Biomedical subjects

Patrick Sung

Publications and source records attributed to Patrick Sung.

7 recordsLinked to original sources

PubMed2026

The 1H, 15N and 13C backbone resonance assignments of an intrinsically disordered region (467-696) of breast cancer type 1 susceptibility protein (BRCA1).

The tumor suppressor protein breast cancer type 1 susceptibility protein (BRCA1) plays a central role in maintaining genome stability through its involvement in DNA damage repair, transcriptional regulation, and cell-cycle control. BRCA1 functions as an obligate heterodimer with its binding partner, the BRCA1-associated RING domain protein 1 (BARD1), to coordinate accurate DNA repair. While the structured N- and C-terminal domains of BRCA1 have been well-characterized, the large central region encoded largely by exon 11 that comprises ~ 80% of the protein, is intrinsically disordered, and remains poorly structurally characterized. This intrinsically disordered region (IDR) harbors critical interaction interfaces for key proteins involved in genome maintenance, including RAD50, RAD51, MYC, and RB. Here, we report the backbone resonance assignments of a BRCA1 IDR construct spanning residues 467-696, providing a foundation for future studies aimed at understanding how the disordered central region of BRCA1 contributes to homologous recombination, interactions with BARD1, and overall BRCA1 tumor suppressor function.

BRCA1 Protein↗

PubMed2026

The1H, 15N and13C backbone resonance assignments of an intrinsically disordered region (124-270) of BRCA1 associated RING domain 1 (BARD1).

The BRCA1-associated RING domain protein 1 (BARD1) is the obligate binding partner of the tumor suppressor breast cancer type 1 susceptibility protein (BRCA1) and plays a critical role in maintaining genome integrity. BARD1 contains structured N- and C-terminal domains that mediate heterodimerization with BRCA1, recognition of chromatin marks, and DNA repair functions. Approximately 40% of BARD1 is intrinsically disordered, particularly in the central region of the protein. This intrinsically disordered region (IDR) engages DNA and key repair proteins such as RAD51, BLM, and WRN. DNA binding through the BARD1 IDR facilitates H2A ubiquitination by the BRCA1-BARD1 complex and is essential for stimulating long-range DNA end resection during homologous recombination, underscoring its role in accurate DNA repair. Despite these insights, structural characterization of the IDR remains limited, leaving questions regarding its functional interplay with BRCA1 and other repair factors unresolved. Here, we report the backbone resonance assignments of a BARD1 IDR construct spanning residues 124-270, providing a foundation for future studies aimed at understanding how the disordered regions of BARD1 interact with various binding partners, and cooperates with itself and BRCA1 to regulate genome stability.

Nuclear Magnetic Resonance, Biomolecular↗

PubMed2026

Antibody-Mediated Targeting of Secretory Protein SCUBE3 Suppresses Cancer Progression by Inhibiting Oncogenic Signaling and Inducing Antitumor Immunity.

UNLABELLED: Approaches targeting factors that simultaneously promote tumor growth and progression, induce therapy resistance, and inhibit antitumor immunity offer clear benefits over therapies targeting only one of these tumor-promoting processes. Through comprehensive loss-of-function genomic screening, we identified SCUBE3 as a pivotal factor that supports survival and therapy resistance and also orchestrates an immunosuppressive tumor microenvironment. Secretory SCUBE3 supported oncogenic activity through interactions with key oncogenic cell surface receptor proteins, including EGFR, mutant CALR, and TGFβRI/II. These interactions activated the transcription factors FOXR2 and c-Myc, promoting cancer cell proliferation and therapy resistance by enhancing DNA damage repair. Additionally, the SCUBE3-FOXR2 axis created an immunosuppressive tumor microenvironment by facilitating recruitment of the DNMT1 epigenetic repressor complex to the transcription regulator IRF1, thereby inhibiting the expression of MHC-I and MHC-II genes. A first-in-class neutralizing antibody targeting SCUBE3, which was developed using a sophisticated antibody discovery platform and engineered with specific mutations in the heavy chain for enhanced specificity and efficacy, demonstrated profound therapeutic potential across various cancer types in preclinical models, including patient-derived breast and ovarian cancer xenografts. This discovery marks an advancement toward developing a targeted therapy for cancers characterized by hyperactive SCUBE3-associated signaling pathways. SIGNIFICANCE: Targeting SCUBE3 with a neutralizing antibody inhibits tumor growth and metastasis by blocking oncogenic signaling through FOXR2 and c-Myc and by circumventing immunosuppression, providing a promising pan-cancer treatment approach.

Humans↗

PubMed2025

Phosphoregulation of RAD51AP1 function in homology-directed repair.

Homology-directed DNA repair (HDR) is critical for genome stability and tumor suppression. HDR is initiated by the RAD51 single-stranded (ss)DNA nucleoprotein filament which conducts the homology search and invades a homologous DNA template, creating a displacement-loop (D-loop). The RAD51 filament is assisted in these processes by several proteins. One such protein is RAD51-Associated-Protein 1 (RAD51AP1) which binds DNA and RNA and directly interacts with RAD51. Of note, RAD51AP1 overexpression is associated with poor prognosis in several different cancer types. Here, we show that RAD51AP1 activity is regulated by phosphorylation. RAD51AP1 bearing S277/282A mutations is more proficient in the stimulation of D-loop formation than wild type RAD51AP1 or phosphomimetic RAD51AP1-S277/282D. In EMSAs, RAD51AP1 with S277/282A mutations more avidly binds ssDNA, double-stranded (ds)DNA, and the nucleosome core particle than wild type RAD51AP1 or RAD51AP1-S277/282D. In cells, RAD51AP1-S277/282A confers no rescue of RAD51AP1 deficiency in toxicity tests and DNA replication assays. In contrast, RAD51AP1-S277/282D fully rescues RAD51AP1 deficiency. We provide evidence that RAD51AP1-S277 is a CDK2 target and propose a model in which RAD51AP1-S277/282 phosphorylation ensures RAD51AP1 flexibility for dynamic engagement in consecutive steps of the HDR reaction. Our results provide new mechanistic insights into RAD51AP1 regulation by a CDK.

CDK1/2↗

PubMed2025

Distinct roles of the two BRCA2 DNA-binding domains in DNA damage repair and replication fork preservation.

Homologous recombination (HR) removes DNA double-strand breaks (DSBs) and preserves stressed DNA replication forks. Successful HR execution requires the tumor suppressor BRCA2, which harbors distinct DNA-binding domains (DBDs): one that possesses three oligonucleotide/oligosaccharide-binding (OB) folds (OB-DBD) and another residing in the C-terminal recombinase binding domain (CTRB-DBD). Here, we employ multi-faceted approaches to delineate the contributions of these domains toward HR and replication fork maintenance. We show that OB-DBD and CTRB-DBD confer single-strand DNA (ssDNA)- and dsDNA-binding capabilities, respectively, and that BRCA2 variants mutated in either domain are impaired in their ability to load the recombinase RAD51 onto ssDNA pre-occupied by RPA. While the CTRB-DBD mutant is modestly affected by DNA break repair, it exhibits a strong defect in the protection of stressed replication forks. In contrast, the OB-DBD is indispensable for both BRCA2 functions. Our study thus defines the unique contributions of the two BRCA2 DBDs in genome maintenance.

BRCA2 Protein↗

PubMed2023

DNA binding and RAD51 engagement by the BRCA2 C-terminus orchestrate DNA repair and replication fork preservation.

The tumor suppressor BRCA2 participates in DNA double-strand break repair by RAD51-dependent homologous recombination and protects stressed DNA replication forks from nucleolytic attack. We demonstrate that the C-terminal Recombinase Binding (CTRB) region of BRCA2, encoded by gene exon 27, harbors a DNA binding activity. CTRB alone stimulates the DNA strand exchange activity of RAD51 and permits the utilization of RPA-coated ssDNA by RAD51 for strand exchange. Moreover, CTRB functionally synergizes with the Oligonucleotide Binding fold containing DNA binding domain and BRC4 repeat of BRCA2 in RPA-RAD51 exchange on ssDNA. Importantly, we show that the DNA binding and RAD51 interaction attributes of the CTRB are crucial for homologous recombination and protection of replication forks against MRE11-mediated attrition. Our findings shed light on the role of the CTRB region in genome repair, reveal remarkable functional plasticity of BRCA2, and help explain why deletion of Brca2 exon 27 impacts upon embryonic lethality.

DNA Replication↗

PubMed2015

NUCKS1 is a novel RAD51AP1 paralog important for homologous recombination and genome stability.

NUCKS1 (nuclear casein kinase and cyclin-dependent kinase substrate 1) is a 27 kD chromosomal, vertebrate-specific protein, for which limited functional data exist. Here, we demonstrate that NUCKS1 shares extensive sequence homology with RAD51AP1 (RAD51 associated protein 1), suggesting that these two proteins are paralogs. Similar to the phenotypic effects of RAD51AP1 knockdown, we find that depletion of NUCKS1 in human cells impairs DNA repair by homologous recombination (HR) and chromosome stability. Depletion of NUCKS1 also results in greatly increased cellular sensitivity to mitomycin C (MMC), and in increased levels of spontaneous and MMC-induced chromatid breaks. NUCKS1 is critical to maintaining wild type HR capacity, and, as observed for a number of proteins involved in the HR pathway, functional loss of NUCKS1 leads to a slow down in DNA replication fork progression with a concomitant increase in the utilization of new replication origins. Interestingly, recombinant NUCKS1 shares the same DNA binding preference as RAD51AP1, but binds to DNA with reduced affinity when compared to RAD51AP1. Our results show that NUCKS1 is a chromatin-associated protein with a role in the DNA damage response and in HR, a DNA repair pathway critical for tumor suppression.

Cell Line↗