INACTIVATION OF THE E-CADHERIN GENE IN PRIMARY GASTRIC CARCINOMAS ANDGASTRIC-CARCINOMA CELL-LINES

We investigated the E (epithelial)-cadherin gene for mutations and los s of heterozygosity (LOH) in 24 primary gastric carcinomas (12 differe ntiated and 12 undifferentiated types, including 3 signet-ring cell ca rcinomas), as well as 4 gastric carcinoma cell lines of the undifferen tiated type (MKN-45, GCIY, HGC-27 and GT3TKB). We utilized PCR-SSCP an d RT-PCR followed by direct sequencing to detect gene mutations and sk ipped exons, and RT-PCR-SSCP to examine LOH. In primary carcinomas, ge ne mutations or skipped exons were detected in 4 of 9 (44%) undifferen tiated carcinomas of the scattered type, including 2 signet-ring cell carcinomas, and in none of the 3 undifferentiated carcinomas of the ad herent type and 12 differentiated carcinomas. Demonstrated mutations o f the E-cadherin gene included an 18 bp deletion (codon 418-423) and a 3 bp deletion (codon 400, calcium-binding domain), both located in ex on 9. Skipping of exon 9 with a 1 bp insertion at codon 337, and skipp ing of exon 8 with a 1 bp deletion at codon 336, also were detected. L OH was confirmed in all of the carcinomas in which gene mutations or s kipped exons (3/3 informative cases) were demonstrated. The MKN-45 cel l line exhibited an 18 bp deletion at the exon 6-intron 6 boundary wit h loss of the wild-type allele, and 2 of the remaining 3 cell lines (H GC-27 and GT3TKB) had lost expression without detectable structural al teration of the E-cadherin gene. These data provide support for classi c two-hit inactivation of the E-cadherin gene in a high percentage of undifferentiated carcinomas of the scattered type.