Regulation of Mammalian DNA Replication via the Ubiquitin-Proteasome System

Identifying key inflammatory genes in psoriasis via weighted gene co-expression network analysis: Potential targets for therapy

Psoriasis is a globally prevalent chronic inflammatory skin disease. This study aimed to scrutinize the hub genes related to inflammation and potential molecular mechanisms in psoriasis. Utilizing mRNA expression profiles from public datasets GSE13355, GSE78097, and GSE14905, we set up a comprehensive analysis. Initially, we selected differentially expressed genes (DEGs) from psoriasis and control samples in GSE13355, followed by calculating inflammatory indices using genomic set variation analysis (GSVA). Weighted gene co-expression network analysis (WGCNA) was then applied to link significant modules with the inflammatory index. This process helped us identify differentially expressed inflammation-related genes (DE-IRGs). A protein-protein interaction (PPI) network was established, with the molecular complex detection (MCODE) plug-in pinpointing six chemokine genes (CCR7, CCL2, CCL19, CXCL8, CXCL1, and CXCL2) as central hub genes. These genes demonstrated pronounced immunohistochemical staining in psoriatic tissues compared to normal skin. Notably, the CCR7 gene exhibited the highest potential for m6A modification sites. Furthermore, we constructed transcription factor-microRNA-mRNA networks, identifying 139 microRNAs and 52 transcription factors associated with the hub genes. For the LASSO logistic regression model, the area under the curve (AUC) in the training set was 1, and in the two validation cohorts GSE78097 and GSE14905 were 1 and 0.872, respectively. In conclusion, our study highlights six chemokine genes (CCR7, CCL2, CCL19, CXCL8, CXCL1, and CXCL2) as potential biomarkers in psoriasis, providing insights into the immune and inflammatory responses as pivotal instances in disease pathogenesis. These findings pave the way for exploring new therapeutic targets, particularly focusing on chemokine-associated pathways in psoriasis treatment.

Plasmodium falciparum contains functional SCF and CRL4 ubiquitin E3 ligases, and CRL4 is critical for cell division and membrane integrity

Protein ubiquitination is essential for cellular homeostasis and regulation of several processes, including cell division and genome integrity. Ubiquitin E3 ligases determine substrate specificity for ubiquitination, and Cullin-RING E3 ubiquitin ligases (CRLs) make the largest group among the ubiquitin E3 ligases. Although conserved and most studied in model eukaryotes, CRLs remain underappreciated in Plasmodium and related parasites. To investigate the CRLs of human malaria parasite Plasmodium falciparum, we generated parasites expressing tagged P. falciparum cullin-1 (PfCullin-1), cullin-2 (PfCullin-2), Rbx1 (PfRbx1) and Skp1 (PfSkp1). PfCullin-1 and PfCullin-2 were predominantly expressed in erythrocytic trophozoite and schizont stages, with nucleocytoplasmic localization and chromatin association, suggesting their roles in different cellular compartments and DNA-associated processes. Immunoprecipitation, in vitro protein-protein interaction, and ubiquitination assay confirmed the presence of a functional Skp1-Cullin-1-Fbox (PfSCF) complex, comprising of PfCullin-1, PfRbx1, PfSkp1, PfFBXO1, and calcyclin binding protein. Immunoprecipitation, sequence analysis, and ubiquitination assay indicated that PfCullin-2 forms a functional human CRL4-like complex (PfCRL4), consisting of PfRbx1, cleavage and polyadenylation specificity factor subunit_A and WD40 repeat proteins. PfCullin-2 knock-down at the protein level, which would hinder PfCRL4 assembly, significantly decreased asexual and sexual erythrocytic stage development. The protein levels of several pathways, including protein translation and folding, lipid biosynthesis and transport, DNA replication, and protein degradation were significantly altered upon PfCullin-2 depletion, which likely reflects association of PfCRL4 with multiple pathways. PfCullin-2-depleted schizonts had poorly delimited merozoites and internal membraned structures, suggesting a role of PfCRL4 in maintaining membrane integrity. PfCullin-2-depleted parasites had a significantly lower number of nuclei/parasite than the normal parasites, indicating a crucial role of PfCRL4 in cell division. We demonstrate the presence of functional CRLs in P. falciparum, with crucial roles for PfCRL4 in cell division and maintaining membrane integrity.

Estrogen Receptor Signaling in Breast Cancer

Estrogen receptor (ER) signaling is a critical regulator of cell proliferation, differentiation, and survival in breast cancer (BC) and other hormone-sensitive cancers. In this review, we explore the mechanism of ER-dependent downstream signaling in BC and the role of estrogens as growth factors necessary for cancer invasion and dissemination. The significance of the clinical implications of ER signaling in BC, including the potential of endocrine therapies that target estrogens' synthesis and ER-dependent signal transmission, such as aromatase inhibitors or selective estrogen receptor modulators, is discussed. As a consequence, the challenges associated with the resistance to these therapies resulting from acquired ER mutations and potential strategies to overcome them are the critical point for the new treatment strategies' development.

UBQLN1 deficiency mediates telomere shortening and IPF through interacting with RPA1

Premature telomere shortening is a known factor correlated to idiopathic pulmonary fibrosis (IPF) occurrence, which is a chronic, progressive, age-related disease with high mortality. The etiology of IPF is still unknown. Here, we found that UBQLN1 plays a key role in telomere length maintenance and is potentially relevant to IPF. UBQLN1 involves in DNA replication by interacting with RPA1 and shuttling it off from the replication fork. The deficiency of UBQLN1 retains RPA1 at replication fork, hinders replication and thus causes cell cycle arrest and genome instability. Especially at telomere regions of the genome, where more endogenous replication stress exists because of G rich sequences, UBQLN1 depletion leads to rapid telomere shortening in HeLa cells. It revealed that UBQLN1 depletion also shortens telomere length at mouse lung and accelerates mouse lung fibrosis. In addition, the UBQLN1 expression level in IPF patients is downregulated and correlated to poor prognosis. Altogether, these results uncover a new role of UBQLN1 in ensuring DNA replication and maintaining telomere stability, which may shed light on IPF pathogenesis and prevention.

Contribution of Microhomology to Genome Instability: Connection between DNA Repair and Replication Stress

Microhomology-mediated end joining (MMEJ) is a highly mutagenic pathway to repair double-strand breaks (DSBs). MMEJ was thought to be a backup pathway of homologous recombination (HR) and canonical nonhomologous end joining (C-NHEJ). However, it attracts more attention in cancer research due to its special function of microhomology in many different aspects of cancer. In particular, it is initiated with DNA end resection and upregulated in homologous recombination-deficient cancers. In this review, I summarize the following: (1) the recent findings and contributions of MMEJ to genome instability, including phenotypes relevant to MMEJ; (2) the interaction between MMEJ and other DNA repair pathways; (3) the proposed mechanistic model of MMEJ in DNA DSB repair and a new connection with microhomology-mediated break-induced replication (MMBIR); and (4) the potential clinical application by targeting MMEJ based on synthetic lethality for cancer therapy.

Crypt and Villus Transcriptomic Responses in Mouse Small Intestine Following Oral Exposure to Hexavalent Chromium

Oral exposure to hexavalent chromium (Cr(VI)) induces tumors in the mouse duodenum. Previous microarray-based transcriptomic analyses of homogenized mouse duodenal tissue have demonstrated Cr(VI)-induced alterations in various cellular pathways and processes. However, X-ray fluorescence microscopy indicates that chromium localizes primarily to the duodenal villi following exposure to Cr(VI), suggesting that previous transcriptomic analyses of homogenized tissue provide an incomplete picture of transcriptomic responses in the duodenum. Herein, transcriptomic analyses were conducted separately on crypt and villus tissue from formalin-fixed paraffin-embedded transverse duodenal sections from the same study in which microarray-based analyses were previously conducted. A total of 28 groups (7 doses × 2 timepoints × 2 tissue compartments) were analyzed for differential gene expression, dose-response, and gene set enrichment. Tissue compartment isolation was confirmed by differences in expression of typical markers of crypt and villus compartments. Fewer than 21 genes were altered in the crypt compartment of mice exposed to 0.1-5 ppm Cr(VI) for 7 or 90 days, which increased to hundreds or thousands of genes at ≥20 ppm Cr(VI). Consistent with histological evidence for crypt proliferation, a significant, dose-dependent increase in genes that regulate mitotic cell cycle was prominent in the crypt, while subtle in the villus, when compared with samples from time-matched controls. Minimal transcriptomic evidence of DNA damage response in either the crypts or the villi is consistent with published in vivo genotoxicity data. These results are also discussed in the context of modes of action that have been proposed for Cr(VI)-induced small intestine tumors in mice.

USP7 and VCPFAF1 define the SUMO/Ubiquitin landscape at the DNA replication fork

The AAA⁺ ATPase VCP regulates the extraction of SUMO and ubiquitin-modified DNA replication factors from chromatin. We have previously described that active DNA synthesis is associated with a SUMO-high/ubiquitin-low environment governed by the deubiquitylase USP7. Here, we unveil a functional cooperation between USP7 and VCP in DNA replication, which is conserved from Caenorhabditis elegans to mammals. The role of VCP in chromatin is defined by its cofactor FAF1, which facilitates the extraction of SUMOylated and ubiquitylated proteins that accumulate after the block of DNA replication in the absence of USP7. The inactivation of USP7 and FAF1 is synthetically lethal both in C. elegans and mammalian cells. In addition, USP7 and VCP inhibitors display synergistic toxicity supporting a functional link between deubiquitylation and extraction of chromatin-bound proteins. Our results suggest that USP7 and VCP^FAF1 facilitate DNA replication by controlling the balance of SUMO/Ubiquitin-modified DNA replication factors on chromatin.

Dynamics of replication origin over-activation

Safeguards against excess DNA replication are often dysregulated in cancer, and driving cancer cells towards over-replication is a promising therapeutic strategy. We determined DNA synthesis patterns in cancer cells undergoing partial genome re-replication due to perturbed regulatory interactions (re-replicating cells). These cells exhibited slow replication, increased frequency of replication initiation events, and a skewed initiation pattern that preferentially reactivated early-replicating origins. Unlike in cells exposed to replication stress, which activated a novel group of hitherto unutilized (dormant) replication origins, the preferred re-replicating origins arose from the same pool of potential origins as those activated during normal growth. Mechanistically, the skewed initiation pattern reflected a disproportionate distribution of pre-replication complexes on distinct regions of licensed chromatin prior to replication. This distinct pattern suggests that circumventing the strong inhibitory interactions that normally prevent excess DNA synthesis can occur via at least two pathways, each activating a distinct set of replication origins.

Switching DCAFs: Beyond substrate receptors

Deciphering how DCAFs (DDB1-CUL4 Associated Factors) modulate a broad spectrum of cellular processes, including cell cycle progression and maintenance of genomic integrity is critical to better understand cellular homeostasis and diseases. Cells contain more than 100 DCAFs that associate with the Cullin-Ring Ubiquitin Ligase 4 (CRL4) complex that target specific protein substrates for degradation. DCAFs are thought to act as substrate receptors that dictate the specificity of the ubiquitination machinery ("catalytic DCAFs"). However, recent studies have suggested that some DCAFs might play a different role by targeting CRL4 complexes to distinct cellular compartments ("structural DCAFs"). Once localized to their correct cellular domains, these CRLs dissociate from the structural DCAFs prior to their association with other, substrate-specific catalytic DCAFs. Thus, we propose that DCAF switches can provide a mechanistic basis for the degradation of proteins that regulate cell growth and proliferation at precise points in space and time.

SCF FBXW17 E3 ubiquitin ligase regulates FBXL19 stability and cell migration

The Skp1-Cul1-F-box protein (SCF) E3 ligase complex is one of the largest ubiquitin E3 ligase families. FBXL19, a F-box protein in SCF^FBXL19 E3 ligase complex, regulates a variety of cellular responses including cell migration. We have shown that FBXL19 is not stable and its degradation is mediated by the ubiquitin-proteasome system, while the ubiquitin E3 ligase for FBXL19 ubiquitination and degradation has not been identified. In the study, we discovered that a new ubiquitin E3 ligase, SCF^FBXW17 , ubiquitinates and induces FBXL19 degradation. Exogenous FBXW17 targets FBXL19 for its ubiquitination and degradation. Lysine 114 in FBXL19 is a potential ubiquitin acceptor site. Acetylation of FBXL19 attenuated SCF^FBXW17 -mediated FBXL19 degradation. SCF^FBXL19 E3 ligase reduced Rac1 levels and cell migration, while the effects were attenuated by exogenous FBXW17. Downregulation of FBXW17 attenuated lysophosphatidic acid-induced lamellipodia formation and Rac1 accumulation at migration leading edge. Taken together with our previous studies, FBXL19 is degraded by the ubiquitin-proteasome system and its site-specific ubiquitination is mediated by SCF^FBXW17 E3 ligase, which promotes cell migration.

Skp2 regulates DNA damage repair and apoptosis via interaction with Ku70

PURPOSE

Skp2, an oncoprotein, regulates tumor proliferation, invasion and metastasis. Ku70 is a critical component of the non-homologous end-joining (NHEJ) process. Both Skp2 and Ku70 are positively associated in multiple cancers. However, there is no report about the relationship between Skp2 and Ku70 proteins.

METHODS

In this study, we carried out Bioinformatics and molecular biological methods to investigate the relationship between Skp2 and Ku70 proteins.

RESULTS

We first observed Skp2 and Ku70 mRNAs were significantly increased in cervical cancer tissues. And we identified Ku70 as a Skp2-binding protein and the binding site located in the C-terminal of Ku70 protein. We further found that Skp2 knockdown decreased the Ku70 protein level in cells, and increase the cellular apoptosis and DNA damage, suggesting Skp2 mediates the Ku70 protein stability and function via post-translational modification.

CONCLUSION

The direct interaction between Skp2 and Ku70 proteins mediates the DNA damage repair and cellular apoptosis by regulating Ku70 stability and function via post-translational modification. The molecular mechanisms how Skp2 stabilize Ku70 would be clarified in our following research work.

TRIM2 directly deubiquitinates and stabilizes Snail1 protein, mediating proliferation and metastasis of lung adenocarcinoma

Background

Lung adenocarcinoma has surpassed lung squamous cell carcinoma as the most common type of non-small cell lung cancer. In this study, we had tested the biological role of TRIM2 in lung adenocarcinoma.

Methods

TRIM2 abundance in clinical tissues and six cell lines were examined with quantitative real-time PCR test (qRT-PCR) and western blot. TRIM2 overexpression treated H322 cells and TRIM2 knockdown treated A549 cells were used to study cell proliferation, migration, colony formation, invasion, and the expression of epithelial mesenchymal transformation (EMT) biomarkers. Moreover, ubiquitination related Snail1 degradation were studied with qRT-PCR and western blot. The relationships between TRIM2 and Snail1 were investigated with western blot, co-immunoprecipitation, migration, and invasion.

Results

TRIM2 was highly expressed in lung adenocarcinoma tissues. TRIM2 overexpression and knockdown treatments could affect cell proliferation, colony formation, migration, invasion, and the expression of EMT associated biomarkers. Moreover, TRIM2 can regulate the ubiquitination related Snail1 degradation. In addition, TRIM2 can regulate Snail1 degradation in lung adenocarcinoma via ubiquitination pathway. TRIM2 could promote the proliferation, migration, and invasion of lung adenocarcinoma. Meanwhile, TRIM2 can deubiquitinate and stabilize Snail1 protein, which play important role in the function of lung adenocarcinoma.

Conclusion

A high TRIM2 expression could be detected in lung adenocarcinoma tissues and cells. TRIM2 could aggravate cell proliferation, invasion, and migration in colorectal cancer by regulating Snail1 ubiquitylation degradation. Our results could provide detailed information for further studies in lung adenocarcinoma.

The RepID-CRL4 ubiquitin ligase complex regulates metaphase to anaphase transition via BUB3 degradation

The spindle assembly checkpoint (SAC) prevents premature chromosome segregation by inactivating the anaphase promoting complex/cyclosome (APC/C) until all chromosomes are properly attached to mitotic spindles. Here we identify a role for Cullin–RING ubiquitin ligase complex 4 (CRL4), known for modulating DNA replication, as a crucial mitotic regulator that triggers the termination of the SAC and enables chromosome segregation. CRL4 is recruited to chromatin by the replication origin binding protein RepID/DCAF14/PHIP. During mitosis, CRL4 dissociates from RepID and replaces it with RB Binding Protein 7 (RBBP7), which ubiquitinates the SAC mediator BUB3 to enable mitotic exit. During interphase, BUB3 is protected from CRL4-mediated degradation by associating with promyelocytic leukemia (PML) nuclear bodies, ensuring its availability upon mitotic onset. Deficiencies in RepID, CRL4 or RBBP7 delay mitotic exit, increase genomic instability and enhance sensitivity to paclitaxel, a microtubule stabilizer and anti-tumor drug.

The spindle assembly checkpoint (SAC) safeguards chromosome segregation by regulating the anaphase promoting complex/cyclosome (APC/C), allowing chromosomes to correctly attach to mitotic spindles. Here the authors reveal a role for Cullin–RING ubiquitin ligase complex 4 (CRL4) in regulating metaphase to anaphase transition via BUB3 degradation.

The Identification of Potential Therapeutic Targets for Cutaneous Squamous Cell Carcinoma

We performed a small interfering RNA screen to identify targets for cutaneous squamous cell carcinoma (cSCC) therapy in the ubiquitin/ubiquitin-like system. We provide evidence for selective anti-cSCC activity of knockdown of the E3 ubiquitin ligase MARCH4, the ATPase p97/VCP, the deubiquitinating enzyme USP8, the cullin-RING ligase (CRL) 4 substrate receptor CDT2/DTL, and components of the anaphase-promoting complex/cyclosome (APC/C). Specifically attenuating CRL4^CDT2 by CDT2 knockdown can be more potent in killing cSCC cells than targeting CRLs or CRL4s in general by RBX1 or DDB1 depletion. Suppression of the APC/C or forced APC/C activation by targeting its repressor EMI1 are both potential therapeutic approaches. We observed that cSCC cells can be selectively killed by small-molecule inhibitors of USP8 (DUBs-IN-3/compound 22c) and the NEDD8 E1 activating enzyme/CRLs (MLN4924/pevonedistat). A substantial proportion of cSCC cell lines are very highly MLN4924-sensitive. Pathways that respond to defects in proteostasis are involved in the anti-cSCC activity of p97 suppression. Targeting USP8 can reduce the expression of growth factor receptors that participate in cSCC development. EMI1 and CDT2 depletion can selectively cause DNA re-replication and DNA damage in cSCC cells.

Stilbene Compounds Inhibit Tumor Growth by the Induction of Cellular Senescence and the Inhibition of Telomerase Activity

Cellular senescence is a state of cell cycle arrest characterized by a distinct morphology, gene expression pattern, and secretory phenotype. It can be triggered by multiple mechanisms, including those involved in telomere shortening, the accumulation of DNA damage, epigenetic pathways, and the senescence-associated secretory phenotype (SASP), and so on. In current cancer therapy, cellular senescence has emerged as a potent tumor suppression mechanism that restrains proliferation in cells at risk for malignant transformation. Therefore, compounds that stimulate the growth inhibition effects of senescence while limiting its detrimental effects are believed to have great clinical potential. In this review article, we first review the current knowledge of the pro- and antitumorigeneic functions of senescence and summarize the key roles of telomerase in the regulation of senescence in tumors. Second, we review the current literature regarding the anticancer effects of stilbene compounds that are mediated by the targeting of telomerase and cell senescence. Finally, we provide future perspectives on the clinical utilization of stilbene compounds, especially resveratrol and pterostilbene, as novel cancer therapeutic remedies. We conclude and propose that stilbene compounds may induce senescence and may potentially be used as the therapeutic or adjuvant agents for cancers with high telomerase activity.

Chromatin-Bound Cullin-Ring Ligases: Regulatory Roles in DNA Replication and Potential Targeting for Cancer Therapy

Cullin-RING (Really Interesting New Gene) E3 ubiquitin ligases (CRLs), the largest family of E3 ubiquitin ligases, are functional multi-subunit complexes including substrate receptors, adaptors, cullin scaffolds, and RING-box proteins. CRLs are responsible for ubiquitination of ~20% of cellular proteins and are involved in diverse biological processes including cell cycle progression, genome stability, and oncogenesis. Not surprisingly, cullins are deregulated in many diseases and instances of cancer. Recent studies have highlighted the importance of CRL-mediated ubiquitination in the regulation of DNA replication/repair, including specific roles in chromatin assembly and disassembly of the replication machinery. The development of novel therapeutics targeting the CRLs that regulate the replication machinery and chromatin in cancer is now an attractive therapeutic strategy. In this review, we summarize the structure and assembly of CRLs and outline their cellular functions and their diverse roles in cancer, emphasizing the regulatory functions of nuclear CRLs in modulating the DNA replication machinery. Finally, we discuss the current strategies for targeting CRLs against cancer in the clinic.