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Principal Investigator: BINGHUI SHEN
Organization: BECKMAN RESEARCH INSTITUTE/CITY OF HOPE
Fiscal Year: 2024
Award: $316,742
Funding agency: National Cancer Institute
SUMMARY
Cancer cells arise and progress due to accumulation of genetic and epigenetic alterations that contribute to
cancer phenotypes. One potential cause of these alterations are DNA sequences that are “difficult-to-replicate”
(DTR) and act as an endogenous source of replication stress. Across the genome there are two major classes
of mutually overlapping DTR sequences, including mini-satellites and micro-satellites in the centromere regions
and G-quadruplexes (G4s) in the telomeres. Such secondary structures formed in DTRs, if not properly resolved,
may block DNA replication fork movement and lead to genome instability. However, cells have developed
mechanisms to resolve these barriers for efficient and faithful DNA replication. The most well-known way to
resolve G4 and other secondary structures is unwinding the structure through DNA helicases. During the last
funding period, we elucidated that the nuclease/helicase DNA2 facilitates DNA replication at DTR sequences. In
our preliminary studies, we showed that the DNA mismatch repair protein MSH2, a component of the MutSα
complex, binds to both G4s and DNA2 and strongly stimulates DNA2 to cleave G4 structures. Radiation,
elimination of DNA2 or MSH2, or lack of histone H1c ubiquitination cause G4 accumulation. Therefore, we
hypothesize that: 1) DNA2 in complex with MutSα excises and repairs G4 structures to facilitate DNA replication
through DTRs; 2) ubiquitinated H1c recruits the DNA2/MutSα complex onto G4-bearing DNA ends at double-
strand breaks (DSBs) for homology-directed DNA repair (HDR) of DSBs; and 3) gene mutations that impair G4
resolution processes sensitize individuals to chemicals that induce or stabilize G4 structures, leading to genome
rearrangements and cancer initiation. We propose to define the important molecular aspects of the G4 excision
pathways during DNA replication or DSB repair. Because G4s are implicated as chromosome structural elements
and epigenetic motifs that regulate gene expression, G4 excision must be tightly controlled. It is important to
elucidate how the DNA2/MutSα is signaled to be recruited to the G4 structure for excision repair. We will define
how H1c ubiquitination mediated by ubiquitin E3 ligases ITCH or RNF8 induces DNA2/MutSα to cleave G4
structures during DNA replication and DSB repair. Moreover, a large number of environmentally contaminating
compounds (ECCs) can specifically bind to G4 structures and alter the dynamics of G4 resolution. We expect
that once genetic mutations impair a G4 resolution pathway, a G4 stabilizer can act synergistically to cause DNA
replication stresses, DSBs, and genome rearrangements. Therefore, we will determine if combined genetic and
environmental factors that inhibit proper G4 resolution/repair show synergy in promoting genome instability and
cancer initiation. Our comprehensive analyses will define the pathway for G4 excision in S phase and during
DNA DSB repair via HDR, and will provide evidence that G4-stabilizing ECCs lower the cancer threshold,
particularly for individuals with defects in DNA2-mediated G4 and other secondary structure resolution pathways.
Terms: <Abscission><Aflatoxin B1><Binding><Binding Proteins><Biological><COCA1><Cancer Biology><Cancer Cause><Cancer Etiology><Cancer Treatment><Cancers><Cell Body><Cell Communication and Signaling><Cell Signaling><Cells><Centromere><Chemical Exposure><Chemicals><Chromosomes><Complex><DNA><DNA Alteration><DNA Damage Repair><DNA Double Strand Break><DNA Helicases><DNA Mismatch Repair Protein MSH2><DNA Mismatch Repair Protein MSH6><DNA Repair><DNA Replication><DNA Sequence><DNA Sequence Alteration><DNA Structure><DNA Synthesis><DNA Unwinding Proteins><DNA biosynthesis><DNA mutation><DNA replication fork><DNA unwinding enzyme><Defect><Deoxyribonucleic Acid><Development><Double Strand Break Repair><E3 Ligase><E3 Ubiquitin Ligase><Elements><Environment><Environmental Factor><Environmental Risk Factor><Epigenetic><Epigenetic Change><Epigenetic Mechanism><Epigenetic Process><Excision><Excision Repair><Extirpation><FCC1><Foundations><Funding><G-Quadruplex><G-Quadruplexes DNA><G-Quartet Structures><G-Quartets><G-T mismatch-binding protein><G-Tetrads><G4-DNA><GTMBP><Gene Alteration><Gene Expression><Gene Mutation><Genetic><Genetic mutation><Genome><Genome Instability><Genomic Instability><Goals><Histones><Human><Impairment><In Vitro><Individual><Intracellular Communication and Signaling><Knowledge><Ligand Binding Protein><Ligand Binding Protein Gene><MSH2><MSH2 gene><MSH6><MSH6 gene><Malignant Cell><Malignant Neoplasm Therapy><Malignant Neoplasm Treatment><Malignant Neoplasms><Malignant Tumor><Mammalian Cell><Mediating><Mice><Mice Mammals><Microsatellite Markers><Microsatellite Repeats><Microsatellites><Minisatellite Repeats><Minisatellites><Modeling><Modern Man><Molecular><Molecular Interaction><Movement><Murine><Mus><MutS Homolog 2><MutS Homolog 6><Non-Polyadenylated RNA><Nuclear><Oncogenesis><Pathway interactions><Phenotype><Pigments><Predisposition><Process><Protein Binding><RNA><RNA Gene Products><Radiation><Removal><Resolution><Ribonucleic Acid><Role><S Period><S phase><Sequence Alteration><Signal Transduction><Signal Transduction Systems><Signaling><Simple Repetitive Sequence><Single-Stranded DNA><Site><Solid><Source><Structure><Surgical Removal><Susceptibility><Synthesis Period><Synthesis Phase><Tail><Treatment Protocols><Treatment Regimen><Treatment Schedule><Ubiquitilation><Ubiquitin Protein Ligase><Ubiquitin-Protein Ligase Complexes><Ubiquitin-Protein Ligase E3><Ubiquitination><Ubiquitinoylation><Unscheduled DNA Synthesis><VNTR><VNTR Loci><VNTR Region><VNTR Sequences><Variable Number of Tandem Repeats><Variable Tandem Repeats><anti-cancer therapy><biologic><biological signal transduction><body movement><bound protein><cancer cell><cancer initiation><cancer progression><cancer therapy><cancer-directed therapy><design><designing><developmental><environmental risk><epigenetically><genomic alteration><helicase><malignancy><neoplasm progression><neoplasm/cancer><neoplastic progression><novel><nuclease><pathway><pigment><protoporphyrin IX><recruit><repair><repaired><replication fork><replication stress><resection><resolutions><response><social role><ssDNA><synergism><telomere><tumor progression><tumorigenesis><ubiquination><ubiquitin conjugation><ubiquitin-protein ligase>