hSSB2 (NABP1) is required for the recruitment of RPA during the cellular response to DNA UV damage

Abstract

Maintenance of genomic stability is critical to prevent diseases such as cancer. As such, eukaryotic cells have multiple pathways to efficiently detect, signal and repair DNA damage. One common form of exogenous DNA damage comes from ultraviolet B (UVB) radiation. UVB generates cyclobutane pyrimidine dimers (CPD) that must be rapidly detected and repaired to maintain the genetic code. The nucleotide excision repair (NER) pathway is the main repair system for this type of DNA damage. Here, we determined the role of the human Single-Stranded DNA Binding protein 2, hSSB2, in the response to UVB exposure. We demonstrate that hSSB2 levels increase in vitro and in vivo after UVB irradiation and that hSSB2 rapidly binds to chromatin. Depletion of hSSB2 results in significantly decreased Replication Protein A (RPA32) phosphorylation and impaired RPA32 localisation to the site of UV-induced DNA damage. Delayed recruitment of NER protein Xeroderma Pigmentosum group C (XPC) was also observed, leading to increased cellular sensitivity to UVB. Finally, hSSB2 was shown to have affinity for single-strand DNA containing a single CPD and for duplex DNA with a two-base mismatch mimicking a CPD moiety. Altogether our data demonstrate that hSSB2 is involved in the cellular response to UV exposure.

DNA‐dependent phase separation by human SSB2 (NABP1/OBFC2A) protein points to adaptations to eukaryotic genome repair processes

“…Generally high basal expression levels of hSSB1 could be adaptive in terms of oxidation-induced hSSB1 phase separation, whereas hSSB2 LLPS could be regulated by inducible protein abundance. hSSB2 appears to be dispensable for DNA replication and cell cycle progression under normal conditions, but it has important DNA repair functions under stress, and may thus be implicated as a useful target for cancer therapy (Adams et al, 2023;Boucher et al, 2015Boucher et al, , 2021Li et al, 2009;Par et al, 2021;Skaar et al, 2009;Zhang et al, 2009). hSSB2 downregulation sensitizes cells for DNA damage, as evidenced by increased UV sensitivity, increased amounts cyclobutane pyrimidine dimer lesions, impaired RPA localization to DNA damage sites, and delayed recruitment of the XPC nucleotide excision repair protein upon UV irradiation (Boucher et al, 2021;Lawson et al, 2020).…”

DNA-dependent phase separation by human SSB2 (NABP1/OBFC2A) protein points to adaptations to eukaryotic genome repair processes

“…Importantly, however, hSSB2 expression is tissue specific, with epithelial and immune cells showing high transcription levels (the highest level, 345.3 nTPM, was detected in Langerhans cells (Human Protein Atlas database, single-cell RNA data)). Moreover, hSSB2 expression may well be enhanced upon genomic stress, as indicated by the protein's involvement in genome maintenance processes and its increased expression levels upon hSSB1 ablation or UV-stress (5,14). All in all, hSSB2 levels may greatly vary among cell types, and robust LLPS may manifest in cells showing high expression levels.…”

“…Available data indicate the functional involvement of hSSB2 in DNA repair and the response to various forms of genomic stress (5,6,9,13,14). A mouse model with a deleted mouse (m) SSB2 gene is viable with no obvious phenotype under stress-free conditions (15).…”

“…Recent data also indicate distinct functional specialization for hSSB paralogs. hSSB2 is involved in the nucleotide excision repair pathway (NER) and can recognize and rapidly localize to cyclobutene pyrimidine dimers formed upon UV irradiation (14,27), whereas hSSB1 is selectively involved in the base excision repair pathway due to its unique ability to recognize oxidized guanine bases (28)(29)(30).…”

Foamy Cell Angiosarcoma in a Patient with Xeroderma Pigmentosum: A Case Report and Comprehensive Review of the Literature

“…Xeroderma pigmentosum (XP) is a rare inherited condition transmitted in an autosomal recessive pattern ( 1 - 3 ). The main problem in more than 80% of cases is nucleotide excision repair (NER) defect causing a disturbed function of DNA repair harmed by sunlight ultraviolet radiation ( 1 , 4 ). This heightened photosensitivity results in sunburn, pigmentary changes, accelerated skin aging, anda significantly elevated incidence of skin neoplasms, including basal cell carcinoma, squamous cell carcinoma, and melanoma ( 5 , 6 ).…”