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


METHODS
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.
Baranovskaya
Svetlana
S
Burnham Institute for Medical Research, La Jolla, California 92037, USA.
Martin
Yolanda
Y
Alonso
Sergio
S
Pisarchuk
Ksenia L
KL
Falchetti
Mario
M
Dai
Yuichi
Y
Khaldoyanidi
Sophia
S
Krajewski
Stan
S
Novikova
Inna
I
Sidorenko
Yuri S
YS
Perucho
Manuel
M
Malkhosyan
Sergei R
SR
D020121:5' Untranslated Regions / Q000235:genetics; D001483:Base Sequence; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D004252:DNA Mutational Analysis; D018900:Dinucleotide Repeats / Q000235:genetics*; D015536:Down-Regulation; D066246:ErbB Receptors / Q000235:genetics*; D005434:Flow Cytometry; D005787:Gene Frequency; D011905:Genes, ras / Q000235:genetics; D005838:Genotype; D006801:Humans; D053842:Microsatellite Instability; D016254:Mutagenesis, Insertional; D009154:Mutation; D011061:Poly A / Q000235:genetics; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D017384:Sequence Deletion; D013274:Stomach Neoplasms / Q000235:genetics / Q000473:pathology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics
D020121:5' Untranslated Regions; D016159:Tumor Suppressor Protein p53; D011061:Poly A; D066246:ErbB Receptors; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf