Formation of higher-order nuclear Rad51 structures is functionally linked to p21 expression and protection from DNA damage-induced apoptosis.
After exposure of mammalian cells to DNA damage, the endogenous Rad51 recombination protein is concentrated in multiple discrete foci, which are thought to represent nuclear domains for recombinational DNA repair. Overexpressed Rad51 protein forms foci and higher-order nuclear structures, even in the absence of DNA damage, in cells that do not undergo DNA replication synthesis. This correlates with increased expression of the cyclin-dependent kinase (Cdk) inhibitor p21. Following DNA damage, constitutively Rad51-overexpressing cells show reduced numbers of DNA breaks and chromatid-type chromosome aberrations and a greater resistance to apoptosis. In contrast, Rad51 antisense inhibition reduces p21 protein levels and sensitizes cells to etoposide treatment. Downregulation of p21 inhibits Rad51 foci formation in both normal and Rad51-overexpressing cells. Collectively, our results show that Rad51 expression, Rad51 foci formation and p21 expression are interrelated, suggesting a functional link between mammalian Rad51 protein and p21-mediated cell cycle regulation. This mechanism may contribute to a highly effective recombinational DNA repair in cell cycle-arrested cells and protection against DNA damage-induced apoptosis.
Raderschall
Elke
E
Max Planck Institute of Molecular Genetics, 14195 Berlin, Germany.
Bazarov
Alex
A
Cao
Jiangping
J
Lurz
Rudi
R
Smith
Avril
A
Mann
Wolfgang
W
Ropers
Hans-Hilger
HH
Sedivy
John M
JM
Golub
Efim I
EI
Fritz
Eberhard
E
Haaf
Thomas
T
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D015153:Blotting, Western; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D002869:Chromosome Aberrations; D002999:Clone Cells; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000648:ultrastructure*; D005047:Etoposide / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D051135:Rad51 Recombinase; D011839:Radiation, Ionizing; D051381:Rats; D014162:Transfection; D014466:Ultraviolet Rays
C493956:CDKN1A protein, human; C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D005047:Etoposide; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; C495155:Rad51 protein, rat