Post-transcriptional control of IL-1 gene expression in the acute monocytic leukemia line THP-1

Expression profile of pattern recognition receptors in skeletal muscle of SOD1(G93A) amyotrophic lateral sclerosis (ALS) mice and sporadic ALS patients

AIMS

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motoneurons and progressive muscle wasting. Inflammatory processes, mediated by non-neuronal cells, such as glial cells, are known to contribute to disease progression. Inflammasomes consist of pattern recognition receptors (PRRs), apoptosis-associated speck-like protein (ASC) and caspase 1 and are essential for interleukin (IL) processing and a rapid immune response after tissue damage. Recently, we described inflammasome activation in the spinal cord of ALS patients and in SOD1^(G93A) ALS mice. Since pathological changes in the skeletal muscle are early events in ALS, we hypothesized that PRRs might be abnormally expressed in muscle fibre degeneration.

METHODS

Western blot analysis, real-time PCR and immunohistochemistry were performed with muscle tissue from presymptomatic and early-symptomatic male SOD1^(G93A) mice and with muscle biopsies of control and sporadic ALS (sALS) patients. Analysed PRRs include nucleotide-binding oligomerization domain-like (NOD-like) receptor protein 1 (NLRP1), NLR protein 3 (NLRP3), NLR family CARD domain-containing 4 (NLRC4) and absent in melanoma 2. Additionally, expression levels of ASC, caspase 1, interleukin 1 beta (IL1β) and interleukin 18 (IL18) were evaluated.

RESULTS

Expression of PRRs and ASC was detected in murine and human tissue. The PRR NLRC4, caspase 1 and IL1β were significantly elevated in denervated muscle of SOD1^(G93A) mice and sALS patients. Furthermore, levels of caspase 1 and IL1β were already increased in presymptomatic animals.

CONCLUSION

Our findings suggest that increased inflammasome activation may be involved in skeletal muscle pathology in ALS. Furthermore, elevated levels of NLRC4, caspase 1 and IL1β reflect early changes in the skeletal muscle and may contribute to the denervation process.

Activity of gelatins to induce secretion of a variety of cytokines from murine peritoneal exudate macrophages

Previously, we observed that liquid form bovine bone (BB) gelatin stimulates murine spleen cells to proliferate in vitro. In this study, activity of BB gelatin to stimulate murine-adherent peritoneal exudate cells (PEC) to secrete cytokines has been examined. Quantitatively, BB gelatin stimulated adherent PEC of C3H/HeN mice to secrete interleukin (IL)-12 (+p40), TNF-alpha, and IL-6 but not IL-1beta, IL-2, IL-10, and IFN-gamma. Qualitatively, BB gelatin-induced secretion of KC, MIP-2, MCP-1, RANTES, and MIP-1a as well as IL-6 but not 6Ckine, CTACK, Eotaxin, G-CSF, GM-CSF, IL-2,-3,-4,-5,-9,-10,-12,-13,-17, Leptin, IFN-gamma, SCF, sTNFri, TARC, TNF-alpha, TIMP-1, Tpo, and VEGF. BB gelatin acted on adherent PEC of C3H/HeN mice but not C3H/HeJ mice, which lack Toll-like receptor 4. Polymyxin B, a LPS antagonist, did not inhibit the activity of BB gelatin. Lipopolysaccharide (LPS) but not BB gelatin induced secretion of an appreciable amount of mIL-1beta. These results suggest that the activity of BB gelatin is not attributed to contamination of LPS but BB gelatin itself. It was also suggested that BB gelatin stimulated adherent PEC to newly produce and secrete cytokines.

Peptide Mapping Identifies Hotspot Site of Modification in Human Serum Albumin by Methylglyoxal Involved in Ligand Binding and Esterase Activity

Methylglyoxal is a potent glycating agent under physiological conditions. Human serum albumin is modified by methylglyoxal in vivo. The glycation adducts formed and structural and functional changes induced by methylglyoxal modification have not been fully disclosed. Methylglyoxal reacted with human serum albumin under physiological conditions to form mainly the hydroimidazolone N(delta)-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (92% of total modification) with a minor formation of argpyrimidine, N(epsilon)-(1-carboxyethyl)lysine, and methylglyoxal lysine dimer. When human serum albumin was modified minimally with methylglyoxal, tryptic peptide mapping indicated a hotspot of modification at Arg-410 located in drug-binding site II and the active site of albumin-associated esterase activity. Modification of Arg-410 by methylglyoxal was found in albumin glycated in vivo. Other sites of minor modification were: Arg-114, Arg-186, Arg-218, and Arg-428. Hydroimidazolone formation at Arg-410 inhibited ketoprofen binding and esterase activity; correspondingly, glycation in the presence of ketoprofen inhibited Arg-410 modification and loss of esterase activity. The pH dependence of esterase activity indicated a catalytic group with pK(a) = 7.9 +/- 0.1, assigned to the catalytic base Tyr-411 with the conjugate base stabilized by interaction with the guanidinium group of Arg-410. Modification by methylglyoxal destabilized Tyr-411 and increased the pK(a) to 8.8 +/- 0.1. Molecular dynamics and modeling studies indicated that hydroimidazolone formation caused structural distortion leading to disruption of arginine-directed hydrogen bonding and loss of electrostatic interactions. Methylglyoxal modification of critical arginine residues, therefore, whether experimental or physiological, is expected to disrupt protein-ligand interactions and inactivate enzyme activity by hydroimidazolone formation.

Progesterone mediates decreases in uterine smooth muscle cell interleukin-1alpha by a mechanism involving decreased stability of IL-1alpha mRNA

The regulation, by progesterone, of serotonin-induced interleukin-1alpha production was studied in primary cultures of rat uterine smooth muscle cells. Prior reports from this laboratory have demonstrated that these cells produce IL-1alpha and IL-1beta mRNAs in response to the hormonal action of serotonin. Results of the present study indicate that treatment of myometrial smooth muscle cells with medroxyprogesterone acetate (MPA) results in a marked decrease in IL-1alpha protein as measured by western blot analysis. These decreases occur even in the presence of maximally-inducing concentrations of serotonin. MPA-mediated changes in IL-1alpha protein are characterized by a rapid decline in IL-1alpha mRNA levels. This inhibition by medroxyprogesterone also occurs when cells are stimulated to produce IL-1alpha by PMA rather than serotonin. Thus, when cells are cultured in the presence of both inducer and inhibitor, the inhibitor, progesterone, clearly dominates in the control of IL-1alpha expression. This effect is concentration-dependent, can be mimicked by native progesterone or glucocorticoids, but is unaffected by estradiol. The ability of progestins to decrease IL-1alpha mRNA is blocked by both inhibitors of transcription and translation and by treatment with RU-486. Progesterone had no effect on chloramphenicol acetyl transferase (CAT) transcription from two different IL-1alpha promoter constructs, indicating that progesterone's action appears to be dependent on post-transcriptional rather than transcriptional regulation. Conversely, progesterone accelerated the normal rate of decay of IL-1alpha mRNA that occurs following the removal of serotonin from the cultures. These results suggest that progesterone decreases IL-1alpha levels by stimulating the production of an intracellular intermediate that decreases the stability of IL-1alpha mRNA.

Interleukin-1beta secreted from monocytic cells induces the expression of matrilysin in the prostatic cell line LNCaP

Matrilysin is a matrix metalloprotease that is overexpressed in cancer cells of epithelial origin and in normal tissues during events involving matrix remodeling such as the cycling endometrium. We previously observed that inflamed ductule and acinar epithelia in the prostate also overexpress matrilysin. The presence of infiltrating macrophages in these areas prompted us to determine if factors secreted from monocytes could induce matrilysin expression in a human prostatic cell line. Conditioned media collected from the monocyte cell line THP-1 following lipopolysaccharide treatment substantially induced matrilysin protein and mRNA expression in LNCaP prostate carcinoma cells. Matrilysin expression in LNCaP cells was also induced by recombinant interleukin (IL)-1 (50 pM), but not by equimolar concentrations of recombinant tumor necrosis factor-alpha or IL-6. The matrilysin-inducing activity of THP-1 conditioned medium was completely abrogated by preincubation with a neutralizing antibody to IL-1beta. Transient transfection analyses with a chimeric human matrilysin promoter-chloramphenicol acetyltransferase reporter construct demonstrated that IL-1beta activates transcription through the matrilysin promoter in LNCaP cells. This is the first report of matrilysin induction by an inflammatory cytokine in a cell line of epithelial origin, and the results suggest a potential mechanism for the overexpression of matrilysin in inflamed ducts and glands of the prostate.

Synthesis and secretion of macrophage colony stimulating factor by mature human monocytes and human monocytic THP-1 cells induced by human serum albumin derivatives modified with methylglyoxal and glucose-derived advanced glycation endproducts

Human serum albumin minimally-modified by methylglyoxal (MGmin-HSA) stimulated the synthesis and secretion of macrophage-colony stimulating factor (M-CSF) by mature human monocytes in vitro. Human serum albumin minimally-modified by glucose-derived advanced glycation endproducts (AGEmin-HSA) and human serum albumin highly-modified by glucose-derived advanced glycation endproducts (AGE-HSA) stimulated much lower secretion of M-CSF from human monocytes than did MGmin-HSA. MGmin-HSA and AGE-HSA but not AGEmin-HSA also stimulated the growth of human monocytic THP-1 cells in vitro which was inhibited by polyclonal antibodies to human M-CSF. For MGmin-HSA, the median growth stimulatory concentration EC50 value was 0.24 +/- 0.07 microM and the maximal increase in cell growth was 36% of control cell growth (n = 24). Similar induction of secretion of M-CSF from monocytes in vivo may contribute to atherosclerosis in macro- and micro-angiopathy, particularly in the development of diabetic complications.

Interleukin-1 and its inhibitors: implications for disease biology and therapy

IL-1 alpha and IL-1 beta are polypeptide hormones that exhibit a broad spectrum of beneficial and harmful biologic activities. Clinical trials designed to benefit from its stimulatory effects on human hematopoiesis and from its role in improving host defenses, are being currently conducted. Other in vivo studies, using IL-1 inhibitors with an attempts to block the detrimental effects of IL-1, are underway. Because of the multifunctional effects of IL-1 in human physiology and its pathogenetic role in several diseases, the capability to control the effects of IL-1 may prove to be a useful tool in medical practice.

A CRE/ATF-like site in the upstream regulatory sequence of the human interleukin 1 beta gene is necessary for induction in U937 and THP-1 monocytic cell lines

Transfection of U937 and THP-1 cells with a recombinant plasmid, pIL1(4.0kb)-CAT, containing 4 kb of the interleukin 1 beta (IL-1 beta) gene upstream regulatory sequence resulted in inducer-dependent expression of chloramphenicol acetyltransferase activity. Treatment of the transfected cells with various combinations of the inducers lipopolysaccharide, phorbol myristate acetate, and dibutyryl cyclic AMP upregulated the IL-1 beta promoter. In U937 and THP-1 cells, maximum stimulation of both the endogenous IL-1 beta gene and pIL1(4.0kb)-CAT transfectants was observed following treatment with the combination of inducing agents lipopolysaccharide-phorbol myristate acetate-dibutyryl cyclic AMP. This combination of inducing agents was used to identify and study, at the molecular level, some of the regulatory elements necessary for induction of the IL-1 beta gene. A series of 5' deletion derivatives of the upstream regulatory sequence were used in transient transfection assays to identify an 80-bp fragment located between -2720 and -2800 bp upstream of the mRNA start site that was required for induction. Exonuclease III mapping, electrophoretic mobility shift assays (EMSA), and DNA sequence analysis of this region were used to identify a transcription factor binding sequence which contained a potential cyclic AMP response element (CRE/ATF)- and NF-kappa B-like binding site. Site-directed mutagenesis of the CRE/ATF-like site resulted in the loss of binding of a specific factor or factors as determined by EMSA. The loss of binding activity directly correlated with a loss of approximately 75% of promoter activity as determined in transient transfection assays. As determined by EMSA, the factor binding to the CRE/ATF-like site was present in nuclear extracts prepared from both uninduced and induced THP-1 and U937 cells. However, the intensity of the band appeared to be increased when nuclear extracts from induced cells were used. In contrast to the CRE/ATF mutation, which resulted in the loss of promoter activity, mutation of the NF-kappa B-like site resulted in a moderate increase in activity in U937 cells. A similar increase in promoter activity was not observed in THP-1 cells. From these studies, we conclude that a CRE/ATF-like site and a factor or factors interacting with this site are essential for the maximum induction of the IL-1 beta gene in stimulated U937 and THP-1 cells.

A CRE/ATF-like site in the upstream regulatory sequence of the human interleukin 1 beta gene is necessary for induction in U937 and THP-1 monocytic cell lines

Transfection of U937 and THP-1 cells with a recombinant plasmid, pIL1(4.0kb)-CAT, containing 4 kb of the interleukin 1 beta (IL-1 beta) gene upstream regulatory sequence resulted in inducer-dependent expression of chloramphenicol acetyltransferase activity. Treatment of the transfected cells with various combinations of the inducers lipopolysaccharide, phorbol myristate acetate, and dibutyryl cyclic AMP upregulated the IL-1 beta promoter. In U937 and THP-1 cells, maximum stimulation of both the endogenous IL-1 beta gene and pIL1(4.0kb)-CAT transfectants was observed following treatment with the combination of inducing agents lipopolysaccharide-phorbol myristate acetate-dibutyryl cyclic AMP. This combination of inducing agents was used to identify and study, at the molecular level, some of the regulatory elements necessary for induction of the IL-1 beta gene. A series of 5' deletion derivatives of the upstream regulatory sequence were used in transient transfection assays to identify an 80-bp fragment located between -2720 and -2800 bp upstream of the mRNA start site that was required for induction. Exonuclease III mapping, electrophoretic mobility shift assays (EMSA), and DNA sequence analysis of this region were used to identify a transcription factor binding sequence which contained a potential cyclic AMP response element (CRE/ATF)- and NF-kappa B-like binding site. Site-directed mutagenesis of the CRE/ATF-like site resulted in the loss of binding of a specific factor or factors as determined by EMSA. The loss of binding activity directly correlated with a loss of approximately 75% of promoter activity as determined in transient transfection assays. As determined by EMSA, the factor binding to the CRE/ATF-like site was present in nuclear extracts prepared from both uninduced and induced THP-1 and U937 cells. However, the intensity of the band appeared to be increased when nuclear extracts from induced cells were used. In contrast to the CRE/ATF mutation, which resulted in the loss of promoter activity, mutation of the NF-kappa B-like site resulted in a moderate increase in activity in U937 cells. A similar increase in promoter activity was not observed in THP-1 cells. From these studies, we conclude that a CRE/ATF-like site and a factor or factors interacting with this site are essential for the maximum induction of the IL-1 beta gene in stimulated U937 and THP-1 cells.

Inhibition of interferon-gamma- and phorbol ester-induced HLA-DR and interleukin-1 production by the expression of a transfected poly(ADP-ribose) synthetase gene in human leukemia THP-1 cells

We have examined a correlation between an expression level of poly(ADP-ribose) synthetase gene and the stage of monocytic differentiation. We selected three human leukemia cell lines, U937, THP-1, and J111, whose differentiation stage was characterized by nitroblue tetrazolium reduction activity, non-specific esterase activity, phagocytic activity and a cell surface marker. Enzyme activity and mRNA level of the synthetase decreased in accompaniment with the progress of monocytic differentiation. When THP-1 cells were treated with either interferon-gamma or phorbol ester, mRNA level of the synthetase decreased and HLA-DR or interleukin-1 was induced, respectively. We transfected expression plasmid of the exogenous synthetase gene to examine whether the down-regulation of the synthetase is a necessary step to induce these proteins. An expression of the exogenous synthetase gene inhibited the interferon-gamma- and phorbol ester-dependent induction of HLA-DR and interleukin-1. The results suggest that down-regulation of the synthetase may be a signal mediator of immunological response such as HLA-DR or interleukin-1 production in monocytes.

Review: transcriptional and post-transcriptional regulation of interleukin 1 gene expression

Interleukin 1 alpha (IL-1 alpha) and beta (IL-1 beta) are proinflammatory cytokines that are encoded by distinct genes, but share most biological activities. During the past several years, intense investigation has focused on elucidating the molecular basis for the regulation of IL-1 alpha and beta gene expression. While the overall organization of both genes is conserved in mammals, the DNA sequence homology is surprisingly limited. This supports the growing body of evidence suggesting that each gene is regulated by distinct cis- and transacting elements. Most recently, novel regulatory DNA sequence elements and several nuclear regulatory proteins have been identified, which ultimately participate in the control of IL-1 beta gene transcription. In addition to transcriptional controls, the stability of IL-1 mRNA can be selectively regulated by various inducing stimuli and other cytokines. Taken together, these transcriptional and post-transcriptional regulatory mechanisms provide stringent, yet flexible, control over expression of the IL-1 alpha and beta genes.

Different activation signals are required for the expression of interleukin-1 alpha and beta genes in human monocytes

The production and mRNA expression of IL-1 alpha and IL-1 beta by human monocytes was examined after two different stimuli, a protein kinase C (PKC) activator phorbol myristate acetate (PMA) and bacterial lipopolysaccharide (LPS). LPS induced production of high levels of both IL-1 alpha and IL-1 beta protein (quantitated with type-specific ELISA assays), while after PMA stimulation only IL-1 beta protein could be detected. The IL-1 alpha and IL-1 beta mRNA levels quantitated by Northern blotting were in line with the respective protein levels and nuclear run off analysis revealed that PMA did not activate the IL-1 alpha transcription. The production of the IL-1 alpha and IL-1 beta protein as well as the mRNA expression could be inhibited with protein kinase inhibitor H7, but not with HA1004, indicating that PKC activation is essential for the activation of these genes. Thus these data indicate that PKC activation alone is sufficient for the induction of the IL-1 beta gene, but some additional signals (provided by LPS) are required for the activation of the IL-1 alpha gene.

The human leukemia cell line, THP-1: a multifacetted model for the study of monocyte-macrophage differentiation

THP-1 is a human monocytic leukemia cell line. After treatment with phorbol esters, THP-1 cells differentiate into macrophage-like cells which mimic native monocyte-derived macrophages in several respects. Compared to other human myeloid cell lines, such as HL-60, U937, KG-1, or HEL cell lines, differentiated THP-1 cells behave more like native monocyte-derived macrophages. Because of these characteristics, the THP-1 cell line provides a valuable model for studying the mechanisms involved in macrophage differentiation, and for exploring the regulation of macrophage-specific genes as they relate to physiological functions displayed by these cells.

Regulation of gene expression by tumor promoters

Tumor promoters change the program of genes expressed in cells in culture and in the multicellular organism. The growing list of genes that are induced or repressed includes protooncogenes, transcription factors, secreted proteases and viruses. Most of the regulation is at the level of transcription. Several of the cis-acting promoter elements mediating regulation, the transcription factors binding to these elements and their post-translational activation, as well as some of the initial steps of the interaction of cells with tumor promoters have been characterized. The components of the signal transduction chain to the nucleus are, however, still unknown. Mutant and inhibitor studies suggest that the activation or inactivation of certain genes constitute the basis for the development of the tumor promotion phenotype.

Demonstration of IL-1 alpha, and IL-1 beta secretion by the monocytic leukemia cell line, THP-1

This study examined the secretion of IL-1 alpha and IL-1 beta by THP-1 leukemia cells following activation with mezerein and promotion of synthesis by interferon (IFN-gamma). Interleukin-1 (IL-1) was not detected by co-mitogenic thymocyte assays of crude supernates. Isoelectrofocusing of concentrated medium showed that all biologically active IL-1 migrated at a pH of 6.8-7.2, indicating that the major secreted form was IL-1 beta. Double antibody ELISA confirmed the presence of IL-1 beta, but failed to detect IL-1 alpha in isofocused fractions. Although it appeared that THP-1 cells do not secrete IL-1 alpha; an inhibitor of thymocyte response to IL-1 was present in conditioned medium, migrated in an acidic pH range and masked the expression of biologically active rIL-1 alpha and rIL-1 beta. In contrast, IL-1 alpha was detected using a cell blotting assay. This technique permitted visualization of subpicogram levels of IL-1 when secreted by cells attached to an immunoblotting paper. Cell blotting showed that a greater proportion of attached cells incubated for 24 h in medium containing mezerein and IFN-gamma secreted IL-1 than cells in control medium. In conclusion, the amount of immunoreactive or biologically active IL-1 alpha secreted by stimulated THP-1 cells appeared to be much lower than that reported for human peripheral blood monocytes.

Interleukin-1 and hematopoiesis

Interleukin-1 alpha and interleukin-1 beta are 17.5 kDa peptides which exert a wide variety of biological activities. Both forms of interleukin bind to a common 60-70 kDa receptor expressed by most somatic cells. One major effect of interleukin-1 is to induce the expression of other genes, including genes for other interleukins (IL-6), colony stimulating factors (GM-CSF and G-CSF) and growth factors (PDGFA) and adhesion proteins (ELAM-1, ICAM-1). In vitro, cells of the hematopoietic stroma including thymic epithelium, endothelial cells, fibroblasts, T-lymphocytes, and macrophages, are all capable of responding to interleukin-1 by expressing most of these IL-1 inducible genes. Accordingly, because interleukin-1 has no direct effect on hematopoietic progenitor cells, its major effect on hematopoiesis is to regulate the expression of hematopoietic growth factor genes by other cells. The mechanism by which interleukin-1 induces gene expression is to first induce mRNA accumulation which accounts for an increase in translation of the mRNA. The accumulation of RNA, interestingly, does not result from increased transcription of these genes but by the stabilization of the mRNA. Ordinarily, the hematopoietic growth factor gene transcripts have a very short half-life but in an interleukin-1 induced cell, the half-life of these transcripts is markedly prolonged (greater than 24 h). This particular effect of IL-1 on transcript stability likely accounts for virtually all of the hematopoietic activities of interleukin-1 including: (1) induction of growth factors; (2) synergy with other factors; (3) priming; and (4) auto-induction. Three clinical models of hematopoiesis are presented which suggest that the interleukin-1 CSF network is operative in vivo. The ability of interleukin-1 to induce the expression of hematopoietic growth factor genes as well as genes whose products regulate cellular function and traffic suggest that interleukin-1 is an essential molecular master switch for a number of cellular responses occurring in organisms facing the vicissitudes of their environment.