Inhibition of glioma cell growth by a truncated platelet-derived growth factor-beta receptor.

Abnormal expression of platelet-derived growth factor (PDGF) receptors has been observed in malignant glioma and other tumors such as osteosarcomas and malignant melanomas. However, their role in the development and maintenance of the tumors is not understood. Signaling through the PDGF receptors is activated by ligand-induced dimerization. Thus, introduction of mutant receptors that are kinase deficient but still dimerization competent is one strategy to study the importance of PDGF receptors in glioma cell growth. A truncated PDGF-beta receptor was introduced into C6 rat glioma cells and the PDGF-mediated signaling and subsequent cell growth studied. In clones expressing the mutant receptor, PDGF-BB-induced tyrosine phosphorylation of the endogenous receptor was significantly reduced. In addition, these cells grew to lower density in culture and formed smaller colonies in soft agar than the C6 parental cells. Furthermore, the ability of cells expressing the truncated receptor to grow as xenografts in nude mice was significantly impaired. These results support the important role for the PDGF-beta receptor in C6 glioma cell growth. They also demonstrate the usefulness of dominant-negative mutants of the PDGF receptor for the evaluation of the role of the receptor in tumorigenesis.