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

The role of alternative splicing in lung cancer

Aberrant alternative splicing (AS) events are frequently observed in lung cancer, which can be attributed to aberrant gene AS, alterations in splicing regulatory factors, or changes in splicing regulatory mechanisms. Consequently, the dysregulation of alternative RNA splicing is the fundamental cause of lung cancer. In this review, we have summarized the pivotal role of AS in the development, progression, invasion, metastasis, angiogenesis, and drug resistance of lung cancer. Ultimately, this review emphasizes the potential of AS as biomarkers in lung cancer prognosis and diagnosis, and introduces some applications of AS isoform in the treatment of lung cancer. The comprehension of the AS may provide a glimmer of hope for the eradication of lung cancer.

hnRNP A1 in RNA metabolism regulation and as a potential therapeutic target

Abnormal RNA metabolism, regulated by various RNA binding proteins, can have functional consequences for multiple diseases. Heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is an important RNA binding protein, that regulates various RNA metabolic processes, including transcription, alternative splicing of pre-mRNA, translation, miRNA processing and mRNA stability. As a potent splicing factor, hnRNP A1 can regulate multiple splicing events, including itself, collaborating with other cooperative or antagonistical splicing factors by binding to splicing sites and regulatory elements in exons or introns. hnRNP A1 can modulate gene transcription by directly interacting with promoters or indirectly impacting Pol II activities. Moreover, by interacting with the internal ribosome entry site (IRES) or 3′-UTR of mRNAs, hnRNP A1 can affect mRNA translation. hnRNP A1 can alter the stability of mRNAs by binding to specific locations of 3′-UTR, miRNAs biogenesis and Nonsense-mediated mRNA decay (NMD) pathway. In this review, we conclude the selective sites where hnRNP A1 binds to RNA and DNA, and the co-regulatory factors that interact with hnRNP A1. Given the dysregulation of hnRNP A1 in diverse diseases, especially in cancers and neurodegeneration diseases, targeting hnRNP A1 for therapeutic treatment is extremely promising. Therefore, this review also provides the small-molecule drugs, biomedicines and novel strategies targeting hnRNP A1 for therapeutic purposes.

Putting human Tid-1 in context: an insight into its role in the cell and in different disease states

Background

Tumorous imaginal disc 1 (hTid-1) or DnaJ homolog subfamily A member 3 (DNAJA3), is a part of the heat shock protein (Hsp) 40 family and is predominantly found to reside in the mitochondria. hTid-1 has two mRNA splicing variants, hTid-1S and hTid-1L of 40 and 43 kDa respectively in the cytosol which are later processed upon import into the mitochondrial matrix. hTid-1 protein is a part of the DnaJ family of proteins which are co-chaperones and specificity factors for DnaK proteins of the Hsp70 family, and bind to Hsp70, thereby activating its ATPase activity. hTid-1 has been found to be critical for a lot of important cellular processes such as proliferation, differentiation, growth, survival, senescence, apoptosis, and movement and plays key roles in the embryo and skeletal muscle development.

Main body

hTid-1 participates in several protein–protein interactions in the cell, which mediate different processes such as proteasomal degradation and autophagy of the interacting protein partners. hTid-1 also functions as a co-chaperone and participates in interactions with several different viral oncoproteins. hTid-1 also plays a critical role in different human diseases such as different cancers, cardiomyopathies, and neurodegenerative disorders.

Conclusion

This review article is the first of its kind presenting consolidated information on the research findings of hTid-1 to date. This review suggests that the current knowledge of the role of hTid-1 in disorders like cancers, cardiomyopathies, and neurodegenerative diseases can be correlated with the findings of its protein–protein interactions that can provide a deep insight into the pathways by which hTid-1 affects disease pathogenesis and it can be stated that hTid-1 may serve as an important therapeutic target for these disorders.

Graphical Abstract

Drug delivery approaches for HuR-targeted therapy for lung cancer

Lung cancer (LC) is often diagnosed at an advanced stage and conventional treatments for disease management have limitations associated with them. Novel therapeutic targets are thus avidly sought for the effective management of LC. RNA binding proteins (RBPs) have been convincingly established as key players in tumorigenesis, and their dysregulation is linked to multiple cancers, including LC. In this context, we review the role of Human antigen R (HuR), an RBP that is overexpressed in LC, and further associated with various aspects of LC tumor growth and response to therapy. Herein, we describe the role of HuR in LC progression and outline the evidences supporting various pharmacologic and biologic approaches for inhibiting HuR expression and function. These approaches, including use of small molecule inhibitors, siRNAs and shRNAs, have demonstrated favorable results in reducing tumor cell growth, invasion and migration, angiogenesis and metastasis. Hence, HuR has significant potential as a key therapeutic target in LC. Use of siRNA-based approaches, however, have certain limitations that prevent their maximal exploitation as cancer therapies. To address this, in the conclusion of this review, we provide a list of nanomedicine-based HuR targeting approaches currently being employed for siRNA and shRNA delivery, and provide a rationale for the immense potential therapeutic benefits offered by nanocarrier-based HuR targeting and its promise for treating patients with LC.

Growth Suppression in Lung Cancer Cells Harboring EGFR-C797S Mutation by Quercetin

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are approved treatments for non-small-cell lung cancer (NSCLC) patients harboring activating EGFR mutations. The EGFR C797S mutation is one of the known acquired-resistance mutations to the latest third-generation TKIs. At present, there are no clear options for treating patients who acquire resistance to third-generation TKIs. The acquisition of the EGFR C797S mutation was shown to upregulate the expression of AXL, a receptor tyrosine kinase of the TAM (TYRO3-AXL-MER) family, and the suppression of AXL is effective in reducing the growth of NSCLC cells harboring EGFR C797S. As quercetin was recently shown to inhibit AXL, quercetin may be effective in treating NSCLC cells harboring the EGFR C797S mutation. In this work, the cytotoxic effects of quercetin and its ability to inhibit tumor growth were examined in TKI-resistant NSCLC cells harboring the EGFR C797S mutation. We demonstrated that quercetin exhibited potent cytotoxic effects on NSCLC cells harboring the EGFR C797S mutation by inhibiting AXL and inducing apoptosis. Quercetin inhibited the tumor growth of xenografted NSCLC cells harboring the EGFR C797S mutation and appeared to act synergistically with brigatinib to inhibit of tumor growth in vivo. In summary, herein, we revealed that quercetin is an effective inhibitor for the treatment of non-small-cell lung cancer harboring the EGFR C797S mutation.

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.

Integrated Omics Analysis of Non-Small-Cell Lung Cancer Cells Harboring the EGFR C797S Mutation Reveals the Potential of AXL as a Novel Therapeutic Target in TKI-Resistant Lung Cancer

Simple Summary

In this study, we employed CRISPR/Cas9 editing technology to introduce the EGFR C797S mutation into an NSCLC cell line harboring EGFR L858R/T790M to establish a cellular model for the investigation of the resistance mechanism associated with the acquired C797S mutation and to explore strategies to battle this type of TKI resistance. Transcriptome and proteome analyses revealed that the differentially expressed genes/proteins in the cells harboring the EGFR C797S mutation are associated with elevated expression of AXL. Furthermore, we presented evidence that inhibition of AXL is effective in slowing the growth of NSCLC cells harboring EGFR C797S. Our findings suggest that AXL inhibition could be a second-line or a potential adjuvant treatment for NSCLC harboring the EGFR C797S mutation.

Abstract

Oncogenic mutations of epidermal growth factor receptor (EGFR) are responsive to targeted tyrosine kinase inhibitor (TKI) treatment in non-small-cell lung cancer (NSCLC). However, NSCLC patients harboring activating EGFR mutations inevitably develop resistance to TKIs. The acquired EGFR C797S mutation is a known mechanism that confers resistance to third-generation EGFR TKIs such as AZD9291. In this work, we employed CRISPR/Cas9 genome-editing technology to knock-in the EGFR C797S mutation into an NSCLC cell line harboring EGFR L858R/T790M. The established cell model was used to investigate the biology and treatment strategy of acquired EGFR C797S mutations. Transcriptome and proteome analyses revealed that the differentially expressed genes/proteins in the cells harboring the EGFR C797S mutation are associated with a mesenchymal-like cell state with elevated expression of AXL receptor tyrosine kinase. Furthermore, we presented evidence that inhibition of AXL is effective in slowing the growth of NSCLC cells harboring EGFR C797S. Our findings suggest that AXL inhibition could be a second-line or a potential adjuvant treatment for NSCLC harboring the EGFR C797S mutation.

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.

Evolving paradigms on the interplay of mitochondrial Hsp70 chaperone system in cell survival and senescence

The role of mitochondria within a cell has grown beyond being the prime source of cellular energy to one of the major signaling platforms. Recent evidence provides several insights into the crucial roles of mitochondrial chaperones in regulating the organellar response to external triggers. The mitochondrial Hsp70 (mtHsp70/Mortalin/Grp75) chaperone system plays a critical role in the maintenance of proteostasis balance in the organelle. Defects in mtHsp70 network result in attenuated protein transport and misfolding of polypeptides leading to mitochondrial dysfunction. The functions of Hsp70 are primarily governed by J-protein cochaperones. Although human mitochondria possess a single Hsp70, its multifunctionality is characterized by the presence of multiple specific J-proteins. Several studies have shown a potential association of Hsp70 and J-proteins with diverse pathological states that are not limited to their canonical role as chaperones. The role of mitochondrial Hsp70 and its co-chaperones in disease pathogenesis has not been critically reviewed in recent years. We evaluated some of the cellular interfaces where Hsp70 machinery associated with pathophysiological conditions, particularly in context of tumorigenesis and neurodegeneration. The mitochondrial Hsp70 machinery shows a variable localization and integrates multiple components of the cellular processes with varied phenotypic consequences. Although Hsp70 and J-proteins function synergistically in proteins folding, their precise involvement in pathological conditions is mainly idiosyncratic. This machinery is associated with a heterogeneous set of molecules during the progression of a disorder. However, the precise binding to the substrate for a specific physiological response under a disease subtype is still an undocumented area of analysis.

Psorachromene Suppresses Oral Squamous Cell Carcinoma Progression by Inhibiting Long Non-coding RNA GAS5 Mediated Epithelial-Mesenchymal Transition

The extract of the seeds of Psoralea corylifolia Linn. (P. corylifolia) have been shown to display anti-tumor activity. However, the prospects of the active compounds from this plant in the treatment of oral squamous cell carcinoma (OSCC) remains unclear. In the present study, the antitumor effects of psorachromene, a flavonoid extracted from the seeds of P. corylifolia, were investigated using cells and animal models of OSCC; the downstream regulatory mechanisms were also elucidated. The results showed that psorachromene significantly repressed cell proliferation, migration, and invasiveness and increased the toxic effects of chemotherapeutic agents against OSCC cells. The repressive effects of psorachromene were attributable to the inhibition of EGFR-Slug signaling, and the induction of G2/M arrest and apoptosis in the OSCC cells. Additionally, we found that psorachromene induced the expression of tumor suppressor long non-coding ribonucleic acid (RNA) growth arrest-specific transcript 5 (GAS5) and the activation of its downstream anticancer mechanisms. Animal experiments also showed noticeable inhibition of tumor growth, without significant physiological toxicity. The findings indicate that psorachromene displays anti-tumor activity in OSCC, and warrants further investigation as a potential agent for clinical application.

Alternative splicing in lung cancer

Lung cancer has the highest mortality rate of all cancers worldwide. Lung cancer is a very heterogeneous disease that is often diagnosed at later stages which have a poor prognosis. Aberrant alternative splicing patterns found in lung cancer contribute to important cell functions. These include changes in splicing for the BCL2L1, MDM2, MDM4, NUMB and MET genes during lung tumourigenesis, to affect pathways involved in apoptosis, cell proliferation and cellular cohesion. Global analyses of RNASeq datasets suggest there may be many more potentially influential aberrant splicing events that need to be investigated in lung cancer. Changes in expression of the splicing factors that regulate alternative splicing events have also been identified in lung cancer. Of these, changes in expression of QKI, RBM4, RBM5, RBM6, RBM10 and SRSF1 proteins regulate many of the most frequently referenced aberrant splicing events in lung cancer. The expanding list of genes known to be aberrantly spliced in lung cancer along with the altered expression of splicing factors that regulate them are providing new clues as to how lung cancer develops, and how these events can be exploited for better treatment. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.

Heterogeneous Nuclear Ribonucleoproteins A1 and A2 Function in Telomerase-Dependent Maintenance of Telomeres

The A/B subfamily of heterogeneous nuclear ribonucleoproteins (hnRNPs A/B), which includes hnRNP A1, A2/B1, and A3, plays an important role in cell proliferation. The simultaneous suppression of hnRNP A1/A2, but not the suppression of hnRNP A1 or A2 alone, has been shown to inhibit cell proliferation and induce apoptosis in cancer cells, but not in mortal normal cells. However, the molecular basis for such a differential inhibition of cell proliferation remains unknown. Here, we show that the simultaneous suppression of hnRNP A1 and hnRNP A2 resulted in dysfunctional telomeres and induced DNA damage responses in cancer cells. The inhibition of apoptosis did not alleviate the inhibition of cell proliferation nor the formation of dysfunctional telomeres in cancer cells depleted of hnRNP A1/A2. Moreover, while proliferation of mortal normal fibroblasts was not sensitive to the depletion of hnRNP A1/A2, the ectopic expression of hTERT in normal fibroblasts rendered these cells sensitive to proliferation inhibition, which was associated with the production of dysfunctional telomeres. Our study demonstrates that hnRNP A1 and A2 function to maintain telomeres in telomerase-expressing cells only, suggesting that the maintenance of functional telomeres in telomerase-expressing cancer cells employs factors that differ from those used in the telomerase-negative normal cells.

Prognostic value and oncogene function of heterogeneous nuclear ribonucleoprotein A1 overexpression in HBV-related hepatocellular carcinoma

Previous study has shown heterogeneous nuclear ribonucleoprotein A1(HNRNPA1) is highly expressed in various human cancers. In order to study the clinical value and potential function of HNRNPA1 in HBV-related hepatocellular carcinoma (HCC), three datasets from the GEPIA, GEO and TCGA were analyzed. HNRNPA1 expression was found to be significantly higher in HBV-positive HCC samples, which was supported with IHC validation. Both GO and KEGG analyses demonstrated that HNRNPA1 co-expressed genes were involved in translation, ribonucleoprotein complex biogenesis and assembly, ribosome biogenesis, RNA processing, RNA splicing, etc. Survival analysis showed a significant reduction in overall survival of patients with high HNRNPA1 expression from both the GSE14520 cohort and 151 patients with HBV-related HCC cohort. Furthermore, Gene set enrichment analysis (GSEA) revealed that HNRNPA1 may regulate HCC progression by influencing the cell cycle and WNT signaling pathway, etc. HNRNPA1 overexpression has diagnostic value in distinguishing between HCC and non-HCC liver tissue (AUC = 0.730). Finally, HNRNPA1 was a directly target gene of miR-22 manifested by the reduced luciferase activity and decreased HNRNPA1 expression in the cells with overexpression of miR-22. HNRNPA1 might function as an oncogene through the EGFR signaling pathway in HBV-related HCC, which has not been reported in previous studies.

HSP40 co-chaperone protein Tid1 suppresses metastasis of head and neck cancer by inhibiting Galectin-7-TCF3-MMP9 axis signaling

Human tumorous imaginal disc (Tid1), a DnaJ co-chaperone protein, is classified as a tumor suppressor. Previously, we demonstrated that Tid1 reduces head and neck squamous cell carcinoma (HNSCC) malignancy. However, the molecular details of Tid1-mediated anti-metastasis remain elusive.

Methods: We used affinity chromatography and systemic mass spectrometry to identify Tid1-interacting client proteins. Immunohistochemical staining of Tid1 in HNSCC patient tissues was examined to evaluate the association between the expression profile of Tid1-interacting client proteins with pathologic features and prognosis. The roles of Tid1-interacting client proteins in metastasis were validated both in vitro and in vivo. The interacting partner and downstream target of Tid1-interacting client protein were determined.

Results: Herein, we first revealed that Galectin-7 was one of the Tid1-interacting client proteins. An inverse association of protein expression profile between Tid1 and Galectin-7 was determined in HNSCC patients. Low Tid1 and high Galectin-7 expression predicted poor overall survival in HNSCC. Furthermore, Tid1 abolished the nuclear translocation of Galectin-7 and suppressed Galectin-7-induced tumorigenesis and metastasis. Keratinocyte-specific Tid1-deficient mice with 4-nitroquinoline-1-oxide (4NQO) treatment exhibited increased protein levels of Galectin-7 and had a poor survival rate. Tid1 interacted with Galectin-7 through its N-linked glycosylation to promote Tid1-mediated ubiquitination and proteasomal degradation of Galectin-7. Additionally, Galectin-7 played a critical role in promoting tumorigenesis and metastatic progression by enhancing the transcriptional activity of TCF3 transcription factor through elevating MMP-9 expression.

Conclusions: Overall, future treatments through activating Tid1 expression or inversely repressing the oncogenic function of Galectin-7 may exhibit great potential in targeting HNSCC progression.

Tid1-S regulates the mitochondrial localization of EGFR in non-small cell lung carcinoma

The epidermal growth factor receptor (EGFR) is the major driver of non-small cell lung carcinoma (NSCLC). Mitochondrial accumulation of EGFR has been shown to promote metastasis in NSCLC, yet little is known about how the mitochondrial localization of EGFR is regulated. In this work, we show that Tid1 (also known as mitochondrial HSP40) is involved in the mitochondrial localization of EGFR, and that the DnaJ domain of Tid1-S is essential for the Tid1-S-mediated transportation of EGFR into mitochondria. Overexpression of Tid1-S increased the migration and invasion of NSCLC cells cultured in vitro. High levels of EGFR and Tid1-S were detected in the mitochondria of cancerous lesions from stage IV NSCLC patients, and high levels of mitochondrial Tid1-S/EGFR were correlated with lymph node metastasis and poor overall survival of NSCLC patients. We thus conclude that Tid1-S critically governs the mitochondrial localization of EGFR through the mtHSP70 transportation pathway, and that the mitochondrial accumulation of EGFR appears to promote metastasis in NSCLC.

2-O-Methylmagnolol upregulates the long non-coding RNA, GAS5, and enhances apoptosis in skin cancer cells

Magnolol, a hydroxylated biphenol compound isolated from the bark of Magnolia officinalis, has been shown to exhibit anti-proliferative effect in various cancer cells, including skin cancer cells. Methoxylation of magnolol appears to improve its anti-inflammatory activity, yet the effect of this modification on the agent's antitumor activity remains unknown. In this work, we report that 2-O-methylmagnolol (MM1) displays improved antitumor activity against skin cancer cells compared to magnolol both in vitro and in vivo. The increased antitumor activity of MM1 appears to correlate with its increased ability to induce apoptosis. DNA microarray and network pathway analyses suggest that MM1 affects certain key factors involved in regulating apoptosis and programmed cell death. Interestingly, the level of the long non-coding (lnc) RNA of growth arrest-specific 5 (GAS5) was increased in MM1-treated cells, and inhibition of lncRNA GAS5 inhibited MM1-induced apoptosis. Conversely, overexpression of lncRNA GAS5 inhibited cell proliferation and promoted cell apoptosis in skin cancer cells. The expression of lncRNA GAS5 in the skin cancer tissues was found to be lower than that in the adjacent normal tissues in a majority of patients. Taken together, our findings suggest that MM1 has improved antitumor activity in skin cancer cells, and that this is due, at least in part, to the upregulation of lncRNA GAS5 and the enhancement of apoptosis.