RFWD3 modulates response to platinum chemotherapy and promotes cancer associated phenotypes in high grade serous ovarian cancer

Background

DNA damage repair is frequently dysregulated in high grade serous ovarian cancer (HGSOC), which can lead to changes in chemosensitivity and other phenotypic differences in tumours. RFWD3, a key component of multiple DNA repair and maintenance pathways, was investigated to characterise its impact in HGSOC.

Methods

RFWD3 expression and association with clinical features was assessed using in silico analysis in the TCGA HGSOC dataset, and in a further cohort of HGSOC tumours stained for RFWD3 using immunohistochemistry. RFWD3 expression was modulated in cell lines using siRNA and CRISPR/cas9 gene editing, and cells were characterised using cytotoxicity and proliferation assays, flow cytometry, and live cell microscopy.

Results

Expression of RFWD3 RNA and protein varied in HGSOCs. In cell lines, reduction of RFWD3 expression led to increased sensitivity to interstrand crosslinking (ICL) inducing agents mitomycin C and carboplatin. RFWD3 also demonstrated further functionality outside its role in DNA damage repair, with RFWD3 deficient cells displaying cell cycle dysregulation, reduced cellular proliferation and reduced migration. In tumours, low RFWD3 expression was associated with increased tumour mutational burden, and complete response to platinum chemotherapy.

Conclusion

RFWD3 expression varies in HGSOCs, which can lead to functional effects at both the cellular and tumour levels.

Further Evidence for RFWD3 Gene Causing Fanconi Anemia Complementation Group W: Detailed Clinical Report of the Second Case in the Literature

Introduction

Fanconi anemia (FA) is a heterogeneous genetic disorder that is characterized by progressive bone marrow failure, congenital malformations, predisposition to malignancy, and short stature. The RFWD3 gene was recently associated with FA complementation group W, and only 1 patient is reported in the literature so far.

Case Presentation

Here, we report the second patient, a 10-year-old male, who has failure to thrive, central nervous system abnormalities, bilateral radial ray defects, urogenital anomalies, facial dysmorphism, and thrombocytopenia. The patient was suspected to have FA according to the aforementioned findings, and the homozygous c.1501C>T variant in the RFWD3 gene was detected by whole-exome sequencing. The diepoxybutane test and mitomycin C-induced peripheral blood cultures revealed 0.46 and 0.90 chromosomal breaks, respectively.

Conclusion

In this article, clinical findings of the second patient with FA complementation group W are discussed in detail, aiming to expand the clinical and molecular spectrums of the disease.

RFWD3 Participates in the Occurrence and Development of Colorectal Cancer via E2F1 Transcriptional Regulation of BIRC5

Objectives: Colorectal cancer (CRC) is one of the most common human malignancies. It was reported that the alterations in the DNA damage response (DDR) pathways are emerging as novel targets for treatment across different cancer types including CRC. RFWD3 plays a critical role in replication protein A (RPA)-mediated DNA damage in cancer cells. More importantly, RFWD3 can response to DNA damage by positively regulating p53 stability when the G1 cell cycle checkpoint is activated. However, the functional significance of RFWD3 in CRC has not been reported in the existing documents.

Materials and Methods: Here, we revealed high expression of RFWD3 in CRC tissues by IHC analysis and The Cancer Genome Atlas (TCGA) database. Besides, overexpression of RFWD3 in CRC cell lines was also confirmed by qRT-PCR and western blot assay. The Celigo cell counting method and wound-healing/transwell migration assay were applied to evaluate CRC cell proliferation and migration. The tumor growth indicators were quantified in nude mice xenografted with shRFWD3 and shCtrl RKO cells.

Results: The results indicated that RFWD3 knockdown restricted CRC development in vitro and in vivo. In exploring the downstream mechanism of RFWD3’s action, we found that RFWD3 could transcriptionally activate BIRC5 by interacting with E2F transcription factor 1 (E2F1). Accordingly, we identified BIRC5 as a downstream gene of RFWD3 regulating CRC. Subsequent loss- and gain- of function experiments demonstrated that upon overexpressing BIRC5 in RKO cells with down-regulated RFWD3, the inhibitory effects of cell proliferation, migration and colony formation could be reversed, while the capacity of cell apoptosis was ameliorated, suggesting that the effects of RFWD3 depletion was mainly due to BIRC5 suppression.

Conclusion: Taken together, this study revealed that RFWD3 participates in the occurrence and development of colorectal cancer via E2F1 transcriptional regulation of BIRC5.

The Valproate Mediates Radio-Bidirectional Regulation Through RFWD3-Dependent Ubiquitination on Rad51

Ionizing radiation (IR) can induce DNA double-strand breaks (DSBs) in tumor cells during radiotherapy (RT), but the efficiency of RT is limited because of the toxicity to normal cells. Locating an adjuvant treatment to alleviate damage in normal cells while sensitizing tumor cells to IR has attracted much attention. Here, using the 7,12-dimethylbenz[α]anthracene (DMBA)-induced malignant transformed MCF10A cells, we found that valproate (VPA), a histone deacetylase inhibitor (HDACi), radiosensitized transformed cells while alleviated IR-induced damage in normal cells at a safe dose (0.5 mM). We further demonstrated the decrease of homologous recombination (HR)-associated Rad51 in the transformed cells was related to the increase of its ubiquitination regulated by E3 ligase RFWD3 for the radiosensitization, which was opposite to normal cells, indicating that RFWD3-dependent ubiquitination on Rad51 was involved in the VPA-mediated radio-bidirectional effect. Through DMBA-transformed breast cancer rat model, VPA at 200 mg/kg radiosensitized tumor tissue cells by increasing RFWD3 and inhibited Rad51, while radioprotected normal tissue cells by decreasing RFWD3 and enhanced Rad51. In addition, we found high-level Rad51 was associated with tumorigenesis and poor prognosis in breast cancer patients. Our findings uncovered RFWD3-dependent Rad51 ubiquitination was the novel mechanism of VPA-mediated radio-bidirectional effect, VPA is a potential adjuvant treatment for tumor RT.

The ubiquitin ligase RFWD3 is required for translesion DNA synthesis

Lesions on DNA uncouple DNA synthesis from the replisome, generating stretches of unreplicated single-stranded DNA (ssDNA) behind the replication fork. These ssDNA gaps need to be filled in to complete DNA duplication. Gap-filling synthesis involves either translesion DNA synthesis (TLS) or template switching (TS). Controlling these processes, ubiquitylated PCNA recruits many proteins that dictate pathway choice, but the enzymes regulating PCNA ubiquitylation in vertebrates remain poorly defined. Here we report that the E3 ubiquitin ligase RFWD3 promotes ubiquitylation of proteins on ssDNA. The absence of RFWD3 leads to a profound defect in recruitment of key repair and signaling factors to damaged chromatin. As a result, PCNA ubiquitylation is inhibited without RFWD3, and TLS across different DNA lesions is drastically impaired. We propose that RFWD3 is an essential coordinator of the response to ssDNA gaps, where it promotes ubiquitylation to drive recruitment of effectors of PCNA ubiquitylation and DNA damage bypass.

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RFWD3 promotes ubiquitylation of proteins on ssDNA

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RFWD3 regulates DNA damage-induced PCNA ubiquitylation

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RFWD3 stimulates gap-filling DNA synthesis across different DNA lesions

RPA, RFWD3 and BRCA2 at stalled forks: a balancing act

We recently identified E3 ligase RFWD3 as a modulator of stalled fork stability in BRCA2-deficient cells. We also show that BRCA1 might function upstream of BRCA2 during fork repair and that blocking fork degradation by depleting MRE11 does not guarantee fork repair. These findings provide new insights into the workings of BRCA1 and BRCA2 in the stalled fork repair pathway.

The E3 ligase RFWD3 stabilizes ORC in a p53-dependent manner

RFWD3 is an E3 ubiquitin ligase that plays important roles in DNA damage response and DNA replication. We have previously demonstrated that the stabilization of RFWD3 by PCNA at the replication fork enables ubiquitination of the single-stranded binding protein, RPA and its subsequent degradation for replication progression. Here, we report that RFWD3 associates with the Origin Recognition Complex (ORC) and ORC-Associated (ORCA/LRWD1), components of the pre-replicative complex required for the initiation of DNA replication. Overexpression of ORC/ORCA leads to the stabilization of RFWD3. Interestingly, RFWD3 seems to stabilize ORC/ORCA in cells expressing wild type p53, as the depletion of RFWD3 reduces the levels of ORC/ORCA. Further, the catalytic activity of RFWD3 is required for the stabilization of ORC. Our results indicate that the RFWD3 promotes the stability of ORC, enabling efficient pre-RC assembly.

PCNA-mediated stabilization of E3 ligase RFWD3 at the replication fork is essential for DNA replication

RING finger and WD repeat domain-containing protein 3 (RFWD3) is an E3 ligase known to facilitate homologous recombination by removing replication protein A (RPA) and RAD51 from DNA damage sites. Further, RPA-mediated recruitment of RFWD3 to stalled replication forks is essential for interstrand cross-link repair. Here, we report that in unperturbed human cells, RFWD3 localizes at replication forks and associates with proliferating cell nuclear antigen (PCNA) via its PCNA-interacting protein (PIP) motif. PCNA association is critical for the stability of RFWD3 and for DNA replication. Cells lacking RFWD3 show slower fork progression, a prolonged S phase, and an increase in the loading of several replication-fork components on the chromatin. These findings all point to increased frequency of stalled forks in the absence of RFWD3. The S-phase defect is rescued by WT RFWD3, but not by the PIP mutant, suggesting that the interaction of RFWD3 with PCNA is critical for DNA replication. Finally, we observe reduced ubiquitination of RPA in cells lacking RFWD3. We conclude that the stabilization of RFWD3 by PCNA at the replication fork enables the polyubiquitination of RPA and its subsequent degradation for proper DNA replication.

RPA-Mediated Recruitment of the E3 Ligase RFWD3 Is Vital for Interstrand Crosslink Repair and Human Health

Defects in the repair of DNA interstrand crosslinks (ICLs) are associated with the genome instability syndrome Fanconi anemia (FA). Here we report that cells with mutations in RFWD3, an E3 ubiquitin ligase that interacts with and ubiquitylates replication protein A (RPA), show profound defects in ICL repair. An amino acid substitution in the WD40 repeats of RFWD3 (I639K) found in a new FA subtype abolishes interaction of RFWD3 with RPA, thereby preventing RFWD3 recruitment to sites of ICL-induced replication fork stalling. Moreover, single point mutations in the RPA32 subunit of RPA that abolish interaction with RFWD3 also inhibit ICL repair, demonstrating that RPA-mediated RFWD3 recruitment to stalled replication forks is important for ICL repair. We also report that unloading of RPA from sites of ICL induction is perturbed in RFWD3-deficient cells. These data reveal important roles for RFWD3 localization in protecting genome stability and preserving human health.

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RFWD3-deficient human cells show profound defects in ICL repair

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RFWD3 regulates RPA dynamics to promote homologous recombination

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The FA-associated I639K mutation prevents RPA-dependent recruitment of RFWD3 to ICLs

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RPA32 mutations that abolish interaction with RFWD3 also inhibit ICL repair

RFWD3-Mediated Ubiquitination Promotes Timely Removal of Both RPA and RAD51 from DNA Damage Sites to Facilitate Homologous Recombination

RFWD3 is a recently identified Fanconi anemia protein FANCW whose E3 ligase activity toward RPA is essential in homologous recombination (HR) repair. However, how RPA ubiquitination promotes HR remained unknown. Here, we identified RAD51, the central HR protein, as another target of RFWD3. We show that RFWD3 polyubiquitinates both RPA and RAD51 in vitro and in vivo. Phosphorylation by ATR and ATM kinases is required for this activity in vivo. RFWD3 inhibits persistent mitomycin C (MMC)-induced RAD51 and RPA foci by promoting VCP/p97-mediated protein dynamics and subsequent degradation. Furthermore, MMC-induced chromatin loading of MCM8 and RAD54 is defective in cells with inactivated RFWD3 or expressing a ubiquitination-deficient mutant RAD51. Collectively, our data reveal a mechanism that facilitates timely removal of RPA and RAD51 from DNA damage sites, which is crucial for progression to the late-phase HR and suppression of the FA phenotype.