Down-regulation of Epidermal Growth Factor Receptor by Selective Expansion of a 5′-End Regulatory Dinucleotide Repeat in Colon Cancer with Microsatellite Instability

Abstract

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.

Prognostic effect of activated EGFR expression in human colon carcinomas: comparison with EGFR status

“…EGFR protein expression was unrelated to tumour MMR status. This finding does not support a recent study that found elongation of a dinucleotide repeat in 55% of colon cancers with defective MMR, that was associated with significantly reduced EGFR mRNA levels (Baranovskaya et al, 2009). EGFR intensity as a continuous EGFR variable was significantly associated with shorter DFS and OS rates in a univariate analysis.…”

“…Recently, elongation of a microsatellite repeat at the 5 0 UTR was found in colon cancers with defective MMR, but not in those with intact MMR (Baranovskaya et al, 2009), and elongation of this repeat was associated with downregulation of EGFR mRNA levels. Accordingly, we compared EGFR expression with MMR status in our study population.…”

“…Recently, elongation of a microsatellite repeat at the 5 0 untranslated region (UTR) was found in colon cancers with microsatellite instability (MSI), but not in microsatellite stable tumours (Baranovskaya et al, 2009). Elongation of this repeat was shown to result in the downregulation of EGFR mRNA levels in human colon cancer cells and in human tumours with MSI.…”

Candidate Serum Biomarkers for Early Intestinal Cancer Using 15N Metabolic Labeling and Quantitative Proteomics in the ApcMin/+ Mouse

“…53 The frequency of upregulation ranges anywhere from 25–90%, but EGFR downregulation is also known, and EFGR-negative tumors have been reported. 52–55 Because EGFR positive tumors have been implicated in poor prognosis, we believe that EGFR may be a good marker to indicate prognosis and subsequent method of treatment. 56 …”

Epidermal growth factor receptor inhibits colitis-associated cancer in mice

“…First, mammary and epidermoid tumor cells undergo growth arrest and apoptosis following EGF treatment (74,75). Second, mutations that decrease EGFR expression in a subset of colon and gastric tumors are associated with increased tumor progression (76). Finally, activating EGFR mutations in non-small cell lung cancer are associated with…”