Chromatin regulators in retinoblastoma: Biological roles and therapeutic applications

Therapeutic Strategies for RB1-Deficient Cancers: Intersecting Gene Regulation and Targeted Therapy

The retinoblastoma (RB) transcriptional corepressor 1 (RB1) is a critical tumor suppressor gene, governing diverse cellular processes implicated in cancer biology. Dysregulation or deletion in RB1 contributes to the development and progression of various cancers, making it a prime target for therapeutic intervention. RB1's canonical function in cell cycle control and DNA repair mechanisms underscores its significance in restraining aberrant cell growth and maintaining genomic stability. Understanding the complex interplay between RB1 and cellular pathways is beneficial to fully elucidate its tumor-suppressive role across different cancer types and for therapeutic development. As a result, investigating vulnerabilities arising from RB1 deletion-associated mechanisms offers promising avenues for targeted therapy. Recently, several findings highlighted multiple methods as a promising strategy for combating tumor growth driven by RB1 loss, offering potential clinical benefits in various cancer types. This review summarizes the multifaceted role of RB1 in cancer biology and its implications for targeted therapy.

EZH2 Promotes Corneal Endothelial Cell Apoptosis by Mediating H3K27me3 and Inhibiting HO-1 Transcription

PURPOSE

This paper aims to explore the molecular mechanism of Enhancer of Zeste Homolog 2 (EZH2)-mediated H3K27me3 in human corneal endothelial cells (HCEC) apoptosis by inhibiting Heme oxygenase-1 (HO-1) transcription to provide a potential target for the treatment of corneal apoptosis.

METHODS

HCECs were cultured in vitro and transfected with si-EZH2, pcDNA3.1-EZH2, pcDNA3.1-HO-1, GSK-J4 (an effective H3K27me3 demethylase inhibitor), and corresponding controls. Western Blot assay was used to detect the levels of EZH2, HO-1, H3K27me3, and apoptosis-related proteins (Bcl-2, Bax, and Cleaved-caspase-3) in HCECs; CCK-8 assay was conducted to detect cell viability and flow cytometry to analyze the apoptosis. HO-1 mRNA levels were detected by RT-qPCR and changes in H3K27me3 levels on the HO-1 promoter were detected by chromatin immunoprecipitation.

RESULTS

HCECs transfected with si-EZH2 showed significantly lower EZH2 mRNA and protein levels, higher HCEC viability, lower apoptosis rates, higher antiapoptotic protein Bcl-2 expression, lower proapoptotic protein (Bax and Cleaved-caspase-3) levels, and significantly higher HO-1 expression. HCECs transfected with pcDNA3.1-EZH2 showed the opposite results. EZH2 repressed HO-1 transcription by mediating H3K27me3. H3K27me27 was enriched in the HO-1 promoter and overexpression of EZH2 increased H3K27me27 levels. Promotion of H3K27me3 partially reversed the mitigating effect of si-EZH2 on HCEC apoptosis. Overexpression of HO-1 partially reversed the apoptosis-promoting effects of EZH2 and H3K27me3 on HCECs.

CONCLUSIONS

EZH2 promotes HCE cell apoptosis by mediating H3K27me3 to inhibit HO-1 transcription.

BET Inhibition Sensitizes Immunologically Cold Rb-Deficient Prostate Cancer to Immune Checkpoint Blockade

Non-T-cell-inflamed immunologically "cold" tumor microenvironments (TME) are associated with poor responsiveness to immune checkpoint blockade (ICB) and can be sculpted by tumor cell genomics. Here, we evaluated how retinoblastoma (Rb) tumor-suppressor loss-of-function (LOF), one of the most frequent alterations in human cancer and associated with lineage plasticity, poor prognosis, and therapeutic outcomes, alters the TME, and whether therapeutic strategies targeting the molecular consequences of Rb loss enhance ICB efficacy. We performed bioinformatics analysis to elucidate the impact of endogenous Rb LOF on the immune TME in human primary and metastatic tumors. Next, we used isogenic murine models of Rb-deficient prostate cancer for in vitro and in vivo mechanistic studies to examine how Rb loss and bromodomain and extraterminal (BET) domain inhibition (BETi) reprograms the immune landscape, and evaluated in vivo therapeutic efficacy of BETi, singly and in combination with ICB and androgen deprivation therapy. Rb loss was enriched in non-T-cell-inflamed tumors, and Rb-deficient murine tumors demonstrated decreased immune infiltration in vivo. The BETi JQ1 increased immune infiltration into the TME through enhanced tumor cell STING/NF-κB activation and type I IFN signaling within tumor cells, resulting in differential macrophage and T-cell-mediated tumor growth inhibition and sensitization of Rb-deficient prostate cancer to ICB. BETi can reprogram the immunologically cold Rb-deficient TME via STING/NF-κB/IFN signaling to sensitize Rb-deficient prostate cancer to ICB. These data provide the mechanistic rationale to test combinations of BETi and ICB in clinical trials of Rb-deficient prostate cancer.

Development and validation of a chromatin regulator prognostic signature in colon adenocarcinoma

Aberrant expression of chromatin regulators (CRs) could lead to the development of various diseases including cancer. However, the biological function and prognosis role of CRs in colon adenocarcinoma (COAD) remains unclear. We performed the clustering analyses for expression profiling of COAD downloaded from The Cancer Genome Atlas. We developed a chromatin regulator prognostic model, which was validated in an independent cohort data. Time-intendent receiver operating characteristics curve was used to evaluate predict ability of model. Univariate and multivariate cox regression were used to assess independence of risk score. Nomogram was established to assess individual risk. Gene ontology, and Kyoto Encyclopedia of genes and genomes, gene set variation analysis and gene set enrichment analysis were performed to explore the function of CRs. Immune infiltration and drug sensitivity were also performed to assess effect of CRs on treatment in COAD. COAD can be separated into two subtypes with different clinical characteristics and prognosis. The C2 had elevated immune infiltration levels and low tumor purity. Using 12 chromatin regulators, we developed and validated a prognostic model that can predict the overall survival of COAD patients. We built a risk score that can be an independent prognosis predictor of COAD. The nomogram score system achieved the best predict ability and were also confirmed by decision curve analysis. There were significantly different function and pathway enrichment, immune infiltration levels, and tumor mutation burden between high-risk and low-risk group. The external validation data also indicated that high-risk group had higher stable disease/progressive disease response rate and poorer prognosis than low-risk group. Besides, the signature genes included in the model could cause chemotherapy sensitivity to some small molecular compounds. Our integrative analyses for chromatin regulators could provide new insights for the risk management and individualized treatment in COAD.

Retinoblastoma: Review and new insights

Retinoblastoma (Rb), the most frequent malignant intraocular tumor in childhood, is caused by mutations in the retinoblastoma gene (RB1) situated on chromosome 13q14.2. The incidence of retinoblastoma is approximately 1 in 17,000 live births with approximately 8,000 new cases diagnosed each year worldwide. Rb is the prototypical hereditary cancer in humans. Autosomal dominant inheritance is seen in 30-40% of cases whereas the non-inherited sporadic type accounts for the remaining 60-70%. Rb arises due to inactivation of both alleles of the Rb tumor suppressor gene, which results in a defective Rb protein (pRB) with subsequent cell cycle impairment and uncontrolled cell proliferation. Patients with Rb have survival rates higher than 95-98% in industrialized countries but mortality remains high in developing countries. For example, the mortality rate in Africa is 70%. In all cases of intraocular and extraocular retinoblastoma, there is a need for new therapies that are more effective and carry less risk of toxicity. The Bruckner test is a practical and easy test for the detection of Rb, this test consists of assessing the fundus reflex through the pupil (red reflex) in both eyes simultaneously with a bright coaxial light produced with the direct ophthalmoscope. Rb can be detected by the Bruckner test showing a pupil that shines white or “Leukocoria”. Although the diagnosis of Rb remains essentially clinical, the newly identified biomarkers could contribute to early molecular detection, timely detection of micrometastases and establish new therapeutic options for Rb.

Comprehensive Analysis of Serum Small Extracellular Vesicles-Derived Coding and Non-Coding RNAs from Retinoblastoma Patients for Identifying Regulatory Interactions

The present study employed nanoparticle tracking analysis, transmission electron microscopy, immunoblotting, RNA sequencing, and quantitative real-time PCR validation to characterize serum-derived small extracellular vesicles (sEVs) from RB patients and age-matched controls. Bioinformatics methods were used to analyze functions, and regulatory interactions between coding and non-coding (nc) sEVs RNAs. The results revealed that the isolated sEVs are round-shaped with a size < 150 nm, 5.3 × 1011 ± 8.1 particles/mL, and zeta potential of 11.1 to −15.8 mV, and expressed exosome markers CD9, CD81, and TSG101. A total of 6514 differentially expressed (DE) mRNAs, 123 DE miRNAs, and 3634 DE lncRNAs were detected. Both miRNA-mRNA and lncRNA-miRNA-mRNA network analysis revealed that the cell cycle-specific genes including CDKNI1A, CCND1, c-MYC, and HIF1A are regulated by hub ncRNAs MALAT1, AFAP1-AS1, miR145, 101, and 16-5p. Protein-protein interaction network analysis showed that eye-related DE mRNAs are involved in rod cell differentiation, cone cell development, and retinol metabolism. In conclusion, our study provides a comprehensive overview of the RB sEV RNAs and regulatory interactions between them.

Advances in the research of plant-derived natural products against retinoblastoma

Retinoblastoma (RB) is a highly aggressive ocular tumor, and due to socioeconomic and medical constraints, many children receive treatment only in the metaphase and advanced clinical stages, resulting in high rates of blindness and disability. Although several approaches exist in the treatment of RB, some children with the disease do not have satisfactory results because of various factors. Plant-derived natural products have shown definite therapeutic effects in the treatment of various tumors and are also widely used in the study of RB. We review plant-derived natural products used in the study of anti-RB to provide ideas for the clinical application of these drugs and the development of new therapeutic drugs.

Genome maintenance in retinoblastoma: Implications for therapeutic vulnerabilities (Review)

Retinoblastoma (RB) is a pediatric ocular malignancy that is initiated mostly by biallelic inactivation of the RB transcriptional corepressor 1 (RB1) tumor suppressor gene in the developing retina. Unlike the prevailing prediction based on multiple studies involving RB1 gene disruption in experimental models, human RB tumors have been demonstrated to possess a relatively stable genome, characterized by a low mutation rate and a few recurrent chromosomal alterations related to somatic copy number changes. This suggests that RB may harbor heightened genome maintenance mechanisms to counteract or compensate for the risk of massive genome instability, which can potentially be driven by the early RB1 loss as a tumor-initiating event. Although the genome maintenance mechanisms might have been evolved to promote RB cell survival by preventing lethal genomic defects, emerging evidence suggests that the dependency of RB cells on these mechanisms also exposes their unique vulnerability to chemotherapy, particularly when the genome maintenance machineries are tumor cell-specific. This review summarizes the genome maintenance mechanisms identified in RB, including findings on the roles of chromatin regulators in DNA damage response/repair and protein factors involved in maintaining chromosome stability and promoting survival in RB. In addition, advantages and challenges for exploiting these therapeutic vulnerabilities in RB are discussed.

Applications of Non-Coding RNAs in Patients With Retinoblastoma

Retinoblastoma (RB) is the most common primary intraocular malignancy in childhood. In the carcinogenic process of neoplasms such as RB, the role of non-coding RNAs (ncRNAs) has been widely demonstrated recently. In this review, we aim to provide a clinical overview of the current knowledge regarding ncRNAs in relation to RB. Although ncRNAs are now considered as potential diagnostic biomarkers, prognostic factors, and therapeutic targets, further studies will facilitate enhanced understanding of ncRNAs in RB physiopathology and define the roles ncRNAs can play in clinical practice.

Targeting of histone methyltransferase DOT1L plays a dual role in chemosensitization of retinoblastoma cells and enhances the efficacy of chemotherapy

Aberrant and exclusive expression of chromatin regulators in retinoblastoma (RB) in contrast to terminally differentiated normal retina presents a unique opportunity of selective targeting for RB. However, precise roles of these chromatin regulators in RB development and their potential as therapeutic targets have not been defined thoroughly. Here, we report that targeting of disruptor of telomeric silencing 1-like (DOT1L), a histone H3K79 methyltransferase, sensitizes RB cells to chemotherapeutic drugs by impairing the DNA damage response and thereby potentiating apoptosis while it is largely inefficacious as a single-agent therapy. Moreover, we identified high mobility group AT-hook 2 (HMGA2) as a novel DOT1L target gene in RB cells and found that its aberrant expression is dependent on DOT1L. As HMGA2 depletion reduced CHK1 phosphorylation during DNA damage response and augmented the drug sensitivity in RB cells, our results suggested that DOT1L targeting has a dual role in chemosensitization of RB cells by directly interfering with the immediate involvement of DOT1L in early DNA damage response upon genotoxic insults and also by downregulating the expression of HMGA2 as a rather late effect of DOT1L inhibition. Furthermore, we provide the first preclinical evidence demonstrating that combined therapy with a DOT1L inhibitor significantly improves the therapeutic efficacy of etoposide in murine orthotopic xenografts of RB by rendering the response to etoposide more potent and stable. Taken together, these results support the therapeutic benefits of DOT1L targeting in combination with other chemotherapeutic agents in RB, with mechanistic insights into how DOT1L targeting can improve the current chemotherapy in an RB cell-selective manner.

RNF12 Promotes Glioblastoma Malignant Proliferation via Destructing RB1 and Regulating MAPK Pathway

Background

RNF12 has been linked to a variety of biological activities, including the control of the MDM2/P53 pathway, although its additional functions remain unclear. RNF12 was discovered to be a new ubiquitin ligase (E3) for RB1, amongst the most frequently repressed proteins in cancer of human.

Method

Cell Counting Kit-8 was used to detect the cell proliferation; coimmunoprecipitation was used to determine that RNF12 interacts with RB1. Xenograft studies were used to verify the results.

Result

In vivo and in vitro RNF12 interacts with RB1 regardless of E3 ligase activity. The ubiquitination of RB1 by RNF12 had an effect on its stability. RNF12 inhibits the RB1 protein and stimulates the MAPK pathway, promoting the growth of GBMs.

Conclusion

Our findings show that RNF12 may operate as a tumour promoter by modulating the cancerous proliferation of glioblastoma by controlling the activity of a new RNF12/RB1/MAPK pathway regulatory axis and that this regulatory axis might be a valuable diagnostic focus in glioblastoma.

Netrin-1 promotes retinoblastoma-associated angiogenesis

BACKGROUND

Retinoblastoma (Rb) is the most common intraocular cancer of infancy and childhood, with an incidence of nearly 0.006% in all live births. Although a functional loss or inactivation of both alleles of the retinoblastoma 1 (RB1) gene during retinal development appears to be the predominant etiology for Rb, genes associated with tumor angiogenesis are also likely to be involved in the development of this condition. Netrin-1 is a factor that regulates pathological angiogenesis, while its role in Rb is largely unknown. The present study examined the role of netrin-1 in Rb.

METHODS

The expression of netrin-1 in Rb was assessed using public databases and using clinical specimens by RT-qPCR for mRNA and by ELISA for protein. The expression of netrin-1 was suppressed in Rb by siRNA and the effects on cell growth were determined by a CCK-8 assay, while the effects on angiogenesis were examined in vitro using human umbilical vein endothelial cell (HUVEC) assays and in vivo by quantification of tumor vessel density.

RESULTS

Analysis of published databases revealed that the netrin-1 gene is significantly upregulated in Rb, which was confirmed by immunohistochemistry on clinical specimens. Inhibition of netrin-1 in Rb cell lines significantly reduced their effects on angiogenesis in vitro using a HUVEC co-culture assay without affecting cell growth. Inhibition of netrin-1 expression in vivo suppressed the growth of grafted Rb, and this effect could be abolished by co-expression of vascular endothelial growth factor A (VEGF-A).

CONCLUSIONS

This data demonstrated a novel role for netrin-1 in the regulation of Rb-associated cancer vascularization and may represent a novel therapeutic target for patients with Rb.

Roles of the microRNA‑338‑3p/NOVA1 axis in retinoblastoma

Retinoblastoma (RB) is an intraocular malignancy that mainly affects young children. Previous reports have demonstrated that mutations or the inactivation of the RB1 gene were the main cause of RB; however, disruption of the intracellular signaling pathways following deficiency of RB1 requires further investigation. Based on the Gene Expression Omnibus data and bioinformatics prediction, the present study aimed to investigate the microRNA (miR)-338-3p/neuro-oncological ventral antigen 1 (NOVA1) axis in RB. Subsequently, overexpression and knockdown of miR-338-3p and NOVA1, respectively, were performed to study the role of miR-338-3p/NOVA1 in the progression of the RB cells. The results demonstrated that overexpression of miR-338-3p significantly inhibited cell proliferation, migration and invasion, and promoted apoptosis of the RB cells. Moreover, knockdown of NOVA1 showed similar results. A dual-luciferase reporter assay and rescue experiments further confirmed the direct binding between miR-338-3p and NOVA1. Taken together, the results indicated that miR-338-3p acted as tumor suppressor by targeting the oncogene of NOVA1 in RB, which may serve as potential therapeutic targets in RB.

Chromatin regulators in retinoblastoma: Biological roles and therapeutic applications

Retinoblastoma (RB) is a pediatric ocular tumor mostly occurring due to the biallelic loss of RB1 gene in the developing retina. Early studies of genomic aberrations in RB have provided a valuable insight into how RB can progress following the tumor-initiating RB1 mutations and have established a notion that inactivation of RB1 gene is critical to initiate RB but this causative genetic lesion alone is not sufficient for malignant progression. With the advent of high-throughput sequencing technologies, we now have access to the comprehensive genomic and epigenetic landscape of RB and have come to appreciate that RB tumorigenesis requires both genetic and epigenetic alterations that might be directly or indirectly driven by RB1 loss. This integrative perspective on RB tumorigenesis has inspired research efforts to better understand the types and functions of epigenetic mechanisms contributing to RB development, leading to the identification of multiple epigenetic regulators misregulated in RB in recent years. A complete understanding of the intricate network of genetic and epigenetic factors in modulation of gene expression during RB tumorigenesis remains a major challenge but would be crucial to translate these findings into therapeutic interventions. In this review, we will provide an overview of chromatin regulators identified to be misregulated in human RB among the numerous epigenetic factors implicated in RB development. For a subset of these chromatin regulators, recent findings on their functions in RB development and potential therapeutic applications are discussed.