Depletion of SAG/RBX2 E3 ubiquitin ligase suppresses prostate tumorigenesis via inactivation of the PI3K/AKT/mTOR axis

Ubiquitination and deubiquitination in cancer: from mechanisms to novel therapeutic approaches

Ubiquitination, a pivotal posttranslational modification of proteins, plays a fundamental role in regulating protein stability. The dysregulation of ubiquitinating and deubiquitinating enzymes is a common feature in various cancers, underscoring the imperative to investigate ubiquitin ligases and deubiquitinases (DUBs) for insights into oncogenic processes and the development of therapeutic interventions. In this review, we discuss the contributions of the ubiquitin-proteasome system (UPS) in all hallmarks of cancer and progress in drug discovery. We delve into the multiple functions of the UPS in oncology, including its regulation of multiple cancer-associated pathways, its role in metabolic reprogramming, its engagement with tumor immune responses, its function in phenotypic plasticity and polymorphic microbiomes, and other essential cellular functions. Furthermore, we provide a comprehensive overview of novel anticancer strategies that leverage the UPS, including the development and application of proteolysis targeting chimeras (PROTACs) and molecular glues.

Corynoxine triggers cell death via activating PP2A and regulating AKT-mTOR/GSK3β axes in NSCLC

This study investigates the anticancer activity and pharmacological mechanisms of Corynoxine (Cory) in non-small cell lung cancer (NSCLC). Cory, a natural product derived from the Chinese herbal medicine Uncaria rhynchophylla, demonstrates promising pharmacological activity. Cell proliferation and viability were evaluated via MTT and colony formation assays. Flow cytometry was employed to analyze cell apoptosis, cycle distribution, and mitochondrial membrane potential. Autophagy was detected using fluorescence microscopy and electron microscopy. Western blotting, protein overexpression, gene knockdown, co-immunoprecipitation, and bioinformatics characterized Cory's impact on signaling pathways. The research indicates that Cory inhibits the proliferation of NSCLC cells in vivo and in vitro. Cory enhances PP2A activity, inhibits the AKT/mTOR signaling pathway triggering autophagy, while suppressing the AKT/GSK3β signaling pathway to induce cellular apoptosis in NSCLC. Notably, the activation of PP2A plays a crucial role in Cory's antitumor effects by inhibiting AKT. In vivo experiments validated Cory's efficacy in NSCLC treatment. These findings highlight the promising role of Cory as a lead compound for drug development in NSCLC therapy, providing a viable option for addressing this challenging disease.

Post-translational regulation of the mTORC1 pathway: A switch that regulates metabolism-related gene expression

The mechanistic target of rapamycin complex 1 (mTORC1) is a kinase complex that plays a crucial role in coordinating cell growth in response to various signals, including amino acids, growth factors, oxygen, and ATP. Activation of mTORC1 promotes cell growth and anabolism, while its suppression leads to catabolism and inhibition of cell growth, enabling cells to withstand nutrient scarcity and stress. Dysregulation of mTORC1 activity is associated with numerous diseases, such as cancer, metabolic disorders, and neurodegenerative conditions. This review focuses on how post-translational modifications, particularly phosphorylation and ubiquitination, modulate mTORC1 signaling pathway and their consequential implications for pathogenesis. Understanding the impact of phosphorylation and ubiquitination on the mTORC1 signaling pathway provides valuable insights into the regulation of cellular growth and potential therapeutic targets for related diseases.

Advancements and perspectives of RBX2 as a molecular hallmark in cancer

Cancer is a challenging issue for human health. One of the key methods to address this issue is by comprehending the molecular causes of tumors and creating medications that target those causes. RBX2 (RING box protein 2), also known as ROC2 (Regulator of Cullins 2), RNF7 (RING Finger Protein 7), or SAG (Sensitive to Apoptosis Gene) is a key component of the Cullin-RING-type E3 ubiquitin ligases (CRLs) and overexpressed in various human cancers. RBX2 is a potential drug target, the expression of which correlates with tumor staging, grading, and prognosis analysis. Through a synergistically biological interaction with Kras mutation in preclinical models, RBX2 accelerated the progression of skin cancer, pancreatic cancer, and lung cancer. In accordance, the aberrant expression of RBX2 will lead to dysregulation of many signaling pathways, which is crucial for tumor initiation and growth. However, the impact of RBX2 on tumors also intriguingly demonstrates a spatial reliance manner. In this review, we summarized the current understanding of RBX2 in multiple cancer types and suggested a significant potential of RBX2 as a therapeutic target.

The role of ubiquitination and deubiquitination in PI3K/AKT/mTOR pathway: A potential target for cancer therapy

The PI3K/AKT/mTOR pathway controls key cellular processes, including proliferation and tumor progression, and abnormally high activation of this pathway is a hallmark in human cancers. The post-translational modification, such as Ubiquitination and deubiquitination, fine-tuning the protein level and the activity of members in this pathway play a pivotal role in maintaining normal physiological process. Emerging evidence show that the unbalanced ubiquitination/deubiquitination modification leads to human diseases via PI3K/AKT/mTOR pathway. Therefore, a comprehensive understanding of the ubiquitination/deubiquitination regulation of PI3K/AKT/mTOR pathway may be helpful to uncover the underlying mechanism and improve the potential treatment of cancer via targeting this pathway. Herein, we summarize the latest research progress of ubiquitination and deubiquitination of PI3K/AKT/mTOR pathway, systematically discuss the associated crosstalk between them, as well as focus the clinical transformation via targeting ubiquitination process.

NAP1L5 facilitates pancreatic ductal adenocarcinoma progression via TRIM29-mediated ubiquitination of PHLPP1

Pancreatic ductal adenocarcinoma (PDAC) is considered one of the most aggressive solid tumours in humans. Despite its high mortality rate, effective targeted therapeutic strategies remain limited due to incomplete understanding of the underlying biological mechanisms. The NAP1L gene family has been implicated in the development and progression of various human tumours. However, the specific function and role of NAP1L5 (nucleosome assembly protein-like 5) in PDAC have not been fully elucidated. Therefore, in this study, we aimed to investigate the role of NAP1L5 in PDAC and explore the regulatory relationship between NAP1L5 and its potential downstream molecule PHLPP1 (PH domain Leucine-rich repeat Protein Phosphatase 1) in PDAC. Our study revealed that NAP1L5 is notably upregulated in PDAC. Moreover, both in vivo and in vitro experiments demonstrated that knockdown of NAP1L5 suppressed the proliferation of PDAC cells. Mechanistically, NAP1L5 was found to promote PDAC progression by activating the AKT/mTOR signalling pathway in a PHLPP1-dependent manner. Specifically, NAP1L5 binds to PHLPP1 and facilitates the ubiquitination-mediated degradation of PHLPP1, ultimately resulting in reduced PHLPP1 expression. Notably, TRIM29, recruited by NAP1L5, was found to be involved in facilitating K48-linked ubiquitination of PHLPP1. Our findings indicate that NAP1L5 overexpression promotes the proliferation of PDAC cells by inhibiting PHLPP1 expression. These novel insights suggest that NAP1L5 may serve as a potential therapeutic target for PDAC.

Gut microbiota: key facilitator in metastasis of colorectal cancer

Colorectal cancer (CRC) ranks third in terms of incidence among all kinds of cancer. The main cause of death is metastasis. Recent studies have shown that the gut microbiota could facilitate cancer metastasis by promoting cancer cells proliferation, invasion, dissemination, and survival. Multiple mechanisms have been implicated, such as RNA-mediated targeting effects, activation of tumor signaling cascades, secretion of microbiota-derived functional substances, regulation of mRNA methylation, facilitated immune evasion, increased intravasation of cancer cells, and remodeling of tumor microenvironment (TME). The understanding of CRC metastasis was further deepened by the mechanisms mentioned above. In this review, the mechanisms by which the gut microbiota participates in the process of CRC metastasis were reviewed as followed based on recent studies.

Discovery of neddylation E2s inhibitors with therapeutic activity

Neddylation is the writing of monomers or polymers of neural precursor cells expressed developmentally down-regulated 8 (NEDD8) to substrate. For neddylation to occur, three enzymes are required: activators (E1), conjugators (E2), and ligators (E3). However, the central role is played by the ubiquitin-conjugating enzymes E2M (UBE2M) and E2F (UBE2F), which are part of the E2 enzyme family. Recent understanding of the structure and mechanism of these two proteins provides insight into their physiological effects on apoptosis, cell cycle arrest and genome stability. To treat cancer, it is therefore appealing to develop novel inhibitors against UBE2M or UBE2F interactions with either E1 or E3. In this evaluation, we summarized the existing understanding of E2 interaction with E1 and E3 and reviewed the prospective of using neddylation E2 as a pharmacological target for evolving new anti-cancer remedies.

LINC01088/miR-22/CDC6 Axis Regulates Prostate Cancer Progression by Activating the PI3K/AKT Pathway

Background

Prostate cancer (PCa) harms the male reproductive system, and lncRNA may play an important role in it. Here, we report that the LINC01088/microRNA- (miRNA/miR-) 22/cell division cycle 6 (CDC6) axis regulated through the phosphatidylinositide 3-kinases- (PI3K-) protein kinase B (AKT) signaling pathway controls the development of PCa.

Methods

lncRNA/miRNA/mRNA associated with PCa was downloaded and analyzed by Gene Expression Omnibus. The expression and correlation of LINC01088/miR-22/CDC6 in PCa were analyzed and verified by RT-qPCR. Dual-luciferase was used to analyze the binding between miR-22 and LINC01088 or CDC6. Cell Counting Kit-8 and Transwell were used to analyze the effects of LINC01088/miR-22/CDC6 interactions on PCa cell viability or migration/invasion ability. Localization of LINC01088 in cells was analyzed by nuclear cytoplasmic separation. The effect of LINC01088/miR-22/CDC6 interaction on downstream PI3K/AKT signaling was analyzed by Western blot.

Results

LINC01088 or CDC6 was upregulated in prostate tumor tissues or cells, whereas miR-22 was downregulated, miR-22 directly targets both LINC01088 and CDC6. si-LINC01088 inhibits the PCa process by suppressing the PI3K/AKT pathway. CDC6 reverses si-linc01088-mediated cell growth inhibition and reduction of PI3K and AKT protein levels.

Conclusion

Our results demonstrate that the LINC01088/miR-22/CDC6 axis functions in PCa progression and provide a promising diagnostic and therapeutic target.

RNF7 Induces Skeletal Muscle Cell Apoptosis and Arrests Cell Autophagy via Upregulation of THBS1 and Inactivation of the PI3K/Akt Signaling Pathway in a Rat Sepsis Model

Recently, long noncoding RNAs (lncRNAs) have been highlighted for extensive functionality in sepsis. In this study, we aimed to explore the role of RNF7 in the progression of sepsis. We initially established a rat model of sepsis through cecal ligation and puncture induction, whereupon RNF7 expression was determined by RT-qPCR. Following adenovirus infection, the role of RNF7 in muscle injury, skeletal muscle protein metabolism, oxidative stress, and inflammation in sepsis rats was analyzed. Then, downstream mechanisms of RNF7 were identified and validated. Further, lipopolysaccharide was applied to treat myoblast to further demonstrate the in vitro role of RNF7. Our results showed that RNF7 expression was upregulated during sepsis. Overexpression of RNF7 worsened the sepsis-induced skeletal muscle injury, induced skeletal muscle protein metabolism, oxidative stress, and inflammation in sepsis rats. Meanwhile, overexpression of RNF7 elevated thrombospondin-1 (THBS1) expression. Silencing of RNF7 inhibited THBS1 and activated the PI3K/Akt signaling pathway, arresting the release of inflammatory factors and oxidative stress levels in skeletal muscle cells. Altogether, RNF7 may promote skeletal muscle cell apoptosis while simultaneously inhibiting cell autophagy through the promotion of THBS1 and inactivation of the PI3K/Akt signaling pathway.

Sag/Rbx2 Partial Inactivation Sensitizes Mice to Radiation and Radiation-Induced Tumorigenesis1

SAG (sensitive to apoptosis gene)/RBX2 (RING box-2), is the second family member of RING component of cullin-RING ligase (CRL) complex required for its enzymatic activity. Using total or conditional Sag knockout mouse models, we previously showed that Sag plays an essential role in embryonic development, apoptosis, vasculogenesis, angiogenesis and tumorigenesis. We also found that Sag-null ES cells are more sensitive to radiation. In this study, we generated the SagΔ/flneo mice with partial Sag inactivation due to deletion in one allele (Δ allele), and disrupted expression in the another (by a neo cassette). Compared to wild-type, SagΔ/fl-neo mice are more sensitive to a lethal dose of radiation with significantly shortened life span, resulting from an increased tissue damage with reduced proliferation and increased apoptosis in the intestines. Similar observations were made when SagΔ/fl-neo mice received a high dose of radiation directly delivered to the abdomen with reduced proliferation and prolonged DNA damage repair. Mechanistically, we found accumulations of Sag substrates, p21 and p27, explaining the proliferation defect. Finally, we found that SagΔ/fl-neo mice are more prone to tumorigenesis induced by a low dose of radiation with shortened life-span and increased incidence of lymphoma. Collectively, our study demonstrates that Sag protects mice from radiation-induced tissue damages and tumorigenesis.

The UBE2C/CDH1/DEPTOR axis is an oncogene and tumor suppressor cascade in lung cancer cells

Ubiquitin-conjugating enzyme E2C (UBE2C) mediates ubiquitylation chain formation via the K11 linkage. While previous in vitro studies showed that UBE2C plays a growth-promoting role in cancer cell lines, the underlying mechanism remains elusive. Still unknown is whether and how UBE2C plays a promoting role in vivo. Here we report that UBE2C was indeed essential for growth and survival of lung cancer cells harboring Kras mutations, and UBE2C was required for KrasG12D-induced lung tumorigenesis, since Ube2c deletion significantly inhibited tumor formation and extended the lifespan of mice. Mechanistically, KrasG12D induced expression of UBE2C, which coupled with APC/CCDH1 E3 ligase to promote ubiquitylation and degradation of DEPTOR, leading to activation of mTORC signaling. Importantly, DEPTOR levels fluctuated during cell cycle progression in a manner dependent on UBE2C and CDH1, indicating their physiological connection. Finally, Deptor deletion fully rescued the tumor inhibitory effect of Ube2c deletion in the KrasG12D lung tumor model, indicating a causal role of Deptor. Taken together, our study shows that the UBE2C/CDH1/DEPTOR axis forms an oncogene and tumor suppressor cascade that regulates cell cycle progression and autophagy and validates UBE2C an attractive target for lung cancer associated with Kras mutations.

RNF7 Facilitated the Tumorigenesis of Pancreatic Cancer by Activating PI3K/Akt Signaling Pathway

RING finger protein-7 (RNF7) functions as a positive regulator in the progression of multiple malignancies. However, the underlying mechanism by which RNF7 contributes to pancreatic cancer (PC) is lacking. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to test the level of RNF7expression in PC cell lines and tissues. The role of RNF7 in PC tumorigenesis was analyzed by Cell Counting Kit-8 (CCK-8). 5-Ethynyl-20-deoxyuridine (EdU), wound-healing/Transwell assays, as well as a subcutaneous tumorigenesis model were constructed to assess the role of RNF7 in PC cells. The association between RNF7 and PI3K/Akt signaling were assessed by western blot and further confirmed by rescue experiments. The PC patients with upregulated expression of RNF7 had poor survival. Overexpression of RNF7 significantly facilitated PC proliferative and migrative and invasive properties in vitro and vivo; however, knockdown of RNF7exhibited the opposite results. Mechanistically, RNF7 promoted PANC-1 and SW1990 cell growth through impacting the activation of the PI3K/Akt signaling pathway. Our data demonstrated that RNF7 promoted PC tumorigenesis via activating the PI3K/Akt signaling pathway and might be regarded as one of the potential therapies to PC.

The Sag-Shoc2 axis regulates conversion of mPanINs to cystic lesions in Kras pancreatic tumor model

SAG/RBX2 is an E3 ligase, whereas SHOC2 is a RAS-RAF positive regulator. In this study, we address how Sag-Shoc2 crosstalk regulates pancreatic tumorigenesis induced by Kras^G12D. Sag deletion increases the size of pancreas and causes the conversion of murine pancreatic intraepithelial neoplasms (mPanINs) to neoplastic cystic lesions with a mechanism involving Shoc2 accumulation, suggesting that Sag determines the pathological process via targeting Shoc2. Shoc2 deletion significantly inhibits pancreas growth, mPanIN formation, and acinar cell transdifferentiation, indicating that Shoc2 is essential for Kras^G12D-induced pancreatic tumorigenesis. Likewise, in a primary acinar 3D culture, Sag deletion inhibits acinar-to-ductal transdifferentiation, while Shoc2 deletion significantly reduces the duct-like structures. Mechanistically, SAG is an E3 ligase that targets SHOC2 for degradation to affect both Mapk and mTorc1 pathways. Shoc2 deletion completely rescues the phenotype of neoplastic cystic lesions induced by Sag deletion, indicating physiological relevance of the Sag-Shoc2 crosstalk. Thus, the Sag-Shoc2 axis specifies the pancreatic tumor types induced by Kras^G12D.

The roles of KLHL family members in human cancers

The Kelch-like (KLHL) family members consist of three domains: bric-a-brac, tramtrack, broad complex/poxvirus and zinc finger domain, BACK domain and Kelch domain, which combine and interact with Cullin3 to form an E3 ubiquitin ligase. Research has indicated that KLHL family members ubiquitinate target substrates to regulate physiological and pathological processes, including tumorigenesis and progression. KLHL19, a member of the KLHL family, is associated with tumorigenesis and drug resistance. However, the regulation and cross talks of other KLHL family members, which also play roles in cancer, are still unclear. Our review mainly explores studies concerning the roles of other KLHL family members in tumor-related regulation to provide novel insights into KLHL family members.

Mechanisms of chronic alcohol exposure-induced aggressiveness in cellular model of HCC and recovery after alcohol withdrawal

Alcohol-related liver disease is the most prevalent chronic liver disease worldwide, accounting for 30% of hepatocellular carcinoma (HCC) cases and HCC-specific deaths. However, the knowledge on mechanisms by which alcohol consumption leads to cancer progression and its aggressiveness is limited. Better understanding of the clinical features and the mechanisms of alcohol-induced HCC are of critical importance for prevention and the development of novel treatments. Early stage Huh-7 and advanced SNU449 liver cancer cell lines were subjected to chronic alcohol exposure (CAE), at different doses for 6 months followed by 1-month alcohol withdrawal period. ADH activity and ALDH expression were much lower in SNU449 compared with Huh-7 cells and at the 270 mM dose, CAE decreased cell viability by about 50% and 80%, respectively, in Huh-7 and SNU449 cells but induced mortality only in Huh-7 cells. Thus, Huh-7 may be more vulnerable to ethanol toxicity because of the higher levels of acetaldehyde. CAE induced a dose-dependent increase in cell migration and invasion and also in the expression of cancer stem cells markers (CD133, CD44, CD90). CAE in Huh-7 cells selectively activated ERK1/2 and inhibited GSK3β signaling pathways. Most of the changes induced by CAE were reversed after alcohol withdrawal. Interestingly, we confirmed the increase in CD133 mRNA levels in the tumoral tissue of patients with ethanol-related HCC compared to other HCC etiologies. Our results may explain the benefits observed in epidemiological studies showing a significant increase of overall survival in abstinent compared with non-abstinent patients.

The androgen receptor inhibits transcription of GPER1 by preventing Sp1 and Sp3 from binding to the promoters in prostate cancer cells

G-1, a GPER1 agonist, was shown to inhibit the growth of castration-resistant mouse xenografts but not their parental androgen-dependent tumors. It is currently unknown how the androgen receptor (AR) represses GPER1 expression. Here, we found that two GPER1 mRNA variants (GPER1v2 and GPER1v4) were transcriptionally repressed, not via transcript destabilization, by the androgen-activated AR. Although no AR binding was found in all active promoters near GPER1, data from promoter assays suggested that both variants' promoters were inhibited by androgen treatment. Site-directed mutagenesis on Sp1/Sp3 binding sites revealed their role in supporting the basal expression of GPER1. Knockdown of Sp1 and Sp3 together but not separately repressed GPER1 expression whereas overexpression of both Sp1 and Sp3 together was required to alleviate AR repression of GPER1. Based on the chromatin immunoprecipitation data, Sp3 was found to bind to the promoters prior to the binding of Sp1 and RNA polymerase II. However, the binding of all three transcription factors was inhibited by DHT treatment. Concordantly, DHT treatment induced nuclear interactions between AR and Sp1 or Sp3. Taken together, these results indicate that AR represses transcription of GPER1 by binding to Sp1 and Sp3 independently to prevent their transactivation of the GPER1 promoters.

BoxCar and shotgun proteomic analyses reveal molecular networks regulated by UBR5 in prostate cancer

Prostate cancer (PC) is a major health and economic problem in industrialized countries, yet our understanding of the molecular mechanisms of PC progression and drug response remains limited. Accumulating evidence showed that certain E3 ubiquitin ligases such as SIAH2, RNF7, and SPOP play important roles in PC development and progression. However, the roles and mechanisms of other E3s in PC progression remain largely unexplored. Through an integration analysis of clinical genomic and transcriptomic profiles of PC tumors, this study identified UBR5 as a top PC-relevant E3 ubiquitin ligase whose expression levels are strongly associated with PC progression and aggressiveness. BoxCar and shotgun proteomic analyses of control and UBR5-knockdown PC3 cells complementarily identified 75 UBR5-regulated proteins. Bioinformatic analysis suggested that the 75 proteins form four molecular networks centered around FANCD2, PAF1, YY1, and LAMB3 via direct protein-protein interactions. Experimental analyses demonstrated that UBR5 associates with and downregulates two key DNA damage repair proteins (XRCC3 and FANCD2) and confers PC cell sensitivity to olaparib, a PARP inhibitor in clinical use for cancer therapy. This study represents the first application of BoxCar in PC research, provides new insights into the molecular functions of UBR5 in PC, and suggests that PC patients with UBR5-high tumors may potentially benefit from PARP inhibitor treatment.

Post-translational modification of KRAS: potential targets for cancer therapy

Aberrant activation of the RAS superfamily is one of the critical factors in carcinogenesis. Among them, KRAS is the most frequently mutated one which has inspired extensive studies for developing approaches to intervention. Although the cognition toward KRAS remains far from complete, mounting evidence suggests that a variety of post-translational modifications regulate its activation and localization. In this review, we summarize the regulatory mode of post-translational modifications on KRAS including prenylation, post-prenylation, palmitoylation, ubiquitination, phosphorylation, SUMOylation, acetylation, nitrosylation, etc. We also highlight the recent studies targeting these modifications having exhibited potent anti-tumor activities.

The Negative Cross-Talk between SAG/RBX2/ROC2 and APC/C E3 Ligases in Regulation of Cell Cycle Progression and Drug Resistance

Anaphase-promoting complex/cyclosome (APC/C) is a well-characterized E3 ligase that couples with UBE2C and UBE2S E2s for substrate ubiquitylation by the K11 linkage. Our recent data show that SAG/RBX2/ROC2, a RING component of Cullin-RING E3 ligase, also complexes with these E2s for K11-linked substrate polyubiquitylation. Whether these two E3s cross-talk with each other was previously unknown. Here, we report that SAG competes with APC2 for UBE2C/UBE2S binding to act as a potential endogenous inhibitor of APC/C, thereby regulating the G2-to-M progression. As such, SAG knockdown triggers premature activation of APC/C, leading to mitotic slippage and resistance to anti-microtubule drugs. On the other hand, SAG itself is a substrate of APC/C^CDH1 for targeted degradation at the G1 phase. The degradation-resistant mutant of SAG-R98A/L101A accelerates the G1-to-S progression. Our study reveals that the negative cross-talk between SAG and APC/C is likely a mechanism to ensure the fidelity of cell cycle progression.

Zhang et al. provide a mechanistic insight of how negative cross-talk between E3 ligases SAG and APC/C ensures proper cell cycle progression. SAG knockdown prematurely activates APC/C to promote mitotic progression and trigger anti-microtubule drugs resistance, whereas SAG degradation by APC/C^CDH1 mainly occurs in G1 phase for proper G1-to-S transition.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

Identification of a Ubiquitination-Related Gene Risk Model for Predicting Survival in Patients With Pancreatic Cancer

Pancreatic cancer is known as "the king of cancer," and ubiquitination/deubiquitination-related genes are key contributors to its development. Our study aimed to identify ubiquitination/deubiquitination-related genes associated with the prognosis of pancreatic cancer patients by the bioinformatics method and then construct a risk model. In this study, the gene expression profiles and clinical data of pancreatic cancer patients were downloaded from The Cancer Genome Atlas (TCGA) database and the Genotype-tissue Expression (GTEx) database. Ubiquitination/deubiquitination-related genes were obtained from the gene set enrichment analysis (GSEA). Univariate Cox regression analysis was used to identify differentially expressed ubiquitination-related genes selected from GSEA which were associated with the prognosis of pancreatic cancer patients. Using multivariate Cox regression analysis, we detected eight optimal ubiquitination-related genes (RNF7, NPEPPS, NCCRP1, BRCA1, TRIM37, RNF25, CDC27, and UBE2H) and then used them to construct a risk model to predict the prognosis of pancreatic cancer patients. Finally, the eight risk genes were validated by the Human Protein Atlas (HPA) database, the results showed that the protein expression level of the eight genes was generally consistent with those at the transcriptional level. Our findings suggest the risk model constructed from these eight ubiquitination-related genes can accurately and reliably predict the prognosis of pancreatic cancer patients. These eight genes have the potential to be further studied as new biomarkers or therapeutic targets for pancreatic cancer.

The role of ubiquitination and deubiquitination in cancer metabolism

Metabolic reprogramming, including enhanced biosynthesis of macromolecules, altered energy metabolism, and maintenance of redox homeostasis, is considered a hallmark of cancer, sustaining cancer cell growth. Multiple signaling pathways, transcription factors and metabolic enzymes participate in the modulation of cancer metabolism and thus, metabolic reprogramming is a highly complex process. Recent studies have observed that ubiquitination and deubiquitination are involved in the regulation of metabolic reprogramming in cancer cells. As one of the most important type of post-translational modifications, ubiquitination is a multistep enzymatic process, involved in diverse cellular biological activities. Dysregulation of ubiquitination and deubiquitination contributes to various disease, including cancer. Here, we discuss the role of ubiquitination and deubiquitination in the regulation of cancer metabolism, which is aimed at highlighting the importance of this post-translational modification in metabolic reprogramming and supporting the development of new therapeutic approaches for cancer treatment.

Role of PI3K/AKT pathway in cancer: the framework of malignant behavior

Given that the PI3K/AKT pathway has manifested its compelling influence on multiple cellular process, we further review the roles of hyperactivation of PI3K/AKT pathway in various human cancers. We state the abnormalities of PI3K/AKT pathway in different cancers, which are closely related with tumorigenesis, proliferation, growth, apoptosis, invasion, metastasis, epithelial-mesenchymal transition, stem-like phenotype, immune microenvironment and drug resistance of cancer cells. In addition, we investigated the current clinical trials of inhibitors against PI3K/AKT pathway in cancers and found that the clinical efficacy of these inhibitors as monotherapy has so far been limited despite of the promising preclinical activity, which means combinations of targeted therapy may achieve better efficacies in cancers. In short, we hope to feature PI3K/AKT pathway in cancers to the clinic and bring the new promising to patients for targeted therapies.

Transgenic expression of Sag/Rbx2 E3 causes early stage tumor promotion, late stage cytogenesis and acinar loss in the Kras-PDAC model

SAG (Sensitive to Apoptosis Gene), also known as RBX2 or ROC2, is a RING component of CRL (Cullin-RING ligase), required for its activity. Our previous studies showed that Sag/Rbx2 co-operated with Kras or Pten loss to promote tumorigenesis in the lung and prostate, respectively, but antagonized Kras to inhibit skin tumorigenesis, suggesting a tissue/context dependent function of Sag. The role of SAG in KRAS-induced pancreatic tumorigenesis is unknown. In this study, we mined a cancer database and found that SAG is overexpressed in pancreatic cancer tissues and correlates with decreased patient survival. Whether Sag overexpression plays a causal role in pancreatic tumorigenesis is unknown. Here, we reported the generation of Sag transgenic mouse model alone (CS), or in combination with KrasG12D, driven by p48-Cre (KCS mice) for pancreatic specific Sag expression. Sag transgenic expression alone has no phenotypical abnormality, but in combination with KrasG12D promotes ADM (acinar-to-ductal metaplasia) conversion in vitro and mPanIN1 formation in vivo at the early stage, and impairs pancreatic functions at the late stage, as evidenced by poor glucose tolerance and significantly reduced α-Amylase activity, and induction of cytogenesis and acinar cell loss, eventually leading to atrophic pancreata and shortened mouse life-span. Mechanistically, Sag transgenic expression altered several key signaling pathways, particularly inactivation of mTORC1 signaling due to Deptor accumulation, and activation of the antioxidant Nrf2-Nqo1 axis. Thus, Sag plays a stage dependent promotion (early) and fate-changing (late) role during Kras-pancreatic tumorigenesis, likely via regulating its key substrates, which control growth-related signal transduction pathways.

Cullin-RING Ligase 5: Functional characterization and its role in human cancers

Cullin-RING ligase 5 (CRL5) is a multi-protein complex and consists of a scaffold protien cullin 5, a RING protein RBX2 (also known as ROC2 or SAG), adaptor proteins Elongin B/C, and a substrate receptor protein SOCS. Through targeting a variety of substrates for proteasomal degradation or modulating various protein-protein interactions, CRL5 is involved in regulation of many biological processes, such as cytokine signal transduction, inflammation, viral infection, and oncogenesis. As many substrates of CRL5 are well-known oncoproteins or tumor suppressors, abnormal regulation of CRL5 is commonly found in human cancers. In this review, we first briefly introduce each of CRL5 components, and then discuss the biological processes regulated by four members of SOCS-box-containing substrate receptor family through substrate degradation. We next describe how CRL5 is hijacked by a variety of viral proteins to degrade host anti-viral proteins, which facilitates virus infection. We further discuss the regulation of CUL5 and its various roles in human cancers, acting as either a tumor suppressor or an oncoprotein in a context-dependent manner. Finally, we propose novel insights for future perspectives on the validation of cullin5 and other CRL5 components as potential targets, and possible targeting strategies to discover CRL5 inhibitors for anti-cancer and anti-virus therapies.

SAG expression associates with COPB2-related signaling and a poorer prognosis in breast cancer

SAG is an essential RING component of the Cullin-RING ligase (CRL) E3 ubiquitin ligase complex, which regulates diverse signaling pathways and biological processes, including cell apoptosis, embryonic development, angiogenesis, and tumorigenesis. In the present study, we revealed that SAG gene expression is upregulated in breast cancer cells and that SAG overexpression is associated with significant poorer survival in breast cancer, especially the luminal A subtype. We also detected highly correlated co-overexpression of SAG and COPB2 in breast cancers. Subsequent in vitro experiments demonstrated that SAG and COPB2 act cooperatively to stimulate breast cancer cell proliferation, migration and invasion. Our findings suggest that levels of SAG and COPB2 expression may be useful prognostic indicators in breast cancers and that SAG may be involved in COPB2-related signaling during breast cancer development.

Divergent Modulation of Proteostasis in Prostate Cancer

Proteostasis regulates key cellular processes such as cell proliferation, differentiation, transcription, and apoptosis. The mechanisms by which proteostasis is regulated are crucial and the deterioration of cellular proteostasis has been significantly associated with tumorigenesis since it specifically targets key oncoproteins and tumor suppressors. Prostate cancer (PCa) is the second most common cause of cancer death in men worldwide. Androgens mediate one of the most central signaling pathways in all stages of PCa via the androgen receptor (AR). In addition to their regulation by hormones, PCa cells are also known to be highly secretory and are particularly prone to ER stress as proper ER function is essential. Alterations in various complex signaling pathways and cellular processes including cell cycle control, transcription, DNA repair, apoptosis, cell adhesion, epithelial-mesenchymal transition (EMT), and angiogenesis are critical factors influencing PCa development through key molecular changes mainly by posttranslational modifications in PCa-related proteins, including AR, NKX3.1, PTEN, p53, cyclin D1, and p27. Several ubiquitin ligases like MDM2, Siah2, RNF6, CHIP, and substrate-binding adaptor SPOP; deubiquitinases such as USP7, USP10, USP26, and USP12 are just some of the modifiers involved in the regulation of these key proteins via ubiquitin-proteasome system (UPS). Some ubiquitin-like modifiers, especially SUMOs, have been also closely associated with PCa. On the other hand, the proteotoxicity resulting from misfolded proteins and failure of ER adaptive capacity induce unfolded protein response (UPR) that is an indispensable signaling mechanism for PCa development. Lastly, ER-associated degradation (ERAD) also plays a crucial role in prostate tumorigenesis. In this section, the relationship between prostate cancer and proteostasis will be discussed in terms of UPS, UPR, SUMOylation, ERAD, and autophagy.

The FBXW2-MSX2-SOX2 axis regulates stem cell property and drug resistance of cancer cells

SOX2 is a key transcription factor that plays critical roles in maintaining stem cell property and conferring drug resistance. However, the underlying mechanisms by which SOX2 level is precisely regulated remain elusive. Here we report that MLN4924, also known as pevonedistat, a small-molecule inhibitor of neddylation currently in phase II clinical trials, down-regulates SOX2 expression via causing accumulation of MSX2, a known transcription repressor of SOX2 expression. Mechanistic characterization revealed that MSX2 is a substrate of FBXW2 E3 ligase. FBXW2 binds to MSX2 and promotes MSX2 ubiquitylation and degradation. Likewise, FBXW2 overexpression shortens the protein half-life of MSX2, whereas FBXW2 knockdown extends it. We further identified hypoxia as a stress condition that induces VRK2 kinase to facilitate MSX2-FBXW2 binding and FBXW2-mediated MSX2 ubiquitylation and degradation, leading to SOX2 induction via derepression. Biologically, expression of FBXW2 or SOX2 promotes tumor sphere formation, which is blocked by MSX2 expression. By down-regulating SOX2 through inactivation of FBXW2 E3 ligase, MLN4924 sensitizes breast cancer cells to tamoxifen in both in vitro and in vivo cancer cell models. Thus, a negative cascade of the FBXW2-MSX2-SOX2 axis was established, which regulates stem cell property and drug resistance. Finally, an inverse correlation of expression was found between FBXW2 and MSX2 in lung and breast cancer tissues. Collectively, our study revealed an anticancer mechanism of MLN4924. By inactivating FBXW2, MLN4924 caused MSX2 accumulation to repress SOX2 expression, leading to suppression of stem cell property and sensitization of breast cancer cells to tamoxifen.

Control of mTOR signaling by ubiquitin

The evolutionarily conserved mTOR signaling pathway plays essential roles in cell growth, proliferation, metabolism and responses to cellular stresses. Hyperactivation of the mTOR signaling is observed in virtually all solid tumors and has been an attractive drug target. In addition to changes at genetic levels, aberrant activation of the mTOR signaling is also a result from dysregulated posttranslational modifications on key pathway members, such as phosphorylation that has been extensively studied. Emerging evidence also supports a critical role for ubiquitin-mediated modifications in dynamically regulating the mTOR signaling pathway, while a comprehensive review for relevant studies is missing. In this review, we will summarize characterized ubiquitination events on major mTOR signaling components, their modifying E3 ubiquitin ligases, deubiquitinases and corresponding pathophysiological functions. We will also reveal methodologies that have been used to identify E3 ligases or DUBs to facilitate the search for yet-to-be discovered ubiquitin-mediated regulatory mechanisms in mTOR signaling. We hope that our review and perspectives provide rationales and strategies to target ubiquitination for inhibiting mTOR signaling to treat human diseases.

Transcriptional repression by androgen receptor: roles in castration-resistant prostate cancer

Androgen receptor (AR), a hormonal transcription factor, plays important roles during prostate cancer progression and is a key target for therapeutic interventions. While androgen-deprivation therapies are initially successful in regressing prostate tumors, the disease ultimately comes back as castration-resistant prostate cancer (CRPC) or at the late stage as neuroendocrine prostate cancer (NEPC). CRPC remains largely dependent on hyperactive AR signaling in the milieu of low androgen, while NEPC is negative of AR expression but positive of many AR-repressed genes. Recent technological advances in genome-wide analysis of transcription factor binding sites have revealed an unprecedented set of AR target genes. In addition to its well-known function in activating gene expression, AR is increasingly known to also act as a transcriptional repressor. Here, we review the molecular mechanisms by which AR represses gene expression. We also summarize AR-repressed genes that are aberrantly upregulated in CRPC and NEPC and represent promising targets for therapeutic intervention.

Genetically Engineered Mouse Models of Prostate Cancer in the Postgenomic Era

Recent genomic sequencing analyses have unveiled the spectrum of genomic alterations that occur in primary and advanced prostate cancer, raising the question of whether the corresponding genes are functionally relevant for prostate tumorigenesis, and whether such functions are associated with particular disease stages. In this review, we describe genetically engineered mouse models (GEMMs) of prostate cancer, focusing on those that model genomic alterations known to occur in human prostate cancer. We consider whether the phenotypes of GEMMs based on gain or loss of function of the relevant genes provide reliable counterparts to study the predicted consequences of the corresponding genomic alterations as occur in human prostate cancer, and we discuss exceptions in which the GEMMs do not fully emulate the expected phenotypes. Last, we highlight future directions for the generation of new GEMMs of prostate cancer and consider how we can use GEMMs most effectively to decipher the biological and molecular mechanisms of disease progression, as well as to tackle clinically relevant questions.

DEPTOR at the Nexus of Cancer, Metabolism, and Immunity

DEP domain-containing mechanistic target of rapamycin (mTOR)-interacting protein (DEPTOR) is an important modulator of mTOR, a kinase at the center of two important protein complexes named mTORC1 and mTORC2. These highly studied complexes play essential roles in regulating growth, metabolism, and immunity in response to mitogens, nutrients, and cytokines. Defects in mTOR signaling have been associated with the development of many diseases, including cancer and diabetes, and approaches aiming at modulating mTOR activity are envisioned as an attractive strategy to improve human health. DEPTOR interaction with mTOR represses its kinase activity and rewires the mTOR signaling pathway. Over the last years, several studies have revealed key roles for DEPTOR in numerous biological and pathological processes. Here, we provide the current state of the knowledge regarding the cellular and physiological functions of DEPTOR by focusing on its impact on the mTOR pathway and its role in promoting health and disease.

Inactivation of ribosomal protein S27-like confers radiosensitivity via the Mdm2-p53 and Mdm2-MRN-ATM axes

RPS27L (ribosomal protein S27-like) is an evolutionarily conserved ribosomal protein and a direct p53 target. We recently reported that Rps27l disruption triggers ribosomal stress to induce p53, causing postnatal death, which can be rescued by Trp53^+/−. Whether and how Rps27l modulates radiosensitivity is unknown. Here we report that Rps27l^−/−; Trp53^+/− mice are extremely sensitive to radiation due to reduced proliferation and massive induction of apoptosis in radiation-sensitive organs. Mechanistically, the radiation sensitivity is mediated by two signaling pathways: (1) activated p53 pathway due to imbalanced Mdm2/Mdm4 levels and reduced E3 ligase activity; and (2) reduced DNA damage response due to reduced MRN/Atm signal as a result of elevated Mdm2 binding of Nbs1 to inhibit Nbs1–Atm binding and subsequent Atm activation. Indeed, heterozygous deletion of Mdm2 restores the MRN/Atm signal. Collectively, our study revealed a physiological condition under which Rps27l regulates the Mdm2/p53 and MRN/Atm axes to maintain DNA damage response and to confer radioprotection in vivo.

LincRNA-p21 knockdown enhances radiosensitivity of hypoxic tumor cells by reducing autophagy through HIF-1/Akt/mTOR/P70S6K pathway

Hypoxic conditions are common in solid tumors and have a significant effect on tumor progression, therapeutic and prognosis. Long noncoding RNAs (lncRNAs) are longer than 200 nucleotides and cannot be translated into proteins, which play important roles in some diseases including cancer. Although previous analysis have showed that long intergenic non-coding RNA (lincRNA)-p21 is hypoxia-responsive and functions as a new regulator of cell cycle, apoptosis and warburg effect in cervical cancer, its biological roles in hypoxic hepatoma and glioma are unknown. In this work, we found that X-ray irradiation or hypoxia treatment elevated lincRNA-p21 expression in SMMC7721 hepatoma and U251MG glioma cells. Knockdown of lincRNA-p21 induced G2/M phase arrest, promoted apoptosis, decreased cell proliferation and motility, and reduced autophagy through HIF-1/Akt/mTOR/P70S6K pathway in hypoxic tumor cells. Our results delineated a novel mechanism of lincRNA-p21 in enhancing hypoxic tumor cell radiosensitivity, which might provide valuable targets for radiation therapy for solid tumors, such as hepatoma and glioma.

Identification of RING-box 2 as a potential target for combating colorectal cancer growth and metastasis

Development of cancer metastasis is a key contributor to mortality in patients with colorectal cancer. High expression of RING-box 2 (RBX2) in cancer cells is known to play a key role in tumor progression. However, the role of RBX2 in colorectal cancer progression is not well elucidated. In this study, we silenced RBX2 via CRISPR/Cas9 in two colorectal cancer cell lines, HCT116 and SW480. RBX2 knockout attenuated proliferation, colony formation and enhanced sensitivity of colorectal cancer cells to paclitaxel treatment. Invasive property of HCT116 and SW480 cells was also attenuated by RBX2 silencing. We confirmed that increased RBX2 correlated with higher tumor cells growth and metastasis abilities by ectopic expression of RBX2 in HCT116 and SW480 cells. In vivo studies suggested that knockout of RBX2 inhibited xenografts growth and metastasis to lung tissue, whereas ectopic expression of RBX2 promoted these cellular functions. Mechanically, RBX2 induced gastric cancer cell growth and metastasis by activating mammalian target of rapamycin/S6 kinase 1 (mTOR/S6K1). Treatment of everolimus, the specific mTOR inhibitor, significantly attenuated RBX2-mediated cell proliferation and mobility in vitro. Taken together, these results revealed a novel role of RBX2 in colorectal cancer cell growth and metastasis via the mTOR pathway and suggested RBX2 may serve as a therapeutic target in colorectal cancer.

RNF7 knockdown inhibits prostate cancer tumorigenesis by inactivation of ERK1/2 pathway

Development of castration resistance is a key contributor to mortality in patients with prostate cancer. High expression of RING finger protein 7 (RNF7) in cancer cells is known to play a key role in tumor progression. However, the role of RNF7 in prostate cancer progression is not well elucidated. In this study, we silenced RNF7 by shRNA interference in two castration resistant prostate cancer (CRPC) cell lines, DU145 and PC3. RNF7 knockdown attenuated proliferation and enhanced sensitivity of prostate cancer cells to cisplatin treatment. Invasive property of DU145 and PC3 cells was also attenuated by RNF7 silencing. The underlying mechanisms appear to be associated with accumulation of tumor suppressive proteins p21, p27 and NOXA, while inactivation of ERK1/2 by RNF7 knockdown. We demonstrated that RNF7 knockdown induced growth suppression of prostate cancer cells and inactivated ERK1/2 pathway, which suggested RNF7 might be a potential novel therapeutic target for CRPC.