Factors Affecting Liquid-Liquid Phase Separation of RGG Peptides with DNA G-Quadruplex.

Liquid-liquid phase separation (LLPS), mediated by G-quadruplexes (G4s) and intrinsically disordered proteins, particularly those containing RGG domains, plays a critical role in cellular processes and diseases. However, the molecular mechanism and the role of individual amino acid residues of the protein in LLPS with G4 (G4-LLPS) are still unknown. Here, we systematically designed peptides and investigated the roles of arginine residues in G4-LLPS. It was found that the FMRP-derived RGG peptide induced LLPS with G4-forming Myc-DNA, whereas a point-mutated peptide, in which all arginine residues were replaced with lysine, was unable to undergo LLPS, indicating the importance of arginine residues. Moreover, systematically truncated peptides showed that at least five positive net charges of peptide are required to induce G4-LLPS. Furthermore, quantitative investigation demonstrated that the higher binding affinity of peptides with G4 led to a higher LLPS ability, whereas threshold of the binding affinity for undergoing LLPS was identified. These insights elucidate the pivotal role of arginine in G4-LLPS and the specific requirement for multiple arginine residues, contributing to a deeper understanding of the complex interplay between intrinsically disordered proteins and nucleic acids.

Non-canonical olfactory pathway activation induces cell fusion of cervical cancer cells.

Multinucleation occurs in various types of advanced cancers and contributes to their malignant characteristics, including anticancer drug resistance. Therefore, inhibiting multinucleation can improve cancer prognosis; however, the molecular mechanisms underlying multinucleation remain elusive. Here, we introduced a genetic mutation in cervical cancer cells to induce cell fusion-mediated multinucleation. The olfactory receptor OR1N2 was heterozygously mutated in these fused cells; the same OR1N2 mutation was detected in multinucleated cells from clinical cervical cancer specimens. The mutation-induced structural change in the OR1N2 protein activated protein kinase A (PKA), which, in turn, mediated the non-canonical olfactory pathway. PKA phosphorylated and activated furin protease, resulting in the cleavage of the fusogenic protein syncytin-1. Because this cleaved form of syncytin-1, processed by furin, participates in cell fusion, furin inhibitors could suppress multinucleation and reduce surviving cell numbers after anticancer drug treatment. The improved anticancer drug efficacy indicates a promising therapeutic approach for advanced cervical cancers.

Quantitative Effects of the Loop Region on Topology, Thermodynamics, and Cation Binding of DNA G-quadruplexes.

The thermal stability of G-quadruplexes is important for their biological roles. G-quadruplexes are stable in the presence of cations such as K+ and Na+ because these cations coordinate in the G-quartet of four guanine bases. It is well known that the number of G-quartets and the configuration of the guanine bases affect the binding affinity of the cation. Recently, structures formed in the loop regions connecting the guanine stretches have attracted significant attention, because the loop region affects G-quadruplex properties, such as topology, thermal stability, and interactions with proteins and small molecules. Considering these effects, the loop region can also affect the binding affinity of the cations. Here, we designed a series of G-quadruplex-forming DNA sequences that contain a hairpin in a loop region and investigated the effects of the sequence and structure of the loop region on the cation binding affinity as well as the thermal stability of the G-quadruplex as a whole. First, structural analysis of the DNA sequences showed that the hairpin at the loop plays a key role in determining G4 topology (strand orientation). Second, in the case of the G-quadruplexes with the hairpin-forming loop region, it was found that a longer loop length led to a higher thermodynamic stability of the G-quadruplex as well as higher cation binding affinity. In contrast, an unstructured loop region did not lead to such effects. Interestingly, the cation binding affinity was correlated to the thermodynamic stability of the hairpin structure at the loop region. It was quantitatively demonstrated that the stable loop region stabilized the whole G-quadruplex structure, which induced higher cation binding affinity. These systematic and quantitative results showed that the loop region is one of the determinants of cation binding and expanded the possibilities of drug development targeting G4s by stabilizing the loop region.

Development of a Pseudocellular System to Quantify Specific Interactions Determining the G-Quadruplex Function in Cells.

Intracellular chemical microenvironments, including ion concentrations and molecular crowding, play pivotal roles in cell behaviors, such as proliferation, differentiation, and cell death via regulation of gene expression. However, there is no method for quantitative analysis of intracellular environments due to their complexity. Here, we have developed a system for highlighting the environment inside of the cell (SHELL). SHELL is a pseudocellular system, wherein small molecules are removed from the cell and a crowded intracellular environment is maintained. SHELL offers two prominent advantages: (1) It allows for precise quantitative biochemical analysis of a specific factor, and (2) it enables the study of any cell, thereby facilitating the study of target molecule effects in various cellular environments. Here, we used SHELL to study G-quadruplex formation, an event that implicated cancer. We show that G-quadruplexes are more stable in SHELL compared with in vitro conditions. Although malignant transformation perturbs cellular K+ concentrations, environments in SHELL act as buffers against G-quadruplex destabilization at lower K+ concentrations. Notably, the buffering effect was most pronounced in SHELL derived from nonaggressive cancer cells. Stable G-quadruplexes form due to the binding of the G-quadruplex with K+ in different cancer cells. Furthermore, the observed pattern of G-quadruplex-induced transcriptional inhibition in SHELL is consistent with that in living cells at different cancer stages. Our results indicate that ion binding to G-quadruplexes regulates gene expression during pathogenesis.

Inhibitory Effects of Shikonin Dispersion, an Extract of Lithospermum erythrorhizon Encapsulated in ß-1,3-1,6 Glucan, on Streptococcus mutans and Non-Mutans Streptococci.

Shikonin is extracted from the roots of Lithospermum erythrorhizon, and shikonin extracts have been shown to have inhibitory effects on several bacteria. However, shikonin extracts are difficult to formulate because of their poor water solubility. In the present study, we prepared a shikonin dispersion, which was solubilized by the inclusion of ß-1,3-1,6 glucan, and analysed the inhibitory effects of this dispersion on Streptococcus mutans and non-mutans streptococci. The shikonin dispersion showed pronounced anti-S. mutans activity, and inhibited growth of and biofilm formation by this bacterium. The shikonin dispersion also showed antimicrobial and antiproliferative effects against non-mutans streptococci. In addition, a clinical trial was conducted in which 20 subjects were asked to brush their teeth for 1 week using either shikonin dispersion-containing or non-containing toothpaste, respectively. The shikonin-containing toothpaste decreased the number of S. mutans in the oral cavity, while no such effect was observed after the use of the shikonin-free toothpaste. These results suggest that shikonin dispersion has an inhibitory effect on S. mutans and non-mutans streptococci, and toothpaste containing shikonin dispersion may be effective in preventing dental caries.

Loss of p53 function promotes DNA damage-induced formation of nuclear actin filaments.

Tumor suppressor p53 plays a central role in response to DNA damage. DNA-damaging agents modulate nuclear actin dynamics, influencing cell behaviors; however, whether p53 affects the formation of nuclear actin filaments remains unclear. In this study, we found that p53 depletion promoted the formation of nuclear actin filaments in response to DNA-damaging agents, such as doxorubicin (DOXO) and etoposide (VP16). Even though the genetic probes used for the detection of nuclear actin filaments exerted a promotive effect on actin polymerization, the detected formation of nuclear actin filaments was highly dependent on both p53 depletion and DNA damage. Whilst active p53 is known to promote caspase-1 expression, the overexpression of caspase-1 reduced DNA damage-induced formation of nuclear actin filaments in p53-depleted cells. In contrast, co-treatment with DOXO and the pan-caspase inhibitor Q-VD-OPh or the caspase-1 inhibitor Z-YVAD-FMK induced the formation of nuclear actin filament formation even in cells bearing wild-type p53. These results suggest that the p53-caspase-1 axis suppresses DNA damage-induced formation of nuclear actin filaments. In addition, we found that the expression of nLifeact-GFP, the filamentous-actin-binding peptide Lifeact fused with the nuclear localization signal (NLS) and GFP, modulated the structure of nuclear actin filaments to be phalloidin-stainable in p53-depleted cells treated with the DNA-damaging agent, altering the chromatin structure and reducing the transcriptional activity. The level of phosphorylated H2AX (γH2AX), a marker of DNA damage, in these cells also reduced upon nLifeact-GFP expression, whilst details of the functional relationship between the formation of nLifeact-GFP-decorated nuclear actin filaments and DNA repair remained to be elucidated. Considering that the loss of p53 is associated with cancer progression, the results of this study raise a possibility that the artificial reinforcement of nuclear actin filaments by nLifeact-GFP may enhance the cytotoxic effect of DNA-damaging agents in aggressive cancer cells through a reduction in gene transcription.

Inhibitory Effect of Adsorption of Streptococcus mutans onto Scallop-Derived Hydroxyapatite.

Hydroxyapatite adsorbs various substances, but little is known about the effects on oral bacteria of adsorption onto hydroxyapatite derived from scallop shells. In the present study, we analyzed the effects of adsorption of Streptococcus mutans onto scallop-derived hydroxyapatite. When scallop-derived hydroxyapatite was mixed with S. mutans, a high proportion of the bacterial cells adsorbed onto the hydroxyapatite in a time-dependent manner. An RNA sequencing analysis of S. mutans adsorbed onto hydroxyapatite showed that the upregulation of genes resulted in abnormalities in pathways involved in glycogen and histidine metabolism and biosynthesis compared with cells in the absence of hydroxyapatite. S. mutans adsorbed onto hydroxyapatite was not killed, but the growth of the bacteria was inhibited. Electron microscopy showed morphological changes in S. mutans cells adsorbed onto hydroxyapatite. Our results suggest that hydroxyapatite derived from scallop shells showed a high adsorption ability for S. mutans. This hydroxyapatite also caused changes in gene expression related to the metabolic and biosynthetic processes, including the glycogen and histidine of S. mutans, which may result in a morphological change in the surface layer and the inhibition of the growth of the bacteria.

The iron chelator deferriferrichrysin induces paraptosis via extracellular signal-related kinase activation in cancer cells.

Cancer cells generally exhibit increased iron uptake, which contributes to their abnormal growth and metastatic ability. Iron chelators have thus recently attracted attention as potential anticancer agents. Here, we show that deferriferrichrysin (Dfcy), a natural product from Aspergillus oryzae acts as an iron chelator to induce paraptosis (a programmed cell death pathway characterized by ER dilation) in MCF-7 human breast cancer cells and H1299 human lung cancer cells. We first examined the anticancer efficacy of Dfcy in cancer cells and found that Dfcy induced ER dilation and reduced the number of viable cells. Extracellular signal-related kinase (ERK) was activated by Dfcy treatment, and the MEK inhibitor U0126, a small molecule commonly used to inhibit ERK activity, prevented the increase in ER dilation in Dfcy-treated cells. Concomitantly, the decrease in the number of viable cells upon treatment with Dfcy was attenuated by U0126. Taken together, these results demonstrate that the iron chelator Dfcy exhibits anticancer effects via induction of ERK-dependent paraptosis.

Biomolecular Liquid-Liquid Phase Separation for Biotechnology.

The liquid-liquid phase separation (LLPS) of biomolecules induces condensed assemblies called liquid droplets or membrane-less organelles. In contrast to organelles with lipid membrane barriers, the liquid droplets induced by LLPS do not have distinct barriers (lipid bilayer). Biomolecular LLPS in cells has attracted considerable attention in broad research fields from cellular biology to soft matter physics. The physical and chemical properties of LLPS exert a variety of functions in living cells: activating and deactivating biomolecules involving enzymes; controlling the localization, condensation, and concentration of biomolecules; the filtration and purification of biomolecules; and sensing environmental factors for fast, adaptive, and reversible responses. The versatility of LLPS plays an essential role in various biological processes, such as controlling the central dogma and the onset mechanism of pathological diseases. Moreover, biomolecular LLPS could be critical for developing new biotechnologies such as the condensation, purification, and activation of a series of biomolecules. In this review article, we introduce some fundamental aspects and recent progress of biomolecular LLPS in living cells and test tubes. Then, we discuss applications of biomolecular LLPS toward biotechnologies.

Simple and fast screening for structure-selective G-quadruplex ligands.

Structural selectivity of G-quadruplex ligands is essential for cellular applications since there is an excess of nucleic acids forming duplex structures compared to G-quadruplex structures in living cells. In this study, we developed new structure-selective G-quadruplex ligands utilizing a simple and fast screening system. The affinity, selectivity, enzymatic inhibitory activity and cytotoxicity of the structure-selective G-quadruplex ligands were demonstrated along with a structural selectivity-cytotoxicity relationship of G-quadruplex ligands.

Controlling liquid-liquid phase separation of G-quadruplex-forming RNAs in a sequence-specific manner.

We constructed a minimum liquid-liquid phase separation model system to form liquid droplets using only G-quadruplex-forming oligonucleotides and R- and G-rich oligopeptides. We found that the G-quadruplex structure is an essential component for RNA to form droplets with the peptide. Based on this model system and our findings, droplet redissolution via structure transition from a G-quadruplex to a duplex was achieved in a sequence-specific manner.

Anti-Malignant Effect of Tensile Loading to Adherens Junctions in Cutaneous Squamous Cell Carcinoma Cells.

Actomyosin contractility regulates various cellular processes including proliferation and differentiation while dysregulation of actomyosin activity contributes to cancer development and progression. Previously, we have reported that actomyosin-generated tension at adherens junctions is required for cell density-dependent inhibition of proliferation of normal skin keratinocytes. However, it remains unclear how actomyosin contractility affects the hyperproliferation ability of cutaneous squamous cell carcinoma (cSCC) cells. In this study, we find that actomyosin activity is impaired in cSCC cells both in vitro and in vivo. External application of tensile loads to adherens junctions by sustained mechanical stretch attenuates the proliferation of cSCC cells, which depends on intact adherens junctions. Forced activation of actomyosin of cSCC cells also inhibits their proliferation in a cell-cell contact-dependent manner. Furthermore, the cell cycle arrest induced by tensile loading to adherens junctions is accompanied by epidermal differentiation in cSCC cells. Our results show that the degree of malignant properties of cSCC cells can be reduced by applying tensile loads to adherens junctions, which implies that the mechanical status of adherens junctions may serve as a novel therapeutic target for cSCC.

Intramolecular G-quadruplex-hairpin loop structure competition of a GC-rich exon region in the TMPRSS2 gene.

We identified cytosine-rich regions adjacent to guanine-rich regions in protease genes. A typical GC-rich sequence derived from the TMPRSS2 gene showed structural competition between a G-quadruplex and a hairpin loop, and this competition significantly affected transcription efficiency. These results suggest an impact of neighboring sequences on the gene expression of guanine-rich sequences.

Detection of Intracellular Reactive Oxidative Species Using the Fluorescent Probe Hydroxyphenyl Fluorescein.

Various fluorescent probes for the detection of intracellular reactive oxidative species (ROS) have been developed because ROS levels are closely associated with cellular states. Here, we describe a method for detection of intracellular ROS in living cells using the fluorescent probe, hydroxyphenyl fluorescein (HPF), which detects hydroxyl radicals and peroxynitrite. NIH3T3 cells and p53 knockout (p53-/-) mouse embryonic fibroblasts (MEFs) were transformed by expressing oncogenic RAS using a retrovirus system. The cells were treated with HPF at 37 °C for 30 min, and subsequently, images were acquired using a confocal fluorescence microscope at an excitation wavelength of 488 nm after washing with PBS.

Photosensitizers Based on G-Quadruplex Ligand for Cancer Photodynamic Therapy.

G-quadruplex (G4) is the non-canonical secondary structure of DNA and RNA formed by guanine-rich sequences. G4-forming sequences are abundantly located in telomeric regions and in the promoter and untranslated regions (UTR) of cancer-related genes, such as RAS and MYC. Extensive research has suggested that G4 is a potential molecular target for cancer therapy. Here, we reviewed G4 ligands as photosensitizers for cancer photodynamic therapy (PDT), which is a minimally invasive therapeutic approach. The photosensitizers, such as porphyrins, were found to be highly toxic against cancer cells via the generation of reactive oxidative species (ROS) upon photo-irradiation. Several porphyrin derivatives and analogs, such as phthalocyanines, which can generate ROS upon photo-irradiation, have been reported to act as G4 ligands. Therefore, they have been implicated as promising photosensitizers that can selectively break down cancer-related DNA and RNA forming G4. In this review, we majorly focused on the potential application of G4 ligands as photosensitizers, which would provide a novel strategy for PDT, especially molecularly targeted PDT (mtPDT).

MMP24 as a Target of YAP is a Potential Prognostic Factor in Cancer Patients.

The extracellular matrix (ECM) surrounding cancer cells becomes stiffer during tumor progression, which influences cancer cell behaviors such as invasion and proliferation through modulation of gene expression as well as remodeling of the actin cytoskeleton. In this study, we show that MMP24 encoding matrix metalloproteinase (MMP)-24 is a novel target gene of Yes-associated protein (YAP), a transcription coactivator known as a mechanotransducer. We first examined the effect of substrate stiffness on MMP24 expression in MCF-7 human breast cancer cells and showed that the expression of MMP24 was significantly higher in cells grown on stiff substrates than that on soft substrates. The MMP24 expression was significantly reduced by knockdown of YAP. In contrast, the expression of constitutively active YAP increased MMP24 promoter activity. In addition, binding of YAP to the MMP24 promoter was confirmed by the chromatin immunoprecipitation (ChIP) assay. These results show that ECM stiffening promotes YAP activation, thereby inducing MMP24 expression. Based on the Human Protein Atlas database, breast cancer patients with lower MMP24 expression exhibit the worse survival rates overall. Thus, MMP24 may negatively regulate the aggressiveness of cancer cells under the stiff ECM environment during tumor progression.

DMPK is a New Candidate Mediator of Tumor Suppressor p53-Dependent Cell Death.

Tumor suppressor p53 plays an integral role in DNA-damage induced apoptosis, a biological process that protects against tumor progression. Cell shape dramatically changes when cells undergo apoptosis, which is associated with actomyosin contraction; however, it remains entirely elusive how p53 regulates actomyosin contraction in response to DNA-damaging agents. To identify a novel p53 regulating gene encoding the modulator of myosin, we conducted DNA microarray analysis. We found that, in response to DNA-damaging agent doxorubicin, expression of myotonic dystrophy protein kinase (DMPK), which is known to upregulate actomyosin contraction, was increased in a p53-dependent manner. The promoter region of DMPK gene contained potential p53-binding sequences and its promoter activity was increased by overexpression of the p53 family protein p73, but, unexpectedly, not of p53. Furthermore, we found that doxorubicin treatment induced p73 expression, which was significantly attenuated by downregulation of p53. These data suggest that p53 induces expression of DMPK through upregulating p73 expression. Overexpression of DMPK promotes contraction of the actomyosin cortex, which leads to formation of membrane blebs, loss of cell adhesion, and concomitant caspase activation. Taken together, our results suggest the existence of p53-p73-DMPK axis which mediates DNA-damage induced actomyosin contraction at the cortex and concomitant cell death.

Mitochondrial protein E2F3d, a distinctive E2F3 product, mediates hypoxia-induced mitophagy in cancer cells.

Mitochondrial damage is caused by changes in the micro-environmental conditions during tumor progression. Cancer cells require mechanisms for mitochondrial quality control during this process; however, how mitochondrial integrity is maintained is unclear. Here we show that E2F3d, a previously unidentified E2F3 isoform, mediates hypoxia-induced mitophagy in cancer cells. Aberrant activity and expression of the E2F3 transcription factor is frequently observed in many cancer cells. Loss of retinoblastoma (Rb) protein family function increases the expression of E2F3d and E2F3a. E2F3d localizes to the outer mitochondrial membrane and its cytosolic domain contains an LC3-interacting region motif. Overexpression of E2F3d induces mitochondrial fragmentation and mitophagy, suggesting that E2F3d plays an important role in mitophagy. Furthermore, depletion of E2F3s attenuates hypoxia-induced mitophagy and increases intracellular levels of reactive oxygen species, which is reversed by the reintroduction of E2F3d. This study presents another key player that regulates mitochondrial quality control in cancer cells.

An anionic phthalocyanine decreases NRAS expression by breaking down its RNA G-quadruplex.

Aberrant activation of RAS signalling pathways contributes to aggressive phenotypes of cancer cells. The RAS-targeted therapies for cancer, therefore, have been recognised to be effective; however, current developments on targeting RAS have not advanced due to structural features of the RAS protein. Here, we show that expression of NRAS, a major isoform of RAS, can be controlled by photo-irradiation with an anionic phthalocyanine, ZnAPC, targeting NRAS mRNA. In vitro experiments reveal that ZnAPC binds to a G-quadruplex-forming oligonucleotide derived from the 5'-untranslated region of NRAS mRNA even in the presence of excess double-stranded RNA, which is abundant in cells, resulting in selective cleavage of the target RNA's G-quadruplex upon photo-irradiation. In line with these results, upon photo-irradiation, ZnAPC decreases NRAS mRNA and NRAS expression and thus viability of cancer cells. These results indicate that ZnAPC may be a prominent photosensitiser for a molecularly targeted photodynamic therapy for cancer.

Nanocomposite injectable gels capable of self-replenishing regenerative extracellular microenvironments for in vivo tissue engineering.

Injectable hydrogels are biomaterials that have the potential to provide scaffolds to cells for in situ tissue regeneration with a minimally invasive implantation procedure. The success of in vivo tissue engineering utilizing injectable gels depends on providing cells with appropriate scaffolds that present an instructive extracellular microenvironment, which strongly influences the survival, proliferation, organization, and function of cells encapsulated within gels. One of the most important abilities of injectable gels to achieve this function is to adsorb and retain a wide variety of requisite bioactive molecules including nutrients, extracellular matrices, and growth/differentiation factors within gels. Previously, we developed nanocomposite injectable gels fabricated by simple combination of common biodegradable copolymers, poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA), and synthetic clay nanoparticles (LAPONITE®). We revealed that the nanocomposite injectable gels strongly adsorb ECM molecules including collagen and heparin within gels and retain them due to the ability of LAPONITE® in synchronization with the degradation of PLGA-PEG-PLGA and subsequent release of the degradation products. Human dermal fibroblast cells cultured on the nanocomposite gels showed enough high cell viability and proliferation for at least a week. Moreover, various kinds of human cells encapsulated within the nanocomposite gels exhibited significantly higher survival, proliferation, and three-dimensional organization in comparison with the PLGA-PEG-PLGA gel, LAPONITE® gel, and Matrigel. Furthermore, transplantation of mouse myoblast cells with the nanocomposite gels in model mice of skeletal muscle injury dramatically enhanced tissue regeneration and functional recovery, whereas cell transplantation with the PLGA-PEG-PLGA gel did not. Thus, the nanocomposite injectable gels possess unique abilities to self-replenish the regenerative extracellular microenvironment within the gels in the body, demonstrating the potential utility of the nanocomposite injectable gels for in vivo tissue engineering.