Identification of regulatory sequences in the promoter of the PDGF B-chain gene in malignant mesothelioma cell lines.

Platelet-derived growth factor (PDGF) B-chain mRNA is readily detectable in malignant mesothelioma (MM) cell lines, but not in normal mesothelial (NM) cell lines. The high affinity receptor for PDGF B-chain dimers, the PDGF beta-receptor, is expressed in MM cell lines. NM cell lines predominantly express the PDGF alpha-receptor. Coexpression of the PDGF beta-receptor and its ligand may lead to an autocrine growth stimulating loop in the malignant cell type. In nuclear run off experiments, PDGF B-chain mRNA was detectable in MM cells only, indicating an increased level of transcription in this cell type. The proximal promoter of the PDGF B-chain gene contains DNaseI hypersensitive (DH) sites and mediates reporter gene activation in both normal and malignant cells. Nuclear proteins, extracted from both cell types, interact with DNA sequences within the proximal promoter around bp-64 to -61 relative to the transcription start site. Electrophoretic mobility shift assays (EMSAs) indicate that these factors are more abundantly present in the malignant than in the normal cell type. A DH site around -9.9 kb was found in both cell types. When tested in CAT assays, this region exerted a stimulatory effect on transcription in malignant cells. The elevated level of transcription of the PDGF B-chain gene in malignant cells may well be the result of interaction of regulatory sites in the proximal promoter and an enhancing element located at -9.9 kb from the transcription start site.

Expression of ICAM-1 and VCAM-1 in human malignant mesothelioma.

Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are cytokine-inducible adhesion molecules which recognize ligands that are highly expressed on leukocytes. Expression of ICAM-1 and VCAM-1 was investigated in tissue sections of 16 cases of malignant mesothelioma (seven epithelial, eight biphasic, and one sarcomatoid) using immunohistochemistry. Neoplastic cells were diffusely and intensely stained for ICAM-1 in all cases. VCAM-1 was detected in 14 of 16 cases. The percentage of VCAM-1-positive tumour cells was more than 50 per cent in eight cases and the staining was observed mainly in epithelial-like cells. VCAM-1 was rarely expressed in other malignant tumours of epithelial origin, being present in only 1 of 58 cases of carcinoma originating from different anatomical sites. At the cellular level, ICAM-1 and VCAM-1 appeared co-distributed, the staining for both being cytoplasmic with a membrane reinforcement. The regulation of VCAM-1 expression by neoplastic mesothelial cells was investigated in vitro using 14 mesothelioma cell lines. ICAM-1 was expressed by cultured cells of all mesothelioma cell lines, even in the absence of cytokines. VCAM-1 was detected in 10-50 per cent of the cells in three non-stimulated mesothelioma cell lines (mero-95, mero-96, and mero-134), and was absent or poorly expressed in the remaining 11. Exposure of a negative cell line (mero-48a) to an optimal concentration of tumour necrosis factor alpha (TNF alpha) or interleukin-13 (IL-13) for 6-18 h resulted in the induction of VCAM-1 mRNA synthesis and in VCAM-1 expression at the membrane level in 60-70 per cent of the cells. These findings are consistent with the possibility that TNF alpha, IL-13, or other activating signals are released in the tumour micro-environment and regulate the expression of VCAM-1 in malignant mesothelioma cells.

Expression of platelet-derived growth factor (PDGF) and PDGF receptors in human malignant mesothelioma in vitro and in vivo.

The expression of platelet-derived growth factor (PDGF) and PDGF receptors was studied in human normal and malignant mesothelial cells in vitro and in vivo. Staining with anti-cytokeratin and ME1 antibodies and ultrastructural analysis confirmed the mesothelial nature of the cell lines used to study PDGF and PDGF receptor expression in vitro. Using antibodies, mesothelioma cell lines were found to express PDGF and both the PDGF alpha- and the PDGF beta-receptor, whereas cultured normal mesothelial cells expressed PDGF and PDGF alpha-receptor. This PDGF and PDGF receptor staining pattern largely reflects the earlier described mRNA expression in these cell lines. The only exception was the immunocytochemical detection of PDGF alpha-receptors in the mesothelioma cell lines, which is different from the inability to detect alpha-receptor transcripts on Northern blots. Expression was also investigated in mesothelial cells in vivo. Expression of PDGF was observed in malignant mesothelioma cells on frozen tissue sections. In pleural effusions, a double immunofluorescence staining procedure for PDGF and epithelial membrane antigen (EMA) revealed PDGF expression by EMA-positive malignant mesothelioma cells. PDGF beta-receptors and occasionally PDGF alpha-receptors were detected in frozen tissue sections of malignant mesotheliomas, whereas mesothelioma cells in effusions showed faint expression of only the PDGF beta-receptor. In contrast, in effusions containing non-malignant mesothelial cells, only a very low level of PDGF alpha-receptor could be detected. Taken together, these results indicate that the pattern of PDGF and PDGF receptor expression in mesothelial cells in vivo largely corresponds to expression of PDGF and its receptors in vitro. Malignant mesothelioma cell lines thus constitute a good model system for studies on the role of PDGF in this malignancy. Furthermore, the data reported in this paper are consistent with the idea that an autocrine growth stimulatory effect of PDGF via PDGF receptors may play a role in the pathogenesis of malignant mesothelioma.

Human ovarian tumors of epithelial origin express PDGF in vitro and in vivo.

In human malignant mesothelioma cell lines an elevation of the expression of the genes for the PDGF A-chain, PDGF B-chain, and PDGF beta-receptor was found compared to normal mesothelial cells. As ovarian epithelial tumors originate from the ovarian surface epithelium, which is of mesothelial origin, we investigated PDGF chain and PDGF receptor mRNA expression in six human ovarian cell lines of epithelial origin and a granulosa tumor cell line. All six investigated ovarian epithelial tumor cell lines expressed the PDGF A- and B-chain genes, while the granulosa tumor cell line expressed the PDGF A-chain gene only. Expression of PDGF receptors was not found in the epithelial or granulosa tumor cell lines. Cytogenetic and molecular biological studies did not provide evidence for rearrangement or genomic amplification of the PDGF B-chain. Expression of PDGF was also demonstrated in ovarian tumors in vivo. Frozen sections of six serous ovarian carcinomas stained positive with an antibody against PDGF and negative with antibodies against the PDGF alpha- and beta-receptors. These results suggest that PDGF expression might be a useful marker for ovarian carcinomas.

In vitro drug sensitivity of normal peripheral blood lymphocytes and childhood leukaemic cells from bone marrow and peripheral blood.

In vitro drug sensitivity of leukaemic cells might be influenced by the contamination of such a sample with non-malignant cells and the sample source. To study this, sensitivity of normal peripheral blood (PB) lymphocytes to a number of cytostatic drugs was assessed with the MTT assay. We compared this sensitivity with the drug sensitivity of leukaemic cells of 38 children with acute lymphoblastic leukaemia. We also studied a possible differential sensitivity of leukaemic cells from bone marrow (BM) and PB. The following drugs were used: Prednisolone, dexamethasone, 6-mercaptopurine, 6-thioguanine, cytosine arabinoside, vincristine, vindesine, daunorubicin, doxorubicin, mafosfamide (Maf), 4-hydroperoxy-ifosfamide, teniposide, mitoxantrone, L-asparaginase, methotrexate and mustine. Normal PB lymphocytes were significantly more resistant to all drugs tested, except to Maf. Leukaemic BM and PB cells from 38 patients (unpaired samples) showed no significant differences in sensitivity to any of the drugs. Moreover, in 11 of 12 children with acute leukaemia of whom we investigated simultaneously obtained BM and PB (paired samples), their leukaemic BM and PB cells showed comparable drug sensitivity profiles. In one patient the BM cells were more sensitive to most drugs than those from the PB, but the actual differences in sensitivity were small. We conclude that the contamination of a leukaemic sample with normal PB lymphocytes will influence the results of the MTT assay. The source of the leukaemic sample, BM or PB, does not significantly influence the assay results.

Human peripheral blood dendritic cells concentrate in contrast to monocytes intracellular HLA class II molecules in a juxtanuclear position.

The localization of histocompatibility antigens of the HLA-D locus in dendritic cells (DC) and monocytes (Mo) isolated from human peripheral blood was investigated. Functionally DC were characterized by their capacity to act as strong stimulators in an allogeneic mixed leucocyte reaction. In cytospins, DC were differentiated from Mo by dendritic morphology, strong HLA class II and moderate RFD1 expression on the plasma membrane and acid phosphatase activity in a juxtanuclear spot. Ultrathin cryosections showed that DC had a heavily labelled plasma membrane for HLA-D. In addition, these antigens were found in intracellular vesicles predominantly located in the juxtanuclear zone. This pattern of labelling was not seen in Mo. Obviously, DC concentrate intracellular class II antigens in the same area as lysosomal activity. These results may indicate that this juxtanuclear area is a center of antigen processing in DC.