Oncoprotein Tudor-SN is a key determinant providing survival advantage under DNA damaging stress

A novel partnership between lncTCF7 and SND1 regulates the expression of the TCF7 gene via recruitment of the SWI/SNF complex

Long non-coding RNAs (lncRNAs) play key roles in cellular pathways and disease progression, yet their molecular mechanisms remain largely understudied. The lncRNA lncTCF7 has been shown to promote tumor progression by recruiting the SWI/SNF complex to the TCF7 promoter, activating its expression and the WNT signaling pathway. However, how lncTCF7 recruits SWI/SNF remains to be determined, and lncTCF7-specific binding partners are unknown. Using RNA-pulldown and quantitative mass spectrometry, we identified a novel interacting protein partner for lncTCF7, SND1, a multifunctional RNA binding protein that can also function as a transcription co-activator. Knockdown analysis of lncTCF7 and SND1 reveals that they are both required for the expression of TCF7. Chromatin immunoprecipitation assays suggest that both SND1 and lncTCF7 are required for recruiting the SWI/SNF chromatin remodeling complex, and these functions, in tandem, activate the expression of TCF7. Finally, using structural probing and RNA-pulldown of lncTCF7 and its subdomains, we highlight the potential binding region for SND1 in the 3'-end of lncTCF7. Overall, this study highlights the critical roles lncRNAs play in regulating gene expression and provides new insights into the complex network of interactions that underlie this process.

SND1 Regulates Organic Anion Transporter 2 Protein Expression and Sensitivity of Hepatocellular Carcinoma Cells to 5-Fluorouracil

Hepatocellular carcinoma (HCC) is one of the most malignant tumors in the world. Inadequate efficacy of 5-fluorouracil (5-FU) on HCC could be related to low expression of human organic anion transporter 2 (OAT2). However, the knowledge of downregulation of OAT2 in HCC remains limited. We explored the underlying mechanism focusing on protein expression regulation and attempted to design a strategy to sensitize HCC cells to 5-FU. In this study, we revealed that the 1 bp to 300 bp region of OAT2 mRNA 3' untranslated region (UTR) reduced its protein expression and uptake activity in Li-7 and PLC/PRF/5 cells. Mechanistically, it was demonstrated that staphylococcal nuclease and Tudor domain containing 1 (SND1) bound at the 1 bp to 300 bp region of OAT2 mRNA 3' UTR, leading to a decrease in OAT2 protein expression. Enrichment analysis results indicated reduction of OAT2 might be mediated by translational inhibition. Furthermore, the knockdown of SND1 upregulated OAT2 protein expression and uptake activity. Based on this, decreasing SND1 expression enhanced 5-FU-caused G1/S phase arrest in Li-7 and PLC/PRF/5 cells, resulting in suppression of cell proliferation. Additionally, the knockdown of SND1 augmented the inhibitory effect of 5-FU on PLC/PRF/5 xenograft tumor growth in vivo by increasing OAT2 protein expression and accumulation of 5-FU in the tumor. Collectively, a combination of inhibition of SND1 with 5-FU might be a potential strategy to sensitize HCC cells to 5-FU from the perspective of restoring OAT2 protein level. SIGNIFICANCE STATEMENT: We investigated the regulatory mechanism of OAT2 protein expression in HCC cells and designed a strategy to sensitize them to 5-FU (OAT2 substrate) via restoring OAT2 protein level. It found that SND1, an RNA binding protein, regulated OAT2 protein expression by interacting with OAT2 mRNA 3' UTR 1-300 bp region. Through decreasing SND1, the antitumor effect of 5-FU on HCC was enhanced in vitro and in vivo, indicating that SND1 could be a potential target for sensitizing HCC cells to 5-FU.

SND1 Promotes Radioresistance in Cervical Cancer Cells by Targeting the DNA Damage Response

Background: Radiotherapy is one of the most effective therapeutic strategies for cervical cancer patients, although radioresistance-mediated residual and recurrent tumors are the main cause of treatment failure. However, the mechanism of tumor radioresistance is still elusive. DNA damage response pathways are key determinants of radioresistance. The purpose of this study was to investigate the role and mechanism of SND1 in radioresistance of cervical cancer. Methods: A stable HeLa cell line with SND1 knockout (HeLa-KO) was generated through a modified CRISPR/Cas9 double-nicking gene editing system. The stable CaSki cell lines with SND1 knockdown (CaSki-Ctrl, CaSki-SND1-sh-1, CaSki-SND1-sh-2) were constructed through lentivirus transfection with the pSil-SND1-sh-1 and pSil-SND1-sh-2 plasmids. Results: It was observed that SND1 deficiency significantly increased the radiosensitivity of cervical cancer cells. It was also found that silencing SND1 promotes radiation-induced apoptosis. Significantly, the cells with a loss of SND1 function exhibited inefficient ataxia telangiectasia mutated pathway activation, subsequently impairing DNA repair and G2/M checkpoint arrest. In addition, threonine 103 is an important phosphorylation site of SND1 under DNA damaging stress. Conclusion: Collectively, the results of this study reveal a potent radiosensitizing effect of silencing SND1 or T103 mutation on cervical cancer cells, providing novel insights into potential therapeutic strategies for cervical cancer treatment.

KDM6A-SND1 interaction maintains genomic stability by protecting the nascent DNA and contributes to cancer chemoresistance

Genomic instability is one of the hallmarks of cancer. While loss of histone demethylase KDM6A increases the risk of tumorigenesis, its specific role in maintaining genomic stability remains poorly understood. Here, we propose a mechanism in which KDM6A maintains genomic stability independently on its demethylase activity. This occurs through its interaction with SND1, resulting in the establishment of a protective chromatin state that prevents replication fork collapse by recruiting of RPA and Ku70 to nascent DNA strand. Notably, KDM6A-SND1 interaction is up-regulated by KDM6A SUMOylation, while KDM6AK90A mutation almost abolish the interaction. Loss of KDM6A or SND1 leads to increased enrichment of H3K9ac and H4K8ac but attenuates the enrichment of Ku70 and H3K4me3 at nascent DNA strand. This subsequently results in enhanced cellular sensitivity to genotoxins and genomic instability. Consistent with these findings, knockdown of KDM6A and SND1 in esophageal squamous cell carcinoma (ESCC) cells increases genotoxin sensitivity. Intriguingly, KDM6A H101D & P110S, N1156T and D1216N mutations identified in ESCC patients promote genotoxin resistance via increased SND1 association. Our finding provides novel insights into the pivotal role of KDM6A-SND1 in genomic stability and chemoresistance, implying that targeting KDM6A and/or its interaction with SND1 may be a promising strategy to overcome the chemoresistance.

EGC enhances tumor antigen presentation and CD8+ T cell-mediated antitumor immunity via targeting oncoprotein SND1

The Staphylococcal nuclease and Tudor domain containing 1 (SND1) has been identified as an oncoprotein. Our previous study demonstrated that SND1 impedes the major histocompatibility complex class I (MHC-I) assembly by hijacking the nascent heavy chain of MHC-I to endoplasmic reticulum-associated degradation. Herein, we aimed to identify inhibitors to block SND1-MHC-I binding, to facilitate the MHC-I presentation and tumor immunotherapy. Our findings validated the importance of the K490-containing sites in SND1-MHC-I complex. Through structure-based virtual screening and docking analysis, (-)-Epigallocatechin (EGC) exhibited the highest docking score to prevent the binding of MHC-I to SND1 by altering the spatial conformation of SND1. Additionally, EGC treatment resulted in increased expression levels of membrane-presented MHC-I in tumor cells. The C57BL/6J murine orthotopic melanoma model validated that EGC increases infiltration and activity of CD8+ T cells in both the tumor and spleen. Furthermore, the combination of EGC with programmed death-1 (PD-1) antibody demonstrated a superior antitumor effect. In summary, we identified EGC as a novel inhibitor of SND1-MHC-I interaction, prompting MHC-I presentation to improve CD8+ T cell response within the tumor microenvironment. This discovery presents a promising immunotherapeutic candidate for tumors.

Vascular injury activates the ELK1/SND1/SRF pathway to promote vascular smooth muscle cell proliferative phenotype and neointimal hyperplasia

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation is the leading cause of vascular stenosis or restenosis. Therefore, investigating the molecular mechanisms and pivotal regulators of the proliferative VSMC phenotype is imperative for precisely preventing neointimal hyperplasia in vascular disease.

METHODS

Wire-induced vascular injury and aortic culture models were used to detect the expression of staphylococcal nuclease domain-containing protein 1 (SND1). SMC-specific Snd1 knockout mice were used to assess the potential roles of SND1 after vascular injury. Primary VSMCs were cultured to evaluate SND1 function on VSMC phenotype switching, as well as to investigate the mechanism by which SND1 regulates the VSMC proliferative phenotype.

RESULTS

Phenotype-switched proliferative VSMCs exhibited higher SND1 protein expression compared to the differentiated VSMCs. This result was replicated in primary VSMCs treated with platelet-derived growth factor (PDGF). In the injury model, specific knockout of Snd1 in mouse VSMCs reduced neointimal hyperplasia. We then revealed that ETS transcription factor ELK1 (ELK1) exhibited upregulation and activation in proliferative VSMCs, and acted as a novel transcription factor to induce the gene transcriptional activation of Snd1. Subsequently, the upregulated SND1 is associated with serum response factor (SRF) by competing with myocardin (MYOCD). As a co-activator of SRF, SND1 recruited the lysine acetyltransferase 2B (KAT2B) to the promoter regions leading to the histone acetylation, consequently promoted SRF to recognize the specific CArG motif, and enhanced the proliferation- and migration-related gene transcriptional activation.

CONCLUSIONS

The present study identifies ELK1/SND1/SRF as a novel pathway in promoting the proliferative VSMC phenotype and neointimal hyperplasia in vascular injury, predisposing the vessels to pathological remodeling. This provides a potential therapeutic target for vascular stenosis.

SND1, a novel co-activator of HIF1α, promotes tumor initiation in PyMT-induced breast tumor

The multifunctional protein staphylococcal nuclease domain-containing protein 1 (SND1) is conserved and has been implicated in several aspects of tumor development, such as proliferation, epithelial-mesenchymal transition, and immune evasion. Despite this, the precise role of SND1 in the initiation and metastasis of mammary gland tumors remains largely unexplored. In this study, we utilized a mouse model of breast tumors induced by polyomavirus middle T antigen (PyMT) to demonstrate that the knockout of SND1 significantly delayed the onset of primary mammary tumor formation induced by PyMT. Histological staining and cytometric analysis were conducted to confirm the reduction of tumor-initiating cells and lung metastasis following depletion of SND1. Additionally, our findings demonstrate that enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), a crucial epigenetic modifier implicated in PyMT-induced breast tumors, serves as an essential mediator of SND1-promoted primary mammary tumor formation. Mechanistic investigations revealed that SND1 functions as a transcriptional co-activator of hypoxia-inducible factor 1 subunit alpha (HIF1α), thereby regulating the downstream target gene EZH2 and promoting tumorigenesis. Overall, this study provides novel insights into the role of SND1 as a co-activator of HIF1α in the acceleration of PyMT-induced spontaneous breast tumor formation through the promotion of EZH2 transcription. The findings provide novel insights into the relationship between SND1 and the formation of tumor-initiating cells.

ELFN1-AS1 promotes GDF15-mediated immune escape of colorectal cancer from NK cells by facilitating GCN5 and SND1 association

The ability of colorectal cancer (CRC) cells to escape from natural killer (NK) cell immune surveillance leads to anti-tumor treatment failure. The long non-coding RNA (lncRNA) ELFN1-AS1 is aberrantly expressed in multiple tumors suggesting a role as an oncogene in cancer development. However, whether ELFN1-AS1 regulates immune surveillance in CRC is unclear. Here, we determined that ELFN1-AS1 enhanced the ability of CRC cells to escape from NK cell surveillance in vitro and in vivo. In addition, we confirmed that ELFN1-AS1 in CRC cells attenuated the activity of NK cell by down-regulating NKG2D and GZMB via the GDF15/JNK pathway. Furthermore, mechanistic investigations demonstrated that ELFN1-AS1 enhanced the interaction between the GCN5 and SND1 protein and this influenced H3k9ac enrichment at the GDF15 promotor to stimulate GDF15 production in CRC cells. Taken together, our findings indicate that ELFN1-AS1 in CRC cells suppresses NK cell cytotoxicity and ELFN1-AS1 is a potential therapeutic target for CRC.

Molecular Design, Spectroscopic, DFT, Pharmacological, and Molecular Docking Studies of Novel Ruthenium(III)-Schiff Base Complex: An Inhibitor of Progression in HepG2 Cells

A novel ruthenium(III)-pyrimidine Schiff base was synthesized and characterized using different analytical and spectroscopic techniques. Molecular geometries of the ligand and ruthenium complex were investigated using the DFT-B3LYP level of theory. The quantum global reactivity descriptors were also calculated. Various biological and molecular docking studies of the complex are reported to explore its potential application as a therapeutic drug. Cytotoxicity of the complex was screened against cancer colorectal (HCT116), breast (MCF-7 and T47D), and hepatocellular (HepG2) cell lines as well as a human normal cell line (HSF). The complex effectively inhibited the tested cancer cells with variable degree with higher activity towards HepG2 (IC₅₀ values were 29 μM for HepG2, 38.5 μM for T47D, 39.7 μM for HCT, and 46.7 μM for MCF-7 cells). The complex induced apoptosis and cell cycle arrest in the S phase of HepG2 cells. The complex significantly induced the expression of H2AX and caspase 3 and caspase 7 gene and the protein level of caspase 3, as well as inhibited VEGF-A and mTOR/AKT, SND1, and NF-kB gene expression. The molecular docking studies supported the increased total apoptosis of treated HepG2 cells due to strong interaction of the complex with DNA. Additionally, the possible binding interaction of the complex with caspase 3 could be responsible for the elevated activity of caspase 3-treated cells. The score values for the two receptors were -3.25 and -3.91 kcal/mol.

SND1 confers chemoresistance to cisplatin-induced apoptosis by targeting GAS6-AKT in SKOV3 ovarian cancer cells

Platinum-based (especially cisplatin) chemotherapy is the main treatment after surgery for ovarian cancer. Although the initial treatment is effective, chemotherapy resistance develops rapidly. Therefore, chemotherapy resistance has always been a huge obstacle in the treatment of ovarian cancer. Staphylococcal nuclease domain-containing protein 1 (SND1) is an evolutionarily conserved multifunctional protein that plays a role in promoting tumorigenesis under various stress states. In this study, using MTT and SKOV3 ovarian cancer cells deficient in SND1 were observed to be more apoptotic and to express more apoptotic protein after treatment with cisplatin through the MTT, clone formation, and flow cytometry assays, while cells overexpressing SND1 exhibited a decreased number of apoptotic cells and expression of apoptotic proteins. Moreover, SND1 can regulate the expression of Growth arrest-specific 6 (GAS6) and then activate the AKT signaling pathway to achieve the regulation of sensitivity to cisplatin-induced apoptosis in ovarian cancer.

Impact of hepatocyte-specific deletion of staphylococcal nuclease and tudor domain containing 1 (SND1) on liver insulin resistance and acute liver failure of mice

Although our previous research shows an ameliorated high-fat diet (HFD)-induced hepatic steatosis and insulin resistance in global SND1 transgenic mice, the involvement of SND1 loss-of-function in hepatic metabolism remains elusive. Herein, we aim to explore the potential impact of hepatocyte-specific SND1 deletion on insulin-resistant mice. As SND1 is reported to be linked to inflammatory response, the pathobiological feature of acute liver failure (ALF) is also investigated. Hence, we construct the conditional liver knockout (LKO) mice of SND1 for the first time. Under the condition of HFD, the absence of hepatic SND1 affects the weight of white adipose tissue, but not the gross morphology, body weight, cholesterol level, liver weight, and hepatic steatosis of mice. Furthermore, we fail to observe significant differences in either HFD-induced insulin resistance or lipopolysaccharide/D-galactosamine-induced (LPS/D-GaIN) ALF between LKO and wild type (WT) mice in terms of inflammation and tissue damage. Compared with negative controls, there is no differential SND1 expression in various species of sample with insulin resistance or ALF, based on several gene expression omnibus datasets, including GSE23343, GSE160646, GSE120243, GSE48794, GSE13271, GSE151268, GSE62026, GSE120652, and GSE38941. Enrichment result of SND1-binding partners or related genes indicates a sequence of issues related to RNA or lipid metabolism, but not glucose homeostasis or hepatic failure. Overall, hepatic SND1 is insufficient to alter the phenotypes of hepatic insulin resistance and acute liver failure in mice. The SND1 in various organs is likely to cooperate in regulating glucose homeostasis by affecting the expression of lipid metabolism-related RNA transcripts during stress.

The GCN5: its biological functions and therapeutic potentials

General control non-depressible 5 (GCN5) or lysine acetyltransferase 2A (KAT2A) is one of the most highly studied histone acetyltransferases. It acts as both histone acetyltransferase (HAT) and lysine acetyltransferase (KAT). As an HAT it plays a pivotal role in the epigenetic landscape and chromatin modification. Besides, GCN5 regulates a wide range of biological events such as gene regulation, cellular proliferation, metabolism and inflammation. Imbalance in the GCN5 activity has been reported in many disorders such as cancer, metabolic disorders, autoimmune disorders and neurological disorders. Therefore, unravelling the role of GCN5 in different diseases progression is a prerequisite for both understanding and developing novel therapeutic agents of these diseases. In this review, we have discussed the structural features, the biological function of GCN5 and the mechanical link with the diseases associated with its imbalance. Moreover, the present GCN5 modulators and their limitations will be presented in a medicinal chemistry perspective.

Translation of Tudor-SN, a novel terminal oligo-pyrimidine (TOP) mRNA, is regulated by the mTORC1 pathway in cardiomyocytes

The mechanisms that regulate cell-cycle arrest of cardiomyocytes during heart development are largely unknown. We have previously identified Tudor staphylococcal nuclease (Tudor-SN) as a cell-cycle regulator and have shown that its expression level was closely related to cell-proliferation capacity. Herein, we found that Tudor-SN was highly expressed in neonatal mouse myocardia, but it was lowly expressed in that of adults. Using Data Base of Transcription Start Sites (DBTSS), we revealed that Tudor-SN was a terminal oligo-pyrimidine (TOP) mRNA. We further confirmed that the translational efficiency of Tudor-SN mRNA was controlled by the mammalian target of rapamycin complex 1 (mTORC1) pathway, as revealed via inhibition of activated mTORC1 in primary neonatal mouse cardiomyocytes and activation of silenced mTORC1 in adult mouse myocardia; additionally, this result was recapitulated in H9c2 cells. We also demonstrated that the downregulation of Tudor-SN in adult myocardia was due to inactivation of the mTORC1 pathway to ensure that heart growth was in proportion to that of the rest of the body. Moreover, we revealed that Tudor-SN participated in the mTORC1-mediated regulation of cardiomyocytic proliferation, which further elucidated the correlation between Tudor-SN and the mTORC1 pathway. Taken together, our findings suggest that the translational efficiency of Tudor-SN is regulated by the mTORC1 pathway in myocardia and that Tudor-SN is involved in mTORC1-mediated regulation of cardiomyocytic proliferation and cardiac development.

Phospho-Tudor-SN coordinates with STAT5 to regulate prolactin-stimulated milk protein synthesis and proliferation of bovine mammary epithelial cells

Tudor staphylococcal nuclease (Tudor-SN) participates in milk synthesis and cell proliferation in response to prolactin (PRL) and plays a regulatory role on mTOR phosphorylation. However, the complicated molecular mechanism of Tudor-SN regulating milk protein synthesis and cell proliferation still remains to be illustrated. In present study, we observed that the proteins level of phosphorylated Tudor-SN and phosphorylated STAT5 were simultaneously enhanced upon PRL treatment in bovine mammary epithelial cells (BMECs). Tudor-SN overexpression and knockdown experiment showed that Tudor-SN positively regulated the synthesis of milk protein, cell proliferation and the phosphorylation of STAT5, which was dependent on Tudor-SN phosphorylation. STAT5 knockdown experiment showed that Tudor-SN stimulated mTOR pathway through regulating STAT5 activation, which was required for PRL to activate the mTOR pathway. Thus, these results demonstrate the primary mechanism of Tudor-SN coordinating with STAT5 to regulate milk protein synthesis and cell proliferation under stimulation of PRL in BMECs, which may provide some new perspectives for increasing milk production.

SND1 promotes Th1/17 immunity against chlamydial lung infection through enhancing dendritic cell function

To date, no reports have linked the multifunctional protein, staphylococcal nuclease domain-containing protein 1 (SND1), to host defense against intracellular infections. In this study, we investigated the role and mechanisms of SND1, by using SND1 knockout (SND1-/-) mice, in host defense against the lung infection of Chlamydia muridarum, an obligate intracellular bacterium. Our data showed that SND1-/- mice exhibited significantly greater body weight loss, higher organism growth, and more severe pathological changes compared with wild-type mice following the infection. Further analysis showed significantly reduced Chlamydia-specific Th1/17 immune responses in SND1-/- mice after infection. Interestingly, the dendritic cells (DCs) isolated from SND1-/- mice showed lower costimulatory molecules expression and IL-12 production, but higher IL-10 production compared with those from wild-type control mice. In the DC-T cell co-culture system, DCs isolated from SND1-/- infected mice showed significantly reduced ability to promote Chlamydia-specific IFN-γ producing Th1 cells but enhanced capacity to induce CD4+T cells into Foxp3+ Treg cells. Adoptive transfer of DCs isolated from SND1-/- mice, unlike those from wild-type control mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that SND1 plays an important role in host defense against intracellular bacterial infection, and suggest that SND1 can promote Th1/17 immunity and inhibit the expansion of Treg cells through modulation of the function of DCs.

The interactome of the prostate-specific protein Anoctamin 7

BACKGROUND

Elevated Anoctamin 7 (ANO7) expression is associated with poor survival in prostate cancer patients.

OBJECTIVE

The aim was to discover proteins that interact with ANO7 to understand its functions and regulatory mechanisms.

METHODS

The proximity-dependent biotin identification (BioID) method was utilized. ANO7 fused to biotin ligase was transiently transfected into LNCaP cells, and the biotinylated proteins were collected and analysed by mass spectrometry. Four identified proteins were stained with dual fluorescent immunostaining and visualized using Stimulated emission depletion microscopy (STED).

RESULTS

After bioinformatic filtering steps, 64 potentially ANO7-interacting proteins were identified and analysed with the GO enrichment analysis tool. One of the most prominently enriched cellular components was cellular vesicle. Co-localization was showed for staphylococcal nuclease and tudor domain containing 1 (SND1), heat shock protein family A (Hsp70) member 1A (HSPA1A), adaptor related protein complex 2 subunit beta 1 (AP2B1) and coatomer protein complex subunit gamma 2 (COPG2).

CONCLUSIONS

This is the first study in which ANO7 interacting proteins have been identified. Although further studies are needed, the findings reported here expand our understanding of the role and regulation of ANO7 in prostate cancer cells. Furthermore, these results are likely to introduce new targets for the novel cancer therapies.

The Role of the PRMT5-SND1 Axis in Hepatocellular Carcinoma

Arginine methylation is an essential post-translational modification (PTM) deposited by protein arginine methyltransferases (PRMTs) and recognized by Tudor domain-containing proteins. Of the nine mammalian PRMTs, PRMT5 is the primary enzyme responsible for the deposition of symmetric arginine methylation marks in cells. The staphylococcal nuclease and Tudor domain-containing 1 (SND1) effector protein is a key reader of the marks deposited by PRMT5. Both PRMT5 and SND1 are broadly expressed and their deregulation is reported to be associated with a range of disease phenotypes, including cancer. Hepatocellular carcinoma (HCC) is an example of a cancer type that often displays elevated PRMT5 and SND1 levels, and there is evidence that hyperactivation of this axis is oncogenic. Importantly, this pathway can be tempered with small-molecule inhibitors that target PRMT5, offering a therapeutic node for cancer, such as HCC, that display high PRMT5–SND1 axis activity. Here we summarize the known activities of this writer–reader pair, with a focus on their biological roles in HCC. This will help establish a foundation for treating HCC with PRMT5 inhibitors and also identify potential biomarkers that could predict sensitivity to this type of therapy.

Circ SMARCA5 Inhibited Tumor Metastasis by Interacting with SND1 and Downregulating the YWHAB Gene in Cervical Cancer

Cervical cancer is one of the diseases that seriously endanger women's health. Circular RNA plays an important role in regulating the occurrence and development of cervical cancer. Here, we investigated the mechanisms of circ SMARCA5 in the development of cervical cancer. Quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) results showed that the expression of SMARCA5 was downregulated in cervical cancer tissues and cell lines. Then we found that overexpression of SMARCA5 inhibited proliferation and invasion, but promoted apoptosis in cervical cancer cells. These were detected by Cell Counting Kit-8, Transwell, and Annexin V-fluorescein isothiocyanate/propidium iodide detection kit, respectively, and the expression of the apoptosis-related proteins was determined by western blotting. Then we predicted that SMARCA5 combined with Staphylococcal nuclease domain-containing 1 (SND1) by starBase, and verified by RNA pull-down assay. To further reveal the molecular mechanisms of SMARCA5 in the progression of cervical cancer, the interaction protein of SND1 was predicted by STRING, and the interaction was verified by co-immunoprecipitation assay. Then, the effects of SND1 or YWHAB on the development of cervical cancer were detected by the gain and loss function test, and we found that knockdown of SND1 or YWHAB reversed the effects of SMARCA5 short interfering RNA on proliferation, invasion, and apoptosis of cervical cancer cells. Overexpression of SMARCA5 inhibited cervical cancer metastasis in vivo. Our results showed that overexpression of circ SMARCA5 inhibits the binding of SND1 to YWHAB, and inhibits the proliferation and invasion, but promotes apoptosis in cervical cancer cells, thus inhibiting the metastasis of cervical cancer.

The E2F1 transcription factor and RB tumor suppressor moonlight as DNA repair factors

The E2F1 transcription factor and RB tumor suppressor are best known for their roles in regulating the expression of genes important for cell cycle progression but, they also have transcription-independent functions that facilitate DNA repair at sites of damage. Depending on the type of DNA damage, E2F1 can recruit either the GCN5 or p300/CBP histone acetyltransferases to deposit different histone acetylation marks in flanking chromatin. At DNA double-strand breaks, E2F1 also recruits RB and the BRG1 ATPase to remodel chromatin and promote loading of the MRE11-RAD50-NBS1 complex. Knock-in mouse models demonstrate important roles for E2F1 post-translational modifications in regulating DNA repair and physiological responses to DNA damage. This review highlights how E2F1 moonlights in DNA repair, thus revealing E2F1 as a versatile protein that recruits many of the same chromatin-modifying enzymes to sites of DNA damage to promote repair that it recruits to gene promoters to regulate transcription.

The novel chromatin architectural regulator SND1 promotes glioma proliferation and invasion and predicts the prognosis of patients

BACKGROUND

Upregulation of staphylococcal nuclease domain-containing protein 1 (SND1) is a common phenomenon in different human malignant tissues. However, little information is available on the underlying mechanisms through which SND1 affects glioma cell proliferation and invasion.

METHODS

SND1, Ras homolog family member A (RhoA), and marker of proliferation Ki-67 (MKI67) were analyzed in 187 gliomas by immunostaining. The correlation between those markers and patients' prognoses was assessed using the Kaplan-Meier estimator. Gene Ontology, chromatin immunoprecipitation, electrophoretic mobility shift assay, and chromosome conformation capture were applied to identify SND1-activated target genes. We also used MTT, colony formation, transwell and orthotopic implantation assays to investigate SND1 function in glioma cell proliferative and invasive activity.

RESULTS

We identified SND1 and RhoA as independent predictors of poor prognosis in glioma patients. SND1 knockdown significantly suppressed the proliferation and invasion of glioma cells. Mechanistically, we discovered that SND1 facilitated malignant glioma phenotypes by epigenetically inducing chromatin topological interaction, which activated downstream RhoA transcription. RhoA sequentially regulated expression of CCND1, CCNE1, CDK4, and CDKN1B and accelerated G1/S phase transition in glioma cell proliferation.

CONCLUSIONS

Our findings identify SND1 as a novel chromatin architectural modifier and promising prognostic indicator for glioma classification and treatment.

Protective effects of SND1 in retinal photoreceptor cell damage induced by ionizing radiation

Staphylococcal nuclease and tudor domain containing 1 (SND1) has multiple functions in a variety of cellular processes. Here, we assessed the effects of SND1 in cellular DNA damage after ionizing radiation (IR). Knocking down SND1 in the mouse-derived photoreceptor 661 W cell line markedly inhibited cell proliferation and increased apoptosis after IR treatment. After DNA damage, SND1 induced Ataxia telangiectasia mutated kinase (ATM) signaling to launch DNA repair. Defects of SND1 were associated with missing response to DNA damage signal to cell cycle checkpoints or DNA repair. The current findings reveal SND1 as a new regulatory factor in DNA damage response.

Insights Into SND1 Oncogene Promoter Regulation

The staphylococcal nuclease and Tudor domain containing 1 gene (SND1), also known as Tudor-SN, TSN or p100, encodes an evolutionarily conserved protein with invariant domain composition. SND1 contains four repeated staphylococcal nuclease domains and a single Tudor domain, which confer it endonuclease activity and extraordinary capacity for interacting with nucleic acids, individual proteins and protein complexes. Originally described as a transcriptional coactivator, SND1 plays fundamental roles in the regulation of gene expression, including RNA splicing, interference, stability, and editing, as well as in the regulation of protein and lipid homeostasis. Recently, SND1 has gained attention as a potential disease biomarker due to its positive correlation with cancer progression and metastatic spread. Such functional diversity of SND1 marks this gene as interesting for further analysis in relation with the multiple levels of regulation of SND1 protein production. In this review, we summarize the SND1 genomic region and promoter architecture, the set of transcription factors that can bind the proximal promoter, and the evidence supporting transactivation of SND1 promoter by a number of signal transduction pathways operating in different cell types and conditions. Unraveling the mechanisms responsible for SND1 promoter regulation is of utmost interest to decipher the SND1 contribution in the realm of both normal and abnormal physiology.

Global Tudor-SN transgenic mice are protected from obesity-induced hepatic steatosis and insulin resistance

In the current study, we explored the impact of Tudor-staphylococcal nuclease (SN) on obesity induced by a high-fat diet (HFD) in mice, because the functional involvement of Tudor-SN in lipid metabolism in vivo is unknown. HFD-transgenic (Tg) mice exhibited reductions in hepatic steatosis and systemic insulin resistance. There was no difference in hepatic lipid accumulation between chow-fed wild-type (WT) and chow-fed Tg mice; consistently, no difference in activation of the lipogenic pathway was detected. Overactivation of hepatic nuclear sterol regulatory element-binding protein (nSrebp2)-2, the central regulator of cholesterol metabolic proteins, was observed in HFD-Tg livers along with improved cholesterol homeostasis, but no such changes were observed in HFD-WT livers. Consistent results were observed in vitro in α-mouse liver 12 cells treated with palmitate mimicking the HFD state. In addition, global gene analysis indicated that various downstream targets of nSrebp2, were up-regulated in HFD-Tg livers. Moreover, HFD-WT mice displayed islet hypertrophy and suppression of glucose-induced insulin secretion from islets, whereas HFD-Tg mice had normal pancreatic islets. This finding suggests that the improved pancreatic metabolism of HFD-Tg mice is related to the systemic effect of insulin resistance, not to the autonomous influence of pancreatic cells. Tudor-SN is likely to be a key regulator for ameliorating HFD-induced hepatic steatosis and systemic insulin resistance in vivo.-Wang, X., Xin, L., Duan, Z., Zuo, Z., Wang, Y., Ren, Y., Zhang, W., Sun, X., Liu, X., Ge, L., Yang, X., Yao, Z., Yang, J. Global Tudor-SN transgenic mice are protected from obesity-induced hepatic steatosis and insulin resistance.

SND1 acts as an anti-apoptotic factor via regulating the expression of lncRNA UCA1 in hepatocellular carcinoma

Multifunctional SND1 (staphylococcal nuclease and tudor domain containing 1) protein is reportedly associated with different types of RNA molecules, including mRNA, miRNA, pre-miRNA, and dsRNA. SND1 has been implicated in a number of biological processes in eukaryotic cells, including cell cycle, DNA damage repair, proliferation, and apoptosis. However, the specific molecular mechanism regarding the anti-apoptotic role of SND1 in mammalian cells remains largely elusive. In this study, the analysis of the online HPA (human protein atlas) and TCGA (the cancer genome atlas) databases showed the significantly high expression of SND1 in liver cancer patients. We found that the downregulation or complete depletion of SND1 enhanced the apoptosis levels of HepG2 and SMMC-7721 cells upon stimulation with 5-Fu (5-fluorouracil), a chemotherapeutic drug for HCC (hepatocellular carcinoma). SND1 affected the 5-Fu-induced apoptosis levels of HCC cells by modulating the expression of UCA1 (urothelial cancer associated 1), which is a lncRNA (long non-coding RNA). Moreover, MYB (MYB proto-oncogene, transcription factor) may be involved in the regulation of SND1 in UCA1 expression. In summary, our study identified SND1 as an anti-apoptotic factor in hepatocellular carcinoma cells via the modulation of lncRNA UCA1, which sheds new light on the relationship between SND1 protein and lncRNA.

The multifaceted oncogene SND1 in cancer: focus on hepatocellular carcinoma

Staphylococcal nuclease and tudor domain containing 1 (SND1) is a protein that regulates a complex array of functions. It controls gene expression through transcriptional activation, mRNA degradation, mRNA stabilization, ubiquitination and alternative splicing. More than two decades of research has accumulated evidence of the role of SND1 as an oncogene in various cancers. It is a promoter of cancer hallmarks like proliferation, invasion, migration, angiogenesis and metastasis. In addition to these functions, it has a role in lipid metabolism, inflammation and stress response. The participation of SND1 in such varied functions makes it distinct from most oncogenes that are relatively more focused in their role. This becomes important in the case of hepatocellular carcinoma (HCC) since in addition to typical cancer drivers, factors like lipid metabolism deregulation and chronic inflammation can predispose hepatocytes to HCC. The objective of this review is to provide a summary of the current knowledge available on SND1, specifically in relation to HCC and to shed light on its prospect as a therapeutic target.