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Mol. Cell. Biol., 12 1997, 7151-7158, Vol 17, No. 12
SJ Xia, MA Shammas and RJ Reis
Normal diploid cells have a limited replicative potential in culture, with
progressively increasing interdivision time. Rarely, cell lines arise which
can divide indefinitely; like tumor cells, such "immortal" lines display
frequent chromosomal aberrations which may reflect high rates of
recombination. Recombination frequencies within a plasmid substrate were
3.5-fold higher in nine immortal human cell lines than in six untransformed
cell strains. Expression of HsRAD51, a human homolog of the yeast RAD51 and
Escherichia coli recA recombinase genes, was 4.5-fold higher in immortal
cell lines than in mortal cells. Stable transformation of human fibroblasts
with simian virus 40 large T antigen prior to cell immortalization
increased both chromosomal recombination and the level of HsRAD51
transcripts by two- to fivefold. T-antigen induction of recombination was
efficiently blocked by introduction of HsRAD51 antisense (but not control)
oligonucleotides spanning the initiation codon, implying that HsRAD51
expression mediates augmented recombination. Since p53 binds and
inactivates HsRAD51, T-antigen-p53 association may block such inactivation
and liberate HsRAD51. Upregulation of HsRAD51 transcripts in T-antigen-
transformed and other immortal cells suggests that recombinase activation
can also occur at the RNA level and may facilitate cell transformation to
immortality.
Copyright © 1997, American Society for Microbiology
Elevated recombination in immortal human cells is mediated by HsRAD51 recombinase
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
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