hnRNP A2/B1 modulates epithelial-mesenchymal transition in lung cancer cell lines

LINC00645 inhibits renal cell carcinoma progression by interacting with HNRNPA2B1 to regulate the ROCK1 mRNA stability

The lncRNA plays an important role in tumorigenesis and the progression of renal cell carcinoma (RCC). LINC00645 is one of the most different expressed lncRNA between RCC and normal renal tissue. However, the regulatory mechanism of LINC00645 in RCC remains unknown. Our results indicated that LINC00645 inhibited RCC proliferation, migration, and invasion. Mechanistically, HNRNPA2B1 directly bound to ROCK1 mRNA and strengthened its stability. LINC00645 competitively bound to the RRM1 domain, which is responsible for interacting with ROCK1 mRNA, reducing ROCK1 mRNA level by affecting posttranscriptional destabilization. The expression of LINC00645 was significantly reduced in RCC cells, significantly upregulating ROCK1 by abolishing the interaction with HNRNPA2B1, finally promoting RCC proliferation, migration, and invasion. Moreover, RCC cells with lower LINC00645 expression were more sensitive to the ROCK1 inhibitor Y-27632. Our study indicates that decreased expression of LINC00645 promotes the RCC progression via HNRNPA2B1/ROCK1 axis, providing a promising treatment strategy for RCC patients with decreased LINC00645 expression.

The nexus of long noncoding RNAs, splicing factors, alternative splicing and their modulations

The process of alternative splicing (AS) is widely deregulated in a variety of cancers. Splicing is dependent upon splicing factors. Recently, several long noncoding RNAs (lncRNAs) have been shown to regulate AS by directly/indirectly interacting with splicing factors. This review focuses on the regulation of AS by lncRNAs through their interaction with splicing factors. AS mis-regulation caused by either mutation in splicing factors or deregulated expression of splicing factors and lncRNAs has been shown to be involved in cancer development and progression, making aberrant splicing, splicing factors and lncRNA suitable targets for cancer therapy. This review also addresses some of the current approaches used to target AS, splicing factors and lncRNAs. Finally, we discuss research challenges, some of the unanswered questions in the field and provide recommendations to advance understanding of the nexus of lncRNAs, AS and splicing factors in cancer.

Regulation of Epithelial-Mesenchymal Transitions by Alternative Splicing: Potential New Area for Cancer Therapeutics

The epithelial-mesenchymal transition (EMT) is a complicated biological process in which cells with epithelial phenotype are transformed into mesenchymal cells with loss of cell polarity and cell-cell adhesion and gain of the ability to migrate. EMT and the reverse mesenchymal-epithelial transitions (METs) are present during cancer progression and metastasis. Using the dynamic switch between EMT and MET, tumour cells can migrate to neighbouring organs or metastasize in the distance and develop resistance to traditional chemotherapy and targeted drug treatments. Growing evidence shows that reversing or inhibiting EMT may be an advantageous approach for suppressing the migration of tumour cells or distant metastasis. Among different levels of modulation of EMT, alternative splicing (AS) plays an important role. An in-depth understanding of the role of AS and EMT in cancer is not only helpful to better understand the occurrence and regulation of EMT in cancer progression, but also may provide new therapeutic strategies. This review will present and discuss various splice variants and splicing factors that have been shown to play a crucial role in EMT.

RNA-binding protein-regulated fibronectin is essential for EGFR-activated metastasis of head and neck squamous cell carcinoma

There is a higher expression level of epidermal growth factor receptor (EGFR) in up to 90% of advanced head and neck squamous cell carcinoma (HNSCC) tissue than in normal surrounding tissues. However, the role of RNA-binding proteins (RBPs) in EGFR-associated metastasis of HNSCC remains unclear. In this study, we reveal that RBPs, specifically nucleolin (NCL) and heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1), correlated with the mesenchymal phenotype of HNSCC. The depletion of RBPs significantly attenuated EGF-induced HNSCC metastasis. Intriguingly, the EGF-induced EMT markers, such as fibronectin, were regulated by RBPs through the ERK and NF-κB pathway, followed by the enhancement of mRNA stability of fibronectin through the 5' untranslated region (5'-UTR) of the gene. The upregulation of fibronectin triggered the integrin signaling activation to enhance tumor cells' attachment to endothelial cells and increase endothelial permeability. In addition, the concurrence of EGFR and RBPs or EGFR and fibronectin was associated with overall survival and disease-free survival of HNSCC. The in vivo study showed that depletion of NCL, hnRNPA2B1, and fibronectin significantly inhibited EGF-promoted extravasation of tumor cells into lung tissues. The depletion of fibronectin or treatment with integrin inhibitors dramatically attenuated EGF-induced HNSCC metastatic nodules in the lung. Our data suggest that the RBPs/fibronectin axis is essential for EGF-induced tumor-endothelial cell interactions to enhance HNSCC cell metastasis.

Surmounting Cancer Drug Resistance: New Perspective on RNA-Binding Proteins

RNA-binding proteins (RBPs), being pivotal elements in both physiological and pathological processes, possess the ability to directly impact RNA, thereby exerting a profound influence on cellular life. Furthermore, the dysregulation of RBPs not only induces alterations in the expression levels of genes associated with cancer but also impairs the occurrence of post-transcriptional regulatory mechanisms. Consequently, these circumstances can give rise to aberrations in cellular processes, ultimately resulting in alterations within the proteome. An aberrant proteome can disrupt the equilibrium between oncogenes and tumor suppressor genes, promoting cancer progression. Given their significant role in modulating gene expression and post-transcriptional regulation, directing therapeutic interventions towards RBPs represents a viable strategy for combating drug resistance in cancer treatment. RBPs possess significant potential as diagnostic and prognostic markers for diverse cancer types. Gaining comprehensive insights into the structure and functionality of RBPs, along with delving deeper into the molecular mechanisms underlying RBPs in tumor drug resistance, can enhance cancer treatment strategies and augment the prognostic outcomes for individuals afflicted with cancer.

Biological function and research progress of N6-methyladenosine binding protein heterogeneous nuclear ribonucleoprotein A2B1 in human cancers

N6-methyladenosine (m6A) is the most prevalent internal modification found in both mRNA and lncRNA. It exerts reversible regulation over RNA function and affects RNA processing and metabolism in various diseases, especially tumors. The m6A binding protein, hnRNPA2B1, is extensively studied as a member of the heterogeneous nuclear ribonucleoprotein (hnRNP) protein family. It is frequently dysregulated and holds significant importance in multiple types of tumors. By recognizing m6A sites for variable splicing, maintaining RNA stability, and regulating translation and transport, hnRNPA2B1 plays a vital role in various aspects of tumor development, metabolism, and regulation of the immune microenvironment. In this review, we summarized the latest research on the functional roles and underlying molecular mechanisms of hnRNPA2B1. Moreover, we discussed its potential as a target for tumor therapy.

Mutant p53 activates hnRNPA2B1-AGAP1-mediated exosome formation to promote esophageal squamous cell carcinoma progression

p53 mutations predispose cancer cell development, promote their survival and metastasis, and lead to ineffective therapeutic responses and unfavorable prognosis. No drug that abrogates the oncogenic functions of mutant p53 has been approved for cancer treatment. Here, we performed whole-genome sequencing of 663 esophageal squamous cell carcinoma (ESCC) tumor tissues and paired normal tissues. The results indicated that ESCC samples from our cohort had a more dispersed distribution of TP53 mutants and a higher proportion of nonsense mutants than European and American ESCC samples in the International Agency for Research on Cancer (IARC) database. The most frequent p53 mutations disrupt the inhibition of proliferation, migration, and invasion mediated by wild-type p53 in ESCC. Furthermore, p53 mutations alter its protein nucleoplasmic localization and protein stability. The p53 mutation G245S (p53-G245S) interacts with heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) to increase protein translation of phosphatidylinositol-dependent Arf GAP (AGAP1) by promoting AGAP1 mRNA stability. AGAP1 promotes cancer cell proliferation and metastasis by enhancing exosome formation. Furthermore, we explored the combination of the HSP90 inhibitor HSP90i and the AGAP1 inhibitor QS11 could inhibit ESCC cell proliferation and metastasis. Thus, the p53-G245S/hnRNPA2B1/AGAP1 axis promotes ESCC progression by enhancing exosome formation, and the combination of an HSP90 inhibitor and an AGAP1 inhibitor may serve as a potential therapeutic strategy.

SUMOylation of HNRNPA2B1 modulates RPA dynamics during unperturbed replication and genotoxic stress responses

Replication protein A (RPA) is a major regulator of eukaryotic DNA metabolism involved in multiple essential cellular processes. Maintaining appropriate RPA dynamics is crucial for cells to prevent RPA exhaustion, which can lead to replication fork breakage and replication catastrophe. However, how cells regulate RPA availability during unperturbed replication and in response to stress has not been well elucidated. Here, we show that HNRNPA2B1SUMO functions as an endogenous inhibitor of RPA during normal replication. HNRNPA2B1SUMO associates with RPA through recognizing the SUMO-interacting motif (SIM) of RPA to inhibit RPA accumulation at replication forks and impede local ATR activation. Declining HNRNPA2SUMO induced by DNA damage will release nuclear soluble RPA to localize to chromatin and enable ATR activation. Furthermore, we characterize that HNRNPA2B1 hinders homologous recombination (HR) repair via limiting RPA availability, thus conferring sensitivity to PARP inhibitors. These findings establish HNRNPA2B1 as a critical player in RPA-dependent surveillance networks.

RNA binding proteins (RBPs) and their role in DNA damage and radiation response in cancer

Traditionally majority of eukaryotic gene expression is influenced by transcriptional and post-transcriptional events. Alterations in the expression of proteins that act post-transcriptionally can affect cellular signaling and homeostasis. RNA binding proteins (RBPs) are a family of proteins that specifically bind to RNAs and are involved in post-transcriptional regulation of gene expression and important cellular processes such as cell differentiation and metabolism. Deregulation of RNA-RBP interactions and any changes in RBP expression or function can lead to various diseases including cancer. In cancer cells, RBPs play an important role in regulating the expression of tumor suppressors and oncoproteins involved in various cell-signaling pathways. Several RBPs such as HuR, AUF1, RBM38, LIN28, RBM24, tristetrapolin family and Musashi play critical roles in various types of cancers and their aberrant expression in cancer cells makes them an attractive therapeutic target for cancer treatment. In this review we provide an overview of i). RBPs involved in cancer progression and their mechanism of action ii). the role of RBPs, including HuR, in breast cancer progression and DNA damage response and iii). explore RBPs with emphasis on HuR as therapeutic target for breast cancer therapy.

Emerging roles of hnRNP A2B1 in cancer and inflammation

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a group of RNA-binding proteins with important roles in multiple aspects of nucleic acid metabolism, including the packaging of nascent transcripts, alternative splicing, transactivation of gene expression, and regulation of protein translation. As a core component of the hnRNP complex in mammalian cells, heterogeneous nuclear ribonucleoprotein A2B1 (hnRNP A2B1) participates in and coordinates various molecular events. Given its regulatory role in inflammation and cancer progression, hnRNP A2B1 has become a novel player in immune response, inflammation, and cancer development. Concomitant with these new roles, a surprising number of mechanisms deemed to regulate hnRNP A2B1 functions have been identified, including post-translational modifications, changes in subcellular localization, direct interactions with multiple DNAs, RNAs, and proteins or the formation of complexes with them, which have gradually made hnRNP A2B1 a molecular target for multiple drugs. In light of the rising interest in the intersection between cancer and inflammation, this review will focus on recent knowledge of the biological roles of hnRNP A2B1 in cancer, immune response, and inflammation.

Heterogeneous nuclear ribonucleoprotein A/B: an emerging group of cancer biomarkers and therapeutic targets

Heterogeneous nuclear ribonucleoprotein A/B (hnRNPA/B) is one of the core members of the RNA binding protein (RBP) hnRNPs family, including four main subtypes, A0, A1, A2/B1 and A3, which share the similar structure and functions. With the advance in understanding the molecular biology of hnRNPA/B, it has been gradually revealed that hnRNPA/B plays a critical role in almost the entire steps of RNA life cycle and its aberrant expression and mutation have important effects on the occurrence and progression of various cancers. This review focuses on the clinical significance of hnRNPA/B in various cancers and systematically summarizes its biological function and molecular mechanisms.

iTRAQ proteomics of sentinel lymph nodes for identification of extracellular matrix proteins to flag metastasis in early breast cancer

Patients with early breast cancer are affected by metastasis to axillary lymph nodes. Metastasis to these nodes is crucial for staging and quality of surgery. Sentinel Lymph Node Biopsy that is currently used to assess lymph node metastasis is not effective. This necessitates identification of biomarkers that can flag metastasis. Early stage breast cancer patients were recruited. Surgical resection of breast was followed by identification of sentinel lymph nodes. Fresh frozen section biopsy was used to assign metastatic and non-metastatic sentinel lymph nodes. Discovery phase included iTRAQ proteomics coupled with mass spectrometric analysis to identify differentially expressed proteins. Data is available via ProteomeXchange with identifier PXD027668. Validation was done by bioinformatic analysis and ELISA. There were 2398 unique protein groups and 109 differentially expressed proteins comparing metastatic and non-metastatic lymph nodes. Forty nine proteins were up-regulated, and sixty proteins that were down regulated in metastatic group. Bioinformatic analysis showed ECM-receptor interaction pathways to be implicated in lymph node metastasis. ELISA confirmed up-regulation of ECM proteins in metastatic lymph nodes. ECM proteins have requisite parameters to be developed as a diagnostic tool to assess status of sentinel lymph nodes to guide surgical intervention in early breast cancer.

SYNCRIP Modulates the Epithelial-Mesenchymal Transition in Hepatocytes and HCC Cells

Heterogeneous nuclear ribonucleoproteins (hnRNPs) control gene expression by acting at multiple levels and are often deregulated in epithelial tumors; however, their roles in the fine regulation of cellular reprogramming, specifically in epithelial–mesenchymal transition (EMT), remain largely unknown. Here, we focused on the hnRNP-Q (also known as SYNCRIP), showing by molecular analysis that in hepatocytes it acts as a “mesenchymal” gene, being induced by TGFβ and modulating the EMT. SYNCRIP silencing limits the induction of the mesenchymal program and maintains the epithelial phenotype. Notably, in HCC invasive cells, SYNCRIP knockdown induces a mesenchymal–epithelial transition (MET), negatively regulating their mesenchymal phenotype and significantly impairing their migratory capacity. In exploring possible molecular mechanisms underlying these observations, we identified a set of miRNAs (i.e., miR-181-a1-3p, miR-181-b1-3p, miR-122-5p, miR-200a-5p, and miR-let7g-5p), previously shown to exert pro- or anti-EMT activities, significantly impacted by SYNCRIP interference during EMT/MET dynamics and gathered insights, suggesting the possible involvement of this RNA binding protein in their transcriptional regulation.

The role of RNA processing and regulation in metastatic dormancy

Tumor dormancy is a major contributor to the lethality of metastatic disease, especially for cancer patients who develop metastases years-to-decades after initial diagnosis. Indeed, tumor cells can disseminate during early disease stages and persist in new microenvironments at distal sites for months, years, or even decades before initiating metastatic outgrowth. This delay between primary tumor remission and metastatic relapse is known as "dormancy," during which disseminated tumor cells (DTCs) acquire quiescent states in response to intrinsic (i.e., cellular) and extrinsic (i.e., microenvironmental) signals. Maintaining dormancy-associated phenotypes requires DTCs to activate transcriptional, translational, and post-translational mechanisms that engender cellular plasticity. RNA processing is emerging as an essential facet of cellular plasticity, particularly with respect to the initiation, maintenance, and reversal of dormancy-associated phenotypes. Moreover, dysregulated RNA processing, particularly that associated with alternative RNA splicing and expression of noncoding RNAs (ncRNAs), can occur in DTCs to mediate intrinsic and extrinsic metastatic dormancy. Here we review the pathophysiological impact of alternative RNA splicing and ncRNAs in promoting metastatic dormancy and disease recurrence in human cancers.

HNRNPA2B1 as a trigger of RNA switch modulates the miRNA-mediated regulation of CDK6

The functional inactivation of tumor suppressor microRNA (miRNA) is closely related to the tumorigenesis of cancer. There are instances where the miRNA and the corresponding target both exist in a cell, but the target gene silencing do not occur as expected. Herein, we found that both miR-506 and its target CDK6 are highly co-expressed in lung cancer cells. Sequence analyses suggested that a miR-506 binding site (1648–1654) and a cis-element (1785–1795) for binding by heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) are evolutionarily conserved and forms a stem structure in the 3′ untranslated region (3′UTR) of CDK6. Furthermore, HNRNPA2B1 can bind to the stem structure to denature it and recruit the RNA helicase DExH-box helicase 9 (DHX9) to the 3′UTR, which ultimately facilitates miRNAs-mediated CDK6 silencing. These results indicate that the cis-element of the 3′UTR of CDK6, where HNRNPA2B1 binds, serves as an RNA switch to regulate miRNAs’ function in cancer cells.

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Both miR-506 and its target CDK6 are highly co-expressed in lung cancer

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HNRNPA2B1 facilitates miR-506-mediated CDK6 silence by switching structure in 3′UTR

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HNRNPA2B1 also recruits the DHX9 to the 3′UTR of its targets

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HNRNPA2B1 extensively regulates miRNAs-mediated gene silencing through binding to 3′UTR

hnRNPA2B1 Promotes Colon Cancer Progression via the MAPK Pathway

HNRNPA2B1, an RNA-binding protein, plays a key role in primary microRNA processing, alternative splicing, mRNA metabolism and transport. Interestingly, hnRNPA2B1 also works as an N6-methyladenosine (m6A) reader and is critical during tumorigenesis of various tissue types. However, its role in colon cancer is still unclear. In this study, we aimed to elucidate the biological functions of hnRNPA2B1 and to explore its underlying mechanisms in colon cancer. We examined the expression of hnRNPA2B1 in Oncomine and TCGA databases. Then verified the findings in colon cancer cells and clinical samples with western blotting and immunohistochemistry (IHC). We used CRISPR/Cas9 directed gene editing to knockout hnRNPA2B1 expression in human colon cancer cell line SW480 and HCT-116 and carried out both in vivo and in vitro experiments. The results were further confirmed by RNA-seq analyses. We found that hnRNPA2B1 significantly promoted colon cancer cell proliferation both in vitro and in vivo, while knockout of hnRNPA2B1 induced apoptosis and cell cycle arrest in SW480. RNA-seq analyses revealed that the ERK/MAPK pathway was activated by hnRNPA2B1 upregulation. In addition, both hnRNPA2B1 and MAPK pathway were activated in clinical colon cancer specimens and positively correlated. Mechanistically, hnRNPA2B1 appeared to be an upstream regulator of the ERK/MAPK pathway and inhibition of MAPK signaling blocked the effects of hnRNPA2B1. Taken together, our data demonstrated that the RNA-binding protein hnRNPA2B1 promotes cell proliferation and regulates cell cycle and apoptosis of human colon cancer by activating the ERK/MAPK signaling, which may provide a new insight into the development of hnRNPA2B1 as a potential therapeutic target for treatment of colon cancer.

MicroRNA‑8063 targets heterogeneous nuclear ribonucleoprotein AB to inhibit the self‑renewal of colorectal cancer stem cells via the Wnt/β‑catenin pathway

The presence of cancer stem cells (CSCs) is a major cause of therapeutic failure in a variety of cancer types, including colorectal cancer (CRC). However, the underlying mechanisms that regulate the self-renewal of colorectal cancer stem cells (CRCSCs) remain unclear. Our previous study utilized CRCSCs and their parent cells; through gene microarray screening and bioinformatics analysis, we hypothesized that microRNA (miR)-8063 may bind to, and regulate the expression of, heterogeneous nuclear ribonucleoprotein AB (hnRNPAB) to facilitate the regulation of CRCSC self-renewal. The aim of the present study was to confirm this conjecture through relevant experiments. The results indicated that compared with that in parent cells, miR-8063 expression was significantly downregulated in CRCSCs, while hnRNPAB expression was increased. Furthermore, hnRNPAB was identified as a direct target of miR-8063 using a dual-Luciferase assay. Overexpression of hnRNPAB promoted the acquisition of CSC characteristics in CRC cells (increased colony formation ability, enhanced tumorigenicity, and upregulated expression of CSC markers), as well as the upregulation of key proteins (Wnt3a, Wnt5a and β-catenin) in the Wnt/β-catenin signaling pathway. Similarly, after silencing miR-8063 in CRC cells, the characteristics of CSC were altered, and the expression of hnRNPAB protein was promoted. However, post overexpression of miR-8063 in CRCSCs, the self-renewal ability of CSCs was weakened with the downregulation of hnRNPAB protein, Wnt3a, Wnt5a and β-catenin. These results suggest that as a tumor suppressor, miR-8063 is involved in regulating the self-renewal of CRCSCs, where loss of miR-8063 expression weakens its inhibition on hnRNPAB, which leads to the activation of Wnt/β-catenin signaling to promote the self-renewal of CRCSCs.

hnRNP A/B Proteins: An Encyclopedic Assessment of Their Roles in Homeostasis and Disease

The hnRNP A/B family of proteins is canonically central to cellular RNA metabolism, but due to their highly conserved nature, the functional differences between hnRNP A1, A2/B1, A0, and A3 are often overlooked. In this review, we explore and identify the shared and disparate homeostatic and disease-related functions of the hnRNP A/B family proteins, highlighting areas where the proteins have not been clearly differentiated. Herein, we provide a comprehensive assembly of the literature on these proteins. We find that there are critical gaps in our grasp of A/B proteins' alternative splice isoforms, structures, regulation, and tissue and cell-type-specific functions, and propose that future mechanistic research integrating multiple A/B proteins will significantly improve our understanding of how this essential protein family contributes to cell homeostasis and disease.

Heterogeneous nuclear ribonucleoprotein A2/B1 regulates the ERK and p53/HDM2 signaling pathways to promote the survival, proliferation and migration of non‑small cell lung cancer cells

Lung cancer is the most frequent cause of cancer‑associated mortality worldwide. Upregulation of heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) has been reported in non‑small cell lung cancer (NSCLC) cells, but its contribution to NSCLC remains poorly understood. hnRNPA2/B1 is involved in carcinogenesis by interacting with a number of proteins; however, little is known about its interaction with p53. The results of the present study revealed that hnRNPA2/B1 expression levels were upregulated in NSCLC cells under tumorsphere culture conditions and cisplatin treatment compared with those in cells under the adherent condition and dimethyl sulfoxide treatment, respectively, suggesting that hnRNPA2/B1 expression is induced under stress conditions. hnRNPA2/B1 knockdown decreased the number and size of NSCLC cell colonies in a clonogenic survival assay and led to a decreased migratory potential of NSCLC cells, suggesting that hnRNPA2/B1 may promote the survival, proliferation and migration of NSCLC cells. hnRNPA2/B1 knockdown induced G₀/G₁ phase arrest in NSCLC cells through cyclin E degradation and phosphorylation of cyclin‑dependent kinase 2. In addition, hnRNPA2/B1 knockdown inhibited extracellular signal‑regulated kinase (ERK)1/2 phosphorylation, suggesting that hnRNPA2/B1 may promote the G₁/S phase transition in NSCLC cells through ERK signaling. hnRNPA2/B1 knockdown resulted in increased expression levels of p21 and p27 in NSCLC cells, as well as p53 induction and phosphorylation. Additionally, hnRNPA2/B1 knockdown inhibited human double minute 2 protein (HDM2) stability and phosphorylation, whereas overexpression of hnRNPA2 induced the opposite effects. These results suggested that hnRNPA2/B1 may promote the survival, proliferation and migration of NSCLC cells through preventing the activation of p53, which is induced by ERK‑mediated HDM2 activation. The results of the present study also indicated that the components of the hnRNPA2/B1/ERK/p53/HDM2 signaling pathway may be novel potential molecular targets for the treatment of patients with NSCLC.

Importance of N6-methyladenosine RNA modification in lung cancer (Review)

The N6-methyladenosine (m6A) modification is the most common mRNA modification in eukaryotes and exerts biological functions by affecting RNA metabolism. The m6A modification is installed by m6A methyltransferases, removed by demethylases and recognized by m6A-binding proteins. The interaction between these three elements maintains the dynamic equilibrium of m6A in cells. Accumulating evidence indicates that m6A RNA methylation has a significant impact on RNA metabolism and is involved in the pathogenesis of cancer. Lung cancer is the leading cause of cancer-related deaths worldwide. The treatment options for lung cancer have developed considerably over the past few years; however, the survival rate of patients with lung cancer still remains very low. Although diagnostic methods and targeted therapies have been rapidly developed in recent years, the underlying mechanism and importance of m6A RNA methylation in the pathogenesis of lung cancer remains ambiguous. The current review summarized the biological functions of m6A modification and considers the potential roles of m6A regulators in the occurrence and development of lung cancer.

HNRNPA2B1 promotes multiple myeloma progression by increasing AKT3 expression via m6A-dependent stabilization of ILF3 mRNA

N6-methyladenosine (m6A) modification is the most prevalent modification in eukaryotic RNAs while accumulating studies suggest that m6A aberrant expression plays an important role in cancer. HNRNPA2B1 is a m6A reader which binds to nascent RNA and thus affects a perplexing array of RNA metabolism exquisitely. Despite unveiled facets that HNRNPA2B1 is deregulated in several tumors and facilitates tumor growth, a clear role of HNRNPA2B1 in multiple myeloma (MM) remains elusive. Herein, we analyzed the function and the regulatory mechanism of HNRNPA2B1 in MM. We found that HNRNPA2B1 was elevated in MM patients and negatively correlated with favorable prognosis. The depletion of HNRNPA2B1 in MM cells inhibited cell proliferation and induced apoptosis. On the contrary, the overexpression of HNRNPA2B1 promoted cell proliferation in vitro and in vivo. Mechanistic studies revealed that HNRNPA2B1 recognized the m6A sites of ILF3 and enhanced the stability of ILF3 mRNA transcripts, while AKT3 downregulation by siRNA abrogated the cellular proliferation induced by HNRNPA2B1 overexpression. Additionally, the expression of HNRNPA2B1, ILF3 and AKT3 was positively associated with each other in MM tissues tested by immunohistochemistry. In summary, our study highlights that HNRNPA2B1 potentially acts as a therapeutic target of MM through regulating AKT3 expression mediated by ILF3-dependent pattern.

Function and Regulation of Nuclear DNA Sensors During Viral Infection and Tumorigenesis

IFI16, hnRNPA2B1, and nuclear cGAS are nuclear-located DNA sensors that play important roles in initiating host antiviral immunity and modulating tumorigenesis. IFI16 triggers innate antiviral immunity, inflammasome, and suppresses tumorigenesis by recognizing double-stranded DNA (dsDNA), single-stranded DNA (ssDNA), damaged nuclear DNA, or cooperatively interacting with multiple tumor suppressors such as p53 and BRCA1. hnRNPA2B1 initiates interferon (IFN)-α/β production and enhances STING-dependent cytosolic antiviral signaling by directly binding viral dsDNA from invaded viruses and facilitating N⁶ -methyladenosine (m⁶A) modification of cGAS, IFI16, and STING mRNAs. Nuclear cGAS is recruited to double-stranded breaks (DSBs), suppresses DNA repair, and promotes tumorigenesis. This review briefly describes the nuclear functions of IFI16, hnRNPA2B1, and cGAS, and summarizes the transcriptional, post-transcriptional, and post-translational regulation of these nuclear DNA sensors.

HnRNPA2/B1 Is a Novel Prognostic Biomarker for Breast Cancer Patients

Aims: Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) is highly expressed in multiple types of tumor tissues and could potentially be used as a biomarker for the early detection of lung cancer. However, there is little evidence supporting its clinical significance as a prognostic marker in breast cancer. Materials and Methods: We retrospectively analyzed the protein expression and localization of hnRNPA2/B1 protein in breast cancer tissues and adjacent normal tissues from 50 patients with Stage II and III breast cancer who were treated at Shanxi Provincial People's Hospital from May 2018 to May 2019 using western blot, and immunofluorescent and immunohistochemical staining assays. In addition, bioinformatic analyses using the Affymetrix Human Genome database were performed to examine the mRNA levels of hnRNPA2/B1 in normal and breast cancer tissues, and to determine their correlation with the survival rates of breast cancer patients. Results: Based on the cohort of 50 patients, HnRNPA2/B1 protein was expressed in both the cytoplasm and nucleus of breast cancer cells. The protein levels of hnRNPA2/B1 in breast cancer tissues were significantly higher than those in adjacent normal tissues (p < 0.001). Furthermore, bioinformatic analyses of hnRNPA2/B1 mRNA expression levels demonstrated that they were negatively correlated with overall survival and disease-specific survival rates in breast cancer patients. Conclusion: Our study indicates that hnRNPA2/B1 could serve as a novel prognostic biomarker for breast cancer.

RNA-Binding Proteins in Cancer: Functional and Therapeutic Perspectives

Simple Summary

RNA-binding proteins (RBPs) play central roles in regulating posttranscriptional expression of genes. Many of them are known to be deregulated in a wide variety of cancers. Dysregulated RBPs influence the expression levels of target RNAs related to cancer phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and EMT/invasion/metastasis. Thus, understanding the molecular functions of RBPs and their roles in cancer-related phenotypes can lead to improved therapeutic strategies.

Abstract

RNA-binding proteins (RBPs) crucially regulate gene expression through post-transcriptional regulation, such as by modulating microRNA (miRNA) processing and the alternative splicing, alternative polyadenylation, subcellular localization, stability, and translation of RNAs. More than 1500 RBPs have been identified to date, and many of them are known to be deregulated in cancer. Alterations in the expression and localization of RBPs can influence the expression levels of oncogenes, tumor-suppressor genes, and genome stability-related genes. RBP-mediated gene regulation can lead to diverse cancer-related cellular phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and epithelial-mesenchymal transition (EMT)/invasion/metastasis. This regulation can also be associated with cancer prognosis. Thus, RBPs can be potential targets for the development of therapeutics for the cancer treatment. In this review, we describe the molecular functions of RBPs, their roles in cancer-related cellular phenotypes, and various approaches that may be used to target RBPs for cancer treatment.

The roles of hnRNP A2/B1 in RNA biology and disease

The RNA-binding protein hnRNPA2/B1 is a member of the hnRNPs family and is widely expressed in various tissues. hnRNPA2/B1 recognizes and binds specific RNA substrates and DNA motifs and is involved in the transcription, splicing processing, transport, stability, and translation regulation of a variety of RNA molecules and in regulating the expression of a large number of genes. hnRNPA2/B1 is also involved in telomere maintenance and DNA repair, while its expression changes and mutations are involved in the development of various tumors and neurodegenerative and autoimmune diseases. This paper reviews the role and mechanism of hnRNPA2/B1 in RNA metabolism, tumors, and neurodegenerative and autoimmune diseases. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA in Disease and Development > RNA in Disease.

The Role of RNA Splicing Factors in Cancer: Regulation of Viral and Human Gene Expression in Human Papillomavirus-Related Cervical Cancer

The spliceosomal complex components, together with the heterogeneous nuclear ribonucleoproteins (hnRNPs) and serine/arginine-rich (SR) proteins, regulate the process of constitutive and alternative splicing, the latter leading to the production of mRNA isoforms coding multiple proteins from a single pre-mRNA molecule. The expression of splicing factors is frequently deregulated in different cancer types causing the generation of oncogenic proteins involved in cancer hallmarks. Cervical cancer is caused by persistent infection with oncogenic human papillomaviruses (HPVs) and constitutive expression of viral oncogenes. The aberrant activity of hnRNPs and SR proteins in cervical neoplasia has been shown to trigger the production of oncoproteins through the processing of pre-mRNA transcripts either derived from human genes or HPV genomes. Indeed, hnRNP and SR splicing factors have been shown to regulate the production of viral oncoprotein isoforms necessary for the completion of viral life cycle and for cell transformation. Target-therapy strategies against hnRNPs and SR proteins, causing simultaneous reduction of oncogenic factors and inhibition of HPV replication, are under development. In this review, we describe the current knowledge of the functional link between RNA splicing factors and deregulated cellular as well as viral RNA maturation in cervical cancer and the opportunity of new therapeutic strategies.

hnRNPA2/B1 Ameliorates LPS-Induced Endothelial Injury through NF-κB Pathway and VE-Cadherin/β-Catenin Signaling Modulation In Vitro

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) is a protein involved in the regulation of RNA processing, cell metabolism, migration, proliferation, and apoptosis. However, the effect of hnRNPA2/B1 on injured endothelial cells (ECs) remains unclear. We investigated the effect of hnRNPA2/B1 on lipopolysaccharide- (LPS-) induced vascular endothelial injury in human umbilical vein endothelial cells (HUVECs) and the underlying mechanisms. LPS was used to induce EC injury, and the roles of hnRNPA2/B1 in EC barrier dysfunction and inflammatory responses were measured by testing endothelial permeability and the expression of inflammatory factors after the suppression and overexpression of hnRNPA2/B1. To explore the underlying mechanism by which hnRNPA2/B1 regulates endothelial injury, we studied the VE-cadherin/β-catenin pathway and NF-κB activation in HUVECs. The results showed that hnRNPA2/B1 was elevated in LPS-stimulated HUVECs. Moreover, knockdown of hnRNPA2/B1 aggravated endothelial injury by increasing EC permeability and promoting the secretion of the inflammatory cytokines TNF-α, IL-1β, and IL-6. Overexpression of hnRNPA2/B1 can reduce the permeability and inflammatory response of HUVEC stimulated by LPS in vitro, while increasing the expression of VE-Cadherin and β-catenin. Furthermore, the suppression of hnRNPA2/B1 increased the LPS-induced NF-κB activation and reduced the VE-cadherin/β-catenin pathway. Taken together, these results suggest that hnRNPA2/B1 can regulate LPS-induced EC damage through regulating the NF-κB and VE-cadherin/β-catenin pathways.

Profiling of subcellular EGFR interactome reveals hnRNP A3 modulates nuclear EGFR localization

The aberrant subcellular translocation and distribution of epidermal growth factor receptor (EGFR) represent a major yet currently underappreciated cancer development mechanism in non-small cell lung cancer (NSCLC). In this study, we investigated the subcellular interactome of EGFR by using a spectral counting-based approach combined with liquid chromatography–tandem mass spectrometry to understand the associated protein networks involved in the tumorigenesis of NSCLC. A total of 54, 77, and 63 EGFR-interacting proteins were identified specifically in the cytosolic, mitochondrial, and nuclear fractions from a NSCLC cell line, respectively. Pathway analyses of these proteins using the KEGG database shown that the EGFR-interacting proteins of the cytosol and nucleus are involved in the ribosome and spliceosome pathways, respectively, while those of the mitochondria are involved in metabolizing propanoate, fatty acid, valine, leucine, and isoleucine. A selected nuclear EGFR-interacting protein, hnRNP A3, was found to modulate the accumulation of nuclear EGFR. Downregulation of hnRNP A3 reduced the nuclear accumulation of EGFR, and this was accompanied by reduced tumor growth ability in vitro and in vivo. These results indicate that variations in the subcellular translocation and distribution of EGFR within NSCLC cells could affect tumor progression.

A tumor-specific modulation of heterogeneous ribonucleoprotein A0 promotes excessive mitosis and growth in colorectal cancer cells

RNA regulation mediating RNA-binding proteins (RBPs) have been shown to be related to the maintenance of homeostasis as well as cancer progression. However, the tumor-associated functions as well as the detailed mechanisms underlying the anti-tumor effects of most RBPs have yet to be explored. We herein report that the phosphorylated heterogeneous ribonucleoprotein (hnRNP) A0 promotes mitosis through the RAS-associated protein 3 GTPase-activating protein catalytic subunit 1 (RAB3GAP1)-Zeste white 10 interactor (ZWINT1) cascade. The downregulation assay of 20 representative hnRNPs, a major family of RNA-binding proteins, in colorectal cancer cells revealed that hnRNPA0 is a strong regulator of cancer cell growth. The tumor promotive function of hnRNPA0 was confirmed in gastrointestinal cancer cells, including pancreatic, esophageal, and gastric cancer cells, but not in non-cancerous cells. Flow cytometry and Western blotting analyses revealed that hnRNPA0 inhibited the apoptosis through the maintenance of G2/M phase promotion in colorectal cancer cells. A comprehensive analysis of mRNAs regulated by hnRNP A0 and immunostaining revealed that mitotic events were regulated by the hnRNPA0-RAB3GAP1 mRNA-mediated ZWINT-1 stabilization in colorectal cancer cells, but not in non-tumorous cells. The interaction of hnRNP A0 with mRNAs was dramatically changed by the deactivation of its phosphorylation site in cancer cells, but not in non-tumorous cells. Therefore, the tumor-specific biological functions characterized by the abnormal phosphorylation of RBPs are considered to be an attractive target for tumor treatment.

Loss of hnRNPA2B1 inhibits malignant capability and promotes apoptosis via down-regulating Lin28B expression in ovarian cancer

Ovarian cancer has the highest mortality rate among all gynecological cancers with its pathogenic mechanisms largely unknown. Here, we uncovered that ovarian cancer tissues exhibit higher heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) expression than normal ovarian epithelium tissues. Increased hnRNPA2B1 level matches along with poor prognosis of ovarian cancer patients. Importantly, hnRNPA2B1 inhibition hampers growth, reduces mobility of ovarian cancer cells in vitro and hinders xenograft tumor formation in vivo. Transcriptome profiling analysis reveals that hnRNPA2B1 dictates the expression of various important genes involved in tumorigenesis and Lin-28 Homolog B (Lin28B) is down-regulated upon hnRNPA2B1 loss. hnRNPA2B1 regulates expression of Lin28B via binding to Lin28B mRNA and enhancing its stability. Furthermore, knockdown of Lin28B reduces proliferation and mobility of ovarian cancer cells and impairs tumorigenesis in vivo, whereas Lin28B overexpression promotes xenograft tumor formation. Finally, re-expression of Lin28B in hnRNPA2B1 knockdown cells results in rescued phenotypes. Collectively, our results demonstrate that hnRNPA2B1 facilitates the malignant phenotype of ovarian cancer through activating Lin28B expression.

Heterogeneous nuclear ribonucleoprotein A2/B1 is a negative regulator of human breast cancer metastasis by maintaining the balance of multiple genes and pathways

Background

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 is an important RNA-binding protein that affects the RNA processing, splicing, transport and stability of many genes. hnRNPA2/B1 is expressed during proliferation and metastasis of various cancer types and promotes such processes. However, the precise role and mechanism of hnRNPA2/B1 in breast cancer remain unclear.

Methods

The association of hnRNPA2/B1 with breast cancer metastasis was assessed using tissue chips, mouse models and publicly available data. The role and mechanism of hnRNPA2/B1 in breast cancer metastasis were studied in cell lines and mouse models.

Findings

In contrast to other cancer research findings, hnRNPA2/B1 expression was negatively correlated with breast cancer metastasis. hnRNPA2/B1 inhibited MDA-MB-231 triple-negative breast cancer (TNBC) cell metastasis in vitro and in vivo. hnRNPA2/B1 knockout activated ERK-MAPK/Twist and GR-beta/TCF4 pathways but inhibited STAT3 and WNT/TCF4 signalling pathways. Profilin 2 (PFN2) promoted breast cancer cell migration and invasion, whereas hnRNPA2/B1 bound directly to the UAGGG locus in the 3′-untranslated region of PFN2 mRNA and reduced the stability of PFN2 mRNA.

Interpretation

Our data supported the role of hnRNPA2/B1 in tumour metastasis risk and survival prediction in patients with breast cancer. The inhibitory role of hnRNPA2/B1 in metastasis was a balance of downstream multiple genes and signalling pathways. PFN2 downregulation by hnRNPA2/B1 might partly explain the inhibitory mechanism of hnRNPA2/B1 in breast cancer metastasis. Therefore, hnRNPA2/B1 might be used as a new prognostic biomarker and valuable molecular target for breast cancer treatments.

Anti-Inflammatory Action of Heterogeneous Nuclear Ribonucleoprotein A2/B1 in Patients with Autoimmune Endocrine Disorders

Our previous studies documented that human fibroblast-limbal stem cells (f-LSCs) possess immunosuppressive capabilities, playing a role in regulating T-cell activity. This study highlights the molecular activities by which human f-LSCs can attenuate the inflammatory responses of self-reactive peripheral blood mononuclear cells (PBMCs) collected from patients with autoimmune endocrine diseases (AEDs). Anti-CD3 activated PBMCs from twenty healthy donors and fifty-two patients with AEDs were cocultured on f-LSC monolayer. 2D-DIGE proteomic experiments, mass spectrometry sequencing and functional in vitro assays were assessed in cocultured PBMCs. We identified the downmodulation of several human heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) isoforms in healthy and AED activated PBMCs upon f-LSC interaction. The reduction of hnRNPA2/B1 protein expression largely affected the cycling ki67⁺, CD25⁺, PD-1⁺ reactive cells and the double marked CD8⁺/hnRNPA2B1⁺ T cell subset. Anti-PD1 blocking experiments evoked hnRNPA2/B1 overexpression, attributing putative activation function to the protein. hnRNPA2/B2 transient silencing inverted immunopolarization of the self-reactive PBMCs from AEDs toward a M2/Th2-type background. Pharmacological inhibition and co-immunoprecipitation experiments demonstrated the involvement of NF-ĸB in hnRNPA2/B activity and turnover. Our data indicate cardinal involvement of hnRNP A2/B1 protein in peripheral mechanisms of tolerance restoration and attenuation of inflammation, identifying a novel immunoplayer potentially targetable in all AEDs.

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.

HNRNPAB-regulated lncRNA-ELF209 inhibits the malignancy of hepatocellular carcinoma

Our previous study demonstrated that heterogeneous nuclear ribonucleoprotein AB (HNRNPAB) is a key gene that facilitates metastasis of hepatocellular carcinoma (HCC). However, the molecular mechanisms behind this relationship are not fully understood. In our study, we utilized long-noncoding RNA (lncRNA) microarrays to identify a HNRNPAB-regulated lncRNA named lnc-ELF209. Our findings from chromatin immunoprecipitation assays indicate that HNRNPAB represses lnc-ELF209 transcription by directly binding to its promoter region. We also analyzed clinical samples from HCC patients and cell lines with quantitative real-time polymerase chain reactions, RNA in situ hybridization and immunohistochemistry, and found that there is a negative relationship between HNRNPAB and lnc-ELF209 expression. Up/downregulation assays and rescue assays indicate that lnc-ELF209 inhibits cell migration, invasion and epithelial-mesenchymal transition regulated by HNRNPAB. This suggests a new regulatory mechanism for HNRNPAB-promoted HCC progression. RNA pull-down and LC-MS/MS were used to determine triosephosphate isomerase, heat shock protein 90-beta and vimentin may be involved in the tumor-suppressed function of lnc-ELF209. Furthermore, we found lnc-ELF209 could stabilize TPI protein expression. We also found that lnc-ELF209 overexpression in HCCLM3 cell resulted in a lower rate of lung metastatic, which suggested a less aggressive HCC phenotype. Collectively, these findings offer new insights into the regulatory mechanisms that underlie HNRNPAB cancer-promoting activities and demonstrate that lnc-ELF209 is a HNRNPAB-regulated lncRNA that may play an important role in the inhibition of HCC progression.

Mechanism of the natural product moracin-O derived MO-460 and its targeting protein hnRNPA2B1 on HIF-1α inhibition

Hypoxia-inducible factor-1α (HIF-1α) mediates tumor cell adaptation to hypoxic conditions and is a potentially important anticancer therapeutic target. We previously developed a method for synthesizing a benzofuran-based natural product, (R)-(-)-moracin-O, and obtained a novel potent analog, MO-460 that suppresses the accumulation of HIF-1α in Hep3B cells. However, the molecular target and underlying mechanism of action of MO-460 remained unclear. In the current study, we identified heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) as a molecular target of MO-460. MO-460 inhibits the initiation of HIF-1α translation by binding to the C-terminal glycine-rich domain of hnRNPA2B1 and inhibiting its subsequent binding to the 3’-untranslated region of HIF-1α mRNA. Moreover, MO-460 suppresses HIF-1α protein synthesis under hypoxic conditions and induces the accumulation of stress granules. The data provided here suggest that hnRNPA2B1 serves as a crucial molecular target in hypoxia-induced tumor survival and thus offer an avenue for the development of novel anticancer therapies.

A synthetic analog of a chemical found in fruit suppresses tumor growth by targeting an RNA-binding protein (hnRNPA2B1) and preventing the production of a pro-cancer regulatory factor. Nak-Kyun Soung from the Korea Research Institute of Bioscience and Biotechnology, Cheongju, South Korea, and coworkers built on their previous discovery that a compound derived from a medicinal plant metabolite can suppress the activity of hypoxia-inducible factor-1α (HIF-1α). This protein, which is involved in many aspects of cancer biology, is activated in the low-oxygen microenvironments found inside tumors. The researchers show that the compound binds to a protein that helps with the conversion of HIF-1α–encoding RNA transcripts into HIF-1α proteins. Liver cancer cells treated with the compound grew slowly and produced less HIF-1α under both normal and low-oxygen culture conditions, highlighting the potential of this anti-cancer strategy.

EZH2-mediated epigenetic suppression of EphB3 inhibits gastric cancer proliferation and metastasis by affecting E-cadherin and vimentin expression

EphB3 is a member of the EPH family of receptors and has been found to play a role in the carcinogenesis of some human cancers. However, its expression and clinical significance in gastric cancer (GC) have not been well documented. In the present study, we detected the expression of EphB3 in GC and adjacent noncancerous tissues and explored its relationships with the clinicopathological features and prognosis of GC patients. It was found that EphB3 silenced GC cells epigenetically by direct transcriptional repression of GC cells via polycomb group protein EZH2 mediation. EphB3 was downregulated in GC cells and tissues, and EphB3 depletion promoted GC cell growth and invasion, while ectopic overexpression of EphB3 produced a significant anti-tumor effect. EphB3 was found to be involved in epithelial-mesenchymal transition by regulating E-cadherin and vimentin expression. In addition, patients with reduced EphB3 expression had shorter disease-free survival (DFS), indicating that EphB3 may prove to be a biomarker for prognosis of GC. These results demonstrated that EphB3 functioned as a tumor-suppressor and prognostic biomarker in GC.

Roles of Albumin-Binding Proteins in Cancer Progression and Biomimetic Targeted Drug Delivery

Nutrient transporters have attracted significant attention for their promising application in biomimetic delivery. Due to the active consumption of nutrients, cancer cells generally overexpress nutrient transporters to meet their increased need for energy and materials. For example, albumin-binding proteins (ABPs) are highly overexpressed in malignant cells, stromal cells, and tumor vessel endothelial cells responsible for albumin uptake. ABP (e.g., SPARC) is a promising target for tumor-specific drug delivery, and albumin has been widely used as a biomimetic delivery carrier. Apart from the transportation function, ABPs are closely associated with neoplasia, invasion, and metastasis. Herein, a summary of the roles of ABP in cancer progression and the application of albumin-based biomimetic tumor-targeted delivery through the ABP pathway is presented.

The homeostasis-maintaining metabolites from bacterial stress response to bacteriophage infection suppress tumor metastasis

The antiviral metabolites from bacterial stress response to bacteriophage infection can maintain homeostasis of host cells, while metabolism disorder is a remarkable characteristic of tumorigenesis. In the aspect of metabolic homeostasis, therefore, the antiviral homeostasis-maintaining metabolites of bacteria may possess anti-tumor activity. However, this issue has not been addressed. Here we show that the homeostasis-challenged maintaining metabolites from deep-sea bacteriophage-challenged thermophile can suppress tumor metastasis. The results indicated that the metabolic profiles of the bacteriophage GVE2-infected and virus-free thermophile Geobacillus sp. E263 from a deep-sea hydrothermal vent were remarkably different. Thirteen metabolites were significantly elevated and two metabolites were downregulated in thermophile stress response to GVE2 infection. As an example, the upregulated L-norleucine was characterized. The data showed that L-norleucine had antiviral activity in thermophile. Furthermore, the in vitro and in vivo assays revealed that L-norleucine, as well as its derivative, significantly suppressed metastasis of gastric and breast cancer cells. L-norleucine interacted with hnRNPA2/B1 protein to inhibit the expressions of Twist1 and Snail, two inhibitors of E-cadherin, and promote the E-cadherin expression, leading to the inhibition of tumor metastasis. Therefore, our study presented that antiviral homeostasis-maintaining metabolites of microbes might be a promising source for anti-tumor drugs.

β-Asarone Inhibits Invasion and EMT in Human Glioma U251 Cells by Suppressing Splicing Factor HnRNP A2/B1

β-asarone, the main component in the volatile oil of Acori tatarinowii Rhizoma, has been found to possess antitumor activity. However, its effect and mechanisms against tumor invasion and epithelial–mesenchymal transition (EMT) are still unclear. In this study, no or less cytotoxicity was caused by β-asarone within 0–120 μM in human glioma U251 cells for 48 h. β-asarone (30 and 60 μM) inhibited the migration of U251 cells in the wound healing assay, suppressed the invasion of U251 cells in the Boyden chamber invasion assay, and inhibited the adhesion of U251 cells onto the Matrigel. Moreover, β-asarone suppressed EMT with the up-regulation of E-cadherin and the down-regulation of vimentin. HnRNP A2/B1, a well-characterized oncogenic protein, was shown at a high basal level in U251 cells and β-asarone reduced hnRNP A2/B1 expression in a concentration and time-dependent way. Importantly, hnRNP A2/B1 overexpression significantly counteracted the inhibition of β-asarone on the migration, invasion, and adhesion of U251 cells and reversed the modulation of EMT markers by β-asarone. Additionally, β-asarone decreased the MMP-9 and p-STAT3 in U251 cells, which was also reversed by hnRNP A2/B1 overexpression. Together, our results suggest that hnRNP A2/B1 may be a potential molecular target underlying the inhibitory effect of β-asarone on invasion and EMT in glioma cells.

High expression of hnRNPA1 promotes cell invasion by inducing EMT in gastric cancer

Advanced gastric cancer (GC) has a poor prognosis and its treatment strategies are not very efficient. Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) has emerged as a plausible GC marker, however the role and molecular mechanism of hnRNPA1 in cell invasion and migration remains unknown. In the present study, the gene expression across normal and tumor tissue (GENT) database was used to evaluate the mRNA expression of hnRNPA1 in various types of cancer. Western blot analysis (WB) and immunohistochemistry (IHC) were performed to detect the protein expression of hnRNPA1 in GC tissues and adjacent non-tumor tissues. The expression of multiple oncogenes was detected by western blot analysis and quantitative RT-PCR in hnRNPA1 overexpressing GC cells. Soft agar colony formation, EdU incorporation, wound healing and invasion assays were applied to verify the role of hnRNPA1 in anchorage-independent cell growth, migration and invasion in GC cells. Epithelial-to-mesenchymal transition (EMT) markers were detected by immunofluorescence, western blot analysis and IHC in vitro. A nude mice model of metastasis carcinoma was established to confirm the role of hnRNPA1 during EMT in vivo. Our results revealed that hnRNPA1 was significantly upregulated in GC tissue. HnRNPA1 overexpression significantly induced cell growth, migration and invasion ability in GC cells. In addition, hnRNPA1 promoted EMT of GC cells in vitro and in vivo. These findings indicated that hnRNPA1 is highly expressed in GC and promoted invasion by inducing EMT transition in GC cells. Thus, hnRNPA1 may be a potential therapeutic target for GC.

Knockdown of hnRNP A2/B1 inhibits cell proliferation, invasion and cell cycle triggering apoptosis in cervical cancer via PI3K/AKT signaling pathway

Cervical cancer is currently one of the major threats to women's health. The overexpression of heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) as the biomarker has been investigated in various cancers. In our previous study, we found that lobaplatin induced apoptosis and cell cycle arrest via downregulation of proteins including hnRNP A2/B1 in cervical cancer cells. However, the underlying relationship between hnRNP A2/B1 and cervical cancer remained largely unknown. hnRNP A2/B1 knock-down in HeLa and CaSki cells was performed by shRNA transfection. The expression of hnRNP A2/B1 was detected by western blot and Quantitative Real-time PCR. Cell proliferation, migration, invasion and the IC₅₀ of lobaplatin and irinotecan were determined by MTT assay, Transwell assay, Plate colony formation assay and wound healing assay. Flow cytometry was perfomed to investigate cell apoptosis and the cell cycle. The expression of PI3K, AKT, p-AKT, p21, p27, caspase-3, cleaved caspase-3 were revealed by western blot. Nude mouse xenograft model was undertaken with HeLa cells and the xenograft tumor tissue samples were analyzed for the expression of PCNA and Ki-67 by immunohistochemistry and the cell morphology was evaluated by hematoxylin and eosin (H&E). Results revealed that hnRNP A2/B1 was successfully silenced in HeLa and CaSki cells. hnRNP A2/B1 knock-down significantly induced the suppression of proliferation, migration, invasion and also enhancement of apoptosis and reduced the IC₅₀ of lobaplatin and irinotecan. The expression of p21, p27 and cleaved caspase-3 in shRNA group were significantly upregulated and the expression of p-AKT was reduced both in vitro and in vivo. The results of immunohistochemistry showed that PCNA and Ki-67 were significantly downregulated in vivo. The growth of nude mouse xenograft tumor was significantly reduced by hnRNP A2/B1 knock-down. Taken together, these data indicate that inhibition of hnRNP A2/B1 in cervical cancer cells can inhibit cell proliferation and invasion, induce cell-cycle arrestment and trigger apoptosis via PI3K/AKT signaling pathway. In addition, after silencing hnRNP A2/B1 can increase the sensitivity of cervical cancer cells to lobaplatin and irinotecan.

Heterogeneous nuclear ribonucleoproteins A1 and A2 modulate expression of Tid1 isoforms and EGFR signaling in non-small cell lung cancer

The Tid1 protein is a DnaJ co-chaperone that has two alternative splicing isoforms: Tid1 long form (Tid1-L) and Tid1 short form (Tid1-S). Recent studies have shown that Tid1-L functions as a tumor suppressor by decreasing EGFR signaling in various cancers, including head and neck cancer and non-small cell lung cancer (NSCLC). However, the molecular mechanism responsible for regulating the alternative splicing of Tid1 is not yet known. Two splicing factors, heterogeneous nuclear ribonucleoproteins (hnRNP) A1 and A2, participate in alternative splicing and are known to be overexpressed in lung cancers. In this work, we examined if hnRNP A1 and A2 could regulate the alternative splicing of Tid1 to modulate tumorigenesis in NSCLC. We report that RNAi-mediated depletion of both hnRNP A1/A2 (but not single depletion of either) increased Tid1-L expression, inhibited cell proliferation and attenuated EGFR signaling. Analyses of the expression levels of hnRNP A1, hnRNP A2, EGFR and Tid1-L in NSCLC tissues revealed that hnRNP A1 and A2 are positively correlated with EGFR, but negatively correlated with Tid1-L. NSCLC patients with high-level expression of hnRNP A1, hnRNP A2 and EGFR combined with low-level expression of Tid1-L were associated with poor overall survival. Taken together, our results suggest that hnRNP A1 or A2 are both capable of facilitating the alternative splicing of exon 11 in the Tid1 pre-mRNA, thereby suppressing the expression of Tid1-L and allowing EGFR-related signaling to facilitate NSCLC tumorigenesis.

Nm23-H1-stabilized hnRNPA2/B1 promotes internal ribosomal entry site (IRES)-mediated translation of Sp1 in the lung cancer progression

Our recent studies have indicated that specificity protein-1 (Sp1) accumulates substantially in the early stage of lung cancer but is partially decreased in the late stages, which is an important factor in the progression of the cancer. In this study, we found that Nm23-H1 and hnRNPA2/B1 could be recruited to the 5'UTR of Sp1 mRNA. In investigating the clinical relevance of Nm23-H1/Sp1 levels, we found a positive correlation between lung cancer patients with poor prognosis and low levels of Sp1 and Nm23-H1, suggesting an association between Nm23-H1/Sp1 levels and survival rate. Knockdown of Nm23-H1 inhibits lung cancer growth but increases lung cancer cell malignancy, which could be rescued by overexpression of Sp1, indicating that Nm23-H1-induced Sp1 expression is critical for lung cancer progression. We also found that Nm23-H1 increases the protein stability of hnRNPA2/B1and is thereby co-recruited to the 5'UTR of Sp1 mRNA to regulate cap-independent translational activity. Since the Sp1 level is tightly regulated during lung cancer progression, understanding the molecular mechanisms underlying the regulation by Nm23-H1/hnRNPA2B1 of Sp1 expression in the various stages of lung cancer will be beneficial for lung cancer therapy in the future.

RNA-Binding Proteins in Cancer: Old Players and New Actors

RNA-binding proteins (RBPs) are key players in post-transcriptional events. The combination of versatility of their RNA-binding domains with structural flexibility enables RBPs to control the metabolism of a large array of transcripts. Perturbations in RBP-RNA networks activity have been causally associated with cancer development, but the rational framework describing these contributions remains fragmented. We review here the evidence that RBPs modulate multiple cancer traits, emphasize their functional diversity, and assess future trends in the study of RBPs in cancer.

Splicing factor hnRNPA2B1 contributes to tumorigenic potential of breast cancer cells through STAT3 and ERK1/2 signaling pathway

Increasing evidence has indicated that the splicing factor hnRNPA2B1 plays a direct role in cancer development, progression, gene expression, and signal transduction. Previous studies have shown that knocking down hnRNPA2B1 in breast cancer cells induces apoptosis, but the mechanism and other functions of hnRNPA2B1 in breast cancer are unknown. The goal of this study was to investigate the biological function, clinical significance, and mechanism of hnRNPA2B1 in breast cancer. The expression of hnRNPA2B1 in 92 breast cancer and adjacent normal tissue pairs was analyzed by immunohistochemical staining. Stable clones exhibiting knockdown of hnRNPA2B1 via small hairpin RNA expression were generated using RNA interference technology in breast cancer cell lines. The effects of hnRNPA2B1 on cell proliferation were examined by MTT and EdU assay, and cellular apoptosis and the cell cycle were examined by flow cytometry. A nude mouse xenograft model was established to elucidate the function of hnRNPA2B1 in tumorigenesis in vivo. The role of hnRNPA2B1 in signaling pathways was investigated in vitro. Our data revealed that hnRNPA2B1 was overexpressed in breast cancer tissue specimens and cell lines. Knockdown of hnRNPA2B1 reduced breast cancer cell proliferation, induced apoptosis, and prolonged the S phase of the cell cycle in vitro. In addition, hnRNPA2B1 knockdown suppressed subcutaneous tumorigenicity in vivo. On a molecular level, hnRNPA2B1 knockdown decreased signal transducer and activator of transcription 3 and extracellular-signal-regulated kinase 1/2 phosphorylation. We concluded that hnRNPA2B1 promotes the tumorigenic potential of breast cancer cells, MCF-7 and MDA-MB-231, through the extracellular-signal-regulated kinase 1/2 or signal transducer and activator of transcription 3 pathway, which may serve as a target for future therapies.

Identification of autoantibodies to ECH1 and HNRNPA2B1 as potential biomarkers in the early detection of lung cancer

Identification of biomarkers for early detection of lung cancer (LC) is important, in turn leading to more effective treatment and reduction of mortality. Serological proteome analysis (SERPA) was used to identify proteins around 34 kD as ECH1 and HNRNPA2B1, which had been recognized by serum autoantibody from 25 LC patients. In the validation study, including 90 sera from LC patients and 89 sera from normal individuals, autoantibody to ECH1 achieved an area under the curve (AUC) of 0.799 with sensitivity of 62.2% and specificity of 95.5% in discriminating LC from normal individuals, and showed negative correlation with tumor size (r_s = -0.256, p = 0.023). Autoantibody to HNRNPA2B1 performed an AUC of 0.874 with sensitivity of 72.2% and specificity of 95.5%, and showed negative correlation with lymph node metastasis (r_s = -0.279, p = 0.012). By using longitudinal preclinical samples, autoantibody to ECH1 showed an AUC of 0.763 with sensitivity of 60.0% and specificity of 89.3% in distinguishing early stage LC from matched normal controls, and elevated autoantibody levels could be detected greater than 2 y before LC diagnosis. ECH1 and HNRNPA2B1 are autoantigens that elicit autoimmune responses in LC and their autoantibody can be the potential biomarkers for the early detection of LC.

EMT and stemness: flexible processes tuned by alternative splicing in development and cancer progression

Epithelial-to-mesenchymal transition (EMT) is associated with metastasis formation as well as with generation and maintenance of cancer stem cells. In this way, EMT contributes to tumor invasion, heterogeneity and chemoresistance. Morphological and functional changes involved in these processes require robust reprogramming of gene expression, which is only partially accomplished at the transcriptional level. Alternative splicing is another essential layer of gene expression regulation that expands the cell proteome. This step in post-transcriptional regulation of gene expression tightly controls cell identity between epithelial and mesenchymal states and during stem cell differentiation. Importantly, dysregulation of splicing factor function and cancer-specific splicing isoform expression frequently occurs in human tumors, suggesting the importance of alternative splicing regulation for cancer biology.

In this review, we briefly discuss the role of EMT programs in development, stem cell differentiation and cancer progression. Next, we focus on selected examples of key factors involved in EMT and stem cell differentiation that are regulated post-transcriptionally through alternative splicing mechanisms. Lastly, we describe relevant oncogenic splice-variants that directly orchestrate cancer stem cell biology and tumor EMT, which may be envisioned as novel targets for therapeutic intervention.

HNRNPA2B1 regulates the epithelial-mesenchymal transition in pancreatic cancer cells through the ERK/snail signalling pathway

Background

Heterogeneous nuclear ribonucleoprotein A2B1 (HNRNPA2B1) is closely related to tumour occurrence and development, oncogene expression, apoptosis inhibition and invasion and metastasis capacities. However, its function in the epithelial–mesenchymal transition (EMT) of pancreatic cancer is not fully understood.

Methods

By comparing various wild-type pancreatic cancer cell lines, we determined which have a higher expression level of HNRNPA2B1 accompanied by the higher expression of N-cadherin and vimentin and lower expression of E-cadherin. Therefore, to elucidate the role of HNRNPA2B1 in EMT, we generated models of HNRNPA2B1 knockdown and overexpression in different types of pancreatic cancer cell lines (MIA Paca-2, PANC-1 and Patu-8988) and examined changes in expression of EMT-related factors, including CDH1, CDH2, vimentin and snail.

Results

The results show that HNRNPA2B1 promotes EMT development by down-regulating E-cadherin and up-regulating N-cadherin and vimentin, and also stimulates the invasion capacity and inhibits viability in human pancreatic cancer cell lines, the similar results in vivo experiments. Moreover, we found that HNRNPA2B1 likely regulates EMT progression in pancreatic carcinoma via the ERK/snail signalling pathway.

Conclusions

The results of this work suggest that HNRNPA2B1 inhibition has potential antitumour effects, which warrants in-depth investigation.