title: p97 Promotes a Conserved Mechanism of Helicase Unloading during DNA Cross-Link Repair.
abstract: Interstrand cross-links (ICLs) are extremely toxic DNA lesions that create an impassable roadblock to DNA replication. When a replication fork collides with an ICL, it triggers a damage response that promotes multiple DNA processing events required to excise the cross-link from chromatin and resolve the stalled replication fork. One of the first steps in this process involves displacement of the CMG replicative helicase (comprised of Cdc45, MCM2-7, and GINS), which obstructs the underlying cross-link. Here we report that the p97/Cdc48/VCP segregase plays a critical role in ICL repair by unloading the CMG complex from chromatin. Eviction of the stalled helicase involves K48-linked polyubiquitylation of MCM7, p97-mediated extraction of CMG, and a largely degradation-independent mechanism of MCM7 deubiquitylation. Our results show that ICL repair and replication termination both utilize a similar mechanism to displace the CMG complex from chromatin. However, unlike termination, repair-mediated helicase unloading involves the tumor suppressor protein BRCA1, which acts upstream of MCM7 ubiquitylation and p97 recruitment. Together, these findings indicate that p97 plays a conserved role in dismantling the CMG helicase complex during different cellular events, but that distinct regulatory signals ultimately control when and where unloading takes place.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: George
authors.initials: G
authors.lastname: Fullbright
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: Halley B
authors.initials: HB
authors.lastname: Rycenga
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: Jordon D
authors.initials: JD
authors.lastname: Gruber
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, USA longdt@musc.edu.
authors.forename: David T
authors.initials: DT
authors.lastname: Long
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002843:Chromatin / Q000201:enzymology; D004265:DNA Helicases / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D054875:Ubiquitination; D000074405:Valosin Containing Protein; D029867:Xenopus Proteins / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics* / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D029867:Xenopus Proteins; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D000074405:Valosin Containing Protein