Polysomy of chromosome 7 is associated with amplification and overexpression of the EGF‐receptor gene in a human carcinoma cell line derived from a brain metastasis

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Abstract
Overexpression of the EGF‐receptor gene is associated with the malignant nature of some tumors. We have recently reported the establishment of a human carcinoma cell line (T‐CAR1), derived from a brain metastasis, that had 7 million EGF receptors per cell and was growth inhibited by EGF. The present study was carried out in order to furhter characterize the EGF‐receptor protein in T‐CAR1 cells, and to see if the overexpression of the EGF‐receptor gene in these cells was associated with abnormalities at the genomic level. We have compared the T‐CAR1 cells with the human glioblastoma cell line T‐MG1, which has 135,000 EGF‐receptors and is growth stimulated by EGF. The MW of the EGF receptors in T‐CAR1 cells and T‐MG1 cells was estimated to be 170 kDa, equal to the normal EGF‐receptor. However, in T‐CAR1 cells an additional protein reacted with the monoclonal antibody directed against the internal domain of the EGF receptor. The levels of EGF receptor‐related RNAs in T‐CAR1 cells and T‐MG1 cells reflected the number of EGF receptors in these cell lines. The EGF‐receptor gene was amplified ten‐fold in T‐CAR1 cells, while it was not amplified in T‐MG1 cells. No restriction fragment length polymorphism of DNA digested with various restriction enzymes was seen in either of the cell lines. Chromosomal analysis of T‐CAR1 cells showed polysomy of chromosome 7 and marker chromosomes derived partly from chromosome 7. Thus, in the T‐CAR1 cell line it was an association between polysomy of chromosome 7 and EGF‐receptor gene amplification.