Nucleolin Promotes Heat Shock-Associated Translation of VEGF-D to Promote Tumor Lymphangiogenesis

Engineering a Dual-Receptor Targeted Multivalent Probe for Enhanced Magnetic Resonance Imaging of Metastatic Cancer

Noninvasive monitoring of cancer metastasis is essential to improving clinical outcomes. Molecular MRI (mMRI) is a special implementation of noninvasive molecular imaging that promises to offer a powerful means for early detection and analysis of pathological states of cancer by tracking molecular markers. However, this is often hindered by the challenging issue of obtaining transformable mMRI contrast agents with high sensitivity, specificity, and broad applicability, given the high tumor heterogeneity and complex metastatic features. Herein, we present a dual-receptor targeted, multivalent recognition strategy and report a new class of mMRI probes for enhanced imaging of metastatic cancer. This probe is designed by covalently conjugating Gd-chelate with phenylboronic acid and an aptamer via an affordable polymerization chemistry to concurrently target two different cell-membrane receptors that are commonly overexpressed and highly implicated in both tumorigenesis and metastasis. Moreover, the polymerization chemistry allows the probe to contain a bunch of targeting ligands and signal reporters in a single chain, which not only leads to more than 2-fold enhancement in T1 relaxivity at 1.5 T compared to the commercial contrast agent but also enables it to actively target tumor cells in a multivalent recognition manner, contributing to a much higher imaging contrast than single-receptor targeted probes and the commercial agent in mouse models with lung metastases, yet without inducing systemic side effects. We expect this study to offer a useful molecular tool to promote transformable applications of mMRI and a better understanding of molecular mechanisms involved in cancer development.

Fates and functions of RNA-binding proteins under stress

Exposure to stress activates a well-orchestrated set of changes in gene expression programs that allow the cell to cope with and adapt to the stress, or undergo programmed cell death. RNA-protein interactions, mediating all aspects of post-transcriptional regulation of gene expression, play crucial roles in cellular stress responses. RNA-binding proteins (RBPs), which interact with sequence/structural elements in RNAs to control the steps of RNA metabolism, have therefore emerged as central regulators of post-transcriptional responses to stress. Following exposure to a variety of stresses, the dynamic alterations in the RNA-protein interactome enable cells to respond to intracellular or extracellular perturbations by causing changes in mRNA splicing, polyadenylation, stability, translation, and localization. As RBPs play a central role in determining the cellular proteome both qualitatively and quantitatively, it has become increasingly evident that their abundance, availability, and functions are also highly regulated in response to stress. Exposure to stress initiates a series of signaling cascades that converge on post-translational modifications (PTMs) of RBPs, resulting in changes in their subcellular localization, association with stress granules, extracellular export, proteasomal degradation, and RNA-binding activities. These alterations in the fate and function of RBPs directly impact their post-transcriptional regulatory roles in cells under stress. Adopting the ubiquitous RBP HuR as a prototype, three scenarios illustrating the changes in nuclear-cytoplasmic localization, RNA-binding activity, export and degradation of HuR in response to inflammation, genotoxic stress, and heat shock depict the complex and interlinked regulatory mechanisms that control the fate and functions of RBPs under stress. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

SNHG15-Mediated Localization of Nucleolin at the Cell Protrusions Regulates CDH2 mRNA Expression and Cell Invasion

LncRNAs are emerging as important regulators of gene expression by controlling transcription in the nucleus and by modulating mRNA translation in the cytoplasm. In this study, we reveal a novel function of lncRNA SNHG15 in mediating breast cancer cell invasion through regulating the local translation of CDH2 mRNA. We show that SNHG15 preferentially localizes at the cellular protrusions or cell leading edge and that this localization is directed by IMP1, a multifunctional protein involved in many aspects of RNA regulation. We demonstrate that SNHG15 also forms a complex with nucleolin, allowing nucleolin to be co-transported with SNHG15 to the cell protrusions, where the accumulated nucleolin is able to bind to CDH2 mRNA. Interaction with nucleolin stabilizes local CDH2 mRNA and regulates its translation, thus promoting cell invasive potential. Our findings reveal an underlying mechanism by which lncRNA could serve as a carrier to transport a protein regulator into a specific cell compartment to enhance target mRNA expression.

Long non-coding RNA Neat1 and paraspeckle components are translational regulators in hypoxia

Internal ribosome entry sites (IRESs) drive translation initiation during stress. In response to hypoxia, (lymph)angiogenic factors responsible for tissue revascularization in ischemic diseases are induced by the IRES-dependent mechanism. Here, we searched for IRES trans-acting factors (ITAFs) active in early hypoxia in mouse cardiomyocytes. Using knock-down and proteomics approaches, we show a link between a stressed-induced nuclear body, the paraspeckle, and IRES-dependent translation. Furthermore, smiFISH experiments demonstrate the recruitment of IRES-containing mRNA into paraspeckle during hypoxia. Our data reveal that the long non-coding RNA Neat1, an essential paraspeckle component, is a key translational regulator, active on IRESs of (lymph)angiogenic and cardioprotective factor mRNAs. In addition, paraspeckle proteins p54^nrb and PSPC1 as well as nucleolin and RPS2, two p54^nrb-interacting proteins identified by mass spectrometry, are ITAFs for IRES subgroups. Paraspeckle thus appears as a platform to recruit IRES-containing mRNAs and possibly host IRESome assembly. Polysome PCR array shows that Neat1 isoforms regulate IRES-dependent translation and, more widely, translation of mRNAs involved in stress response.

The plasticity of mRNA translation during cancer progression and therapy resistance

Translational control of mRNAs during gene expression allows cells to promptly and dynamically adapt to a variety of stimuli, including in neoplasia in response to aberrant oncogenic signalling (for example, PI3K-AKT-mTOR, RAS-MAPK and MYC) and microenvironmental stress such as low oxygen and nutrient supply. Such translational rewiring allows rapid, specific changes in the cell proteome that shape specific cancer phenotypes to promote cancer onset, progression and resistance to anticancer therapies. In this Review, we illustrate the plasticity of mRNA translation. We first highlight the diverse mechanisms by which it is regulated, including by translation factors (for example, eukaryotic initiation factor 4F (eIF4F) and eIF2), RNA-binding proteins, tRNAs and ribosomal RNAs that are modulated in response to aberrant intracellular pathways or microenvironmental stress. We then describe how translational control can influence tumour behaviour by impacting on the phenotypic plasticity of cancer cells as well as on components of the tumour microenvironment. Finally, we highlight the role of mRNA translation in the cellular response to anticancer therapies and its promise as a key therapeutic target.

Coordinating Effect of VEGFC and Oleic Acid Participates to Tumor Lymphangiogenesis

Simple Summary

In cancer, the lymphatic system is hijacked by tumor cells that escape from primary tumor and metastasize to the sentinel lymph nodes. Tumor lymphangiogenesis is stimulated by the vascular endothelial growth factors-C (VEGFC) after binding to its receptor VEGFR-3. However, how VEGFC cooperates with other molecules to promote lymphatic neovessel growth has not been fully determined. Here, we showed that tumor lymphangiogenesis developed in tumoral lesions and in their surrounding adipose tissue (AT). Interestingly, lymphatic vessel density correlated with an increase in circulating free fatty acids (FFA) in the lymph from tumor-bearing mice. We showed that adipocyte-released FFA are uploaded by lymphatic endothelial cells (LEC) to stimulate their sprouting. Lipidomic analysis identified the monounsaturated oleic acid (OA) as the major circulating FFA in the lymph in a tumoral context. OA transporters FATP-3, -6 and CD36 were only upregulated on LEC in the presence of VEGFC showing a collaborative effect of these molecules. OA released from adipocytes is taken up by LECs to stimulate the fatty acid β-oxidation, leading to increased adipose tissue lymphangiogenesis. Our results provide new insights on the dialogue between tumors and adipocytes via the lymphatic system and identify a key role for adipocyte-derived FFA in the promotion of lymphangiogenesis, revealing novel therapeutic opportunities for inhibitors of lymphangiogenesis in cancer.

Abstract

In cancer, the lymphatic system is hijacked by tumor cells that escape from primary tumor and metastasize to the sentinel lymph nodes. Tumor lymphangiogenesis is stimulated by the vascular endothelial growth factors-C (VEGFC) after binding to its receptor VEGFR-3. However, how VEGFC cooperates with other molecules to promote lymphatics growth has not been fully determined. We showed that lymphangiogenesis developed in tumoral lesions and in surrounding adipose tissue (AT). Interestingly, lymphatic vessel density correlated with an increase in circulating free fatty acids (FFA) in the lymph from tumor-bearing mice. We showed that adipocyte-released FFA are uploaded by lymphatic endothelial cells (LEC) to stimulate their sprouting. Lipidomic analysis identified the monounsaturated oleic acid (OA) as the major circulating FFA in the lymph in a tumoral context. OA transporters FATP-3, -6 and CD36 were only upregulated on LEC in the presence of VEGFC showing a collaborative effect of these molecules. OA stimulates fatty acid β-oxidation in LECs, leading to increased AT lymphangiogenesis. Our results provide new insights on the dialogue between tumors and adipocytes via the lymphatic system and identify a key role for adipocyte-derived FFA in the promotion of lymphangiogenesis, revealing novel therapeutic opportunities for inhibitors of lymphangiogenesis in cancer.

Cell surface nucleolin as active bait for nanomedicine in cancer therapy: a promising option

Conventional chemotherapy used against cancer is mostly limited due to their non-targeted nature, affecting normal tissue and causing undesirable toxic effects to the affected tissue. With the aim of improving these treatments both therapeutically and in terms of their safety, numerous studies are currently being carried out using nanoparticles (NPs) as a vector combining tumor targeting and carrying therapeutic tools. In this context, it appears that nucleolin, a molecule over-expressed on the surface of tumor cells, is an interesting therapeutic target. Several ligands, antagonists of nucleolin of various origins, such as AS1411, the F3 peptide and the multivalent pseudopeptide N6L have been developed and studied as therapeutic tools against cancer. Over the last ten years or so, numerous studies have been published demonstrating that these antagonists can be used as tumor targeting agents with NPs from various origins. Focusing on nucleolin ligands, the aim of this article is to review the literature recently published or under experimentation in our research team to evaluate the efficacy and future development of these tools as anti-tumor agents.

circEHBP1 promotes lymphangiogenesis and lymphatic metastasis of bladder cancer via miR-130a-3p/TGFβR1/VEGF-D signaling

Lymphatic metastasis constitutes a leading cause of recurrence and mortality in bladder cancer. Accumulating evidence indicates that lymphangiogenesis is indispensable to trigger lymphatic metastasis. However, the specific mechanism is poorly understood. In the present study, we revealed a pathway involved in lymphatic metastasis of bladder cancer, in which a circular RNA (circRNA) facilitated lymphangiogenesis in a vascular endothelial growth factor C (VEGF-C)-independent manner. Novel circRNA circEHBP1 was markedly upregulated in bladder cancer and correlated positively with lymphatic metastasis and poor prognosis of patients with bladder cancer. circEHBP1 upregulated transforming growth factor beta receptor 1 (TGFBR1) expression through physically binding to miR-130a-3p and antagonizing the suppression effect of miR-130a-3p on the 3′ UTR region of TGFBR1. Subsequently, circEHBP1-mediated TGFβR1 overexpression activated the TGF-β/SMAD3 signaling pathway, thereby promoting the secretion of VEGF-D and driving lymphangiogenesis and lymphatic metastasis in bladder cancer. Importantly, administration of VEGF-D neutralizing antibodies remarkably blocked circEHBP1-induced lymphangiogenesis and lymphatic metastasis in vivo. Our findings highlighted that the circEHBP1/miR-130a-3p/TGFβR1/VEGF-D axis contributes to lymphangiogenesis and lymphatic metastasis of bladder cancer independent of VEGF-C, which might lead to the development of circEHBP1 as a potential biomarker and promising therapeutic target for lymphatic metastasis in bladder cancer.

Translational Regulation of Cancer Metastasis

Deregulation of the mRNA translational process has been observed during tumorigenesis. However, recent findings have shown that deregulation of translation also contributes specifically to cancer cell spread. During metastasis, cancer cells undergo changes in cellular state, permitting the acquisition of features necessary for cell survival, dissemination, and outgrowth. In addition, metastatic cells respond to external cues, allowing for their persistence under significant cellular and microenvironmental stresses. Recent work has revealed the importance of mRNA translation to these dynamic changes, including regulation of cell states through epithelial-to-mesenchymal transition and tumor dormancy and as a response to external stresses such as hypoxia and immune surveillance. In this review, we focus on examples of altered translation underlying these phenotypic changes and responses to external cues and explore how they contribute to metastatic progression. We also highlight the therapeutic opportunities presented by aberrant mRNA translation, suggesting novel ways to target metastatic tumor cells.

Translational Regulations in Response to Endoplasmic Reticulum Stress in Cancers

During carcinogenesis, almost all the biological processes are modified in one way or another. Among these biological processes affected, anomalies in protein synthesis are common in cancers. Indeed, cancer cells are subjected to a wide range of stresses, which include physical injuries, hypoxia, nutrient starvation, as well as mitotic, oxidative or genotoxic stresses. All of these stresses will cause the accumulation of unfolded proteins in the Endoplasmic Reticulum (ER), which is a major organelle that is involved in protein synthesis, preservation of cellular homeostasis, and adaptation to unfavourable environment. The accumulation of unfolded proteins in the endoplasmic reticulum causes stress triggering an unfolded protein response in order to promote cell survival or to induce apoptosis in case of chronic stress. Transcription and also translational reprogramming are tightly controlled during the unfolded protein response to ensure selective gene expression. The majority of stresses, including ER stress, induce firstly a decrease in global protein synthesis accompanied by the induction of alternative mechanisms for initiating the translation of mRNA, later followed by a translational recovery. After a presentation of ER stress and the UPR response, we will briefly present the different modes of translation initiation, then address the specific translational regulatory mechanisms acting during reticulum stress in cancers and highlight the importance of translational control by ER stress in tumours.

Paclitaxel induces lymphatic endothelial cells autophagy to promote metastasis

Cytotoxic therapy for breast cancer inhibits the growth of primary tumors, but promotes metastasis to the sentinel lymph nodes through the lymphatic system. However, the effect of first-line chemotherapy on the lymphatic endothelium has been poorly investigated. In this study, we determined that paclitaxel, the anti-cancer drug approved for the treatment of metastatic or locally advanced breast cancer, induces lymphatic endothelial cell (LEC) autophagy to increase metastases. While paclitaxel treatment was largely efficacious in inhibiting LEC adhesion, it had no effect on cell survival. Paclitaxel inhibited LEC migration and branch point formation by inducing an autophagy mechanism independent of Akt phosphorylation. In vivo, paclitaxel mediated a higher permeability of lymphatic endothelium to tumor cells and this effect was reversed by chloroquine, an autophagy-lysosome inhibitor. Despite a strong effect on reducing tumor size, paclitaxel significantly increased metastasis to the sentinel lymph nodes. This effect was restricted to a lymphatic dissemination, as chemotherapy did not affect the blood endothelium. Taken together, our findings suggest that the lymphatic system resists to chemotherapy through an autophagy mechanism to promote malignant progression and metastatic lesions. This study paves the way for new combinative therapies aimed at reducing the number of metastases.

Vasohibin1, a new mouse cardiomyocyte IRES trans-acting factor that regulates translation in early hypoxia

Hypoxia, a major inducer of angiogenesis, triggers major changes in gene expression at the transcriptional level. Furthermore, under hypoxia, global protein synthesis is blocked while internal ribosome entry sites (IRES) allow specific mRNAs to be translated. Here, we report the transcriptome and translatome signatures of (lymph)angiogenic genes in hypoxic HL-1 mouse cardiomyocytes: most genes are induced at the translatome level, including all IRES-containing mRNAs. Our data reveal activation of (lymph)angiogenic factor mRNA IRESs in early hypoxia. We identify vasohibin1 (VASH1) as an IRES trans-acting factor (ITAF) that is able to bind RNA and to activate the FGF1 IRES in hypoxia, but which tends to inhibit several IRESs in normoxia. VASH1 depletion has a wide impact on the translatome of (lymph)angiogenesis genes, suggesting that this protein can regulate translation positively or negatively in early hypoxia. Translational control thus appears as a pivotal process triggering new vessel formation in ischemic heart.

Arterial Lymphatics in Atherosclerosis: Old Questions, New Insights, and Remaining Challenges

The lymphatic network is well known for its role in the maintenance of tissue fluid homeostasis, absorption of dietary lipids, trafficking of immune cells, and adaptive immunity. Aberrant lymphatic function has been linked to lymphedema and immune disorders for a long time. Discovery of lymphatic cell markers, novel insights into developmental and postnatal lymphangiogenesis, development of genetic mouse models, and the introduction of new imaging techniques have improved our understanding of lymphatic function in both health and disease, especially in the last decade. Previous studies linked the lymphatic vasculature to atherosclerosis through regulation of immune responses, reverse cholesterol transport, and inflammation. Despite extensive research, many aspects of the lymphatic circulation in atherosclerosis are still unknown and future studies are required to confirm that arterial lymphangiogenesis truly represents a therapeutic target in patients with cardiovascular disease. In this review article, we provide an overview of factors and mechanisms that regulate lymphangiogenesis, summarize recent findings on the role of lymphatics in macrophage reverse cholesterol transport, immune cell trafficking and pathogenesis of atherosclerosis, and present an overview of pharmacological and genetic strategies to modulate lymphatic vessel density in cardiovascular tissue.

IRES Trans-Acting Factors, Key Actors of the Stress Response

The cellular stress response corresponds to the molecular changes that a cell undergoes in response to various environmental stimuli. It induces drastic changes in the regulation of gene expression at transcriptional and posttranscriptional levels. Actually, translation is strongly affected with a blockade of the classical cap-dependent mechanism, whereas alternative mechanisms are activated to support the translation of specific mRNAs. A major mechanism involved in stress-activated translation is the internal ribosome entry site (IRES)-driven initiation. IRESs, first discovered in viral mRNAs, are present in cellular mRNAs coding for master regulators of cell responses, whose expression must be tightly controlled. IRESs allow the translation of these mRNAs in response to different stresses, including DNA damage, amino-acid starvation, hypoxia or endoplasmic reticulum stress, as well as to physiological stimuli such as cell differentiation or synapse network formation. Most IRESs are regulated by IRES trans-acting factor (ITAFs), exerting their action by at least nine different mechanisms. This review presents the history of viral and cellular IRES discovery as well as an update of the reported ITAFs regulating cellular mRNA translation and of their different mechanisms of action. The impact of ITAFs on the coordinated expression of mRNA families and consequences in cell physiology and diseases are also highlighted.

Meeting the needs of breast cancer: A nucleolin's perspective

A major challenge in the management of breast cancer disease has been the development of metastases. Finding new molecular targets and the design of targeted therapeutic approaches to improve the overall survival and quality of life of these patients is, therefore, of great importance. Nucleolin, which is overexpressed in cancer cells and tumor-associated blood vessels, have been implicated in various processes supporting tumorigenesis and angiogenesis. Additionally, its overexpression has been demonstrated in a variety of human neoplasias as an unfavorable prognostic factor, associated with a high risk of relapse and low overall survival. Hence, nucleolin has emerged as a relevant target for therapeutic intervention in cancer malignancy, including breast cancer. This review focus on the contribution of nucleolin for cancer disease and on the development of therapeutic strategies targeting this protein. In this respect, it also provides a critical analysis about the potential and pitfalls of nanomedicine for cancer therapy.

Cell surface expression of nucleolin mediates the antiangiogenic and antitumor activities of kallistatin

Kallistatin is a unique serine proteinase inhibitor and heparin-binding protein. A previous study conducted by our group indicated that kallistatin has antiangiogenic and antitumoral activities. In the present study, we report that kallistatin specifically binds to membrane surface-expressed nucleolin with high affinity. Antibody-mediated neutralization or siRNA-induced nucleolin knockdown results in loss of kallistatin suppression of endothelial cell proliferation and migration in vitro and tumor angiogenesis and growth in vivo. In addition, we show that kallistatin is internalized and transported into cell nuclei of endothelial cells via nucleolin. Within the nucleus, kallistatin inhibits the phosphorylation of nucleolin, which is a critical step required for cell proliferation. Thus, we demonstrate that nucleolin is a novel functional receptor of kallistatin that mediates its antiangiogenic and antitumor activities. These findings provide mechanistic insights into the inhibitory effects of kallistatin on endothelial cell growth, tumor cell proliferation, and tumor-related angiogenesis.

Multifaceted Nucleolin Protein and Its Molecular Partners in Oncogenesis

Discovered in 1973, nucleolin is one of the most abundant phosphoproteins of the nucleolus. The ability of nucleolin to be involved in many cellular processes is probably related to its structural organization and its capability to form many different interactions with other proteins. Many functions of nucleolin affect cellular processes involved in oncogenesis-for instance: in ribosome biogenesis; in DNA repair, remodeling, and genome stability; in cell division and cell survival; in chemokine and growth factor signaling pathways; in angiogenesis and lymphangiogenesis; in epithelial-mesenchymal transition; and in stemness. In this review, we will describe the different functions of nucleolin in oncogenesis through its interaction with other proteins.

New perspectives of physiological and pathological functions of nucleolin (NCL)

Nucleolin (NCL) is a multifunctional protein that mainly localized in the nucleolus, it is also found in the nucleoplasm, cytoplasm and cell membrane. The three main structural domains allow the interaction of NCL with different proteins and RNA sequences. Moreover, specific post-translational modifications and its shuttling property also contribute to its multifunctionality. NCL has been demonstrated to be involved in a variety of aspects such as ribosome biogenesis, chromatin organization and stability, DNA and RNA metabolism, cytokinesis, cell proliferation, angiogenesis, apoptosis regulation, stress response and microRNA processing. NCL has been increasingly implicated in several pathological processes, especially in tumorigenesis and viral infection, which makes NCL a potential target for the development of anti-tumor and anti-viral strategies. In this review, we present an overview on the structure, localizations and various functions of NCL, and further describe how the multiple functions of NCL are correlated to its multiple cellular distributions.

[Cardiac lymphatic system]

The lymphatic system is a network of vessels and lymphoid tissues that maintain tissue fluid homeostasis, transport intestinal fat, and regulate immune surveillance. Despite a large body of evidence showing the importance of lymphatic vessels in cardiovascular diseases, the role of cardiac lymphatics has not been extensively investigated. This review highlights the chronology of key discoveries in cardiac lymphatic development and function. In physiology, the cardiac lymphatic system dynamically regulates interstitial fluid drainage to the mediastinal lymph nodes to maintain homeostasis and prevent edema. After myocardial infarction, lymphatic vessels in the ischemic heart become dysfunctional and contribute to the development of chronic myocardial edema that aggravates cardiac fibrosis and dysfunction. Stimulation of cardiac lymphangiogenesis, based on the delivery of lymphangiogenic growth factors, such as VEGF-C, may represent a novel therapeutic strategy to improve cardiac function.

Nucleolin Staining May Aid in the Identification of Circulating Prostate Cancer Cells

INTRODUCTION

Circulating tumor cells (CTCs) have great potential as circulating biomarkers for solid malignancies. Currently available assays for CTC detection rely on epithelial markers with somewhat limited sensitivity and specificity. We found that the staining pattern of nucleolin, a common nucleolar protein in proliferative cells, separates CTCs from white blood cells (WBCs) in men with metastatic prostate cancer.

PATIENTS AND METHODS

Whole peripheral blood from 3 men with metastatic prostate cancer was processed with the AccuCyte CTC system (RareCyte, Seattle, WA). Slides were immunostained with 4',6-diamidino-2-phenylindole (DAPI), anti-pan-cytokeratin, anti-CD45/CD66b/CD11b/CD14/CD34, and anti-nucleolin antibodies and detected using the CyteFinder system. DAPI nucleolin colocalization and staining pattern wavelet entropy were measured with novel image analysis software.

RESULTS

A total of 33,718 DAPI-positive cells were analyzed with the novel imaging software, of which 45 (0.13%) were known CTCs based on the established AccuCyte system criteria. Nucleolin staining pattern for segmentable CTCs demonstrated greater wavelet entropy than that of WBCs (median wavelet entropy, 6.86 × 107 and 3.03 × 106, respectively; P = 2.92 × 10-22; approximated z statistic = 9.63). Additionally, the total nucleolin staining of CTCs was greater than that of WBCs (median total pixel intensity, 1.20 × 105 and 2.55 × 104 integrated pixel units, respectively; P = 2.40 × 10-21; approximated z statistic = 9.41).

CONCLUSION

Prostate cancer CTCs displayed unique nucleolin expression and localization compared to WBCs. This finding has the potential to serve as the basis for a sensitive and specific CTC detection method.