Snm1B/Apollo mediates replication fork collapse and S Phase checkpoint activation in response to DNA interstrand cross-links.
The removal of DNA interstrand cross-links (ICLs) has proven to be notoriously complicated due to the involvement of multiple pathways of DNA repair, which include the Fanconi anemia/BRCA pathway, homologous recombination and components of the nucleotide excision and mismatch repair pathways. Members of the SNM1 gene family have also been shown to have a role in mediating cellular resistance to ICLs, although their precise function has remained elusive. Here, we show that knockdown of Snm1B/Apollo in human cells results in hypersensitivity to mitomycin C (MMC), but not to IR. We also show that Snm1B-deficient cells exhibit a defective S phase checkpoint in response to MMC, but not to IR, and this finding may account for the specific sensitivity to the cross-linking drug. Interestingly, although previous studies have largely implicated ATR as the major kinase activated in response to ICLs, we show that it is activation of the ATM-mediated checkpoint that is defective in Snm1B-deficient cells. The requirement for Snm1B in ATM checkpoint activation specifically after ICL damage is correlated with its role in promoting double-strand break formation, and thus replication fork collapse. Consistent with this result Snm1B was found to interact directly with Mus81-Eme1, an endonuclease previously implicated in fork collapse. In addition, we also show that Snm1B interacts with the Mre11-Rad50-Nbs1 (MRN) complex and with FancD2 further substantiating its role as a checkpoint/DNA repair protein.
Bae
J-B
JB
Department of Cancer Genetics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Mukhopadhyay
S S
SS
Liu
L
L
Zhang
N
N
Tan
J
J
Akhter
S
S
Liu
X
X
Shen
X
X
Li
L
L
Legerski
R J
RJ
D017766:Acid Anhydride Hydrolases; D018797:Cell Cycle Proteins / Q000378:metabolism; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000633:toxicity*; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000378:metabolism / Q000502:physiology*; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005090:Exodeoxyribonucleases; D052236:Fanconi Anemia Complementation Group D2 Protein / Q000378:metabolism; D018816:Genes, cdc / Q000502:physiology; D006801:Humans; D000076228:MRE11 Homologue Protein; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D016196:S Phase / Q000235:genetics*
D018797:Cell Cycle Proteins; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; C499905:FANCD2 protein, human; D052236:Fanconi Anemia Complementation Group D2 Protein; C121766:MRE11 protein, human; D046912:Multiprotein Complexes; C112156:NBN protein, human; D009687:Nuclear Proteins; C493741:DCLRE1B protein, human; D005090:Exodeoxyribonucleases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes