Control of the reversibility of cellular quiescence by the transcriptional repressor HES1

Transcriptomic study of the mechanism of anoikis resistance in head and neck squamous carcinoma

Background

Normal epithelial cells rapidly undergo apoptosis as soon as they lose contact with the extracellular matrix (ECM), which is termed as anoikis. However, cancer cells tend to develop a resistance mechanism to anoikis. This acquired ability is termed as anoikis resistance. Cancer cells, with anoikis resistance, can spread to distant tissues or organs via the peripheral circulatory system and cause cancer metastasis. Thus, inhibition of anoikis resistance blocks the metastatic ability of cancer cells.

Methods

Anoikis-resistant CAL27 (CAL27^AR) cells were induced from CAL27 cells using the suspension culture approach. Transcriptome analysis was performed using RNA-Seq to study the differentially expressed genes (DEGs) between the CAL27^ARcells and the parental CAL27 cells. Gene function annotation and Gene Ontology (GO) enrichment analysis were performed using DAVID database. Signaling pathways involved in DEGs were analyzed using Gene Set Enrichment Analysis (GSEA) software. Analysis results were confirmed by reverse transcription PCR (RT-PCR), western blotting, and gene correlation analysis based on the TCGA database.

Results

GO enrichment analysis indicated that the biological process (BP) of the DEGs was associated with epidermal development, DNA replication, and G1/S transition of the mitotic cell cycle. The analysis of cellular component (CC) showed that the most significant up-regulated genes were related to extracellular exosome. KEGG Pathway analysis revealed that 23 signaling pathways were activated (p-value ≤ 0.05, FDR q-value ≤ 0.05) and 22 signaling pathways were suppressed (p-value ≤ 0.05, FDR q-value ≤ 0.05). The results from the GSEA indicated that in contrast to the inhibition of EGFR signaling pathway, the VEGF signaling pathway was activated. The VEGF signaling pathway possibly activates STAT3 though induction of STAT3 phosphorylation. Gene correlation analysis revealed that the VEGFA- STAT3-KLF4-CDKN1A signal axis was not only present in head and neck squamous carcinoma (HNSCC) but also two other epithelial-derived carcinomas that highly express VEGFA, including kidney renal clear cell carcinoma (KIRC) and ovarian serous cystadenocarcinoma (OV).

Novel therapeutic strategies and targets in advanced uveal melanoma

PURPOSE OF REVIEW

Currently, there are no U.S. Food and Drug Administration-approved or effective treatment options for advanced-stage uveal melanoma. In this article, we focus on therapeutic targets in pathways/mechanisms associated with common mutations in uveal melanoma. We review the challenges associated with targeting of these pathways and novel treatment strategies.

RECENT FINDINGS

Common mutations that promote uveal melanoma initiation and progression include alterations in G protein subunit alpha q/11 (GNAQ/GNA11) and breast cancer gene 1-associated protein 1 (BAP1). Mutant GNAQ/GNA11 induces constitutive activation of tumorigenic pathways such as extracellular signal-regulated kinase (ERK)1/2 and yes-associated protein. Inhibition of mitogen-activated protein kinase kinase (MEK) downstream of ERK1/2, however, was shown in trials to have limited clinical benefit. Recent reports suggested that combination therapies of MEK inhibition and modulators of mechanisms of drug resistance may improve tumor responses to MEK inhibitors. BAP1 has been shown to be involved in modulating chromatin dynamics and deubiquitination of proteins. Hence, epigenetic inhibitors are being investigated in BAP1 mutant uveal melanoma. However, other functions of BAP1, such as in DNA damage repair and cell cycle regulation, indicate additional targets for treatment of BAP1 mutant uveal melanoma. In addition, the frequent delayed development of uveal melanoma macrometastases is likely due to cellular dormancy mechanisms. Nuclear receptor subfamily 2, group F, member 1 and transforming growth factor beta 2 were among factors that have been shown in other cancers to induce dormant phenotypes.

SUMMARY

Findings from studies in uveal melanoma and in other cancers provide evidence for potential strategies that may be tested preclinically and clinically in advanced-stage uveal melanoma to improve treatment outcome and overall survival of patients.

Nuclear orphan receptor NR2F6 confers cisplatin resistance in epithelial ovarian cancer cells by activating the Notch3 signaling pathway

The primary challenge facing treatment of epithelial ovarian cancer (EOC) is the high frequency of chemoresistance, which severely impairs the quality of life and survival of patients with EOC. Our study aims to investigate the mechanisms by which upregulation of NR2F6 induces chemoresistance in EOC. The biological roles of NR2F6 in EOC chemoresistance were explored in vitro by Sphere, MTT and AnnexinV/PI assay, and in vivo using an ovarian cancer orthotopic transplantation model. Bioinformatics analysis, luciferase assay, CHIP and IP assays were performed to identify the mechanisms by which NR2F6 promotes chemoresistance in EOC. The expression of NR2F6 was significantly upregulated in chemoresistant EOC tissue, and NR2F6 expression was correlated with poorer overall survival. Moreover, overexpression of NR2F6 promotes the EOC cancer stem cell phenotype; conversely, knockdown of NR2F6 represses the EOC cancer stem cell phenotype and sensitizes EOC to cisplatin in vitro and in vivo. Our results further demonstrate that NR2F6 sustains activated Notch3 signaling, resulting in chemoresistance in EOC cells. Notably, NR2F6 acts as an informative biomarker to identify the population of EOC patients who are likely to experience a favorable objective response to gamma‐secretase inhibitors (GSI), which inhibit Notch signaling. Therefore, concurrent inhibition of NR2F6 and treatment with GSI and cisplatin‐based chemotherapy may be a novel therapeutic approach for NR2F6‐overexpressing EOC. In summary, we have, for the first time, identified an important role for NR2F6 in EOC cisplatin resistance. Our study suggests that GSI may serve as a potential targeted treatment for patients with NR2F6‐overexpressing EOC.

What's new?

Chemoresistance is a major challenge in women afflicted with epithelial ovarian cancer (EOC), but molecular mechanisms of EOC chemoresistance remain unclear. Here the authors connect nuclear receptor subfamily 2 group F member 6 (NR2F6) with this process. They find NR2F6 upregulated in tissues from chemoresistant EOC patients. High NR2F6 expression promoted a cancer stem cell phenotype and suppressed cisplatin‐induced apoptosis by transcriptionally upregulating Notch3 signaling, thereby promoting EOC chemoresistance.

High Hes1 expression and resultant Ascl1 suppression regulate quiescent vs. active neural stem cells in the adult mouse brain

Sueda et al. show that in quiescent neural stem cells, Hes1 levels are oscillatory, although the peaks and troughs are higher than those in active neural stem cells, causing Ascl1 expression to be continuously suppressed.

Somatic stem/progenitor cells are active in embryonic tissues but quiescent in many adult tissues. The detailed mechanisms that regulate active versus quiescent stem cell states are largely unknown. In active neural stem cells, Hes1 expression oscillates and drives cyclic expression of the proneural gene Ascl1, which activates cell proliferation. Here, we found that in quiescent neural stem cells in the adult mouse brain, Hes1 levels are oscillatory, although the peaks and troughs are higher than those in active neural stem cells, causing Ascl1 expression to be continuously suppressed. Inactivation of Hes1 and its related genes up-regulates Ascl1 expression and increases neurogenesis. This causes rapid depletion of neural stem cells and premature termination of neurogenesis. Conversely, sustained Hes1 expression represses Ascl1, inhibits neurogenesis, and maintains quiescent neural stem cells. In contrast, induction of Ascl1 oscillations activates neural stem cells and increases neurogenesis in the adult mouse brain. Thus, Ascl1 oscillations, which normally depend on Hes1 oscillations, regulate the active state, while high Hes1 expression and resultant Ascl1 suppression promote quiescence in neural stem cells.

Quiescence, an individual journey

Quiescence is operationally characterized as a temporary and reversible proliferation arrest. There are many preconceived ideas about quiescence, quiescent cells being generally viewed as insignificant sleeping G1 cells. In fact, quiescence is central for organism physiology and its dysregulation involved in many pathologies. The quiescent state encompasses very diverse cellular situations depending on the cell type and its environment. This diversity challenges not only quiescence uniformity but also the universality of the molecular mechanisms beyond quiescence regulation. In this mini-perspective, we discuss recent advances in the concept of quiescence, and illustrate that this multifaceted cellular state is gaining increasing attention in many fields of biology.

Raman and infrared spectroscopy reveal that proliferating and quiescent human fibroblast cells age by biochemically similar but not identical processes

Dermal fibroblast cells can adopt different cell states such as proliferation, quiescence, apoptosis or senescence, in order to ensure tissue homeostasis. Proliferating (dividing) cells pass through the phases of the cell cycle, while quiescent and senescent cells exist in a non-proliferating cell cycle-arrested state. However, the reversible quiescence state is in contrast to the irreversible senescence state. Long-term quiescent cells transit into senescence indicating that cells age also when not passing through the cell cycle. Here, by label-free in vitro vibrational spectroscopy, we studied the biomolecular composition of quiescent dermal fibroblast cells and compared them with those of proliferating and senescent cells. Spectra were examined by multivariate statistical analysis using a PLS-LDA classification model, revealing differences in the biomolecular composition between the cell states mainly associated with protein alterations (variations in the side chain residues of amino acids and protein secondary structure), but also within nucleic acids and lipids. We observed spectral changes in quiescent compared to proliferating cells, which increased with quiescence cultivation time. Raman and infrared spectroscopy, which yield complementary biochemical information, clearly distinguished contact-inhibited from serum-starved quiescent cells. Furthermore, the spectra displayed spectral differences between quiescent cells and proliferating cells, which had recovered from quiescence. This became more distinct with increasing quiescence cultivation time. When comparing proliferating, (in particular long-term) quiescent and senescent cells, we found that Raman as well as infrared spectroscopy can separate these three cellular states from each other due to differences in their biomolecular composition. Our spectroscopic analysis shows that proliferating and quiescent fibroblast cells age by similar but biochemically not identical processes. Despite their aging induced changes, over long time periods quiescent cells can return into the cell cycle. Finally however, the cell cycle arrest becomes irreversible indicating senescence.

Alternative polyadenylation factors link cell cycle to migration

BACKGROUND

In response to a wound, fibroblasts are activated to migrate toward the wound, to proliferate and to contribute to the wound healing process. We hypothesize that changes in pre-mRNA processing occurring as fibroblasts enter the proliferative cell cycle are also important for promoting their migration.

RESULTS

RNA sequencing of fibroblasts induced into quiescence by contact inhibition reveals downregulation of genes involved in mRNA processing, including splicing and cleavage and polyadenylation factors. These genes also show differential exon use, especially increased intron retention in quiescent fibroblasts compared to proliferating fibroblasts. Mapping the 3' ends of transcripts reveals that longer transcripts from distal polyadenylation sites are more prevalent in quiescent fibroblasts and are associated with increased expression and transcript stabilization based on genome-wide transcript decay analysis. Analysis of dermal excisional wounds in mice reveals that proliferating cells adjacent to wounds express higher levels of cleavage and polyadenylation factors than quiescent fibroblasts in unwounded skin. Quiescent fibroblasts contain reduced levels of the cleavage and polyadenylation factor CstF-64. CstF-64 knockdown recapitulates changes in isoform selection and gene expression associated with quiescence, and results in slower migration.

CONCLUSIONS

Our findings support cleavage and polyadenylation factors as a link between cellular proliferation state and migration.

Skin Cell Heterogeneity in Development, Wound Healing, and Cancer

Skin architecture and function depend on diverse populations of epidermal cells and dermal fibroblasts. Reciprocal communication between the epidermis and dermis plays a key role in skin development, homeostasis and repair. While several stem cell populations have been identified in the epidermis with distinct locations and functions, it is now recognised that there is additional heterogeneity within the mesenchymal cells of the dermis. Here, we discuss recent insights into how these distinct cell populations are maintained and coordinated during development, homeostasis, and wound healing. We highlight the importance of the local environment, or niche, in cellular plasticity. We also discuss new mechanisms that have been identified as influencing wound repair and cancer progression.

Hes1 negatively regulates neurogenesis in the adult mouse dentate gyrus following traumatic brain injury

Traumatic brain injury (TBI) results in the activation of neurogenesis, but it also triggers multiple cell signaling pathways that may lead to either cell damage or cell survival. In general, the repair processes following TBI are characterized by a failure to replenish the neuronal population entirely. To date, the factors that determine whether neurogenesis will be sufficient for the replacement of lost neurons following brain injury are not fully understood. Decreased activation of Hes1, a transcriptional repressor, is observed as neural differentiation proceeds, and this gene continues to play a role in the quiescence of stem cells into adulthood. Since Hes1 is negatively correlated with neurogenesis in adult rodents, the present study investigated whether this gene inhibits TBI-induced neurogenesis by use of adenovirus-mediated gene transfer to upregulate Hes1 expression in the dentate gyrus (DG) in a mouse model of TBI. Western blot analysis and immunofluorescent staining revealed increased Hes1 protein expression in the subgranular zone (SGZ) of the DG following adenovirus-Hes1 (Ad-Hes1) transfection and a decreased number of bromodeoxyuridine-positive and doublecortin-positive cells in the SGZ in the transfection group following TBI. These data indicated a negative association between the expression of Hes1 and adult neurogenesis following the induction of TBI. Furthermore, the present findings demonstrate the value of downregulating Hes1 expression following TBI to promote the initiation of endogenous neurogenesis, which may be of therapeutic value for patients with brain injuries.

Quiescence status of glioblastoma stem-like cells involves remodelling of Ca2+ signalling and mitochondrial shape

Quiescence is a reversible cell-cycle arrest which allows cancer stem-like cells to evade killing following therapies. Here, we show that proliferating glioblastoma stem-like cells (GSLCs) can be induced and maintained in a quiescent state by lowering the extracellular pH. Through RNAseq analysis we identified Ca²⁺ signalling genes differentially expressed between proliferating and quiescent GSLCs. Using the bioluminescent Ca²⁺ reporter EGFP-aequorin we observed that the changes in Ca²⁺ homeostasis occurring during the switch from proliferation to quiescence are controlled through store-operated channels (SOC) since inhibition of SOC drives proliferating GSLCs to quiescence. We showed that this switch is characterized by an increased capacity of GSLCs’ mitochondria to capture Ca²⁺ and by a dramatic and reversible change of mitochondrial morphology from a tubular to a donut shape. Our data suggest that the remodelling of the Ca²⁺ homeostasis and the reshaping of mitochondria might favours quiescent GSLCs’ survival and their aggressiveness in glioblastoma.

Controlling Depth of Cellular Quiescence by an Rb-E2F Network Switch

Quiescence is a non-proliferative cellular state that is critical to tissue repair and regeneration. Although often described as the G0 phase, quiescence is not a single homogeneous state. As cells remain quiescent for longer durations, they move progressively deeper and display a reduced sensitivity to growth signals. Deep quiescent cells, unlike senescent cells, can still re-enter the cell cycle under physiological conditions. Mechanisms controlling quiescence depth are poorly understood, representing a currently underappreciated layer of complexity in growth control. Here, we show that the activation threshold of a Retinoblastoma (Rb)-E2F network switch controls quiescence depth. Particularly, deeper quiescent cells feature a higher E2F-switching threshold and exhibit a delayed traverse through the restriction point (R-point). We further show that different components of the Rb-E2F network can be experimentally perturbed, following computer model predictions, to coarse- or fine-tune the E2F-switching threshold and drive cells into varying quiescence depths.

Cellular Senescence, Neurological Function, and Redox State

SIGNIFICANCE

Cellular senescence, characterized by permanent cell cycle arrest, has been extensively studied in mitotic cells such as fibroblasts. However, senescent cells have also been observed in the brain. Even though it is recognized that cellular energetic metabolism and redox homeostasis are perturbed in the aged brain and neurodegenerative diseases (NDDs), it is still unknown which alterations in the overall physiology can stimulate cellular senescence induction and their relationship with the former events. Recent Advances: Recent findings have shown that during prolonged inflammatory and pathologic events, the blood-brain barrier could be compromised and immune cells might enter the brain; this fact along with the brain's high oxygen dependence might result in oxidative damage to macromolecules and therefore senescence induction. Thus, cellular senescence in different brain cell types is revised here.

CRITICAL ISSUES

Most information related to cellular senescence in the brain has been obtained from research in glial cells since it has been assumed that the senescent phenotype is a feature exclusive to mitotic cells. Nevertheless, neurons with senescence hallmarks have been observed in old mouse brains. Therefore, although this is a controversial topic in the field, here we summarize and integrate the observations from several studies and propose that neurons indeed senesce.

FUTURE DIRECTIONS

It is still unknown which alterations in the overall metabolism can stimulate senescence induction in the aged brain, what are the mechanisms and signaling pathways, and what is their relationship to NDD development. The understanding of these processes will expose new targets to intervene age-associated pathologies.-Antioxid. Redox Signal. 28, 1704-1723.

Sleeping Beauty and the Microenvironment Enchantment: Microenvironmental Regulation of the Proliferation-Quiescence Decision in Normal Tissues and in Cancer Development

Cells from prokaryota to the more complex metazoans cease proliferating at some point in their lives and enter a reversible, proliferative-dormant state termed quiescence. The appearance of quiescence in the course of evolution was essential to the acquisition of multicellular specialization and compartmentalization and is also a central aspect of tissue function and homeostasis. But what makes a cell cease proliferating even in the presence of nutrients, growth factors, and mitogens? And what makes some cells "wake up" when they should not, as is the case in cancer? Here, we summarize and discuss evidence showing how microenvironmental cues such as those originating from metabolism, extracellular matrix (ECM) composition and arrangement, neighboring cells and tissue architecture control the cellular proliferation-quiescence decision, and how this complex regulation is corrupted in cancer.

The oncogenic effects of HES1 on salivary adenoid cystic carcinoma cell growth and metastasis

Background

Our previous study demonstrated a close relationship between NOTCH signaling pathway and salivary adenoid cystic carcinoma (SACC). HES1 is a well-known target gene of NOTCH signaling pathway. The purpose of the present study was to further explore the molecular mechanism of HES1 in SACC.

Methods

Comparative transcriptome analyses by RNA-Sequencing (RNA-Seq) were employed to reveal NOTCH1 downstream gene in SACC cells. Immunohistochemical staining was used to detect the expression of HES1 in clinical samples. After HES1-siRNA transfected into SACC LM cells, the cell proliferation and cell apoptosis were tested by suitable methods; animal model was established to detect the change of growth ability of tumor. Transwell and wound healing assays were used to evaluate cell metastasis and invasion.

Results

We found that HES1 was strongly linked to NOTCH signaling pathway in SACC cells. The immunohistochemical results implied the high expression of HES1 in cancerous tissues. The growth of SACC LM cells transfected with HES1-siRNAs was significantly suppressed in vitro and tumorigenicity in vivo by inducing cell apoptosis. After HES1 expression was silenced, the SACC LM cell metastasis and invasion ability was suppressed.

Conclusions

The results of this study demonstrate that HES1 is a specific downstream gene of NOTCH1 and that it contributes to SACC proliferation, apoptosis and metastasis. Our findings serve as evidence indicating that HES1 may be useful as a clinical target in the treatment of SACC.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4350-5) contains supplementary material, which is available to authorized users.

Single-cell profiling of the developing mouse brain and spinal cord with split-pool barcoding

To facilitate scalable profiling of single cells, we developed split-pool ligation-based transcriptome sequencing (SPLiT-seq), a single-cell RNA-seq (scRNA-seq) method that labels the cellular origin of RNA through combinatorial barcoding. SPLiT-seq is compatible with fixed cells or nuclei, allows efficient sample multiplexing, and requires no customized equipment. We used SPLiT-seq to analyze 156,049 single-nucleus transcriptomes from postnatal day 2 and 11 mouse brains and spinal cords. More than 100 cell types were identified, with gene expression patterns corresponding to cellular function, regional specificity, and stage of differentiation. Pseudotime analysis revealed transcriptional programs driving four developmental lineages, providing a snapshot of early postnatal development in the murine central nervous system. SPLiT-seq provides a path toward comprehensive single-cell transcriptomic analysis of other similarly complex multicellular systems.

Cancer reversion with oocyte extracts is mediated by cell cycle arrest and induction of tumour dormancy

Inducing stable control of tumour growth by tumour reversion is an alternative approach to cancer treatment when eradication of the disease cannot be achieved. The process requires re-establishment of normal control mechanisms that are lost in cancer cells so that abnormal proliferation can be halted. Embryonic environments can reset cellular programmes and we previously showed that axolotl oocyte extracts can reprogram breast cancer cells and reverse their tumorigenicity. In this study, we analysed the gene expression profiles of oocyte extract-treated tumour xenografts to show that tumour reprogramming involves cell cycle arrest and acquisition of a quiescent state. Tumour dormancy is associated with increased P27 expression, restoration of RB function and downregulation of mitogen-activated signalling pathways. We also show that the quiescent state is associated with increased levels of H4K20me3 and decreased H4K20me1, an epigenetic profile leading to chromatin compaction. The epigenetic reprogramming induced by oocyte extracts is required for RB hypophosphorylation and induction of P27 expression, both occurring during exposure to the extracts and stably maintained in reprogrammed tumour xenografts. Therefore, this study demonstrates the value of oocyte molecules for inducing tumour reversion and for the development of new chemoquiescence-based therapies.

Fanconi anemia core complex-dependent HES1 mono-ubiquitination regulates its transcriptional activity

OBJECTIVE

The Hairy Enhancer of Split 1 (HES1) is a transcriptional repressor that regulates cellular proliferation and differentiation during development. We previously found an interaction between HES1 and Fanconi anemia (FA) proteins. FA is a hematological and developmental disorder caused by mutations in more than 20 different genes. Eight FA gene products form a nuclear core complex containing E3 ligase activity required for mono-ubiquitination of FANCD2 and FANCI, both of which are FA proteins. Given that HES1 interacts with members of the FA core complex, the aim of this study was to determine whether HES1 is mono-ubiquitinated via the FA core complex.

RESULTS

We show that HES1 is mono-ubiquitinated on a highly-conserved lysine residue that is located within a FA-like recognition motif. HES1 modification is dependent on a functional FA complex. Absence of HES1 mono-ubiquitination affects transcriptional repression of its own promoter. This study uncovers a novel post-translational modification of HES1 that regulates its transcriptional activity and suggests that ubiquitination of HES1 occurs in a FA core complex-dependent manner.

FOXOs Maintaining the Equilibrium for Better or for Worse

A paradigm shift is emerging within the FOXO field and accumulating evidence indicates that we need to reappreciate the role of FOXOs, at least in cancer development. Here, we discuss the possibility that FOXOs are both tumor suppressors as well as promoters of tumor progression. This is mostly dependent on the biological context. Critical to this dichotomous role is the notion that FOXOs are central in preserving cellular homeostasis in redox control, genomic stability, and protein turnover. From this perspective, a paradoxical role in both suppressing and enhancing tumor progression can be reconciled. As many small molecules targeting the PI3K pathway are developed by big pharmaceutical companies and/or are in clinical trial, we will discuss what the consequences may be for the context-dependent role of FOXOs in tumor development in treatment options based on active PI3K signaling in tumors.

Notch and Senescence

Cellular senescence, previously thought of as an autonomous tumour suppressor mechanism, is emerging as a phenotype and effector present throughout the life of an organism from embryogenesis to senile decline. Senescent cells have powerful non-autonomous effects upon multiple players within their microenvironment mainly through their secretory phenotype. How senescent cells co-ordinate numerous, sometimes functionally contrasting outputs through their secretome had previously been unclear. The Notch pathway, originally identified for its involvement in Drosophila wing development, has more recently been found to underpin diverse effects in human cancer. Here we discuss recent findings that suggest that Notch is intimately involved in the development of senescence and how it acts to co-ordinate the composition and functional effects of the senescence secretome. We also highlight the complex physical and functional interplay between Notch and p53, critical to both senescence and cancer. Understanding the interplay between Notch, p53 and senescence could allow us develop the therapeutics of the future for cancer and ageing.

Analysis of MicroRNA-Mediated Translation Activation of In Vitro Transcribed Reporters in Quiescent Cells

Quiescence (G0) is defined as an assortment of cell cycle arrested states that exhibit distinct properties. Leukemias harbor a subpopulation of G0 cells that can be enriched by growth factor deprivation or serum starvation. Target site reporters with shortened poly(A) tails show translation activation by microRNAs, via a noncanonical mechanism, when introduced into the nucleus of G0 cells. This is because recruitment by the activation causing FXR1a-microRNA-protein complex (FXR1a-microRNP) is nuclear and requires shortened poly(A) tails to avoid repressive factors and canonical translation. When introduced into the cytoplasm, target mRNAs and microRNAs are directed toward repression rather than translation activation. Leukemic cell lines are difficult to transfect but can be routinely nucleofected-where in vitro transcribed mRNA reporters and microRNAs are introduced into the nucleus of G0 leukemic cells. Nucleofection of a microRNA target reporter and either cognate, targeting microRNA, or control microRNA, into the nucleus of G0 cells, enables analysis of translation activation by microRNAs in G0. We discuss a modified protocol that we developed for transfection of mRNAs along with microRNAs to test translation regulation by microRNAs in G0 leukemic cells.

ML-Space: Hybrid Spatial Gillespie and Particle Simulation of Multi-Level Rule-Based Models in Cell Biology

Spatio-temporal dynamics of cellular processes can be simulated at different levels of detail, from (deterministic) partial differential equations via the spatial Stochastic Simulation algorithm to tracking Brownian trajectories of individual particles. We present a spatial simulation approach for multi-level rule-based models, which includes dynamically hierarchically nested cellular compartments and entities. Our approach ML-Space combines discrete compartmental dynamics, stochastic spatial approaches in discrete space, and particles moving in continuous space. The rule-based specification language of ML-Space supports concise and compact descriptions of models and to adapt the spatial resolution of models easily.

A Novel Notch-YAP Circuit Drives Stemness and Tumorigenesis in Embryonal Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), a cancer characterized by skeletal muscle features, is the most common soft-tissue sarcoma of childhood. While low- and intermediate-risk groups have seen improved outcomes, high-risk patients still face a 5-year survival rate of <30%, a statistic that has not changed in over 40 years. Understanding the biologic underpinnings of RMS is critical. The developmental pathways of Notch and YAP have been identified as potent but independent oncogenic signals that support the embryonal variant of RMS (eRMS). Here, the cross-talk between these pathways and the impact on eRMS tumorigenesis is reported. Using human eRMS cells grown as three-dimensional (3D) rhabdospheres, which enriches in stem cells, it was found that Notch signaling transcriptionally upregulates YAP1 gene expression and YAP activity. Reciprocally, YAP transcriptionally upregulates the Notch ligand genes JAG1 and DLL1 and the core Notch transcription factor RBPJ This bidirectional circuit boosts expression of key stem cell genes, including SOX2, which is functionally required for eRMS spheres. Silencing this circuit for therapeutic purposes may be challenging, because the inhibition of one node (e.g., pharmacologic Notch blockade) can be rescued by upregulation of another (constitutive YAP expression). Instead, dual inhibition of Notch and YAP is necessary. Finally, supporting the existence of this circuit beyond a model system, nuclear Notch and YAP protein expression are correlated in human eRMS tumors, and YAP suppression in vivo decreases Notch signaling and SOX2 expression.Implications: This study identifies a novel oncogenic signaling circuit driving eRMS stemness and tumorigenesis, and provides evidence and rationale for combination therapies co-targeting Notch and YAP. Mol Cancer Res; 15(12); 1777-91. ©2017 AACR.

Survival in Quiescence Requires the Euchromatic Deployment of Clr4/SUV39H by Argonaute-Associated Small RNAs

Quiescence (G0) is a ubiquitous stress response through which cells enter reversible dormancy, acquiring distinct properties including reduced metabolism, resistance to stress, and long life. G0 entry involves dramatic changes to chromatin and transcription of cells, but the mechanisms coordinating these processes remain poorly understood. Using the fission yeast, here, we track G0-associated chromatin and transcriptional changes temporally and show that as cells enter G0, their survival and global gene expression programs become increasingly dependent on Clr4/SUV39H, the sole histone H3 lysine 9 (H3K9) methyltransferase, and RNAi proteins. Notably, G0 entry results in RNAi-dependent H3K9 methylation of several euchromatic pockets, prior to which Argonaute1-associated small RNAs from these regions emerge. Overall, our data reveal another function for constitutive heterochromatin proteins (the establishment of the global G0 transcriptional program) and suggest that stress-induced alterations in Argonaute-associated sRNAs can target the deployment of transcriptional regulatory proteins to specific sequences.

ATRX is a regulator of therapy induced senescence in human cells

Senescence is a state of stable cell cycle exit with important implications for development and disease. Here, we demonstrate that the chromatin remodeling enzyme ATRX is required for therapy-induced senescence. ATRX accumulates in nuclear foci and is required for therapy-induced senescence in multiple types of transformed cells exposed to either DNA damaging agents or CDK4 inhibitors. Mobilization into foci depends on the ability of ATRX to interact with H3K9me3 histone and HP1. Foci form soon after cells exit the cell cycle, before other hallmarks of senescence appear. Eliminating ATRX in senescent cells destabilizes the senescence-associated heterochromatic foci. Additionally, ATRX binds to and suppresses expression from the HRAS locus; repression of HRAS is sufficient to promote the transition of quiescent cells into senescence and preventing repression blocks progression into senescence. Thus ATRX is a critical regulator of therapy-induced senescence and acts in multiple ways to drive cells into this state.

Therapy induced senescence (TIS) is a growth suppressive program activated by cytostatic agents in some cancer cells. Here the authors show that the chromatin remodeling enzyme ATRX is a regulator of TIS and drives cells into this state via multiple mechanisms.

Exit from quiescence displays a memory of cell growth and division

Reactivating quiescent cells to proliferate is critical to tissue repair and homoeostasis. Quiescence exit is highly noisy even for genetically identical cells under the same environmental conditions. Deregulation of quiescence exit is associated with many diseases, but cellular mechanisms underlying the noisy process of exiting quiescence are poorly understood. Here we show that the heterogeneity of quiescence exit reflects a memory of preceding cell growth at quiescence induction and immediate division history before quiescence entry, and that such a memory is reflected in cell size at a coarse scale. The deterministic memory effects of preceding cell cycle, coupled with the stochastic dynamics of an Rb-E2F bistable switch, jointly and quantitatively explain quiescence-exit heterogeneity. As such, quiescence can be defined as a distinct state outside of the cell cycle while displaying a sequential cell order reflecting preceding cell growth and division variations.

The quiescence-exit process is noisy even in genetically identical cells under the same environmental conditions. Here the authors show that the heterogeneity of quiescence exit reflects a memory of preceding cell growth at quiescence induction and immediate division history prior to quiescence entry.

Epigenetic modification of TLE1 induce abnormal differentiation in diabetic mice intestinal epithelium

The intestinal epithelium cells (IECs) in diabetes mellitus (DM) patients have been proven to be abnormally differentiated. During the differentiation of IECs, epigenetic modification acts as an important regulator. In this study, we aimed to examine the epigenetic alteration of Transducin-like Enhancer of Split 1 (TLE1), a multitask transcriptional co-repressor, contributing to the differentiation homeostasis in IECs of DM mice. The IECs of type 2 diabetic mice model were isolated and collected. Methylation states of whole genomic DNA promoter regions were investigated by microarray. Methylated-specific PCR was used to detect the methylation state of TLE1 promoter in DM mice IECs. The expression of TLE1, Hes1, and differentiated cell markers were measured through real-time PCR, Western blots, and immunohistochemistry; by transfection assay, TLE1 or Hes1 was independently down-regulated in intestinal epithelium cell line, IEC-6. Subsequent modulation on TLE1, Hes1, and differentiated intestinal cell markers were detected. Global gene promoter regions in DM intestinal epithelium were less methylated comparing to normal control. The expression of TLE1 was significantly increased via hypomethylated activation in DM mice IECs. Hes1 was significantly suppressed and the terminal cell markers abnormally expressed in DM mice IECs (P < 0.05). Inhibition or induction on the abundance of TLE1 in IEC-6 cell line resulted in the corresponding dysregulation of Hes1 and intestinal epithelium differentiation (P < 0.05). Demethylation of TLE1 promoter region activates the self-expression in diabetic mice IECs. Subsequently, TLE1, through the transcriptional suppression on expression of Hes1, contributes to the aberrant differentiation of IECs in DM mice.

A Notch-independent mechanism contributes to the induction of Hes1 gene expression in response to hypoxia in P19 cells

Hes1 is a Notch target gene that plays a major role during embryonic development. Previous studies have shown that HIF-1α can interact with the Notch intracellular domain and enhance Notch target gene expression. In this study, we have identified a Notch-independent mechanism that regulates the responsiveness of the Hes1 gene to hypoxia. Using P19 cells we show that silencing the Notch DNA binding partner CSL does not prevent hypoxia-dependent upregulation of Hes1 expression. In contrast to CSL, knockdown of HIF-1α or Arnt expression prevents Hes1 induction in hypoxia. Deletion analysis of the Hes1 promoter identified a minimal region near the transcription start site that is still responsive to hypoxia. In addition, we show that mutating the GA-binding protein (GABP) motif significantly reduced Hes1 promoter-responsiveness to hypoxia or to HIF-1 overexpression whereas mutation of the hypoxia-responsive element (HRE) present in this region had no effect. Chromatin immunoprecipitation assays demonstrated that HIF-1α binds to the proximal region of the Hes1 promoter in a Notch-independent manner. Using the same experimental approach, the presence of GABPα and GABPβ1 was also observed in the same region of the promoter. Loss- and gain-of-function studies demonstrated that Hes1 gene expression is upregulated by hypoxia in a GABP-dependent manner. Finally, co-immunoprecipitation assays demonstrated that HIF-1α but not HIF-2α is able to interact with either GABPα or GABPβ1. These results suggest a Notch-independent mechanism where HIF-1 and GABP contribute to the upregulation of Hes1 gene expression in response to hypoxia.

Hairy/enhancer of Split Homologue-1 Suppresses Vascular Endothelial Growth Factor-induced Angiogenesis via Downregulation of Osteopontin Expression

Angiogenesis plays a critical role in the progression and vulnerability of atherosclerotic plaques; however, the orchestration of angiogenesis in atherosclerotic plaque formation remains unclear. The results of microarray analysis, real-time PCR and immunohistochemical analyses showed that Hairy/enhancer of split homologue-1 (Hes-1) expression was significantly decreased, while that of osteopontin (OPN) was increased, in atherosclerotic plaques. Meanwhile, immunofluorescence results demonstrated that both Hes-1 and OPN were expressed in endothelial cells (ECs) of neovessels in atherosclerotic plaques. The results of an in vitro study showed that Hes-1 was downregulated, while OPN was upregulated, in a time- and dose-dependent manner in human umbilical vein endothelial cells (HUVECs) by VEGF treatment. In addition, Hes-1 knockdown was found to have transcriptional promotion effect on OPN expression in HUVECs and enhance OPN-induced angiogenesis in response to VEGF. On the contrary, Hes-1 overexpression inhibited OPN expression in HUVECs and reduced angiogenesis in vitro and in vivo. The results of this study suggest that decreased Hes-1 expression in atherosclerotic plaques exaggerate VEGF-induced angiogenesis by upregulating OPN. Therefore, restoring Hes-1 expression and inhibiting OPN expression may be a promising strategy to prevent vulnerable plaque formation in patients with atherosclerosis.

NOTCH1 Signaling Regulates Self-Renewal and Platinum Chemoresistance of Cancer Stem-like Cells in Human Non-Small Cell Lung Cancer

Cancer stem-like cells (CSC) are thought to drive tumor initiation, metastasis, relapse, and therapeutic resistance, but their specific pathogenic characters in many cancers, including non-small cell lung cancer (NSCLC), have yet to be well defined. Here, we develop findings that the growth factor HGF promotes CSC sphere formation in NSCLC cell populations. In patient-derived sphere-forming assays (PD-SFA) with HGF, CD49f and CD104 were defined as novel markers of lung CSC (LCSC). In particular, we isolated a subpopulation of CD166⁺CD49f^hiCD104^-Lin^- LCSC present in all human specimens of NSCLC examined, regardless of their histologic subtypes or genetic driver mutations. This specific cell population was tumorigenic and capable of self-renewal, giving rise to tumor spheres in vitro and orthotopic lung tumors in immune-compromised mice. Mechanistic investigations established that NOTCH1 was preferentially expressed in this cell subpopulation and required for self-renewal via the transcription factor HES1. Through a distinct HES1-independent pathway, NOTCH1 also protected LCSCs from cisplatin-induced cell death. Notably, treatment with a γ-secretase inhibitor that blunts NOTCH1 function ablated self-renewing LCSC activity and restored platinum sensitivity in vitro and in vivo Overall, our results define the pathogenic characters of a cancer stem-like subpopulation in lung cancer, the targeting of which may relieve platinum resistance in this disease. Cancer Res; 77(11); 3082-91. ©2017 AACR.

Widespread changes in mRNA stability contribute to quiescence-specific gene expression patterns in a fibroblast model of quiescence

Background

Quiescence, reversible exit from the cell division cycle, is characterized by large-scale changes in steady-state gene expression, yet mechanisms controlling these changes are in need of further elucidation. In order to characterize the effects of post-transcriptional control on the quiescent transcriptome in human fibroblasts, we determined mRNA decay rates for over 10,000 genes using a transcription shut-off time-course.

Results

We found that ~500 of the genes monitored exhibited significant changes in decay rate upon quiescence induction. Genes involved in RNA processing and ribosome biogenesis were destabilized with quiescence, while genes involved in the developmental process were stabilized with quiescence. Moreover, extracellular matrix genes demonstrated an upregulation of gene expression that corresponded with a stabilization of these transcripts. Additionally, targets of a quiescence-associated microRNA (miR-29) were significantly enriched in the fraction of transcripts that were stabilized during quiescence.

Conclusion

Coordinated stability changes in clusters of genes with important functions in fibroblast quiescence maintenance are highly correlated with quiescence gene expression patterns. Analysis of miR-29 target decay rates suggests that microRNA-induced changes in RNA stability are important contributors to the quiescence gene expression program in fibroblasts. The identification of multiple stability-related gene clusters suggests that other posttranscriptional regulators of transcript stability may contribute to the coordination of quiescence gene expression. Such regulators may ultimately prove to be valuable targets for therapeutics that target proliferative cells, for instance, in cancer or fibrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3521-0) contains supplementary material, which is available to authorized users.

Spatio-temporal models of synthetic genetic oscillators

Signal transduction pathways play a major role in many important aspects of cellular function e.g. cell division, apoptosis. One important class of signal transduction pathways is gene regulatory networks (GRNs). In many GRNs, proteins bind to gene sites in the nucleus thereby altering the transcription rate. Such proteins are known as transcription factors. If the binding reduces the transcription rate there is a negative feedback leading to oscillatory behaviour in mRNA and protein levels, both spatially (e.g. by observing fluorescently labelled molecules in single cells) and temporally (e.g. by observing protein/mRNA levels over time). Recent computational modelling has demonstrated that spatial movement of the molecules is a vital component of GRNs and may cause the oscillations. These numerical findings have subsequently been proved rigorously i.e. the diffusion coefficient of the protein/mRNA acts as a bifurcation parameter and gives rise to a Hopf bifurcation. In this paper we first present a model of the canonical GRN (the Hes1 protein) and show the effect of varying the spatial location of gene and protein production sites on the oscillations. We then extend the approach to examine spatio-temporal models of synthetic gene regulatory networks e.g. n-gene repressilators and activator-repressor systems.

Cell cycle proliferation decisions: the impact of single cell analyses

Cell proliferation is a fundamental requirement for organismal development and homeostasis. The mammalian cell division cycle is tightly controlled to ensure complete and precise genome duplication and segregation of replicated chromosomes to daughter cells. The onset of DNA replication marks an irreversible commitment to cell division, and the accumulated efforts of many decades of molecular and cellular studies have probed this cellular decision, commonly called the restriction point. Despite a long-standing conceptual framework of the restriction point for progression through G1 phase into S phase or exit from G1 phase to quiescence (G0), recent technical advances in quantitative single cell analysis of mammalian cells have provided new insights. Significant intercellular heterogeneity revealed by single cell studies and the discovery of discrete subpopulations in proliferating cultures suggests the need for an even more nuanced understanding of cell proliferation decisions. In this review, we describe some of the recent developments in the cell cycle field made possible by quantitative single cell experimental approaches.

Mimicking Muscle Stem Cell Quiescence in Culture: Methods for Synchronization in Reversible Arrest

Growing evidence supports the view that in adult stem cells, the defining stem cell features of potency and self-renewal are associated with the quiescent state. Thus, uncovering the molecular logic of this reversibly arrested state underlies not only a fundamental understanding of adult tissue dynamics but also hopes for therapeutic regeneration and rejuvenation of damaged or aging tissue. A key question concerns how adult stem cells use quiescence to establish or reinforce the property of self-renewal. Since self-renewal is largely studied by assays that measure proliferation, the concept of self-renewal programs imposed during non-proliferating conditions is counterintuitive. However, there is increasing evidence generated by deconstructing the quiescent state that highlights how programs characteristic of this particular cell cycle exit may enhance stem cell capabilities, through both cell-intrinsic and extrinsic programs.Toward this end, culture models that recapitulate key aspects of stem cell quiescence are useful for molecular analysis to explore attributes and regulation of the quiescent state. In this chapter, we review the different methods used to generate homogeneous populations of quiescent muscle cells, largely by manipulating culture conditions that feed into core signaling programs that regulate the cell cycle. We also provide detailed protocols developed or refined in our lab over the past two decades.

FXR1a-associated microRNP: A driver of specialized non-canonical translation in quiescent conditions

Eukaryotic protein synthesis is a multifaceted process that requires coordination of a set of translation factors in a particular cellular state. During normal growth and proliferation, cells generally make their proteome via conventional translation that utilizes canonical translation factors. When faced with environmental stress such as growth factor deprivation, or in response to biological cues such as developmental signals, cells can reduce canonical translation. In this situation, cells adapt alternative modes of translation to make specific proteins necessary for required biological functions under these distinct conditions. To date, a number of alternative translation mechanisms have been reported, which include non-canonical, cap dependent translation and cap independent translation such as IRES mediated translation. Here, we discuss one of the alternative modes of translation mediated by a specialized microRNA complex, FXR1a-microRNP that promotes non-canonical, cap dependent translation in quiescent conditions, where canonical translation is reduced due to low mTOR activity.

Cancer Stem Cells in Squamous Cell Carcinoma

Cancer stem cells (CSCs) are found in many cancer types, including squamous cell carcinoma (SCC). CSCs initiate cancer formation and are linked to metastasis and resistance to therapies. Studies have revealed that several distinct CSC populations coexist in SCC and that tumor initiation and metastatic potential of these populations can be uncoupled. Therefore, it is critical to understand CSC biology to develop novel CSC-targeted therapies for patients with SCC with poor prognoses. This review compares the properties of CSCs in SCC with normal stem cells in the skin, summarizes current advances and characteristics of CSCs, and considers the challenges for CSC-targeted treatment of SCC.

Extracellular Signal-Regulated Kinase 2 and CHOP Restrict the Expression of the Growth Arrest-Specific p20K Lipocalin Gene to G0

The activation of the growth arrest-specific (gas) p20K gene depends on the interaction of C/EBPβ with two elements of a 48-bp promoter region termed the quiescence-responsive unit (QRU). Here we identify extracellular signal-related kinase 2 (ERK2) as a transcriptional repressor of the p20K QRU in cycling chicken embryo fibroblasts (CEF). ERK2 binds to repeated GAAAG sequences overlapping the C/EBPβ sites of the QRU. The recruitment of ERK2 and C/EBPβ is mutually exclusive and dictates the expression of p20K. C/EBP homologous protein (CHOP) was associated with C/EBPβ under conditions promoting endoplasmic reticulum (ER) stress and, to a lesser extent, in cycling CEF but was not detectable when C/EBPβ was immunoprecipitated from contact-inhibited cells. During ER stress, overexpression of CHOP inhibited p20K, while its downregulation promoted p20K, indicating that CHOP is also a potent inhibitor of p20K. Transcriptome analyses revealed that hypoxia-responsive genes are strongly induced in contact-inhibited but not serum-starved CEF, and elevated levels of nitroreductase activity, a marker of hypoxia, were detected at confluence. Conditions of hypoxia (2% O₂) induced growth arrest in subconfluent CEF and markedly stimulated p20K expression, suggesting that the control of proliferation and gas gene expression is closely linked to limiting oxygen concentrations associated with high cell densities.

Effects of Differentiation and Antisenescence from BMSCs to Hepatocy-Like Cells of the PAAm-IGF-1/TNF-α Biomaterial

Aiming at the cells' differentiation phenomenon and senescence problem in liver tissue engineering, this work is designed to synthesize three different chargeable polymers (polypropylene acid (PAAc), polyethylene glycol (PEG), and polypropylene amine (PAAm)) coimmobilized by the insulin-like growth factor 1 (IGF-1) and tumor necrosis factor-α (TNF-α). We explore the hepatocyte differentiation effect and the antisenecence effect of PSt-PAAm-IGF-1/TNF-α biomaterial which was selected from the three different chargeable polymers in bone marrow mesenchymal stem cells (BMSCs). Our work will establish a model for studying the biochemical molecular regulation mechanism and signal transduction pathway of cell senescence in liver tissue engineering, which provide a molecular basis for developing biomaterials for liver tissue engineering.

Phase correlation imaging of unlabeled cell dynamics

We present phase correlation imaging (PCI) as a novel approach to study cell dynamics in a spatially-resolved manner. PCI relies on quantitative phase imaging time-lapse data and, as such, functions in label-free mode, without the limitations associated with exogenous markers. The correlation time map outputted in PCI informs on the dynamics of the intracellular mass transport. Specifically, we show that PCI can extract quantitatively the diffusion coefficient map associated with live cells, as well as standard Brownian particles. Due to its high sensitivity to mass transport, PCI can be applied to studying the integrity of actin polymerization dynamics. Our results indicate that the cyto-D treatment blocking the actin polymerization has a dominant effect at the large spatial scales, in the region surrounding the cell. We found that PCI can distinguish between senescent and quiescent cells, which is extremely difficult without using specific markers currently. We anticipate that PCI will be used alongside established, fluorescence-based techniques to enable valuable new studies of cell function.

HES1 in immunity and cancer

Hairy and enhancer of split homolog-1 (HES1) is a part of an extensive family of basic helix-loop-helix (bHLH) proteins and plays a crucial role in the control and regulation of cell cycle, proliferation, cell differentiation, survival and apoptosis in neuronal, endocrine, T-lymphocyte progenitors as well as various cancers. HES1 is a transcription factor which is regulated by the NOTCH, Hedgehog and Wnt signalling pathways. Aberrant expression of these pathways is a common feature of cancerous cells. There appears to be a fine and complicated crosstalk at the molecular level between the various signalling pathways and HES1, which contributes to its effects on the immune response and cancers such as leukaemia. Several mechanisms have been proposed, including an enhanced invasiveness and metastasis by inducing epithelial mesenchymal transition (EMT), in addition to its strict requirement for tumour cell survival. In this review, we summarize the current biology and molecular mechanisms as well as its use as a clinical target in cancer therapeutics.

Combination with γ-secretase inhibitor prolongs treatment efficacy of BRAF inhibitor in BRAF-mutated melanoma cells

Oncogenic triggering of the MAPK pathway in melanocytes results in senescence, and senescence escape is considered as one critical step for melanocytic transformation. In melanoma, induction of a senescent-like state by BRAF-inhibitors (BRAFi) in a fraction of treated cells - instead of killing - contributes to the repression of tumor growth, but may also provide a source for relapse. Here, we demonstrate that NOTCH activation in melanocytes is not only growth-promoting but it also protects these cells against oncogene-induced senescence. In turn, treatment of melanoma cells with an inhibitor of the NOTCH-activating enzyme γ-secretase led to induction of a senescent-like status in a fraction of the cells but overall achieved only a moderate inhibition of melanoma cell growth. However, combination of γ-secretase inhibitor (GSI) with BRAFi markedly increased the treatment efficacy particularly in long-term culture. Moreover, even melanoma cells starting to regrow after continuous BRAFi treatment - the major problem of BRAFi therapy in patients - can still be affected by the combination treatment. Thus, combining GSI with BRAFi increases the therapeutic efficacy by, at least partially, prolonging the senescent-like state of treated cells.

C-type natriuretic peptide in combination with sildenafil attenuates proliferation of rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is a malignant mesenchymal tumor and the most common soft tissue sarcoma in children. Because of several complications associated with intensive multimodal therapies, including growth disturbance and secondary cancer, novel therapies with less toxicity are urgently needed. C‐type natriuretic peptide (CNP), an endogenous peptide secreted by endothelial cells, exerts antiproliferative effects in multiple types of mesenchymal cells. Therefore, we investigated whether CNP attenuates proliferation of RMS cells. We examined RMS patient samples and RMS cell lines. All RMS clinical samples expressed higher levels of guanylyl cyclase B (GC‐B), the specific receptor for CNP, than RMS cell lines. GC‐B expression in RMS cells decreased with the number of passages in vitro. Therefore, GC‐B stable expression lines were established to mimic clinical samples. CNP increased cyclic guanosine monophosphate (cGMP) levels in RMS cells in a dose‐dependent manner, demonstrating the biological activity of CNP. However, because cGMP is quickly degraded by phosphodiesterases (PDEs), the selective PDE5 inhibitor sildenafil was added to inhibit its degradation. In vitro, CNP, and sildenafil synergistically inhibited proliferation of RMS cells stably expressing GC‐B and decreased Raf‐1, Mitogen‐activated protein kinase kinase (MEK), and extracellular signal‐regulated kinase (ERK) phosphorylation. These results suggested that CNP in combination with sildenafil exerts antiproliferative effects on RMS cells by inhibiting the Raf/MEK/ERK pathway. This regimen exerted synergistic effects on tumor growth inhibition without severe adverse effects in vivo such as body weight loss. Thus, CNP in combination with sildenafil represents a promising new therapeutic approach against RMS.

Hes1: a key role in stemness, metastasis and multidrug resistance

Hes1 is one mammalian counterpart of the Hairy and Enhancer of split proteins that play a critical role in many physiological processes including cellular differentiation, cell cycle arrest, apoptosis and self-renewal ability. Recent studies have shown that Hes1 functions in the maintenance of cancer stem cells (CSCs), metastasis and antagonizing drug-induced apoptosis. Pathways that are involved in the up-regulation of Hes1 level canonically or non-canonically, such as the Hedgehog, Wnt and hypoxia pathways are frequently aberrant in cancer cells. Here, we summarize the recent data supporting the idea that Hes1 may have an important function in the maintenance of cancer stem cells self-renewal, cancer metastasis, and epithelial-mesenchymal transition (EMT) process induction, as well as chemotherapy resistance, and conclude with the possible mechanisms by which Hes1 functions have their effect, as well as their crosstalk with other carcinogenic signaling pathways.

Coordinating cell proliferation and differentiation: Antagonism between cell cycle regulators and cell type-specific gene expression

Cell proliferation and differentiation show a remarkable inverse relationship. Precursor cells continue division before acquiring a fully differentiated state, while terminal differentiation usually coincides with proliferation arrest and permanent exit from the division cycle. Mechanistic insight in the temporal coordination between cell cycle exit and differentiation has come from studies of cells in culture and genetic animal models. As initially described for skeletal muscle differentiation, temporal coordination involves mutual antagonism between cyclin-dependent kinases that promote cell cycle entry and transcription factors that induce tissue-specific gene expression. Recent insights highlight the contribution of chromatin-regulating complexes that act in conjunction with the transcription factors and determine their activity. In particular SWI/SNF chromatin remodelers contribute to dual regulation of cell cycle and tissue-specific gene expression during terminal differentiation. We review the concerted regulation of the cell cycle and cell type-specific transcription, and discuss common mutations in human cancer that emphasize the clinical importance of proliferation versus differentiation control.

[Neural stem cells and Notch signalling]

Development and repair of the nervous system are based on the existence of neural stem cells (NSCs) able to generate neurons and glial cells. Among the mechanisms that are involved in the control of embryo or adult NSCs, the Notch signalling plays a major role. In embryo, the pathway participates in the maintenance of NSCs during all steps of development of the central nervous system which starts with the production of neurons also called neurogenesis and continues with gliogenesis giving rise to astrocytes and oligodendrocytes. During the postnatal and adult period, Notch signalling is still present in the major neurogenic areas, the subventricular zone of the lateral ventricles and the subgranular zone of the hippocampus. In these regions, Notch maintains NSC quiescence, contributes to the heterogeneity of these cells and displays pleiotropic effects during the regeneration process occurring after a lesion.

Hes1 Increases the Invasion Ability of Colorectal Cancer Cells via the STAT3-MMP14 Pathway

The Notch pathway contributes to self-renewal of tumor-initiating cell and inhibition of normal colonic epithelial cell differentiation. Deregulated expression of Notch1 and Jagged1 is observed in colorectal cancer. Hairy/enhancer of split (HES) family, the most characterized targets of Notch, involved in the development of many cancers. In this study, we explored the role of Hes1 in the tumorigenesis of colorectal cancer. Knocking down Hes1 induced CRC cell senescence and decreased the invasion ability, whereas over-expression of Hes1 increased STAT3 phosphorylation activity and up-regulated MMP14 protein level. We further explored the expression of Hes1 in human colorectal cancer and found high Hes1 mRNA expression is associated with poor prognosis in CRC patients. These findings suggest that Hes1 regulates the invasion ability through the STAT3-MMP14 pathway in CRC cells and high Hes1 expression is a predictor of poor prognosis of CRC.

Cell cycle and p53 gate the direct conversion of human fibroblasts to dopaminergic neurons

The direct conversion of fibroblasts to induced dopaminergic (iDA) neurons and other cell types demonstrates the plasticity of cell fate. The low efficiency of these relatively fast conversions suggests that kinetic barriers exist to safeguard cell-type identity. Here we show that suppression of p53, in conjunction with cell cycle arrest at G1 and appropriate extracellular environment, markedly increase the efficiency in the transdifferentiation of human fibroblasts to iDA neurons by Ascl1, Nurr1, Lmx1a and miR124. The conversion is dependent on Tet1, as G1 arrest, p53 knockdown or expression of the reprogramming factors induces Tet1 synergistically. Tet1 knockdown abolishes the transdifferentiation while its overexpression enhances the conversion. The iDA neurons express markers for midbrain DA neurons and have active dopaminergic transmission. Our results suggest that overcoming these kinetic barriers may enable highly efficient epigenetic reprogramming in general and will generate patient-specific midbrain DA neurons for Parkinson's disease research and therapy.

The efficiency of reprogramming of fibroblasts into induced dopaminergic neurons is often low. Here, Jiang et al. demonstrate increased transdifferentiation rates by inducing cell cycle arrest, suppressing p53, Tet 1 and by adding neurotrophic factors to the media.

The helix-loop-helix protein id1 controls stem cell proliferation during regenerative neurogenesis in the adult zebrafish telencephalon

The teleost brain has the remarkable ability to generate new neurons and to repair injuries during adult life stages. Maintaining life-long neurogenesis requires careful management of neural stem cell pools. In a genome-wide expression screen for transcription regulators, the id1 gene, encoding a negative regulator of E-proteins, was found to be upregulated in response to injury. id1 expression was mapped to quiescent type I neural stem cells in the adult telencephalic stem cell niche. Gain and loss of id1 function in vivo demonstrated that Id1 promotes stem cell quiescence. The increased id1 expression observed in neural stem cells in response to injury appeared independent of inflammatory signals, suggesting multiple antagonistic pathways in the regulation of reactive neurogenesis. Together, we propose that Id1 acts to maintain the neural stem cell pool by counteracting neurogenesis-promoting signals.

Mislocalization of p27 to the cytoplasm of breast cancer cells confers resistance to anti-HER2 targeted therapy

As a cell cycle inhibitor and tumor suppressor, p27 is frequently misregulated in human cancers. Increased degradation is the most common mechanism of misregulation, however in some cancers, p27 is mislocalized from its cell cycle inhibitory location in the nucleus, to the cytoplasm. In normal cells cytoplasmic p27 has functions that are distinct from its cell cycle-regulatory nuclear functions. Therefore, an important question is whether localization of p27 to the cytoplasm in tumor cells is primarily a mechanism for cancelling its inhibitory effect on cell proliferation, or whether cytoplasmic p27 has more direct oncogenic actions. To study p27 mislocalization in human cancers we screened a panel of common breast cancer cell lines. We observed that p27 accumulated in the cytoplasm exclusively in cell lines that are Her2+. To address the significance of p27 mislocalization in Her2+ breast cancer cells we interrogated the cellular response to the dual-Her2/EGFR kinase inhibitor, lapatinib. Knockdown of p27 using shRNA sensitized Her2+ cells to lapatinib-induced apoptosis. Moreover, expression of a constitutively cytoplasmic form of p27 (p27ΔNLS) reversed the lapatinib-induced apoptosis, suggesting that cytoplasmic p27 contributed to lapatinib resistance in Her2+ breast cancer cells by suppressing apoptosis. Our results suggest that p27 localization may be useful as a predictive biomarker of therapeutic response in patients with Her2+ breast cancers.

Hes1 triggers epithelial-mesenchymal transition (EMT)-like cellular marker alterations and promotes invasion and metastasis of nasopharyngeal carcinoma by activating the PTEN/AKT pathway

Overexpression of the transcriptional factor Hes1 (hairy and enhancer of split-1) has been observed in numerous cancers, but the precise roles of Hes1 in epithelial-mesenchymal transition (EMT), cancer invasion and metastasis remain unknown. Our current study firstly revealed that Hes1 upregulation in a cohort of human nasopharyngeal carcinoma (NPC) biopsies is significantly associated with the EMT, invasive and metastatic phenotypes of cancer. In the present study, we found that Hes1 overexpression triggered EMT-like cellular marker alterations of NPC cells, whereas knockdown of Hes1 through shRNA reversed the EMT-like phenotypes, as strongly supported by Hes1-mediated EMT in NPC clinical specimens described above. Gain-of-function and loss-of-function experiments demonstrated that Hes1 promoted the migration and invasion of NPC cells in vitro. In addition, exogenous expression of Hes1 significantly enhanced the metastatic ability of NPC cells in vivo. Chromatin immunoprecipitation (ChIP) assays showed that Hes1 inhibited PTEN expression in NPC cells through binding to PTEN promoter region. Increased Hes1 expression and decreased PTEN expression were also observed in a cohort of NPC biopsies. Additional studies demonstrated that Hes1-induced EMT-like molecular changes and increased motility and invasion of NPC cells were mediated by PTEN. Taken together, our results suggest, for what we believe is the first time, that Hes1 plays an important role in the invasion and metastasis of NPC through inhibiting PTEN expression to trigger EMT-like phenotypes.