A mismatch recognition defect in colon carcinoma confers DNA microsatellite instability and a mutator phenotype.
We have analyzed spontaneous mutations in the adenine phosphoribosyltransferase gene of Chinese hamster clone B cells that exhibit a mutator phenotype because of defective mismatch binding. The mutator phenotype conferred increases in a limited number of mutational classes. The rates of transitions and most transversions were not significantly increased. The rates of A to T transversions and -2 frameshifts were strikingly elevated. These mutations were in repeated elements and 5 of 9 of the frameshifts were dinucleotide deletions in DNA sequences resembling microsatellites. The mismatch binding protein that is defective in the mutator line is a G-T mismatch recognition factor. Band-shift analysis indicated that the preferred substrate for the mismatch recognition protein is duplex DNA containing an extrahelical mono- or dinucleotide within repeated sequences. In agreement with a role in preventing minus frameshifts, a defective binding protein conferred an instability in clone B microsatellite DNA. A mismatch binding defect was also detected in Lo Vo, a human colorectal carcinoma cell line. Extracts of clone B or a second mismatch binding-deficient line, Raji-F12, did not complement Lo Vo extracts, indicating that these lines share a common defect. Our data provide a mechanistic explanation for the relation between defective mismatch recognition and the microsatellite instability of human colon cancer.
Aquilina
G
G
Istituto Superiore di Sanità, Section of Chemical Carcinogenesis, Rome, Italy.
Hess
P
P
Branch
P
P
MacGeoch
C
C
Casciano
I
I
Karran
P
P
Bignami
M
M
D000228:Adenine Phosphoribosyltransferase / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D003110:Colonic Neoplasms / Q000235:genetics*; D006224:Cricetinae; D004260:DNA Repair; D005796:Genes; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011110:Polymorphism, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D014407:Tumor Cells, Cultured
D000228:Adenine Phosphoribosyltransferase