| Abstract: | A series of nontransformed human and murine cells and derivative cell lines transformed by methylcholanthrene; by simian virus 40, Kirsten and Moloney murine sarcoma viruses, simian sarcoma virus, and adenovirus; and by a "spontaneous" event in culture were examined for the expression of receptors for the platelet-derived growth factor (PDGF) and for production of substances able to compete with 125I-labeled PDGF for binding to the cell-surface PDGF receptor. In each case, transformation resulted in a 50-100% decrease in available PDGF receptors. All transformed cells except the methylcholanthrene-transformed mouse cells produce a PDGF competitor into the conditioned medium. Levels of PDGF competitor in conditioned medium at the end of a 48-hr collection were as high as 2 ng/ml--high enough to be measured by radioreceptor assay diluted 1:30 and to maximally stimulate [3H]thymidine incorporation by human fibroblasts. The PDGF competitor activity detected in a radioreceptor assay does not reflect irreversible (e.g., proteolytic) damage to the receptor of test cells since its effects are reversed by acetic acid dissociation. Antiserum against human PDGF neutralizes 20-80% of the PDGF competitor found in conditioned medium from different transformed human cells and 100% of the activity from normal human endothelial cells. The possibility that induction of expression of the cellular PDGF gene may be involved in the mechanism of transformation of PDGF-responsive mesenchymal cells is discussed. |
