Transportin regulates nuclear import of CD44

Human birth tissue products as a regenerative medicine to inhibit post-surgical pain through multi-modal action

Pain after surgery causes significant suffering. Opioid analgesics cause severe side effects and accidental death. Therefore, there is an urgent need to develop non-opioid therapies for managing post-surgical pain and, more importantly, preventing its transition to a chronic state. In a mouse model of post-surgical pain, local application of Clarix Flo (FLO), a human amniotic membrane (AM) product, attenuated established post-surgical pain hypersensitivity without exhibiting known side effects of opioid use in mice. Importantly, preemptive drug treatment also inhibited the transition of post-surgical pain to a prolonged state. This effect was achieved through direct inhibition of nociceptive dorsal root ganglion (DRG) neurons via CD44-dependent pathways, and indirect pain relief by attenuating immune cell recruitment. We further purified the major matrix component, the heavy chain-hyaluronic acid/pentraxin 3 (HC-HA/PTX3) from human AM that has greater purity and water solubility than FLO. HC-HA/PTX3 replicated FLO- induced neuronal and pain inhibition. Mechanistically, HC-HA/PTX3 induced cytoskeleton rearrangements to inhibit sodium current and high-voltage activated calcium current on nociceptive neurons, suggesting it is a key bioactive component mediating pain relief. Collectively, our findings highlight the potential of naturally derived biologics from human birth tissues as an effective non-opioid treatment for post-surgical pain and unravel the underlying mechanisms.

Cell aggregation activates small GTPase Rac1 and induces CD44 cleavage by maintaining lipid raft integrity

Lipid rafts are highly ordered membrane domains that are enriched in cholesterol and glycosphingolipids and serve as major platforms for signal transduction. Cell detachment from the extracellular matrix (ECM) triggers lipid raft disruption and anoikis, which is a barrier for cancer cells to metastasize. Compared to single circulating tumor cells (CTCs), our recent studies have demonstrated that CD44-mediatd cell aggregation enhances the stemness, survival and metastatic ability of aggregated cells. Here, we investigated whether and how lipid rafts are involved in CD44-mediated cell aggregation. We found that cell detachment, which mimics the condition when tumor cells detach from the ECM to metastasize, induced lipid raft disruption in single cells, but lipid raft integrity was maintained in aggregated cells. We further found that lipid raft integrity in aggregated cells was required for Rac1 activation to prevent anoikis. In addition, CD44 and γ-secretase coexisted at lipid rafts in aggregated cells, which promoted CD44 cleavage and generated CD44 intracellular domain (CD44 ICD) to enhance stemness of aggregated cells. Consequently, lipid raft disruption inhibited Rac1 activation, CD44 ICD generation, and metastasis. Our findings reveal two new pathways regulated by CD44-mediated cell aggregation via maintaining lipid raft integrity. These findings also suggest that targeting cell aggregation-mediated pathways could be a novel therapeutic strategy to prevent CTC cluster-initiated metastasis.

In vivo inhibition of nuclear ACE2 translocation protects against SARS-CoV-2 replication and lung damage through epigenetic imprinting

In vitro, ACE2 translocates to the nucleus to induce SARS-CoV-2 replication. Here, using digital spatial profiling of lung tissues from SARS-CoV-2-infected golden Syrian hamsters, we show that a specific and selective peptide inhibitor of nuclear ACE2 (NACE2i) inhibits viral replication two days after SARS-CoV-2 infection. Moreover, the peptide also prevents inflammation and macrophage infiltration, and increases NK cell infiltration in bronchioles. NACE2i treatment increases the levels of the active histone mark, H3K27ac, restores host translation in infected hamster bronchiolar cells, and leads to an enrichment in methylated ACE2 in hamster bronchioles and lung macrophages, a signature associated with virus protection. In addition, ACE2 methylation is increased in myeloid cells from vaccinated patients and associated with reduced SARS-CoV-2 spike protein expression in monocytes from individuals who have recovered from infection. This protective epigenetic scarring of ACE2 is associated with a reduced latent viral reservoir in monocytes/macrophages and enhanced immune protection against SARS-CoV-2. Nuclear ACE2 may represent a therapeutic target independent of the variant and strain of viruses that use the ACE2 receptor for host cell entry.

TIMP-1 Dependent Modulation of Metabolic Profiles Impacts Chemoresistance in NSCLC

The development of chemoresistance remains a significant barrier to treating NSCLC. Alteration of cancer cell metabolism is an important mechanism for chemoresistance. This study explored the role of aberrant metabolism in TIMP-1-mediated chemoresistance. Bioinformatics analysis identified an association of high TIMP-1 with altered energy metabolism. We have defined the role of depolarized mitochondria through a reduction in lactate secretion, higher ROS levels in TIMP-1 KD cells and reduced GSH levels. TIMP-1 modulates the metabolic profile via acetylation of mitochondrial STAT3 and its interaction with CD44. Intriguingly, monomers of acetylated STAT3 were critical for altered metabolism, whereas STAT3 dimers abrogated this function. Further, the mitochondrial metabolic profile was also altered in a cisplatin-resistant clone of A549 cells. We also correlated the immunoexpression of CD44, STAT3 and TIMP-1 in patient samples. This study provided evidence that TIMP-1 alters the metabolic profile by modulating mitochondrial metabolism via the CD44-STAT3 axis through its effects on STAT3 acetylation. It also lent further support to the critical role of TIMP-1 in chemoresistance. Interrogation of the TCGA-LUAD dataset revealed perturbations in the critical modulator that can alter metabolic states in cancer cells. Higher expression of a five-gene signature, including TIMP-1, correlated with immunosuppressive cells and was found to be associated with overall survival. This study identified several metabolic mechanisms that could influence therapeutic options and prognosis in NSCLC patients.

CD44 In Sarcomas: A Comprehensive Review and Future Perspectives

It is widely accepted that the tumor microenvironment, particularly the extracellular matrix, plays an essential role in the development of tumors through the interaction with specific protein-membrane receptors. One of the most relevant proteins in this context is the transmembrane protein CD44. The role of CD44 in tumor progression, invasion, and metastasis has been well established in many cancers, although a comprehensive review concerning its role in sarcomas has not been published. CD44 is overexpressed in most sarcomas and several in vitro and in vivo experiments have shown a direct effect on tumor progression, dissemination, and drug resistance. Moreover, CD44 has been revealed as a useful marker for prognostic and diagnostic (CD44v6 isoform) in osteosarcoma. Besides, some innovative treatments such as HA-functionalized liposomes therapy have become an excellent CD44-mediated intracellular delivery system for osteosarcoma. Unfortunately, the reduced number of studies deciphering the prognostic/diagnostic value of CD44 in other sarcoma subgroups, neither than osteosarcoma, in addition to the low number of patients involved in those studies, have produced inconclusive results. In this review, we have gone through the information available on the role of CD44 in the development, maintenance, and progression of sarcomas, analyzing their implications at the prognostic, therapeutic, and mechanistic levels. Moreover, we illustrate how research involving the specific role of CD44 in the different sarcoma subgroups could suppose a chance to advance towards a more innovative perspective for novel therapies and future clinical trials.

CD44/ERM/F-actin complex mediates targeted nuclear degranulation and excessive neutrophil extracellular trap formation during sepsis

Neutrophils release neutrophil extracellular traps (NETs) to capture and kill pathogens, but excessive NET release can damage the surrounding tissues. Myeloperoxidase (MPO) and neutrophil elastase (NE) are thought to be important in promoting histone depolymerization and DNA breakage in the nucleus. However, the detailed path by which MPO and NE enter the nucleus is unknown. In the present study, we observed that delayed fusion of azurophilic granules with the nuclear membrane 15–20 min after extracellular degranulation in activated neutrophils. In a subsequent experiment, we further demonstrated that this fusion leads to MPO entry into the nucleus and promotes nuclear histone depolymerization and DNA breakage, a process called ‘targeted nuclear degranulation’. This process can be effectively inhibited by dexamethasone and accompanied by the continuous low levels of MPO in the nucleus after PMA stimulation. Meanwhile, we found that ‘targeted nuclear degranulation’ is dependent on the CD44 translocation and subsequent redistribution of CD44 / ERM (Ezrin/Radixin/Moesin) / F‐actin complexes, which guides the movement of azurophilic granules towards the nucleus. Application of ERM phosphorylation inhibitors and importin activity inhibitors significantly reduced the complexes formation and redistribution. Taken together, these findings indicate for the first time that delayed ‘targeted nuclear degranulation’ after neutrophil activation is a key mechanism of NET formation. CD44/ERM/F‐actin complex mediates this process, which providing targets with promising prospects for the precise regulation of NET formation.

TNPO2 variants associate with human developmental delays, neurologic deficits, and dysmorphic features and alter TNPO2 activity in Drosophila

Transportin-2 (TNPO2) mediates multiple pathways including non-classical nucleocytoplasmic shuttling of >60 cargoes, such as developmental and neuronal proteins. We identified 15 individuals carrying de novo coding variants in TNPO2 who presented with global developmental delay (GDD), dysmorphic features, ophthalmologic abnormalities, and neurological features. To assess the nature of these variants, functional studies were performed in Drosophila. We found that fly dTnpo (orthologous to TNPO2) is expressed in a subset of neurons. dTnpo is critical for neuronal maintenance and function as downregulating dTnpo in mature neurons using RNAi disrupts neuronal activity and survival. Altering the activity and expression of dTnpo using mutant alleles or RNAi causes developmental defects, including eye and wing deformities and lethality. These effects are dosage dependent as more severe phenotypes are associated with stronger dTnpo loss. Interestingly, similar phenotypes are observed with dTnpo upregulation and ectopic expression of TNPO2, showing that loss and gain of Transportin activity causes developmental defects. Further, proband-associated variants can cause more or less severe developmental abnormalities compared to wild-type TNPO2 when ectopically expressed. The impact of the variants tested seems to correlate with their position within the protein. Specifically, those that fall within the RAN binding domain cause more severe toxicity and those in the acidic loop are less toxic. Variants within the cargo binding domain show tissue-dependent effects. In summary, dTnpo is an essential gene in flies during development and in neurons. Further, proband-associated de novo variants within TNPO2 disrupt the function of the encoded protein. Hence, TNPO2 variants are causative for neurodevelopmental abnormalities.

Identify specific gene pairs for subarachnoid hemorrhage based on wavelet analysis and genetic algorithm

Subarachnoid hemorrhage (SAH) is a fatal stroke caused by bleeding in the brain. SAH can be caused by a ruptured aneurysm or head injury. One-third of patients will survive and recover. One-third will survive with disability; one-third will die. The focus of treatment is to stop bleeding, restore normal blood flow, and prevent vasospasm. Treatment for SAH varies, depending on the bleeding’s underlying cause and the extent of damage to the brain. Treatment may include lifesaving measures, symptom relief, repair of the bleeding vessel, and complication prevention. However, the useful diagnostic biomarkers of SAH are still limited due to the instability of gene marker expression. To overcome this limitation, we developed a new protocol pairing genes and screened significant gene pairs based on the feature selection algorithm. A classifier was constructed with the selected gene pairs and achieved a high performance.

A CD44/Brg1 nuclear complex confers mesenchymal progenitor cells with enhanced fibrogenicity in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease. We previously identified fibrogenic mesenchymal progenitor cells (MPCs) in the lungs of patients with IPF who serve as drivers of progressive fibrosis. Recent single-cell RNA sequencing work revealed that IPF MPCs with the highest transcriptomic network entropy differ the most from control MPCs and that increased CD44 was a marker of these IPF MPCs. We hypothesize that IPF MPCs with high CD44 (CD44^hi) expression will display enhanced fibrogenicity. We demonstrate that CD44-expressing MPCs are present at the periphery of the IPF fibroblastic focus, placing them in regions of active fibrogenesis. In a humanized mouse xenograft model, CD44^hi IPF MPCs are more fibrogenic than CD44^lo IPF MPCs, and knockdown of CD44 diminishes their fibrogenicity. CD44^hi IPF MPCs display increased expression of pluripotency markers and enhanced self-renewal compared with CD44^lo IPF MPCs, properties potentiated by IL-8. The mechanism involves the accumulation of CD44 within the nucleus, where it associates with the chromatin modulator protein Brahma-related gene 1 (Brg1) and the zinc finger E-box binding homeobox 1 (Zeb1) transcription factor. This CD44/Brg1/Zeb1 nuclear protein complex targets the Sox2 gene, promoting its upregulation and self-renewal. Our data implicate CD44 interaction with the epigenetic modulator protein Brg1 in conveying IPF MPCs with cell-autonomous fibrogenicity.

Hyaluronan/CD44 axis regulates S100A4-mediated mesenchymal progenitor cell fibrogenicity in idiopathic pulmonary fibrosis

Despite modest improvement in patient outcomes from recent advances in pharmacotherapy targeting fibrogenic signaling pathways, idiopathic pulmonary fibrosis (IPF) remains a major unsolved clinical problem. One reason for this is that available antifibrotic agents slow down but do not arrest fibrotic progression. To arrest fibrotic progression, its obligatory drivers need to be identified. We previously discovered that fibrogenic mesenchymal progenitor cells (MPCs) are key drivers of fibrotic progression in IPF, serving as cells of origin for disease-mediating myofibroblasts. IPF MPCs have high levels of nuclear S100A4, which interacts with the proteasome to promote p53 degradation and self-renewal. However, the mechanism underlying S100A4 accumulation in the nucleus of IPF MPCs remains unknown. Here we show that hyaluronan (HA) is present in the fibroblastic focus together with CD44-expressing MPCs and that ligation of CD44 by HA triggers S100A4 nuclear translocation to support IPF MPC self-renewal. The mechanism involves HA-mediated formation of a CD44/S100A4/transportin 1 complex, which promotes S100A4 nuclear import. In a humanized mouse model of pulmonary fibrosis, IPF MPC fibrogenicity was significantly attenuated by 1) knockdown of CD44 or 2) introduction of an S100A4 mutant construct that prevents S100A4 nuclear import. These data indicate that signaling through the HA/CD44/S100A4 axis is an integral component of IPF MPC fibrogenicity.

Doublecortin undergo nucleocytoplasmic transport via the RanGTPase signaling to promote glioma progression

Background

Nuclear translocation of several oncogenic proteins have previously been reported, but neither the translocation of doublecortin (DCX) nor the mechanism involved has been studied. DCX is a neuronal microtubule-associated protein (MAP) that is crucial for adult neurogenesis and neuronal migration and has been associated with poor prognosis in gliomas.

Methods

We probed DCX expression in different grades of glioma tissues and conventional cells via western blotting. Then we analyzed the expression pattern in the Oncomine cancer profiling database. Confocal Immunofluorescence was used to detect DCX expression in the cellular compartments, while subcellular fractionation was probed via western blotting. Pulse shape height analysis was utilized to verify DCX localization in a larger population of cells. Co-immunoprecipitation was used in detecting DCX-import receptors interactions. To probe for DCX functions, stable cells expressing high DCX expression or knockdown were generated using CRISPR-Cas9 viral transfection, while plasmid site-directed mutant constructs were used to validate putative nuclear localization sequence (NLS) predicted via conventional algorithms and comparison with classical NLSs. in-silico modeling was performed to validate DCX interactions with import receptors via the selected putative NLS. Effects of DCX high expression, knockdown, mutation, and/or deletion of putative NLS sites were probed via Boyden’s invasion assay and wound healing migration assays, and viability was detected by CCK8 assays in-vitro, while xenograft tumor model was performed in nude mice.

Results

DCX undergoes nucleocytoplasmic movement via the RanGTPase signaling pathway with an NLS located on the N-terminus between serine47-tyrosine70. This translocation could be stimulated by MARK’s phosphorylation of the serine 47 residue flanking the NLS due to aberrant expression of glial cell line-derived neurotrophic factor (GDNF). High expression and nuclear accumulation of DCX improve invasive glioma abilities in-vitro and in-vivo. Moreover, knocking down or blocking DCX nuclear import attenuates invasiveness and proliferation of glioma cells.

Conclusion

Collectively, this study highlights a remarkable phenomenon in glioma, hence revealing potential glioma dependencies on DCX expression, which is amenable to targeted therapy.

The NAE Pathway: Autobahn to the Nucleus for Cell Surface Receptors

Various growth factors and full-length cell surface receptors such as EGFR are translocated from the cell surface to the nucleoplasm, baffling cell biologists to the mechanisms and functions of this process. Elevated levels of nuclear EGFR correlate with poor prognosis in various cancers. In recent years, nuclear EGFR has been implicated in regulating gene transcription, cell proliferation and DNA damage repair. Different models have been proposed to explain how the receptors are transported into the nucleus. However, a clear consensus has yet to be reached. Recently, we described the nuclear envelope associated endosomes (NAE) pathway, which delivers EGFR from the cell surface to the nucleus. This pathway involves transport, docking and fusion of NAEs with the outer membrane of the nuclear envelope. EGFR is then presumed to be transported through the nuclear pore complex, extracted from membranes and solubilised. The SUN1/2 nuclear envelope proteins, Importin-beta, nuclear pore complex proteins and the Sec61 translocon have been implicated in the process. While this framework can explain the cell surface to nucleus traffic of EGFR and other cell surface receptors, it raises several questions that we consider in this review, together with implications for health and disease.

The COOH-Terminal Proline-Rich Region of GRP78 Is a Key Regulator of Its Cell Surface Expression and Viability of Tamoxifen-Resistant Breast Cancer Cells

Translocation of 78-kDa glucose-regulated protein (GRP78) from endoplasmic reticulum (ER) to plasma membrane represents a paradigm shift beyond its traditional function as an ER chaperone protein. Cell surface GRP78 (csGRP78) exerts novel signaling functions, and mechanisms underlying its cell surface expression are just emerging. Acquired tamoxifen resistance of breast cancer cells is accompanied with elevated level of csGRP78. Therefore, the tamoxifen-resistant MCF7 breast cancer cells (MCF7-LR) represents a clinically relevant model to study mechanisms of csGRP78 expression. We discovered that a proline-rich region (PRR) containing three consecutive prolines close to the COOH-terminus of GRP78 is important for its ability to form a complex with the partner protein, CD44v, as demonstrated by in vitro glutathione S-transferase pull-down assay. Proline to alanine mutations at the PRR compromised GRP78 expression level on the cell surface as evidenced by purification of biotinylated cell surface proteins. Reconstitution of MCF7-LR cells with the PRR mutant after knockdown of endogenous GRP78 diminished the capacity of GRP78 to stimulate STAT3 activation. The enforced expression of a short peptide bearing the PRR region of GRP78 led to reduction of CD44v and Cyclin D1 protein levels as well as cell viability, accompanied with increase in apoptotic signaling including cleaved Caspase-3 and PARP. These findings suggest that the COOH-terminal PRR of GRP78 is critical for its interaction with CD44v as well as its cell surface expression, and enforced expression of the short peptide bearing the PRR region may provide a new approach to lower the viability of tamoxifen-resistant breast cancer cells.

Nuclear CD44 Mediated by Importin β Participated in Naïve Genes Transcriptional Regulation in C3A-iCSCs

CD44 is one of biomarkers of liver cancer stem cells (CSCs). The investigation of mechanism of CD44 translocation helps to uncover new molecular pathways participated in the regulation of various cellular processes in CSCs. In the present study, we observed the translocation of CD44 from cytoplasm to nuclear in the reprogramming process of C3A cells, full-length CD44 presented in the nucleus of liver iCSCs. CD44 was bound with importin β and transportin 1 in liver iCSCs. Inhibition of importin β transport leads to reduction of CD44 in the nucleus. Translocation of CD44 is also influenced by importin α. Besides, overexpression of naïve pluripotent genes, KLF2, KLF5, DNMT3L, GBX2, ZFP42, ESRRB and DPPA4 were found in liver iCSCs. Inhibition of CD44 leads to the reduction of these naïve genes. Luciferase and chromatin immunoprecipitation (ChIP) assays further identified nuclear CD44 bound to the promoter regions of naïve genes, KLF2, KLF5, and ESRRB functioned as transcriptional activators in liver iCSCs. Our present work provides new insight into the dynamic states and functions of CD44 in iCSCs.

Potentially critical roles of TNPO1, RAP1B, ZDHHC17, and PPM1B in the progression of coronary atherosclerosis through microarray data analysis

OBJECTIVE

This study aimed to identify more potentially critical genes associated with atherosclerotic coronary artery disease (CAD).

MATERIALS AND METHODS

Gene expression profile of GSE12288 was downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were screened in atherosclerotic CAD samples compared with controls, followed by weighed gene coexpression network analysis (WGCNA) by which the most significant module was identified. Gene coexpression network was constructed based on genes in the most significant module, and functional annotation was also performed. In addition, microRNAs (miRNAs) that were directly associated with CAD were screened from the literature, and the miRNA-target regulatory network was constructed based on genes in the most significant module, followed by Gene Ontology (GO) and pathway enrichment analysis. Furthermore, we used another data set of GSE42148 from the GEO database to perform data validation.

RESULTS

WGCNA analysis showed that the turquoise module may have the most important role in atherosclerotic CAD. Genes in this module were involved in translational elongation and intracellular signal transduction. Besides, we identified five confirmed CAD-related miRNAs. TNPO1, RAP1B, and ZDHHC17 could be targeted by four of these miRNAs. Genes such as PPM1B could be regulated by three miRNAs. Moreover, TNPO1 and ZDHHC17 were involved in the GO terms associated with protein localization and transport and the immune system; RAP1B and PPM1B were linked with intracellular signal transduction-related pathways. In addition, PPM1B and ZDHHC17 had accordantly significant expression changes in another data set GSE42148.

CONCLUSION

TNPO1, RAP1B, ZDHHC17, and PPM1B may play essential roles in the progression of coronary atherosclerosis.

Nuclear Localization of Cancer Stem Cell Marker CD133 in Triple-Negative Breast Cancer: A Case Report

Aim and background

It has been recently demonstrated that the detection of stem cell niches in triple-negative (TN) breast cancer may provide good prognostic clues for this tumor.

Methods and study design

We investigated the subcellular expression and localization of the cancer stem cell marker CD133 in a TN breast cancer biopsy from a 42-year-old Caucasian woman with a histological diagnosis of high-grade invasive ductal breast carcinoma by immunohistochemistry, flow cytometry and quantitative real-time PCR (qRT-PCR).

Results

We describe for the first time in a TN breast cancer the nuclear mislocalization of CD133, which normally shows membrane localization and more sporadically cytoplasmic localization. We also found this aberrant expression with qRT-PCR analysis but not flow cytometry.

Conclusions

Nuclear localization of CD133 may be an indicator of poor prognosis in TN breast cancer, as it is known that surface molecules, when moving into the nucleus, can act as transcriptional regulators by interfering with molecular pathways directly connected to the proliferation and differentiation of tumor cells.

Low-dose cadmium exposure induces peribronchiolar fibrosis through site-specific phosphorylation of vimentin

Exposure to cadmium (Cd) has been associated with development of chronic obstructive lung disease (COPD). The mechanisms and signaling pathways whereby Cd causes pathological peribronchiolar fibrosis, airway remodeling, and subsequent airflow obstruction remain unclear. We aimed to evaluate whether low-dose Cd exposure induces vimentin phosphorylation and Yes-associated protein 1 (YAP1) activation leading to peribronchiolar fibrosis and subsequent airway remodeling. Our data demonstrate that Cd induces myofibroblast differentiation and extracellular matrix (ECM) deposition around small (<2 mm in diameter) airways. Upon Cd exposure, α-smooth muscle actin (α-SMA) expression and the production of ECM proteins, including fibronectin and collagen-1, are markedly induced in primary human lung fibroblasts. Cd induces Smad2/3 activation and the translocation of both Smad2/3 and Yes-associated protein 1 (YAP1) into the nucleus. In parallel, Cd induces AKT and cdc2 phosphorylation and downstream vimentin phosphorylation at Ser³⁹ and Ser⁵⁵, respectively. AKT and cdc2 inhibitors block Cd-induced vimentin fragmentation and secretion in association with inhibition of α-SMA expression, ECM deposition, and collagen secretion. Furthermore, vimentin silencing abrogates Cd-induced α-SMA expression and decreases ECM production. Vimentin-deficient mice are protected from Cd-induced peribronchiolar fibrosis and remodeling. These findings identify two specific sites on vimentin that are phosphorylated by Cd and highlight the functional significance of vimentin phosphorylation in YAP1/Smad3 signaling that mediates Cd-induced peribronchiolar fibrosis and airway remodeling.

[Molecular markers of cancer stem cells verified in vivo]

This systematic review aims to analyze molecular markers of cancer stem cells. Only studies that confirmed tumor-initiating capacity of this population by in vivo assay in immunodeficient mice were included. Final sample of papers that fully correspond with initial aim consists of 97 original studies. The results of their analysis reveal that markers commonly used for cancer stem cells deriving were as follows: CD133, СD44, ALDH, CD34, CD24 and EpCAM. The review also contains description of molecular features of some cancer stem cell markers, modern approaches to cancer treatment by targeting this population and brief assessment of cancer stem cell theory development.

Knock out CD44 in reprogrammed liver cancer cell C3A increases CSCs stemness and promotes differentiation

CD44 is a widely known cancer stem cells marker in various cancers and validated to function in tumor growth, survival and tumor metastasis. In this study, we first established C3A-derived liver cancer stem cells by OSKM method [OCT4, SOX2, KLF4, and c-MYC], termed C3A-induced cancer stem cells (C3A-iCSCs) which acquired self-renewal and stemness abilities. Then we found CD44 was positive in C3A-iCSCs and mainly located in cell nuclear. Chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) results showed nuclear CD44 combined promoter regions of c-MYC and SOX2. These results suggested that CD44 participated in C3A-iCSCs transcriptional regulation. To explore CD44 overall influence in liver cancer stem cells, CD44 was knocked out in C3A-iCSCs using CRISPR/Cas9 technology. Our results showed a dramatic increase in the expression of stem cell markers OCT4, SOX2 and NANOG in CD44⁻ C3A-iCSCs compared with that in CD44⁺ C3A-iCSCs. Tumor derived from CD44⁻ C3A-iCSCs also displayed well-differentiated tumor cells compared to CD44⁺ C3A-iCSCs, which suggested CD44⁻ C3A-iCSCs derived tumor cells exhibited lower malignant degree. Our data indicated nuclear CD44 in liver cancer stem cells is responsible for the poorly differentiated highly malignant tumor cells by maintenance of low stemness state.

Cleaved CD44 intracellular domain supports activation of stemness factors and promotes tumorigenesis of breast cancer

CD44 plays a role in the progression of tumors and is expressed in cancer stem cells (CSCs). However, the mechanisms underlying the crosstalk of CD44 with stemness genes in CSC maintenance remains unclear. In this study, we demonstrated how the cleaved intracellular domain of CD44 (CD44ICD) activates stemness factors such as Nanog, Sox2 and Oct4, and contributes to the tumorigenesis of breast cancer. We have found that the overexpression of CD44ICD increased mammosphere formation in breast cancer cells. Treatment with a γ-secretase inhibitor (GSI), which blocks the cleavage of CD44ICD, interfered with mammosphere formation. Interestingly, CD44ICD decreased the expression levels and nuclear localization of stemness factors, but overexpression of CD44ICD reversed these effects. In addition, we showed that nuclear localization of CD44ICD is important for transcriptional activation of the stemness factors. Furthermore, CD44ICD-overexpressed cells exhibited strong tumorigenecity and greater metastatic potential than did the control cells or CD44-depleted cells in vivo in mice models. Taken together, it was supposed that CD44 promotes tumorigenesis through the interaction and nuclear-translocation of its intracellular domain and stemness factors. We suggest that the prevention of cleavage and nuclear-translocation of CD44ICD is a potential target in treating breast cancer.

Nuclear localization signals for four distinct karyopherin-β nuclear import systems

The Karyopherin-β family of proteins mediates nuclear transport of macromolecules. Nuclear versus cytoplasmic localization of proteins is often suggested by the presence of NLSs (nuclear localization signals) or NESs (nuclear export signals). Import-Karyopherin-βs or Importins bind to NLSs in their protein cargos to transport them through nuclear pore complexes into the nucleus. Until recently, only two classes of NLS had been biochemically and structurally characterized: the classical NLS, which is recognized by the Importin-α/β heterodimer and the PY-NLS (proline-tyrosine NLS), which is recognized by Karyopherin-β2 or Transportin-1. Structures of two other Karyopherin-βs, Kap121 and Transportin-SR2, in complex with their respective cargos were reported for the first time recently, revealing two new distinct classes of NLSs. The present paper briefly describes the classical NLS, reviews recent literature on the PY-NLS and provides in-depth reviews of the two newly discovered classes of NLSs that bind Kap121p and Transportin-SR respectively.

A Hyaluronan-Based Injectable Hydrogel Improves the Survival and Integration of Stem Cell Progeny following Transplantation

The utility of stem cells and their progeny in adult transplantation models has been limited by poor survival and integration. We designed an injectable and bioresorbable hydrogel blend of hyaluronan and methylcellulose (HAMC) and tested it with two cell types in two animal models, thereby gaining an understanding of its general applicability for enhanced cell distribution, survival, integration, and functional repair relative to conventional cell delivery in saline. HAMC improves cell survival and integration of retinal stem cell (RSC)-derived rods in the retina. The pro-survival mechanism of HAMC is ascribed to the interaction of the CD44 receptor with HA. Transient disruption of the retinal outer limiting membrane, combined with HAMC delivery, results in significantly improved rod survival and visual function. HAMC also improves the distribution, viability, and functional repair of neural stem and progenitor cells (NSCs). The HAMC delivery system improves cell transplantation efficacy in two CNS models, suggesting broad applicability.

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An injectable biomaterial improves rod survival/integration into adult retina

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The same material improves neural stem cell distribution/survival into adult brain

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Functional repair is demonstrated after cell transplantation in both retina and brain

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Hyaluronan-CD44 interaction is implicated in the pro-survival effect on stem cell progeny

Transportin-1 and Transportin-2: protein nuclear import and beyond

Nearly 20 years after its identification as a new β-karyopherin mediating the nuclear import of the RNA-binding protein hnRNP A1, Transportin-1 is still commonly overlooked in comparison with its best known cousin, Importin-β. Transportin-1 is nonetheless a considerable player in nucleo-cytoplasmic transport. Over the past few years, significant progress has been made in the characterization of the nuclear localization signals (NLSs) that Transportin-1 recognizes, thereby providing the molecular basis of its diversified repertoire of cargoes. The recent discovery that mutations in the Transportin-dependent NLS of FUS cause mislocalization of this protein and result in amyotrophic lateral sclerosis illustrates the importance of Transportin-dependent import for human health. Besides, new functions of Transportin-1 are emerging in processes other than nuclear import. Here, we summarize what is known about Transportin-1 and the related β-karyopherin Transportin-2.

Nuclear translocation of heparan sulfate proteoglycans and their functional significance

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) are important constituents of the cell membrane and they act as co-receptors for cellular signaling. Syndecan-1, glypican and perlecan also translocate to the nucleus in a regulated manner. Similar nuclear transport of growth factors and heparanase indicate a possible co-regulation and functional significance.

SCOPE OF REVIEW

In this review we dissect the structural requirement for the nuclear translocation of HSPGs and their functional implications.s

MAJOR CONCLUSIONS

The functions of the nuclear HSPGs are still incompletely understood. Evidence point to possible functions in hampering cell proliferation, inhibition of DNA topoisomerase I activity and inhibition of gene transcription.

GENERAL SIGNIFICANCE

HSPGs influence the behavior of malignant tumors in many different ways. Modulating their functions may offer powerful tools to control fundamental biological processes and provide the basis for subsequent targeted therapies in cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Receptor tyrosine kinases in the nucleus

To date, 18 distinct receptor tyrosine kinases (RTKs) are reported to be trafficked from the cell surface to the nucleus in response to ligand binding or heterologous agonist exposure. In most cases, an intracellular domain (ICD) fragment of the receptor is generated at the cell surface and translocated to the nucleus, whereas for a few others the intact receptor is translocated to the nucleus. ICD fragments are generated by several mechanisms, including proteolysis, internal translation initiation, and messenger RNA (mRNA) splicing. The most prevalent mechanism is intramembrane cleavage by γ-secretase. In some cases, more than one mechanism has been reported for the nuclear localization of a specific RTK. The generation and use of RTK ICD fragments to directly communicate with the nucleus and influence gene expression parallels the production of ICD fragments by a number of non-RTK cell-surface molecules that also influence cell proliferation. This review will be focused on the individual RTKs and to a lesser extent on other growth-related cell-surface transmembrane proteins.

Silencing of CD44 gene expression in human 143-B osteosarcoma cells promotes metastasis of intratibial tumors in SCID mice

Osteosarcoma (OS) is the most frequent primary malignant bone cancer in children and adolescents with a high propensity for lung metastasis. Therefore, it is of great importance to identify molecular markers leading to increased metastatic potential in order to devise more effective therapeutic strategies that suppress metastasis, the major cause of death in OS. CD44, the principal receptor for the extracellular matrix component hyaluronan (HA), is frequently found overexpressed in tumor cells and has been implicated in metastatic spread in various cancer types. Here, we investigated the effects of stable shRNA-mediated silencing of CD44 gene products on in vitro and in vivo metastatic properties of the highly metastatic human 143-B OS cell line. In vitro, CD44 knockdown resulted in a 73% decrease in the adhesion to HA, a 57% decrease in the migration rate in a trans-filter migration assay, and a 28% decrease in the cells' capacity for anchorage-independent growth in soft agar compared to the control cells, implicating that CD44 expression contributes to the metastatic activity of 143-B cells. However, making use of an orthotopic xenograft OS mouse model, we demonstrated that reduced CD44 expression facilitated primary tumor growth and formation of pulmonary metastases. The enhanced malignant phenotype was associated with decreased adhesion to HA and reduced expression of the tumor suppressor merlin in vivo. In conclusion, our study identified CD44 as a metastasis suppressor in this particular experimental OS model.

CD44 regulates vascular endothelial barrier integrity via a PECAM-1 dependent mechanism

Vascular integrity is a critical parameter in normal growth and development. Loss of appropriate vascular barrier function is present in various immune- and injury-mediated pathological conditions. CD44 is an adhesion molecule expressed by multiple cell types, including endothelial cells (EC). The goal of the present study was to examine how loss of CD44 affected vascular permeability. Using C57BL/6 WT and CD44-KO mice, we found no significant permeability to Evan's Blue in either strain at baseline. However, there was significantly increased histamine-induced permeability in CD44-deficient mice compared to WT counterparts. Similar results were observed in vitro, where CD44-deficient endothelial monolayers were also impermeable to 40kD-FITC dextran in the absence of vasoactive challenge, but exhibited enhanced and prolonged permeability following histamine. However, CD44-KO monolayers have reduced baseline barrier strength by electrical resistance, which correlated with increased permeability, at baseline, to smaller molecular weight 4-kD FITC-dextran, suggesting weakly formed endothelial junctions. The CD44-KO EC displayed several characteristics consistent with impaired barrier function/dysfunctional EC junctions, including differential expression, phosphorylation, and localization of endothelial junction proteins, increased matrix metalloprotease expression, and altered cellular morphology. Reduced platelet endothelial cell adhesion molecule-1 (PECAM-1) expression by CD44-KO EC in vivo and in vitro was also observed. Reconstitution of murine CD44 or PECAM-1 restored these defects to near WT status, suggesting CD44 regulates vascular permeability and integrity through a PECAM-1 dependent mechanism.

CD44 integrates signaling in normal stem cell, cancer stem cell and (pre)metastatic niches

The stem cell niche provides a regulatory microenvironment for cells as diverse as totipotent embryonic stem cells to cancer stem cells (CSCs) which exhibit stem cell-like characteristics and have the capability of regenerating the bulk of tumor cells while maintaining self-renewal potential. The transmembrane glycoprotein CD44 is a common component of the stem cell niche and exists as a standard isoform (CD44s) and a range of variant isoforms (CD44v) generated though alternative splicing. CD44 modulates signal transduction through post-translational modifications as well as interactions with hyaluronan, extracellular matrix molecules and growth factors and their cognate receptor tyrosine kinases. While the function of CD44 in hematopoietic stem cells has been studied in considerable detail, our knowledge of CD44 function in tissue-derived stem cell niches remains limited. Here we review CD44s and CD44v in both hematopoietic and tissue-derived stem cell niches, focusing on their roles in regulating stem cell behavior including self-renewal and differentiation in addition to cell-matrix interactions and signal transduction during cell migration and tumor progression. Determining the role of CD44 and CD44v in normal stem cell, CSC and (pre)metastatic niches and elucidating their unique functions could provide tools and therapeutic strategies for treating diseases as diverse as fibrosis during injury repair to cancer progression.

Critical role for lysyl oxidase in mesenchymal stem cell-driven breast cancer malignancy

Mesenchymal stem cells (MSCs) are multipotent progenitor cells with the ability to differentiate into multiple mesoderm lineages in the course of normal tissue homeostasis or during injury. We have previously shown that MSCs migrate to sites of tumorigenesis, where they become activated by cancer cells to promote metastasis. However, the molecular and phenotypic attributes of the MSC-induced metastatic state of the cancer cells remained undetermined. Here, we show that bone marrow-derived human MSCs promote de novo production of lysyl oxidase (LOX) from human breast carcinoma cells, which is sufficient to enhance the metastasis of otherwise weakly metastatic cancer cells to the lungs and bones. We also show that LOX is an essential component of the CD44-Twist signaling axis, in which extracellular hyaluronan causes nuclear translocation of CD44 in the cancer cells, thus triggering LOX transcription by associating with its promoter. Processed and enzymatically active LOX, in turn, stimulates Twist transcription, which mediates the MSC-triggered epithelial-to-mesenchymal transition (EMT) of carcinoma cells. Surprisingly, although induction of EMT in breast cancer cells has been tightly associated with the generation of cancer stem cells, we find that LOX, despite being critical for EMT, does not contribute to the ability of MSCs to promote the formation of cancer stem cells in the carcinoma cell populations. Collectively, our studies highlight a critical role for LOX in cancer metastasis and indicate that the signaling pathways controlling stroma-induced EMT are distinct from pathways regulating the development of cancer stem cells.

Soluble CD44 interacts with intermediate filament protein vimentin on endothelial cell surface

CD44 is a cell surface glycoprotein that functions as hyaluronan receptor. Mouse and human serum contain substantial amounts of soluble CD44, generated either by shedding or alternative splicing. During inflammation and in cancer patients serum levels of soluble CD44 are significantly increased. Experimentally, soluble CD44 overexpression blocks cancer cell adhesion to HA. We have previously found that recombinant CD44 hyaluronan binding domain (CD44HABD) and its non-HA-binding mutant inhibited tumor xenograft growth, angiogenesis, and endothelial cell proliferation. These data suggested an additional target other than HA for CD44HABD. By using non-HA-binding CD44HABD Arg41Ala, Arg78Ser, and Tyr79Ser-triple mutant (CD443MUT) we have identified intermediate filament protein vimentin as a novel interaction partner of CD44. We found that vimentin is expressed on the cell surface of human umbilical vein endothelial cells (HUVEC). Endogenous CD44 and vimentin coprecipitate from HUVECs, and when overexpressed in vimentin-negative MCF-7 cells. By using deletion mutants, we found that CD44HABD and CD443MUT bind vimentin N-terminal head domain. CD443MUT binds vimentin in solution with a Kd in range of 12–37 nM, and immobilised vimentin with Kd of 74 nM. CD443MUT binds to HUVEC and recombinant vimentin displaces CD443MUT from its binding sites. CD44HABD and CD443MUT were internalized by wild-type endothelial cells, but not by lung endothelial cells isolated from vimentin knock-out mice. Together, these data suggest that vimentin provides a specific binding site for soluble CD44 on endothelial cells.

Direct reprogramming of stem cell properties in colon cancer cells by CD44

Cancer progression is commonly segregated into processes of primary tumour growth and secondary metastasis. Recent evidence suggests that a subpopulation of cancer cells, cancer stem cells (CSCs), is responsible for tumour growth in cancer. However, the role of CSCs in cancer metastasis is unclear. In this study, we found that the C terminus of CD44 contributes to sphere formation and survival in vitro via the CD44-SRC-integrin axis. In addition, nuclear CD44/acetylated-STAT3 is required for clonal formation in vitro and tumourigenicity in vivo. Nuclear CD44 binds to various promoters identified by chromatin immunoprecipitation-seq, including that of c-myc and Twist1, leading to cell fate change through transcriptional reprogramming. We propose that nuclear CD44/acetylated-STAT3 performs an unexpected tumour-progressing function by enhancing cell outgrowth into structures where cells with properties of CSCs can be generated from differentiated somatic cells in suspension culture, and then exhibit attributes of cells that have undergone an epithelial-mesenchymal transition, leading to tumour metastasis, and a resulting worse prognosis.