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Characterization of platelet-derived growth factor and platelet-derived growth factor receptor expression in
C Walker1, E Bermudez, W Stewart
1Chemical Industry Institute of Toxicology, Research Triangle Park, North Carolina 27709.
Abstract:
Although altered expression of platelet-derived growth factor (PDGF) is a hallmark of human mesothelioma, expression of PDGF receptors has not been characterized in this cell type. In addition, the expression of this growth factor and its cognate receptor in rodent mesothelioma has not been investigated. In this study, examination of transformed mesothelial cells derived from asbestos-induced rat mesotheliomas revealed that these cells expressed high affinity PDGF receptors (Kd = 0.5 nM) and receptor number was 1.6 x 10(5)/cell. Western analysis using antibodies specific for either the alpha-type or beta-type PDGF receptor and Northern analysis using probes specific for alpha- and beta-type receptor RNA transcripts indicated that these cells expressed beta-type PDGF receptors but that alpha-type receptors could not be detected. However, when the mesothelioma-derived cells were examined for the expression of PDGF, no expression of this growth factor could be detected. The transformed cells expressed no detectable A- or B-chain PDGF RNA transcripts; and using a competitive enzyme immunoassay specific for isoforms containing the B chain of PDGF and a sandwich enzyme-linked immunosorbent assay specific for A-chain-containing isoforms, neither AA, nor AB, nor BB isoforms of this growth factor could be detected in medium conditioned by these cells. The absence of alterations in PDGF expression in rat mesothelioma, in contrast to the data for the human disease, suggests that the production of this growth factor by transformed mesothelial cells may be species specific.
Insights
Rat mesothelioma cells express beta-type platelet-derived growth factor (PDGF) receptors but not PDGF itself. This contrasts with human mesothelioma, suggesting species-specific PDGF production in this cancer.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- Altered platelet-derived growth factor (PDGF) expression is characteristic of human mesothelioma.
- PDGF receptor expression in mesothelioma cells is not well understood.
- PDGF and its receptor expression in rodent mesothelioma models are uninvestigated.
Purpose of the Study:
- To characterize PDGF receptor expression in rat mesothelioma cells.
- To investigate PDGF and its receptor expression in asbestos-induced rat mesotheliomas.
- To compare PDGF expression in rat versus human mesothelioma.
Main Methods:
- Cultured transformed mesothelial cells from asbestos-induced rat mesotheliomas.
- Quantified high-affinity PDGF receptors using radioligand binding assays.
- Utilized Western and Northern blot analyses for PDGF receptor (alpha and beta types) expression.
- Assessed PDGF A- and B-chain RNA transcripts.
- Employed enzyme immunoassays to detect PDGF isoforms (AA, AB, BB) in conditioned medium.
Main Results:
- Rat mesothelioma cells express high-affinity PDGF receptors (Kd = 0.5 nM; 1.6 x 10(5) receptors/cell).
- Western and Northern analyses confirmed expression of beta-type PDGF receptors, with no detectable alpha-type receptors.
- No detectable PDGF expression (A- or B-chain RNA transcripts) was found in the transformed cells.
- Enzyme immunoassays detected no PDGF isoforms (AA, AB, BB) in the conditioned medium.
Conclusions:
- Transformed rat mesothelioma cells express beta-type PDGF receptors but do not produce PDGF.
- This finding contrasts with human mesothelioma, where PDGF alterations are common.
- PDGF production by transformed mesothelial cells appears to be species-specific.