Somatic mutation rates and specificities at TC/AG and GT/CA microsatellite sequences in nontumorigenic human lymphoblastoid cells

Suzanne E. Hile, Guang Yan, Kristin A. Eckert

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Abstract

We have examined mutational events at TC/AG microsatellites, the second most abundant dinucleotide repetitive motif in the human genome. Mutational targets were constructed containing TC/AG alleles up to 20 units in-frame within the coding region of the herpes simplex virus thymidine kinase (HSV- tk) gene. These targets were incorporated into oriP shuttle vectors, which replicate episomally in human lymphoblastoid cells. The overall HSV-tk mutant frequencies measured after 10 population doublings in cells derived from a clinically normal donor were slightly increased over the background of mutations recovered in Escherichia coli. DNA sequence analyses revealed that replication of TC/AG vectors in human cells increased the mutation frequencies at the microsatellite motif up to 3-fold, relative to background. Additionally, the median HSV-tk mutation rate of single-cell clones carrying the [TC/AG]17 vector was significantly different from that of clones harboring the control vector. The median rate of allele length alterations within the [TC/AGJ11 tract was 2 x 10-6 mutations/cell generation, with an equivalent rate of deletion and expansion mutations. In contrast, a [GT/CA]10 vector showed no increase in microsatellite mutation frequency after replication in human cells, and mutation rates of clones carrying a [GT/CA]16 vector were not significantly different from controls. Intriguingly, replication in human cells of all microsatellite-containing vectors resulted in elevated mutation frequencies at the downstream HSV-tk coding sequence of up to 20-fold, an effect not observed for the control vector. These results demonstrate that the frequency of mutational events at TC/AG motifs is slightly greater than at GT/CA motifs of similar allele length. This is the first report to our knowledge of the mutation rates at TC/AG microsatellite alleles in eukaryotic or prokaryotic cells.

Original languageEnglish (US)
Pages (from-to)1698-1703
Number of pages6
JournalCancer Research
Volume60
Issue number6
StatePublished - Mar 15 2000

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All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research

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