Frameshift Mutagenesis and Microsatellite Instability Induced by Human Alkyladenine DNA Glycosylase

• Published in: Molecular cell Vol. 37; no. 6; pp. 843 - 853
• Main Authors: Klapacz, Joanna, Lingaraju, Gondichatnahalli M., Guo, Haiwei H., Shah, Dharini, Moar-Shoshani, Ayelet, Loeb, Lawrence A., Samson, Leona D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26-03-2010
• Subjects: Catalytic Domain; DNA; DNA Glycosylases - chemistry; DNA Glycosylases - genetics; DNA Glycosylases - metabolism; DNA Mismatch Repair; Frameshift Mutation; Gene Expression Regulation, Enzymologic; Humans; K562 Cells; Microsatellite Instability; Models, Molecular; Phenotype; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; DNA
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2010.01.038

Human alkyladenine DNA glycosylase (hAAG) excises alkylated purines, hypoxanthine, and etheno bases from DNA to form abasic (AP) sites. Surprisingly, elevated expression of hAAG increases spontaneous frameshift mutagenesis. By random mutagenesis of eight active site residues, we isolated hAAG-Y127I/H136L double mutant that induces even higher rates of frameshift mutation than does the wild-type hAAG; the Y127I mutation accounts for the majority of the hAAG-Y127I/H136L-induced mutator phenotype. The hAAG-Y127I/H136L and hAAG-Y127I mutants increased the rate of spontaneous frameshifts by up to 120-fold in S. cerevisiae and also induced high rates of microsatellite instability (MSI) in human cells. hAAG and its mutants bind DNA containing one and two base-pair loops with significant affinity, thus shielding them from mismatch repair; the strength of such binding correlates with their ability to induce the mutator phenotype. This study provides important insights into the mechanism of hAAG-induced genomic instability.
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► hAAG expression induces spontaneous frameshifts in yeast and MSI in human cells ► hAAG binds one and two base-pair loops generated in microsatellite DNA sequences ► Amino acid changes in hAAG active site increase spontaneous mutagenesis > 100-fold ► Loop-binding strength correlates with the extent of hAAG-induced mutation