Dual Deletion of Keap1 and Rbpjκ Genes in Liver Leads to Hepatomegaly and Hypercholesterolemia.

The hepatic deletion of Rbpjκ (RbpjF/F::AlbCre) in the mouse leads to exhibition of the Alagille syndrome phenotype during early postnatal liver development with hyperlipidemia and cholestasis due to attenuated disruption of NOTCH signaling. Given the roles of NRF2 signaling in the regulation of lipid metabolism and bile ductal formation, it was anticipated that these symptoms could be alleviated by enhancing NRF2 signaling in the RbpjF/F::AlbCre mouse by hepatic deletion of Keap1 in compound Keap1F/F::RbpjF/F::AlbCre mice. Unexpectedly, these mice developed higher hepatic and plasma cholesterol levels with more severe cholestatic liver damage during the pre-weaning period than in the RbpjF/F::AlbCre mice. In addition, hypercholesterolemia and hepatic damage were sustained throughout the growth period unlike in the RbpjF/F::AlbCre mouse. These enhanced abnormalities in lipid metabolism appear to be due to NRF2-dependent changes in gene expression related to cholesterol synthetic and subsequent bile acid production pathways. Notably, the hepatic expression of Cyp1A7 and Abcb11 genes involved in bile acid homeostasis was significantly reduced in Keap1F/F::RbpjF/F::AlbCre compared to RbpjF/F::AlbCre mice. The accumulation of liver cholesterol and the weakened capacity for bile excretion during the 3 pre-weaning weeks in the Keap1F/F::RbpjF/F::AlbCre mice may aggravate hepatocellular damage level caused by both excessive cholesterol and residual bile acid toxicity in hepatocytes. These results indicate that a tuned balance of NOTCH and NRF2 signaling is of biological importance for early liver development after birth.

Hypoxic environment promotes angiogenesis and bone bridge formation by activating Notch/RBPJ signaling pathway in HUVECs.

After epiphyseal fracture, the epiphyseal plate is prone to ischemia and hypoxia, leading to the formation of bone bridge and deformity. However, the exact mechanism controlling the bone bridge formation remains unclear. Notch/RBPJ signaling axis has been indicated to regulate angiogenesis and osteogenic differentiation. Our study aims to investigate the mechanism of bone bridge formation after epiphyseal plate injury, and to provide a theoretical basis for new therapeutic approaches to prevent the bone bridge formation. The expression of DLL4 and RBPJ was significantly up-regulated in HUVECs after ischemia and hypoxia treatment. Notch/RBPJ pathway positively regulated the osteogenic differentiation of BMSCs. HUVECs can induce osteogenic differentiation of BMSCs under ischemia and hypoxia. Notch/RBPJ pathway is involved in the regulation of the trans-epiphyseal bridge formation. Notch/RBPJ in HUVECs is associated with osteogenic differentiation of BMSCs and may participate in the regulation of the bone bridge formation across the epiphyseal plate.

NOTCH2 sensitizes the chondrocyte to the inflammatory response of tumor necrosis factor α.

Notch regulates the immune and inflammatory response and has been associated with the pathogenesis of osteoarthritis in humans and preclinical models of the disease. Notch2tm1.1Ecan mice harbor a NOTCH2 gain-of-function and are sensitized to osteoarthritis, but the mechanisms have not been explored. We examined the effects of tumor necrosis factor α (TNFα) in chondrocytes from Notch2tm1.1Ecan mice and found that NOTCH2 enhanced the effect of TNFα on Il6 and Il1b expression. Similar results were obtained in cells from a conditional model of NOTCH2 gain-of-function, Notch22.1Ecan mice, and following the expression of the NOTCH2 intracellular domain in vitro. Recombination signal-binding protein for immunoglobulin Kappa J region partners with the NOTCH2 intracellular domain to activate transcription; in the absence of Notch signaling it inhibits transcription, and Rbpj inactivation in chondrocytes resulted in Il6 induction. Although TNFα induced IL6 to a greater extent in the context of NOTCH2 activation, there was a concomitant inhibition of Notch target genes Hes1, Hey1, Hey2, and Heyl. Electrophoretic mobility shift assay demonstrated displacement of recombination signal-binding protein for immunoglobulin Kappa J region from DNA binding sites by TNFα explaining the increased Il6 expression and the concomitant decrease in Notch target genes. NOTCH2 enhanced the effect of TNFα on NF-κB signaling, and RNA-Seq revealed increased expression of pathways associated with inflammation and the phagosome in NOTCH2 overexpressing cells in the absence and presence of TNFα. Collectively, NOTCH2 has important interactions with TNFα resulting in the enhanced expression of Il6 and inflammatory pathways in chondrocytes.

RBPJ Deficiency Sensitizes Pancreatic Acinar Cells to KRAS-Mediated Pancreatic Intraepithelial Neoplasia Initiation.

BACKGROUND AND AIMS: Development of pancreatic ductal adenocarcinoma (PDAC) is a multistep process intensively studied; however, precocious diagnosis and effective therapy still remain unsatisfactory. The role for Notch signaling in PDAC has been discussed controversially, as both cancer-promoting and cancer-antagonizing functions have been described. Thus, an improved understanding of the underlying molecular mechanisms is necessary. Here, we focused on RBPJ, the receiving transcription factor in the Notch pathway, examined its expression pattern in PDAC, and characterized its function in mouse models of pancreatic cancer development and in the regeneration process after acute pancreatitis. METHODS: Conditional transgenic mouse models were used for functional analysis of RBPJ in the adult pancreas, initiation of PDAC precursor lesions, and pancreatic regeneration. Pancreata and primary acinar cells were tested for acinar-to-ductal metaplasia together with immunohistology and comprehensive transcriptional profiling by RNA sequencing. RESULTS: We identified reduced RBPJ expression in a subset of human PDAC specimens. Ptf1α-CreERT-driven depletion of RBPJ in transgenic mice revealed that its function is dispensable for the homeostasis and maintenance of adult acinar cells. However, primary RBPJ-deficient acinar cells underwent acinar-to-ductal differentiation in ex vivo. Importantly, oncogenic KRAS expression in the context of RBPJ deficiency facilitated the development of pancreatic intraepithelial neoplasia lesions with massive fibrotic stroma formation. Interestingly, RNA-sequencing data revealed a transcriptional profile associated with the cytokine/chemokine and extracellular matrix changes. In addition, lack of RBPJ delays the course of acute pancreatitis and critically impairs it in the context of KRASG12D expression. CONCLUSIONS: Our findings imply that downregulation of RBPJ in PDAC patients derepresses Notch targets and promotes KRAS-mediated pancreatic acinar cells transformation and desmoplasia development.

Rbpj Deficiency Disrupts Vascular Remodeling via Abnormal Apelin and Cdc42 (Cell Division Cycle 42) Activity in Brain Arteriovenous Malformation.

BACKGROUND: Brain arteriovenous malformations (bAVM) are characterized by enlarged blood vessels, which direct blood through arteriovenous shunts, bypassing the artery-capillary-vein network and disrupting blood flow. Clinically, bAVM treatments are invasive and not routinely applicable. There is critical need to understand mechanisms of bAVM pathologies and develop pharmacological therapies. METHODS: We used an in vivo mouse model of Rbpj-mediated bAVM, which develops pathologies in the early postnatal period and an siRNA in vitro system to knockdown RBPJ in human brain microvascular endothelial cells (ECs). To understand molecular events regulated by endothelial Rbpj, we conducted RNA-Seq and chromatin immunoprecipitation-Seq analyses from isolated brain ECs. RESULTS: Rbpj-deficient (mutant) brain ECs acquired abnormally rounded shape (with no change to cell area), altered basement membrane dynamics, and increased endothelial cell density along arteriovenous shunts, compared to controls, suggesting impaired remodeling of neonatal brain vasculature. Consistent with impaired endothelial cell dynamics, we found increased Cdc42 (cell division cycle 42) activity in isolated mutant ECs, suggesting that Rbpj regulates small GTPase (guanosine triphosphate hydrolase)-mediated cellular functions in brain ECs. siRNA-treated, RBPJ-deficient human brain ECs displayed increased Cdc42 activity, disrupted cell polarity and focal adhesion properties, and impaired migration in vitro. RNA-Seq analysis from isolated brain ECs identified differentially expressed genes in mutants, including Apelin, which encodes a ligand for G protein-coupled receptor signaling known to influence small GTPase activity. Chromatin immunoprecipitation-Seq analysis revealed chromatin loci occupied by Rbpj in brain ECs that corresponded to G-protein and Apelin signaling molecules. In vivo administration of a competitive peptide antagonist against the Apelin receptor (Aplnr/Apj) attenuated Cdc42 activity and restored endothelial cell morphology and arteriovenous connection diameter in Rbpj-mutant brain vessels. CONCLUSIONS: Our data suggest that endothelial Rbpj promotes rearrangement of brain ECs during cerebrovascular remodeling, through Apelin/Apj-mediated small GTPase activity, and prevents bAVM. By inhibiting Apelin/Apj signaling in vivo, we demonstrated pharmacological prevention of Rbpj-mediated bAVM.

Targeted inhibition of RBPJ transcription complex alleviates the exhaustion of CD8+ T cells in hepatocellular carcinoma.

Impaired function of CD8+ T cells in hepatocellular carcinoma (HCC) is an important reason for acquired resistance. Compared with single-target inhibitors, small-molecule compounds that could both inhibit tumor cells and alleviate T cell exhaustion are more promising to reduce resistance. In this study, we screened immunosuppressive targets in HCC by combining cancer-immunity cycle score with weighted gene co-expression network and system analysis. Through in vitro and in vivo validation experiments, we found that one of the screened molecules, recombination signal binding protein for immunoglobulin kappa J region (RBPJ), was negatively correlated with CD8+ T cell mediated killing function. More importantly, its transcription complex inhibitor RIN1 not only inhibited the malignant biological behaviors of HCC cells by inhibiting mTOR pathway, but also reduced the expression of PD-L1 and L-kynurenine synthesis in HCC cells, thus alleviating T cell exhaustion. Meanwhile, the combination of RIN1 and anti-PD-1/PD-L1 antibodies could further activate CD8+ T cells. In short, RBPJ is an important factor regulating the function of T cells. Target inhibition of RBPJ transcription complex by small molecule compound may be a new strategy for immunotherapy of HCC.

Endothelial Rbpj Is Required for Cerebellar Morphogenesis and Motor Control in the Early Postnatal Mouse Brain.

Intercellular influences are necessary for coordinated development and function of vascular and neural components in the brain. In the early postnatal period after birth, the mammalian cerebellum undergoes extensive morphogenesis - developing its characteristic lobules, organizing its diverse cell types into defined cellular layers, and establishing neural circuits that support cerebellar function, such as coordinated movement. In parallel, the cerebellar vasculature undergoes extensive postnatal growth and maturation, keeping pace with the expanding neural compartment. Endothelial deletion of Rbpj leads to neurovascular abnormalities in mice, including arteriovenous (AV) shunts that supplant capillaries and instead direct high-pressure/high-flow arterial blood directly to veins. Gross and histopathological cerebellar abnormalities, associated with these Rbpj-mediated brain AV malformations (AVMs), led to our hypothesis that early postnatal morphogenesis and lamination of cerebellum was perturbed in mice harboring endothelial Rbpj deficiency from birth. Here, we show that endothelial Rbpj-mutant mice developed enlarged vascular malformations on the cerebellar surface, by 2-week post-Rbpj deletion. In addition, outgrowth of cerebellar lobules was impaired through decreased cell proliferation, but not increased apoptosis, in the external granule layer. Molecular layer thickness was reduced, and the Purkinje layer was affected, by decreased Purkinje cell number, primary dendrite length, and dendritic arbor density. Endothelial deletion of Rbpj also led to impaired motor behaviors, consistent with abnormal cerebellar morphogenesis and lamination. Thus, our data suggest that Rbpj is required, in early postnatal vascular endothelium, to ensure proper cerebellar outgrowth, morphogenesis, and function in mice.

Endothelial Rbpj deletion normalizes Notch4-induced brain arteriovenous malformation in mice.

Upregulation of Notch signaling is associated with brain arteriovenous malformation (bAVM), a disease that lacks pharmacological treatments. Tetracycline (tet)-regulatable endothelial expression of constitutively active Notch4 (Notch4*tetEC) from birth induced bAVMs in 100% of mice by P16. To test whether targeting downstream signaling, while sustaining the causal Notch4*tetEC expression, induces AVM normalization, we deleted Rbpj, a mediator of Notch signaling, in endothelium from P16, by combining tet-repressible Notch4*tetEC with tamoxifen-inducible Rbpj deletion. Established pathologies, including AV connection diameter, AV shunting, vessel tortuosity, intracerebral hemorrhage, tissue hypoxia, life expectancy, and arterial marker expression were improved, compared with Notch4*tetEC mice without Rbpj deletion. Similarly, Rbpj deletion from P21 induced advanced bAVM regression. After complete AVM normalization induced by repression of Notch4*tetEC, virtually no bAVM relapsed, despite Notch4*tetEC re-expression in adults. Thus, inhibition of endothelial Rbpj halted Notch4*tetEC bAVM progression, normalized bAVM abnormalities, and restored microcirculation, providing proof of concept for targeting a downstream mediator to treat AVM pathologies despite a sustained causal molecular lesion.

Hsa_circ_0001535 Regulates Colorectal Cancer Progression via the miR-433-3p/RBPJ Axis.

A large number of studies have shown that circular RNAs (circRNAs) are of great significance in the occurrence and development of colorectal cancer (CRC). The purpose of this study was to explore the mechanism of circ_0001535 in CRC. The expressions of circ_0001535, miR-433-3p and recombination signal-binding protein Jκ (RBPJ) mRNA and protein in CRC tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. The effect of circ_0001535 on cell proliferation was detected using the Cell Counting Kit-8 (CCK-8) assay, colony formation assay and 5-ethynyl-2'-deoxyuridine (EdU) assay. The effects of circ_0001535 on migration, invasion, angiogenesis and apoptosis were investigated by wound healing assay, transwell assay, tube formation assay and flow cytometry, respectively. The interactions between miR-433-3p and circ_0001535 or RBPJ were studied using dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Xenograft tumor assay was performed to verify the role of circ_0001535 in tumor growth in vivo. The results showed that circ_0001535 and RBPJ mRNA expression levels were up-regulated and miR-433-3p was down-regulated in CRC tissues and cells. Circ_0001535 knockdown inhibited cell proliferation, migration, invasion, angiogenesis as well as promoted apoptosis in CRC cells. After analysis, it was found that circ_0001535 acted as a competing endogenous RNA (ceRNA) to inhibit miR-433-3p and then up-regulate RBPJ in CRC cells. In addition, in vivo experiment had shown that circ_0001535 knockdown inhibited tumor growth by up-regulating miR-433-3p and inhibiting RBPJ expression. The circ_0001535/miR-433-3p/ RBPJ axis plays a catalytic role in the progression of CRC, which may provide new insights into the molecular mechanism of CRC.

The structure, binding and function of a Notch transcription complex involving RBPJ and the epigenetic reader protein L3MBTL3.

The Notch pathway transmits signals between neighboring cells to elicit downstream transcriptional programs. Notch is a major regulator of cell fate specification, proliferation, and apoptosis, such that aberrant signaling leads to a pleiotropy of human diseases, including developmental disorders and cancers. The pathway signals through the transcription factor CSL (RBPJ in mammals), which forms an activation complex with the intracellular domain of the Notch receptor and the coactivator Mastermind. CSL can also function as a transcriptional repressor by forming complexes with one of several different corepressor proteins, such as FHL1 or SHARP in mammals and Hairless in Drosophila. Recently, we identified L3MBTL3 as a bona fide RBPJ-binding corepressor that recruits the repressive lysine demethylase LSD1/KDM1A to Notch target genes. Here, we define the RBPJ-interacting domain of L3MBTL3 and report the 2.06 Å crystal structure of the RBPJ-L3MBTL3-DNA complex. The structure reveals that L3MBTL3 interacts with RBPJ via an unusual binding motif compared to other RBPJ binding partners, which we comprehensively analyze with a series of structure-based mutants. We also show that these disruptive mutations affect RBPJ and L3MBTL3 function in cells, providing further insights into Notch mediated transcriptional regulation.

Endothelial RBPJ Is Essential for the Education of Tumor-Associated Macrophages.

Epithelial ovarian cancer (EOC) is one of the most lethal gynecologic cancers worldwide. EOC cells educate tumor-associated macrophages (TAM) through CD44-mediated cholesterol depletion to generate an immunosuppressive tumor microenvironment (TME). In addition, tumor cells frequently activate Notch1 receptors on endothelial cells (EC) to facilitate metastasis. However, further work is required to establish whether the endothelium also influences the education of recruited monocytes. Here, we report that canonical Notch signaling through RBPJ in ECs is an important player in the education of TAMs and EOC progression. Deletion of Rbpj in the endothelium of adult mice reduced infiltration of monocyte-derived macrophages into the TME of EOC and prevented the acquisition of a typical TAM gene signature; this was associated with stronger cytotoxic activity of T cells and decreased tumor burden. Mechanistically, CXCL2 was identified as a novel Notch/RBPJ target gene that regulated the expression of CD44 on monocytes and subsequent cholesterol depletion of TAMs. Bioinformatic analysis of ovarian cancer patient data showed that increased CXCL2 expression is accompanied by higher expression of CD44 and TAM education. Together, these findings indicate that EOC cells induce the tumor endothelium to secrete CXCL2 to establish an immunosuppressive microenvironment. SIGNIFICANCE: Endothelial Notch signaling favors immunosuppression by increasing CXCL2 secretion to stimulate CD44 expression in macrophages, facilitating their education by tumor cells.

Therapeutic targeting of RBPJ, an upstream regulator of ETV6 gene, abrogates ETV6-NTRK3 fusion gene transformations in glioblastoma.

Fusion genes are abnormal genes resulting from chromosomal translocation, insertion, deletion, inversion, etc. ETV6, a rather promiscuous partner forms fusions with several other genes, most commonly, the NTRK3 gene. This fusion leads to the formation of a constitutively activated tyrosine kinase which activates the Ras-Raf-MEK and PI3K/AKT/MAPK pathways, leading the cells through cycles of uncontrolled division and ultimately resulting in cancer. Targeted therapies against this ETV6-NTRK3 fusion protein are much needed. Therefore, to find a targeted approach, a transcription factor RBPJ regulating the ETV6 gene was established and since the ETV6-NTRK3 fusion gene is downstream of the ETV6 promoter/enhancer, this fusion protein is also regulated. The regulation of the ETV6 gene via RBPJ was validated by ChIP analysis in human glioblastoma (GBM) cell lines and patient tissue samples. This study was further followed by the identification of an inhibitor, Furamidine, against transcription factor RBPJ. It was found to be binding with the DNA binding domain of RBPJ with antitumorigenic properties and minimal organ toxicity. Hence, a new target RBPJ, regulating the production of ETV6 and ETV6-NTRK3 fusion protein was found along with a potent RBPJ inhibitor Furamidine.

Notch-dependent and -independent functions of transcription factor RBPJ.

Signal transduction pathways often involve transcription factors that promote activation of defined target gene sets. The transcription factor RBPJ is the central player in Notch signaling and either forms an activator complex with the Notch intracellular domain (NICD) or a repressor complex with corepressors like KYOT2/FHL1. The balance between these two antagonizing RBPJ-complexes depends on the activation state of the Notch receptor regulated by cell-to-cell interaction, ligand binding and proteolytic cleavage events. Here, we depleted RBPJ in mature T-cells lacking active Notch signaling and performed RNA-Seq, ChIP-Seq and ATAC-seq analyses. RBPJ depletion leads to upregulation of many Notch target genes. Ectopic expression of NICD1 activates several Notch target genes and enhances RBPJ occupancy. Based on gene expression changes and RBPJ occupancy we define four different clusters, either RBPJ- and/or Notch-regulated genes. Importantly, we identify early (Hes1 and Hey1) and late Notch-responsive genes (IL2ra). Similarly, to RBPJ depletion, interfering with transcriptional repression by squelching with cofactor KYOT2/FHL1, leads to upregulation of Notch target genes. Taken together, RBPJ is not only an essential part of the Notch co-activator complex but also functions as a repressor in a Notch-independent manner.

Interaction between BEND5 and RBPJ suppresses breast cancer growth and metastasis via inhibiting Notch signaling.

High frequent metastasis is the major cause of breast cancer (BC) mortality among women. However, the molecular mechanisms underlying BC metastasis remain largely unknown. Here, we identified six hub BC metastasis driver genes (BEND5, HSD11B1, NEDD9, SAA2, SH2D2A and TNFSF4) through bioinformatics analysis, among which BEND5 is the most significant gene. Low BEND5 expression predicted advanced stage and shorter overall survival in BC patients. Functional experiments showed that BEND5 could suppress BC growth and metastasis in vitro and in vivo. Mechanistically, BEND5 inhibits Notch signaling via directly interacting with transcription factor RBPJ/CSL. BEN domain of BEND5 interacts with the N-terminal domain (NTD) domain of RBPJ, thus preventing mastermind like transcriptional coactivator (MAML) from forming a transcription activation complex with RBPJ. Our study provides a novel insight into regulatory mechanisms underlying Notch signaling and suggests that BEND5 may become a promising target for BC therapy.

Notch effector recombination signal binding protein for immunoglobulin kappa J signaling is required for the initiation of endometrial stromal cell decidualization†.

The Notch signaling pathway is required for reproductive success. This pathway activates its transcriptional effector, recombination signal binding protein for immunoglobulin kappa J (Rbpj), to induce transcription of its target genes. This signaling pathway is required for successful decidualization, implantation, and uterine repair following parturition. To identify the compartmental specific roles of the Notch signaling pathway in the establishment of pregnancy, we generated epithelial and decidual stromal cell specific knockouts of Rbpj utilizing lactoferrin iCre and Prl8A2 iCre, respectively. Both conditional knockout mouse models were fertile. The Rbpj epithelial knockout mice displayed 27% resorption sites at E15.5, but this did not significantly impact the number of live born pups compared with controls. In addition, the Rbpj epithelial knockout mice displayed increased estrogen signaling in their stromal compartment. Given that both mouse models exhibited fertility comparable to control animals, the epithelial and stromal specific nature of the iCre recombinases utilized, and previously published Rbpj total uterine knockout mouse models, we conclude that Notch effector Rbpj signaling is required at the initiation of pregnancy to support decidualization in stromal cells, but that Rbpj is not required in the epithelial compartment nor is it required for post-implantation pregnancy success.

Analyzing the Interaction of RBPJ with Mitotic Chromatin and Its Impact on Transcription Reactivation upon Mitotic Exit.

The sequence-specific transcription factor RBPJ, also known as CSL (CBF1, Su(H), Lag1), is an evolutionarily conserved protein that mediates Notch signaling to guide cell fates. When cells enter mitosis, DNA is condensed and most transcription factors dissociate from chromatin; however, a few, select transcription factors, termed bookmarking factors, remain associated. These mitotic chromatin-bound factors are believed to play important roles in maintaining cell fates through cell division. RBPJ is one such factor that remains mitotic chromatin associated and therefore could function as a bookmarking factor. Here, we describe how to obtain highly purified mitotic cells from the mouse embryonal carcinoma cell line F9, perform chromatin immunoprecipitation with mitotic cells, and measure the first run of RNA synthesis upon mitotic exit. These methods serve as basis to understand the roles of mitotic bookmarking by RBPJ in propagating Notch signals through cell division.

RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells in both in vitro and in vivo studies.

Although Notch signalling pathway could control the proliferation and differentiation of neural stem cells (NSCs), it is largely unknown about the effect of Notch signalling pathway on the neurogenesis of CD133-positive cells. By using the primary cultured ependymal cells and the transgenic mouse, we found that CD133 immunoreactivity was exclusively localized in the ependymal layer of ventricles; moreover, most CD133-positive cells were co-labelled with Nestin. In addition, recombination signal binding protein J (RBP-J), a key nuclear effector of Notch signalling pathway, was highly active in CD133-positive cells. CD133-positive cells can differentiate into the immature and mature neurons; in particular, the number of CD133-positive cells differentiating into the immature and mature neurons was significantly increased following the deficiency or interference of RBP-J in vivo or in vitro. By using real-time qPCR and Western blot, we found that RBP-J and Hes1 were downregulated, whereas Notch1 was upregulated in the expression levels of mRNAs and proteins following the deficiency or interference of RBP-J. These results demonstrated RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells. Therefore, we speculated that RBP-J could maintain CD133-positive cells in the characteristics of NSCs possibly by regulating Notch1/RBP-J/Hes1 pathway. It will provide a novel molecular insight into the function of RBP-J as well as facilitate a future investigation of CD133-positive cells with respect to their potential application in neurodegenerative disorder.

RITA1 drives the growth of bladder cancer cells by recruiting TRIM25 to facilitate the proteasomal degradation of RBPJ.

Bladder cancer (BC) is one of the most prevalent malignancies worldwide, but it lacks effective targeted therapy due to its elusive molecular mechanism. Therefore, it is important to further investigate the molecular mechanisms that mediate BC progression. By performing a tumor tissue-based gene microarray and shRNA library screening, we found that recombination signal binding protein for immunoglobulin kappa J region (RBPJ) interacting and tubulin associated 1 (RITA1) is crucial for the growth of BC cells. Moreover, RITA1 is aberrantly highly expressed in BC tissues and is also correlated with poor prognosis in patients with BC. Mechanistically, we determined that RITA1 recruits tripartite motif containing 25 (TRIM25) to ubiquitinate RBPJ to accelerate its degradation via proteasome, which leads to the transcriptional inhibition of Notch1 downstream targets. Our results suggest that aberrant high expression of RITA1 drives the growth of BC cells via the RITA1/TRIM25/RBPJ axis and RITA1 may serve as a promising therapeutic target for BC.

The RBPJ/DAPK3/UBE3A signaling axis induces PBRM1 degradation to modulate the sensitivity of renal cell carcinoma to CDK4/6 inhibitors.

Renal cell carcinoma (RCC) is a kind of malignant tumor originating from the renal tubular epithelium. Approximately 30% of patients with renal cancer are found to have metastasis when first diagnosed. Exploring other effective treatment methods in addition to surgery is an urgent need in the research field of renal cell carcinoma. Polybromo 1 (PBRM1) is the second most mutated gene in RCC, with a mutation rate of ~40%. Notably, the posttranscriptional modification of PBRM1 in RCC is unclear. In this study, we performed unbiased mass spectrometry of PBRM1 and identified ubiquitin-protein ligase E3A (UBE3A), an extensively studied E3 ligase that can bind with PBRM1 and regulate the stability of PBRM1 in renal cancer cells. We further found that RBPJ/DAPK3 modulated the E3 ligase activity of UBE3A by interfering with the PKA phosphorylation of UBE3A. Finally, we demonstrated that the RBPJ/DAPK3/UBE3A/PBRM1/p21 axis contributed to the sensitivity of renal cancer cells to CDK4/6 inhibitors. In addition, in combination with RBPJ inhibitors, CDK4/6 inhibitors showed synergistically enhanced effects on renal cancer cells. In summary, we not only revealed a novel RBPJ/DAPK3/UBE3A/PBRM1/p21 signaling axis but also identified a combination strategy for overcoming the resistance of renal cancer cells to CDK4/6 inhibitors.