Antisense inhibition of Chk2/hCds1 expression attenuates DNA damage‐induced S and G2 checkpoints and enhances apoptotic activity in HEK‐293 cells

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Abstract
The cellular response to DNA damage involves checkpoint controls that delay cell cycle progression in order to provide time for repair of damaged DNA. Chk2/hCds1 is a recently identified homolog of the yeast Cds1 kinase that is involved in cell cycle checkpoint response to DNA damage. To investigate the functions of Chk2/hCds1 in response to DNA damage in mammalian cells, we established a stable human kidney embryonic cell line (HEK‐293) that expresses antisense Chk2/hCds1 (Chk2AS) under the control of an inducible promoter. Cells that express Chk2AS display defective S‐phase delay in response to DNA replication‐mediated DNA damage induced by the topoisomerase I inhibitor camptothecin. The defective G2 checkpoint was also observed in Chk2AS cells exposed to the DNA damaging agent VP‐16 or γ‐radiation. Enhanced apoptosis was observed in Chk2AS cells after exposure to γ‐radiation or camptothecin. No p53 activation was observed after DNA damage in HEK‐293 or Chk2AS cells. Our results indicate that perturbation of Chk2/hCds1 expression adversely affects the S‐ and G2‐phase checkpoints following DNA damage or DNA replication block, and suggest that reduced expression of Chk2/hCds1 might promote a p53‐independent apoptotic response.