Numb regulates cell-cell adhesion and polarity in response to tyrosine kinase signalling

Alternative splicing in aging and aging-related diseases: From pathogenesis to therapy

Aging is a complex biological process associated with nearly all diseases. Alternative splicing is increasingly recognized as an important contributor to aging and a key research pathway for extending human lifespan. In this review, we highlight the findings of alternative splicing in the hallmarks of aging including key processes such as genomic instability, telomere length, protein stability, autophagy processes, etc., as well as antagonistic hallmarks of aging such as various metabolic signals, energy metabolism, clearance of senescent cells, stem cell self-renewal, cell communication and inflammatory process, etc. We also discuss the roles of alternative splicing in age-related diseases, including neurodegenerative diseases, cardiovascular diseases, skeletal muscle-related diseases, metabolic disorders, cancer, sensory degeneration, and chronic inflammation, etc. These studies suggest that new anti-aging therapies could be developed by regulating key splicing proteins or specific splicing events.

Multiple anti-tumor programs are activated by blocking BAD phosphorylation

The Bcl-2 family member BAD is a candidate disease modulator because it stimulates apoptosis in a cell context basis and inhibits cell migration during normal mammary gland morphogenesis. This activity depends on 3 key regulatory serines (S75, 99, 118) in the unphosphorylated state. Given that developmental programs are often hijacked in cancer, we hypothesized that BAD would impede breast cancer progression. We generated breast cancer mouse models representing loss-of-function or phosphorylation deficient mutations (PyMT-Bad-/- and PyMT-Bad3SA/3SA, respectively). Preventing BAD phosphorylation significantly decreased breast cancer progression and metastasis. The knock-out phenocopied the control PyMT-Bad+/+ suggesting that phosphorylated BAD protein was inert. Thus, the BAD3SA mutation unmasked latent anti-tumor activity. Indeed, transcriptomics showed PyMT-Bad3SA/3SA activated multiple anti-tumor programs including apoptosis, inflammation, cellular differentiation, and diminished cell migration. This anti-tumor effect associated with clinical survival of breast cancer patients whose tumors had high levels of unphosphorylated BAD. Kinase screens identified ERK as the major BAD kinase in breast cells, and ERK inhibition impeded tumoroid invasion. Our data suggest that unphosphorylated BAD modulates anti-tumor pathways that contribute to excellent patient prognosis. Thus, targeting ERK to dephosphorylate BAD may be an exciting therapeutic opportunity in the future.

Mechanical control of the alternative splicing factor PTBP1 regulates extracellular matrix stiffness induced proliferation and cell spreading

Cells sense mechanical cues and convert them into biochemical responses to regulate biological processes such as embryonic development, aging, cellular homeostasis, and disease progression. In this study, we introduce a large-scale, systematic approach to identify proteins with mechanosensitive nuclear localization, highlighting their potential roles in mechanotransduction. Among the proteins identified, we focus here on the splicing factor PTBP1. We demonstrate that its nuclear abundance is regulated by mechanical cues such as cell density, size, and extracellular matrix (ECM) stiffness and that PTBP1 medicates the mechanosensitive alternative splicing of the endocytic adapter protein Numb. Furthermore, we show that PTBP1 and Numb alternative splicing is critical for ECM stiffness-induced epithelial cell spreading and proliferation as well as for mesenchymal stem cell differentiation into osteoblasts on a stiff matrix. Our results underscore the emerging role of alternative splicing in mechanotransduction and provide novel mechanistic insights into how matrix stiffness modulates cellular mechanoresponses.

NUMB alternative splicing and isoform-specific functions in development and disease

The NUMB gene encodes a conserved adaptor protein with roles in asymmetric cell division and cell fate determination. First described as an inhibitor of Notch signaling, multifunctional NUMB proteins regulate multiple cellular pathways through protein complexes with ubiquitin ligases, polarity proteins and the endocytic machinery. The vertebrate NUMB protein isoforms were identified over 2 decades ago, yet the majority of functional studies exploring NUMB function in endocytosis, cell migration and adhesion, development and disease have largely neglected the potential for distinct isoform activity in design and interpretation. In this review we consolidate the literature that has directly addressed individual NUMB isoform functions, as well as interpret other functional studies through the lens of the specific isoforms that were utilized. We also summarize the emerging literature on the mechanisms that regulate alternative splicing of NUMB, and how this is subverted in disease. Finally, the importance of relative NUMB isoform expression as a determinant of activity and considerations for future studies of NUMB isoforms as unique proteins with distinct functions are discussed.

Beyond destruction: emerging roles of the E3 ubiquitin ligase Hakai

Hakai protein (CBLL1 gene) was identified as an E3 ubiquitin ligase of E-cadherin complex, inducing its ubiquitination and degradation, thus inducing epithelial-to-mesenchymal transition. Most of the knowledge about the protein was associated to its E3 ubiquitin ligase canonical role. However, important recent published research has highlighted the noncanonical role of Hakai, independent of its E3 ubiquitin ligase activity, underscoring its involvement in the N6-methyladenosine (m6A) writer complex and its impact on the methylation of RNA. The involvement of Hakai in this mRNA modification process has renewed the relevance of this protein as an important contributor in cancer. Moreover, Hakai potential as a cancer biomarker and its prognostic value in malignant disease also emphasize its untapped potential in precision medicine, which would also be discussed in detail in our review. The development of the first small-molecule inhibitor that targets its atypical substrate binding domain is a promising step that could eventually lead to patient benefit, and we would cover its discovery and ongoing efforts toward its use in clinic.

Spatial and Temporal Relationship between Epithelial-Mesenchymal Transition (EMT) and Stem Cells in Cancer

BACKGROUND

Epithelial-mesenchymal transition (EMT) is often linked with carcinogenesis. However, EMT is also important for embryo development and only reactivates in cancer. Connecting how EMT occurs during embryonic development and in cancer could help us further understand the root mechanisms of cancer diseases.

CONTENT

There are key regulatory elements that contribute to EMT and the induction and maintenance of stem cell properties during embryogenesis, tissue regeneration, and carcinogenesis. Here, we explore the implications of EMT in the different stages of embryogenesis and tissue development. We especially highlight the necessity of EMT in the mesodermal formation and in neural crest cells. Through EMT, these cells gain epithelial-mesenchymal plasticity (EMP). With this transition, crucial morphological changes occur to progress through the metastatic cascade as well as tissue regeneration after an injury. Stem-like cells, including cancer stem cells, are generated from EMT and during this process upregulate factors necessary for stem cell maintenance. Hence, it is important to understand the key regulators allowing stem cell awakening in cancer, which increases plasticity and promotes treatment resistance, to develop strategies targeting this cell population and improve patient outcomes.

SUMMARY

EMT involves multifaceted regulation to allow the fluidity needed to facilitate adaptation. This regulatory mechanism, plasticity, involves many cooperating transcription factors. Additionally, posttranslational modifications, such as splicing, activate the correct isoforms for either epithelial or mesenchymal specificity. Moreover, epigenetic regulation also occurs, such as acetylation and methylation. Downstream signaling ultimately results in the EMT which promotes tissue generation/regeneration and cancer progression.

Functionalized Parylene Films for Enhancement of Antibody Production by Hybridoma Cells

In this study, the influence of microenvironments on antibody production of hybridoma cells was analyzed using six types of functionalized parylene films, parylene-N and parylene-C (before and after UV radiation), parylene-AM, and parylene-H, and using polystyrene as a negative control. Hybridoma cells were cultured on modified parylene films that produced a monoclonal antibody against the well-known fungal toxin ochratoxin-A. Surface properties were analyzed for each parylene film, such as roughness, chemical functional groups, and hydrophilicity. The proliferation rate of the hybridoma cells was observed for each parylene film by counting the number of adherent cells, and the total amount of produced antibodies from different parylene films was estimated using indirect ELISA. In comparison with the polystyrene, the antibody-production by parylene-H and parylene-AM was estimated to be observed to be as high as 210-244% after the culture of 24 h. These results indicate that the chemical functional groups of the culture plate could influence antibody production. To analyze the influence of the microenvironments of the modified parylene films, we performed cell cycle analysis to estimate the ratio of the G0/G1, S, and G2/M phases of the hybridoma cells on each parylene film. From the normalized proportion of phases of the cell cycle, the difference in antibody production from different surfaces was considered to result from the difference in the proliferation rate of hybridoma cells, which occurred from the different physical and chemical properties of the parylene films. Finally, protein expression was analyzed using an mRNA array to determine the effect of parylene films on protein expression in hybridoma cells. The expression of three antibody production-related genes (CD40, Sox4, and RelB) was analyzed in hybridoma cells cultured on modified parylene films.

Par3 promotes breast cancer invasion and migration through pull tension and protein nanoparticle-induced osmotic pressure

Cancer cell invasion and metastasis are closely related to intracellular tension. The cell-polarity protein, Par3, is a mechanical transmitter that affects cytoskeletal forces and determines breast cancer aggressiveness. Increased Par3 tension caused by aPKC inactivation is involved in filopodia and lamellipodia formation. Blocking the connection between Par3 and aPKC increases breast cancer aggressiveness both in vitro and in vivo. Meanwhile, aPKC-induced Par3 cytoplasmic translocation results in JAM-A phase separation and microfilament depolymerization, which is associated with increased intracellular protein nanoparticle-induced osmotic pressure. This study demonstrated the effects of aPKC on Par3 tension and osmotic pressure in breast cancer metastasis, and introduced Par3-associated mechanical mechanisms as potential targets for breast cancer treatment.

The Role of Alternative Splicing in Cancer: Regulatory Mechanism, Therapeutic Strategy, and Bioinformatics Application

[Formula: see text] Alternative splicing (AS) can generate distinct transcripts and subsequent isoforms that play differential functions from the same pre-mRNA. Recently, increasing numbers of studies have emerged, unmasking the association between AS and cancer. In this review, we arranged AS events that are closely related to cancer progression and presented promising treatments based on AS for cancer therapy. Obtaining proliferative capacity, acquiring invasive properties, gaining angiogenic features, shifting metabolic ability, and getting immune escape inclination are all splicing events involved in biological processes. Spliceosome-targeted and antisense oligonucleotide technologies are two novel strategies that are hopeful in tumor therapy. In addition, bioinformatics applications based on AS were summarized for better prediction and elucidation of regulatory routines mingled in. Together, we aimed to provide a better understanding of complicated AS events associated with cancer biology and reveal AS a promising target of cancer treatment in the future.

Numb exon 9 inclusion regulates Integrinβ5 surface expression and promotes breast cancer metastasis

The endocytic adaptor protein Numb acts as a tumor suppressor through downregulation of oncogenic pathways in multiple cancer types. The identification of splicing alterations giving rise to changes in Numb protein isoform expression indicate that Numb also has tumor promoting activity, though the underlying mechanisms are unknown. Here we report that NUMB exon 9 inclusion, which results in production of a protein isoform with an additional 49 amino acids, is a feature of multiple cancer types including all subtypes of breast cancer and correlates with worse progression-free survival. Specific deletion of exon 9-included Numb isoforms (Exon9in) from breast cancer cells reduced cell growth and prevents spontaneous lung metastasis in a mouse model. Quantitative proteome profiling showed that loss of Exon9in causes downregulation of membrane receptors and adhesion molecules, as well as proteins involved in extracellular matrix organization and the epithelial-mesenchymal transition (EMT) state. In addition, exon 9 deletion caused remodeling of the endocytic network, decreased ITGβ5 surface localization, cell spreading on vitronectin and downstream signaling to ERK and SRC. Together these observations suggest that Exon9in isoform expression disrupts the endocytic trafficking functions of Numb, resulting in increased surface expression of ITGβ5 as well as other plasma membrane proteins to promote cell adhesion, EMT, and tumor metastasis.

Interactions of Severe Acute Respiratory Syndrome Coronavirus 2 Protein E With Cell Junctions and Polarity PSD-95/Dlg/ZO-1-Containing Proteins

The C-terminus of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein E contains a PBM (PDZ-binding motif) targeting PDZ (PSD-95/Dlg/ZO-1) domains, which is identical to the PBM of SARS-CoV. The latter is involved in the pathogenicity of the virus. Recently, we identified 10 human PDZ-containing proteins showing significant interactions with SARS-CoV-2 protein E PBM. We selected several of them involved in cellular junctions and cell polarity (TJP1, PARD3, MLLT4, and LNX2) and MPP5/PALS1 previously shown to interact with SARS-CoV E PBM. Targeting cellular junctions and polarity components is a common strategy by viruses to hijack cell machinery to their advantage. In this study, we showed that these host PDZ domains TJP1, PARD3, MLLT4, LNX2, and MPP5/PALS1 interact in a PBM-dependent manner in vitro and colocalize with the full-length E protein in cellulo, sequestrating the PDZ domains to the Golgi compartment. We solved three crystal structures of complexes between human LNX2, MLLT4, and MPP5 PDZs and SARS-CoV-2 E PBM highlighting its binding preferences for several cellular targets. Finally, we showed different affinities for the PDZ domains with the original SARS-CoV-2 C-terminal sequence containing the PBM and the one of the beta variant that contains a mutation close to the PBM. The acquired mutations in the E protein localized near the PBM might have important effects both on the structure and the ion-channel activity of the E protein and on the host machinery targeted by the variants during the infection.

DJExpress: An Integrated Application for Differential Splicing Analysis and Visualization

RNA-seq analysis of alternative pre-mRNA splicing has facilitated an unprecedented understanding of transcriptome complexity in health and disease. However, despite the availability of countless bioinformatic pipelines for transcriptome-wide splicing analysis, the use of these tools is often limited to expert bioinformaticians. The need for high computational power, combined with computational outputs that are complicated to visualize and interpret present obstacles to the broader research community. Here we introduce DJExpress, an R package for differential expression analysis of transcriptomic features and expression-trait associations. To determine gene-level differential junction usage as well as associations between junction expression and molecular/clinical features, DJExpress uses raw splice junction counts as input data. Importantly, DJExpress runs on an average laptop computer and provides a set of interactive and intuitive visualization formats. In contrast to most existing pipelines, DJExpress can handle both annotated and de novo identified splice junctions, thereby allowing the quantification of novel splice events. Moreover, DJExpress offers a web-compatible graphical interface allowing the analysis of user-provided data as well as the visualization of splice events within our custom database of differential junction expression in cancer (DJEC DB). DJEC DB includes not only healthy and tumor tissue junction expression data from TCGA and GTEx repositories but also cancer cell line data from the DepMap project. The integration of DepMap functional genomics data sets allows association of junction expression with molecular features such as gene dependencies and drug response profiles. This facilitates identification of cancer cell models for specific splicing alterations that can then be used for functional characterization in the lab. Thus, DJExpress represents a powerful and user-friendly tool for exploration of alternative splicing alterations in RNA-seq data, including multi-level data integration of alternative splicing signatures in healthy tissue, tumors and cancer cell lines.

Numb inhibits migration and promotes proliferation of colon cancer cells via RhoA/ROCK signaling pathway repression

Numb regulates cell proliferation and differentiation through endocytosis and ubiquitination of signaling molecules. Besides, Numb controls the migration of epithelial cells by regulating intercellular junctions. Studies have shown that Numb promotes or inhibits tumor progression in different tumors. However, its role and mechanism in colorectal cancer remain unclear. We found that the expression level of Numb in colon tumor tissues has a great variety in different patients. Numb expression was negatively correlated with TNM stage and lymph node metastasis but positively correlated with tumor size. Elevated expression of Numb was associated with a good prognosis. Inhibiting Numb expression promoted the migration and invasion of colon cancer cells induced by TGF-β, up-regulated the expression of EMT-related molecule Snail, and prevented the expression of E-cadherin. We also found that Numb promoted the proliferation and clones formation while inhibiting colon cancer cells' late apoptosis. In addition, Numb inhibited the RhoA activation and ROCK inhibitor Y-27632 or interfered with ROCK expression, partially inhibiting Numb-regulated cell proliferation and migration. In vivo tumorigenesis assay in nude mice also found that Numb promoted the proliferation of colon cancer cells, inhibited the expression of E-cadherin, and strengthened the expression of Snail. In conclusion, our study found that Numb plays multiple roles in the occurrence and progression of colon cancer by regulating the RhoA/ROCK signaling pathway, which provides a new theoretical molecular basis for the pathogenesis of colon cancer.

Alternative RNA splicing in stem cells and cancer stem cells: Importance of transcript-based expression analysis

Alternative ribonucleic acid (RNA) splicing can lead to the assembly of different protein isoforms with distinctive functions. The outcome of alternative splicing (AS) can result in a complete loss of function or the acquisition of new functions. There is a gap in knowledge of abnormal RNA splice variants promoting cancer stem cells (CSCs), and their prospective contribution in cancer progression. AS directly regulates the self-renewal features of stem cells (SCs) and stem-like cancer cells. Notably, octamer-binding transcription factor 4A spliced variant of octamer-binding transcription factor 4 contributes to maintaining stemness properties in both SCs and CSCs. The epithelial to mesenchymal transition pathway regulates the AS events in CSCs to maintain stemness. The alternative spliced variants of CSCs markers, including cluster of differentiation 44, aldehyde dehydrogenase, and doublecortin-like kinase, α6β1 integrin, have pivotal roles in increasing self-renewal properties and maintaining the pluripotency of CSCs. Various splicing analysis tools are considered in this study. LeafCutter software can be considered as the best tool for differential splicing analysis and identification of the type of splicing events. Additionally, LeafCutter can be used for efficient mapping splicing quantitative trait loci. Altogether, the accumulating evidence re-enforces the fact that gene and protein expression need to be investigated in parallel with alternative splice variants.

Resurgence of phosphotyrosine binding domains: Structural and functional properties essential for understanding disease pathogenesis

BACKGROUND

Phosphotyrosine Binding (PTB) Domains, usually found on scaffold proteins, are pervasive in many cellular signaling pathways. These domains are the second-largest family of phosphotyrosine recognition domains and since their initial discovery, dozens of PTB domains have been structurally determined.

SCOPE OF REVIEW

Due to its signature sequence flexibility, PTB domains can bind to a large variety of ligands including phospholipids. PTB peptide binding is divided into classical binding (canonical NPXY motifs) and non-classical binding (all other motifs). The first atypical PTB domain was discovered in cerebral cavernous malformation 2 (CCM2) protein, while only one third in size of the typical PTB domain, it remains functionally equivalent.

MAJOR CONCLUSIONS

PTB domains are involved in numerous signaling processes including embryogenesis, neurogenesis, and angiogenesis, while dysfunction is linked to major disorders including diabetes, hypercholesterolemia, Alzheimer's disease, and strokes. PTB domains may also be essential in infectious processes, currently responsible for the global pandemic in which viral cellular entry is suspected to be mediated through PTB and NPXY interactions.

GENERAL SIGNIFICANCE

We summarize the structural and functional updates in the PTB domain over the last 20 years in hopes of resurging interest and further analyzing the importance of this versatile domain.

The role of NUMB/NUMB isoforms in cancer stem cells

Cancer stem cells (CSCs) are a subpopulation of cancer that can self-renew and differentiate into large tumor masses. Evidence accumulated to date shows that CSCs affect tumor proliferation, recurrence, and resistance to chemotherapy. Recent studies have shown that, like stem cells, CSCs maintain cells with self-renewal capacity by means of asymmetric division and promote cell proliferation by means of symmetric division. This cell division is regulated by fate determinants, such as the NUMB protein, which recently has also been confirmed as a tumor suppressor. Loss of NUMB expression leads to uncontrolled proliferation and amplification of the CSC pool, which promotes the Notch signaling pathway and reduces the expression of the p53 protein. NUMB genes are alternatively spliced to produce six functionally distinct isoforms. An interesting recent discovery is that the protein NUMB isoform produced by alternative splicing of NUMB plays an important role in promoting carcinogenesis. In this review, we summarize the known functions of NUMB and NUMB isoforms related to the proliferation and generation of CSCs.

The role of NUMB/NUMB isoforms in cancer stem cells

Cancer stem cells (CSCs) are a subpopulation of cancer that can self-renew and differentiate into large tumor masses. Evidence accumulated to date shows that CSCs affect tumor proliferation, recurrence, and resistance to chemotherapy. Recent studies have shown that, like stem cells, CSCs maintain cells with self-renewal capacity by means of asymmetric division and promote cell proliferation by means of symmetric division. This cell division is regulated by fate determinants, such as the NUMB protein, which recently has also been confirmed as a tumor suppressor. Loss of NUMB expression leads to uncontrolled proliferation and amplification of the CSC pool, which promotes the Notch signaling pathway and reduces the expression of the p53 protein. NUMB genes are alternatively spliced to produce six functionally distinct isoforms. An interesting recent discovery is that the protein NUMB isoform produced by alternative splicing of NUMB plays an important role in promoting carcinogenesis. In this review, we summarize the known functions of NUMB and NUMB isoforms related to the proliferation and generation of CSCs. [BMB Reports 2021; 54(7): 335-343].

Interactions and Feedbacks in E-Cadherin Transcriptional Regulation

Epithelial tissues rely on the adhesion between participating cells to retain their integrity. The transmembrane protein E-cadherin is the major protein that mediates homophilic adhesion between neighbouring cells and is, therefore, one of the critical components for epithelial integrity. E-cadherin downregulation has been described extensively as a prerequisite for epithelial-to-mesenchymal transition and is a hallmark in many types of cancer. Due to this clinical importance, research has been mostly focused on understanding the mechanisms leading to transcriptional repression of this adhesion molecule. However, in recent years it has become apparent that re-expression of E-cadherin is a major step in the progression of many cancers during metastasis. Here, we review the currently known molecular mechanisms of E-cadherin transcriptional activation and inhibition and highlight complex interactions between individual mechanisms. We then propose an additional mechanism, whereby the competition between adhesion complexes and heterochromatin protein-1 for binding to STAT92E fine-tunes the levels of E-cadherin expression in Drosophila but also regulates other genes promoting epithelial robustness. We base our hypothesis on both existing literature and our experimental evidence and suggest that such feedback between the cell surface and the nucleus presents a powerful paradigm for epithelial resilience.

Role for Fgr and Numb in retinoic acid-induced differentiation and G0 arrest of non-APL AML cells

Retinoic acid (RA) is a fundamental regulator of cell cycle and cell differentiation. Using a leukemic patient-derived in vitro model of a non-APL AML, we previously found that RA evokes activation of a macromolecular signaling complex, a signalosome, built of numerous MAPK-pathway-related signaling molecules; and this signaling enabled Retinoic-Acid-Response-Elements (RAREs) to regulate gene expression that results in cell differentiation/cell cycle arrest. Toward mechanistic insight into the nature of this novel signaling, we now find that the NUMB cell fate determinant protein is an apparent scaffold for the signalosome. Numb exists in the cell bound to an ensemble of signalosome molecules, including Raf, Lyn, Slp-76, and Vav. Addition of RA induces the expression of Fgr. Fgr binds NUMB, which is associated with (p-tyr)phosphorylation of NUMB and enhanced NUMB-binding and (p-tyr)phosphorylation of select signalosome components, thereby betraying signalosome activation. Signalosome activation is associated with cell differentiation along the myeloid lineage and G1/0 cell cycle arrest. If RA-induced Fgr expression is ablated by a CRISPR-KO; then the RA-induced (p-tyr) phosphorylation of NUMB and enhanced NUMB-binding and (p-tyr)phosphorylation of select signalosome components are lost. The cells now fail to undergo RA-induced differentiation or G1/0 arrest. In sum we find that NUMB acts as a scaffold for a signaling machine that functions to propel RA-induced differentiation and G1/0 arrest, and that Fgr binding to NUMB turns the function on. The Numb fate determinant protein thus appears to regulate the retinoic acid embryonic morphogen using the Fgr Src-Family-Kinase. These mechanistic insights suggest therapeutic targets for a hitherto incurable AML.

The polarity protein PARD3 and cancer

Tissue disorganisation is one of the main hallmarks of cancer. Polarity proteins are responsible for the arrangement of cells within epithelial tissues through the asymmetric organisation of cellular components. Partition defective 3 (PARD3) is a master regulator of the Par polarity complex primarily due to its ability to form large complexes via its self-homologous binding domain. In addition to its role in polarity, PARD3 is a scaffolding protein that binds to intracellular signalling molecules, many of which are frequently deregulated in cancer. The role of PARD3 has been implicated in multiple solid cancers as either a tumour suppressor or promoter. This dual functionality is both physiologically and cell context dependent. In this review, we will discuss PARD3's role in tumourigenesis in both laboratory and clinical settings. We will also review several of the mechanisms underpinning PARD3's function including its association with intracellular signalling pathways and its role in the regulation of asymmetric cell division.

IFT20 Mediates the Transport of Cell Migration Regulators From the Trans-Golgi Network to the Plasma Membrane in Breast Cancer Cells

IFT20 is a subunit of the intraflagellar transport (IFT) system essential for the formation and function of cilia. Besides predominant research in the cilia field, some IFT subunits perform extraciliary roles in non-ciliated cancer cells. However, the specific roles of IFT subunits in tumorigenesis remain unknown. Here, we found that knockout of IFT20 in mouse breast cancer cells lacking primary cilia promoted epithelial mesenchymal transitions (EMTs), active lamellipodia formation, and cell migration. IFT20 localized at the trans-Golgi and trans-Golgi network (TGN), and displayed vesicular co-distributions with Rab8a, the marker of TGN-to-plasma membrane vesicular trafficking. Proximity-dependent biotin identification (BioID) and colocalization analyzes showed that Numb and Ctnnal1, whose depletion promoted cell migration, co-localized with IFT20 at the trans-Golgi/TGN or intracellular transport vesicles. Furthermore, Strep-Tactin pulldown assays revealed an interaction between IFT20 and Ctnnal1 or Numb. Loss of IFT20 lowered the expression of actin-associated Tagln2, whose knockdown promoted cell migration. Thus, the extraciliary function of ITF20 in breast cancer cell was associated with the negative regulation of migration.

Intracellular Transport in Cancer Metabolic Reprogramming

Tumor progression is a complex process consisting of several steps characterized by alterations in cellular behavior and morphology. These steps include uncontrolled cell division and proliferation, invasiveness and metastatic ability. Throughout these phases, cancer cells encounter a changing environment and a variety of metabolic stress. To meet their needs for energy while they proliferate and survive in their new environment, tumor cells need to continuously fine-tune their metabolism. The connection between intracellular transport and metabolic reprogramming during cancer progression is emerging as a central process of cellular adaptation to these changes. The trafficking of proteolytic enzymes, surface receptors, but also the regulation of downstream pathways, are all central to cancer progression. In this review, we summarize different hallmarks of cancer with a special focus on the role of intracellular trafficking in cell proliferation, epithelial to mesenchymal transition as well as invasion. We will further emphasize how intracellular trafficking contributes to the regulation of energy consumption and metabolism during these steps of cancer progression.

Computational models to explore the complexity of the epithelial to mesenchymal transition in cancer

Epithelial to mesenchymal transition (EMT) is a complex biological process that plays a key role in cancer progression and metastasis formation. Its activation results in epithelial cells losing adhesion and polarity and becoming capable of migrating from their site of origin. At this step the disease is generally considered incurable. As EMT execution involves several individual molecular components, connected by nontrivial relations, in vitro techniques are often inadequate to capture its complexity. Computational models can be used to complement experiments and provide additional knowledge difficult to build up in a wetlab. Indeed in silico analysis gives the user total control on the system, allowing to identify the contribution of each independent element. In the following, two kinds of approaches to the computational study of EMT will be presented. The first relies on signal transduction networks description and details how changes in gene expression could influence this process, both focusing on specific aspects of the EMT and providing a general frame for this phenomenon easily comparable with experimental data. The second integrates single cell and population level descriptions in a multiscale model that can be considered a more accurate representation of the EMT. The advantages and disadvantages of each approach will be highlighted, together with the importance of coupling computational and experimental results. Finally, the main challenges that need to be addressed to improve our knowledge of the role of EMT in the neoplastic disease and the scientific and translational value of computational models in this respect will be presented. This article is categorized under: Analytical and Computational Methods > Computational Methods.

Primary cilia control cell alignment and patterning in bone development via ceramide-PKCζ-β-catenin signaling

Intraflagellar transport (IFT) proteins are essential for cilia assembly and function. IFT protein mutations lead to ciliopathies, which manifest as variable skeletal abnormalities. However, how IFT proteins regulate cell alignment during bone development is unknown. Here, we show that the deletion of IFT20 in osteoblast lineage using Osterix-Cre and inducible type I Collagen-CreERT cause a compromised cell alignment and a reduced bone mass. This finding was validated by the disorganized collagen fibrils and decreased bone strength and stiffness in IFT20-deficient femurs. IFT20 maintains cilia and cell alignment in osteoblasts, as the concentric organization of three-dimensional spheroids was disrupted by IFT20 deletion. Mechanistically, IFT20 interacts with the ceramide-PKCζ complex to promote PKCζ phosphorylation in cilia and induce the apical localization of β-catenin in osteoblasts, both of which were disrupted in the absence of IFT20. These results reveal that IFT20 regulates polarity and cell alignment via ceramide-pPKCζ-β-catenin signaling during bone development.

NUMB regulates the endocytosis and activity of the anaplastic lymphoma kinase in an isoform-specific manner

NUMB is an evolutionarily conserved protein that plays an important role in cell adhesion, migration, polarity, and cell fate determination. It has also been shown to play a role in the pathogenesis of certain cancers, although it remains controversial whether NUMB functions as an oncoprotein or tumor suppressor. Here, we show that NUMB binds to anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase aberrantly activated in several forms of cancer, and this interaction regulates the endocytosis and activity of ALK. Intriguingly, the function of the NUMB-ALK interaction is isoform-dependent. While both p66-NUMB and p72-NUMB isoforms are capable of mediating the endocytosis of ALK, the former directs ALK to the lysosomal degradation pathway, thus decreasing the overall ALK level and the downstream MAP kinase signal. In contrast, the p72-NUMB isoform promotes ALK recycling back to the plasma membrane, thereby maintaining the kinase in its active state. Our work sheds light on the controversial role of different isoforms of NUMB in tumorigenesis and provides mechanistic insight into ALK regulation.

An Intricate Connection between Alternative Splicing and Phenotypic Plasticity in Development and Cancer

During tumor progression, hypoxia, nutrient deprivation or changes in the extracellular environment (i.e., induced by anti-cancer drugs) elicit adaptive responses in cancer cells. Cellular plasticity increases the chance that tumor cells may survive in a challenging microenvironment, acquire new mechanisms of resistance to conventional drugs, and spread to distant sites. Re-activation of stem pathways appears as a significant cause of cellular plasticity because it promotes the acquisition of stem-like properties through a profound phenotypic reprogramming of cancer cells. In addition, it is a major contributor to tumor heterogeneity, depending on the coexistence of phenotypically distinct subpopulations in the same tumor bulk. Several cellular mechanisms may drive this fundamental change, in particular, high-throughput sequencing technologies revealed a key role for alternative splicing (AS). Effectively, AS is one of the most important pre-mRNA processes that increases the diversity of transcriptome and proteome in a tissue- and development-dependent manner. Moreover, defective AS has been associated with several human diseases. However, its role in cancer cell plasticity and tumor heterogeneity remains unclear. Therefore, unravelling the intricate relationship between AS and the maintenance of a stem-like phenotype may explain molecular mechanisms underlying cancer cell plasticity and improve cancer diagnosis and treatment.

Genetic alterations of epithelial polarity genes are associated with loss of polarity in invasive breast cancer

Breast cancer remains a leading cause of cancer-related death for women. The stepwise development of breast cancer through preinvasive to invasive disease is associated with progressive disruption of cellular and tissue organization. Apical-basal polarity is thought to be a barrier to breast cancer development, but the extent and potential mechanisms that contribute to disrupted polarity are incompletely understood. To investigate the cell polarity status of invasive breast cancers, we performed multiplex imaging of polarity markers on tissue cores from 432 patients from a spectrum of grades, stages and molecular subtypes. Apical-basal cell polarity was lost in 100% of cells in all cases studied, indicating that loss of epithelial polarity may be a universal feature of invasive breast cancer. We then analyzed genomic events from the TCGA dataset for an 18-gene set of core polarity genes. Coamplification of polarity genes with established breast oncogenes was found, which is consistent with functional cooperation within signaling amplicons. Gene-expression levels of several polarity genes were significantly associated with survival, and protein localization of Par6 correlated with higher grade, nodal metastasis and molecular subtype. Finally, multiple hotspot mutations in protein-protein interaction domains critical for cell polarity were identified. Our data indicate that genomic events likely contribute to pervasive disruption of epithelial polarity observed in invasive breast cancer.

HMGA1 negatively regulates NUMB expression at transcriptional and post transcriptional level in glioblastoma stem cells

Glioblastoma (GBM) is a lethal, fast-growing brain cancer, affecting 2-3 per 100,000 adults per year. It arises from multipotent neural stem cells which have reduced their ability to divide asymmetrically and hence divide symmetrically, generating increasing number of cancer stem cells, fostering tumor growth. We have previously demonstrated that the architectural transcription factor HMGA1 is highly expressed in brain tumor stem cells (BTSCs) and that its silencing increases stem cell quiescence, reduces self-renewal and sphere-forming efficiency in serial passages, suggesting a shift from symmetric to asymmetric division. Since NUMB expression is fundamental for the fulfillment of asymmetric division in stem cells, and is lost or reduced in many tumors, including GBM, we have investigated the ability of HMGA1 to regulate NUMB expression. Here, we show that HMGA1 negatively regulates NUMB expression at transcriptional level, by binding its promoter and counteracting c/EBP-β and at posttranscriptional level, by regulating the expression of MSI1 and of miR-146a. Finally, we report that HMGA1 knockdown-induced NUMB upregulation leads to the downregulation of the NOTCH1 pathway. Therefore, the data reported here indicate that HMGA1 negatively regulates NUMB expression in BTSCs, further supporting HMGA1 targeting as innovative and effective anti-cancer therapy.

Numb regulates cell tension required for mammary duct elongation

The mammary gland undergoes extensive expansion of a ductal network through the stroma during puberty and is an excellent model for understanding epithelial tube morphogenesis. To investigate a role for Numb, a multifaceted adapter protein, in epithelial tube morphogenesis, we conditionally deleted it from the mammary epithelium. We report that Numb-depletion results in altered extracellular-matrix organization, reduced cell tension, altered cell shape, and increased cell packing density, which results in a 50% reduction in mammary duct elongation. Using laser ablation in vitro and geometric-based cell force inference in vivo, we determined that Numb-deficient cells have altered cortical tension. Duct elongation defects were associated with altered E-cadherin distribution, but were independent of proliferation, apoptosis in ducts or end buds. This highlights a critical role for Numb in a mechanical mechanism that is required to maintain cell packing density during epithelial tube elongation.

Numb inhibits cell proliferation, invasion, and epithelial-mesenchymal transition through PAK1/β-catenin signaling pathway in ovarian cancer

Objective

The present study aimed to investigate the expression of Numb in ovarian cancer tissues and to assess the effect of Numb on cell proliferation, invasion, and EMT in ovarian cancer.

Methods

Real-time PCR and Western blotting were used to detect the mRNA and protein expression of Numb, PAK1, β-catenin, and epithelial–mesenchymal transition (EMT)-related proteins. MTT was employed to check the effect of Numb on proliferation of ovarian cancer cells. Transwell assay was performed to examine the functions of Numb and PAK1 on migration and invasion of ovarian cancer cells.

Results

The Numb expression was significantly downregulated while PAK1 and β-catenin were significantly upregulated in both ovarian cancer tissues and cell lines. Silencing of Numb promoted cell proliferation, migration, invasion, and EMT in ovarian cancer cell lines while overexpressed Numb reversed the above effects. Moreover, the EMT process induced by the inhibition of Numb was regulated through Numb-mediated PAK1/β-catenin signaling pathway.

Conclusion

Numb was downregulated and associated with cell proliferation, invasion, and EMT in ovarian cancer through regulating PAK1/β-catenin signaling, providing a novel potential biomarker and potential therapeutic target for ovarian cancer.

NUMB knockdown enhanced the anti-tumor role of cisplatin on ovarian cancer cells by inhibiting cell proliferation and epithelial-mesenchymal transition

Background

NUMB is an inhibitory regulator of NOTCH signaling, which is critical for the induction of epithelial-mesenchymal transition (EMT). Loss of NUMB expression is correlated with the genesis and development of multiple tumors. Recent studies reported that NUMB expression was upregulated in human ovarian cancer. However, the role of NUMB in ovarian cancer is still unclear. Here, we invested the effect of NUMB knockdown on the proliferation and EMT in ovarian cancer cells and explored the role of NUMB in the effect of cisplatin.

Methods

Two ovarian cancer cells (OVCAR-3 and SK-OV-3) were used in the experiments. The proliferation and apoptosis of ovarian cancer cells was examined using methyl thiazolyl tetrazolium (MTT) test and flow cytometry assays. The invasion and migration of ovarian cancer cells were examined using Transwell assays. The expression of EMT markers were examined using Simple Western analysis.

Results

NUMB knockdown inhibited cell proliferation, invasion, and migration in both ovarian cancer cells. NUMB knockdown enhanced cisplatin-induced cell growth inhibiting and apoptosis in both ovarian cancer cells. NUMB knockdown enhanced cisplatin-induced cell invasion in SK-OV-3 cells. NUMB knockdown also decreased the expression of N-cadherin and Vimentin in SK-OV-3 cells.

Conclusions

NUMB acted as an oncogene in ovarian cancer and NUMB knockdown enhanced the anti-tumor role of cisplatin on ovarian carcinoma cells by inhibiting cell proliferation and EMT.

MiR-31-5p promotes the cell growth, migration and invasion of colorectal cancer cells by targeting NUMB

The aim of this study was to investigate the role and specific molecular mechanism of miR-31-5 in colorectal cancer. The relative expression of miR-31-5p and NUMB in colorectal cancer tissues was analyzed by qRT-PCR. To knock down the expression of miR-31-5p, the transfection of miR-31-5p inhibitor was performed. The transfection with miR-31-5p mimic was used for miR-31-5p overexpression and pcDNA3.0-NUMB plasmid was used for NUMB overexpression. CCK-8 assay was used to analyze the cell proliferation. Flow cytometry was used to evaluate the cell apoptosis and cell cycle. Matrigel invasion assay was performed to assess the invasion potency and migration assay was performed to assess the migration potency. Hoechst 33258 staining assay was performed to analyze the cell apoptosis of HT29 cells after the indicated transfection. Luciferase activity assays were performed to confirmed the potential binding site for miR-31-5p in 3'-UTR region of NUMB. MiR-31-5p is highly expressed in colorectal cancer and is critical for the cell proliferation, cell cycle, migration, invasion and apoptosis. NUMB is target of miR-31-5p and NUMB overexpression inhibited the cell proliferation, migration, invasion and induced cell cycle arrest and apoptosis in HT29 colorectal cancer cells. In conclusion, miR-31-5p promoted the cell growth, migration and invasion by targeting NUMB in colorectal cancer cells.

Interactome Mapping Uncovers a General Role for Numb in Protein Kinase Regulation

Cellular functions are frequently regulated by protein-protein interactions involving the binding of a modular domain in one protein to a specific peptide sequence in another. This mechanism may be explored to identify binding partners for proteins harboring a peptide-recognition domain. Here we report a proteomic strategy combining peptide and protein microarray screening with biochemical and cellular assays to identify modular domain-mediated protein-protein interactions in a systematic manner. We applied this strategy to Numb, a multi-functional protein containing a phosphotyrosine-binding (PTB) domain. Through the screening of a protein microarray, we identified >100 protein kinases, including both Tyr and Ser/Thr kinases, that could potentially interact with the Numb PTB domain, suggesting a general role for Numb in regulating kinase function. The putative interactions between Numb and several tyrosine kinases were subsequently validated by GST pull-down and/or co-immunoprecipitation assays. Furthermore, using the Oriented Peptide Array Library approach, we defined the specificity of the Numb PTB domain which, in turn, allowed us to predict binding partners for Numb at the genome level. The combination of the protein microarray screening with computer-aided prediction produced the most expansive interactome for Numb to date, implicating Numb in regulating phosphorylation signaling through protein kinases and phosphatases. Not only does the data generated from this study provide an important resource for hypothesis-driven research to further define the function of Numb, the proteomic strategy described herein may be employed to uncover the interactome for other peptide-recognition domains whose consensus motifs are known or can be determined.

The implication of Numb-induced Notch signaling in endothelial-mesenchymal transition of diabetic nephropathy

AIM

This study was purposed to figure out the contribution of Numb-induced Notch signaling to the development of diabetic nephropathy (DN).

METHODS

Two hundred and twenty six DN patients were included, and human glomerular endothelial cells (RGEC) were cultured. MSCV-Numb-IRES-GFP, MSCV-Notch1-IRES-GFP and MSCV-Hes1-IRES-GFP were transfected to construct the recombinant retroviral vectors.

RESULT

The over-expressed Numb and Notch1, as well as the under-expressed Hes-1 were correlated with the undesirable prognosis of DN patients (P < 0.05). Within the cell lines transfection with si-Numb would cut down E-cadherin and CD31 expressions (P < 0.05), yet elevated α-SMA and vimentin expressions (P < 0.05). The apoptotic rate of si-Numb cell lines underperformed ones categorized into the hyperglucose group (P < 0.05), whereas the lowly-expressed Notch1 and Hes1 were observably associated with inhibited proliferation of myofibroblasts (P < 0.05). Addition of ADPT caused under-expressed α-SMA and vimentin, along with the over-expressed E-cadherin and CD31 (P < 0.05). Silencing of Notch1 and Hes1 reversed the epithelial-mesenchymal transition (EMT) process that was triggered by high glucose (P < 0.05).

CONCLUSION

Numb negatively regulated Notch signaling pathway in EMT of DN, implying that they had great potentials to serve as therapeutic targets or diagnostic biomarkers for DN.

A NUMB-EFA6B-ARF6 recycling route controls apically restricted cell protrusions and mesenchymal motility

The endocytic protein NUMB has been implicated in the control of various polarized cellular processes, including the acquisition of mesenchymal migratory traits through molecular mechanisms that have only been partially defined. Here, we report that NUMB is a negative regulator of a specialized set of understudied, apically restricted, actin-based protrusions, the circular dorsal ruffles (CDRs), induced by either PDGF or HGF stimulation. Through its PTB domain, NUMB binds directly to an N-terminal NPLF motif of the ARF6 guanine nucleotide exchange factor, EFA6B, and promotes its exchange activity in vitro. In cells, a NUMB-EFA6B-ARF6 axis regulates the recycling of the actin regulatory cargo RAC1 and is critical for the formation of CDRs that mark the acquisition of a mesenchymal mode of motility. Consistently, loss of NUMB promotes HGF-induced cell migration and invasion. Thus, NUMB negatively controls membrane protrusions and the acquisition of mesenchymal migratory traits by modulating EFA6B-ARF6 activity.

Cell-Cell Contact and Receptor Tyrosine Kinase Signaling

The behavior of cells within tissues is governed by the activities of adhesion receptors that provide spatial cues and transmit forces through intercellular junctions, and by growth-factor receptors, particularly receptor tyrosine kinases (RTKs), that respond to biochemical signals from the environment. Coordination of these two activities is essential for the patterning and polarized migration of cells during morphogenesis and for homeostasis in mature tissues; loss of this coordination is a hallmark of developing cancer and driver of metastatic progression. Although much is known about the individual functions of adhesion and growth factor receptors, we have a surprisingly superficial understanding of the mechanisms by which their activities are coordinated.

Junctional adhesion molecule-A: functional diversity through molecular promiscuity

Cell adhesion molecules (CAMs) of the immunoglobulin superfamily (IgSF) regulate important processes such as cell proliferation, differentiation and morphogenesis. This activity is primarily due to their ability to initiate intracellular signaling cascades at cell-cell contact sites. Junctional adhesion molecule-A (JAM-A) is an IgSF-CAM with a short cytoplasmic tail that has no catalytic activity. Nevertheless, JAM-A is involved in a variety of biological processes. The functional diversity of JAM-A resides to a large part in a C-terminal PDZ domain binding motif which directly interacts with nine different PDZ domain-containing proteins. The molecular promiscuity of its PDZ domain motif allows JAM-A to recruit protein scaffolds to specific sites of cell-cell adhesion and to assemble signaling complexes at those sites. Here, we review the molecular characteristics of JAM-A, including its dimerization, its interaction with scaffolding proteins, and the phosphorylation of its cytoplasmic domain, and we describe how these characteristics translate into diverse biological activities.

Nrf2 antioxidant pathway suppresses Numb-mediated epithelial-mesenchymal transition during pulmonary fibrosis

Epithelial mesenchymal transition (EMT) is a key progression that promotes pulmonary fibrosis (PF). Numb, a phosphotyrosine-binding domain (PTB) protein, is implicated with EMT. Nuclear factor erythroid 2-related factor2 (Nrf2) and its downstream proteins heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQO1) constitute an important pathway of antioxidant defense signal for protecting against PF. It remains elusive whether Nrf2 antioxidant pathway and Numb have a potential relationship in EMT-mediated PF. Here, we observed the effects of Nrf2 pathway and Numb on bleomycin(BLM)-induced PF in Nrf2-knockout (Nrf2-/-) and wild-type (WT) mice. Meanwhile, rat type II alveolar epithelial cells line (RLE-6TN) and human epithelial cells line (A549) were both treated with an Nrf2 activator sulforaphane (SFN), or transfected siRNAs of Nrf2 and Numb to unravel roles of Nrf2 pathway, Numb and the link between them on transforming growth factor β1 (TGF-β1)-induced EMT. We found BLM-induced lung fibrosis were more severe in Nrf2-/- mice compared to WT mice with reduced expressions of HO-1 and NQO1. Numb was enhanced with down-regulated expressions of Nrf2 in BLM groups and further increased in Nrf2-/- groups. In vitro, given exogenous TGF-β1 on RLE-6TN and A549 up-regulated Numb expressions, accompanied with down-regulations of Nrf2 and its target proteins HO-1 and NQO1. Transfected with Nrf2 and Numb siRNAs further aggravated and relieved the progression of EMT, respectively. Inversely, activating Nrf2 pathway by SFN reduced the expression of Numb and EMT-related protein. Moreover, Numb deficiency by siRNA relieved the protection of activating Nrf2 against EMT. In conclusion, activating Nrf2 antioxidant pathway suppresses EMT during PF via inhibiting the abnormal expression of Numb. These findings provide insight into PF pathogenesis and a basis for novel treatment approaches.

Numb prevents a complete epithelial-mesenchymal transition by modulating Notch signalling

Epithelial-mesenchymal transition (EMT) plays key roles during embryonic development, wound healing and cancer metastasis. Cells in a partial EMT or hybrid epithelial/mesenchymal (E/M) phenotype exhibit collective cell migration, forming clusters of circulating tumour cells-the primary drivers of metastasis. Activation of cell-cell signalling pathways such as Notch fosters a partial or complete EMT, yet the mechanisms enabling cluster formation remain poorly understood. Using an integrated computational-experimental approach, we examine the role of Numb-an inhibitor of Notch intercellular signalling-in mediating EMT and clusters formation. We show via an mathematical model that Numb inhibits a full EMT by stabilizing a hybrid E/M phenotype. Consistent with this observation, knockdown of Numb in stable hybrid E/M cells H1975 results in a full EMT, thereby showing that Numb acts as a brake for a full EMT and thus behaves as a 'phenotypic stability factor' by modulating Notch-driven EMT. By generalizing the mathematical model to a multi-cell level, Numb is predicted to alter the balance of hybrid E/M versus mesenchymal cells in clusters, potentially resulting in a higher tumour-initiation ability. Finally, Numb correlates with a worse survival in multiple independent lung and ovarian cancer datasets, hence confirming its relationship with increased cancer aggressiveness.

Interleukin-7 and Immunosenescence

The age of an individual is an important, independent risk factor for many of the most common diseases afflicting modern societies. Interleukin-7 (IL-7) plays a central, critical role in the homeostasis of the immune system. Recent studies support a critical role for IL-7 in the maintenance of a vigorous healthspan. We describe the role of IL-7 and its receptor in immunosenescence, the aging of the immune system. An understanding of the role that IL-7 plays in aging may permit parsimonious preventative or therapeutic solutions for diverse conditions. Perhaps IL-7 might be used to "tune" the immune system to optimize human healthspan and longevity.

Behind the Scenes: Endo/Exocytosis in the Acquisition of Metastatic Traits

Alterations of endo/exocytic proteins have long been associated with malignant transformation, and genes encoding membrane trafficking proteins have been identified as bona fide drivers of tumorigenesis. Focusing on the mechanisms underlying the impact of endo/exocytic proteins in cancer, a scenario emerges in which altered trafficking routes/networks appear to be preferentially involved in the acquisition of prometastatic traits. This involvement in metastasis frequently occurs through the integration of programs leading to migratory/invasive phenotypes, survival and resistance to environmental stresses, epithelial-to-mesenchymal transition, and the emergence of cancer stem cells. These findings might have important implications in the clinical setting for the development of metastasis-specific drugs and for patient stratification to optimize the use of available therapies. Cancer Res; 77(8); 1813-7. ©2017 AACR.

Numb regulates somatic cell lineage commitment during early gonadogenesis in mice

During early gonadogenesis, proliferating cells in the coelomic epithelium (CE) give rise to most of the somatic cells in both XX and XY gonads. Previous dye-labeling experiments showed that a single CE cell could give rise to additional CE cells and to both supporting and interstitial cell lineages, implying that cells in the CE domain are multipotent progenitors, and suggesting that an asymmetric division is involved in the acquisition of gonadal cell fates. We found that NUMB is asymmetrically localized in CE cells, suggesting that it might be involved. To test this hypothesis, we conditionally deleted Numb on a Numbl mutant background just prior to gonadogenesis. Mutant gonads showed a loss of cell polarity in the surface epithelial layers, large interior cell patches expressing the undifferentiated cell marker LHX9, and a loss of differentiated cells in somatic cell lineages. These results indicate that NUMB is necessary for establishing polarity in CE cells, and that asymmetric divisions resulting from CE polarity are required for commitment to differentiated somatic cell fates. Surprisingly, germ cells, which do not arise from the CE, were also affected in mutants, which may be a direct or indirect effect of loss of Numb.

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

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

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

Molecular targets of developmental exposure to bisphenol A in diabesity: a focus on endoderm-derived organs

Several studies associate foetal human exposure to bisphenol A (BPA) to metabolic/endocrine diseases, mainly diabesity. They describe the role of BPA in the disruption of pancreatic beta cell, adipocyte and hepatocyte functions. Indeed, the complexity of the diabesity phenotype is due to the involvement of different endoderm-derived organs, all targets of BPA. Here, we analyse this point delineating a picture of different mechanisms of BPA toxicity in endoderm-derived organs leading to diabesity. Moving from epidemiological data, we summarize the in vivo experimental data of the BPA effects on endoderm-derived organs (thyroid, pancreas, liver, gut, prostate and lung) after prenatal exposure. Mainly, we gather molecular data evidencing harmful effects at low-dose exposure, pointing to the risk to human health. Although the fragmentation of molecular data does not allow a clear conclusion to be drawn, the present work indicates that the developmental exposure to BPA represents a risk for endoderm-derived organs development as it deregulates the gene expression from the earliest developmental stages. A more systematic analysis of BPA impact on the transcriptomes of endoderm-derived organs is still missing. Here, we suggest in vitro toxicogenomics approaches as a tool for the identification of common mechanisms of BPA toxicity leading to the diabesity in organs having the same developmental origin.

Plasticity of tumor cell invasion: governance by growth factors and cytokines

Tumor cell migration, the basis for metastatic dissemination, is an adaptive process which depends upon coordinated cell interaction with the environment, influencing cell-matrix and cell-cell adhesion, cytoskeletal dynamics and extracellular matrix remodeling. Growth factors and cytokines, released within the reactive tumor microenvironment and their intracellular effector signals strongly impact mechanocoupling functions in tumor cells and thereby control the mode and extent of tumor invasion, including collective and single-cell migration and their interconversions. Besides their role in controlling tumor cell growth and survival, cytokines and growth factors thus provide complex orchestration of the metastatic cascade and tumor cell adaptation to environmental challenge. We here review the mechanisms by which growth factors and cytokines control the reciprocal interactions between tumor cells and their microenvironment, and the consequences for the efficacy and plasticity of invasion programs and metastasis.

NUMB negatively regulates the epithelial-mesenchymal transition of triple-negative breast cancer by antagonizing Notch signaling

Triple-negative breast cancer (TNBC), an aggressive subtype of breast cancer with higher rates of early relapse and metastasis, is frequently associated with aberrant activation of epithelial-mesenchymal transition (EMT). Nonetheless, how EMT is initiated and regulated during TNBC progression is not well understood. Here, we report that NUMB is a negative regulator of EMT in both human mammary epithelial cells and breast cancer cells. Reduced NUMB expression was significantly associated with elevated EMT in TNBC. Conversely, overexpression of NUMB strongly attenuated the EMT program and metastasis of TNBC cell lines. Interestingly, we showed that NUMB employs different molecular mechanisms to regulate EMT. In normal mammary epithelial cells and breast cancer cells expressing wild-type p53, NUMB suppressed EMT by stabilizing p53. However, in TNBC cells, loss of NUMB facilitated the EMT program by activating Notch signaling. Consistent with these findings, low NUMB expression and high Notch activity were significantly correlated with the TNBC subtype in patients. Collectively, these findings reveal novel molecular mechanisms of NUMB in the regulation of breast tumor EMT, especially in TNBC.

Dual function of partitioning-defective 3 in the regulation of YAP phosphorylation and activation

Partitioning-defective 3 (Par3), a key component of the evolutionarily conserved polarity PAR complex (Par3/Par6/aPKC), controls cell polarity and contributes to cell migration, proliferation and tumor development. Emerging evidence indicates that cell polarity proteins function as upstream modulators that regulate the Hippo pathway. However, little is known about Par3’s involvement in the Hippo pathway. Here, we find Par3 and YAP dynamically co-localize in different subcellular compartments; that is, the membrane, cytoplasm and nucleus, in a cell-density-dependent manner. Interestingly, Par3 knockdown promotes YAP phosphorylation, leading to a significant impairment of YAP nuclear translocation at low cell density, but not at high density, in MDCK cells. Furthermore, via its third PDZ domain, Par3 directly binds to the PDZ-binding motif of YAP. The interaction is required for regulating YAP phosphorylation and nuclear localization. Mechanistically, Par3, as a scaffold protein, associates with LATS1 and protein phosphatase 1, α subunit (PP1A) in the cytoplasm and nucleus. Par3 promotes the dephosphorylation of LATS1 and YAP, thus enhancing YAP activation and cell proliferation. Strikingly, we also find that under the condition of PP1A knockdown, Par3 expression promotes YAP hyperphosphorylation, leading to the suppression of YAP activity and its downstream targets. Par3 expression results in differential effects on YAP phosphorylation and activation in different tumor cell lines. These findings indicate that Par3 may have a dual role in regulating the activation of the Hippo pathway, in a manner possibly dependent on cellular context or cell type in response to cell–cell contact and cell polarity signals.

Numb contributes to renal fibrosis by promoting tubular epithelial cell cycle arrest at G2/M

Numb is a multifunctional protein involved in diverse cellular processes. However, the function of Numb in kidney remains unclear. Here, we reported that Numb is expressed in renal tubules and glomeruli in normal adult kidney. Numb expression was upregulated in fibrotic kidneys induced by unilateral ureteral obstruction (UUO) in mice as well as in human fibrotic kidney tissues. Numb overexpression in cultured proximal tubular cells increased the G2/M cell population and upregulated the expression of TGF-β1 and CTGF. Whereas, proximal tubule Numb knockout (PEPCK-Numb-KO) mice showed reduced G2/M arrest, decreased expression of TGF-β1 and CTGF, and attenuated fibrotic lesions due to either UUO or unilateral ischemia reperfusion nephropathy. Inhibiting p53 activity by pifithrin-` dramatically mitigated Numb-induced G2/M arrest, indicating that Numb potentiates G2/M arrest via stabilizing p53 protein. Together, these data suggest that Numb is a potential target for anti-fibrosis therapy.

RNA-binding Protein Musashi Homologue 1 Regulates Kidney Fibrosis by Translational Inhibition of p21 and Numb mRNA

RNA-binding proteins (RBPs) are recognized as key posttranscriptional regulators that not only modulate the spatiotemporal expression of genes during organism development but also regulate disease pathogenesis. Very limited information exists on the potential role of RBPs in modulating kidney fibrosis, which is a major hallmark of chronic kidney disease. Here, we report a novel mechanism in kidney fibrosis involving a RBP, Musashi homologue 1 (Msi1), which is expressed in tubular epithelial cells. Using two mechanistically distinct mouse models of kidney fibrosis, we show that Msi1 protein levels are significantly down-regulated in the kidneys following fibrosis. We found that Msi1 functions by negatively regulating the translation of its target mRNAs, p21 and Numb, whose protein levels are markedly increased in kidney fibrosis. Also, Msi1 overexpression and knockdown in kidney epithelial cells cause p21- and Numb-mediated cell cycle arrest. Furthermore, we observed that Numb looses its characteristic membrane localization in fibrotic kidneys and therefore is likely unable to inhibit Notch resulting in tubular cell death. Oleic acid is a known inhibitor of Msi1 and injecting oleic acid followed by unilateral ureteral obstruction surgery in mice resulted in enhanced fibrosis compared with the control group, indicating that inhibiting Msi1 activity renders the mice more susceptible to fibrosis. Given that deregulated fatty acid metabolism plays a key role in kidney fibrosis, these results demonstrate a novel connection between fatty acid and Msi1, an RNA-binding protein, in kidney fibrosis.

The Expression and Function of NUMB in Endometrial Cancer and the Interaction with HDM2 and P53

Background: Since more and more evidences support that NUMB orchestrates many cell physiological and pathological processes of diseases including cancer, based on our previous work, we studied deeply the function of NUMB in endometrial cancer (EC) and tried to understand the mechanism of NUMB's nucleus translocation which might be relative to the occurrence of EC and will contribute to find a new targeting therapeutic strategy for EC.

Methods: Immunohistochemistry was employed to test NUMB and HDM2 expression in endometrial cancer tissue from clinical patients. CCK-8 assay, cell cycle tested by Flow cytometer and PCNA determined by RT-PCR were employed to test the effects of NUMB on cell proliferation and apoptosis. In order to investigate the mechanism how NUMB, HDM2 and p53 interact in EC cell, western blot, Co-IP and immunofluorescent were used to observe the combination and location of NUMB, HDM2 and p53 as well as the interaction among them.

Results: Both NUMB and HDM2 expressed greater in endometrial cancer tissues than in normal endometrial tissues. Overexpression of NUMB induced apoptosis in Ishikawa cell while inhibition of NUMB increased cell proliferation. NUMB could combine HDM2 and p53, moreover the PTB domain of NUMB is the main site combining with p53. The effects of NUMB in cell was closely associated with p53. Not only NUMB regulated P53 expression level but also NUMB acts depending on P53, in turn p53 impacted the NUMB level as a feedback. Overexpression of NUMB could not bring itself into nuclear. Both siHDM2 and siP53 didn't bring NUMB into nucleus, However overexpression of HDM2 and p53 increased the NUMB level in nucleus, and the NUMB nuclear location induced by overexpression of HDM2 was stronger than that of p53 overexpression.

Conclusions: Based on present data, we think NUMB acts as an anti-oncogene role and could regulate p53 level and function in endometrial cancer like in other cancers, meanwhile, the function of NUMB depend on P53. On the other hand, the location of NUMB could be regulated mainly by HDM2. So far we are not able to explain why endometrial cancer patients had high NUMB expression level since NUMB was regarded as a tumor suppressor, which is worthy studying further to explore underlying mechanism.