Amplification of the structurally and functionally altered epidermal growth factor receptor gene (c-erbB) in human brain tumors.

Abstract

By using Southern blot analysis, we found that in two cases of human glioblastoma multiforme, cells carried amplified c-erbB genes which bore short deletion mutations within the ligand-binding domain of the epidermal growth factor (EGF) receptor. The products of these mutated c-erbB genes were about 30 kilodalton (kDa) smaller than the normal 170-kDa EGF receptor, and the tumor cell membrane fractions containing the 140-kDa abnormal EGF receptor showed a significant elevation of tyrosine kinase activity without its ligand. In view of the similarity to the activated viral and cellular erbB genes in the avian system, these mutated and overexpressed EGF receptors might play a role in the onset or development of human glioblastoma cells.The c-erbB gene is known to be a proto-oncogene which encodes the epidermal growth factor (EGF) receptor (4,25,30). The v-erbB gene product of avian erythroblastosis virus in chickens has a truncated form of EGF receptor and expresses a higher level of tyrosine kinase activity without its ligand (11). Thus, qualitative and quantitative alterations appear to be crucial for the activation of the c-erbB gene in chickens. In human tumors, amplification of the c-erbB gene has been reported in several squamous cell carcinomas and glioblastomas (3,10,13,14,17,27,29). However, it was not certain whether the c-erbB gene in those tumor cells was also structurally altered.Since the activation of oncogenes in human brain tumors has not yet been extensively studied, we screened several transplantable brain tumors for the presence of abnormal proto-oncogenes, using Southern blot analysis (24). Table 1 lists the tumors tested; six were glioblastomas, and two were ependymomas. The histological characteristics of these tumors have not drastically changed during serial passages in athymic nude mice.Among 19 onc probes employed (myc, N-myc, myb, K-ras, N-ras, sis, src, fpslfes, yes, mos, fos, ros, fms, fgr, abl, rel, rafimil, erbB, erbB-2/neu), no amplification or rearrangement was detected in the transplantable brain tumors except for the v-erbB probe (26); two glioblastomas, GL-3 and GL-5, carried an amplified c-erbB gene (data not shown). Recently Libermann et al. have reported that about one-third of glioblastomas in primary human brain tumors contain an amplified c-erbB gene (13). They also indicated that this gene amplification is associated with a possible DNA rearrangement, but the details were not examined due to the limited availability of primary tumors. The frequency of amplification of the c-erbB gene in transplantable glioblastomas examined here is similar to that of their report.To examine the fine structure of the amplified c-erbB gene in glioblastomas, we used a human EGF receptor cDNA as a probe (kindly provided by I. Pastan, National Cancer Institute, Bethesda, Md.) (16, 28). EcoRI-digested DNAs of GL-3 and GL-5 cells carry a high copy number of the c-erbB gene (Fig. la), and the degree of amplification was almost the same as in the A431 squamous carcinoma cell line, which is known t...

A monoclonal antibody recognizing human cancers with amplification/overexpression of the human epidermal growth factor receptor

“…EGFR overexpression is often associated with gene amplification (4)(5)(6)(7)(8). In glioblastoma, EGFR amplification has been shown to be accompanied by gene rearrangement (9)(10)(11), frequently with deletions in the coding region. Several mutant forms have been found (12,13), and among these the most common mutation is the ⌬2-7 deletion (⌬EGFR), which lacks exons 2-7 of the external EGFR domain, resulting in the loss of an 801-bp fragment of the wild-type (wt) gene (14).…”

Detection of chromosome aberrations in metaphase and interphase tumor cells by in situ hybridization using chromosome-specific library probes

“…The c-erbB oncogene (EGFR) has been mapped to 7p12-14 (Merlino et al 1985). It can be over-expressed in human glioblastoma cell lines with polysomy of chromosome 7 (Henn et al 1986), and amplification of c-erbB has often been found in malignant gliomas (Liberman et al 1985;Yamazaki et al 1988;Bigner et al 1988). This oncogene does not show amplification on Southern blot analysis in either TC 620 or TC 593, and in TC 593 there are no rearrangements, insertions or deletions involving c-erbB (T. Chen and L. Manuelidis, unpublished data).…”

Enhanced tumorigenicity caused by truncation of the extracellular domain of GP125/CD98 heavy chain

“…Similarly, enhanced malignant phenotypes have been observed in glioblastoma cells expressing a truncated EGF receptor (Nishikawa et al, 1994). In these cases, constitutive tyrosine phosphorylation of receptors is associated with the ability of the mutant receptor to confer enhanced malignant phenotype on tumor cells (Martin, 1986;Yamazaki et al, 1988).…”