Vol 22 (19) ◽

pp. 3625-3633 ◽

Cited By ~ 6

Author(s):

Agnès Desroches-Castan ◽

Nadia Cherradi ◽

Jean-Jacques Feige ◽

Delphine Ciais

Keyword(s):

Endothelial Cells ◽

Mrna Expression ◽

Binding Site ◽

Mammalian Cell ◽

Mrna Stability ◽

Untranslated Region ◽

Vascular Network ◽

Mrna Levels ◽

Angiogenic Gene

Tis11b/BRF1 belongs to the tristetraprolin family, the members of which are involved in AU-rich-dependent regulation of mRNA stability/degradation. Mouse inactivation of the Tis11b gene has revealed disorganization of the vascular network and up-regulation of the proangiogenic factor VEGF. However, the VEGF deregulation alone cannot explain the phenotype of Tis11b knockouts. Therefore we investigated the role of Tis11b in expression of Dll4, another angiogenic gene for which haploinsufficiency is lethal. In this paper, we show that Tis11b silencing in endothelial cells leads to up-regulation of Dll4 protein and mRNA expressions, indicating that Dll4 is a physiological target of Tis11b. Tis11b protein binds to endogenous Dll4 mRNA, and represses mRNA expression without affecting its stability. In the Dll4 mRNA 3′ untranslated region, we identified one particular AUUUA motif embedded in a weak noncanonical polyadenylation (poly(A)) signal as the major Tis11b-binding site. Moreover, we observed that inhibition of Tis11b expression changes the ratio between mRNAs that are cleaved or read through at the poly(A) signal position, suggesting that Tis11b can interfere with mRNA cleavage and poly(A) efficiency. Last, we report that this Tis11b-mediated mechanism is used by endothelial cells under hypoxia for controlling Dll4 mRNA levels. This work constitutes the first description of a new function for Tis11b in mammalian cell mRNA 3′-end maturation.

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The Onset of Labor Alters Corticotropin-Releasing Hormone Type 1 Receptor Variant Expression in Human Myometrium: Putative Role of Interleukin-1β

Endocrinology ◽

10.1210/en.2007-0095 ◽

2007 ◽

Vol 148 (7) ◽

pp. 3205-3213 ◽

Cited By ~ 34

Author(s):

Danijela Markovic ◽

Manu Vatish ◽

Mei Gu ◽

Donna Slater ◽

Rob Newton ◽

...

Keyword(s):

Mrna Expression ◽

Nuclear Translocation ◽

Fold Increase ◽

Nuclear Factor Κb ◽

Prolonged Treatment ◽

Human Myometrium ◽

Mrna Levels ◽

Myometrial Cells ◽

Important Regulator ◽

R1 Gene

CRH targets the human myometrium during pregnancy. The efficiency of CRH actions is determined by expression of functional receptors (CRH-R), which are dynamically regulated. Studies in myometrial tissue biopsies using quantitative RT-PCR demonstrated that the onset of labor, term or preterm, is associated with a significant 2- to 3-fold increase in CRH-R1 mRNA levels. Detailed analysis of myometrial CRH-R1 mRNA variants showed a decline of the pro-CRH-R1 mRNA encoding the CRH-R1β variant during labor and increased mRNA levels of CRH-R1d mRNA. Studies in myometrial cells identified IL-1β as an important regulator of myometrial CRH-R1 gene expression because prolonged treatment of myometrial cells with IL-1β (1 ng/ml) for 18 h induced expression of CRH-R1 mRNA levels by 1.5- to 2-fold but significantly attenuated CRH-R1β mRNA expression by 70%. In contrast, IL-1β had no effect on CRH-R1d mRNA expression. Studies using specific inhibitors suggest that ERK1/2, p38 MAPK, and downstream nuclear translocation of nuclear factor-κB mediate IL-1β effects on myometrial CRH-R1 gene. However, the increased CRH-R1 mRNA expression was associated with a dampening of the receptor efficacy to activate the adenylyl cyclase/cAMP signaling cascade. Thus, our findings suggest that IL-1β is an important regulator of CRH-R1 expression and functional activity, and this interaction might play a role in the transition of the uterus from quiescence to active contractions necessary for the onset of parturition.

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Differential Expression of Neutrophil Granule Protein Genes in Bone Marrow Myeloid Cells at the Peak and Nadir of Neutrophil Counts in Cyclic Neutropenia

Blood ◽

10.1182/blood.v126.23.2194.2194 ◽

2015 ◽

Vol 126 (23) ◽

pp. 2194-2194

Author(s):

Olga Klimenkova ◽

Maksim Klimiankou ◽

Lothar Kanz ◽

Cornelia Zeidler ◽

Karl Welte ◽

...

Keyword(s):

Bone Marrow ◽

Mrna Expression ◽

Differential Expression ◽

Myeloid Cells ◽

Myeloid Differentiation ◽

Mrna Levels ◽

Healthy Individuals ◽

Cyclic Neutropenia ◽

Granule Proteins ◽

Myeloid Progenitors

Abstract Cyclic neutropenia (CyN) is a hematologic disorder in which peripheral-blood neutrophil counts show cycles at approx. 21-days intervals. The majority of CyN patients (ca. 90 %) harbor inherited mutations in the ELANE gene. The mechanism of cycling hematopoiesis downstream of ELANE mutations is unclear. In the present study we aimed to identify if there is a geterogeniety of bone marrow (BM) myeloid progenitors and granulocytic cells at the peak and nadir of the cycle of neutrophil counts. We performed FACS analysis of BM populations in CyN patient at the peak and nadir of the cycle and revealed reduced number of CD33high promyelocytes at the peak, as compared to the nadir neutrophil counts (6% vs 47%). Morphological examination of BM smears confirmed this observation. These data suggest differences in myeloid differentiation potential of hematopoietic cells of CyN patient during cycle. To compare the myeloid differentiation of BM cells at the peak and nadir, we performed CFU assay using BM cells isolated at these two different time points. Indeed, we found diminished capacity to produce CFU-G colonies at the peak of cycle, in comparison to the nadir (50 vs 68). This difference might be explained by the presence of different sub-populations of myeloid cells during the cycle. It was shown that the neutrophil populations can be distinguished by membrane expression of CD177, which is GPI-linked neutrophil antigen, localized primarily to the membrane of specific granules and to the plasma membrane. The proportion of CD177+ cells increased during neutrophil maturation in BM. Interestingly, in healthy individuals the fraction of CD177+ cells appeared to be constant in each individual. We evaluated the differences of CD177+ cell populations in CyN patients at the peak and nadir of cycle by FACS. We found that numbers of CD33+ CD177+ and CD16+ CD177+ populations were different during the cycle. At the peak we measured 7,1% of CD33+ CD177+ cells and 83% of CD16+ CD177+ cells. At the nadir 3,78% of cells were CD33+ CD177+ and 69% were CD16+ CD177+. We further performed mRNA expression analysis of CD33+ BM cells isolated from CyN patient at the peak and nadir of cycle and compared it to healthy individuals. We found lower mRNA expression (more than 10-fold) of CRISP3, ELANE, OLFM4, CEACAM6, MMP8, DEFA4 and LCN2 in CD33+ cellsat the peak of the cycle comparing to the nadir. These genes encode for neutrophil granule proteins, playing an important role in the developement and function of mature neutrophils. We further confirmed differential expression of these factors in CFU colonies using BM of CyN patient isolated at the peak and nadir of the cycle: CFU-G colonies grown from cells taken at the peak of the cycle expressed less mRNA levels of granula proteins than CFU-G colonies grown from cells taken at the nadir of the cycle. In summary, we hypothesize that the differential expression of the granule proteins is involved in the regulation of the cycle in myeloid cells in CyN. At the peak and nadir of neutrophil counts different populations (based on CD177 expression) of myeloid progenitors and neutrophils are present in the CyN BM. Disclosures No relevant conflicts of interest to declare.

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PU.1 Cooperates with SOX4 in Myeloid Cells.

Blood ◽

10.1182/blood.v110.11.2633.2633 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2633-2633

Author(s):

Georg Aue ◽

Yang Du ◽

Nancy A. Jenkins ◽

Cynthia E. Dunbar ◽

Neal G. Copeland

Keyword(s):

Bone Marrow ◽

Transcription Factor ◽

Vector Control ◽

Myeloid Leukemia ◽

De Novo ◽

Bone Marrow Cells ◽

Myeloid Cells ◽

P Value ◽

Mrna Levels ◽

Wild Type

Abstract Mice that express 20% the normal levels of the Ets transcription factor PU.1 develop AML, unlike mice that express 50% or 80% the normal levels, indicating that PU.1 is a dosage-sensitive tumor suppressor gene. In addition, 3 of 13 AMLs induced by transplanting mice with cells transduced with a Sox4 oncogene-containing retrovirus were found to carry a Sox4 retroviral integration in one PU.1 allele, suggesting that downregulation of PU.1 may cooperate with Sox4 in AML induction. Since the other PU.1 allele remains intact in these AMLs and a 50% decrease in PU.1 expression is not sufficient to induce AML, we hypothesized that Sox4 might further downregulate PU.1 expression in these AMLs. To test this hypothesis, we transfected HL60 cells with an expression vector carrying GFP and Sox4 cDNA or a GFP vector control alone. PU.1 mRNA levels were consistently downregulated 4 to 10 fold in cells transfected with Sox4 cDNA compared to cells transfected with the vector control, confirming that overexpression of Sox4 downregulates PU.1 expression in myeloid cells. The decrease of PU.1 mRNA was observed as early as 8 hours after Sox4 transfection, further suggesting that Sox4 may directly interact with PU.1 in myeloid cells. Consistent with this, analysis of 2 published microarray databases comprising 401 de novo AML patient samples showed that SOX4 expression is significantly negatively correlated with PU.1 expression (coefficient: −0.337, P-value: 1E-07). In order to confirm that downregulation of PU.1 cooperates with Sox4 in AML induction, we infected wild type or PU.1 heterozygous knockout bone marrow cells with the Sox4 retrovirus and then monitored the time of AML development in transplanted mice. Results showed increased penetrance (95%) of myeloid leukemia in mice transplanted with Sox4-infected PU +/– bone marrow compared to mice receiving Sox4-infected wild type marrow (60%). Myeloid leukemia was confirmed by histology in all animals of the Sox4-infected PU +/ cohort while T cell lymphoma was diagnosed in 3 animals of the Sox4 wild type cohort. Together, all experiments support the hypothesis that Sox4 cooperates with the transcription factor PU.1.

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Mechanism of all trans-retinoic acid and glucocorticoid regulation of surfactant protein mRNA

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1998.274.4.l560 ◽

1998 ◽

Vol 274 (4) ◽

pp. L560-L566 ◽

Cited By ~ 9

Author(s):

Thomas N. George ◽

Olga L. Miakotina ◽

Kelli L. Goss ◽

Jeanne M. Snyder

Keyword(s):

Gene Expression ◽

Retinoic Acid ◽

Gene Transcription ◽

Mrna Stability ◽

Half Life ◽

Normal Function ◽

Mrna Levels ◽

Trans Retinoic Acid ◽

All Trans Retinoic Acid ◽

Mrna Half Life

The surfactant proteins (SPs) are required for the normal function of pulmonary surfactant, a lipoprotein substance that prevents alveolar collapse at end expiration. We characterized the effects of cortisol and all trans-retinoic acid (RA) on SP-A and SP-B gene expression in H441 cells, a human pulmonary adenocarcinoma cell line. Cortisol, at 10−6M, caused a significant inhibition of SP-A mRNA to levels that were 60–70% of controls and a five- to sixfold increase in the levels of SP-B mRNA. RA alone (10−6M) had no effect on SP-A mRNA levels and modestly reduced the inhibitory effect of cortisol. RA alone and the combination of cortisol and RA both significantly increased SP-B mRNA levels. RA had no effect on the rate of SP-A gene transcription or on SP-A mRNA stability. Cortisol alone and the combination of cortisol and RA significantly inhibited the rate of SP-A gene transcription but had no effect on SP-A mRNA half-life. RA at 10−6 M had no effect on the rate of SP-B gene transcription but prolonged SP-B mRNA half-life. Cortisol alone and the combination of cortisol and RA caused a significant increase in the rate of SP-B gene transcription and also caused a significant increase in SP-B mRNA stability. We conclude that RA has no effect on SP-A gene expression and increases SP-B mRNA levels by an effect on SP-B mRNA stability and not on the rate of SP-B gene transcription. In addition, the effects of the combination of RA and cortisol were generally similar to those of cortisol alone.

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Intestinal perfusion induces rapid activation of immediate-early genes in weaning rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.281.4.r1274 ◽

2001 ◽

Vol 281 (4) ◽

pp. R1274-R1282 ◽

Cited By ~ 8

Author(s):

Lan Jiang ◽

Heather Lawsky ◽

Relicardo M. Coloso ◽

Mary A. Dudley ◽

Ronaldo P. Ferraris

Keyword(s):

Mrna Expression ◽

Target Genes ◽

De Novo ◽

Immediate Early Genes ◽

Regulatory Elements ◽

Intestinal Perfusion ◽

Immediate Early ◽

Mrna Levels ◽

Early Genes

C- fos and c- jun are immediate-early genes (IEGs) that are rapidly expressed after a variety of stimuli. Products of these genes subsequently bind to DNA regulatory elements of target genes to modulate their transcription. In rat small intestine, IEG mRNA expression increases dramatically after refeeding following a 48-h fast. We used an in vivo intestinal perfusion model to test the hypothesis that metabolism of absorbed nutrients stimulates the expression of IEGs. Compared with those of unperfused intestines, IEG mRNA levels increased up to 11 times after intestinal perfusion for 0.3–4 h with Ringer solutions containing high (100 mM) fructose (HF), glucose (HG), or mannitol (HM). Abundance of mRNA returned to preperfusion levels after 8 h. Levels of c- fos and c- jun mRNA and proteins were modest and evenly distributed among enterocytes lining the villi of unperfused intestines. HF and HM perfusion markedly enhanced IEG mRNA expression along the entire villus axis. The perfusion-induced increase in IEG expression was inhibited by actinomycin-D. Luminal perfusion induces transient but dramatic increases in c- fos and c- jun expression in villus enterocytes. Induction does not require metabolizable or absorbable nutrients but may involve de novo gene transcription in cells along the villus.

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Interferon augments PML and PML/RAR alpha expression in normal myeloid and acute promyelocytic cells and cooperates with all-trans retinoic acid to induce maturation of a retinoid-resistant promyelocytic cell line

Blood ◽

10.1182/blood.v88.10.3926.bloodjournal88103926 ◽

1996 ◽

Vol 88 (10) ◽

pp. 3926-3936 ◽

Cited By ~ 49

Author(s):

K Nason-Burchenal ◽

D Gandini ◽

M Botto ◽

J Allopenna ◽

JR Seale ◽

...

Keyword(s):

Retinoic Acid ◽

Cell Line ◽

De Novo ◽

Retinoic Acid Receptor ◽

Myeloid Cells ◽

Fusion Transcript ◽

Differentiation Potential ◽

Nb4 Cells ◽

Trans Retinoic Acid ◽

All Trans Retinoic Acid

The PML gene is fused to the retinoic acid receptor alpha gene (RAR alpha) in the acute promyelocytic leukemia (APL) 15; 17 translocation. PML is expressed in diverse tissues and cell lines and localized in the nucleus with a typical speckled pattern. In the bone marrow, it is preferentially expressed in myeloid cells. PML appears to be transcriptionally regulated by class I and II interferons, which raises the possibility that interferons modulate the function and growth and differentiation potential of normal myeloid cells and precursors by activating PML-dependent pathways. Similarly, interferons could act on APL cells, alone or in combination with all-trans retinoic acid (RA), especially if the PML/RAR alpha fusion transcript that results from the t(15; 17) is induced by interferon. We report here that PML is expressed at low levels or not expressed in normal circulating human monocytes, lymphocytes, and polymorphonucleate cells, but is markedly induced by interferon; that PML and PML/RAR alpha expression is augmented by interferon in the NB4 APL cell line, which carries the t(15; 17), and in APL blasts from patients; that interferon inhibits growth and survival of NB4 APL cells in cooperation with RA; that interferons alone have minimal maturation effect on NB4 cells; and, finally, that interferon gamma, but not alpha or beta, induces maturation and growth suppression of NB4 cells with de novo retinoid resistance, and partially restores RA response.

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Transcriptional and posttranscriptional regulation of the interleukin-4 and interleukin-3 genes in human T cells

Blood ◽

10.1182/blood.v81.1.35.35 ◽

1993 ◽

Vol 81 (1) ◽

pp. 35-40 ◽

Cited By ~ 36

Author(s):

WH Dokter ◽

MT Esselink ◽

SJ Sierdsema ◽

MR Halie ◽

E Vellenga

Keyword(s):

T Cells ◽

Mrna Expression ◽

Posttranscriptional Regulation ◽

Interleukin 4 ◽

Mrna Levels ◽

Con A ◽

Mrna Accumulation ◽

Human T Cells ◽

Activation Pathways ◽

The Stability

Abstract Human T cells were studied with regard to the regulation of interleukin- 4 (IL-4) and IL-3 gene expression. IL-4 and IL-3 mRNA were undetectable in unstimulated T cells. On activation with the lectin concanavalin A (Con A), both IL-4 and IL-3 mRNA were expressed. Accumulation of IL-4 mRNA peaked after 6 to 12 hours, whereas IL-3 mRNA levels peaked after 3 to 6 hours of stimulation with Con A. Nuclear run-on assays showed a low constitutive transcription for both genes. The transcription rates were increased by Con A resulting in a peak for IL-4 after 1 hour (30% increase) and for IL-3 after 3 hours (40% increase) of Con A treatment. mRNA stability studies demonstrated that on activation with Con A both messages decayed with a half-life of approximately 90 minutes. No IL-4 or IL-3 mRNA expression was induced by the protein kinase C activator phorbol myristate acetate (PMA). However, PMA augmented the Con A- induced IL-4 and IL-3 mRNA accumulation. This was shown to be mediated at posttranscriptional level by a large increase in the stability of both messages (t 1/2 > 3 hours). The transcription rate of both genes was also enhanced by Con A+PMA and reached peak levels for IL-4 after 1 hour (90% increase) and for IL-3 after 3 hours (70% increase) of stimulation. Furthermore, it appeared that the induction of IL-4 mRNA was dependent on protein synthesis because cycloheximide (CHX) blocked the Con A- and Con A+PMA-induced expression of IL-4 mRNA. In contrast, CHX inhibited, but failed to completely block, the Con A- and Con A+PMA- induced IL-3 mRNA expression, whereas the expression of both genes was completely blocked by cyclosporine A. With regard to the secretion of IL-4 protein it was shown that it closely follows the accumulation of IL-4 mRNA. Taken together, the data show that expression of the IL-4 and IL-3 genes in human T cells is controlled by different activation pathways that affect the gene regulation at transcriptional and posttranscriptional levels.

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Interleukin 4–induced gene 1 is activated in primary mediastinal large B-cell lymphoma

Blood ◽

10.1182/blood-2002-07-2215 ◽

2003 ◽

Vol 101 (7) ◽

pp. 2756-2761 ◽

Cited By ~ 43

Author(s):

Christiane Copie-Bergman ◽

Marie-Laure Boulland ◽

Catherine Dehoulle ◽

Peter Möller ◽

Jean-Pierre Farcet ◽

...

Keyword(s):

Amino Acid ◽

B Cell ◽

Mrna Expression ◽

Cell Lines ◽

Cell Lymphoma ◽

B Cell Lymphoma ◽

Interleukin 4 ◽

Mrna Levels ◽

Large B Cell Lymphoma ◽

Large B Cell

The molecular markers that distinguish primary mediastinal large B-cell lymphoma (PMBL) from nonmediastinal diffuse large B-cell lymphomas (NM-DLBLs) remain to be identified. Using cDNA representational difference analysis to compare PMBL and NM-DLBL transcripts, we isolated a cDNA fragment homologous to the mouse B-cell interleukin 4 (IL-4)–inducible gene FIG1(interleukin 4–induced gene 1) transcript. The human FIG1mRNA encodes a 567 amino acid protein that comprises a signal peptide and a large flavin-binding amino oxidase domain, and shares significant homology with secreted apoptosis-inducing L-amino acid oxidases. Northern blot studies showed that FIG1 mRNA expression is mainly restricted to lymphoid tissues. It is expressed at low levels in thymus, spleen, tonsils, and reactive lymph nodes, and is highly up-regulated in IL-4+CD40–activated tonsillar B cells. Interestingly, in human B-cell lines, FIG1 mRNA expression appeared restricted to the PMBL-derived MedB-1 and Karpas 1106 cell lines. Using real-time reverse transcriptase–polymerase chain reaction (RT-PCR), we demonstrated that all but one PMBL (16/17) displayed high FIG1 mRNA levels, whereas most NM-DLBLs (12/18) and all low-grade B-cell lymphomas tested (8/8) exhibited low FIG1 mRNA levels. The difference between PMBLs and NM-DLBLs was statistically significant (Fisher test;P = .0003). Southern blot studies did not show rearrangement of the FIG1 gene. FIG1 gene expression might be due to a constitutive activation of a cytokine signaling pathway in PMBL.

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