Objective: To determine the microsatellite instability in gastric carcinomas, examine the frameshift mutations of transforming growth factor-beta type II receptor (TGFbetaRII), insulin growth factor II receptor (IGFIIR), bcl-2 associated X protein (BAX) and E2F4, and investigate whether or how alterations of the TGFbetaRII, IGFIIR, BAX and E2F4 gene are associated with MSI in gastric cancer.
Methods: Formalin-fixed, paraffin-embedded gastrectomy specimens and matching normal tissues of 65 cases of gastric carcinomas were retrieved from shanghai Ruijin Hospital and Shanghai East Hospital. DNA was extracted from tissue sections using phenol chloral isoamyl alcohol. Sections with no more than 50% of tumor cell areas were isolated by microdissection. DNA was amplified by PCR-based single strand conformation polymorphism (SSCP) for microsatellite analysis and was sequenced directly. Frameshift mutations in the coding regions, repetitive mononucleotide tracts of (A)10 for TGFbetaRII, (G)8 for IGFIIR, (G)8 for BAX, and trinucleotide repeats of (AGC)13 for transcription factors E2F4 were detected using PCR. Tumors were classified as being microsatellite stable (MSS) or having a low frequency of MSI (MSI-L, one of markers different in the tumor) or a high frequency of MSI (MSI-H, two or more of markers different).
Results: Eleven cases (18.0%) showed MSI-L, 12 (19.7%) showed MSI-H and 38 (62.3%) cases showed MSS. The mutation rates of TGFbetaRII, IGFIIR, BAX and E2F4 gene were 19.7%, 4.9%, 6.6% and 16.4% respectively. Among the 12 MSI-H gastric cancers, there were 10 TGFbetaRII mutations, 3 IGFIIR mutations, 4 BAX mutations and 10 E2F4 gene mutations. The alterations in the repeats of the related genes presented polymorphisms. Associations of MSI-H status and mutations of the 4 genes were highly significant (P < 0.01, respectively). No repeat tracts mutations in TGFbetaRII, IGFIIR, BAX and E2F4 gene were found in MSS tumors.
Conclusions: The repeat coding regions within TGFbetaRII, IGFIIR, BAX and E2F4 gene are the targets of microsatellite instability. Frameshift mutations of the 4 genes play an important role in the development and progression of gastric cancers with microsatellite instability.