The aim of this study was to examine platelet-derived growth factor α receptor (PDGFR-α) expression in gliomas of various degrees of malignancy and to correlate the findings with genetic alterations present in the same tumor samples. We analyzed 83 tumors by in situ hybridization using a PDGFR-α cRNA probe. Increased PDGFR-α mRNA expression was observed in astrocytic tumors of all stages of malignancy, although the highest levels were found in glioblastoma multiforme. To evaluate the frequency of PDGFR-α gene amplification, differential PCR requiring less DNA than Southern analysis was used with fluorescence-labeled primers corresponding to the kinase insert region of the PDGFR-α. Only 7 of 43 glioblastomas and none of the other tumors tested showed amplification of the PDGFR-α gene, suggesting that a mechanism other than gene amplification is responsible for the overexpression of PDGFR-α in glial brain tumors.
Comparison of the in situ hybridization data with genetic alterations in the same tumor material showed a significant correlation of loss of heterozygosity on chromosome 17p (Fisher's exact, P < 0.0002) with high expression levels of PDGFR-α. Because that was the case in both low- and high-grade astrocytomas, our data imply that PDGFR-α is actively involved in tumor cell proliferation in early and late stages of glioma development. The association of PDGFR-α expression with a distinct subset of glioblastomas characterized by loss of heterozygosity 17p further supports the differentiation of these tumors into molecular variants.
This work was supported in part by Swedish Cancer Foundation Grant 2999-B94-05XAC (M. N.), NIH Grant CA 57683 (D. N. L.), and Deutsch Forschungsgemeinschaft Grant SFB 400 (A. v. D., O. D. W.).