Implication of RNA-binding protein La in proliferation, migration and invasion of lymph node-metastasized hypopharyngeal SCC cells

Evaluating the RIST Molecular-Targeted Regimen in a Three-Dimensional Neuroblastoma Spheroid Cell Culture Model

Background: The outcome for patients with high-risk neuroblastoma remains poor and novel treatment strategies are urgently needed. The RIST protocol represents a novel metronomic and multimodal treatment strategy for high-risk neuroblastoma combining molecular-targeted drugs as ‘pre-treatment’ with a conventional chemotherapy backbone, currently evaluated in a phase II clinical trial. For preclinical drug testing, cancer cell growth as spheroid compared to mo-nolayer cultures is of advantage since it reproduces a wide range of tumor characteristics, including the three-dimensional architecture and cancer stem cell (CSC) properties. The objective of this study was to establish a neuroblastoma spheroid model for the rigorous assessment of the RIST treatment protocol. Methods: Evaluation of CSC marker expression was performed by mRNA and protein analysis and spheroid viability by luminescence-based assays. Aberrant expression of RNA-binding protein La in neuroblastoma was assessed by tissue microarray analysis and patients’ data mining. Results: Spheroid cultures showed increased expression of a subgroup of CSC-like markers (CXCR4, NANOG and BMI) and higher Thr389 phosphorylation of the neuroblastoma-associated RNA-binding protein La when compared to monolayer cultures. Molecular-targeted ‘pre-treatment’ of spheroids decreased neoplastic signaling and CSC marker expression. Conclusions: The RIST treatment protocol efficiently reduced the viability of neuroblastoma spheroids characterized by advanced CSC properties.

Upregulated SSB Is Involved in Hepatocellular Carcinoma Progression and Metastasis through the Epithelial-Mesenchymal Transition, Antiapoptosis, and Altered ROS Level Pathway

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors with high morbidity and mortality. Therefore, finding new diagnostic and therapeutic targets is vital for HCC patients. Recent studies have shown that dysregulation of RNA-binding proteins is often associated with cancer progression. Several studies have reported that the RNA-binding protein SSB can promote cancer occurrence and progression and is linked to tumor epithelial-mesenchymal transition (EMT), which could be a new diagnostic marker and therapeutic target. However, the expression and function of SSB in HCC remain to be elucidated. Therefore, this study is aimed at clarifying the expression and biological function of SSB in HCC through bioinformatics analysis combined with in vitro experiments. We found that SSB is highly expressed in HCC and is associated with the poor prognosis of HCC patients, and it can serve as an independent unfavorable prognostic factor. Knockdown of SSB can inhibit the growth of HCC cells in vitro, increase the level of apoptosis and the expression of pro-apoptosis-related proteins, and decrease the expression of antiapoptotic proteins. Meanwhile, SSB knockdown reduced HCC cell invasiveness, and the expression of EMT-related proteins changed significantly. We also found that the gene SSB was associated with the level of oxidative stress in liver cancer cells, and the level of intracellular reactive oxygen species (ROS) increased after knockdown of SSB. The results of bioinformatics analysis also showed that high expression of SSB may affect the effect of checkpoint blockade (ICB) therapy. In conclusion, we found that SSB is highly expressed in HCC and that upregulated SSB can promote the proliferation and metastasis of HCC through antiapoptotic, altered intracellular oxidative stress level, and EMT pathways, which can serve as a new diagnostic marker and therapeutic target, and patients with high SSB expression may not have obvious ICB therapy effect.

La protein regulates protein expression by binding with the mRNAs of target genes and participates the pathological process of ovarian cancer

Research on the mechanism and new targets of ovarian cancer is of great significance to reduce the high mortality and drug resistance of ovarian cancer. Human La protein has been found to be highly expressed in a variety of malignant tumors and plays a role in tumorigenesis and development through its RNA-binding function. However, its role and mechanism in ovarian cancer are not completely clear. The present study showed that La protein was highly expressed in serum and tissues of patients with ovarian cancer by ELISA and immunohistochemistry, and the high expression of La protein was associated with the increased degree of malignancy and poor prognosis by searching the KM plotter database. Interference of the La gene resulted in a significant decrease in the proliferation, migration, and invasion of ovarian cancer cells with growth block in the G1 phase and increasing apoptosis. By RNA binding protein immunoprecipitation, transcriptome sequencing, and proteomics, 14 downstream target genes were screened. The La protein might affect the protein expression of these 14 genes by binding with the mRNAs. Therefore, it played a role in the pathological process of ovarian cancer.

The RNA-binding protein La/SSB associates with radiation-induced DNA double-strand breaks in lung cancer cell lines

BACKGROUND

Platinum-based chemotherapy and radiotherapy are standard treatments for non-small cell lung cancer, which is the commonest, most lethal cancer worldwide. As a marker of treatment-induced cancer cell death, we have developed a radiodiagnostic imaging antibody, which binds to La/SSB. La/SSB is an essential, ubiquitous ribonuclear protein, which is over expressed in cancer and plays a role in resistance to cancer therapies.

AIM

In this study, we examined radiation-induced DNA double strand breaks (DSB) in lung cancer cell lines and examined whether La/SSB associated with these DSB.

METHOD

Three lung cancer lines (A549, H460 and LL2) were irradiated with different X-ray doses or X-radiated with a 5 Gy dose and examined at different time-points post-irradiation for DNA DSB in the form of γ-H2AX and Rad51 foci. Using fluorescence microscopy, we examined whether La/SSB and γ-H2AX co-localise and performed proximity ligation assay (PLA) and co-immunoprecipitation to confirm the interaction of these proteins.

RESULTS

We found that the radio-resistant A549 cell line compared to the radio-sensitive H460 cell line showed faster resolution of radiation-induced γ-H2AX foci over time. Conversely, we found more co-localised γ-H2AX and La/SSB foci by PLA in irradiated A549 cells.

CONCLUSION

The co-localisation of La/SSB with radiation-induced DNA breaks suggests a role of La/SSB in DNA repair, however further experimentation is required to validate this.

ImmunoPET imaging of hematological malignancies: From preclinical promise to clinical reality

Immuno-positron emission tomography (immunoPET) imaging is a paradigm-shifting imaging technique for whole-body and all-lesion tumor detection, based on the combined specificity of tumor-targeting vectors [e.g., monoclonal antibodies (mAbs), nanobodies, and bispecific antibodies] and the sensitivity of PET imaging. By noninvasively, comprehensively, and serially revealing heterogeneous tumor antigen expression, immunoPET imaging is gradually improving the theranostic prospects for hematological malignancies. In this review, we summarize the available literature regarding immunoPET in imaging hematological malignancies. We also highlight the pros and cons of current conjugation strategies, and modular chemistry that can be leveraged to develop novel immunoPET probes for hematological malignancies. Lastly, we discuss the use of immunoPET imaging in guiding antibody drug development.

Positron Emission Tomographic Imaging of Tumor Cell Death Using Zirconium-89-Labeled APOMAB® Following Cisplatin Chemotherapy in Lung and Ovarian Cancer Xenograft Models

PURPOSE

Early detection of tumor treatment responses represents an unmet clinical need with no approved noninvasive methods. DAB4, or its chimeric derivative, chDAB4 (APOMAB®) is an antibody that targets the Lupus associated antigen (La/SSB). La/SSB is over-expressed in malignancy and selectively targeted by chDAB4 in cancer cells dying from DNA-damaging treatment. Therefore, chDAB4 is a unique diagnostic tool that detects dead cancer cells and thus could distinguish between treatment responsive and nonresponsive patients.

PROCEDURES

In clinically relevant tumor models, mice bearing subcutaneous xenografts of human ovarian or lung cancer cell lines or intraperitoneal ovarian cancer xenografts were untreated or given chemotherapy followed 24h later by chDAB4 radiolabeled with [⁸⁹Zr]Zr^IV. Tumor responses were monitored using bioluminescence imaging and caliper measurements. [⁸⁹Zr]Zr-chDAB4 uptake in tumor and normal tissues was measured using an Albira SI Positron-Emission Tomography (PET) imager and its biodistribution was measured using a Hidex gamma-counter.

RESULTS

Tumor uptake of [⁸⁹Zr]Zr-chDAB4 was detected in untreated mice, and uptake significantly increased in both human lung and ovarian tumors after chemotherapy, but not in normal tissues.

CONCLUSION

Given that tumors, rather than normal tissues, were targeted after chemotherapy, these results support the clinical development of chDAB4 as a radiodiagnostic imaging agent and as a potential predictive marker of treatment response.

Anti-Metastatic Effects of Lupeol via the Inhibition of MAPK/ERK Pathway in Lung Cancer

BACKGROUND AND OBJECTIVE

ERK pathway is one of the most crucial pathways in lung cancer metastasis. Targeting its pathway is decisive in lung cancer research. Thus, this study demonstrated for the first time for significant and selective anti-metastatic effects of lupeol against lung cancer A549 cells via perturbations in the ERK signaling pathway.

MATERIALS AND METHODS

Human protein targets of lupeol were predicted in silico. Migration and cytotoxicity assays were carried out in vitro. Expression levels of proteins Erk1/2 and pErk1/2 were ensured using Enzyme- Linked Immunosorbent Assay (ELISA). Semi-quantitative RT-PCR technique was used to estimate changes in crucial mesenchymal marker gene expression levels of N-cadherin and vimentin.

RESULTS

Lupeol was found to target ERK and MEK proteins effectively. Despite having no cytotoxic effects, lupeol also significantly inhibited cell migration in A549 cells with decreased expression of the pErk1/2 protein along with N-cadherin and vimentin genes.

CONCLUSION

Lupeol inhibits cell migration, showed no cytotoxic effects on A549 cells, decreased pErk1/2 and EMT gene expression. Thus, it can serve as a potential ERK pathway inhibitor in lung cancer therapeutics.

RNA-Binding Protein La Mediates TGFβ-Induced Epithelial to Mesenchymal Transition and Cancer Stem Cell Properties

Simple Summary

Reversible epithelial to mesenchymal transition (EMT) plays a key role in establishing a malignant phenotype by assuring cancer cell plasticity critical for cancer progression by allowing a small fraction of cancer cells to detach from primary lesions and outgrow at metastatic sites. Cancer cell plasticity is associated with cancer stem cell properties contributing to chemoresistance, metastasis, and poor clinical outcomes. Dysregulated RNA-binding proteins are key players in controlling the RNA metabolism, including mRNA processing, export, and translation, and have been implicated in cancer cell plasticity. In this study, we demonstrated that aberrantly expressed RNA-binding protein La is critical for transforming growth factor β-induced EMT and for gaining cancer stem cell properties. Understanding the function of aberrant RNA-binding protein expression in cancer cell plasticity reveals prospects for identifying novel therapeutic targets.

Abstract

Background: the aberrant overexpression of predominantly nuclear localizing RNA-binding protein (RBP) La contributes to proliferation, mobility, and chemoresistance of cancer cells and tumor growth in mice. Methods: studies included cancer tissue microarrays (TMAs) analyses, cancer tissue data mining, transforming growth factor β (TGFβ)-induced cancer cell plasticity studies, three dimensional sphere growth, epithelial to mesenchymal transition (EMT) assays, analysis of cancer stem cell (CSC) marker expression, and post-translational modification of cancer-associated La protein. Results: we demonstrated that significant overexpression of RBP La in lung and head and neck cancer tissue correlates with poor overall survival. Furthermore, small interfering RNA-mediated depletion of La reduced proliferation and migration of cancer cells, blocked TGFβ-induced EMT, and diminished both EMT and CSC marker expression. Rescue experiments with La wildtype but not RNA chaperone domain activity-defective La mutant increased the expression of those cancer progression markers, suggesting a critical role of La’s RNA chaperone activity in this process. La depletion in cancer cells also significantly decreased sphere growth in the presence of TGFβ. Interestingly, TGFβ treatment induced phosphorylation of La at threonine 389 (pLa^T389) only in adherents but not in 3D growing cultures. Conclusion: our study suggests that the TGFβ/AKT/pLa^T389 signaling pathway regulates cancer cell plasticity.

Improved non-invasive positron emission tomographic imaging of chemotherapy-induced tumor cell death using Zirconium-89-labeled APOMAB®

Purpose

The chimeric monoclonal antibody (mAb) chDAB4 (APOMAB®) targets the Lupus associated (La)/Sjögren Syndrome-B (SSB) antigen, which is over-expressed in tumors but only becomes available for antibody binding in dead tumor cells. Hence, chDAB4 may be used as a novel theranostic tool to distinguish between responders and nonresponders early after chemotherapy. Here, we aimed to ascertain which positron emitter, Zirconium-89 ([⁸⁹Zr]Zr^IV) or Iodine-124 ([¹²⁴I]I), was best suited to label chDAB4 for post-chemotherapy PET imaging of tumor-bearing mice and to determine which of two different bifunctional chelators provided optimal tumor imaging by PET using [⁸⁹Zr]Zr^IV-labeled chDAB4.

Methods

C57BL/6 J mice bearing subcutaneous syngeneic tumors of EL4 lymphoma were either untreated or given chemotherapy, then administered radiolabeled chDAB4 after 24 h with its biodistribution examined using PET and organ assay. We compared chDAB4 radiolabeled with [⁸⁹Zr] Zr^IV or [¹²⁴I] I, or [⁸⁹Zr]Zr-chDAB4 using either DFO-NCS or DFOSq as a chelator.

Results

After chemotherapy, [⁸⁹Zr]Zr-chDAB4 showed higher and prolonged mean (± SD) tumor uptake of 29.5 ± 5.9 compared to 7.8 ± 1.2 for [¹²⁴I] I -chDAB4. In contrast, antibody uptake in healthy tissues was not affected. Compared to DFO-NCS, DFOSq did not result in significant differences in tumor uptake of [⁸⁹Zr]Zr-chDAB4 but did alter the tumor:liver ratio in treated mice 3 days after injection in favour of DFOSq (8.0 ± 1.1) compared to DFO-NCS (4.2 ± 0.7).

Conclusion

ImmunoPET using chDAB4 radiolabeled with residualizing [⁸⁹Zr] Zr^IV rather than [¹²⁴I] I optimized post-chemotherapy tumor uptake. Further, PET imaging characteristics were improved by DFOSq rather than DFO-NCS. Therefore, the radionuclide/chelator combination of [⁸⁹Zr] Zr^IV and DFOSq is preferred for the imminent clinical evaluation of chDAB4 as a selective tumor cell death radioligand.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s41181-020-00109-6.

Functional and Structural Aspects of La Protein Overexpression in Lung Cancer

La is an abundant phosphoprotein that protects polymerase III transcripts from 3'-5' exonucleolytic degradation and facilitates their folding. Consisting of the evolutionary conserved La motif (LAM) and two consecutive RNA Recognition Motifs (RRMs), La was also found to bind additional RNA transcripts or RNA domains like internal ribosome entry site (IRES), through sequence-independent binding modes which are poorly understood. Although it has been reported overexpressed in certain cancer types and depletion of its expression sensitizes cancer cells to certain chemotherapeutic agents, its role in cancer remains essentially uncharacterized. Herein, we study the effects of La overexpression in A549 lung adenocarcinoma cells, which leads to increased cell proliferation and motility. Expression profiling of several transcription and translation factors indicated that La overexpression leads to downregulation of global translation through hypophosphorylation of 4E-BPs and upregulation of IRES-mediated translation. Moreover, analysis of La localization after nutrition deprivation of the transfected cells showed a normal distribution in the nucleus and nucleoli. Although the RNA binding capacity of La has been primarily linked to the synergy between the conserved LAM and RRM1 domains which act as a module, we show that recombinant stand-alone LAM can specifically bind a pre-tRNA ligand, based on binding experiments combined with NMR analysis. We propose that LAM RNA binding properties could support the expanding and diverse RNA ligand repertoire of La, thus promoting its modulatory role, both under normal and pathogenic conditions like cancer.

Human La Protein: An RNA-Binding Protein Involved in Ovarian Cancer Development and Multidrug Resistance

Multidrug resistance is the main cause of chemotherapy failure and death in patients with advanced ovarian cancer. Drug resistance is a problem that must be solved to improve the survival rate of patients with advanced ovarian cancer. The RNA-binding protein La and the La-related protein family are highly expressed in various malignant tumors, including ovarian cancer. This article reviews the mechanisms of La protein in tumorigenesis, development, and drug resistance. High La protein expression in tumor cells promotes tumor proliferation, invasion, and migration; disrupts cell cycle; and inhibits tumor cell apoptosis caused by chemotherapeutic drugs through various pathways, resulting in chemotherapy resistance in ovarian cancer. Further study of the role of La protein in ovarian cancer multidrug resistance may be conducive to the development of human La protein-specific inhibitors that suppress ovarian cancer drug resistance.

The Role and Impact of Extracellular Vesicles in the Modulation and Delivery of Cytokines during Autoimmunity

Cytokines and extracellular vesicles are two methods of initiating and maintaining cellular crosstalk. The role of cytokines in the initiation, progression, and resolution of inflammation has been well studied and more so, their pathophysiological role in the development of autoimmune disease. In recent years, the impact of extracellular vesicles on the progression of autoimmunity has become more widely appreciated. In this review, we discuss the mechanisms that allow extracellular vesicles of various sources to modulate cytokine production, and release, and how extracellular vesicles might be involved in the direct delivery and modulation of cytokine levels. Moreover, we explore what challenges are faced by current therapies and the promising future for extracellular vesicles as therapeutic agents in conditions driven by immune dysregulation.

RNA-Binding Proteins as Regulators of Migration, Invasion and Metastasis in Oral Squamous Cell Carcinoma

Nearly 7.5% of all human protein-coding genes have been assigned to the class of RNA-binding proteins (RBPs), and over the past decade, RBPs have been increasingly recognized as important regulators of molecular and cellular homeostasis. RBPs regulate the post-transcriptional processing of their target RNAs, i.e., alternative splicing, polyadenylation, stability and turnover, localization, or translation as well as editing and chemical modification, thereby tuning gene expression programs of diverse cellular processes such as cell survival and malignant spread. Importantly, metastases are the major cause of cancer-associated deaths in general, and particularly in oral cancers, which account for 2% of the global cancer mortality. However, the roles and architecture of RBPs and RBP-controlled expression networks during the diverse steps of the metastatic cascade are only incompletely understood. In this review, we will offer a brief overview about RBPs and their general contribution to post-transcriptional regulation of gene expression. Subsequently, we will highlight selected examples of RBPs that have been shown to play a role in oral cancer cell migration, invasion, and metastasis. Last but not least, we will present targeting strategies that have been developed to interfere with the function of some of these RBPs.

La protein contributes to cells proliferation and migration and serves as a potential therapeutic target for hepatocellular carcinoma

AIM

La protein is a multifunctional RNA-binding protein involved in RNA metabolism that has been reported to promote the growth of some solid tumors. However, potential role of La in hepatocellular carcinoma (HCC) has not been fully elucidated. This study aimed to investigate the expression of La and its function in HCC.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis were conducted to detect the expression levels of La mRNA and protein in HCC cells and tissues. The proliferation capability of cells was clarified by Cell Counting Kit-8 and clone formation assays. Wound healing assay was carried out to assess cell migration ability. Related protein expressions were also analyzed by western blot.

RESULTS

Analysis of our clinical samples showed that La mRNA and protein expression of HCC tissues was higher than those of corresponding adjacent tissues, consistent with the result of microarray datasets from Oncomine database. La was also significantly overexpressed in eight HCC cells, compared with normal hepatocytes. According to in vitro experiments, we demonstrated that knockdown of La inhibited HCC cell proliferation and migration.

CONCLUSIONS

Our results revealed that La expression is elevated both at the RNA and protein levels in HCC. Highly expressed La significantly promotes tumorigenesis of HCC, suggesting that La may be a potential therapeutic target for the treatment of HCC.

Role of the RNA-binding protein La in cancer pathobiology

RNA-binding proteins are important regulators of RNA metabolism and are of critical importance in all steps of the gene expression cascade. The role of aberrantly expressed RBPs in human disease is an exciting research field and the potential application of RBPs as a therapeutic target or a diagnostic marker represents a fast-growing area of research.Aberrant overexpression of the human RNA-binding protein La has been found in various cancer entities including lung, cervical, head and neck, and chronic myelogenous leukaemia. Cancer-associated La protein supports tumour-promoting processes such as proliferation, mobility, invasiveness and tumour growth. Moreover, the La protein maintains the survival of cancer cells by supporting an anti-apoptotic state that may cause resistance to chemotherapeutic therapy.The human La protein represents a multifunctional post-translationally modified RNA-binding protein with RNA chaperone activity that promotes processing of non-coding precursor RNAs but also stimulates the translation of selective messenger RNAs encoding tumour-promoting and anti-apoptotic factors. In our model, La facilitates the expression of those factors and helps cancer cells to cope with cellular stress. In contrast to oncogenes, able to initiate tumorigenesis, we postulate that the aberrantly elevated expression of the human La protein contributes to the non-oncogenic addiction of cancer cells. In this review, we summarize the current understanding about the implications of the RNA-binding protein La in cancer progression and therapeutic resistance. The concept of exploiting the RBP La as a cancer drug target will be discussed.

Distinct mechanisms of microRNA sorting into cancer cell-derived extracellular vesicle subtypes

Extracellular vesicles (EVs) encompass a variety of vesicles secreted into the extracellular space. EVs have been implicated in promoting tumor metastasis, but the molecular composition of tumor-derived EV sub-types and the mechanisms by which molecules are sorted into EVs remain mostly unknown. We report the separation of two small EV sub-populations from a metastatic breast cancer cell line, with biochemical features consistent with different sub-cellular origins. These EV sub-types use different mechanisms of miRNA sorting (selective and non-selective), suggesting that sorting occurs via fundamentally distinct processes, possibly dependent on EV origin. Using biochemical and genetic tools, we identified the Lupus La protein as mediating sorting of selectively packaged miRNAs. We found that two motifs embedded in miR-122 are responsible for high-affinity binding to Lupus La and sorting into vesicles formed in a cell-free reaction. Thus, tumor cells can simultaneously deploy multiple EV species using distinct sorting mechanisms that may enable diverse functions in normal and cancer biology.

La-Related Protein 4 as a Suppressor for Motility of Ovarian Cancer Cells

The La-related proteins (LARPs) are a family of RNA binding proteins that control the degradation and stabilization of RNAs. As emerging research reveals the biology of each LARP, it is evident that LARPs are dysregulated in some types of cancer. Upregulation of cell motility potentiates the metastatic potential of ovarian cancer cells; however, the roles of LARPs in cell motility remain unknown. In the present study, we investigated the roles of LARPs in the progression of ovarian cancer using SKOV3 human ovarian cancer cells and a public database that integrates microarray-based gene expression data and clinical data. To explore the involvement of LARPs in the cell motility, we performed RNA interference screening for LARP mRNAs in SKOV3 cells. The screening identified LARP4 as a potential suppressor of the formation of lamellipodia. Conversely, enforced expression of LARP4 suppressed the formation of lamellipodia. Moreover, cell migration was significantly increased in LARP4-depleted SKOV3 cells. Mechanistically, LARP4 depletion was associated with the decrease in RhoA protein expression. These results suggest that LARP4 may limit RhoA-dependent cell motility. In a mouse xenograft model with SKOV3 cells, LARP4 depletion potentiated peritoneal metastasis. Upon analysis of a public database of patients with ovarian cancer, the LARP4 mRNA-high expression group (n = 166) showed longer overall survival compared with the LARP4 mRNA-low expression group (n = 489), implying a positive correlation of LARP4 mRNA levels in ovarian cancer tissues with patient prognosis. Taken together, we propose that LARP4 could suppress motility and metastatic potential of ovarian cancer cells.

The La protein counteracts cisplatin-induced cell death by stimulating protein synthesis of anti-apoptotic factor Bcl2

Up-regulation of anti-apoptotic factors is a critical mechanism of cancer cell resistance and often counteracts the success of chemotherapeutic treatment. Herein, we identified the cancer-associated RNA-binding protein La as novel factor contributing to cisplatin resistance. Our data demonstrate that depletion of the RNA-binding protein La in head and neck squamous cell carcinoma cells (HNSCC) increases the sensitivity toward cisplatin-induced cell death paralleled by reduced expression of the anti-apoptotic factor Bcl2. Furthermore, it is shown that transient expression of Bcl2 in La-depleted cells protects against cisplatin-induced cell death. By dissecting the underlying mechanism we report herein, that the La protein is required for Bcl2 protein synthesis in cisplatin-treated cells. The RNA chaperone La binds in close proximity to the authentic translation start site and unwinds a secondary structure embedding the authentic AUG. Altogether, our data support a novel model, whereby cancer-associated La protein contributes to cisplatin resistance by stimulating the translation of anti-apoptotic factor Bcl2 in HNSCC cells.

SUMO Modification of the RNA-Binding Protein La Regulates Cell Proliferation and STAT3 Protein Stability

The cancer-associated RNA-binding protein La is posttranslationally modified by phosphorylation and sumoylation. Sumoylation of La regulates not only the trafficking of La in neuronal axons but also its association with specific mRNAs. Depletion of La in various types of cancer cell lines impairs cell proliferation; however, the molecular mechanism whereby La supports cell proliferation is not clearly understood. In this study, we address the question of whether sumoylation of La contributes to cell proliferation of HEK293 cells. We show that HEK293 cells stably expressing green fluorescent protein (GFP)-tagged wild-type La (GFP-La^WT) grow faster than cells expressing a sumoylation-deficient mutant La (GFP-La^SD), suggesting a proproliferative function of La in HEK293 cells. Further, we found that STAT3 protein levels were reduced in GFP-La^SD cells due to an increase in STAT3 ubiquitination and that overexpression of STAT3 partially restored cell proliferation. Finally, we present RNA sequencing data from RNA immunoprecipitations (RIPs) and report that mRNAs associated with the cell cycle and ubiquitination are preferentially bound by GFP-La^WT and are less enriched in GFP-La^SD RIPs. Taken together, results of our study support a novel mechanism whereby sumoylation of La promotes cell proliferation by averting ubiquitination-mediated degradation of the STAT3 protein.

Applying a high-throughput fluorescence polarization assay for the discovery of chemical probes blocking La:RNA interactions in vitro and in cells

The RNA-binding protein La is overexpressed in a number of tumor tissues and is thought to support tumorigenesis by binding to and facilitating the expression of mRNAs encoding tumor-promoting and anti-apoptotic factors. Hence, small molecules able to block the binding of La to specific RNAs could have a therapeutic impact by reducing the expression of tumor-promoting and anti-apoptotic factors. Toward this novel therapeutic strategy, we aimed to develop a high-throughput fluorescence polarization assay to screen small compound libraries for molecules blocking the binding of La to an RNA element derived from cyclin D1 mRNA. Herein, we make use of a robust fluorescence polarization assay and the validation of primary hits by electrophoretic mobility shift assays. We showed recently that La protects cells against cisplatin treatment by stimulating the protein synthesis of the anti-apoptotic factor Bcl2. Here, we show by RNA immunoprecipitation experiments that one small compound specifically impairs the association of La with Bcl2 mRNA in cells and sensitizes cells for cipslatin-induced cell death. In summary, we report the application of a high-throughput fluorescence polarization assay to identify small compounds that impair the binding of La to target RNAs in vitro and in cells.

The RNA-binding protein LARP4 regulates cancer cell migration and invasion

LARP4 is a La-related RNA-binding protein implicated in regulating mRNA translation, which interacts with poly(A)-binding protein (PABP). We previously identified LARP4 in an RNAi screen as one of several genes that regulate the shape of PC3 prostate cancer cells. Here we show that LARP4 depletion induces cell elongation in PC3 cells and MDA-MB-231 breast cancer cells. LARP4 depletion increases cell migration and invasion, as well as inducing invasive cell protrusions in 3D Matrigel. Conversely, LARP4 over-expression reduces cell elongation and increases cell circularity. LARP4 mutations are found in a variety of cancers. Introduction of some of these cancer-associated mutations, including a truncation mutant, into LARP4 enhances its effects on cell morphology. The truncation mutant shows enhanced interaction with PABP. We propose that LARP4 inhibits migration and invasion of cancer cells, and that some cancer-associated mutations stimulate these effects of LARP4. © 2016 The Authors. Cytoskeleton Published by Wiley Periodicals, Inc.

SUMO-Modification of the La Protein Facilitates Binding to mRNA In Vitro and in Cells

The RNA-binding protein La is involved in several aspects of RNA metabolism including the translational regulation of mRNAs and processing of pre-tRNAs. Besides its well-described phosphorylation by Casein kinase 2, the La protein is also posttranslationally modified by the Small Ubiquitin-like MOdifier (SUMO), but the functional outcome of this modification has not been defined. The objective of this study was to test whether sumoylation changes the RNA-binding activity of La. Therefore, we established an in vitro sumoylation assay for recombinant human La and analyzed its RNA-binding activity by electrophoretic mobility shift assays. We identified two novel SUMO-acceptor sites within the La protein located between the RNA recognition motif 1 and 2 and we demonstrate for the first time that sumoylation facilitates the RNA-binding of La to small RNA oligonucleotides representing the oligopyrimidine tract (TOP) elements from the 5' untranslated regions (UTR) of mRNAs encoding ribosomal protein L22 and L37 and to a longer RNA element from the 5' UTR of cyclin D1 (CCND1) mRNA in vitro. Furthermore, we show by RNA immunoprecipitation experiments that a La mutant deficient in sumoylation has impaired RNA-binding activity in cells. These data suggest that modulating the RNA-binding activity of La by sumoylation has important consequences on its functionality.

The RNA-binding protein LARP1 is a post-transcriptional regulator of survival and tumorigenesis in ovarian cancer

RNA-binding proteins (RBPs) are increasingly identified as post-transcriptional drivers of cancer progression. The RBP LARP1 is an mRNA stability regulator, and elevated expression of the protein in hepatocellular and lung cancers is correlated with adverse prognosis. LARP1 associates with an mRNA interactome that is enriched for oncogenic transcripts. Here we explore the role of LARP1 in epithelial ovarian cancer, a disease characterized by the rapid acquisition of resistance to chemotherapy through the induction of pro-survival signalling. We show, using ovarian cell lines and xenografts, that LARP1 is required for cancer cell survival and chemotherapy resistance. LARP1 promotes tumour formation in vivo and maintains cancer stem cell-like populations. Using transcriptomic analysis following LARP1 knockdown, cross-referenced against the LARP1 interactome, we identify BCL2 and BIK as LARP1 mRNA targets. We demonstrate that, through an interaction with the 3' untranslated regions (3' UTRs) of BCL2 and BIK, LARP1 stabilizes BCL2 but destabilizes BIK with the net effect of resisting apoptosis. Together, our data indicate that by differentially regulating the stability of a selection of mRNAs, LARP1 promotes ovarian cancer progression and chemotherapy resistance.

The La-Related Proteins, a Family with Connections to Cancer

The evolutionarily-conserved La-related protein (LARP) family currently comprises Genuine La, LARP1, LARP1b, LARP4, LARP4b, LARP6 and LARP7. Emerging evidence suggests each LARP has a distinct role in transcription and/or mRNA translation that is attributable to subtle sequence variations within their La modules and specific C-terminal domains. As emerging research uncovers the function of each LARP, it is evident that La, LARP1, LARP6, LARP7 and possibly LARP4a and 4b are dysregulated in cancer. Of these, LARP1 is the first to be demonstrated to drive oncogenesis. Here, we review the role of each LARP and the evidence linking it to malignancy. We discuss a future strategy of targeting members of this protein family as cancer therapy.

Semaphoring mAb: a new guide in RIT in inhibiting the proliferation of human skin carcinoma

Semaphoring is a transmembrane receptor which participates in many cytokine-mediated signal pathways that are closely related to the angiogenesis, occurrence and development of carcinoma. The present study was designed to access the effect of mono-antibody (mAb) guided radioimmunotherapy (RIT) on skin carcinoma and investigate the potential mechanisms. Semaphoring mAb was acquired from mice (Balb/c), purified with rProtein A column; purity, concentration and activity were tested with SDS-PAGE and indirect ELISA; specificity and expression on the cutanuem carcinoma line and tissue were tested by Western blotting; morphology change was assessed by microscopy. MTT assay and colony inhibition tests were carried out to test the influence on the proliferation of tumor cells; Western blotting was also carried out for expression of apoptosis-associated (caspase-3, Bax, Bcl-2) and proliferation-related (PI3K, p-Akt, Akt, p-ERK1/2, ERK1/2) proteins and analyse the change in signal pathways (PI3K/Akt and MEK/ERK). The purity of purified semaphorin mAb was 96.5% and the titer is about 1?106. Western blotting showed semaphoring mAb to have specifically binding stripes with semaphoring b1b2 protein, B16F10, and A431 cells at 39KDa, 100KDa and 130KDa, respectively. Positive expression was detected both in cutanuem carcinoma line and tissue and it mostly located in cell membranes. MMT assay revealed dose-relate and time-relate inhibitory effect of semaphorin mAb on A431 and B16F10. Colony inhibition tests also showed dose-relate inhibitory effects. Western blotting demonstrated the expression of apoptosis and proliferation-related protein and changes in signal pathway. In conclusion, we demonstrated that semaphorin is highly expressed on the tumor cell-surfaces and RIT with semaphorin mAb has effect in inhibiting proliferation and accelerating apoptosis of tumor cells.

Novel RNA chaperone domain of RNA-binding protein La is regulated by AKT phosphorylation

The cellular function of the cancer-associated RNA-binding protein La has been linked to translation of viral and cellular mRNAs. Recently, we have shown that the human La protein stimulates IRES-mediated translation of the cooperative oncogene CCND1 in cervical cancer cells. However, there is little known about the underlying molecular mechanism by which La stimulates CCND1 IRES-mediated translation, and we propose that its RNA chaperone activity is required. Herein, we show that La binds close to the CCND1 start codon and demonstrate that La's RNA chaperone activity can change the folding of its binding site. We map the RNA chaperone domain (RCD) within the C-terminal region of La in close proximity to a novel AKT phosphorylation site (T389). Phosphorylation at T389 by AKT-1 strongly impairs its RNA chaperone activity. Furthermore, we demonstrate that the RCD as well as T389 is required to stimulate CCND1 IRES-mediated translation in cells. In summary, we provide a model whereby a novel interplay between RNA-binding, RNA chaperoning and AKT phosphorylation of La protein regulates CCND1 IRES-mediated translation.

RNA-binding proteins, multifaceted translational regulators in cancer

RNA-binding proteins (RBPs) orchestrate transcript fate and function. Even though alterations in post-transcriptional events contribute to key steps of tumor initiation and progression, RBP-mediated control has remained relatively unexplored in cancer. Here, we discuss examples of this promising field focusing on translation regulation, and highlight the variety of molecular mechanisms by which RBPs impinge on translation with consequences for tumorigenesis. This article is part of a Special Issue entitled: Translation and Cancer.

Silencing RhoA inhibits migration and invasion through Wnt/β-catenin pathway and growth through cell cycle regulation in human tongue cancer

Ras homolog gene family member A (RhoA) has been identified as a critical regulator of tumor aggressive behavior. In this study, we assessed the role of RhoA in the mechanisms underlying growth, migration, and invasion of squamous cell carcinoma of tongue (TSCC). Stable RhoA knockdown of TSCC cell lines SCC-4 and CAL27 were achieved using Lentiviral transfection. The effects of RhoA depletion on cell migration, invasion, and cell proliferation were determined. The possible underlying mechanism of RhoA depletion on TSCC cell line was also evaluated by determining the expression of Galectin-3 (Gal-3), β-catenin, and matrix metalloproteinase-9 (MMP-9) in vivo. Meanwhile, the underlying mechanism of TSCC growth was studied by analysis of cyclin D1/2, p21CIP1/WAF1, and p27Kip1 protein levels. Immunohistochemical assessments were performed to further prove the alteration of Gal-3 and β-catenin expression. We found that, in mice injected with human TSCC cells in the tongue, RhoA levels were higher in primary tumors and metastasized lymph nodes compared with those in the normal tissues. Silencing of RhoA significantly reduced the tumor growth, decreased the levels of Gal-3, β-catenin, MMP-9, and cyclin D1/2, and increased the levels of p21CIP1/WAF1 and p27Kip1. In vitro, RhoA knockdown also led to inhibition of cell migration, invasion, and proliferation. Our data suggest that RhoA plays a significant role in TSCC progression by regulating cell migration and invasion through Wnt/β-catenin signaling pathway and cell proliferation through cell cycle regulation, respectively. RhoA might be a novel therapeutic target of TSCC.

Postchemotherapy and tumor-selective targeting with the La-specific DAB4 monoclonal antibody relates to apoptotic cell clearance

Early identification of tumor responses to treatment is crucial for devising more effective and safer cancer treatments. No widely applicable, noninvasive method currently exists for specifically detecting tumor cell death after cytotoxic treatment and thus for predicting treatment outcomes.

METHODS

We have further characterized the targeting of the murine monoclonal antibody DAB4 specifically to dead tumor cells in vitro, in vivo, and in clinical samples. We found that sustained DAB4 binding to treated cells was closely associated with markers of intrinsic apoptosis and DNA double-strand break formation. In a competition binding assay, DAB4 bound EL4 murine thymic lymphoma cells in preference to the normal counterpart of murine thymocytes. Defective in vivo clearance of apoptotic cells augmented in vivo accumulation of DAB4 in tumors particularly after chemotherapy but was unchanged in normal tissues. Tumor targeting of DAB4 was selective for syngeneic murine tumors and for human tumor xenografts of prostate cancer (PC-3) and pancreatic cancer (Panc-1) before and more so after chemotherapy. Furthermore, DAB4 was shown to bind to dead primary acute lymphoblastic leukemic blasts cultured with cytotoxic drugs and dead epithelial cancer cells isolated from peripheral blood of small cell lung carcinoma patients given chemotherapy.

CONCLUSION

Collectively, these results further demonstrate the selectivity of DAB4 for chemotherapy-induced dead tumor cells. This postchemotherapy selectivity is related to a relative increase in the availability of DAB4-binding targets in tumor tissue rather than in normal tissues. The in vitro findings were translated in vivo to human xenograft models and to ex vivo analyses of clinical samples, providing further evidence of the potential of DAB4 as a marker of tumor cell death after DNA-damaging cytotoxic treatment that could be harnessed as a predictive marker of treatment responses.

Monte Carlo simulations of dose distributions with necrotic tumor targeted radioimmunotherapy

Radio-resistant hypoxic tumor cells are significant contributors to the locoregional recurrences and distant metastases that mark failure of radiotherapy. Due to restricted tissue oxygenation, chronically hypoxic tumor cells frequently become necrotic and thus there is often an association between chronically hypoxic and necrotic tumor regions. This simulation study is the first in a series to determine the feasibility of hypoxic cell killing after first targeting adjacent areas of necrosis with either an α- or β-emitting radioimmunoconjugate.

The La antigen is over-expressed in lung cancer and is a selective dead cancer cell target for radioimmunotherapy using the La-specific antibody APOMAB®

Background

The lupus-associated (La)-specific murine monoclonal antibody DAB4 (APOMAB®) specifically binds dead cancer cells. Using DAB4, we examined La expression in human lung cancer samples to assess its suitability as a cancer-selective therapeutic target. We evaluated the safety and effectiveness of radioimmunotherapy (RIT) using DAB4 radiolabeled with Lutetium-177 (¹⁷⁷Lu) in the murine Lewis Lung (LL2) carcinoma model, and determined whether combining RIT with DNA-damaging cisplatin-based chemotherapy, a PARP inhibitor (PARPi), or both alters treatment responses.

Methods

The expression of La mRNA in human lung cancer samples was analysed using the online database Oncomine, and the protein expression of La was examined using a TissueFocus Cancer Survey Tissue Microarray. The binding of DAB4 to cisplatin-treated LL2 cells was assessed in vitro. LL2 tumour-bearing mice were administered escalating doses of ¹⁷⁷Lu-DAB4 alone or in combination with chemotherapy, and tumour growth and survival measured. Biodistribution analysis was used to determine tissue uptake of ¹⁷⁷Lu-DAB4 or its isotype control (¹⁷⁷Lu-Sal5), when delivered alone or after chemotherapy. PARPi (rucaparib; AG-014699) was combined with chemotherapy and the effects of combined treatment on tumour growth, tumour cell DNA damage and death, and intratumoural DAB4 binding were also analysed. The effect of the triple combination of PARPi, chemotherapy and ¹⁷⁷Lu-DAB4 on tumour growth and survival of LL2 tumour-bearing mice was tested.

Results

La was over-expressed at both mRNA and protein levels in surgical specimens of human lung cancer and the over-expression of La mRNA conferred a poorer prognosis. DAB4 bound specifically to cisplatin-induced dead LL2 cells in vitro. An anti-tumour dose response was observed when escalating doses of ¹⁷⁷Lu-DAB4 were delivered in vivo, with supra-additive responses observed when chemotherapy was combined with ¹⁷⁷Lu-DAB4. Combining PARPi with chemotherapy was more effective than chemotherapy alone with increased tumour cell DNA damage and death, and intratumoural DAB4 binding. The combination of PARPi, chemotherapy and ¹⁷⁷Lu-DAB4 was well-tolerated and maximised tumour growth delay.

Conclusions

The La antigen represents a dead cancer cell-specific target in lung cancer, and DAB4 specifically targeted tumour tissue in vivo, particularly after chemotherapy. Tumour uptake of DAB4 increased further after the combination of PARPi and chemotherapy, which generated new dead tumour cell-binding targets. Consequently, combining ¹⁷⁷Lu-DAB4 with PARPi and chemotherapy produced the greatest anti-tumour response. Therefore, the triple combination of PARPi, chemotherapy and RIT may have broad clinical utility.

Targeted deletion of the gene encoding the La autoantigen (Sjögren's syndrome antigen B) in B cells or the frontal brain causes extensive tissue loss

La antigen (Sjögren's syndrome antigen B) is a phosphoprotein associated with nascent precursor tRNAs and other RNAs, and it is targeted by autoantibodies in patients with Sjögren's syndrome, systemic lupus erythematosus, and neonatal lupus. Increased levels of La are associated with leukemias and other cancers, and various viruses usurp La to promote their replication. Yeast cells (Saccharomyces cerevisiae and Schizosaccharomyces pombe) genetically depleted of La grow and proliferate, whereas deletion from mice causes early embryonic lethality, raising the question of whether La is required by mammalian cells generally or only to surpass a developmental stage. We developed a conditional La allele and used it in mice that express Cre recombinase in either B cell progenitors or the forebrain. B cell Mb1(Cre) La-deleted mice produce no B cells. Consistent with αCamKII Cre, which induces deletion in hippocampal CA1 cells in the third postnatal week and later throughout the neocortex, brains develop normally in La-deleted mice until ∼5 weeks and then lose a large amount of forebrain cells and mass, with evidence of altered pre-tRNA processing. The data indicate that La is required not only in proliferating cells but also in nondividing postmitotic cells. Thus, La is essential in different cell types and required for normal development of various tissue types.

A head and neck cancer tumor response-specific gene signature for cisplatin, 5-fluorouracil induction chemotherapy fails with added taxanes

Background

It is a major clinical challenge to predict which patients, with advanced stage head and neck squamous cell carcinoma, will not exhibit a reduction in tumor size following induction chemotherapy in order to avoid toxic effects of ineffective chemotherapy and delays for instituting other therapeutic options. Further, it is of interest to know to what extent a gene signature, which identifies patients with tumors that will not respond to a particular induction chemotherapy, is applicable when additional chemotherapeutic agents are added to the regimen.

Methodology/Principal Findings

To identify genes that predict tumor resistance to induction with cisplatin/5-fluorouracil (PF) or PF and a taxane, we analyzed patient tumor biopsies with whole genome microarrays and quantitative reverse transcriptase-PCR (TLDA) cards. A leave one out cross-validation procedure allowed evaluation of the prediction tool. A ten-gene microarray signature correctly classified 12/13 responders and 7/10 non-responders to PF (92% specificity, 82.6% accuracy). TLDA analysis (using the same classifier) of the patients correctly classified 12/12 responders and 8/10 non-responders (100% specificity, 90.9% accuracy). Further, TLDA analysis correctly predicted the response of 5 new patients and, overall, 12/12 responders and 13/15 non-responders (100% specificity, 92.6% accuracy). The protein products of the genes constituting the signature physically associate with 27 other proteins, involved in regulating gene expression, constituting an interaction network. In contrast, TLDA-based prediction (with the same gene signature) of responses to induction with PF and either of two taxanes was poor (0% specificity, 25% accuracy and 33.3% specificity, 25% accuracy).

Conclusions/Significance

Successful transfer of the microarray-based gene signature to an independent, PCR-based technology suggests that TLDA-based signatures could be a useful hospital-based technology for determining therapeutic options. Although highly specific for tumor responses to PF induction, the gene signature is unsuccessful when taxanes are added. The results illustrate the subtlety in developing “personalized medicine”.

Epigallocatechin gallate sensitizes CAL-27 human oral squamous cell carcinoma cells to the anti-metastatic effects of gefitinib (Iressa) via synergistic suppression of epidermal growth factor receptor and matrix metalloproteinase-2

Human head and neck squamous cell carcinoma (HNSCC) is a major cause of cancer-related death during the last decade due to its related metastasis and poor treatment outcomes. Gefitinib (Iressa), a tyrosine kinase inhibitor has been reported to reduce the metastatic abilities of oral cancer. Previous studies have shown that epigallocatechin gallate (EGCG), a green tea polyphenol, possesses cancer chemopreventive and anticancer activity. However, the mechanisms involved in the suppression of invasion and metastasis of human oral cancer cells following co-incubation with gefitinib and EGCG remain poorly understood. In the present study, we attempted to investigate the synergistic effects of a combined treatment of gefitinib and EGCG in CAL-27 cells in vitro and to elucidate the underlying molecular mechanisms associated with the supression of cell migration and invasion. In the present study, we found that the individual treatments or the combined treatment of gefitinib and EGCG synergistically inhibited the invasion and migration of CAL-27 cells using Transwell invasion and wound-healing scratch assays, respectively. Similarly, gefitinib in combination with EGCG synergistically attenuated enzymatic activity and the protein expression of MMP-2 in CAL-27 cells. Furthermore, individual or combined treatment with EGCG and gefitinib suppressed the protein expression of p-EGFR and the phosphorylated protein levels of ERK, JNK, p38 and AKT and displayed inhibitory effects on metastatic ability of CAL-27 cells. Combined effects of EGCG and gefitinib-altered anti-metastatic actions for related gene expression were observed using DNA microarray analysis. Importantly, EGCG sensitizes CAL-27 cells to gefitinib-suppressed phosphorylation of epidermal growth factor receptor (EGFR in vitro. Taken together, our results suggest that the synergistic suppression of the metastatic ability of CAL-27 cells after EGCG and gefitinib individual or combined treatment are mediated through mitogen-activated protein kinase (MAPK) signaling. Our novel findings provide potential insights into the mechanism involved with synergistic responses of gefitinib and EGCG against the progression of oral cancer.

In vitro cell migration and invasion assays

Determining the migratory and invasive capacity of tumor and stromal cells and clarifying the underlying mechanisms is most relevant for novel strategies in cancer diagnosis, prognosis, drug development and treatment. Here we shortly summarize the different modes of cell travelling and review in vitro methods, which can be used to evaluate migration and invasion. We provide a concise summary of established migration/invasion assays described in the literature, list advantages, limitations and drawbacks, give a tabular overview for convenience and depict the basic principles of the assays graphically. In many cases particular research problems and specific cell types do not leave a choice for a broad variety of usable assays. However, for most standard applications using adherent cells, based on our experience we suggest to use exclusion zone assays to evaluate migration/invasion. We substantiate our choice by demonstrating that the advantages outbalance the drawbacks e.g. the simple setup, the easy readout, the kinetic analysis, the evaluation of cell morphology and the feasibility to perform the assay with standard laboratory equipment. Finally, innovative 3D migration and invasion models including heterotypic cell interactions are discussed. These methods recapitulate the in vivo situation most closely. Results obtained with these assays have already shed new light on cancer cell spreading and potentially will uncover unknown mechanisms.

Versatility of RNA-Binding Proteins in Cancer

Posttranscriptional gene regulation is a rapid and efficient process to adjust the proteome of a cell to a changing environment. RNA-binding proteins (RBPs) are the master regulators of mRNA processing and translation and are often aberrantly expressed in cancer. In addition to well-studied transcription factors, RBPs are emerging as fundamental players in tumor development. RBPs and their mRNA targets form a complex network that plays a crucial role in tumorigenesis. This paper describes mechanisms by which RBPs influence the expression of well-known oncogenes, focusing on precise examples that illustrate the versatility of RBPs in posttranscriptional control of cancer development. RBPs appeared very early in evolution, and new RNA-binding domains and combinations of them were generated in more complex organisms. The identification of RBPs, their mRNA targets, and their mechanism of action have provided novel potential targets for cancer therapy.