CYTOGENETIC EVALUATION OF HUMAN GLIAL TUMORS: CORRELATION OF OVEREXPRESSION OF EPIDERMAL GROWTH FACTOR RECEPTOR (EGFR) WITH ABNORMALITIES OF CHROMOSOME 7.

Abstract

Chromosome banding analysis of human glial tumors was performed using G- and Q-banding techniques in an attempt to establish recurring sites of chromosome change. Results revealed a nonrandom karyotypic profile including aneuploidy and considerable variation in chromosome number (range 40 → 200). All tumors examined displayed numerical abnormalities, with the most common numeric change being a gain of chromosome 7. Chromosomes most frequently involved in structural abnormalities included #1, #3, #7, and #11. Double minutes, reported to be frequently associated with human glial tumors, were observed in only one of ten tumors examined. These results (taken in conjunction with previously published reports) suggest that the single most frequently altered chromosome in human glial tumors is chromosome 7. An attempt was then made to correlate the observed chromosome 7 changes with activation of the cellular proto-oncogene c-erb-B, whose product is the epidermal growth factor receptor (EGFR). Six human glial tumors were analyzed for ¹²⁵I-EGF binding, EGFR gene copy number, EGFR gene rearrangement, mRNA expression, and karyotypic profile. Saturation analysis at 4°C revealed significant numbers of EGFR's in all 6 tumors. Southern blotting analysis utilizing cDNA probes for the EGFR failed to demonstrate significant amplification or structural rearrangement of the EFGR gene. Analysis of EGFR mRNA revealed significant levels in 3 of the tumors studied as compared to the A341 cell line. Karyotypic analysis revealed that all six cell lines displayed extra copies of both whole and structurally altered chromosome 7. These results may suggest that EGFR overexpression is associated with alterations of chromosome 7 (the locus for the EGFR gene). In contrast to previous reports, EGFR mRNA levels did not directly parallel EGF receptor numbers. These results suggest that overexpression of the EGFR may be related to an alternative mechanism, other than gene amplification and elevated mRNA levels, such as the regulation of receptor biosynthesis and degradation. In summary, findings indicate that alterations of chromosome 7 are the most prevalent chromosomal change in human glial tumors, and that these alterations may lead to overexpression of the proto-oncogene c-erb-B.