Dephosphorylation and subcellular compartment change of the mitotic Bloom's syndrome DNA helicase in response to ionizing radiation.
Bloom's syndrome is a rare human autosomal recessive disorder that combines a marked genetic instability and an increased risk of developing all types of cancers and which results from mutations in both copies of the BLM gene encoding a RecQ 3'-5' DNA helicase. We recently showed that BLM is phosphorylated and excluded from the nuclear matrix during mitosis. We now show that the phosphorylated mitotic BLM protein is associated with a 3'-5' DNA helicase activity and interacts with topoisomerase III alpha. We demonstrate that in mitosis-arrested cells, ionizing radiation and roscovitine treatment both result in the reversion of BLM phosphorylation, suggesting that BLM could be dephosphorylated through the inhibition of cdc2 kinase. This was supported further by our data showing that cdc2 kinase activity is inhibited in gamma-irradiated mitotic cells. Finally we show that after ionizing radiation, BLM is not involved in the establishment of the mitotic DNA damage checkpoint but is subjected to a subcellular compartment change. These findings lead us to propose that BLM may be phosphorylated during mitosis, probably through the cdc2 pathway, to form a pool of rapidly available active protein. Inhibition of cdc2 kinase after ionizing radiation would lead to BLM dephosphorylation and possibly to BLM recruitment to some specific sites for repair.
Dutertre
Stéphanie
S
CNRS, Unité Mixte de Recherche 1598, Institut Gustave Roussy, 39 Rue Camille Desmoulins, Villejuif Cedex 94 805, France.
Sekhri
Redha
R
Tintignac
Lionel A
LA
Onclercq-Delic
Rosine
R
Chatton
Bruno
B
Jaulin
Christian
C
Amor-Guéret
Mounira
M
D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D001402:B-Lymphocytes; D001816:Bloom Syndrome / Q000201:enzymology / Q000235:genetics*; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000528:radiation effects; D002453:Cell Cycle; D002460:Cell Line; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D005720:Gamma Rays; D006801:Humans; D008938:Mitosis; D053484:RecQ Helicases; D013347:Subcellular Fractions / Q000201:enzymology*
D016203:CDC2 Protein Kinase; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I