Endothelial-like cells derived from human CD14 positive monocytes.

In the present study, we show that endothelial-like cells (ELCs) can develop from human CD14-positive mononuclear cells (CD14 cells) in the presence of angiogenic growth factors. The CD14 cells became loosely adherent within 24 h of culture and subsequently underwent a distinct process of morphological transformation to caudated or oval cells with eccentric nuclei. After 1 week in culture the cells showed a clear expression of endothelial cell markers, including von Willebrand factor (vWF), CD144 (VE-cadherin), CD105 (endoglin), acetylated low-density lipoprotein (AC-LDL)-receptor, CD36 (thrombospondin receptor), FLT-1, which is vascular endothelial cell growth factor (VEGF) receptor-1, and, to a weaker extent, KDR (VEGF receptor-2). Furthermore, in these cells structures resembling Weibel-Palade bodies at different storage stages were identified by electron microscopy, and upon culturing on three-dimensional fibrin gels the cells build network-like structures. In addition, cell proliferation and vWF expression was stimulated by VEGF, and the endothelial cell adhesion molecules CD54 (ICAM-1), and CD106 (VCAM-1) became transiently inducible by tumor necrosis factor-alpha (TNF-alpha). In contrast, the dendritic markers CD1a, and CD83 were not expressed to any significant extent. The expression of CD68, CD80 (B7-1), CD86 (B7-2), HLA-DR and CD36 may also suggest that ELCs might be related to macrophages, sinus lining or microvascular endothelial cells. Taken together, our observations indicate that ELCs can differentiate from cells of the monocytic lineage, suggesting a closer relationship between the monocyte/macrophage- and the endothelial cell systems than previously supposed.

Elevated expression of endoglin, a component of the TGF-beta-receptor complex, correlates with proliferation of tumor endothelial cells.

Endoglin/CD105 is a membrane protein involved in the TGF-beta receptor signalling pathway. Endoglin expression has been reported to be selective for a few cell types, in particular endothelial cells, although a number of conflicting reports have been published. In this study, we performed a detailed analysis of endoglin expression in human lung tumors and different tumor and endothelial cell lines, employing reverse-transcriptase-polymerase-chain reaction as well as immunoblotting and immunohistochemistry using verified antibodies to endoglin. Our data show a clearly preferential expression of both endoglin mRNA and protein in endothelial cells. In tumors, endoglin expression was strongly elevated in the angiogenic endothelium at the tumor edges. In agreement with this observation, we find a clear correlation between endoglin expression and markers of proliferation, such as cyclin A and Ki-67, suggesting that endoglin expression is linked to cell-cycle regulation. These findings not only resolve some of the discrepancies in the literature, but also provide the basis for further applications making use of its selective localization and expression in the tumor vasculature.

Transition from SCLC to NSCLC phenotype is accompanied by an increased TRE-binding activity and recruitment of specific AP-1 proteins.

Transitions from small cell (SCLC) to non-small cell lung cancer (NSCLC) cells have been documented both in vitro and in vivo and are thought to be an important step during tumor progression of human small cell lung cancer towards a treatment-resistant tumor state. We have screened NSCLC and SCLC cell lines for differences in the composition of nuclear transcription factors using consensus oligonucleotide sequences (SRE, Ets, TRE, CRE, B-motif, GAS, E-box). We found NSCLC cells to exhibit significantly higher AP-1 binding activity than SCLC cells consistent with the increased expression of CD44, an AP-1 target gene. To gain more insight into the molecular mechanisms underlying these differences, we analysed SCLC cell lines (NCI-N592 and NCI-H69) which were phenotypically transformed into NSCLC-type cells by transfection with activated H-ras and c-myc oncogenes. In these cells, ras-induced transition is accompanied by a strong induction of AP-1-binding activity along with increased expression of CD44 mRNA and protein. When analysing the composition of the AP-1 complex in more detail and comparing ras-induced versus phorbol ester-induced changes, we found Fra-1 to be the major component induced in ras-transfected but not in phorbol-ester treated or non-treated parental SCLC cells. This finding is paralleled by the observation that among the various members of the Fos and Jun family analysed (c-Fos, FosB, Fra-1, Fra-2, c-Jun, JunD, JunB) fra-1 is the only gene to be exclusively expressed in NSCLC cells but not in cells of SCLC origin. Our data, thus, point to a histiotype-related mechanism of recruitment among AP-1 proteins which may have bearings on the fate of lung cancer development.

A novel small-cell lung carcinoma-specific DNA-binding activity related to the transcription factor ap-1.

A novel TRE-binding protein complex was detected specifically in 12 out of 13 small cell lung carcinoma (SCLC) cell lines. This complex was characterised by a lower electrophoretic mobility than the 'ubiquitous' complex present in all other carcinoma cell lines analysed. As shown by UV-crosslinking and South-Western blotting, the SCLC-specific complex contains a protein with an apparent M(r) > 100 kD, which is far bigger than all Fos and Jun proteins described to date. In addition, the DNA-binding specificity of this complex is different from the specificity of the 'ubiquitous' complex or a Fos/Jun heterodimer.

Mapping of functional domains in Fos and Jun proteins using epitope-specific antibodies.

A panel of epitope-specific antibodies, directed against c-Fos, c-Jun, and FosB derived oligopeptide sequences, was generated and used to study the interaction of Fos and Jun proteins and the binding of the Fos/Jun complex to the AP1-binding site (TRE). Our results strongly support results previously obtained by site-directed mutagenesis experiments. The leucine zipper is the major site of interaction between Fos and Jun. Antibodies directed against this domain of Fos bound free Fos protein efficiently, but were unable to recognize Fos within the Fos/Jun complex. In contrast, all other Fos epitope-specific antibodies showed similar reactivity with both free and complexed Fos. Antibodies directed against sequences adjacent to the leucine zipper inhibited formation of the complex. This may suggest that amino acids in the vicinity of the leucine zipper may also play some role in the formation of the protein complex. Binding of Fos/Jun to the TRE was inhibited only by antibodies directed against the basic regions in Fos or Jun previously suggested to represent the DNA binding sites. The fact that very similar results were obtained by two totally different strategies, i.e., mutagenesis experiments and domain mapping using epitope-specific antibodies, lends strong support to the proposed domain structure of Fos and Jun family members.

A Fos protein containing the Jun leucine zipper forms a homodimer which binds to the AP1 binding site.

The TPA (12-O-tetradecanoyl-phorbol-13-acetate) responsive element (TRE) is recognized by the inducible transcription factor AP1, a heterodimeric complex of Fos- and Jun-protein subunits, which each contain a specific structure known as the leucine zipper through which they interact. Studies using site-directed mutagenesis have shown that a basic region adjacent to the leucine zipper in Fos is crucial for the interaction of the Fos-Jun complex with the TRE, and probably represents a site of interaction with DNA. The functionally crucial amino acids in this region are almost completely conserved between Fos and Jun (refs 6, 7 and 11; M.N. and R.M., unpublished results), indicating the formation of a nearly symmetrical DNA-binding site in the Fos-Jun complex. Whereas Jun can form a homodimeric protein complex which binds to the TRE, Fos is unable to do so. The Fos-Jun heterodimer, however, possesses at least a 30-fold-higher affinity for the TRE than does the Jun-Jun homodimer, indicating cooperative binding. Because Fos cannot form a homodimer it is not known whether Fos specifically recognizes part of the TRE or has a different role in the binding of the Fos-Jun complex to DNA. Here we report that exchanging the leucine zipper in Fos with that of Jun generates a protein (termed psi-Fos) that can form a complex with Fos. This Fos-psi-Fos complex, and to a lesser extent a homodimeric psi-Fos complex, exhibits specific binding to the TRE. This finding strongly supports the hypothesis that Fos and Jun form a nearly symmetrical DNA-binding site that interacts with the palindromic TRE.

Epitopic discrimination by monoclonal antibodies directed against the same alkylated nucleoside.

Epitopic specificity of three monoclonal antibodies (mAb's) (coded as ER-6, ER-3, and EM-1) was examined through the utilization of haptenic structural analogs. The binding affinity expressed by the microscopic equilibrium constant (Ki) (Yuhasz, et al., Biochemistry 26, 2334-2342 (1987] of the immunizing hapten, O6-ethyl-2'-deoxy-guanosine (*G) and eight structural analogs, were analyzed by a nitrocellulose affinity filter assay (NAFA) and radioimmunoassay (RIA) for each mAb to determine the protein-hapten interaction between the epitope and the binding cavity. Several components of the *G hapten were determined to be critical for each mAb recognition, while all three mAb's were found to require the O6-ethyl moiety, conjugated guanine base ring, the glycosyl bond and the sugar ring C [1'] and C [2'] position. This investigation further probes and categorizes the binding specificity of the monoclonal antibodies after incorporation of the *G monomer into three short deoxyribooligomeric haptens: O6-ethyl-2'-deoxyguanylyl 3',5' deoxyadenosine (*GA), 2'-deoxyadenylyl 3',5' O6-ethyl-2'-deoxyguanylyl 3',5' 2'-deoxyadenosine (A*GA), and O6-ethyl-2'-deoxyguanylyl 3',5' 2'-deoxyadenylyl 3',5'-2'-deoxyadenylyl 3',5' 2'-deoxycytosine (*GAAC). Unlike the similar binding profiles for the monoclonal antibodies and the haptenic structural analogs, the binding profiles for the deoxyribooligomeric haptens were found to differ in their modes of recognition. These results will be compared to ascertain the key components of monomer and oligomer interaction of the binding cavity. It is important for investigations where monoclonal antibodies derived from small haptens are utilized in recognition of larger antigens containing those haptens.

Early CT findings after interstitial radiation therapy for primary malignant brain tumors.

The CT findings after interstitial radiation therapy for brain tumors have not been extensively described. We evaluated retrospectively the CT scans of 13 patients who were treated with brachytherapy for malignant glioma. We found no typical CT appearance that differentiates recurrent tumor from radiation effect. After undergoing brachytherapy, eight of the 13 patients scanned demonstrated enhancement of brain tissue beyond the margins of the original enhancing tumor mass. In most cases, the pattern of enhancement diminished and extended more peripherally from the central necrotic area with time. We also report a new CT finding of focal calcification developing at the site of the radioactive implant.

Thermodynamic investigation of monoclonal antibody alkylated nucleoside interaction as a model for epitope recognition on nucleic acids.

The objective of this investigation is examination of the dominant forces that govern complex formation between a series of monoclonal antibodies directed against O6-ethyl-2'-deoxyguanosine. These monoclonal antibodies (coded as ER-6, ER-3, and EM-1) provide the basis for a thermodynamic comparative evaluation of the potentially different forces that stabilize the various monoclonal antibody (mAb) alkylated nucleoside complexes. The binding affinities of ER-6, ER-3, and EM-1 are measured in terms of specific (O6-ethyl-2'-deoxyguanosine, or O6-EtdGuo) and nonspecific (O6-methyl-2'-deoxyguanosine, or O6-MedGuo) antigens, under a variety of experimental conditions, including pH, sodium chloride addition, 1-propanol addition, and temperature, via a nitrocellulose affinity filter assay. The binding isotherms were analyzed via a least-squares routine fit to a two independent binding sites model. The temperature dependence of the van't Hoff enthalpies for the specific O6-EtdGuo interaction ranges from -15.18 to -18.60 kcal mol-1, while for O6-MedGuo the range was extended from -2.72 to -20.66 kcal mol-1. The standard and unitary entropies were negative for those mAb interactions with O6-EtdGuo as well as for ER-6/O6-MedGuo complex formation. However, it was found that the interactions between ER-3 and EM-1 with O6-MedGuo led to decidedly positive entropic values. These results indicate two different dominant forces at work in complex stabilization. The interaction of the three mAb's with their specific antigen, as well as ER-6/O6-MedGuo interaction (nonspecific), may well be controlled by van der Waals type forces, while ER-3 and EM-1 interactions with nonspecific antigen imply formal charge neutralization electrostatics as the dominant force.

Isolation and structural analysis of a biologically active chicken c-fos cDNA: identification of evolutionarily conserved domains in fos protein.

To identify functionally important domains in the fos gene product we have studied the evolutionary divergence between chicken and mammalian fos proteins. A cDNA containing the entire chicken c-fos coding region was isolated and its nucleotide sequence determined. The deduced 367-amino acid sequence was compared to that of the mouse and human proteins. This comparison revealed a highly conserved domain (98% homology between mouse and chicken) in the center of the protein (85 amino acids) that coincides with a region known to be indispensible for transforming activity. This highly charged domain presumably contains contact sites for DNA and other proteins as well as a nuclear location signal sequence. Two other regions, that are dispensable for transformation, are also highly conserved and may thus be important for the physiological function of c-fos. These are the N-terminal 88 amino acids (85% homology) and the C-terminal 62 amino acids (92% homology). The C-terminus not only contains a potential DNA-binding Zn-finger structure but is also the least divergent region in the protein at the nucleotide level (92% conservation between chicken and mouse), supporting the hypothesis that mRNA secondary structures in this region may contribute to post-transcriptional regulatory mechanisms. In contrast, the domains between the terminal sequences and the center region of fos protein show considerable divergence (39% and 45% homology, respectively), indicating a minor role, if any, for these sequences. The significance of these conclusions is emphasized by the observation that the chicken c-fos protein, expressed from the cDNA inserted into a retrovirally-derived expression vector, efficiently induces morphological transformation in rat fibroblasts. The chicken c-fos gene product could be identified by immunoprecipitation and in vitro transcription/translation of the isolated cDNA as a protein of Mr approximately 60 K.

Monoclonal antibody-based immunoanalytical methods for detection of carcinogen-modified DNA components.

Hybridoma cell lines secreting monoclonal antibodies (Mab) directed against the products formed by reaction of alkylating N-nitroso carcinogens with DNA have been established by fusion of rat or mouse myeloma cells, respectively, with spleen cells of rats or mice immunized either with conjugates of various alkyl-ribonucleosides with suitable carrier proteins, or with alkylated DNA electrostatically complexed to carrier proteins. Due to their high affinity and specificity, some of these Mab detect very low amounts of the respective alkyl-deoxynucleosides (e.g., O6-methyl-2'-deoxyguanosine, O6-ethyl-2'-deoxyguanosine, O6-n-butyl-2'-deoxyguanosine, O6-isopropyl-2'-deoxyguanosine, O4-methyl-2'deoxythymidine, O4-ethyl-2'-deoxythymidine) and can be used in various types of immunoassays. With a competitive radioimmunoassay (RIA), specific DNA alkylation products can be quantitated in hydrolysates of cellular DNA, in body fluids, or in urine. The RIA is routinely applicable, reproducible, and sufficiently sensitive to permit the quantitation of femtomole amounts of modified nucleosides in small samples of DNA. When the alkyl-deoxynucleosides in question are separated from bulk DNA by high-performance liquid chromatography prior to analysis by RIA, very low levels of modification in DNA can be detected. The immuno-slot-blot (ISB), a noncompetitive solid-phase immunoassay, is more sensitive than the RIA. For analysis by ISB, alkylated DNA is heat-denatured and immobilized on nitrocellulose filters prior to exposure to the respective Mab and subsequent binding of a second (125I-labelled or biotinylated) antibody. In immunocytological analysis (ICA), the binding of Mab to alkyl-deoxynucleosides is visualized in individual cells by immunostaining of denatured nuclear DNA in situ (direct immunofluorescence; peroxidase-staining).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation and visualization of alkyl deoxynucleosides in the DNA of mammalian cells by monoclonal antibodies.

Conventional radiochromatographic procedures for the quantitation of carcinogen/mutagen-induced structural DNA modifications have a number of limitations. Thus, these techniques for the most part require application of radioactively labeled carcinogens and the use of relatively large amounts of DNA for analysis at low levels of DNA modification. Radiochromatographic methods also preclude analyses at the level of single cells and DNA molecules. Recently developed immunoanalytical methods have improved this situation considerably. Monoclonal antibodies (Mab) characterized by a high substrate specificity and affinity, in combination with radio- and enzyme-immunoassays, or with "immuno-slot-blot" techniques, now permit the detection of femtomole to subfemtomole amounts of, e.g., alkyldeoxynucleosides in small samples of DNA isolated from tissues or cultured cells previously exposed to nonradioactive N-nitroso compounds. Furthermore, selected Mab can be used to quantitate by direct immunofluorescence (with the aid of computer-based image analysis of electronically intensified fluorescence signals), specific alkyldeoxynucleosides in the nuclear DNA of single cells. With this method, the detection limit for the alkylation product O6-ethyldeoxyguanosine (O6-EtdGuo) is presently of the order of 10(2) -10(3) O6-EtdGuo residues per diploid mammalian genome. Individual cells can thus be monitored for the presence of specific carcinogen-DNA adducts, and with respect to their capacity for enzymatic removal of such modified structures from DNA (as exemplified here by the kinetics of the enzymatic elimination of O6-EtdGuo from the DNA of malignant neurogenic rat cell lines). In combination with transmission electron microscopy, Mab also permit direct visualization (via Mab binding sites) of specific carcinogen-modified structures in individual DNA molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological methods for detection of carcinogen-DNA adducts.

Considerable advances have been made during recent years, with regard to the detection and quantification of carcinogen- or mutagen-induced, structural modifications in the DNA of mammalian cells, by the introduction of immunoanalytical methods, in particular in conjunction with monoclonal antibodies (Mab). Antibodies are characterized by an outstanding capacity for the specific recognition of subtle alterations of molecular structure. They can, therefore, be used as sensitive detection probes in assays for DNA modifications caused by low levels of DNA-reactive (e.g., environmental) agents. Depending on the purpose of analysis, various types of immunoassays can be performed. The competitive radioimmunoassay (RIA) represents a routinely applicable, reproducible and sensitive assay for the detection of defined carcinogen-DNA adducts in hydrolysates of cellular DNA, in body fluids or in urine. Depending on their particular design, enzyme immunoassay (EIA) may have exceptionally low detection limits, due to the enzymatic amplification of the measured radioactivity or colour intensity. Similarly, recently established immuno-slot-blot (ISB) techniques are also characterized by very high sensitivity. Immunocytological assays (ICA) use Mab in conjunction with electronically intensified immunofluorescence for detection of modified DNA components in the nuclei of individual cells. Finally, single modified deoxynucleosides can be detected and localized in individual DNA molecules by immuno-electron microscopy (IEM).

High-affinity monoclonal antibodies for the specific recognition and quantification of deoxynucleosides structurally modified by N-nitroso compounds.

The applicability of conventional radiochromatographic procedures to the detection and quantification of specific, carcinogen-induced structural modifications in the DNA of mammalian cells is limited by the necessity of using radioactively labelled agents and by the relatively large amounts of DNA required for analysis of low levels of DNA modification. Recently developed immunoanalytical methods have improved this situation considerably. High-affinity monoclonal antibodies (MAB), in combination with radio- and enzyme-immunoassays, now permit the sensitive detection of alkyldeoxynucleosides in small samples of hydrolysed DNA from tissues and cultured cells exposed previously to non-radioactive (e.g., environmental) alkylating N-nitroso carcinogens. Furthermore, MAB can be used to quantify by direct immunofluorescence (and with the aid of computer-based image analysis of electronically intensified fluorescence signals) specific alkylation products in the DNA of individual cells. With this method, the present detection limit for, e.g. O6-ethyl-2'-deoxyguanosine (O6-EtdGuo) is of the order of 7 X 10(2) O6-EtdGuo molecules per diploid genome. Therefore, cells (e.g. from biopsy material) can now be monitored directly for the presence of specific carcinogen-DNA adducts, or with respect to their capacity to remove enzymatically such modified structures from DNA. In combination with transmission electron microscopy, MAB also permit the direct visualization of specific carcinogen-modified sites in DNA. Thus, O6-EtdGuo can be localized in double-stranded DNA molecules by the binding of a MAB specifically directed against this ethylation product.

Immuno-slot-blot: a highly sensitive immunoassay for the quantitation of carcinogen-modified nucleosides in DNA.

We have established a highly sensitive immuno-slot-blot (ISB) procedure that can be routinely applied for detection and quantitation of any heat- or alkali-stable structural DNA modification (caused by carcinogens or mutagens, for example) for which a specific (monoclonal) antibody (MAB) is available. The essential step in this assay is the immobilization on nitrocellulose filters of the structurally modified DNA in its single-stranded form. The immobilized DNA is first reacted with an MAB specifically directed against a particular modified DNA component (e.g., an alkyldeoxynucleoside), and thereafter with a second antibody directed against the first one. The second antibody can be either labeled with 125I or linked to an enzyme complex capable of eliciting a color reaction with a suitable substrate. The sensitivity of the ISB is demonstrated for two different alkyldeoxynucleosides, O6-ethyldeoxyguanosine (O6-EtdGuo) and O4-ethyldeoxythymidine (O4-EtdThd), both of which are produced in cellular DNA exposed to the alkylating N-nitroso carcinogen N-ethyl-N-nitrosourea and both of which represent DNA lesions miscoding during DNA replication and transcription. Using anti-(O6-EtdGuo) and anti-(O4-EtdThd) MABs, respectively, O6-EtdGuo and O4-EtdThd are detected at levels as low as greater than or equal to 0.3 X 10(-15) mol O6-EtdGuo/3 micrograms DNA (O6-EtdGuo/deoxyguanosine molar ratio in DNA, greater than or equal to 2 X 10(-7) ) and greater than or equal to 0.1 X 10(-15) mol of O4-EtdThd/3 micrograms DNA (O4-EtdThd/deoxythymidine molar ratio in DNA, greater than or equal to 4 X 10(-8) ).

Immunological detection and quantification of carcinogen-modified DNA components.

Both the detection and quantitation of defined reaction products of chemical carcinogens with DNA, especially at low levels of DNA modification and in small numbers of target cells, require highly sensitive analytical techniques. The sensitivity of radiochromatographic methods is limited by the specific radioactivity of the respective carcinogens and by the relatively large amounts of DNA required for analysis. Furthermore, their application is restricted to experiments with radiolabelled carcinogens synthesized in the laboratory. These shortcomings can be circumvented by the use of high-affinity antibodies specifically directed against DNA components structurally modified by carcinogens, in combination with sensitive immunoassay procedures. Such immunological methodology, using both conventional antisera and monoclonal antibodies, has recently become available and is rapidly being developed further. We review here the properties of the antibodies thus far produced, the techniques applied for their development and characterization, and the immunoassay procedures currently in use. Some examples of the application of the new immunoanalytical methods are given.