RNF6 promotes myeloma cell proliferation and survival by inducing glucocorticoid receptor polyubiquitination

RNF6 Inhibits Lung Adenocarcinoma Cell Proliferation by Promoting Cyclin D2 Degradation

The E3 ubiquitin ligase RING finger protein 6 (RNF6) has been widely recognized for its role in promoting tumorigenesis in multiple cancers. However, we found that it is downregulated in lung adenocarcinoma (LUAD), and the molecular rationale for this discrepancy remains unclear. In the present study, we find that RNF6, but not its ΔRING inactive form, inhibits LUAD cell proliferation and migration and sensitizes LUAD to chemotherapy. To understand the molecular mechanism, we utilize affinity purification/tandem mass spectrometry (MS-MS) to analyze RNF6-interacting proteins and find that cyclin D2 (CCND2), a key regulator of the G1-S transition in the cell cycle. RNF6 physically binds to CCND2 and mediates its K48-linked polyubiquitination and subsequent degradation. However, ΔRING RNF6 fails to mediate CCND2 for ubiquitination and degradation. Moreover, Thr280 is critically important for CCND2 stability. When Thr280 is mutated, CCND2 becomes more stable and less ubiquitinated by RNF6. Furthermore, RNF6 arrests LUAD cell cycle at the G1 phase by inhibiting the CCND2/phospho-Rb signaling pathway, which is consistent with decreased cell proliferation. Lastly, RNF6 curtails the growth of LUAD xenografts in vivo, associated with decreased CCND2 expression. Therefore, RNF6 is a novel E3 ligase of CCND2 and suppresses LUAD cell proliferation. Implications: This study reveals a novel regulation on cell-cycle transition in LUAD and suggests the RNF6/CCND2 axis may represent an alternative therapeutic target for the treatment of LUAD.

RNF6 promotes cell proliferation of glioblastoma by targeting ubiquitin-mediated degradation of p27

RNF6 (RING finger protein 6), an atypical RING-type ubiquitin ligase, has been reported to be a potential tumor promoter in several human cancers. However, the role of RNF6 in glioblastoma remains poorly understood. In this study, we found that RNF6 was highly expressed in glioblastoma tissues, and its elevated expression was significantly associated with poor prognosis in glioblastoma patients. RNF6 depletion remarkably inhibited cell growth of glioblastoma cells. Mechanistically, RNF6 depletion stabilized p27 protein expression. We demonstrated that RNF6 interacted with p27 and mediated its ubiquitination and degradation in an E3 ligase activity-dependent manner. Moreover, we provide the first evidence revealing the crucial role RNF6 in mediating SKP2 expression at both transcriptional and post-translational levels. On the one hand, RNF6 played as a transcription factor to regulate the activity of the SKP2 promoter. On the other hand, RNF6 interacted with SKP2 and stabilized its protein levels in an Akt-dependent manner. Collectively, our data indicated that RNF6 accelerated glioblastoma cell proliferation and tumorigenesis by targeting p27 for degradation.

The deubiquitinase USP2a promotes tumor immunosuppression by stabilizing immune checkpoint B7-H4 in lung adenocarcinoma harboring EGFR-activating mutants

B7-H4 is an immune checkpoint crucial for inhibiting CD8+ T-cell activity. A clinical trial is underway to investigate B7-H4 as a potential immunotherapeutic agent. However, the regulatory mechanism of B7-H4 degradation via the ubiquitin-proteasome pathway (UPP) remains poorly understood. In this study, we discovered that proteasome inhibitors effectively increased B7-H4 expression, while EGFR-activating mutants promoted B7-H4 expression through the UPP. We screened B7-H4 binding proteins by co-immunoprecipitation and mass spectrometry and found that USP2a acted as a deubiquitinase of B7-H4 by removing K48- and K63-linked ubiquitin chains from B7-H4, leading to a reduction in B7-H4 degradation. EGFR mutants enhanced B7-H4 stability by upregulating USP2a expression. We further investigated the role of USP2a in tumor growth in vivo. Depletion of USP2a in L858R/LLC cells inhibited tumor cell proliferation, consequently suppressing tumor growth in immune-deficient nude mice by destabilizing downstream molecules such as Cyclin D1. In an immune-competent C57BL/6 mouse tumor model, USP2a abrogation facilitated infiltration of CD95+CD8+ effector T cells and hindered infiltration of Tim-3+CD8+ and LAG-3+CD8+ exhausted T cells by destabilizing B7-H4. Clinical lung adenocarcinoma samples showed a significant correlation between B7-H4 abundance and USP2a expression, indicating the contribution of the EGFR/USP2a/B7-H4 axis to tumor immunosuppression. In summary, this study elucidates the dual effects of USP2a in tumor growth by stabilizing Cyclin D1, promoting tumor cell proliferation, and stabilizing B7-H4, contributing to tumor immunosuppression. Therefore, USP2a represents a potential target for tumor therapy.

RNF6 promotes gastric cancer progression by regulating CCNA1/CREBBP transcription

Ring finger protein 6 (RNF6) is a member of the E3 ubiquitin ligase family. Previous studies have reported the involvement of RNF6 as a ubiquitin ligase in the progression of gastric cancer (GC). However, this study found that RNF6 has a clear localization in the nucleus of GC, indicating a role other than ubiquitin ligase. Further chromatin immunoprecipitation sequencing (ChIP-seq) analysis revealed that RNF6 has DNA binding and transcriptional regulatory effects and is involved in important pathways such as tumor cell cycle and apoptosis. Cyclin A1 (CCNA1) and CREB binding protein (CREBBP) are downstream targets for RNF6 transcription regulation in GC. RNF6 binds to the promoter region of CCNA1/CREBBP and is actively regulating their expression in GC cells. Silencing CCNA1/CREBBP partially reversed the promoting effect of RNF6 overexpression on the biological function of GC cells. Our study suggests that RNF6 promotes the progression of GC by regulating CCNA1/CREBBP transcription.

Zooming into the structure-function of RING finger proteins for anti-cancer therapeutic applications

Cancer is one of the most common and widely diagnosed diseases worldwide. With an increase in prevalence and incidence, many studies in cancer biology have been looking at the role pro-cancer proteins play. One of these proteins is the Really Interesting New Gene (RING), which has been studied extensively due to its structure and functions such as apoptosis, neddylation, and its role in ubiquitination. The RING domain is a cysteine-rich domain known to bind Cysteine and Histidine residues. It also binds two zinc ions that help stabilize the protein in various patterns, often with a 'cross-brace' topology. Different RING finger proteins have been studied and found to have suitable targets for developing anti-cancer therapeutics. These identified candidate proteins include Parkin, COP1, MDM2, BARD1, BRCA-1, PIRH2, c-CBL, SIAH1, RBX1 and RNF8. Inhibiting these candidate proteins provides opportunities for shutting down pathways associated with tumour development and metastasis.

Proximity Proteomics and Biochemical Analysis Reveal a Noncanonical Function for UFM1-Specific Protease 1 in the p62 Body Formation

Protein aggregates play crucial roles in the development of neurodegenerative diseases and p62 is one of the key proteins regulating the formation of protein aggregates. Recently, it has been discovered that depletion of several key enzymes including UFM1-activating enzyme UBA5, UFM1-conjugating enzyme UFC1, UFM1-protein ligase UFL1, and UFM1-specific protease UfSP2 in the UFM1-conjugation system induces p62 accumulation to form p62 bodies in the cytosol. However, it is unknown whether UfSP1 participates in the formation of p62 bodies and whether its enzymatic activity is required for this process. Here, the proximity labeling technique and quantitative proteomics identify SQSTM1/p62 as a UfSP1-interacting protein. Coimmunoprecipitation reveals that p62 indeed interacts with UfSP1 and the immunofluorescence experiment discloses that UfSP1 colocalizes with p62 and promotes the formation of p62-mediated protein aggregates. Mechanistic studies unveil that UfSP1 binds to the ubiquitin-associated domain of p62 and promotes the interaction between p62 and ubiquitinated proteins, thereby increasing the formation of p62 bodies. Interestingly, we further demonstrate that both the catalytic active and inactive UfSP1 promote the formation of p62 bodies through the same mechanism. Taken together, this work discovers that UfSP1 exhibits a noncanonical function independent of its protease activity in the p62 body formation.

TRIM26 promotes non-small cell lung cancer survival by inducing PBX1 degradation

The transcription factor PBX1 is regarded as an oncogene in various cancers, but its role in non-small cell lung cancer (NSCLC) and the detailed mechanism is not known. In the present study, we found that PBX1 is downregulated in NSCLC tissues and inhibits NSCLC cell proliferation and migration. Subsequently, we performed an affinity purification-coupled tandem mass spectrometry (MS/MS) and found the ubiquitin ligase TRIM26 in the PBX1 immunoprecipitates. Moreover, TRIM26 binds to and mediates PBX1 for K48-linked polyubiquitination and proteasomal degradation. Noticeably, TRIM26 activity depends on its C-terminal RING domain when it is deleted TRIM26 loses its function towards PBX1. TRIM26 further inhibits PBX1 transcriptional activity and downregulates the PBX1 downstream genes, such as RNF6. Moreover, we found that overexpression of TRIM26 significantly promotes NSCLC proliferation, colony formation, and migration in contradiction to PBX1. TRIM26 is highly expressed in NSCLC tissues and predicts poor prognosis. Lastly, the growth NSCLC xenografts is promoted by overexpression of TRIM26 but is suppressed by TRIM26 knockout. In conclusion, TRIM26 is a ubiquitin ligase of PBX1 and it promotes while PBX1 inhibits NSCLC tumor growth. TRIM26 might be a novel therapeutic target for the treatment of NSCLC.

MYH10 Combines with MYH9 to Recruit USP45 by Deubiquitinating Snail and Promotes Serous Ovarian Cancer Carcinogenesis, Progression, and Cisplatin Resistance

The poor prognosis of serous ovarian cancer (SOC) is due to its high invasive capacity and cisplatin resistance of SOC cells, whereas the molecular mechanisms remain poorly understood. In the present study, the expression and function of non-muscle myosin heavy chain IIB (MYH10) in SOC are identified by immunohistochemistry, in vitro, and in vivo studies, respectively. The mechanism of MYH10 is demonstrated by co-immunoprecipitation, GST pull-down, confocal laser assays, and so on. The results show that the knockdown of MYH10 suppressed SOC cell proliferation, migration, invasion, metastasis, and cisplatin resistance both in vivo and in vitro. Further studies confirm that the MYH10 protein functional domain combines with non-muscle myosin heavy chain IIA (MYH9) to recruit the deubiquitinating enzyme Ubiquitin-specific proteases 45 and deubiquitinates snail to inhibit snail degradation, eventually promoting tumorigenesis, progression, and cisplatin resistance in SOC. In clinical samples, MYH10 expression is significantly elevated in SOC samples compared to the paratumor samples. And the expression of MYH10 is positively correlated with MYH9 expression. MYH10+/MYH9+ co-expression is an independent prognostic factor for predicting SOC patient survival. These findings uncover a key role of the MYH10-MYH9-snail axis in SOC carcinogenesis, progression, and cisplatin resistance, and provide potential novel therapeutic targets for SOC intervention.

The ubiquitin ligase HERC4 suppresses MafA transcriptional activity triggered by GSK3β in myeloma by atypical K63-linked polyubiquitination

MafA and c-Maf are close members of the Maf transcription factor family and indicators of poor prognosis of multiple myeloma (MM). Our previous study finds that the ubiquitin ligase HERC4 induces c-Maf degradation but stabilizes MafA, and the mechanism is elusive. In the present study we find that HERC4 interacts with MafA and mediates its K63-linked polyubiquitination at K33. Moreover, HERC4 inhibits MafA phosphorylation and its transcriptional activity triggered by glycogen synthase kinase 3β (GSK3β). The K33R MafA variant prevents HERC4 from inhibiting MafA phosphorylation and increases MafA transcriptional activity. Further analyses reveal that MafA can also activate the STAT3 signaling but it is suppressed by HERC4. Lastly, we demonstrate that lithium chloride, a GSK3β inhibitor, can upregulate HERC4 and synergizes dexamethasone, a typical anti-MM drug, in inhibiting MM cell proliferation and xenograft growth in nude mice. These findings thus highlight a novel regulation of MafA oncogenic activity in MM and provide the rationale by targeting HERC4/GSK3β/MafA for the treatment of MM.

Brucein D imparts a growth inhibitory effect in multiple myeloma cells by abrogating the Akt-driven signaling pathway

The Akt signaling pathway is an oncogenic cascade activated in the bone marrow microenvironment of multiple myeloma (MM) cells and contributes to their uncontrolled proliferation. Abrogation of Akt signaling has been presented as one of the prime therapeutic targets in the treatment of MM. In the present report, we have investigated the effect of Brucein D (BD) on Akt-driven signaling events in MM cells. BD (300 nM) substantially inhibited cell viability and imparted growth-inhibitory effects in U266 cells as evidenced by cell viability assays and flow cytometric analysis. Effect of BD on cell viability was evaluated by MTT assay. Apoptotic cells and cell cycle arrest by BD were analyzed by flow cytometer. The results of the TUNEL assay and western blotting showed that BD induces apoptosis of MM cells by activating caspase-8 and 9 with subsequent reduction in the expression of antiapoptotic proteins (Bcl-2, Bcl-xl, survivin, cyclin D1, COX-2, VEGF, MMP-9). Analysis of activated kinases by Phospho-Kinase Array Kit revealed that Akt, p70S6K, HSP60, p53, and WNK1 were strongly expressed in untreated cells and BD treatment reversed this effect. Using transfection experiments, AKT depletion led to a decrease in phosphorylation of Akt, mTOR, p70S6K, and WNK. However, Akt overexpression led to increase in phosphorylation of these proteins. Depletion of Akt potentiated the apoptosis-inducing effect of BD whereas overexpression displayed resistance to BD-induced apoptosis suggesting the role of Akt in chemoresistance. Taken together, BD mitigates Akt-dependent signaling pathways in MM cells to impart its anticancer activity.

Unraveling the Potential Role of NEDD4-like E3 Ligases in Cancer

Cancer is a deadly disease worldwide, with an anticipated 19.3 million new cases and 10.0 million deaths occurring in 2020 according to GLOBOCAN 2020. It is well established that carcinogenesis and cancer development are strongly linked to genetic changes and post-translational modifications (PTMs). An important PTM process, ubiquitination, regulates every aspect of cellular activity, and the crucial enzymes in the ubiquitination process are E3 ubiquitin ligases (E3s) that affect substrate specificity and must therefore be carefully regulated. A surfeit of studies suggests that, among the E3 ubiquitin ligases, neuronal precursor cell-expressed developmentally downregulated 4 (NEDD4)/NEDD4-like E3 ligases show key functions in cellular processes by controlling subsequent protein degradation and substrate ubiquitination. In addition, it was demonstrated that NEDD4 mainly acts as an oncogene in various cancers, but also plays a tumor-suppressive role in some cancers. In this review, to comprehend the proper function of NEDD4 in cancer development, we summarize its function, both its tumor-suppressive and oncogenic role, in multiple types of malignancies. Moreover, we briefly explain the role of NEDD4 in carcinogenesis and progression, including cell survival, cell proliferation, autophagy, cell migration, invasion, metastasis, epithelial-mesenchymal transition (EMT), chemoresistance, and multiple signaling pathways. In addition, we briefly explain the significance of NEDD4 as a possible target for cancer treatment. Therefore, we conclude that targeting NEDD4 as a therapeutic method for treating human tumors could be a practical possibility.

Role of K63-linked ubiquitination in cancer

Ubiquitination is a critical type of post-translational modifications, of which K63-linked ubiquitination regulates interaction, translocation, and activation of proteins. In recent years, emerging evidence suggest involvement of K63-linked ubiquitination in multiple signaling pathways and various human diseases including cancer. Increasing number of studies indicated that K63-linked ubiquitination controls initiation, development, invasion, metastasis, and therapy of diverse cancers. Here, we summarized molecular mechanisms of K63-linked ubiquitination dictating different biological activities of tumor and highlighted novel opportunities for future therapy targeting certain regulation of K63-linked ubiquitination in tumor.

E3 ubiquitin ligase RNF6 promotes antiviral immune responses through enhancing the expression of interferon stimulated genes in myeloid cells

Interferon signaling is closely associated with clearance of viral infections as well as the development of systemic lupus erythematosus (SLE). Therefore, from a clinical perspective, it is important to identify the key regulators involved in interferon signaling pathways. In this study, we identified that RNF6, as an interferon inducible E3 ubiquitin ligase, promoted the interferon-dependent antiviral response. Knock-down of RNF6 greatly attenuated expression of ISGs and the transcriptional activity of ISRE. Specifically, increased RNF6 expression in myeloid cells of patients with SLE correlated with high expression of ISGs. Our results uncover RNF6 as a positive mediator in the antiviral immune responses and suggest that RNF6 may contribute to predict interferon signaling in SLE.

Proteomics and Biochemical Analyses of Secreted Proteins Revealed a Novel Mechanism by Which ADAM12S Regulates the Migration of Gastric Cancer Cells

Gastric cancer is one of the cancers with the highest morbidity and mortality. Although several therapeutic approaches have been developed to treat this disease, the overall survival rate is still very low due to metastasis, drug resistance, and so forth. Therefore, it is necessary to discover new regulatory molecules and signaling pathways that modulate the metastasis of gastric cancer cells. A Disintegrin And Metalloprotease 12 (ADAM12) was highly expressed in gastric cancer tissues and presented in the patient urine. However, it is unclear whether and how ADAM12 regulates the migration of gastric cancer cells. In this work, we used the secretome protein enrichment with click sugars (SPECS) method to purify the secreted glycosylated proteins and performed quantitative proteomics to identify the secreted proteins that were differentially regulated by ADAM12S, the short and secreted form of ADAM12. Our proteomic and biochemical analyses revealed that ADAM12S upregulated the cell surface glycoprotein CD146, a cell adhesion molecule and melanoma marker, which was dependent on the catalytic residue of ADAM12S. Furthermore, we discovered that the ADAM12S-enhanced migration of gastric cancer cells was, at least partially, mediated by CD146. This work may help to evaluate whether ADAM12 could be a potential therapeutic target for the treatment of gastric cancer patients.

Induction of zinc finger protein RNF6 auto-ubiquitination for the treatment of myeloma and chronic myeloid leukemia

The zinc finger ubiquitin ligase RNF6 has been proposed as a potential therapeutic target in several cancers, but understanding its molecular mechanism of degradation has been elusive. In the present study, we find that RNF6 is degraded via auto-ubiquitination in a manner dependent on its Really Interesting New Gene (RING) domain. We determine that when the RING domain is deleted (ΔRING) or the core cysteine residues in the zinc finger are mutated (C632S/C635S), the WT protein, but not the ΔRING or mutant RNF6 protein, undergoes polyubiquitination. We also identify USP7 as a deubiquitinase of RNF6 by tandem mass spectrometry. We show that USP7 interacts with RNF6 and abolishes its K48-linked polyubiquitination, thereby preventing its degradation. In contrast, we found a USP7-specific inhibitor promotes RNF6 polyubiquitination, degradation, and cell death. Furthermore, we demonstrate the anti-leukemic drug Nilotinib and anti-myeloma drug Panobinostat (LBH589) induce RNF6 K48-linked polyubiquitination and degradation in both multiple myeloma (MM) and leukemia cells. In agreement with our hypothesis on the mode of RNF6 degradation, we show these drugs promote RNF6 auto-ubiquitination in an in vitro ubiquitination system without other E3 ligases. Consistently, reexpression of RNF6 ablates drug-induced MM and leukemia cell apoptosis. Therefore, our results reveal that RNF6 is a RING E3 ligase that undergoes auto-ubiquitination, which could be abolished by USP7 and induced by anti-cancer drugs. We propose that chemical induction of RNF6 auto-ubiquitination and degradation could be a novel strategy for the treatment of hematological malignancies including MM and leukemia.

Emerging Roles of Non-proteolytic Ubiquitination in Tumorigenesis

Ubiquitination is a critical type of protein post-translational modification playing an essential role in many cellular processes. To date, more than eight types of ubiquitination exist, all of which are involved in distinct cellular processes based on their structural differences. Studies have indicated that activation of the ubiquitination pathway is tightly connected with inflammation-related diseases as well as cancer, especially in the non-proteolytic canonical pathway, highlighting the vital roles of ubiquitination in metabolic programming. Studies relating degradable ubiquitination through lys48 or lys11-linked pathways to cellular signaling have been well-characterized. However, emerging evidence shows that non-degradable ubiquitination (linked to lys6, lys27, lys29, lys33, lys63, and Met1) remains to be defined. In this review, we summarize the non-proteolytic ubiquitination involved in tumorigenesis and related signaling pathways, with the aim of providing a reference for future exploration of ubiquitination and the potential targets for cancer therapies.

Glaucocalyxin A Inhibits the Malignancies of Gastric Cancer Cells by Downregulating MDM2 and RNF6 via MiR-3658 and the SMG1-UPF mRNA Decay Pathway

Gastric cancer (GC) ranks as the most common gastrointestinal cancer and is among the leading causes of cancer death worldwide. Glaucocalyxin A (GLA), an entkauranoid diterpene isolated from Rab-dosia japonica var., possesses various bioactivities. To date, the data on the effect of GLA on GC are still minimal, and the molecular mechanisms remain largely unknown. Herein, we found that GLA could significantly inhibit the proliferation, cell adhesion, and invasion of HGT-1, SNU-1, SNU-6, and NCI-N87 GC cells in a dose-dependent manner. GLA enhanced the apoptosis of the GC cells as evidenced by the increased caspase-3 activity and the elevated levels of cleaved caspase-3 and cleaved PARP in GC cells in the presence of GLA. We then showed that the downregulation of Murine Double Minute Clone 2 (MDM2) and Ring Finger Protein 6 (RNF6) by GLA was implicated in the GLA-induced inhibition of the GC cells. Furthermore, MDM2 and RNF6 were identified as the targets of miR-3658 that was downregulated in the GC cells and upregulated by GLA. Moreover, it was shown that miR-3658 was hypermethylated in the GC cells, and GLA could rescue the expression of miR-3658 via demethylation by abrogating EZH2-mediated epigenetic silencing. In addition to the miR-3658-MDM2/RNF6 regulatory axis, activation of the SMG1-UPF mRNA decay pathway contributed to the downregulation of MDM2 and RNF6 by GLA in the GC cells. The inhibitory effect of GLA on gastric cancer and the expression of MDM2 and RNF6 was also validated in in vivo study. Our findings suggest that has the therapeutic potential for GC by downregulating oncogenes via posttranscriptional regulation.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

RING-finger protein 6 promotes colorectal tumorigenesis by transcriptionally activating SF3B2

RNF6 is a RING finger protein with oncogenic potential. In this study, we established colon-specific RNF6 transgenic (tg) mice, and demonstrated that RNF6 overexpression accelerated colorectal carcinogenesis compared to wild-type littermates in a chemically induced colorectal cancer (CRC) model. To understand whether transcriptional activity of RNF6 underlies its oncogenic effect, we performed integrated chromatin immunoprecipitation (ChIP)-sequencing and RNA-sequencing analysis to identify splicing factor 3b subunit 2 (SF3B2) as a potential downstream target of RNF6. RNF6 binds to the SF3B2 promoter and the overexpression of RNF6 activates SF3B2 expression in CRC cells, primary CRC organoids, and RNF6 tg mice. SF3B2 knockout abrogated the tumor promoting effect of RNF6 overexpression, whereas the reexpression of SF3B2 recused cell growth and migration/invasion in RNF6 knockout cells, indicating that SF3B2 is a functional downstream target of RNF6 in CRC. Targeting of RNF6-SF3B2 axis with SF3B2 inhibitor with pladienolide B suppressed the growth of CRC cells with RNF6 overexpression in vitro and in vivo. Moreover, the combination of 5-fluorouracil (5-FU) plus pladienolide B exerted synergistic effects in CRC with high RNF6 expression, leading to tumor regression in xenograft models. These findings indicate that tumor promoting effect of RNF6 is achieved mainly via transcriptional upregulation of SF3B2, and that RNF6-SF3B2 axis is a promising target for CRC therapy.

Acquired Glucocorticoid Resistance Due to Homologous Glucocorticoid Receptor Downregulation: A Modern Look at an Age-Old Problem

For over 70 years, the unique anti-inflammatory properties of glucocorticoids (GCs), which mediate their effects via the ligand-activated transcription factor, the glucocorticoid receptor alpha (GRα), have allowed for the use of these steroid hormones in the treatment of various autoimmune and inflammatory-linked diseases. However, aside from the onset of severe side-effects, chronic GC therapy often leads to the ligand-mediated downregulation of the GRα which, in turn, leads to a decrease in GC sensitivity, and effectively, the development of acquired GC resistance. Although the ligand-mediated downregulation of GRα is well documented, the precise factors which influence this process are not well understood and, thus, the development of an acquired GC resistance presents an ever-increasing challenge to the pharmaceutical industry. Recently, however, studies have correlated the dimerization status of the GRα with its ligand-mediated downregulation. Therefore, the current review will be discussing the major role-players in the homologous downregulation of the GRα pool, with a specific focus on previously reported GC-mediated reductions in GRα mRNA and protein levels, the molecular mechanisms through which the GRα functional pool is maintained and the possible impact of receptor conformation on GC-mediated GRα downregulation.

Proximity Labeling, Quantitative Proteomics, and Biochemical Studies Revealed the Molecular Mechanism for the Inhibitory Effect of Indisulam on the Proliferation of Gastric Cancer Cells

Indisulam exhibits antitumor activity against several cancer cells. Although the DCAF15-indisulam-RBM39 axis has been well documented in the inhibition of cancer cell growth, it is unknown whether RBM39 degradation alone is the mechanism of action of indisulam. Here, we verified the inhibitory effect of indisulam on the proliferation of gastric cancer cells and its dependence on DCAF15. Proximity-dependent biotin labeling with TurboID and quantitative proteomics revealed that indisulam indeed promoted the interaction between DCAF15 and RBM39. Immunoblotting and immunofluorescence also revealed that indisulam promoted the ubiquitin-mediated RBM39 degradation and RBM39 colocalized with DCAF15 in the nucleus. DCAF15 knockdown almost completely abolished the indisulam-mediated RBM39 reduction. Further knockdown of RBM39 eliminated the effect of DCAF15 on the proliferation of gastric cancer cells upon indisulam treatment. Immunoblotting of gastric tumor tissues confirmed the downregulation of RBM39 by indisulam. Database analysis unveiled that RBM39 was highly expressed in gastric cancer tissues and its high expression significantly shortened the survival time of gastric cancer patients. Taken together, we demonstrated that indisulam enhanced RBM39 ubiquitination and degradation by promoting its interaction with DCAF15, thus inhibiting the proliferation of gastric cancer cells. This work may provide valuable information for drug discovery through proteolysis targeting chimeras. MS data were deposited in ProteomeXchange (Dataset identifier: PXD024168).

RNF6 as an Oncogene and Potential Therapeutic Target—A Review

The RNF6 gene encodes Ring Finger Protein 6 (RNF6), which functions as a ubiquitin ligase. Its functions are not entirely known, but research shows that it is involved in human cancer development. Initially, this gene was considered to be a tumor suppressor. Numerous statistical analyses on cell lines and animals indicate, however, that RNF6 functions as an oncogene, involved in signaling pathways, including SHP1/STAT3, AKT/mTOR, Wnt/β-catenin, or ERα/Bcl-xL. Due to this fact, it has become a potential prognostic factor and therapeutic target. Studies in tumor cells and model organisms using inhibitors such as total saponins from Paris forrestii (TSPf), ellagic acid, or microRNA molecules show the effectiveness of inhibiting RNF6, and through it, the pathways of tumor cell proliferation. The results of the currently available studies are promising, but the function of RNF6 is not fully understood. More research is needed to assess the role of RNF6 and to check the safety and efficacy of inhibitors.

Latest perspectives on glucocorticoid-induced apoptosis and resistance in lymphoid malignancies

Glucocorticoids are essential drugs in the treatment protocols of lymphoid malignancies. These steroidal hormones trigger apoptosis of the malignant cells by binding to the glucocorticoid receptor (GR), which is a member of the nuclear receptor superfamily. Long term glucocorticoid treatment is limited by two major problems: the development of glucocorticoid-related side effects, which hampers patient quality of life, and the emergence of glucocorticoid resistance, which is a gradual process that is inevitable in many patients. This emphasizes the need to reevaluate and optimize the widespread use of glucocorticoids in lymphoid malignancies. To achieve this goal, a deep understanding of the mechanisms governing glucocorticoid responsiveness is required, yet, a recent comprehensive overview is currently lacking. In this review, we examine how glucocorticoids mediate apoptosis by detailing GR's genomic and non-genomic action mechanisms in lymphoid malignancies. We continue with a discussion of the glucocorticoid-related problems and how these are intertwined with one another. We further zoom in on glucocorticoid resistance by critically analyzing the plethora of proposed mechanisms and highlighting therapeutic opportunities that emerge from these studies. In conclusion, early detection of glucocorticoid resistance in patients remains an important challenge as this would result in a timelier treatment reorientation and reduced glucocorticoid-instigated side effects.

STAT3 Pathway in Gastric Cancer: Signaling, Therapeutic Targeting and Future Prospects

Molecular signaling pathways play a significant role in the regulation of biological mechanisms, and their abnormal expression can provide the conditions for cancer development. The signal transducer and activator of transcription 3 (STAT3) is a key member of the STAT proteins and its oncogene role in cancer has been shown. STAT3 is able to promote the proliferation and invasion of cancer cells and induces chemoresistance. Different downstream targets of STAT3 have been identified in cancer and it has also been shown that microRNA (miR), long non-coding RNA (lncRNA) and other molecular pathways are able to function as upstream mediators of STAT3 in cancer. In the present review, we focus on the role and regulation of STAT3 in gastric cancer (GC). miRs and lncRNAs are considered as potential upstream mediators of STAT3 and they are able to affect STAT3 expression in exerting their oncogene or onco-suppressor role in GC cells. Anti-tumor compounds suppress the STAT3 signaling pathway to restrict the proliferation and malignant behavior of GC cells. Other molecular pathways, such as sirtuin, stathmin and so on, can act as upstream mediators of STAT3 in GC. Notably, the components of the tumor microenvironment that are capable of targeting STAT3 in GC, such as fibroblasts and macrophages, are discussed in this review. Finally, we demonstrate that STAT3 can target oncogene factors to enhance the proliferation and metastasis of GC cells.

PTEN: What we know of the function and regulation of this onco-suppressor factor in bladder cancer?

Bladder cancer accounts for high morbidity and mortality around the world and its incidence rate is suggested to be higher in following years. A number of factors involve in bladder cancer development such as lifestyle and drugs. However, it appears that genetic factors play a significant role in bladder cancer development and progression. Phosphatase and tensin homolog (PTEN) is a cancer-related transcription factor that is corelated with reduced proliferation and invasion of cancer cells by negatively targeting PI3K/Akt/mTOR signaling pathway. In the present review, we aimed to explore the role of PTEN in bladder cancer cells and how upstream modulators affect PTEN in this life-threatening disorder. Down-regulation of PTEN is associated with poor prognosis, chemoresistance and progression of cancer cells. Besides, microRNAs, long non-coding RNAs, circular RNAs and other molecular pathways such as NF-kB are able to target PTEN in bladder cancer cells. Notably, anti-tumor drugs such as kaempferol, β-elemene and sorafenib upregulate the expression of PTEN to exert their inhibitory effects on bladder cancer cells.