RNA-binding protein RBM24 regulates p63 expression via mRNA stability

Role of rs873601 Polymorphisms in Prognosis of Lung Cancer Patients Treated with Platinum-Based Chemotherapy

BACKGROUND

Lung cancer is still the most lethal malignancy in the world, according to the report of Cancer Statistics in 2021. Platinum-based chemotherapy combined with immunotherapy is the first-line treatment in lung cancer patients. However, the 5-year survival rate is always affected by the adverse reactions and drug resistance caused by platinum-based chemotherapy. DNA damage and repair system is one of the important mechanisms that can affect the response to chemotherapy and clinical outcomes in lung cancer patients.

OBJECTIVE

The objective of this study is to find the relationship between the polymorphisms of DNA repair genes with the prognosis of platinum-based chemotherapy in lung cancer patients.

PATIENTS AND METHODS

We performed genotyping in 17 single nucleotide polymorphisms (SNPs) of Excision Repair Cross-Complementation group (ERCC) genes and X-ray Repair Cross-Complementing (XRCC) genes of 345 lung cancer patients via Sequenom MassARRAY. We used Cox proportional hazard models, state, and plink to analyze the associations between SNPs and the prognosis of lung cancer patients.

RESULTS

We found that the ERCC5 rs873601 was associated with the overall survival time in lung cancer patients treated with platinum-based chemotherapy (p = 0.031). There were some polymorphisms that were related to the prognosis in specific subgroups of lung cancer. Rs873601 showed a great influence on the prognosis of patients more than 55 years, Small Cell Lung Cancer (SCLC), and smoking patients. Rs2444933 was associated with prognosis in age less than 55 years, SCLC, metastasis, and stage III/IV/ED patients. Rs3740051 played an important role in the prognosis of SCLC and metastasis patients. Rs1869641 was involved in the prognosis of SCLC patients. Rs1051685 was related to the prognosis in non-metastasis patients.

CONCLUSION

The ERCC5 rs873601 (G>A) was a valuable biomarker for predicting the prognosis in lung cancer patients treated with platinum-based chemotherapy.

RBM24 is required for mouse hair cell development through regulating pre-mRNA alternative splicing and mRNA stability

As the sensory receptor cells in vertebrate inner ear and lateral lines, hair cells are characterized by the hair bundle that consists of one tubulin-based kinocilium and dozens of actin-based stereocilia on the apical surface of each hair cell. Hair cell development is tightly regulated, and deficits in this process usually lead to hearing loss and/or balance dysfunctions. RNA-binding motif protein 24 (RBM24) is an RNA-binding protein that is specifically expressed in the hair cells in the inner ear. Previously, we showed that RBM24 affects hair cell development in zebrafish by regulating messenger RNA (mRNA) stability. In the present work, we further investigate the role of RBM24 in hearing and balance using conditional knockout mice. Our results show that Rbm24 knockout results in severe hearing and balance deficits. Hair cell development is significantly affected in Rbm24 knockout cochlea, as the hair bundles are poorly developed and eventually degenerated. Hair bundle disorganization is also observed in Rbm24 knockout vestibular hair cells, although to a lesser extent. Consistently, significant hair cell loss is observed in the cochlea but not vestibule. RNAseq analysis identified several genes whose mRNA stability or pre-mRNA alternative splicing is affected by Rbm24 knockout. Among them are Cdh23, Pcdh15, and Myo7a, which have been shown to play important roles in stereocilia development as well as mechano-electrical transduction. Taken together, our present work suggests that RBM24 is required for mouse hair cell development through regulating pre-mRNA alternative splicing as well as mRNA stability.

Cellular activity of autophagy and multivesicular bodies in lens fiber cells during early lens development in rbm24a mutant of zebrafish: Ultrastructure analysis

Use of zebrafish as animal model for various diseases during early developmental stages has been exponentially increased with the aim to achieve the best representative results in this transparent fish. Recent studies documented that Rbm24a mutant causes cataract formation and resulted in blindness using the zebrafish model. Therefore, correct interpretation of studies that aimed for molecular approaches, a description of comparative and in-depth analysis of development of lens in wildtype and mutant is crucial to obtain the correct conclusion. In this study, we use a gold standard method the Transmission Electron Microscopy (TEM) to analysis the lens development in rbm24a mutant zebrafish. Firstly, we compare the cellular structures at 16-20 h post fertilization (hpf), the lens placode in ectoderm indicated delay lens development in rbm24a mutant than wildtype (siblings) zebrafish. At 33 hpf, loosely appeared lens fiber cells showed heterogenous electron density with numbers of mitochondria in lens of rbm24a mutant, revealed the influence of gene mutation in lens development. A detail ultrastructure of lens of rbm24a mutant also presented at 33 hpf. Comparatively in wildtype (siblings) at 33 hpf, lens exhibited homogenous electron density in tightly packed lens fiber cells with few mitochondria. Furthermore, to characterize the lens in rbm24a mutant we obtained data of cellular structures on 25 hpf and 1.5 days' post fertilization (dpf). At 25 hpf in mutant zebrafish, the detached solid sphere lens mass from ectoderm showed karyorrhexis, mitophagy and vesicles (also multivesicular bodies), these cellular structures supposed to hamper the development of future fiber cells. Moreover, at 1.5 dpf in mutant, nuclear excisosome, multilamellar bodies and irregular shaped mitochondria in heterogenous electron dense cytoplasm of lens fiber cells, collectively shown affected lens transparency. In summary the ultrastructure results of lens of rbm24a mutant zebrafish expand our knowledge and give reflection of different cellular activities like autophagy, apoptosis, vesicles (multivesicular bodies) and nuclear excisosomes which play their role in transparency achievement.

RBM24 inhibits the translation of SARS-CoV-2 polyproteins by targeting the 5'-untranslated region

SARS-CoV-2 is a betacoronavirus with single-stranded positive-sense RNA, which is a serious global threat to human health. Understanding the molecular mechanism of viral replication is crucial for the development of antiviral drugs. The synthesis of viral polyproteins is a crucial step in viral progression. The synthesis of viral polyproteins in coronaviruses is regulated by the 5'-untranslated region (UTR); however, the detailed regulatory mechanism needs further investigation. The present study demonstrated that the RNA binding protein, RBM24, interacts with the RNA genome of SARS-CoV-2 via its RNA recognition submotifs (RNPs). The findings revealed that RBM24 recognizes and binds to the GUGUG element at stem-loop 4 (SL4) in the 5'-UTR of SARS-CoV-2. The interaction between RBM24 and 5'-UTR prevents 80S ribosome assembly, which in turn inhibits polyproteins translation and the replication of SARS-CoV-2. Notably, other RNA viruses, including SARS-CoV, MERS-CoV, Ebolavirus, rhinovirus, West Nile virus, Zika virus, Japanese encephalitis virus, yellow fever virus, hepatitis C virus, and human immunodeficiency virus-1 also contain one or several G(U/C/A)GUG sequences in the 5'-UTR, which is also targeted by RBM24. In conclusion, the present study demonstrated that RBM24 functions by interacting with the 5'-UTR of SARS-CoV-2 RNA, and elucidated that RBM24 could be a host restriction factor for SARS-CoV-2 and other RNA viruses.

The dual role of p63 in cancer

The p53 family is made up of three transcription factors: p53, p63, and p73. These proteins are well-known regulators of cell function and play a crucial role in controlling various processes related to cancer progression, including cell division, proliferation, genomic stability, cell cycle arrest, senescence, and apoptosis. In response to extra- or intracellular stress or oncogenic stimulation, all members of the p53 family are mutated in structure or altered in expression levels to affect the signaling network, coordinating many other pivotal cellular processes. P63 exists as two main isoforms (TAp63 and ΔNp63) that have been contrastingly discovered; the TA and ΔN isoforms exhibit distinguished properties by promoting or inhibiting cancer progression. As such, p63 isoforms comprise a fully mysterious and challenging regulatory pathway. Recent studies have revealed the intricate role of p63 in regulating the DNA damage response (DDR) and its impact on diverse cellular processes. In this review, we will highlight the significance of how p63 isoforms respond to DNA damage and cancer stem cells, as well as the dual role of TAp63 and ΔNp63 in cancer.

The RNA-binding protein RBM24 regulates lipid metabolism and SLC7A11 mRNA stability to modulate ferroptosis and inflammatory response

Lipids play a critical role in many cellular processes by serving as structural components of cell membranes or functioning as energy fuel and signaling molecules. The RNA-binding proteins RBM24 and RBM38 share an identical RNA-binding domain and thereby, regulate a group of same targets, such as p21. However, it is not certain whether RBM24 and RBM38 participates in lipid homeostasis. Here, lipidomic analysis showed that a deficiency in RBM24 or RBM38 leads to altered lipid metabolism, with more profound alteration by loss of RBM24 in MCF7 cells. We also showed that mice deficient in RBM24 were prone to chronic inflammation and liver steatosis, but not spontaneous tumors. These data let us speculate whether RBM24 regulates ferroptosis, a programmed cell death that links inflammation and liver steatosis via lipid peroxidation. Indeed, we found that over-expression of RBM24 protected, whereas knockout of RBM24 sensitized, cells to Erastin-induced ferroptosis by modulating the mRNA stability of SLC7A11, a ferroptosis inhibitor. Moreover, we showed that knockdown of SLC7A11 reversed the effect of RBM24 on ferroptosis. Together, our study revealed that RBM24 regulates lipid metabolism and SLC7A11 mRNA stability to modulate ferroptosis and inflammatory response.

RBM24 Mediates Lymph Node Metastasis and Epithelial-Mesenchymal Transition in Human Hypopharyngeal Squamous Cell Carcinoma by Regulating Twist1

Objective

Despite the target RNA regulatory action of RBM24 (RNA Binding Motif 24), a protein implicated in multiple carcinomas, its role in HSCC remains unclear. Our study probed to understand the effect of RBM24 on HSCC.

Materials and Methods

A combination of qRT-PCR, IHC, and western blot was employed to assess the HSCC tissue level of RBM24. The colony formation and CCK-8 assays were performed to estimate cellular proliferative potential, whereas the transwell assay was conducted to examine invasive and metastatic potential. The FaDu cell motility was assessed via the scratch-wound assay and EMT (epithelial-mesenchymal transition) by adopting qRT-PCR in conjunction with western blot and IF (immunofluorescence). The in-vivo effect of RBM24 on HSCC was investigated through modeling metastasis to the popliteal LNs (lymph nodes).

Results

Among HSCC patients showing metastasis to LNs, prominent RBM24 downregulation was noted, with an intrinsic association between low RBM24 level and poor outcome. Knocking down RBM24 promoted cell multiplication, migration, and infiltration, while overexpression led to the opposite effects and inhibited the EMT. RBM24's suppressive action against the FaDu cell mobility and invasion was reversed by Twist1 overexpression. RBM24's suppressive actions against the tumor evolution and LN metastasis in HSCC in-vivo were also validated.

Conclusion

As a carcinoma inhibitor gene, RBM24 regulates Twist1 to achieve LN metastasis and EMT suppression in HSCC.

RUNX1T1 function in cell fate

RUNX1T1 (Runt-related transcription factor 1, translocated to 1), a myeloid translocation gene (MTG) family member, is usually investigated as part of the fusion protein RUNX1-RUNX1T1 for its role in acute myeloid leukemia. In the main, by recruiting histone deacetylases, RUNX1T1 negatively influences transcription, enabling it to regulate the proliferation and differentiation of hematopoietic progenitors. Moreover, the formation of blood vessels, neuronal differentiation, microglial activation following injury, and intestinal development all relate closely to the expression of RUNX1T1. Furthermore, through alternative splicing of RUNX1T1, short and long isoforms have been noted to mediate adipogenesis by balancing the differentiation and proliferation of adipocytes. In addition, RUNX1T1 plays wide-ranging and diverse roles in carcinoma as a biomarker, suppressor, or positive regulator of carcinogenesis, closely correlated to specific organs and dominant signaling pathways. The aim of this work was to investigate the structure of RUNX1T1, which contains four conserved nervy homolog domains, and to demonstrate crosstalk with the Notch signaling pathway. Moreover, we endeavored to illustrate the effects of RUNX1T1 on cell fate from multiple aspects, including its influence on hematopoiesis, neuronal differentiation, microglial activation, intestinal development, adipogenesis, angiogenesis, and carcinogenesis.

RBM24 in the Post-Transcriptional Regulation of Cancer Progression: Anti-Tumor or Pro-Tumor Activity?

Simple Summary

RBM24 is a highly conserved RNA-binding protein that plays critical roles in the post-transcriptional regulation of gene expression for initiating cell differentiation during embryonic development and for maintaining tissue homeostasis in adult life. Evidence is now accumulating that it is frequently dysregulated across human cancers. Importantly, RBM24 may act as a tumor suppressor or as an oncogene in a context- or background-dependent manner. Its activity can be regulated by protein–protein interactions and post-translational modifications, making it a potential therapeutic target for cancer treatment. However, molecular mechanisms underlying its function in tumor growth and metastasis remain elusive. Further investigation will be necessary to better understand how its post-transcriptional regulatory activity is controlled and how it is implicated in tumor progression. This review provides a comprehensive analysis of recent findings on the implication of RBM24 in cancer and proposes future research directions to delve more deeply into the mechanisms underlying its tumor-suppressive function or oncogenic activity.

Abstract

RNA-binding proteins are critical post-transcriptional regulators of gene expression. They are implicated in a wide range of physiological and pathological processes by modulating nearly every aspect of RNA metabolisms. Alterations in their expression and function disrupt tissue homeostasis and lead to the occurrence of various cancers. RBM24 is a highly conserved protein that binds to a large spectrum of target mRNAs and regulates many post-transcriptional events ranging from pre-mRNA splicing to mRNA stability, polyadenylation and translation. Studies using different animal models indicate that it plays an essential role in promoting cellular differentiation during organogenesis and tissue regeneration. Evidence is also accumulating that its dysregulation frequently occurs across human cancers. In several tissues, RBM24 clearly functions as a tumor suppressor, which is consistent with its inhibitory potential on cell proliferation. However, upregulation of RBM24 in other cancers appears to promote tumor growth. There is a possibility that RBM24 displays both anti-tumor and pro-tumor activities, which may be regulated in part through differential interactions with its protein partners and by its post-translational modifications. This makes it a potential biomarker for diagnosis and prognosis, as well as a therapeutic target for cancer treatment. The challenge remains to determine the post-transcriptional mechanisms by which RBM24 modulates gene expression and tumor progression in a context- or background-dependent manner. This review discusses recent findings on the potential function of RBM24 in tumorigenesis and provides future directions for better understanding its regulatory role in cancer cells.

ALS-associated KIF5A mutations abolish autoinhibition resulting in a toxic gain of function

Understanding the pathogenic mechanisms of disease mutations is critical to advancing treatments. ALS-associated mutations in the gene encoding the microtubule motor KIF5A result in skipping of exon 27 (KIF5AΔExon27) and the encoding of a protein with a novel 39 amino acid residue C-terminal sequence. Here, we report that expression of ALS-linked mutant KIF5A results in dysregulated motor activity, cellular mislocalization, altered axonal transport, and decreased neuronal survival. Single-molecule analysis revealed that the altered C terminus of mutant KIF5A results in a constitutively active state. Furthermore, mutant KIF5A possesses altered protein and RNA interactions and its expression results in altered gene expression/splicing. Taken together, our data support the hypothesis that causative ALS mutations result in a toxic gain of function in the intracellular motor KIF5A that disrupts intracellular trafficking and neuronal homeostasis.

RBM24 is localized to stress granules in cells under various stress conditions

Stress granules (SGs) are formed when untranslated messenger ribonucleoproteins (mRNPs) accumulate in cells under stress, and are thought to minimize stress-induced damage and promote cell survival. RBM24 (RNA-binding motif protein 24) is an RNA-binding protein that plays pivotal roles in regulating the stability or translation initiation of target mRNAs as well as alternative splicing of target pre-mRNAs. Its important physiological functions are highlighted by the fact that Rbm24 knockout mice or zebrafish suffer from dysfunction of heart, eye, and inner ear. Here we show that RBM24 is recruited into SGs under various stress conditions, suggesting that it might protect its target RNAs in cells under stress. However, SG formation is unaffected when Rbm24 expression is down-regulated. Nevertheless, RBM24 overexpression in cultured cells is sufficient to induce SG formation, suggesting that RBM24 might play an important role in SG formation. In conclusion, our present work reveals that RBM24 is a SG component, which implies that RBM24 could protect its target mRNAs in stressed cells.

RBM22, a Key Player of Pre-mRNA Splicing and Gene Expression Regulation, Is Altered in Cancer

RNA-Binding Proteins (RBP) are very diverse and cover a large number of functions in the cells. This review focuses on RBM22, a gene encoding an RBP and belonging to the RNA-Binding Motif (RBM) family of genes. RBM22 presents a Zinc Finger like and a Zinc Finger domain, an RNA-Recognition Motif (RRM), and a Proline-Rich domain with a general structure suggesting a fusion of two yeast genes during evolution: Cwc2 and Ecm2. RBM22 is mainly involved in pre-mRNA splicing, playing the essential role of maintaining the conformation of the catalytic core of the spliceosome and acting as a bridge between the catalytic core and other essential protein components of the spliceosome. RBM22 is also involved in gene regulation, and is able to bind DNA, acting as a bona fide transcription factor on a large number of target genes. Undoubtedly due to its wide scope in the regulation of gene expression, RBM22 has been associated with several pathologies and, notably, with the aggressiveness of cancer cells and with the phenotype of a myelodysplastic syndrome. Mutations, enforced expression level, and haploinsufficiency of RBM22 gene are observed in those diseases. RBM22 could represent a potential therapeutic target in specific diseases, and, notably, in cancer.

RNA binding Motif protein-38 regulates myocardial hypertrophy in LXR-α-dependent lipogenesis pathway

Myocardial hypertrophy is a pathological thickening of the myocardium, leading to various ailments, such as myocardial infarction and heart failure. RBM38 is critical in modulating mRNA translation for multiple protective activities such as p53 tumor repressor and p21 kinase cell cycle inhibitors. Liver X receptors (LXR-α) agonists reduce cellular hypertrophy initiated by various hypertrophic stimuli as lipopolysaccharides and Ang II. This research investigates the possible cooperation between RBM38 and LXR-α and mechanisms in modulating myocardial hypertrophy. H9C2 cells were treated with PE, TNF-α, and AngII to induce myocardial hypertrophy. RBM38 and LXR- α were overexpressed or silenced in H9C2 cells, and hypertrophy markers (ANF and Myh7) were determined with Western blot and RT-qPCR. Binding assays were done through RNA immunoprecipitation. H&E and Rhodamine-labeled phalloidin staining assays were used to assess the relative cell surface change. The results demonstrated RBM38 downregulation in in vitro models of myocardial hypertrophy. Modulation of RBM38 expression also exerted inverse effects on myocardial hypertrophy markers. Further observations also showed that LXR-α expression regulates the myocardial hypertrophy markers in H9C2 cells and RBM38 binds with LXR-α mRNA, consequently inhibiting LXR-α expression. Finally, overexpression of RBM38 rescues Angiotensin II-induced myocardial hypertrophy by regulating LXR-α dependent lipogenesis pathway. In conclusion, RBM38 Overexpression rescues Angiotensin II-induced myocardial hypertrophy by regulating LXR-α dependent lipogenesis pathway.

Alternative Splicing Mediated by RNA-Binding Protein RBM24 Facilitates Cardiac Myofibrillogenesis in a Differentiation Stage-Specific Manner

Background: Mutations in genes encoding sarcomeric proteins lead to failures in sarcomere assembly, the building blocks of contracting muscles, resulting in cardiomyopathies that are a leading cause of morbidity and mortality worldwide. Splicing variants of sarcomeric proteins are crucial at different stages of myofibrillogenesis, accounting for sarcomeric structural integrity. RNA-binding motif protein 24 (RBM24) is known as a tissue-specific splicing regulator that plays an essential role in cardiogenesis. However, it had been unclear if the developmental stage-specific alternative splicing facilitated by RBM24 contributes to sarcomere assembly and cardiogenesis. Our aim isto study the molecular mechanism by which RBM24 regulates cardiogenesis and sarcomere assembly in a temporal-dependent manner. Methods: We ablated RBM24 from human embryonic stem cells (hESCs) using CRISPR/Cas9 techniques. Results: Although RBM24^-/- hESCs still differentiated into sarcomere-hosting cardiomyocytes, they exhibited disrupted sarcomeric structures with punctate Z-lines due to impaired myosin replacement during early myofibrillogenesis. Transcriptomics revealed >4000 genes regulated by RBM24. Among them, core myofibrillogenesis proteins (e.g. ACTN2, TTN, and MYH10) were misspliced. Consequently, MYH6 cannot replace non-muscle myosin MYH10, leading to myofibrillogenesis arrest at the early premyofibril stage and causing disrupted sarcomeres. Intriguingly, we found that the actin-binding domain (ABD; encoded by exon 6) of the Z-line anchor protein ACTN2 is predominantly excluded from early cardiac differentiation, whereas it is consistently included in human adult heart. CRISPR/Cas9-mediated deletion of exon 6 from ACTN2 in hESCs, as well as forced expression of full-length ACTN2 in RBM24^-/- hESCs, further corroborated that inclusion of exon 6 is critical for sarcomere assembly. Overall, we have demonstrated that RBM24-facilitated inclusion of exon 6 in ACTN2 at distinct stages of cardiac differentiation is evolutionarily conserved and crucial to sarcomere assembly and integrity. Conclusions: RBM24 acts as a master regulator to modulate the temporal dynamics of core myofibrillogenesis genes and thereby orchestrates sarcomere organization.

RNA-binding protein RBM24 represses colorectal tumourigenesis by stabilising PTEN mRNA

BACKGROUND

RNA-binding motif protein 24 (RBM24) functions as a splicing regulator, which is critical for organ development and is dysregulated in human cancers. Here, we aim to uncover the biological function of RBM24 in colorectal tumourigenesis.

METHODS

Xenograft tumour model, Rbm24 knockout and Apcmin/+ mouse models were utilised. Colorectal cancer cells overexpressing or silencing RBM24 were established. RNA immunoprecipitation (RIP) assay was conducted to detect protein-RNA associations. Gene expression was measured by immunohistochemistry, western blotting, or quantitative PCR (qPCR).

RESULTS

Rbm24-knockout mice developed spontaneous colorectal adenomas with lower expression of phosphatase and tensin homolog (PTEN). Immunohistochemical staining for the proliferation markers Ki-67 and pHH3 and BrdU assay showed intestinal hyperplasia in Rbm24-knockout mice compared to wild-type mice. RBM24 expression in colorectal adenoma tissues of Apcmin/+ mouse was downregulated compared with adjacent normal samples and was positively correlated with PTEN expression. In vitro, RBM24 overexpression suppressed cell proliferation, migration, invasion and increased sensitivity to 5-FU or cisplatin in CRC cells. Mechanistically, RBM24 maintained PTEN mRNA stability by directly binding to the GT-rich region at positions 8101-8251 in the 3'-UTR of PTEN mRNA, prolonging the half-life of PTEN mRNA, thereby increasing PTEN expression. Hence, low expression of RBM24 downregulated PTEN mRNA, causing the activation of PI3K-Akt signalling in CRC cells. Furthermore, RBM24 expression in CRC tissues was lower than adjacent normal samples. RBM24 expression was positively correlated with PTEN expression and negatively correlated with Ki-67 level. CRC patients with high RBM24 expression had a favourable outcome.

CONCLUSIONS

Taken together, RBM24 expression is markedly lower in colorectal tumours than in para-carcinoma tissues. Rbm24-knockout mice develop spontaneous colorectal adenomas. RBM24 directly binds and stabilises PTEN mRNA, which could cause the suppression of CRC cell proliferation, migration and invasion, thereby repressing colorectal tumourigenesis. These findings support the tumour-suppressive role of RBM24. Targeting RBM24 holds strong promise for the diagnosis and treatment of CRC.

miR‑383 increases the cisplatin sensitivity of lung adenocarcinoma cells through inhibition of the RBM24‑mediated NF‑κB signaling pathway

The expression of microRNA-383 (miR-383) is downregulated in a variety of tumor tissues, and it exhibits antiproliferative activity in non-small cell lung cancer cells. In the present study, an association between the downregulation of miR-383 expression and the deletion of chr8p22 in patients with lung adenocarcinoma was identified. The promoting effect of miR-383 on cisplatin sensitivity was verified both in vivo and in vitro. Additionally, it was revealed that the expression of RNA binding motif protein 24 (RBM24) protein was regulated by and negatively correlated with miR-383 expression. Ectopic expression of RBM24 or inhibition of miR-383 decreased the chemosensitivity of parental A549 cells, whereas knockdown of RBM24 in cisplatin-resistant A549 cells increased chemosensitivity. Mechanistically, miR-383 interfered with the activation of nuclear factor κB (NF-κB) signaling through repression of RBM24-mediated phosphorylation of Rel-like domain-containing protein A and inhibitor α of NF-κB. Taken together, the downregulation of miR-383 induced RBM24 expression, which was mediated through the activation of NF-κB signaling, to contribute to chemotherapy resistance in lung adenocarcinoma cells. The results of the present study highlight potential therapeutic targets for the clinical reversal of the chemotherapy resistance in lung adenocarcinoma.

Tumor suppressor RBM24 inhibits nuclear translocation of CTNNB1 and TP63 expression in liver cancer cells

RNA-binding protein 24 (RBM24) has been shown to play tumor-suppressive functions in various types of cancer. The present study aimed to investigate the role of RBM24 in liver cancers and its downstream mechanisms. The present study demonstrated that RBM24 functioned as a tumor suppressor in liver cancer cells, and inhibited nuclear translocation of β-catenin and tumor protein 63 expression by immunocytochemistry. In addition, RBM24 could suppress sphere formation in a multicellular tumor spheroid model of liver cancer cells. In conclusion, it is hypothesized that RBM24 is a tumor suppressor of liver cancer cells, which could be a potential novel therapeutic target for treatment of patients with liver cancer.

The master transcription factor SOX2, mutated in anophthalmia/microphthalmia, is post-transcriptionally regulated by the conserved RNA-binding protein RBM24 in vertebrate eye development

Mutations in the key transcription factor, SOX2, alone account for 20% of anophthalmia (no eye) and microphthalmia (small eye) birth defects in humans-yet its regulation is not well understood, especially on the post-transcription level. We report the unprecedented finding that the conserved RNA-binding motif protein, RBM24, positively controls Sox2 mRNA stability and is necessary for optimal SOX2 mRNA and protein levels in development, perturbation of which causes ocular defects, including microphthalmia and anophthalmia. RNA immunoprecipitation assay indicates that RBM24 protein interacts with Sox2 mRNA in mouse embryonic eye tissue. and electrophoretic mobility shift assay shows that RBM24 directly binds to the Sox2 mRNA 3'UTR, which is dependent on AU-rich elements (ARE) present in the Sox2 mRNA 3'UTR. Further, we demonstrate that Sox2 3'UTR AREs are necessary for RBM24-based elevation of Sox2 mRNA half-life. We find that this novel RBM24-Sox2 regulatory module is essential for early eye development in vertebrates. We show that Rbm24-targeted deletion using a constitutive CMV-driven Cre in mouse, and rbm24a-CRISPR/Cas9-targeted mutation or morpholino knockdown in zebrafish, results in Sox2 downregulation and causes the developmental defects anophthalmia or microphthalmia, similar to human SOX2-deficiency defects. We further show that Rbm24 deficiency leads to apoptotic defects in mouse ocular tissue and downregulation of eye development markers Lhx2, Pax6, Jag1, E-cadherin and gamma-crystallins. These data highlight the exquisite specificity that conserved RNA-binding proteins like RBM24 mediate in the post-transcriptional control of key transcription factors, namely, SOX2, associated with organogenesis and human developmental defects.

Highly heterogeneous-related genes of triple-negative breast cancer: potential diagnostic and prognostic biomarkers

Background

Triple-negative breast cancer (TNBC) is a highly heterogeneous subtype of breast cancer, showing aggressive clinical behaviors and poor outcomes. It urgently needs new therapeutic strategies to improve the prognosis of TNBC. Bioinformatics analyses have been widely used to identify potential biomarkers for facilitating TNBC diagnosis and management.

Methods

We identified potential biomarkers and analyzed their diagnostic and prognostic values using bioinformatics approaches. Including differential expression gene (DEG) analysis, Receiver Operating Characteristic (ROC) curve analysis, functional enrichment analysis, Protein-Protein Interaction (PPI) network construction, survival analysis, multivariate Cox regression analysis, and Non-negative Matrix Factorization (NMF).

Results

A total of 105 DEGs were identified between TNBC and other breast cancer subtypes, which were regarded as heterogeneous-related genes. Subsequently, the KEGG enrichment analysis showed that these genes were significantly enriched in ‘cell cycle’ and ‘oocyte meiosis’ related pathways. Four (FAM83B, KITLG, CFD and RBM24) of 105 genes were identified as prognostic signatures in the disease-free interval (DFI) of TNBC patients, as for progression-free interval (PFI), five genes (FAM83B, EXO1, S100B, TYMS and CFD) were obtained. Time-dependent ROC analysis indicated that the multivariate Cox regression models, which were constructed based on these genes, had great predictive performances. Finally, the survival analysis of TNBC subtypes (mesenchymal stem-like [MSL] and mesenchymal [MES]) suggested that FAM83B significantly affected the prognosis of patients.

Conclusions

The multivariate Cox regression models constructed from four heterogeneous-related genes (FAM83B, KITLG, RBM24 and S100B) showed great prediction performance for TNBC patients’ prognostic. Moreover, FAM83B was an important prognostic feature in several TNBC subtypes (MSL and MES). Our findings provided new biomarkers to facilitate the targeted therapies of TNBC and TNBC subtypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08318-1.

RBM24 exacerbates bladder cancer progression by forming a Runx1t1/TCF4/miR-625-5p feedback loop

RNA–binding motif protein 24 (RBM24) acts as a multifunctional determinant of cell fate, proliferation, apoptosis, and differentiation during development by regulating premRNA splicing and mRNA stability. It is also implicated in carcinogenesis, but the functions of RBM24 in bladder cancer (BC) remain unclear. In the present study, we revealed that RBM24 was upregulated in BC tissues. Importantly, we found that a higher level of RBM24 was correlated with poor prognosis in BC patients. Overexpression of RBM24 promoted BC cell proliferation, while depletion of RBM24 inhibited BC cell proliferation in vivo and in vitro. Mechanistically, RBM24 positively regulated Runx1t1 expression in BC cells by binding to and enhancing Runx1t1 mRNA stability. Furthermore, Runx1t1 in turn promoted RBM24 expression by interacting with the transcription factor TCF4 and suppressing the transcription of miR-625-5p, which directly targets RBM24 and suppresses RBM24 expression. RBM24-regulated BC cell proliferation was moderated via the Runx1t1/TCF4/miR-625-5p feedback loop. These results indicate that the RBM24/Runx1t1/TCF4/miR-625-5p positive feedback loop participates in BC progression. Disruption of this pathway may be a potential therapeutic strategy for BC treatment.

A protein called RBM24 promotes progression of bladder cancer (BC) by forming a positive feedback loop with a specific transcription factor, driving cancer cell proliferation. Survival rates for BC are low, and the current imperfect understanding of the underlying mechanisms makes it difficult to treat. Ping-Ying Guo at Hebei Medical University in Shijiazhuang, China, and co-workers investigated the role of RBM24, known to be involved in other cancers, and found increased levels in BC tissues. Higher levels were associated with a poor prognosis. Further investigation revealed that RBM24 boosts levels of the transcription factor, which suppresses a molecule that in turn suppresses RBM24, forming a positive feedback loop promoting BC cell proliferation. Interrupting the feedback loop decreased tumor size in a mouse model. These results may help identify better treatments for BC.

Rbm24 displays dynamic functions required for myogenic differentiation during muscle regeneration

Skeletal muscle has a remarkable capacity of regeneration after injury, but the regulatory network underlying this repair process remains elusive. RNA-binding proteins play key roles in the post-transcriptional regulation of gene expression and the maintenance of tissue homeostasis and plasticity. Rbm24 regulates myogenic differentiation during early development, but its implication in adult muscle is poorly understood. Here we show that it exerts multiple functions in muscle regeneration. Consistent with its dynamic subcellular localization during embryonic muscle development, Rbm24 also displays cytoplasm to nucleus translocation during C2C12 myoblast differentiation. In adult mice, Rbm24 mRNA is enriched in slow-twitch muscles along with myogenin mRNA. The protein displays nuclear localization in both slow and fast myofibers. Upon injury, Rbm24 is rapidly upregulated in regenerating myofibers and accumulates in the myonucleus of nascent myofibers. Through satellite cell transplantation, we demonstrate that Rbm24 functions sequentially to regulate myogenic differentiation and muscle regeneration. It is required for myogenin expression at early stages of muscle injury and for muscle-specific pre-mRNA alternative splicing at late stages of regeneration. These results identify Rbm24 as a multifaceted regulator of myoblast differentiation. They provide insights into the molecular pathway orchestrating the expression of myogenic factors and muscle functional proteins during regeneration.

The foggy world(s) of p63 isoform regulation in normal cells and cancer

The p53 family member p63 exists as two major protein variants (TAp63 and ΔNp63) with distinct expression patterns and functional properties. Whilst downstream target genes of p63 have been studied intensively, how p63 variants are themselves controlled has been relatively neglected. Here, we review advances in understanding ΔNp63 and TAp63 regulation, highlighting their distinct pathways. TAp63 has roles in senescence and metabolism, and in germ cell genome maintenance, where it is activated post-transcriptionally by phosphorylation cascades after DNA damage. The function and regulation of TAp63 in mesenchymal and haematopoietic cells is less clear but may involve epigenetic control through DNA methylation. ΔNp63 functions to maintain stem/progenitor cells in various epithelia and is overexpressed in squamous and certain other cancers. ΔNp63 is transcriptionally regulated through multiple enhancers in concert with chromatin modifying proteins. Many signalling pathways including growth factors, morphogens, inflammation, and the extracellular matrix influence ΔNp63 levels, with inconsistent results reported. There is also evidence for reciprocal regulation, including ΔNp63 activating its own transcription. ΔNp63 is downregulated during cell differentiation through transcriptional regulation, while post-transcriptional events cause proteasomal degradation. Throughout the review, we identify knowledge gaps and highlight discordances, providing potential explanations including cell-context and cell-matrix interactions. Identifying individual p63 variants has roles in differential diagnosis and prognosis, and understanding their regulation suggests clinically approved agents for targeting p63 that may be useful combination therapies for selected cancer patients. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

RBM38 in cancer: role and mechanism

Cancer is the second leading cause of death globally. Abnormity in gene expression regulation characterizes the trajectory of tumor development and progression. RNA-binding proteins (RBPs) are widely dysregulated, and thus implicated, in numerous human cancers. RBPs mainly regulate gene expression post-transcriptionally, but emerging studies suggest that many RBPs can impact transcription by acting on chromatin as transcription factors (TFs) or cofactors. Here, we review the evidence that RBM38, an intensively studied RBP, frequently plays a tumor-suppressive role in multiple human cancer types. Genetic studies in mice deficient in RBM38 on different p53 status also establish RBM38 as a tumor suppressor (TS). By uncovering a spectrum of transcripts bound by RBM38, we discuss the diversity in its mechanisms of action in distinct biological contexts. Examination of the genomic features and expression pattern of RBM38 in human tissues reveals that it is generally lost but rarely mutated, in cancers. By assessing future trends in the study of RBM38 in cancer, we signify the possibility of targeting RBM38 and its related pathways as therapeutic strategies against cancer.

Rbm24a Is Necessary for Hair Cell Development Through Regulating mRNA Stability in Zebrafish

Hair cells in the inner ear and lateral lines are mechanosensitive receptor cells whose development and function are tightly regulated. Several transcription factors as well as splicing factors have been identified to play important roles in hair cell development, whereas the role of RNA stability in this process is poorly understood. In the present work, we report that RNA-binding motif protein 24a (Rbm24a) is indispensable for hair cell development in zebrafish. Rbm24a expression is detected in the inner ear as well as lateral line neuromasts. Albeit rbm24a deficient zebrafish do not survive beyond 9 days post fertilization (dpf) due to effects outside of the inner ear, rbm24a deficiency does not affect the early development of inner ear except for delayed otolith formation and semicircular canal fusion. However, hair cell development is severely affected and hair bundle is disorganized in rbm24a mutants. As a result, the auditory and vestibular function of rbm24a mutants are compromised. RNAseq analyses identified several Rbm24a-target mRNAs that are directly bound by Rbm24a and are dysregulated in rbm24a mutants. Among the identified Rbm24a-target genes, lrrc23, dfna5b, and smpx are particularly interesting as their dysregulation might contribute to the inner ear phenotypes in rbm24a mutants. In conclusion, our data suggest that Rbm24a affects hair cell development in zebrafish through regulating mRNA stability.

Rbm38 Reduces the Transcription Elongation Defect of the SMEK2 Gene Caused by Splicing Deficiency

Pre-mRNA splicing is an essential mechanism for ensuring integrity of the transcriptome in eukaryotes. Therefore, splicing deficiency might cause a decrease in functional proteins and the production of nonfunctional, aberrant proteins. To prevent the production of such aberrant proteins, eukaryotic cells have several mRNA quality control mechanisms. In addition to the known mechanisms, we previously found that transcription elongation is attenuated to prevent the accumulation of pre-mRNA under splicing-deficient conditions. However, the detailed molecular mechanism behind the defect in transcription elongation remains unknown. Here, we showed that the RNA binding protein Rbm38 reduced the transcription elongation defect of the SMEK2 gene caused by splicing deficiency. This reduction was shown to require the N- and C-terminal regions of Rbm38, along with an important role being played by the RNA-recognition motif of Rbm38. These findings advance our understanding of the molecular mechanism of the transcription elongation defect caused by splicing deficiency.

Marek's Disease Virus (Gallid alphaherpesvirus 2)-Encoded miR-M2-5p Simultaneously Promotes Cell Proliferation and Suppresses Apoptosis Through RBM24 and MYOD1-Mediated Signaling Pathways

MicroRNAs (miRNAs) have been demonstrated for their involvement in virus biology and pathogenesis, including functioning as key determinants of virally-induced cancers. As an important oncogenic α-herpesvirus affecting poultry health, Marek’s disease virus serotype 1 [Gallid alphaherpesvirus 2 (GaHV-2)] induces rapid-onset T-cell lymphomatous disease commonly referred to as Marek’s disease (MD), an excellent biological model for the study of virally-induced cancer in the natural hosts. Previously, we have demonstrated that GaHV-2-encoded miRNAs (especially those within the Meq-cluster) have the potential to act as critical regulators of multiple processes such as virus replication, latency, pathogenesis, and/or oncogenesis. In addition to miR-M4-5p (miR-155 homolog) and miR-M3-5p, we have recently found that miR-M2-5p possibly participate in inducing MD lymphomagenesis. Here, we report the identification of two tumor suppressors, the RNA-binding protein 24 (RBM24) and myogenic differentiation 1 (MYOD1), being two biological targets for miR-M2-5p. Our experiments revealed that as a critical miRNA, miR-M2-5p promotes cell proliferation via regulating the RBM24-mediated p63 overexpression and MYOD1-mediated IGF2 signaling and suppresses apoptosis by targeting the MYOD1-mediated Caspase-3 signaling pathway. Our data present a new strategy of a single viral miRNA exerting dual role to potentially participate in the virally-induced T-cell lymphomagenesis by simultaneously promoting the cell proliferation and suppressing apoptosis.

RNA-Binding Protein Rbm24 as a Multifaceted Post-Transcriptional Regulator of Embryonic Lineage Differentiation and Cellular Homeostasis

RNA-binding proteins control the metabolism of RNAs at all stages of their lifetime. They are critically required for the post-transcriptional regulation of gene expression in a wide variety of physiological and pathological processes. Rbm24 is a highly conserved RNA-binding protein that displays strongly regionalized expression patterns and exhibits dynamic changes in subcellular localization during early development. There is increasing evidence that it acts as a multifunctional regulator to switch cell fate determination and to maintain tissue homeostasis. Dysfunction of Rbm24 disrupts cell differentiation in nearly every tissue where it is expressed, such as skeletal and cardiac muscles, and different head sensory organs, but the molecular events that are affected may vary in a tissue-specific, or even a stage-specific manner. Recent works using different animal models have uncovered multiple post-transcriptional regulatory mechanisms by which Rbm24 functions in key developmental processes. In particular, it represents a major splicing factor in muscle cell development, and plays an essential role in cytoplasmic polyadenylation during lens fiber cell terminal differentiation. Here we review the advances in understanding the implication of Rbm24 during development and disease, by focusing on its regulatory roles in physiological and pathological conditions.

Alternative Splicing of Cdh23 Exon 68 Is Regulated by RBM24, RBM38, and PTBP1

Alternative splicing plays a pivotal role in modulating the function of eukaryotic proteins. In the inner ear, many genes undergo alternative splicing, and errors in this process lead to hearing loss. Cadherin 23 (CDH23) forms part of the so-called tip links, which are indispensable for mechanoelectrical transduction (MET) in the hair cells. Cdh23 gene contains 69 exons, and exon 68 is subjected to alternative splicing. Exon 68 of the Cdh23 gene is spliced into its mRNA only in a few cell types including hair cells. The mechanism responsible for the alternative splicing of Cdh23 exon 68 remains elusive. In the present work, we performed a cell-based screening to look for splicing factors that regulate the splicing of Cdh23 exon 68. RBM24 and RBM38 were identified to enhance the inclusion of Cdh23 exon 68. The splicing of Cdh23 exon 68 is affected in Rbm24 knockdown or knockout cells. Moreover, we also found that PTBP1 inhibits the inclusion of Cdh23 exon 68. Taken together, we show here that alternative splicing of Cdh23 exon 68 is regulated by RBM24, RBM38, and PTBP1.

Iron Regulatory Protein 2 Exerts its Oncogenic Activities by Suppressing TAp63 Expression

Iron regulatory protein 2 (IRP2) is a key regulator of iron homeostasis and is found to be altered in several types of human cancer. However, how IRP2 contributes to tumorigenesis remains to be elucidated. In this study, we sought to investigate the role of IRP2 in tumorigenesis and found that IRP2 promotes cell growth by repressing TAp63, a member of p53 tumor suppressor family. Specifically, we found that IRP2 overexpression decreased, whereas IRP2 deficiency increased, TAp63 expression. We also showed that the repression of TAp63 by IRP2 was independent of tumor suppressor p53. To uncover the molecular basis, we found that IRP2 stabilized TAp63 mRNA by binding to an iron response element in the 3'UTR of p63 mRNA. To determine the biological significance of this regulation, we showed that IRP2 facilitates cell proliferation, at least in part, via repressing TAp63 expression. Moreover, we found that IRP2 deficiency markedly alleviated cellular senescence in TAp63-deficient mouse embryo fibroblasts. Together, we have uncovered a novel regulation of TAp63 by IRP2 and our data suggest that IRP2 exerts its oncogenic activities at least in part by repressing TAp63 expression. IMPLICATIONS: We have revealed a novel regulation of TAp63 by IRP2 and our data suggest that IRP2 exerts its oncogenic activities, at least in part, by repressing TAp63 expression.

Rbm24 controls poly(A) tail length and translation efficiency of crystallin mRNAs in the lens via cytoplasmic polyadenylation

Lens transparency critically requires the abundant accumulation of crystallin proteins, and deregulation of this process causes congenital cataracts in humans. Rbm24 is an RNA-binding protein with highly conserved expression in differentiating lens fiber cells among all vertebrates. We use a zebrafish model to demonstrate that loss of Rbm24 function specifically impedes lens fiber cell differentiation, resulting in cataract formation and blindness. Molecular analyses reveal that Rbm24 interacts with cytoplasmic polyadenylation complex and binds to a large number of lens-expressed messenger RNAs to maintain their stability and protect their poly(A) tail length, thereby crucially contributing to their efficient translation into functional proteins. This work identifies an important mechanism by which Rbm24 posttranscriptionally controls lens gene expression to establish transparency and refraction power.

Lens transparency is established by abundant accumulation of crystallin proteins and loss of organelles in the fiber cells. It requires an efficient translation of lens messenger RNAs (mRNAs) to overcome the progressively reduced transcriptional activity that results from denucleation. Inappropriate regulation of this process impairs lens differentiation and causes cataract formation. However, the regulatory mechanism promoting protein synthesis from lens-expressed mRNAs remains unclear. Here we show that in zebrafish, the RNA-binding protein Rbm24 is critically required for the accumulation of crystallin proteins and terminal differentiation of lens fiber cells. In the developing lens, Rbm24 binds to a wide spectrum of lens-specific mRNAs through the RNA recognition motif and interacts with cytoplasmic polyadenylation element-binding protein (Cpeb1b) and cytoplasmic poly(A)-binding protein (Pabpc1l) through the C-terminal region. Loss of Rbm24 reduces the stability of a subset of lens mRNAs encoding heat shock proteins and shortens the poly(A) tail length of crystallin mRNAs encoding lens structural components, thereby preventing their translation into functional proteins. This severely impairs lens transparency and results in blindness. Consistent with its highly conserved expression in differentiating lens fiber cells, the findings suggest that vertebrate Rbm24 represents a key regulator of cytoplasmic polyadenylation and plays an essential role in the posttranscriptional control of lens development.

Cancer the'RBP'eutics-RNA-binding proteins as therapeutic targets for cancer

RNA-binding proteins (RBPs) play a critical role in the regulation of various RNA processes, including splicing, cleavage and polyadenylation, transport, translation and degradation of coding RNAs, non-coding RNAs and microRNAs. Recent studies indicate that RBPs not only play an instrumental role in normal cellular processes but have also emerged as major players in the development and spread of cancer. Herein, we review the current knowledge about RNA binding proteins and their role in tumorigenesis as well as the potential to target RBPs for cancer therapeutics.

A High-Throughput Assay for Congenital and Age-Related Eye Diseases in Zebrafish

Debilitating visual impairment caused by cataracts or microphthalmia is estimated to affect roughly 20 million people in the United States alone. According to the National Eye Institute, by 2050 that number is expected to more than double to roughly 50 million. The identification of candidate disease-causing alleles for cataracts and microphthalmia has been accelerated with advanced sequencing technologies creating a need for verification of the pathophysiology of these genes. Zebrafish pose many advantages as a high-throughput model for human eye disease. By 5 days post-fertilization, zebrafish have quantifiable behavioral responses to visual stimuli. Their small size, many progeny, and external fertilization allows for rapid screening for vision defects. We have adapted the OptoMotor Response to assay visual impairment in zebrafish models of cataracts and microphthalmia. This research demonstrates an inexpensive, high-throughput method for analyzing candidate genes involved in visual impairment.

Serine 195 phosphorylation in the RNA-binding protein Rbm38 increases p63 expression by modulating Rbm38's interaction with the Ago2-miR203 complex

The p63 transcription factor, a p53 family protein, regulates genes involved in various cellular processes, including cell growth and differentiation. We previously showed that RNA-binding motif protein (Rbm38) is a p63 target and, in turn, regulates p63α mRNA stability by binding to the AU/U-rich element in its 3'UTR. Interestingly, Rbm38 can be phosphorylated at serine 195, altering its ability to regulate mRNA translation. However, whether the Ser-195 phosphorylation affects Rbm38's ability to destabilize p63 mRNA remains unclear. Here, using MCF7 and HaCaT cells, we showed that ectopic expression of phosphomimetic Rbm38-S195D increases, whereas WT Rbm38 and nonphosphorylatable Rbm38-S195A decrease p63α protein and transcript levels. We also found that upon activation of glycogen synthase kinase 3β (GSK3β), phosphorylation of Rbm38 at Ser-195 is increased, enhancing p63α expression in an Rbm38-dependent manner. To confirm this, we generated mouse embryo fibroblasts (MEFs) in which Ser-193 in mouse Rbm38 (equivalent to Ser-195 in human Rbm38) was substituted with aspartic acid (Rbm38^S193D/S193D ) or alanine (Rbm38^S193A/S193A ). We observed that the p63 transcript level was increased in Rbm38^S193D/S193D MEFs, but decreased in Rbm38^S193A/S193A MEFs. Mechanistically, we found that WT Rbm38, but not Rbm38-S195D, is required for p63 mRNA degradation mediated by microRNA 203 (miR203). Furthermore, we noted that Argonaute 2 (Ago2), a key regulator in microRNA-mediated mRNA decay, associates with WT Rbm38, and this association was reduced by Ser-195 phosphorylation. Together, our results reveal a critical mechanism by which Ser-195 phosphorylation in Rbm38 increases p63 expression by attenuating the association of Rbm38 with the Ago2-miR203 complex.

RBM24 stabilizes hepatitis B virus pregenomic RNA but inhibits core protein translation by targeting the terminal redundancy sequence

The terminal redundancy (TR) sequence of the 3.5-kb hepatitis B virus (HBV) RNA contains sites that govern many crucial functions in the viral life cycle, including polyadenylation, translation, RNA packaging, and DNA synthesis. In the present study, RNA-binding motif protein 24 (RBM24) is shown to be involved in the modulation of HBV replication by targeting the TR of HBV RNA. In HBV-transfected hepatoma cell lines, both knockdown and overexpression of RBM24 led to decreased HBV replication and transcription. Ectopic expression of RBM24 inhibited HBV replication, which was partly restored by knockdown of RBM24, indicating that a proper level of RBM24 was required for HBV replication. The regulation of RBM24 of HBV replication and translation was achieved by the interaction between the RNA-binding domains of RBM24 and both the 5' and 3' TR of 3.5-kb RNA. RBM24 interacted with the 5' TR of HBV pregenomic RNA (pgRNA) to block 80S ribosome assembly on HBV pgRNA and thus inhibited core protein translation, whereas the interaction between RBM24 and the 3' TR enhanced the stability of HBV RNA. Finally, the regulatory function of RBM24 on HBV replication was further confirmed in a HBV infection model. In conclusion, the present study demonstrates the dual functions of RBM24 by interacting with different TRs of viral RNA and reveals that RBM24 is an important host gene for HBV replication.

p63α modulates c-Myc activity via direct interaction and regulation of MM1 protein stability

Both p53-related p63 and c-Myc are transcription factors playing key roles in cell proliferation, survival, development and tumorigenesis. In the present study, we identified that MM1, a c-Myc inhibitor, specifically binds to C-termini of p63α (including ΔNp63α and TAp63α). Further study demonstrates that p63α facilitates MM1 protein degradation via proteasomal pathway, resulting in elevation of c-Myc transactivation activity. Knockdown of ΔNp63α leads to decrease in c-Myc protein levels, concomitant with reduced expression of CDK4 and Cyclin D1, and impaired cell cycle progression, both of which are effectively reversed by simultaneous knockdown of MM1. Moreover, expression of p63 and CDK4 is concomitantly up-regulated in B-cell acute lymphoblastic leukemia. Together, this study reveals a novel crosstalk between p63 and c-Myc that may play an important role in cell cycle progression and tumorigenesis.

RNA binding protein 24 regulates the translation and replication of hepatitis C virus

The secondary structures of hepatitis C virus (HCV) RNA and the cellular proteins that bind to them are important for modulating both translation and RNA replication. However, the sets of RNA-binding proteins involved in the regulation of HCV translation, replication and encapsidation remain unknown. Here, we identified RNA binding motif protein 24 (RBM24) as a host factor participated in HCV translation and replication. Knockdown of RBM24 reduced HCV propagation in Huh7.5.1 cells. An enhanced translation and delayed RNA synthesis during the early phase of infection was observed in RBM24 silencing cells. However, both overexpression of RBM24 and recombinant human RBM24 protein suppressed HCV IRES-mediated translation. Further analysis revealed that the assembly of the 80S ribosome on the HCV IRES was interrupted by RBM24 protein through binding to the 5'-UTR. RBM24 could also interact with HCV Core and enhance the interaction of Core and 5'-UTR, which suppresses the expression of HCV. Moreover, RBM24 enhanced the interaction between the 5'- and 3'-UTRs in the HCV genome, which probably explained its requirement in HCV genome replication. Therefore, RBM24 is a novel host factor involved in HCV replication and may function at the switch from translation to replication.

Rbm24, a target of p53, is necessary for proper expression of p53 and heart development

Activation of p53-dependent apoptosis is critical for tumor suppression but aberrant activation of p53 also leads to developmental defects and heart failure. Here, we found that Rbm24 RNA-binding protein, a target of p53, regulates p53 mRNA translation. Mechanistically, we found that through binding to p53 mRNA and interaction with translation initiation factor eIF4E, Rbm24 prevents eIF4E from binding to p53 mRNA and inhibits the assembly of translation initiation complex. Importantly, we showed that mice deficient in Rbm24 die in utero due to the endocardial cushion defect in the heart at least in part due to aberrant activation of p53-dependent apoptosis. We also showed that the heart developmental defect in Rbm24-null mice can be partially rescued by p53 deficiency through decreased apoptosis in the heart. Together, we postulate that the p53-Rbm24 loop is critical for the heart development and may be explored for mitigating congenital heart diseases and heart failure.

Global profiling of Rbm24 bound RNAs uncovers a multi-tasking RNA binding protein

RNA binding proteins serve as critical molecular switches in a multitude of post-transcriptional regulatory processes. In the heart and muscles, the tissue specific RNA binding protein, Rbm24, is known to play important developmental roles via driving different post-transcriptional processes. Nonetheless, the currently identified molecular targets and regulatory pathways seem inadequate to completely explain the observed developmental effects upon Rbm24 knockdown/knockout. Here, by performing RNA Immunoprecipitation and coupling it to microarrays (RIP-Chip), we have generated an atlas of the mRNA binding repertoire of Rbm24. Further functional evaluation of its targets led to the elucidation of novel roles for Rbm24 in post-transcriptional processing, besides its already known roles in regulation of mRNA stability and alternative splicing. Interestingly, Rbm24 is found to cause the destabilization of Chrm2 via binding to an element in the coding region. In addition, Rbm24 is also found to have an uncharacterized role in driving the generation of isoforms with alternative transcriptional start sites. We have, for the first time, demonstrated that Rbm24 is a multi-tasking RNA binding protein capable of regulating its bound targets via a range of mechanisms.

The RNA-binding protein Rbm38 is dispensable during pressure overload-induced cardiac remodeling in mice

The importance of tightly controlled alternative pre-mRNA splicing in the heart is emerging. The RNA binding protein Rbm24 has recently been identified as a pivotal cardiac splice factor, which governs sarcomerogenesis in the heart by controlling the expression of alternative protein isoforms. Rbm38, a homolog of Rbm24, has also been implicated in RNA processes such as RNA splicing, RNA stability and RNA translation, but its function in the heart is currently unknown. Here, we investigated the role of Rbm38 in the healthy and diseased adult mouse heart. In contrast to the heart- and skeletal muscle-enriched protein Rbm24, Rbm38 appears to be more broadly expressed. We generated somatic Rbm38 -/- mice and show that global loss of Rbm38 results in hematopoietic defects. Specifically, Rbm38 -/- mice were anemic and displayed enlarged spleens with extramedullary hematopoiesis, as has been shown earlier. The hearts of Rbm38 -/- mice were mildly hypertrophic, but cardiac function was not affected. Furthermore, Rbm38 deficiency did not affect cardiac remodeling (i.e. hypertrophy, LV dilation and fibrosis) or performance (i.e. fractional shortening) after pressure-overload induced by transverse aorta constriction. To further investigate molecular consequences of Rbm38 deficiency, we examined previously identified RNA stability, splicing, and translational targets of Rbm38. We found that stability targets p21 and HuR, splicing targets Mef2d and Fgfr2, and translation target p53 were not altered, suggesting that these Rbm38 targets are tissue-specific or that Rbm38 deficiency may be counteracted by a redundancy mechanism. In this regard, we found a trend towards increased Rbm24 protein expression in Rbm38 -/- hearts. Overall, we conclude that Rbm38 is critical in hematopoiesis, but does not play a critical role in the healthy and diseased heart.

TAp63γ and ΔNp63γ are regulated by RBM38 via mRNA stability and have an opposing function in growth suppression

The p63 gene is expressed as TAp63 from the P1 promoter and as ΔNp63 from the P2 promoter. Through alternative splicing, five TA and five ΔN isoforms (α-ε) are expressed. Isoforms α-β and δ share an identical 3’ untranslated region (3’UTR) whereas isoform γ has a unique 3’UTR. Recently, we found that RBM38 RNA-binding protein is a target of p63 and RBM38 in turn regulates p63α/β expression via mRNA stability. However, it is uncertain whether p63γ has a unique biological activity and whether p63γ is regulated by RBM38. Here, we found that the levels of ΔNp63γ transcript and protein are induced upon overexpression of RBM38 but decreased by RBM38 knockdown. Conversely, we found that the levels of ΔNp63β transcript and protein are decreased by ectopic expression of RBM38 but increased by RBM38 knockdown, consistent with our previous report. Interestingly, RBM38 increases the half-life of p63γ mRNA by binding to a GU-rich element in p63γ 3’UTR. In contrast, our previous studies showed that RBM38 decreases the half-life of p63α/β mRNAs by binding to AU-/U-rich elements in their 3’UTR. We also found that knockout of p63γ in ME180 and HaCaT cells, in which ΔNp63 isoforms are predominant, inhibits cell proliferation and migration, suggesting that ΔNp63γ has a pro-growth activity. In contrast, we found that knockout of TAp63γ in MIA PaCa-2 cells, in which TAp63 isoforms are predominant, promotes cell proliferation, migration, and inhibits cellular senescence. Taken together, we conclude that ΔNp63γ has an oncogenic potential whereas TAp63γ is a tumor suppressor.

Stk38 Modulates Rbm24 Protein Stability to Regulate Sarcomere Assembly in Cardiomyocytes

RNA-binding protein Rbm24 is a key regulator of heart development and required for sarcomere assembly and heart contractility. Yet, its underlying mechanism remains unclear. Here, we link serine/threonine kinase 38 (Stk38) signaling to the regulation of Rbm24 by showing that Rbm24 phosphorylation and its function could be modulated by Stk38. Using co-immunoprecipitation coupled with mass spectrometry technique, we identified Stk38 as an endogenous binding partner of Rbm24. Stk38 knockdown resulted in decreased Rbm24 protein level in cardiomyocytes. Further studies using Stk38 kinase inhibitor or activator showed that Rbm24 protein stability was regulated in a kinase activity-dependent manner. Deficiency of Stk38 caused reduction of sarcomere proteins and disarrangement of sarcomere, suggesting that Stk38 is essential for Rbm24 to regulate sarcomere assembly. Our results revealed that Stk38 kinase catalyzes the phosphorylation of Rbm24 during sarcomerogensis and this orchestrates accurate sarcomere alignment. This furthers our understanding of the regulatory mechanism of cardiac sarcomere assembly in both physiologic and pathologic contexts, and uncovers a potential novel pathway to cardiomyopathy through modulating the Stk38/Rbm24 protein activity.

p63 expression confers significantly better survival outcomes in high-risk diffuse large B-cell lymphoma and demonstrates p53-like and p53-independent tumor suppressor function

The role of p53 family member, p63 in oncogenesis is the subject of controversy. Limited research has been done on the clinical implications of p63 expression in diffuse large B-cell lymphoma (DLBCL). In this study, we assessed p63 expression in de novo DLBCL samples (n=795) by immunohistochemistry with a pan-p63-monoclonal antibody and correlated it with other clinicopathologic factors and clinical outcomes. p63 expression was observed in 42.5% of DLBCL, did not correlate with p53 levels, but correlated with p21, MDM2, p16^INK4A, Ki-67, Bcl-6, IRF4/MUM-1 and CD30 expression, REL gains, and BCL6 translocation. p63 was an independent favorable prognostic factor in DLBCL, which was most significant in patients with International Prognostic Index (IPI) >2, and in activated-B-cell–like DLBCL patients with wide-type TP53. The prognostic impact in germinal-center-B-cell–like DLBCL was not apparent, which was likely due to the association of p63 expression with high-risk IPI, and potential presence of ∆Np63 isoform in TP63 rearranged patients (a mere speculation). Gene expression profiling suggested that p63 has both overlapping and distinct functions compared with p53, and that p63 and mutated p53 antagonize each other. In summary, p63 has p53-like and p53-independent functions and favorable prognostic impact, however this protective effect can be abolished by TP53 mutations.

Modulation of the p53 family network by RNA-binding proteins

Since its discovery more than three decades ago, tumor suppressor p53 has been shown to play pivotal roles in both maintaining genomic integrity and tumor suppression. p53 functions as a transcription factor responding to a multitude of cellular stressors, regulating the transcription of many genes involved in cell-cycle arrest, senescence, autophagy, and apoptosis. Extensive work has revealed that p53 is one of the most commonly mutated tumor suppressor genes. The last three decades have demonstrated that p53 activity is controlled through transcriptional regulation and posttranslational modifications. However, evolving work is now uncovering that p53, and other p53 family members, are post-transcriptionally regulated by multiple RNA-binding proteins (RBPs). Understanding the regulation of p53 by RBPs may potentially open up the possibility for cancer therapeutic intervention. This review focuses on the posttranscriptional regulation of p53, and p53 family members, by RNA binding proteins and the reciprocal feedback pathways between several RNA-biding proteins modulating p53, and p53 family members.

(1)H, (15)N and (13)C backbone and side chain resonance assignments of the RRM domain from human RBM24

Tissue development requires the expression of a regulated subset of genes, and it is becoming clear that the process of alternative splicing also plays an important role in the production of necessary tissue-specific isoforms. However, only a few of these tissue-specific splicing factors in mammals have so far been discovered. One of these factors is the RNA-binding protein RBM24 which has been recently identified as a major regulator of alternative splicing in cardiac and skeletal muscle development. The RBM24 protein contains an RNA recognition motif (RRM) domain that presumably mediates the binding to target pre-mRNA required for regulation of the splicing patterns. Here we report (1)H, (15)N and (13)C chemical shift assignments of the backbone and sidechain atoms for the RRM domain from human RBM24. Secondary chemical shift analysis and relaxation measurement confirm the canonical architecture of the RRM domain. The data will allow for atomic level studies aimed at understanding splicing regulation of target genes in heart and muscle development and investigation into a separate role of RBM24 in modulating mRNA stability of genes involved in the p53 tumor suppressor pathway.

RBM24 suppresses cancer progression by upregulating miR-25 to target MALAT1 in nasopharyngeal carcinoma

Abnormal interaction between non-coding RNAs has been demonstrated to be a common molecular event in various human cancers, but its significance and underlying mechanisms have not been well documented. RNA-binding proteins (RBPs) are key regulators of RNA transcription and post-transcriptional processing. In this study, we found that RNA-binding protein 24 (RBM24) was frequently downregulated in nasopharyngeal carcinoma (NPC). The restoration of RBM24 expression suppressed NPC cellular proliferation, migration and invasion and impeded metastatic colonization in mouse models. Microarray analyses revealed that miR-25 expression was upregulated by RBM24 expression in NPC cells. Similarly, ectopic miR-25 expression suppressed NPC cellular growth and motility by targeting the pro-oncogenic lncRNA MALAT1, and the knockdown of MALAT1 expression exhibited similar effects as RBM24 restoration in NPC cells. Overall, these findings suggest a novel role of RBM24 as a tumor suppressor. Mechanistically, RBM24 acts at least in part through upregulating the expression of miR-25, which in turn targets MALAT1 for degradation.

Negative feedback circuitry between MIR143HG and RBM24 in Hirschsprung disease

Hirschsprung disease (HSCR) is a genetic disorder of neural crest development. It is also believed that epigenetic changes plays a role in the progression of this disease. Here we show that the MIR143 host gene (MIR143HG), the precursor of miR-143 and miR-145, decreased cell proliferation and migration and forms a negative feedback loop with RBM24 in HSCR. As RBM24 mRNA is a target of miR-143, upregulation of RBM24 upon an increase in the level of MIR143HG could be attributed to sequestration of miR-143 by MIR143HG (sponge effect). The RBM24 protein was shown to bind to MIR143HG, and subsequently, accelerated its degradation by destabilizing its transcript and facilitating its interaction with Ago2, thus forming a negative feedback between MIR143HG and RBM24. In addition, experiments using siRNA against DROSHA indicated that RBM24 could promote the biogenesis of miR-143. This feedback loop we describe here represents a novel mode of autoregulation, with implications in HSCR pathogenesis.