Early epigenetic downregulation of WNK2 kinase during pancreatic ductal adenocarcinoma development

Pancreatic ductal adenocarcinoma (PDAC) is usually incurable. Contrary to genetic mechanisms involved in PDAC pathogenesis, epigenetic alterations are ill defined. Here, we determine the contribution of epigenetically silenced genes to the development of PDAC. We analyzed enriched, highly methylated DNAs from PDACs, chronic pancreatitis (CP) and normal tissues using CpG island microarrays and identified WNK2 as a prominent candidate tumor suppressor gene being downregulated early in PDAC development. WNK2 was further investigated in tissue microarrays, methylation analysis of early pancreatic intraepithelial neoplasia (PanIN), mouse models for PDAC and pancreatitis, re-expression studies after demethylation, and cell growth assays using WNK2 overexpression. Demethylation assays confirmed the link between methylation and expression. WNK2 hypermethylation was higher in tumor than in surrounding inflamed tissues and was observed in PanIN lesions as well as in a PDAC mouse model. WNK2 mRNA and protein expressions were lower in PDAC and CP compared with normal tissues both in patients and mouse models. Overexpression of WNK2 led to reduced cell growth, and WNK2 expression in tissues correlated negatively with pERK1/2 expression, a downstream target of WNK2 responsible for cell proliferation. Downregulation of WNK2 by promoter hypermethylation occurs early in PDAC pathogenesis and may support tumor cell growth via the ERK-MAPK pathway.

Expression of type 2 orexin receptor in human endometrium and its epigenetic silencing in endometrial cancer

CONTEXT

Orexins A and B are neuropeptides that bind and activate 2 types of receptors. In addition to direct action in the brain, the orexinergic system has broader implications in peripheral organs, and it has been proposed to have a role in the induction of apoptosis. There are very few data on the endometrium.

OBJECTIVE

The expression and epigenetic regulation of type 2 orexin receptor (OX2R) was investigated in the human endometrium as well as in endometrial endometrioid carcinoma (EEC).

METHODS

OX2R localization was studied by immunohistochemistry in normal endometrium (n = 24) and in EEC (n = 32). The DNA methylation status of a CpG island located in the first exon of OX2R was analyzed by bisulfite sequencing in normal (n = 18), EEC (n = 34), and 3 endometrial cell lines. On the latter, mRNA expression and Western blotting as well as in vitro induction with orexin were performed.

RESULTS

Expression of the OX2R protein was detected in normal endometrial epithelia, whereas it was frequently lacking in EEC. This loss was associated with hypermethylation of OX2R in EEC in comparison with normal endometrium (median CpG methylation percentages of 48.85% and 5.85%, respectively). In cell lines, hypermethylation correlated with weak OX2R expression. Additionally, in vitro treatment of the 3 EEC cell lines with orexins A and B did not result in proliferation change

CONCLUSIONS

Altogether our data provide evidence for the epigenetic silencing of OX2R in EEC. The implication of the OX2R loss in tumoral progression remains to be elucidated.

Expression of CD68 in non-myeloid cell types

CD68, the human homologue of macrosialin, is commonly regarded as a selective marker for human monocytes and macrophages. Its expression is thought to be regulated by a macrophage-specific promoter. However, several immunohistochemical studies have indicated that CD68 antibodies also react with other haematopoietic and non-haematopoietic cell types. We investigated the expression of CD68 in various primary cells and carcinoma cell lines using immunohistochemistry, flow cytometry, Western blot analysis and qRT-PCR. Weak but significant immunoreactivity was detected in lymphocytes and several tumour cell lines whereas staining of primary fibroblasts and endothelial cells was comparable to macrophages. The intensity of CD68 staining in individual cell types depended on the antibody clone and the fixation technique. Anti-CD68 mAb KP1 should be used with great caution for frozen tissue sections due to its reactivity with a wide variety of cell types. Also, care should be taken when distinguishing macrophages from fibroblasts/stromal cells in paraffin sections after formalin fixation since both cell types are stained highly positive for CD68. In accordance, mRNA expression of CD68 was not only detected in macrophages and monocytes but also in fibroblasts as well as endothelial cells and tumour cells, although with a varying intensity. Cloning of full length 5'-sequences and determination of transcription start sites shows that macrophages and fibroblasts initiate transcription within the known promoter region; however, from different start sites, indicating alternative promoter architecture in myeloid versus non-myeloid cells. We suggest that CD68 is not a selective macrophage marker but rather a lysosomal protein that is enriched in macrophages.

Evolution of the TIR, tolls and TLRs: functional inferences from computational biology

The mammalian toll-like receptors (TLRs) are products of an evolutionary process that began prior to the separation of plants and animals. The most conserved protein motif within the TLRs is the TIR, which denotes Toll, the Interleukin-1 receptor, and plant disease Resistance genes. To trace the ancestry of the TLRs, it is desirable to draw upon the sequences of TIR domains from TLRs of diverse vertebrate species, including species with known dates of divergence (i.e., representatives of Mammalia and Aves) in order to establish a relationship between time and genetic divergence. It appears that a gene ancestral to modern TLRs 1 and 6 duplicated approximately 130 million years ago, only shortly before the speciation event that led to humans and mice. Though it is not represented in mice, TLR10 split from the TLR[1/6] precursor about 300 million years ago. The origins of other TLRs are more ancient, dating to the origins of vertebrate life, and some present-day vertebrate species appear to have many more TLRs than others. Moreover, the patterns of TLR expression are quite variable at the level of tissues, even among closely related species. A given TLR in species that are related by descent from a common ancestor may acquire different duties within each descendant line, so that some microbial inducers are avidly recognized in one species but not in others; likewise the intensity and the antomic location of an innate immune response may vary considerably. In this review, we discuss the computational methods used to analyze divergence of the TIR, and the conclusions that may be safely drawn.

[The "classical" macrophage marker CD68 is strongly expressed in primary human fibroblasts]

AIM

Monoclonal antibodies against the human homologue of mouse macrosialin, CD68, are generally commercialized as markers for human monocytes and macrophages. Indeed, CD68 is considered as a selective marker for human myeloid cells, although several previous immunohistochemical studies indicate that some antibody clones also react with other hematopoietic and non-hematopoietic cell types. The aim of our study was to verify these observations and to evaluate the reliability of CD68 as a macrophage marker.

METHODS

We investigated protein and RNA expression of CD68 in various fibroblast types and carcinoma cell lines as compared to monocytes and macrophages using immunohistochemistry, flow cytometry, and specific RT-PCR. Different monoclonal antibody clones against CD68 were applied including KP-1 and EBM11.

RESULTS

As expected, the intensity of immunohistochemical and flow cytometric CD68 staining was dependent on both the antibody clone and the fixation procedure. However, fibroblasts isolated from normal skin, normal breast, breast tumor tissue, and osteoarthritis synovia clearly expressed CD68 protein at levels comparable to macrophages. The specificity of CD68 expression in fibroblasts was verified by RT-PCR which also showed some tumor cell types to express CD68 mRNA.

CONCLUSION

Our findings clearly demonstrate that the expression of CD68 is not restricted to the macrophage lineage. This is highly relevant for experimental and diagnostic purposes, since anti CD68 antibodies cannot be accepted without reservations for the discrimination of myeloid cells and fibroblasts even in paraffin sections after formalin fixation.

The membrane-bound ectopeptidase CPM as a marker of macrophage maturation in vitro and in vivo

During terminal maturation of human blood monocytes into macrophages, a multitude of phenotypic and functional changes occurs: cells increase in size, they enhance their capacity for phagocytosis and tumor cytotoxicity but decrease their ability for T-lymphocyte stimulation. The pattern of secreted cytokines is shifted as is the profile of surface antigens. We recently identified carboxypeptidase M (CPM) as a macrophage maturation-associated antigen detected by mAb MAX. 1/MAX. 11. CPM, a phosphoinositol-linked ectopeptidase, is able to process a multitude of different substrates, among them immunologically important peptides like bradykinin, anaphylatoxins and enkephalins. It was previously shown to be expressed in placenta, lung, and kidney. CPM as detected by MAX. 1/11 shows a strong expression on monocyte-derived macrophages in vitro and on macrophages in vivo accompanying T-lymphocyte activation like during allogeneic transplant rejection or allergic alveolitis. In contrast, its expression is suppressed on macrophages by some types of tumor cells. CPM expression seems to correlate with macrophage cytotoxic functions. However, the biological importance of CPM expression in human macrophages in vivo is difficult to predict. A wide range of biologically active peptides are cleaved by CPM, and the relevance of CPM peptide processing during an immune reaction is only poorly understood. The generation and analysis of CPM-deficient animals might improve our understanding of CPM function. Therefore we cloned a cDNA for the murine homologue of CPM. However, expression of mCPM was undetectable in murine primary macrophages and macrophage cell-lines, suggesting that CPM expression and function is not conserved between human and mouse macrophages.

Adhesion induced expression of the serine/threonine kinase Fnk in human macrophages

Members of the polo subfamily of protein kinases play crucial roles in cell proliferation. To study the function of this family in more detail, we isolated the cDNA of human Fnk (FGF-inducible kinase) which codes for a serine/threonine kinase of 646 aa. Despite the homology to the proliferation-associated polo-like kinase (Plk), tissue distribution of Fnk transcripts and expression kinetics differed clearly. In contrast to Plk no correlation between cell proliferation and Fnk gene expression was found. Instead high levels of Fnk mRNA were detectable in blood cells undergoing adhesion. The transition of monocytes from peripheral blood to matrix bound macrophages was accompanied by increasing levels of Fnk with time in culture. Neither treatment of monocytes with inducers of differentiation nor withdrawal of serum did influence Fnk mRNA levels significantly, suggesting that cell attachment triggers the onset of Fnk gene transcription. The idea that Fnk is part of the signalling network controlling cellular adhesion was supported by the analysis of the cytoplasmic distribution of the Fnk protein and the influence of its overexpression on the cellular architecture. Fnk as fusion protein with GFP localized at the cellular membrane in COS cells. Dysregulated Fnk gene expression disrupted the cellular f-actin network and induced a spherical morphology. Furthermore, Fnk binds to the Ca2+/integrin-binding protein Cib in two-hybrid-analyses and co-immunoprecipitation in assays. Moreover, both proteins were shown to co-localize in mammalian cells. The homology of Cib with calmodulin and with calcineurin B suggests that Cib might be a regulatory subunit of polo-like kinases.

PU.1 and interferon consensus sequence-binding protein regulate the myeloid expression of the human Toll-like receptor 4 gene

The protein product of the Toll-like receptor (TLR) 4 gene has been implicated in the signal transduction events induced by lipopolysaccharide (LPS). In mice, destructive mutations of Tlr4 impede the normal response to LPS and cause a high susceptibility to Gram-negative infection. Expression of TLR4 mRNA in humans is restricted to a small number of cell types, including LPS-responsive myeloid cells, B-cells, and endothelial cells. To investigate the molecular basis for TLR4 expression in cells of myeloid origin, we cloned the human TLR4 gene and analyzed its putative 5'-proximal promoter. In transient transfections a region of only 75 base pairs upstream of the major transcription initiation site was sufficient to induce maximal luciferase activity in THP-1 cells. The sequence of this region is similar in human and mouse TLR4 genes and lacks a TATA box, typical Sp1-sites or CCAAT box sequences. Instead, it contains consensus-binding sites for Ets family transcription factors, octamer-binding factors, and a composite interferon response factor/Ets motif. The activity of the promoter in macrophages was strictly dependent on the integrity of both half sites of the composite interferon response factor/Ets motif, which was constitutively bound by the myeloid and B-cell-specific transcription factor PU.1 and interferon consensus sequence-binding protein. These results indicate that the two tissue-restricted transcription factors PU.1 and interferon consensus sequence-binding protein participate in the basal regulation of human TLR4 in myeloid cells. Cloning of the human TLR4 gene provides a basis for further investigation of the possible impact of genetic variations on the susceptibility to infection and sepsis.

Characterization of MAX.3 antigen, a glycoprotein expressed on mature macrophages, dendritic cells and blood platelets: identity with CD84

MAX.3 is a monoclonal antibody that preferentially reacts with mature macrophages (MAC), monocyte-derived dendritic cells, megakaryocytes and platelets. In this study, we describe the characterization, purification and identification of the MAX.3 antigen. Immunoprecipitation and SDS/PAGE revealed different molecular masses of MAX.3 antigen in MAC (60-90 kDa) and platelets (58-64 kDa), whereas a similar size (45 kDa) was observed in both cell types after digestion with N-glycosidase F. Lectin affinity and sequential treatment with different glycosidases suggests complex type glycosylation of MAX.3 antigen in MAC and hybrid type glycosylation in platelets. Amino acid sequencing led to the identification of a corresponding cDNA clone and showed its identity to the sequence of the CD84 antigen, a member of the CD2 family of cell surface molecules. MAX.3/CD84 was further studied by immunohistochemistry and a variable expression was found on tissue MAC, confirming this antigen to be mainly a marker for MAC in situ.

Cloning and characterization of the murine genes for bHLH-ZIP transcription factors TFEC and TFEB reveal a common gene organization for all MiT subfamily members

The microphthalmia-TFE (MiT) subfamily of basic helix-loop-helix leucine zipper (bHLH-ZIP) transcription factors, including TFE3, TFEB, TFEC, and Mitf, has been implicated in the regulation of tissue-specific gene expression in several cell lineages. In this report, we investigate the genomic organization and structural relatedness of MiT transcription factors. We characterized the gene for mTFEC, which covers a region of more than 50 kb and is composed of seven exons. Further, we cloned a cDNA for the murine TFEB homologue and characterized its genomic structure. The eight coding exons of mTFEB are distributed over a 6-kb region. A multiple alignment of amino acid sequences of known MiT subfamily members indicates undescribed, conserved N-terminal regions and common putative phosphorylation sites for TFE3, TFEB, and Mitf. Also, intron-exon borders for characterized MiT genes appear completely conserved. A new family member and closely related putative transcription factor in Caenorhabditis elegans was identified by database searches that show a similar genomic organization within the bHLH-ZIP region and the acidic domain. Evolutionary aspects and implications for structure-function relationships are discussed.

TFEC is a macrophage-restricted member of the microphthalmia-TFE subfamily of basic helix-loop-helix leucine zipper transcription factors

The murine homologue of the TFEC was cloned as part of an analysis of the expression of the microphthalmia-TFE (MiT) subfamily of transcription factors in macrophages. TFEC, which most likely acts as a transcriptional repressor in heterodimers with other MiT family members, was identified in cells of the mononuclear phagocyte lineage, coexpressed with all other known MiT subfamily members (Mitf, TFE3, TFEB). Northern blot analysis of several different cell lineages indicated that the expression of murine TFEC (mTFEC) was restricted to macrophages. A 600-bp fragment of the TATA-less putative proximal promoter of TFEC shares features with many known macrophage-specific promoters and preferentially directs luciferase expression in the RAW264.7 macrophage cell line in transient transfection assays. Five of six putative Ets motifs identified in the TFEC promoter bind the macrophage-restricted transcription factor PU.1 under in vitro conditions and in transfected 3T3 fibroblasts; the minimal luciferase activity of the TFEC promoter could be induced by coexpression of PU.1 or the related transcription factor Ets-2. The functional importance of the tissue-restricted expression of TFEC and a possible role in macrophage-specific gene regulation require further investigation, but are likely to be linked to the role of the other MiT family members in this lineage.

Platelets induce monocyte differentiation in serum-free coculture

Terminal maturation of blood monocytes (MO) in vitro and in vivo into macrophages (MAC) occurs as a result of interactions with various cell types. To characterize some of the cell-cell connections that may be important for MO differentiation we cocultured human MO with lymphocytes and/or with platelets. We found that intact platelets strongly promoted MO maturation under serum-free conditions as evident from the expression of differentiation-dependent antigens and morphology. To further characterize the differentiation-inducing component(s) we prepared membrane and cytosol fractions of platelets. Both fractions could induce MO maturation, comparable to intact platelets. Further centrifugation of the cytosolic fraction revealed that only the pellet of ultracentrifugation, e.g., membrane fragments, could induce MO differentiation. Digestion with either trypsin or neuraminidase could only partially inhibit this effect. The same was true for heat-treated fractions, indicating that this platelet-derived differentiation stimulus is not solely an intact protein. Next we prepared protein and lipid fractions of platelets. Treatment of MO with platelet proteins or platelet lipids clearly showed that only the lipid components were able to induce MO maturation. We propose components present in the lipid fraction of platelet membranes as possible inducers of MO maturation in vitro.

Carboxypeptidase M as a marker of macrophage maturation

During terminal maturation of blood monocytes (MO) into macrophages (MAC), a multitude of phenotypic and functional changes occur: cells increase in size and enhance their capacity for phagocytosis and tumor cytotoxicity, but decrease their ability for T-lymphocyte stimulation. The pattern of secreted cytokines is shifted as is the profile of surface antigens. The identity of the MAC maturation-associated antigen MAX.I/MAX.II with carboxypeptidase M (CPM), a phosphoinositol-linked endopeptidase, was recently described. CPM is able to process a multitude of different substrates, among them immunologically important peptides such as bradykinin, anaphylatoxins and enkephalins. It was previously shown to be expressed in placenta, lung and kidney. CPM as detected by MAX.I/II shows a strong expression on MO-derived MAC in vitro and on MAC in vivo accompanying T-lymphocyte activation such as during allogeneic transplant rejection or allergic alveolitis. In contrast, its expression is suppressed on MAC by some types of tumor cells. A synchronous expression of CPM together with MAC cytotoxic function makes a functional relationship very well possible. However, the biological importance of CPM expression on MAC in vivo is difficult to predict, since a wide range of biologically active peptides are substrates for CPM, and the relevance for most of those peptides to be processed by CPM during an immune reaction is only poorly understood at present.

Sequence of human carboxypeptidase D reveals it to be a member of the regulatory carboxypeptidase family with three tandem active site domains

We have cloned the cDNA for human carboxypeptidase D (CPD), a new B-type metallocarboxypeptidase that is membrane bound and has an acidic pH optimum. The 5.8 kb of cDNA sequenced contains an open reading frame of 4131 bp encoding 1377 amino acid residues. The sequence is similar (75% identity) to duck gp180, a protein that was isolated, cloned and sequenced as a hepatitis B virus-binding protein but not characterized as a carboxypeptidase. Hydropathic analysis revealed a hydrophobic region at the N-terminus, representing the signal peptide, and one near the C-terminus that probably represents the transmembrane anchor. The most striking feature is the presence of three tandem carboxypeptidase homology domains that have sequence similarity to the regulatory B-type carboxypeptidase family, typified by carboxypeptidases M, E and N. Because of the three repeats, CPD is about three times larger (175-180 kDa) than other members of this family (approx. 50-62 kDa). Domain 2 is most closely related to carboxypeptidases M, E and N (45-48% identity), followed by domain 1 (37-38%) and domain 3 (20-27%). There is a much higher sequence identity in regions containing putative active site residues, and all catalytically important residues are strictly conserved in domains 1 and 2. In domain 3, however, only 1 of 8 active site residues is conserved, indicating that this portion might not be catalytically active. Northern blotting of mRNA from human tissues and cells showed high levels of CPD mRNA in placenta, pancreas and Hep G2 hepatoma cells, and smaller amounts in skeletal muscle, heart and HT-29 colon carcinoma and melanoma cell lines.

Molecular characterization of the gene for human cartilage gp-39 (CHI3L1), a member of the chitinase protein family and marker for late stages of macrophage differentiation

We have previously reported that the expression of HC gp-39, a 39-kDa secretory glycoprotein and member of the chitinase protein family, is associated with late stages of monocyte to macrophage maturation. To allow further investigations of its unique expression pattern and to facilitate studies on the regulation of this "marker gene," we characterized the genomic organization of the HC gp-39 gene (HGMW-approved symbol CHI3L1) and cloned its 5'-proximal promotor region. The gene is composed of 10 exons distributed over an 8-kb region. Two transcriptional initiation sites located 82 and 126 nucleotides upstream of the ATG start codon were identified using primer extension and S1 nuclease protection assays. We sequenced 1.3 kb of the 5'-flanking region and identified a variety of putative regulatory elements.

Molecular cloning of a 1alpha,25-dihydroxyvitamin D3-inducible transcript (DDVit 1) in human blood monocytes

The differentiation and activation of monocytes (MO) and monocytic cells is modulated by 1alpha,25-dihydroxyvitamin D3 (Vitamin D3). In order to investigate early effects on the differentiation process of MO, we used the mRNA Differential Display technology to identify genes that are induced in freshly isolated human blood MO cultured for 4 hours with Vitamin D3. A cDNA fragment was isolated and Northern analysis confirmed a low expression of this cDNA at about 1,4 kb in MO which was increased by the addition of Vitamin D3. Using the rapid amplification of cDNA Ends (RACE)-PCR we got a transcript (DDVit 1) of a length of 1251 bp containing an open reading frame that encodes a putative 16,5 kD protein. Database search revealed an identity with a possible enterocyte differentiation promoting factor with a length of 1177 bp that has not been further characterized. Therefore DDVit 1 may be a differentiation promoting factor for the monocytic lineage. Further investigations will clarify the role of this protein in the differentiation process of MO.

Identification of a membrane-bound carboxypeptidase as the mammalian homolog of duck gp180, a hepatitis B virus-binding protein

A unique membrane-bound carboxypeptidase was discovered and characterized in membrane fractions of human skin fibroblasts and the mouse monocyte-macrophage cell line J774A.1 and was partially purified from human placenta. Enzymatic characterization identified it as a new member of the regulatory B-type metallocarboxypeptidases, different from carboxypeptidases B, E, M, N and U. It is, however, similar to the newly described bovine carboxypeptidase D, suggested to be a homolog of duck gp180, a 180 kDa hepatitis B virus-binding protein. To prove this, a partial cDNA encoding a 20 kDa fragment of the human homolog of duck gp180 was expressed in bacteria and the recombinant protein was purified. Antibodies raised to the protein immunoprecipitated 94% or 72% of the low pH carboxypeptidase activity in human skin fibroblasts or J774A.1 cells and gave a 175 kDa protein band in Western blots. Thus, carboxypeptidase D is the mammalian homolog of duck gp180 and is distributed in a variety of different cell types.

Differential screening identifies genetic markers of monocyte to macrophage maturation

Maturation of cells of the mononuclear phagocyte lineage from bone marrow precursors to tissue macrophages (MAC) via circulating blood monocytes (MO) is a multistep process only partially understood. Similarly, MAC differentiation can be observed if MO are cultured in vitro. In an attempt to further characterize molecular changes occurring during this process we carried out differential screening of a MO-derived MAC cDNA library using MO and MAC cDNA. After subcloning and confirmation by a second round of screening, partial sequencing of 41 cDNA clones was performed. In 33 clones the sequences of 7 different previously identified cDNAs were found. The mRNA expression of two of the corresponding genes (apolipoprotein E, ferritin light chain) is already known to be up-regulated during MAC maturation. For one gene (cathepsin B), a specific up-regulation of mRNA expression could be shown corresponding to previous protein data. For four genes [human cartilage glycoprotein (HC-gp39), osteopontin, type IV collagenase, and tryptophanyl-tRNA synthetase] the specific expression in MAC versus MO was previously unknown but could be confirmed by the use of Northern blot analysis. Of these genes, HC-gp39 is especially interesting because it is only expressed during the late stages of MAC differentiation.

Molecular cloning and expression of mouse procalcitonin

The nucleotide sequence for mouse calcitonin was determined from a cDNA obtained using a polymerase chain reaction (PCR) based method, the rapid amplification of cDNA ends (RACE)-PCR. Primers designed from highly conserved regions in the coding sequences of known rat and human calcitonin cDNAs were used to amplify calcitonin cDNA as 5'-end and 3'-end fragments from mouse thyroid RNA. The obtained cDNA is 850 bp in length most probably representing the entire mouse calcitonin mRNA. It contains an open reading frame coding for a 136 amino acid protein with a calculated M(r) of 15,143. Comparison of the deduced amino acid sequences of preprocalcitonin of mice with other species revealed highest homologies to the rat (93%) and human (77%) sequences. A recombinant form of mouse precalcitonin (rmPCT) of approximately 17 kDa was expressed as a fusion peptide in E.coli transformed with a PCR-cloned expression construct.

Human monocytes induce a carcinoma cell line to secrete high amounts of nitric oxide

Nitric oxide (NO) is a short-lived pleiotropic mediator with a multitude of biologic functions. The inducible form of NO synthase (iNOS) is responsible for the discontinuous production of high amounts of NO and is important for the cytotoxic capacity of macrophages in rodents, whereas NO production by human macrophages or monocytes (MO) is under debate. Here we report that high amounts of NO are synthesized in cocultures of human MO with the human carcinoma cell line RT4 without further stimulation. Both cell types have to be viable and metabolically active for NO production. However, in contrast to reports by others, we could demonstrate that tumor cells and not MO are the producers of NO by the following findings: 1) NO release was induced in RT4 cells, but not in MO, by diluted supernatants (SN) of RT4/MO cocultures; 2) SN of MO stimulated with tumor cell membrane preparations were sufficient to induce NO release by tumor cells; and 3) NOS mRNA expression could be detected only in tumor cells, not in MO. Separating both cells by a cell-impermeable membrane resulted in NO amounts comparable to those in cocultures with direct cell contact, indicating one or more soluble NO-inducing factors. Considerable amounts of IL-1 beta and TNF-alpha were present in cocultures. IL-1 beta and TNF-alpha, mediators produced by activated MO, in combination induce NO release in RT4 cells. Blocking of TNF-alpha or IL-1 in SN inhibited NO release in RT4 cells. This indicates that IL-1 beta and TNF-alpha play prominent roles in iNOS induction by MO in RT4 tumor cells.

Human monocytes induce a carcinoma cell line to secrete high amounts of nitric oxide

Nitric oxide (NO) is a short-lived pleiotropic mediator with a multitude of biologic functions. The inducible form of NO synthase (iNOS) is responsible for the discontinuous production of high amounts of NO and is important for the cytotoxic capacity of macrophages in rodents, whereas NO production by human macrophages or monocytes (MO) is under debate. Here we report that high amounts of NO are synthesized in cocultures of human MO with the human carcinoma cell line RT4 without further stimulation. Both cell types have to be viable and metabolically active for NO production. However, in contrast to reports by others, we could demonstrate that tumor cells and not MO are the producers of NO by the following findings: 1) NO release was induced in RT4 cells, but not in MO, by diluted supernatants (SN) of RT4/MO cocultures; 2) SN of MO stimulated with tumor cell membrane preparations were sufficient to induce NO release by tumor cells; and 3) NOS mRNA expression could be detected only in tumor cells, not in MO. Separating both cells by a cell-impermeable membrane resulted in NO amounts comparable to those in cocultures with direct cell contact, indicating one or more soluble NO-inducing factors. Considerable amounts of IL-1 beta and TNF-alpha were present in cocultures. IL-1 beta and TNF-alpha, mediators produced by activated MO, in combination induce NO release in RT4 cells. Blocking of TNF-alpha or IL-1 in SN inhibited NO release in RT4 cells. This indicates that IL-1 beta and TNF-alpha play prominent roles in iNOS induction by MO in RT4 tumor cells.

Molecular cloning of a novel macrophage maturation-associated transcript encoding a protein with several potential transmembrane domains

Differentiation of tissue macrophages from bone marrow progenitor cells via circulating blood monocytes is a complex and multistep process. In order to analyze macrophage maturation on the molecular level we used the method of mRNA differential display to identify novel genes that are preferentially expressed in mature, in vitro differentiated macrophages. A PCR-fragment could be isolated that was amplified from macrophages, but not from freshly isolated monocytes, and macrophage-specific expression was confirmed by Northern blot analysis. Several corresponding cDNA clones could be isolated from a macrophage cDNA library, covering a nucleotide sequence of 2.5 kb. Nucleotide sequence of this cDNA showed no homology to known genes. The sequence reveals an open reading frame that codes for a 238 amino acid hydrophobic protein with seven potential transmembrane domains, suggesting a possible role as a receptor or an ion channel.

Carboxypeptidase M is identical to the MAX.1 antigen and its expression is associated with monocyte to macrophage differentiation

The two monoclonal antibodies MAX.1 and MAX.11 recognize cell surface antigens that are almost undetectable on monocytes but highly expressed on differentiated macrophages. Biochemical characterization revealed that both antibodies detect the same 58-64-kDa glycoprotein anchored to the plasma membrane by glycosyl-phosphatidylinositol linkage. We purified the MAX.1/11 antigen by immunoaffinity chromatography using monoclonal antibody MAX.11. The NH2-terminal amino acid sequence was determined and turned out to be identical to the NH2-terminal sequence of the membrane-bound carboxypeptidase M. By precipitation with antibodies MAX.1 and MAX.11, membrane preparations of macrophages and placental microvilli were almost completely depleted of enzyme activity, indicating that the two antibodies indeed recognize carboxypeptidase M. Immunoreactivity of both antibodies correlates with the reported tissue distribution of enzyme activity. Expression of carboxypeptidase M on mRNA level and enzymatic activity markedly increase during in vitro differentiation of monocytes, according to the described increase in MAX.1 and MAX.11 antigen expression. Moreover, in vitro differentiated macrophages show the highest specific activity yet described in any tissue. In addition, carboxypeptidase M expression could be detected in HL-60, U937, and THP-1 myeloid cell lines. Vitamin D3-induced monocytic differentiation resulted in an increased carboxypeptidase M expression in all three cell lines. Further studies are needed to elucidate the functional role of carboxypeptidase M during monocytic differentiation and activation.