Co-amplification of transcriptionally active epidermal growth factor receptor and ribosomal genes in the human hepatoma cell line Li7A.

A high level of expression of the functional product of the epidermal growth factor receptor (EGFR) gene was detected in the human hepatocarcinoma cell line Li7A and it was found to correlate with gene amplification. The karyotype was paratriploid, with 15 rearranged chromosomes, several of which contained abnormally banded regions (ABRs). The search for DNA sequences co-amplified with the EGFR gene, using the in-gel renaturation technique, allowed us to detect an amplified DNA band (La1) of about 30 kb. This DNA was used as a probe for in situ hybridization on chromosomes, to locate the amplified segment. In normal lymphocytes, the DNA of band La1 hybridized to chromosome regions in which repetitive DNAs are located, i.e. on juxtacentromeric regions, the site of alphoid and CCATT satellite DNA, and on the short arms of acrocentrics, the site of ribosomal RNA (RNR) genes. In Li7A cells, it hybridized to the same regions and, in addition, to several chromosome arms corresponding to ABRs. The same ABRs hybridized to EGFR and RNR probes, but neither Alu sequences nor various probes for other repetitive sequences were recognized. They also exhibited nucleolus organizer region staining characterizing functionally active (RNR) genes. It was concluded that transcriptionally active genes were co-amplified in the same ABRs, although they originated from different chromosomes, i.e. chromosome 7 for EGFR and acrocentrics for RNR genes.