Inactivation of the E‐Cadherin Gene in Primary Gastric Carcinomas and Gastric Carcinoma Cell Lines

We investigated the E (epithelial)‐cadherin gene for mutations and loss of heterozygosity (LOH) in 24 primary gastric carcinomas (12 differentiated and 12 undifferentiated types, including 3 signet‐ring cell carcinomas), as well as 4 gastric carcinoma cell lines of the undifferentiated type (MKN‐45, GCIY, HGC‐27 and GT3TKB). We utilized PCR‐SSCP and RT‐PCR followed hy direct sequencing to detect gene mutations and skipped exons, and RT‐PCR‐SSCP to examine LOH. In primary carcinomas, gene mutations or skipped exons, were detected in 4 of 9 (44%) undifferentiated carcinomas of the scattered type, including 2 signet‐ring cell carcinomas, and in none of the 3 undifferentiated carcinomas of the adherent type and 12 differentiated carcinomas. Demonstrated mutations of 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 exon 9. Skipping of exon 9 with a 1 bp insertion at codon 337, and skipping of exon 8 with a 1 bp deletion at codon 336, also were detected. LOH was confirmed in all of the carcinomas in which gene mutations or skipped exons (3/3 informative cases) were demonstrated. The MKN‐45 cell line exhibited an 18 bp deletion at the exon 6‐intron 6 boundary with loss of the wild‐type allele, and 2 of the remaining 3 cell lines (HGC‐27 and GT3TKB) had lost expression without detectable structural alteration of the E‐cadherin gene. These data provide support for classic two‐hit inactivation of the E‐cadherin gene in a high percentage of undifferentiated carcinomas of the scattered type.