An improved cDNA selection method was established to isolate expressed genes efficiently from an amplified chromosome region in human cancer. Biotinylated yeast artificial chromosome DNA containing c-ERBB-2 was hybridized in solution with PCR-amplifiable cDNAs of an esophageal cancer cell line bearing the c-ERBB-2 amplification. After capturing the hybrids on avidin-coated magnetic beads, the cDNAs were amplified by PCR. Four new genes (A39, C51, CAB1, and GRB-7) coamplified with c-ERBB-2 were isolated from the enriched cDNA library. CAB1, GRB-7, and c-ERBB-2 were overexpressed in gastric and esophageal cancer cells in correspondence with the amplification. The deduced amino acid sequence of the CAB1 gene had significant homology to the recently discovered steroidogenic acute regulatory protein, StAR, which plays an essential role in cholesterol transport to mitochondria. It was established that multiple overexpressed genes are frequently present in a single amplicon.
This work was supported in part by a Grant-in-Aid for the Second Comprehensive 10-Year Strategy for Cancer Control from the Ministry of Health and Welfare of Japan; by Grants-in-Aid from the Ministry of Health and Welfare of Japan and from the Ministry of Education, Science, Sports and Culture of Japan; by the Bristol-Myers Squibb Foundation; and by the Research Foundation for Cancer and Cardiovascular Diseases, Osaka, Japan. N. A., T. I., and T. K. are recipients of Research Resident Fellowships from the Foundation for Promotion of Cancer Research.