Down-regulation of epidermal growth factor receptor by selective expansion of a 5'-end regulatory dinucleotide repeat in colon cancer with microsatellite instability.

PURPOSE: The epidermal growth factor receptor (EGFR) is overexpressed in several tumor types, and its expression is influenced by the length of a 5'-end microsatellite repeat (CA)n: the longer the repeat, the lower the expression. Dinucleotide repeats accumulate insertion/deletion types of mutations in tumors with microsatellite instability. We designed this study to estimate the occurrence of these mutations in EGFR(CA)n and their relevance in carcinogenesis of microsatellite instability-positive colon and gastric tumors. EXPERIMENTAL DESIGN: We analyzed the frequency of EGFR(CA)n mutations in vivo in 55 colorectal and 14 gastric microsatellite instability-positive cancers, and in vitro in single-cell clone cultures of microsatellite instability-positive colon tumor cell line LS174. Single-cell clone cultures with different repeat lengths were analyzed by fluorescent-activated cell sorter for EGFR cell-surface expression. A correlation analysis was done between EGFR(CA)n mutations and mutations in KRAS, BRAF, and p53. RESULTS: Unlike single-cell clone cultures, which exhibited higher rate of deletions compared with insertions, most of EGFR(CA)n mutations in colon and gastric tumors were insertions. Longer EGFR(CA)n correlated with lower EGFR cell-surface expression in single-cell clone cultures. In colon cancers, the elongation of the repeat was associated negatively with mutations in KRAS and BRAF, but not in p53. CONCLUSIONS: The EGFR(CA)n elongation observed in tumors cannot be explained by an intrinsic property of this repeat favoring insertions versus deletions. Instead, a selection for repeat elongation occurs in microsatellite instability-positive tumors, leading to EGFR down-regulation. These findings suggest that in microsatellite instability-positive tumors current therapies targeting EGFR overexpression may have either no effect or an opposite to the expected effect.

The matrix metalloproteinase-21 gene 572C/T polymorphism and the risk of breast cancer.

BACKGROUND: Matrix metalloproteinases (MMPs) contribute in multiple ways to all stages of tumor development, and a number of DNA polymorphisms in the MMP genes are associated with an increased risk of cancer. We previously identified the MMP-21 gene 572C/T polymorphism leading to Ala191Val substitution within the enzyme's catalytic domain. We performed a case-control study to test association between this polymorphism and the risk of breast cancer. PATIENTS AND METHODS: 572C/T polymorphism was analyzed by RFLP method in 396 unrelated Russian females: 76 breast cancer patients and 320 disease-free blood donors. RESULTS: The frequencies of C/C, T/C and T/T genotypes in patients (69.7%, 25.0% and 5.3%) did not differ significantly from those in controls (61.9%, 34.7% and 3.4%); the polymorphism was not associated with the increased tumor size and the presence of metastases. CONCLUSION: The MMP-21 gene 572C/T polymorphism has no significant effect on the development and progression of breast cancer.