Characterization of the interactions of PARP-1 with UV-damaged DNA in vivo and in vitro

Cisplatin in the era of PARP inhibitors and immunotherapy

Platinum compounds such as cisplatin, carboplatin and oxaliplatin are widely used in chemotherapy. Cisplatin induces cytotoxic DNA damage that blocks DNA replication and gene transcription, leading to arrest of cell proliferation. Although platinum therapy alone is effective against many tumors, cancer cells can adapt to the treatment and gain resistance. The mechanisms for cisplatin resistance are complex, including low DNA damage formation, high DNA repair capacity, changes in apoptosis signaling pathways, rewired cell metabolisms, and others. Drug resistance compromises the clinical efficacy and calls for new strategies by combining cisplatin with other therapies. Exciting progress in cancer treatment, particularly development of poly (ADP-ribose) polymerase (PARP) inhibitors and immune checkpoint inhibitors, opened a new chapter to combine cisplatin with these new cancer therapies. In this Review, we discuss how platinum synergizes with PARP inhibitors and immunotherapy to bring new hope to cancer patients.

UV-DDB as a General Sensor of DNA Damage in Chromatin: Multifaceted Approaches to Assess Its Direct Role in Base Excision Repair

Base excision repair (BER) is a cellular process that removes damaged bases arising from exogenous and endogenous sources including reactive oxygen species, alkylation agents, and ionizing radiation. BER is mediated by the actions of multiple proteins which work in a highly concerted manner to resolve DNA damage efficiently to prevent toxic repair intermediates. During the initiation of BER, the damaged base is removed by one of 11 mammalian DNA glycosylases, resulting in abasic sites. Many DNA glycosylases are product-inhibited by binding to the abasic site more avidly than the damaged base. Traditionally, apurinic/apyrimidinic endonuclease 1, APE1, was believed to help turn over the glycosylases to undergo multiple rounds of damaged base removal. However, in a series of papers from our laboratory, we have demonstrated that UV-damaged DNA binding protein (UV-DDB) stimulates the glycosylase activities of human 8-oxoguanine glycosylase (OGG1), MUTY DNA glycosylase (MUTYH), alkyladenine glycosylase/N-methylpurine DNA glycosylase (AAG/MPG), and single-strand selective monofunctional glycosylase (SMUG1), between three- and five-fold. Moreover, we have shown that UV-DDB can assist chromatin decompaction, facilitating access of OGG1 to 8-oxoguanine damage in telomeres. This review summarizes the biochemistry, single-molecule, and cell biology approaches that our group used to directly demonstrate the essential role of UV-DDB in BER.

The XPA Protein-Life under Precise Control

Nucleotide excision repair (NER) is a central DNA repair pathway responsible for removing a wide variety of DNA-distorting lesions from the genome. The highly choreographed cascade of core NER reactions requires more than 30 polypeptides. The xeroderma pigmentosum group A (XPA) protein plays an essential role in the NER process. XPA interacts with almost all NER participants and organizes the correct NER repair complex. In the absence of XPA's scaffolding function, no repair process occurs. In this review, we briefly summarize our current knowledge about the XPA protein structure and analyze the formation of contact with its protein partners during NER complex assembling. We focus on different ways of regulation of the XPA protein's activity and expression and pay special attention to the network of post-translational modifications. We also discuss the data that is not in line with the currently accepted hypothesis about the functioning of the XPA protein.

XPC-PARP complexes engage the chromatin remodeler ALC1 to catalyze global genome DNA damage repair

Cells employ global genome nucleotide excision repair (GGR) to eliminate a broad spectrum of DNA lesions, including those induced by UV light. The lesion-recognition factor XPC initiates repair of helix-destabilizing DNA lesions, but binds poorly to lesions such as CPDs that do not destabilize DNA. How difficult-to-repair lesions are detected in chromatin is unknown. Here, we identify the poly-(ADP-ribose) polymerases PARP1 and PARP2 as constitutive interactors of XPC. Their interaction results in the XPC-stimulated synthesis of poly-(ADP-ribose) (PAR) by PARP1 at UV lesions, which in turn enables the recruitment and activation of the PAR-regulated chromatin remodeler ALC1. PARP2, on the other hand, modulates the retention of ALC1 at DNA damage sites. Notably, ALC1 mediates chromatin expansion at UV-induced DNA lesions, leading to the timely clearing of CPD lesions. Thus, we reveal how chromatin containing difficult-to-repair DNA lesions is primed for repair, providing insight into mechanisms of chromatin plasticity during GGR.

Cells employ global genome nucleotide excision repair to repair a broad spectrum of genomic DNA lesions. Here, the authors reveal how chromatin is primed for repair, providing insight into mechanisms of chromatin plasticity during DNA repair.

Revisiting the structural features of the xeroderma pigmentosum proteins: Focus on mutations and knowledge gaps

The nucleotide excision repair pathway is a broadly studied DNA repair mechanism because impairments of its key players, the xeroderma pigmentosum proteins (XPA to XPG), are associated with multiple hereditary diseases. Due to the massive number of novel mutations reported for these proteins and new structural data published every year, proper categorization and discussion of relevant observations is needed to organize this extensive inflow of knowledge. This review aims to revisit the structural data of all XP proteins while updating it with the information developed in of the past six years. Discussions and interpretations of mutation outcomes, mechanisms of action, and knowledge gaps regarding their structures are provided, as well as new perspectives based on recent research.

Nucleotide excision repair leaves a mark on chromatin: DNA damage detection in nucleosomes

Global genome nucleotide excision repair (GG-NER) eliminates a broad spectrum of DNA lesions from genomic DNA. Genomic DNA is tightly wrapped around histones creating a barrier for DNA repair proteins to access DNA lesions buried in nucleosomal DNA. The DNA-damage sensors XPC and DDB2 recognize DNA lesions in nucleosomal DNA and initiate repair. The emerging view is that a tight interplay between XPC and DDB2 is regulated by post-translational modifications on the damage sensors themselves as well as on chromatin containing DNA lesions. The choreography between XPC and DDB2, their interconnection with post-translational modifications such as ubiquitylation, SUMOylation, methylation, poly(ADP-ribos)ylation, acetylation, and the functional links with chromatin remodelling activities regulate not only the initial recognition of DNA lesions in nucleosomes, but also the downstream recruitment and necessary displacement of GG-NER factors as repair progresses. In this review, we highlight how nucleotide excision repair leaves a mark on chromatin to enable DNA damage detection in nucleosomes.

PARP-1 overexpression does not protect HaCaT cells from DNA damage induced by SiO2 nanoparticles

Nano-SiO₂ is increasingly used in diagnostic and biomedical research because of its ease of production and relatively low cost and which is generally regarded as safe and has been approved for use as a food or animal feed ingredient. Although recent literature reveals that nano-SiO₂ may present toxicity and DNA damage, however, the underlying mechanism remains poorly understood. Since in previous studies, we found that nano-SiO₂ treatment down-regulated the expression of the poly(ADP-ribose) polymerases-1 (PARP-1), a pivotal DNA repair gene, in human HaCaT cells and PAPR-1 knockdown can aggravate DNA damage induced by nano-SiO₂. Therefore, we speculate whether PARP-1 overexpression can protect DNA from damage induced by nano-SiO₂. However, our data demonstrated that overexpression of PARP-1 in HaCaT cells slightly enhanced the cellular proliferation of undamaged cells, when compared with both empty vector control cells and parental cells, but had drastic consequences for cells treated with nano-SiO₂. The PARP-1 overtransfected cells were sensitized to the cytotoxic effects and DNA damage of nano-SiO₂ compared with control parental cells. Meanwhile, flow cytometric analysis of nano-SiO₂ stimulated poly(ADP-ribose) synthesis revealed consistently larger fractions of cells positive for this polymer in the PARP-1 overexpression cells than in control clones. Combining our previous research on PARP-1 knockdown HaCaT cells, we hypothesize that an optimal level of cellular poly(ADP-ribose) accumulation exists for the cellular recovery from DNA damage.

DNA photolyase from Antarctic marine bacterium Rhodococcus sp. NJ-530 can repair DNA damage caused by ultraviolet

Marine bacterium Rhodococcus sp. NJ-530 has developed several ultraviolet (UV) adaptive characteristics for survival and growth in extreme Antarctic environment. Rhodococcus sp. NJ-530 DNA photolyase encoded by a 1146 bp photolyase-homologous region (phr) was identified in genome. Quantitative real-time PCR demonstrated that transcriptional levels of phr were highly up-regulated by ultraviolet-B (UV-B) radiation (90 μW·cm^-2) and increased to a maximum of 149.17-fold after exposure for 20 min. According to the results of SDS-PAGE and western blot, PHR was effectively induced by isopropyl-β-d-1-thiogalactopyranoside (IPTG) at the genetically engineered BL21(DE3)-pET-32a( +)-phr construct under the condition of 15 °C for 16 h and 37 °C for 4 h. In terms of in vivo activity, compared with a phr-defective E. coli strain, phr-transformed E. coli exhibited higher survival rate under high UV-B intensity of 90 μW·cm^-2. Meanwhile, the purified PHR, with blue light, presented obvious photorepair activity toward UV-induced DNA damage in vitro assays. To sum up, studying the mechanisms of Rhodococcus sp. NJ-530 photolyase is of great interest to understand the adaptation of polar bacteria to high UV radiation, and such data present important therapeutic value for further UV-induced human skin and genetic damage diseases.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02660-8.

Methods to Study Intracellular Movement and Localization of the Nucleotide Excision Repair Proteins at the DNA Lesions in Mammalian Cells

Nucleotide excision repair (NER) is the most versatile DNA repair pathway that removes a wide variety of DNA lesions caused by different types of physical and chemical agents, such as ultraviolet radiation (UV), environmental carcinogen benzo[a]pyrene and anti-cancer drug carboplatin. The mammalian NER utilizes more than 30 proteins, in a multi-step process that begins with the lesion recognition within seconds of DNA damage to completion of repair after few hours to several days. The core proteins and their biochemical reactions are known from in vitro DNA repair assays using purified proteins, but challenge was to understand the dynamics of their rapid recruitment and departure from the lesion site and their coordination with other proteins and post-translational modifications to execute the sequential steps of repair. Here, we provide a brief overview of various techniques developed by different groups over last 20 years to overcome these challenges. However, more work is needed for a comprehensive knowledge of all aspects of mammalian NER. With this aim, here we provide detailed protocols of three simple yet innovative methods developed by many teams that range from local UVC irradiation to in situ extraction and sub-cellular fractionation that will permit study of endogenous as well as exogenous NER proteins in any cellular model. These methods do not require unique reagents or specialized instruments, and will allow many more laboratories to explore this repair pathway in different models. These techniques would reveal intracellular movement of these proteins to the DNA lesion site, their interactions with other proteins during repair and the effect of post-translational modifications on their functions. We also describe how these methods led us to identify hitherto unexpected role of poly(ADP-ribose) polymerase-1 (PARP1) in NER. Collectively these three simple techniques can provide an initial assessment of the functions of known and unknown proteins in the core or auxiliary events associated with mammalian NER. The results from these techniques could serve as a solid foundation and a justification for more detailed studies in NER using specialized reagents and more sophisticated tools. They can also be suitably modified to study other cellular processes beyond DNA repair.

Apoptosis, the only cell death pathway that can be measured in human diploid dermal fibroblasts following lethal UVB irradiation

Ultraviolet radiation (UVR) is a major environmental genotoxic agent. In skin, it can lead to the formation of mutagenic DNA damage. Several mechanisms are in place to prevent the conversion of these DNA damage into skin cancer-driver mutations. An important mutation prevention mechanism is the programmed cell death, which can safely dispose of the damaged cells. Apoptosis is the most studied and best characterised programmed cell death, but an increasing amount of new cell death pathways are emerging. Using different pharmacological cell death inhibitors and antioxidants, we have evaluated the implication of apoptosis, necroptosis, ferroptosis and parthanatos in UVB-induced cell death in human diploid dermal fibroblasts. Our results show that apoptosis is the only known cell death mechanism induced by UVB irradiation in fibroblasts. We also showed that lethal UVB irradiation induces a PARP-dependent drastic loss of cellular metabolic activity caused by an overused of NAD+.

Focus on UV-Induced DNA Damage and Repair-Disease Relevance and Protective Strategies

The protective ozone layer is continually depleting due to the release of deteriorating environmental pollutants. The diminished ozone layer contributes to excessive exposure of cells to ultraviolet (UV) radiation. This leads to various cellular responses utilized to restore the homeostasis of exposed cells. DNA is the primary chromophore of the cells that absorbs sunlight energy. Exposure of genomic DNA to UV light leads to the formation of multitude of types of damage (depending on wavelength and exposure time) that are removed by effectively working repair pathways. The aim of this review is to summarize current knowledge considering cellular response to UV radiation with special focus on DNA damage and repair and to give a comprehensive insight for new researchers in this field. We also highlight most important future prospects considering application of the progressing knowledge of UV response for the clinical control of diverse pathologies.

Metabolic signature of eyelid basal cell carcinoma

PURPOSE

Eyelid basal cell carcinoma (BCC) is the most common eyelid malignancy. Metabolic reprogramming is critical in tumorigenesis, but the metabolic feature of eyelid BCC remains elusive. In this study, we aim to reveal the metabolic profile in eyelid BCC using targeted metabolomics. Eyelid samples were collected from patients who had removal of BCC and from control patients who underwent blepharoplasty. Multivariate analysis of metabolomics data distinguished the two groups, indicating that eyelid BCC has significantly different metabolome than the healthy tissue. We found 16 increased and 11 decreased metabolites in the BCC tissues. These metabolites were highly enriched in the metabolism of nicotinamide adenine dinucleotide (NAD), glutathione metabolism, polyamine metabolism, and the metabolism of glycine, serine, threonine, arginine and proline. amino acid metabolism. Metabolites from NAD metabolism (Nicotinamide; Nicotinamide riboside; N1-Methylnicotinamide) had the highest sensitivity, specificity, and prediction accuracy in a prediction model for eyelid BCC. In conclusion, eyelid BCC has a signature change of cell metabolome. Metabolites in NAD metabolic pathways could potentially be biomarkers or therapeutic targets for eyelid BCC.

Post-translational Modifications of Nucleotide Excision Repair Proteins and Their Role in the DNA Repair

Nucleotide excision repair (NER) is one of the major DNA repair pathways aimed at maintaining genome stability. Correction of DNA damage by the NER system is a multistage process that proceeds with the formation of multiple DNA-protein and protein-protein intermediate complexes and requires precise coordination and regulation. NER proteins undergo post-translational modifications, such as ubiquitination, sumoylation, phosphorylation, acetylation, and poly(ADP-ribosyl)ation. These modifications affect the interaction of NER factors with DNA and other proteins and thus regulate either their recruitment into the complexes or dissociation from these complexes at certain stages of DNA repair, as well as modulate the functional activity of NER proteins and control the process of DNA repair in general. Here, we review the data on the post-translational modifications of NER factors and their effects on DNA repair. Protein poly(ADP-ribosyl)ation catalyzed by poly(ADP-ribose) polymerase 1 and its impact on NER are discussed in detail, since such analysis has not been done before.

Synergistic Cytoprotective Effects of Rutin and Ascorbic Acid on the Proteomic Profile of 3D-Cultured Keratinocytes Exposed to UVA or UVB Radiation

The combination of ascorbic acid and rutin, often used in oral preparations, due to antioxidant and anti-inflammatory properties, can be used to protect skin cells against the effects of UV radiation from sunlight. Therefore, the aim of this study was to investigate the synergistic effect of rutin and ascorbic acid on the proteomic profile of UVA and UVB irradiated keratinocytes cultured in a three-dimensional (3D) system. Results showed that the combination of rutin and ascorbic acid protects skin cells against UV-induced changes. In particular, alterations were observed in the expression of proteins involved in the antioxidant response, DNA repairing, inflammation, apoptosis, and protein biosynthesis. The combination of rutin and ascorbic acid also showed a stronger cytoprotective effect than when using either compound alone. Significant differences were visible between rutin and ascorbic acid single treatments in the case of protein carboxymethylation/carboxyethylation. Ascorbic acid prevented UV or rutin-induced protein modifications. Therefore, the synergistic effect of rutin and ascorbic acid creates a potentially effective protective system against skin damages caused by UVA and UVB radiation.

Treatment of Basal Cell Cancer With a Pulsed Copper Vapor Laser: A Case Series

Introduction: Basal cell carcinoma (BCC) is the most prevalent form of non-melanoma skin cancer commonly arising in elderly patients. Currently, many laser systems are applied for the treatment of BCC. However, up to the present, there have been several reports concerning ocular side effects due to the laser procedure in the borders of the periorbital area. This determines the feasibility of testing new laser surgical modes for the management of periorbital BCC. This stuay aimed to estimate both the efficacy, the early post-radiated side effects and long-term outcomes of the CVL treatment of periorbital BCC. Patients and Methods: Two men and 6 women aged 50 to 77 years were diagnosed with periorbital BCC according to the data of both the clinical evaluation and histological examination of the tissue samples taken from the involved area. Six months after the laser treatment, the histological examination of skin samples from the borderline of the irradiated area was made again. All patients were followed for 24 months after the laser treatment of BCC. The laser treatment was administered during one session of copper vapor laser (CVL) (Yakhroma-Med model). The treatment included CVL radiation with a wavelength of 511 nm and 578 nm, in the ratio of 3:2. The power level was set up to 3 W, and the exposure time was equal from 200 to 600 ms. The pulse duration accounted for 15 ns. The diameter of the light spot on the skin surface amounted to 1 mm. Results: Dual-wavelengths CVL treatment of periorbital BCC provided a complete elimination of malignant cells and dysplastic vessels during one procedure. The duration of skin healing amounted to 2-4 weeks. There were neither ocular injuries or pronounced skin side effects nor relapses within 24 months after the laser procedure. Conclusion: CVL treatment of periorbital BCC provides relevant cosmetic results without ocular injuries and relapses.

Diastereomeric Recognition of 5',8-cyclo-2'-Deoxyadenosine Lesions by Human Poly(ADP-ribose) Polymerase 1 in a Biomimetic Model

5’,8-Cyclo-2’-deoxyadenosine (cdA), in the 5’R and 5’Sdiastereomeric forms, are typical non strand-break oxidative DNA lesions, induced by hydroxyl radicals, with emerging importance as a molecular marker. These lesions are exclusively repaired by the nucleotide excision repair (NER) mechanism with a low efficiency, thus readily accumulating in the genome. Poly(ADP-ribose) polymerase1 (PARP1) acts as an early responder to DNA damage and plays a key role as a nick sensor in the maintenance of the integrity of the genome by recognizing nicked DNA. So far, it was unknown whether the two diastereomeric cdA lesions could induce specific PARP1 binding. Here, we provide the first evidence of PARP1 to selectively recognize the diastereomeric lesions of 5’S-cdA and 5’R-cdA in vitro as compared to deoxyadenosine in model DNA substrates (23-mers) by using circular dichroism, fluorescence spectroscopy, immunoblotting analysis, and gel mobility shift assay. Several features of the recognition of the damaged and undamaged oligonucleotides by PARP1 were characterized. Remarkably, PARP1 exhibits different affinities in binding to a double strand (ds) oligonucleotide, which incorporates cdA lesions in R and S diastereomeric form. In particular, PARP1 proved to bind oligonucleotides, including a 5’S-cdA, with a higher affinity constant for the 5’S lesion in a model of ds DNA than 5’R-cdA, showing different recognition patterns, also compared with undamaged dA. This new finding highlights the ability of PARP1 to recognize and differentiate the distorted DNA backbone in a biomimetic system caused by different diastereomeric forms of a cdA lesion.

PARP1 protects from benzo[a]pyrene diol epoxide-induced replication stress and mutagenicity

Poly(ADP-ribosyl)ation (PARylation) is a complex and reversible posttranslational modification catalyzed by poly(ADP-ribose)polymerases (PARPs), which orchestrates protein function and subcellular localization. The function of PARP1 in genotoxic stress response upon induction of oxidative DNA lesions and strand breaks is firmly established, but its role in the response to chemical-induced, bulky DNA adducts is understood incompletely. To address the role of PARP1 in the response to bulky DNA adducts, we treated human cancer cells with benzo[a]pyrene 7,8-dihydrodiol-9,10-epoxide (BPDE), which represents the active metabolite of the environmental carcinogen benzo[a]pyrene [B(a)P], in nanomolar to low micromolar concentrations. Using a highly sensitive LC-MS/MS method, we revealed that BPDE induces cellular PAR formation in a time- and dose-dependent manner. Consistently, PARP1 activity significantly contributed to BPDE-induced genotoxic stress response. On one hand, PARP1 ablation rescued BPDE-induced NAD⁺ depletion and protected cells from BPDE-induced short-term toxicity. On the other hand, strong sensitization effects of PARP inhibition and PARP1 ablation were observed in long-term clonogenic survival assays. Furthermore, PARP1 ablation significantly affected BPDE-induced S- and G2-phase transitions. Together, these results point towards unresolved BPDE-DNA lesions triggering replicative stress. In line with this, BPDE exposure resulted in enhanced formation and persistence of DNA double-strand breaks in PARP1-deficient cells as evaluated by microscopic co-localization studies of 53BP1 and γH2A.X foci. Consistently, an HPRT mutation assay revealed that PARP inhibition potentiated the mutagenicity of BPDE. In conclusion, this study demonstrates a profound role of PARylation in BPDE-induced genotoxic stress response with significant functional consequences and potential relevance with regard to B[a]P-induced cancer risks.

Poly(ADP-ribose) polymerase 1 escorts XPC to UV-induced DNA lesions during nucleotide excision repair

Xeroderma pigmentosum C (XPC) protein initiates the global genomic subpathway of nucleotide excision repair (GG-NER) for removal of UV-induced direct photolesions from genomic DNA. The XPC has an inherent capacity to identify and stabilize at the DNA lesion sites, and this function is facilitated in the genomic context by UV-damaged DNA-binding protein 2 (DDB2), which is part of a multiprotein UV-DDB ubiquitin ligase complex. The nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1) has been shown to facilitate the lesion recognition step of GG-NER via its interaction with DDB2 at the lesion site. Here, we show that PARP1 plays an additional DDB2-independent direct role in recruitment and stabilization of XPC at the UV-induced DNA lesions to promote GG-NER. It forms a stable complex with XPC in the nucleoplasm under steady-state conditions before irradiation and rapidly escorts it to the damaged DNA after UV irradiation in a DDB2-independent manner. The catalytic activity of PARP1 is not required for the initial complex formation with XPC in the nucleoplasm but it enhances the recruitment of XPC to the DNA lesion site after irradiation. Using purified proteins, we also show that the PARP1-XPC complex facilitates the handover of XPC to the UV-lesion site in the presence of the UV-DDB ligase complex. Thus, the lesion search function of XPC in the genomic context is controlled by XPC itself, DDB2, and PARP1. Our results reveal a paradigm that the known interaction of many proteins with PARP1 under steady-state conditions could have functional significance for these proteins.

Coordination of DNA single strand break repair

The genetic material of all organisms is susceptible to modification. In some instances, these changes are programmed, such as the formation of DNA double strand breaks during meiotic recombination to generate gamete variety or class switch recombination to create antibody diversity. However, in most cases, genomic damage is potentially harmful to the health of the organism, contributing to disease and aging by promoting deleterious cellular outcomes. A proportion of DNA modifications are caused by exogenous agents, both physical (namely ultraviolet sunlight and ionizing radiation) and chemical (such as benzopyrene, alkylating agents, platinum compounds and psoralens), which can produce numerous forms of DNA damage, including a range of "simple" and helix-distorting base lesions, abasic sites, crosslinks and various types of phosphodiester strand breaks. More significant in terms of frequency are endogenous mechanisms of modification, which include hydrolytic disintegration of DNA chemical bonds, attack by reactive oxygen species and other byproducts of normal cellular metabolism, or incomplete or necessary enzymatic reactions (such as topoisomerases or repair nucleases). Both exogenous and endogenous mechanisms are associated with a high risk of single strand breakage, either produced directly or generated as intermediates of DNA repair. This review will focus upon the creation, consequences and resolution of single strand breaks, with a particular focus on two major coordinating repair proteins: poly(ADP-ribose) polymerase 1 (PARP1) and X-ray repair cross-complementing protein 1 (XRCC1).

LncRNA-SLC6A9-5:2: A potent sensitizer in 131I-resistant papillary thyroid carcinoma with PARP-1 induction

Recent studies have indicated that long non-coding RNAs play crucial roles in numerous cancers, including thyroid cancer, while their function in the mechanism of thyroid cancer 131I resistance has not been elucidated to date. The present study identified a functional long non-coding RNA, SLC6A9-5:2, which was involved in the radioactive therapy resistance of thyroid cancer. We demonstrated that SLC6A9-5:2 was remarkably downregulated in 131I-resistant thyroid cancer cell lines and 131I-insensitive patients and was positively correlated with Poly (ADP-ribose) polymerase 1 (PARP-1) expression and its activation. After downregulating SLC6A9 or blocking PARP-1 artificially, the sensitive thyroid cancer cells mostly displayed a tolerant phenotype under 131I exposure. Furthermore, SLC6A9-5:2 overexpression was positively correlated with PARP-1 mRNA and protein levels, which restored the sensitivity of resistant thyroid cancer cells. The present study further revealed that cancer cell death was primarily caused by ATP exhaustion in excessive DNA repair with high PARP-1 activity. In patients with thyroid cancer, a positive correlation between SLC6A9-5:2 and PARP-1 was identified, and low SLC6A9-5:2 expression was associated with a worse prognosis of papillary thyroid carcinoma. Hence, our data provide a new lncRNA-mediated regulatory mechanism implying that SLC6A9-5:2 can be used as a novel therapeutic target for 131I-resistant thyroid cancer.

Radioprotective effects of ultra-small citrate-stabilized cerium oxide nanoparticles in vitro and in vivo

Different radioprotective action mechanisms of CeO₂ nanoparticles in vitro and in vivo are demonstrated and discussed.