Recycling the cell cycle: cyclins revisited

lncRNA MALAT1 participates in metformin inhibiting the proliferation of breast cancer cell

In recent years, the repurposing of conventional and chemotherapeutic drugs is recognized as an alternative strategy for health care. The main purpose of this study is to strengthen the application of non‐oncological drug metformin on breast cancer treatment in the perspective of epigenetics. In the present study, metformin was found to inhibit cell proliferation, promote apoptosis and induce cell cycle arrest in breast cancer cells at a dose‐dependent manner. In addition, metformin treatment elevated acH3K9 abundance and decreased acH3K18 level. The expression of lncRNA MALAT1, HOTAIR, DICER1‐AS1, LINC01121 and TUG1 was up‐regulated by metformin treatment. In metformin‐treated cells, MALAT1 knock‐down increased the Bax/Bcl2 ratio and enhanced p21 but decreased cyclin B1 expression. The expression of Beclin1, VDAC1, LC3‐II, CHOP and Bip was promoted in the cells received combinatorial treatment of metformin and MALAT1 knock‐down. The reduced phosphorylation of c‐Myc was further decreased in the metformin‐treated cells in combination with MALAT1 knock‐down than metformin treatment alone. Taken together, these results provide a promising repurposed strategy for metformin on cancer treatment by modulating epigenetic modifiers.

Mechanisms by Which Kinesin-5 Motors Perform Their Multiple Intracellular Functions

Bipolar kinesin-5 motor proteins perform multiple intracellular functions, mainly during mitotic cell division. Their specialized structural characteristics enable these motors to perform their essential functions by crosslinking and sliding apart antiparallel microtubules (MTs). In this review, we discuss the specialized structural features of kinesin-5 motors, and the mechanisms by which these features relate to kinesin-5 functions and motile properties. In addition, we discuss the multiple roles of the kinesin-5 motors in dividing as well as in non-dividing cells, and examine their roles in pathogenetic conditions. We describe the recently discovered bidirectional motility in fungi kinesin-5 motors, and discuss its possible physiological relevance. Finally, we also focus on the multiple mechanisms of regulation of these unique motor proteins.

Mind the replication gap

Unlike bacteria, mammalian cells need to complete DNA replication before segregating their chromosomes for the maintenance of genome integrity. Thus, cells have evolved efficient pathways to restore stalled and/or collapsed replication forks during S-phase, and when necessary, also to delay cell cycle progression to ensure replication completion. However, strong evidence shows that cells can proceed to mitosis with incompletely replicated DNA when under mild replication stress (RS) conditions. Consequently, the incompletely replicated genomic gaps form, predominantly at common fragile site regions, where the converging fork-like DNA structures accumulate. These branched structures pose a severe threat to the faithful disjunction of chromosomes as they physically interlink the partially duplicated sister chromatids. In this review, we provide an overview discussing how cells respond and deal with the under-replicated DNA structures that escape from the S/G2 surveillance system. We also focus on recent research of a mitotic break-induced replication pathway (also known as mitotic DNA repair synthesis), which has been proposed to operate during prophase in an attempt to finish DNA synthesis at the under-replicated genomic regions. Finally, we discuss recent data on how mild RS may cause chromosome instability and mutations that accelerate cancer genome evolution.

Regulation of tissue regeneration by the circadian clock

Circadian rhythms are regulated by a highly conserved transcriptional/translational feedback loop that maintains approximately 24-hr periodicity from cellular to organismal levels. Much research effort is being devoted to understanding how the outputs of the master clock affect peripheral oscillators, and in turn, numerous biological processes. Recent studies have revealed roles for circadian timing in the regulation of numerous cellular behaviours in support of complex tissue regeneration. One such role involves the interaction between the circadian clockwork and the cell cycle. The molecular mechanisms that control the cell cycle create a system of regulation that allows for high fidelity DNA synthesis, mitosis and apoptosis. In recent years, it has become clear that clock gene products are required for proper DNA synthesis and cell cycle progression, and conversely, elements of the cell cycle cascade feedback to influence molecular circadian timing mechanisms. It is through this crosstalk that the circadian system orchestrates stem cell proliferation, niche exit and control of the signalling pathways that govern differentiation and self-renewal. In this review, we discuss the evidence for circadian control of tissue homeostasis and repair and suggest new avenues for research.

Schlafen 5 as a novel therapeutic target in pancreatic ductal adenocarcinoma

We provide evidence that a member of the human Schlafen (SLFN) family of proteins, SLFN5, is overexpressed in human pancreatic ductal adenocarcinoma (PDAC). Targeted deletion of SLFN5 results in decreased PDAC cell proliferation and suppresses PDAC tumorigenesis in in vivo PDAC models. Importantly, high expression levels of SLFN5 correlate with worse outcomes in PDAC patients, implicating SLFN5 in the pathophysiology of PDAC that leads to poor outcomes. Our studies establish novel regulatory effects of SLFN5 on cell cycle progression through binding/blocking of the transcriptional repressor E2F7, promoting transcription of key genes that stimulate S phase progression. Together, our studies suggest an essential role for SLFN5 in PDAC and support the potential for developing new therapeutic approaches for the treatment of pancreatic cancer through SLFN5 targeting.

Altered metabolism by autophagy defection affect liver regeneration

Autophagy is the primary intracellular catabolic process for degrading and recycling long-lived proteins and damaged organelles, which maintains cellular homeostasis. Autophagy has key roles in development and differentiation. By using the mouse with liver specific knockout of autophagy related gene 5 (Atg5), a gene essential for autophagy, we investigated the possible role of autophagy in liver regeneration after 70% partial hepatectomy (PHx). Ablation of autophagy significantly impaired mouse liver regeneration, and this impairment was associated with reduced hepatocellular proliferation rate, down-regulated expression of cyclins and tumor suppressors, and increased hepatocellular apoptosis via the intrinsic apoptotic pathway. Ablation of autophagy does not affect IL-6 and TNF-α response after PHx, but the altered hepatic and systemic metabolic responses were observed in these mice, including reduced ATP and hepatic free fatty acid levels in the liver tissue, increased glucose level in the serum. Autophagy is required to promote hepatocellular proliferation by maintaining normal hepatic and systemic metabolism and suppress hepatocellular apoptosis in liver regeneration.

Mitochondrial Ca2+ and cell cycle regulation

It has been demonstrated for more than 40 years that intracellular calcium (Ca²⁺) controls a variety of cellular functions, including mitochondrial metabolism and cell proliferation. Cytosolic Ca²⁺ fluctuation during key stages of the cell cycle can lead to mitochondrial Ca²⁺ uptake and subsequent activation of mitochondrial oxidative phosphorylation and a range of signaling. However, the relationship between mitochondrial Ca²⁺ and cell cycle progression has long been neglected because the molecule responsible for Ca²⁺ uptake has been unknown. Recently, the identification of the mitochondrial Ca²⁺ uniporter (MCU) has led to key advances. With improved Ca²⁺ imaging and detection, effects of MCU-mediated mitochondrial Ca²⁺ have been observed at different stages of the cell cycle. Elevated Ca²⁺ signaling boosts ATP and ROS production, remodels cytosolic Ca²⁺ pathways and reprograms cell fate-determining networks. These findings suggest that manipulating mitochondrial Ca²⁺ signaling may serve as a potential strategy in the control of many crucial biological events, such as tumor development and cell division in hematopoietic stem cells (HSCs). In this review, we summarize the current understanding of the role of mitochondrial Ca²⁺ signaling during different stages of the cell cycle and highlight the potential physiological and pathological significance of mitochondrial Ca²⁺ signaling.

MicroRNA-567 inhibits cell proliferation and induces cell apoptosis in A549 NSCLC cells by regulating cyclin-dependent kinase 8

MicroRNA-567 (miR-567) plays a decisive role in cancers whereas its role in non-small cell lung cancer (NSCLC) is still unexplored. This study was therefore planned to explore the regulatory function of miR-567 in A549 NSCLC cells and investigate its possible molecular mechanism that may help in NSCLC treatment. In the current study, miR-567 expression was examined by quantitative real time-polymerase chain reaction (qRT-PCR) in different NSCLC cell lines in addition to normal cell line. A549 NSCLC cells were transfected by miR-567 mimic, miR-567 inhibitor, and negative control siRNA. Cell proliferation was evaluated by MTT and 5-bromo-2'deoxyuridine assays. Cell cycle distribution and apoptosis were studied by flow cytometry. Bioinformatics analysis programs were used to expect the putative target of miR-567. The expression of cyclin-dependent kinase 8 (CDK8) gene at mRNA and protein levels were evaluated by using qRT-PCR and western blotting. Our results found that miR-567 expressions decreased in all the studied NSCLC cells as compared to the normal cell line. A549 cell proliferation was suppressed by miR-567 upregulation while cell apoptosis was promoted. Also, miR-567 upregulation induced cell cycle arrest at sub-G1 and S phases. CDK8 was expected as a target gene of miR-567. MiR-567 upregulation decreased CDK8 mRNA and protein expression while the downregulation of miR-567 increased CDK8 gene expression. These findings revealed that miR-567 may be a tumor suppressor in A549 NSCLC cells through regulating CDK8 gene expression and may serve as a novel therapeutic target for NSCLC treatment.

Unraveling the Big Sleep: Molecular Aspects of Stem Cell Dormancy and Hibernation

Tissue-resident stem cells may enter a dormant state, also known as quiescence, which allows them to withstand metabolic stress and unfavorable conditions. Similarly, hibernating mammals can also enter a state of dormancy used to evade hostile circumstances, such as food shortage and low ambient temperatures. In hibernation, the dormant state of the individual and its cells is commonly known as torpor, and is characterized by metabolic suppression in individual cells. Given that both conditions represent cell survival strategies, we here compare the molecular aspects of cellular quiescence, particularly of well-studied hematopoietic stem cells, and torpor at the cellular level. Critical processes of dormancy are reviewed, including the suppression of the cell cycle, changes in metabolic characteristics, and cellular mechanisms of dealing with damage. Key factors shared by hematopoietic stem cell quiescence and torpor include a reversible activation of factors inhibiting the cell cycle, a shift in metabolism from glucose to fatty acid oxidation, downregulation of mitochondrial activity, key changes in hypoxia-inducible factor one alpha (HIF-1α), mTOR, reversible protein phosphorylation and autophagy, and increased radiation resistance. This similarity is remarkable in view of the difference in cell populations, as stem cell quiescence regards proliferating cells, while torpor mainly involves terminally differentiated cells. A future perspective is provided how to advance our understanding of the crucial pathways that allow stem cells and hibernating animals to engage in their 'great slumbers.'

From the cytoskeleton to the nucleus: An integrated view on early spindle assembly

Accurate chromosome segregation requires a complete restructuring of cellular organization. Microtubules remodel to assemble a mitotic spindle and the actin cytoskeleton rearranges to form a stiff actomyosin cortex. These cytoplasmic events must be spatially and temporally coordinated with mitotic chromosome condensation and nuclear envelope permeabilization, in order to ensure mitotic timing and fidelity. Here, we discuss the main cytoskeletal and nuclear events that occur during mitotic entry in proliferating animal cells, focusing on their coordinated contribution for early mitotic spindle assembly. We will also explore recent progress in understanding their regulatory biochemical and mechanical pathways.

Cyclin-Dependent Kinases (CDK) and Their Role in Diseases Development-Review

Cyclin-dependent kinases (CDKs) are involved in many crucial processes, such as cell cycle and transcription, as well as communication, metabolism, and apoptosis. The kinases are organized in a pathway to ensure that, during cell division, each cell accurately replicates its DNA, and ensure its segregation equally between the two daughter cells. Deregulation of any of the stages of the cell cycle or transcription leads to apoptosis but, if uncorrected, can result in a series of diseases, such as cancer, neurodegenerative diseases (Alzheimer’s or Parkinson’s disease), and stroke. This review presents the current state of knowledge about the characteristics of cyclin-dependent kinases as potential pharmacological targets.

Identification and validation of three core genes in p53 signaling pathway in hepatitis B virus-related hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common cancer and the leading cause is persistent hepatitis B virus (HBV) infection. We aimed to identify some core genes and pathways for HBV-related HCC.

METHODS

Gene expression profiles of GSE62232, GSE121248, and GSE94660 were available from Gene Expression Omnibus (GEO). The GSE62232 and GSE121248 profiles were the analysis datasets and GSE94660 was the validation dataset. The GEO2R online tool and Venn diagram software were applied to analyze commonly differentially expressed genes between HBV-related HCC tissues and normal tissues. Then, functional enrichment analysis using Gene Ontology (GO) and the Kyoto Encyclopedia of Gene and Genome (KEGG) as well as the protein-protein interaction (PPI) network was conducted. The overall survival rates and the expression levels were detected by Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis (GEPIA). Next, gene set enrichment analysis (GSEA) was performed to verify the KEGG pathway analysis. Furthermore, quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was performed to validate the levels of these three core genes in tumor tissues and adjacent non-tumor liver tissues from 12 HBV related HCC patients, HBV-associated liver cancer cell lines and normal liver cell lines, and HepG2 with p53 knockdown or deletion, respectively.

RESULTS

Fifteen highly expressed genes associated with significantly worse prognoses were selected and CCNB1, CDK1, and RRM2 in the p53 signaling pathway were identified as core genes. GSEA results showed that samples highly expressing three core genes were all enriched in the p53 signaling pathway in a validation dataset (P < 0.0001). The expression of these three core genes in tumor tissue samples was higher than that in relevant adjacent non-tumor liver tissues (P < 0.0001). Furthermore, we also found that the above genes were highly expressed in liver cancer cell lines compared with normal liver cells. In addition, we found that the expression of these three core genes in p53 knockdown or knockout HCC cell lines was lower than that in negative control HCC cell lines (P < 0.05).

CONCLUSIONS

CCNB1, CDK1, and RRM2 were enriched in the p53 signaling pathway and could be potential biomarkers and therapeutic targets for HBV-related HCC.

Combined Inactivation of Pocket Proteins and APC/CCdh1 by Cdk4/6 Controls Recovery from DNA Damage in G1 Phase

Most Cyclin-dependent kinases (Cdks) are redundant for normal cell division. Here we tested whether these redundancies are maintained during cell cycle recovery after a DNA damage-induced arrest in G1. Using non-transformed RPE-1 cells, we find that while Cdk4 and Cdk6 act redundantly during normal S-phase entry, they both become essential for S-phase entry after DNA damage in G1. We show that this is due to a greater overall dependency for Cdk4/6 activity, rather than to independent functions of either kinase. In addition, we show that inactivation of pocket proteins is sufficient to overcome the inhibitory effects of complete Cdk4/6 inhibition in otherwise unperturbed cells, but that this cannot revert the effects of Cdk4/6 inhibition in DNA damaged cultures. Indeed, we could confirm that, in addition to inactivation of pocket proteins, Cdh1-dependent anaphase-promoting complex/cyclosome (APC/C^Cdh1) activity needs to be inhibited to promote S-phase entry in damaged cultures. Collectively, our data indicate that DNA damage in G1 creates a unique situation where high levels of Cdk4/6 activity are required to inactivate pocket proteins and APC/C^Cdh1 to promote the transition from G1 to S phase.

New insight into the enantioselective cytotoxicity of cypermethrin: imbalance between cell cycle and apoptosis

Cypermethrin (CP) is a frequently used chiral pesticide comprised of different enantiomers that can induce a variable toxic response in biota, dependent on conformational change. However, the potential mechanism accounting for the enantioselective toxicity induced by CP enantiomers remains unknown. Herein, to shed light on the underlying mechanism of enantioselective cytotoxicity on cell cycle and apoptotic function, an MTT assay, flow cytometric (FCM) approach, and qPCR arrays combining bioinformatic analysis were conducted on HepG2 cell lines following exposure to CP enantiomers. Decreased cell viability in keeping with increased cell arrest and apoptosis was observed in cells exposed to (1S,3R,αR)-CP, relative to the (1R,3S,αS)-CP treatment group. PCR array also reflected an enantioselective difference in expression of cell cycle and apoptosis-related genes. Ingenuity pathway analysis (IPA) showed that cell cycle checkpoints, arrest in interphase, death receptor signaling, and apoptosis were among the top canonical and disease and functions predicted to be affected between CP enantiomers. Data presented here not only provide potential molecular endpoints for evaluating toxicity by cell cycle and apoptosis but also help to guide the scientific application of chiral pesticides.

Non-Thermal Biocompatible Plasma Jet Induction of Apoptosis in Brain Cancer Cells

Glioblastoma multiforme (GBM) is a highly malignant and rapidly advancing astrocytic brain tumor in adults. Current therapy possibilities are chemotherapy, surgical resection, and radiation. The complexity of drug release through the blood-brain barrier, tumor reaction to chemotherapy, and the inherent resistance of tumor cells present challenges. New therapies are needed for individual use or combination with conventional methods for more effective treatment and improved survival for patients. GBM is difficult to treat because it grows quickly, spreads finger-shaped tentacles, and creates an irregular margin of normal tissue surrounding the tumor. Non-thermal biocompatible plasma (NBP) has recently been shown to selectively target cancer cells with minimal effects on regular cells, acting by generating reactive oxygen species (ROS) and reactive nitrogen species (RNS). We applied a soft jet plasma device with a syringe shape to U87 MG cells and astrocytes. Our results show that NBP-J significantly inhibits cell proliferation and changes morphology, induces cell cycle arrest, inhibits the survival pathway, and induces apoptosis. Our results indicate that NBP-J may be an efficient and safe clinical device for brain cancer therapy.

The natural flavones, acacetin and apigenin, induce Cdk-Cyclin mediated G2/M phase arrest and trigger ROS-mediated apoptosis in glioblastoma cells

Brain and CNS-related cancers are rare; however, 0.3 million incidences and 0.24 million deaths in 2018 demonstrates the unrelenting associated dangers. Glioblastoma is a brain cancer of star-shaped glial cells. It is almost universally fatal within 2 years of diagnosis despite maximal medical therapies. This study aims to evaluate the in-depth anticancer activity of acacetin and apigenin on glioblastoma cells (U87). In the present report, we have isolated two flavonoids, acacetin and apigenin; and studied the in-depth anticancer activity on U87 cells. Selective cytotoxicity of acacetin and apigenin was observed towards the U87 cells (IC₅₀: 43.73 ± 1.19 and 48.18 ± 1.37 μM, respectively). The flow cytometer-based result revealed the induction of G2/M phase arrest along with the increase in sub G1 population upon compound treatment. Annexin-V-FLUOS and DAPI staining also confirmed the apoptosis-inducing effects of compounds. Flow cytometer and confocal microscopy-based DCFH-DA staining showed ROS-inducing effect of the compounds. The up-regulation of p21 and down-regulation of Cyclin-A1, Cyclin-B1, and Cdk-1 revealed the G2/M phase arrest mechanism of acacetin and apigenin. Furthermore, western blotting result confirmed the activation of intrinsic pathway of apoptosis upon acacetin treatment and activation of both extrinsic and intrinsic pathways of apoptosis upon apigenin treatment through the regulation of Bax, t-Bid, caspase 8, caspase 9, caspase 3, and PARP. The obtained result showed a significant effect (P < 0.05) of acacetin and apigenin on U87 cells. Acacetin and apigenin-induced ROS is responsible for the induction of cell cycle arrest and activation of caspase-cascade pathways in U87 cells.

Simultaneous Detection of Four Cell Cycle Phases with Live Fluorescence Imaging

Visualizing progression through the cell cycle provides valuable information for the study of development, tissue maintenance, and dysregulated growth in proliferative diseases, such as cancer. Developments in fluorescent biosensors have facilitated dynamic tracking of molecular processes, including the cell cycle. The genetically encoded set of fluorescent indicators, Fucci4, enables the visualization of transitions between each cell cycle phase. Here, we describe a method to track progression through each cell cycle phase using Fucci4 in live epifluorescence imaging. In principle, this approach can be adapted to in vitro time-lapse imaging of any four spectrally resolvable fluorescent indicators.

An Investigation of Post-radiation Gene Expression Profiles: A System Biology Study

Introduction: Genomics and bioinformatics are useful methods for exploring unclear aspects of radiation effects on biological systems. Many radiation-induced alterations in irradiated samples are post-radiation time-dependent. This study aims to evaluate the post-irradiation effects of the gamma ray on human Jurkat cells. Methods: Gene expression profiles of the samples harvested 6 and 24 hours after radiation to find the critical differential expressed genes and the related pathways. Samples are provided from Gene Expression Omnibus (GEO) and analyzed by ClueGO. Results: Twnety-nine critical genes were determined as the important affected genes and 7 classes of related pathways were introduced. CCNE2, PSMD11, CDC25C, ANAPC1, PLK1, AURKA, and CCNB1 that were associated with more than 6 pathways were related to one of the determined pathway groups. Conclusion: Cell protecting pathways were associated with the genes (HSPA5, HSPA8, HSP90B1, HMMR, CEBPB, RXRA, and PSMD11) which were related to the minimum numbers of pathways. The finding of this study corresponds to repair processes which depend on post-radiation time. It seems these sets of genes are suitable candidates for further investigation.

Regulation of hepatocyte cell cycle re-entry by RNA polymerase II-associated Gdown1

Liver is the central organ responsible for whole-body metabolism, and its constituent hepatocytes are the major players that carry out liver functions. Although they are highly differentiated and rarely divide, hepatocytes re-enter the cell cycle following hepatic loss due to liver damage or injury. However, the exact molecular mechanisms underlying cell cycle re-entry remain undefined. Gdown1 is an RNA polymerase II (Pol II)-associated protein that has been linked to the function of the Mediator transcriptional coactivator complex. We recently found that Gdown1 ablation in mouse liver leads to down-regulation of highly expressed liver-specific genes and a concomitant cell cycle re-entry associated with the induction of cell cycle-related genes. Unexpectedly, in view of a previously documented inhibitory effect on transcription initiation by Pol II in vitro, we found that Gdown1 is associated with elongating Pol II on the highly expressed genes and that its ablation leads to a reduced Pol II occupancy that correlates with the reduced expression of these genes. Based on these observations, we discuss the in vitro and in vivo functions of Gdown1 and consider mechanisms by which the dysregulated Pol II recruitment associated with Gdown1 loss might induce quiescent cell re-entry into the cell cycle.

The role of estrogen receptors in rat Sertoli cells at different stages of development

The aim of the study was to investigate the effects of estrogen receptors (ESR1 and ESR2) on the expression of the proteins involved with proliferation (CCND1) and differentiation (CDKN1B and CTNNB) of Sertoli cells from rat in different stages of development. ESR1-selective agonist PPT, but not ESR2-selective agonist DPN, increased CCND1 expression in Sertoli cells from 5- and 15-day old rats. PPT did not have any effect on CCND1 expression in Sertoli cells from 20- and 30-day-old rats. DPN, but not PPT, increased CDKN1B expression in Sertoli cells from 15-, 20-, 30-day-old rats. DPN did not have any effect on Sertoli cells from 5-day-old rats. 17β-estradiol (E2) and PPT enhanced the [Methyl-³H] thymidine incorporation in Sertoli cells from 15-day-old rats, whereas the treatment did not have any effect in 20-day-old rats. E2 and DPN, but not PPT, increased non-phosphorylated CTNNB expression in Sertoli cells from 20-day-old rats. This upregulation was blocked by ESR2-selective antagonist PHTPP. The activation of ESR1 and ESR2, respectively, plays a role in the proliferation and differentiation of Sertoli cells in a critical period of testicular development. Furthermore, in Sertoli cells from 20-day-old rats, upregulation of non-phosphorylated CTNNB by E2/ESR2, via c-SRC/ERK1/2 and PI3K/AKT, may play a role in the interaction between Sertoli cells and/or in cell-germ cell adhesion and/or in the stabilization and accumulation of CTNNB in the cytosol. CTNNB could be translocated to the nucleus and modulate the transcriptional activity of specific target genes. The present study reinforces the important role of estrogen in normal testis development.

The multifaceted role of cell cycle regulators in the coordination of growth and metabolism

Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi‐directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin‐dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho‐physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.

Synthesis of some novel methyl β-orsellinate based 3, 5-disubstituted isoxazoles and their anti-proliferative activity: Identification of potent leads active against MCF-7 breast cancer cell

A series of sixteen novel methyl β-orsellinate based 3, 5-disubstituted isoxazole hybrids (3-18) were synthesized in excellent yields by employing 1,3-dipolar cycloaddition reaction of terminal alkyne and corresponding nitriloxides as the key step. The structures of all the synthesized compounds were elucidated by spectroscopic data such as ¹H &¹³C NMR and HRMS. The anti-proliferative activity of newly synthesized compounds were assessed in vitro against a panel of four human cancer cell lines, namely IMR-32 (neuroblastoma), DU-145 (prostate), MIAPACA (pancreatic), MCF-7 (breast) along with a normal cell line HEK-293T (embryonic kidney) by employing Sulforhodamine B (SRB) assay. The biological results revealed that majority of synthesized compounds exhibited anti-proliferative activity. In particular, compound 12 was found to be the most potent one as it exhibited five fold higher activity (IC₅₀: 7.9 ± 0.07 µM) than parent compound 1 (IC₅₀: 40.63 ± 0.11 µM) against MCF-7 breast cancer cell line. Flow cytometric analysis of compound 12 revealed that it induced apoptosis and arrested cell cycle in G2/M phase. Mechanistic studies have shown the compound as a potent activator of pro-apoptotic proteins, Bax and Cytochrome-c via the upregulation of tumour suppressor proteins, p53 and PTEN. From the docking studies, it can be inferred that Compound 12 acts as a novel and attractive anti-cancer therapeutic inhibiting the CDK1-Cyclin B complex.

Emerging Roles of Single-Cell Multi-Omics in Studying Developmental Temporal Patterning

The complexity of brain structure and function is rooted in the precise spatial and temporal regulation of selective developmental events. During neurogenesis, both vertebrates and invertebrates generate a wide variety of specialized cell types through the expansion and specification of a restricted set of neuronal progenitors. Temporal patterning of neural progenitors rests on fine regulation between cell-intrinsic and cell-extrinsic mechanisms. The rapid emergence of high-throughput single-cell technologies combined with elaborate computational analysis has started to provide us with unprecedented biological insights related to temporal patterning in the developing central nervous system (CNS). Here, we present an overview of recent advances in Drosophila and vertebrates, focusing both on cell-intrinsic mechanisms and environmental influences. We then describe the various multi-omics approaches that have strongly contributed to our current understanding and discuss perspectives on the various -omics approaches that hold great potential for the future of temporal patterning research.

Amiodarone's major metabolite, desethylamiodarone inhibits proliferation of B16-F10 melanoma cells and limits lung metastasis formation in an in vivo experimental model

Previously, we demonstrated the in vitro anti-tumor effects of desethylamiodarone (DEA) in bladder and cervix cancer cell lines. In the present study, we intended to establish its potentiality in B16-F10 metastatic melanoma cells in vitro and in vivo. We assessed cell proliferation, apoptosis and cell cycle by using sulforhodamine B assay, Muse™ Annexin V & Dead Cell and Muse® Cell Cycle assays, respectively. We determined colony formation after crystal violet staining. For studying mechanistic aspects, immunoblotting analysis was performed. We used a C57BL/6 experimental lung metastasis model for demonstrating in vivo anti-metastatic potential of DEA. DEA inhibited in vitro proliferation and colony formation, and in vivo lung metastasizing properties of B16-F10 cells. It arrested the cells in G0/G1 phase of their cycle likely via p21 in a p53-dependent fashion, and induced caspase mediated apoptosis likely via inversely regulating Bcl-2 and Bax levels, and reducing Akt and ERK1/2 activation. In this study, we provided in vitro and in vivo experimental evidences for DEA’s potentiality in the therapy of metastatic melanomas. Since DEA is the major metabolite of amiodarone, a worldwide used antiarrhythmic drug, safety concerns could be resolved more easily for it than for a novel pharmacological agent.

Deubiquitinase UCHL5 is elevated and associated with a poor clinical outcome in lung adenocarcinoma (LUAD)

Lung cancer is one of the most common malignant tumors in the world, with a high rate of malignancy and mortality. Seeking new biomarkers and potential drug targets is urgent for effective treatment of the disease. Deubiquitinase UCHL5/UCH37, as an important component of the 26S proteasome, plays critical roles in ubiquitinated substrate degradation. Although previous studies have shown that UCHL5 promotes tumorigenesis, its role in lung cancer remains largely unknown. In this study, we evaluated the expression and clinical significance of UCHL5 in non-small cell lung cancer (NSCLC). The results demonstrated that the UCHL5 expression level was significantly upregulated in NSCLC tissues compared with the adjacent noncancerous tissues. The level of UCHL5 was associated with tumor size, lymph node invasion, TNM stage and malignant tumor history in patients with lung adenocarcinoma (LUAD). Importantly, high UCHL5 expression predicted a poor overall survival (OS) and a poor disease-free survival (DFS) in patients with LUAD. Univariate regression analysis showed that tumor size, lymph node invasion, TNM stage and UCHL5 expression were associated with OS and DFS in patients with LUAD. The multivariate analysis indicated that the UCHL5 expression level was an independent prognostic factor for OS (HR=1.171, 95% CI=1.052-1.303) and DFS (HR=1.143, 95% CI=1.031-1.267) in these patients. UCHL5 knockdown in LUAD cells significantly inhibited cell proliferation and reduced the expression of key cell cycle proteins. These findings indicate that UCHL5 may serve as a potential prognostic marker and a new therapeutic target for patients with LUAD.

Splicing to Keep Cycling: The Importance of Pre-mRNA Splicing during the Cell Cycle

Pre-mRNA splicing is a fundamental process in mammalian gene expression, and alternative splicing plays an extensive role in generating protein diversity. Because the majority of genes undergo pre-mRNA splicing, most cellular processes depend on proper spliceosome function. We focus on the cell cycle and describe its dependence on pre-mRNA splicing and accurate alternative splicing. We outline the key cell-cycle factors and their known alternative splicing isoforms. We discuss different levels of pre-mRNA splicing regulation such as post-translational modifications and changes in the expression of splicing factors. We describe the effect of chromatin dynamics on pre-mRNA splicing during the cell cycle. In addition, we focus on spliceosome component SF3B1, which is mutated in many types of cancer, and describe the link between SF3B1 and its inhibitors and the cell cycle.

A novel analysis of gene array data: yeast cell cycle

Many gene array studies of the yeast cell cycle have been performed (Cho RJ, Campbell MJ, Winzeler EA et al. A genome-wide transcriptional analysis of the mitotic cell cycle. Mol Cell 1998;2:65–73; Orlando DA, Lin CY, Bernard A et al. Global control of cell-cycle transcription by coupled CDK and network oscillators. Nature 2008;453:944–7; Pramila T, Wu W, Miles S et al. The Forkhead transcription factor Hcm1 regulates chromosome segregation genes and fills the S-phase gap in the transcriptional circuitry of the cell cycle. Genes Dev 2006;20:2266–78; Spellman PT, Sherlock G, Zhang MQ et al. Comprehensive identification of cell cycle–regulated genes of the yeast Saccharomyces cerevisiae by microarray hybridization. MBoC 1998;9:3273–97). Largely, these studies contain elements drawn from laboratory experiments. The present investigation determines cell division cycle (CDC) genes solely from the data (Orlando DA, Lin CY, Bernard A et al. Global control of cell-cycle transcription by coupled CDK and network oscillators. Nature 2008;453:944–7). It is shown by simple reasoning that the dynamics of the approximately 6000 yeast genes are described by an approximately six-dimensional space. This leads a precisely determined cell-cycle period, along with the quality and timing of the identified CDC genes. Convincing evidence for the role of the identified genes is obtained. While these show good agreement with standard CDC gene representatives (Orlando DA, Lin CY, Bernard A et al. Global control of cell-cycle transcription by coupled CDK and network oscillators. Nature 2008;453:944–7; Spellman PT, Sherlock G, Zhang MQ et al. Comprehensive identification of cell cycle–regulated genes of the yeast Saccharomyces cerevisiae by microarray hybridization. MBoC 1998;9:3273–97; de Lichtenberg U, Jensen LJ, Fausbøll A et al. Comparison of computational methods for the identification of cell cycle-regulated genes. Bioinformatics 2005;21:1164–71) several hundred newly revealed CDC genes appear, which merit attention. The present approach employs an adaptation of a method introduced to study turbulent flows (Schmid PJ. Dynamic mode decomposition of numerical and experimental data. J Fluid Mech 2010;656:5–28), “dynamic mode decomposition” (DMD). From this, one can infer that singular value decomposition, analysis of the data entangles the underlying (gene) dynamics implicit in the data; and that DMD produces the disentangling transformation. It is the assertion of this study that a new tool now exists for the analysis of the gene array signals, and in particular for investigating the yeast cell cycle.

WDHD1 facilitates G1 checkpoint abrogation in HPV E7 expressing cells by modulating GCN5

Background

Genomic instability is a hallmark of cancer. The G1 checkpoint allows cells to repair damaged DNA that may lead to genomic instability. The high-risk human papillomavirus (HPV) E7 gene can abrogate the G1 checkpoint, yet the mechanism is still not fully understood. Our recent study showed that WDHD1 (WD repeat and high mobility group [HMG]-box DNA-binding protein 1) plays a role in regulating G1 checkpoint of E7 expressing cells. In this study, we explored the mechanism by which WDHD1 regulates G1 checkpoint in HPV E7 expressing cells.

Methods

NIKS and RPE1 derived cell lines were used. Real-time PCR, Rescue experiment, FACS and BrdU labeling experiments were performed to examine role of GCN5 in G1 checkpoint abrogation in HPV-16 E7 expressing cells.

Results

In this study, we observed that WDHD1 facilitates G1 checkpoint abrogation by modulating GCN5 in HPV E7 expressing cells. Notably, depletion of WDHD1 caused G1 arrest while overexpression of GCN5 rescued the inhibitory effects of WDHD1 knockdown on G1/S progression. Furthermore, siWDHD1 significantly decreased cell cycle proliferation and DNA synthesis that was correlated with Akt phosphorylation (p-Akt), which was reversed by GCN5 overexpression in HPV E7 expressing cells.

Conclusions

In summary, our data identified a WDHD1/GCN5/Akt pathway leading to the abrogation of G1 checkpoint in the presence of damaged DNA, which may cause genomic instability and eventually HPV induced tumorigenesis.

Recent trends in targeting miRNAs for cancer therapy

OBJECTIVES

MicroRNAs (miRNAs) are a type of small noncoding RNA employed by the cells for gene regulation. A single miRNA, typically 22 nucleotides in length, can regulate the expression of numerous genes. Over the past decade, the study of miRNA biology in the context of cancer has led to the development of new diagnostic and therapeutic opportunities.

KEY FINDINGS

MicroRNA dysregulation is commonly associated with cancer, in part because miRNAs are actively involved in the mechanisms like genomic instabilities, aberrant transcriptional control, altered epigenetic regulation and biogenesis machinery defects. MicroRNAs can regulate oncogenes or tumour suppressor genes and thus when altered can lead to tumorigenesis. Expression profiling of miRNAs has boosted the possibilities of application of miRNAs as potential cancer biomarkers and therapeutic targets, although the feasibility of these approaches will require further validation.

SUMMARY

In this review, we will focus on how miRNAs regulate tumour development and the potential applications of targeting miRNAs for cancer therapy.

Quantifying the Landscape and Transition Paths for Proliferation-Quiescence Fate Decisions

The cell cycle, essential for biological functions, experiences delicate spatiotemporal regulation. The transition between G1 and S phase, which is called the proliferation–quiescence decision, is critical to the cell cycle. However, the stability and underlying stochastic dynamical mechanisms of the proliferation–quiescence decision have not been fully understood. To quantify the process of the proliferation–quiescence decision, we constructed its underlying landscape based on the relevant gene regulatory network. We identified three attractors on the landscape corresponding to the G0, G1, and S phases, individually, which are supported by single-cell data. By calculating the transition path, which quantifies the potential barrier, we built expression profiles in temporal order for key regulators in different transitions. We propose that the two saddle points on the landscape characterize restriction point (RP) and G1/S checkpoint, respectively, which provides quantitative and physical explanations for the mechanisms of Rb governing the RP while p21 controlling the G1/S checkpoint. We found that Emi1 inhibits the transition from G0 to G1, while Emi1 in a suitable range facilitates the transition from G1 to S. These results are partially consistent with previous studies, which also suggested new roles of Emi1 in the cell cycle. By global sensitivity analysis, we identified some critical regulatory factors influencing the proliferation–quiescence decision. Our work provides a global view of the stochasticity and dynamics in the proliferation–quiescence decision of the cell cycle.

Maintenance of genome integrity and active homologous recombination in embryonic stem cells

Embryonic stem cells (ESCs) possess specific gene expression patterns that confer the ability to proliferate indefinitely and enable pluripotency, which allows ESCs to differentiate into diverse cell types in response to developmental signals. Compared to differentiated cells, ESCs harbor an elevated level of homologous recombination (HR)-related proteins and exhibit exceptional cell cycle control, characterized by a high proliferation rate and a prolonged S phase. HR is involved in several aspects of chromosome maintenance. For instance, HR repairs impaired chromosomes and prevents the collapse of DNA replication forks during cell proliferation. Thus, HR is essential for the maintenance of genomic integrity and prevents cellular dysregulation and lethal events. In addition, abundant HR proteins in the prolonged S phase can efficiently protect ESCs from external damages and protect against genomic instability caused by DNA breaks, facilitating rapid and accurate DNA break repair following chromosome duplication. The maintenance of genome integrity is key to preserving the functions of ESCs and reducing the risks of cancer development, cell cycle arrest, and abnormal replication. Here, we review the fundamental links between the stem cell-specific HR process and DNA damage response as well as the different strategies employed by ESCs to maintain genomic integrity.

Embryonic stem cells (ESCs), which give rise to the many specialized cells of the body, have highly effective molecular processes of DNA maintenance and repair which protect their genetic information from damage. Keun Pil Kim and colleagues at Chung-Ang University, Seoul, South Korea, review the strategies found in ESCs to maintain the integrity of their DNA as they develop and multiply. A key feature is the process of homologous recombination (HR) in which one copy of a section of DNA acts as the template allowing a damaged version of the DNA to be repaired. HR also facilitates swapping of sections of DNA when sperm and egg cells form, promoting genetic diversity. HR appears to be especially significant in maintaining ESC DNA as ESCs possess higher levels of key proteins involved in its maintenance and regulation.

Squamous differentiation requires G2/mitosis slippage to avoid apoptosis

The cellular mechanisms controlling cell fate in self-renewal tissues remain unclear. Cell cycle failure often leads to an apoptosis anti-oncogenic response. We have inactivated Cdk1 or Polo-like-1 kinases, essential targets of the mitotic checkpoints, in the epithelia of skin and oral mucosa. Here, we show that inactivation of the mitotic kinases leading to polyploidy in vivo, produces a fully differentiated epithelium. Cells within the basal layer aberrantly differentiate and contain large or various nuclei. Freshly isolated KO cells were also differentiated and polyploid. However, sustained metaphase arrest downstream of the spindle anaphase checkpoint (SAC) due to abrogation of CDC20 (essential cofactor of anaphase-promoting complex), impaired squamous differentiation and resulted in apoptosis. Therefore, upon prolonged arrest keratinocytes need to slip beyond G2 or mitosis in order to initiate differentiation. The results altogether demonstrate that mitotic checkpoints drive squamous cell fate towards differentiation or apoptosis in response to genetic damage.

A natural flavonoid, apigenin isolated from Clerodendrum viscosum leaves, induces G2/M phase cell cycle arrest and apoptosis in MCF-7 cells through the regulation of p53 and caspase-cascade pathway

BACKGROUND

With 9.6 million deaths in 2018, cancer remains the second leading cause of death worldwide. Breast cancer is the most deadly type of cancer among females, with 55.2% of crude incidence rate and 16.6% of crude mortality rate.

PURPOSE

The present study was aimed to investigate the anti-breast cancer potential of natural dietary flavonoid, apigenin isolated from Clerodendrum viscosum leaves.

METHODS

Apigenin was evaluated for in-depth anticancer activity in MCF-7 cells using cell viability assay, cell cycle analysis, Annexin-V-FLUOS staining, ROS induction, morphological analysis, and western blot analysis.

RESULTS

Apigenin showed selective cytotoxicity on MCF-7 cells with an IC₅₀-56.72 ± 2.35 µM, while negligible cytotoxicity was observed on WI-38 cells. Further, the flow cytometer-based analysis showed that apigenin halted MCF-7 cells in the G2/M phase arrest followed by dose-dependent apoptosis. Moreover, the FACS and confocal microscopy results confirmed the elevation of intracellular ROS and nuclear fragmentation in apigenin-treated MCF-7 cells. Western blots showed up-regulation of cell cycle regulatory proteins, increased p53 expression, Bax/Bcl-2 ratio, activation of caspases, and cleavage of PARP. Finally, apigenin treatment in the presence of Pifithrin-µ showed decreased apoptotic population and it was further confirmed through western blotting study. The results revealed the vital role of p53 in apigenin-induced apoptosis in MCF-7 cells.

CONCLUSIONS

In the present findings, treatment of apigenin-induced intracellular ROS in MCF-7 cells followed by induction of G2/M phase cell cycle arrest and further apoptosis through the regulation of p53 and caspase-cascade signaling pathway.

CDK Regulation of Meiosis: Lessons from S. cerevisiae and S. pombe

Meiotic progression requires precise orchestration, such that one round of DNA replication is followed by two meiotic divisions. The order and timing of meiotic events is controlled through the modulation of the phosphorylation state of proteins. Key components of this phospho-regulatory system include cyclin-dependent kinase (CDK) and its cyclin regulatory subunits. Over the past two decades, studies in budding and fission yeast have greatly informed our understanding of the role of CDK in meiotic regulation. In this review, we provide an overview of how CDK controls meiotic events in both budding and fission yeast. We discuss mechanisms of CDK regulation through post-translational modifications and changes in the levels of cyclins. Finally, we highlight the similarities and differences in CDK regulation between the two yeast species. Since CDK and many meiotic regulators are highly conserved, the findings in budding and fission yeasts have revealed conserved mechanisms of meiotic regulation among eukaryotes.

Cell Cycle Genes Are Potential Diagnostic and Prognostic Biomarkers in Hepatocellular Carcinoma

BACKGROUND

The cell cycle pathway genes are comprised of 113 members which are critical to the maintenance of cell cycle and survival of tumor cells. This study was performed to investigate the diagnostic and prognostic values of cell cycle gene expression in hepatocellular carcinoma (HCC) patients.

METHODS

Clinical features and cell cycle pathway gene expression data were obtained from the Gene Expression Omnibus and The Cancer Genome Atlas databases. Differentially expressed genes (DEGs) were determined by the student t-test between HCC and noncancerous samples. Kaplan-Meier survival, univariate, and multivariate survival analyses and validation analysis were performed to characterize the associations between cell cycle gene expression and patients' overall survival and recurrence-free survival.

RESULTS

47 and 5 genes were significantly upregulated and downregulated genes in HCC samples, respectively. The high expression of BUB3, CDK1, and CHEK1 was associated with increased mortality (adjusted P value = 0.04, odds ratio (OR): 1.89 (95% confidence interval (CI): 1.04-3.46); adjusted P value = 0.02, OR: 2.06 (95% CI:1.15-3.75); and adjusted P value = 0.04, OR: 1.84 (%95 CI: 1.03-3.32), respectively). The expression of PTTG2 and RAD21 was significantly associated with cancer recurrence (adjusted P value = 0.01, OR: 2.17 (95% CI: 1.24-3.86); adjusted P value = 0.03, OR: 1.88[95% CI:1.08-3.28], respectively), while the low expression of MAD1L1 was associated with cancer recurrence (adjusted P value = 0.03, OR: 0.53 (%95 CI: 0.3-0.93)).

CONCLUSIONS

The present study demonstrated that BUB3, CDK1, and CHEK1 may serve as a prognostic biomarker for HCC patients. PTTG2, RAD21, and MAD1L1 expression is a major factor affecting the recurrence of HCC patients.

Critical slowing down and attractive manifold: A mechanism for dynamic robustness in the yeast cell-cycle process

Biological processes that execute complex multiple functions, such as the cell cycle, must ensure the order of sequential events and maintain dynamic robustness against various fluctuations. Here, we examine the mechanisms and fundamental structure that achieve these properties in the cell cycle of the budding yeast Saccharomyces cerevisiae. We show that this process behaves like an excitable system containing three well-decoupled saddle-node bifurcations to execute DNA replication and mitosis events. The yeast cell-cycle regulatory network can be divided into three modules-the G1/S phase, early M phase, and late M phase-wherein both positive feedback loops in each module and interactions among modules play important roles. Specifically, when the cell-cycle process operates near the critical points of the saddle-node bifurcations, a critical slowing down effect takes place. Such interregnum then allows for an attractive manifold and sufficient duration for cell-cycle events, within which to assess the completion of DNA replication and mitosis, e.g., spindle assembly. Moreover, such arrangement ensures that any fluctuation in an early module or event will not transmit to a later module or event. Thus, our results suggest a possible dynamical mechanism of the cell-cycle process to ensure event order and dynamic robustness and give insight into the evolution of eukaryotic cell-cycle processes.

CDK7 Mediates the Beta-Adrenergic Signaling in Thermogenic Brown and White Adipose Tissues

Cyclin-dependent kinases (CDKs) are emerging regulators of adipose tissue metabolism. Here we aimed to explore the role of CDK7 in thermogenic fat. We found that CDK7 brown adipose tissue (BAT)-specific knockout mice (Cdk7^bKO) have decreased BAT mass and impaired β3-adrenergic signaling and develop hypothermia upon cold exposure. We found that loss of CDK7 in BAT disrupts the induction of thermogenic genes in response to cold. However, Cdk7^bKO mice do not show systemic metabolic dysfunction. Increased expression of genes of the creatine metabolism compensates for the heat generation in the BAT of Cdk7^bKO mice in response to cold. Finally, we show that CDK7 is required for beta 3-adrenergic agonist-induced browning of white adipose tissue (WAT). Indeed, Cdk7 ablation in all adipose tissues (Cdk7^aKO) has impaired browning in WAT. Together, our results demonstrate that CDK7 is an important mediator of beta-adrenergic signaling in thermogenic brown and beige fat.

Par-4 mediated Smad4 induction in PDAC cells restores canonical TGF-β/ Smad4 axis driving the cells towards lethal EMT

Deregulation of TGF-β signaling is intricately engrossed in the pathophysiology of pancreatic adenocarcinomas (PDACs). The role of TGF-β all through pancreatic cancer initiation and progression is multifarious and somewhat paradoxical. TGF-β plays a tumor suppressive role in early-stage pancreatic cancer by promoting apoptosis and inhibiting epithelial cell cycle progression, but incites tumor promotion in late-stage by modulating genomic instability, neo-angiogenesis, immune evasion, cell motility, and metastasis. Here, we provide evidences that Par-4 acts as one of the vital mediators to regulate TGF-β/Smad4 pathway, wherein, Par-4 induction/over-expression induced EMT which was later culminated in to apoptosis in presence of TGF-β via positive regulation of Smad4. Intriguingly, Par-4^-/- cells were devoid of significant Smad4 induction compared to Par-4^+/+ cells in presence of TGF-β and ectopic Par-4 steadily augmented Smad4 expression by restoring TGF-β/Smad4 axis in Panc-1 cells. Further, our FACS and western blotting results unveiled that Par-4 dragged the PDAC cells to G₁ arrest in presence of TGF-β byelevating p21 and p27 levels while attenuating Cyclin E and A levels and augmenting caspase 3 cleavage triggering lethal EMT. Through restoration of Smad4, we further establish that in BxPC3 cell line (Smad4^-/-), Smad4 is essential for Par-4 to indulge TGF-β dependent lethal EMT program. The mechanistic relevance of Par-4 mediated Smad4 activation was additionally validated by co-immunoprecipitation wherein disruption of NM23H1-STRAP interaction by Par-4 rescues TGF-β/Smad4 pathway in PDAC and mediates the tumor suppressive role of TGF-β, therefore serving as a vital cog to restore the apoptotic functions of TGF-β pathway.

Skp2 in the ubiquitin-proteasome system: A comprehensive review

The ubiquitin-proteasome system (UPS) is a complex process that regulates protein stability and activity by the sequential actions of E1, E2 and E3 enzymes to influence diverse aspects of eukaryotic cells. However, due to the diversity of proteins in cells, substrate selection is a highly critical part of the process. As a key player in UPS, E3 ubiquitin ligases recruit substrates for ubiquitination specifically. Among them, RING E3 ubiquitin ligases which are the most abundant E3 ubiquitin ligases contribute to diverse cellular processes. The multisubunit cullin-RING ligases (CRLs) are the largest family of RING E3 ubiquitin ligases with tremendous plasticity in substrate specificity and regulate a vast array of cellular functions. The F-box protein Skp2 is a component of CRL1 (the prototype of CRLs) which is expressed in many tissues and participates in multiple cellular functions such as cell proliferation, metabolism, and tumorigenesis by contributing to the ubiquitination and subsequent degradation of several specific tumor suppressors. Most importantly, Skp2 plays a pivotal role in a plethora of cancer-associated signaling pathways. It enhances cell growth, accelerates cell cycle progression, promotes migration and invasion, and inhibits cell apoptosis among others. Hence, targeting Skp2 may represent a novel and attractive strategy for the treatment of different human cancers overexpressing this oncogene. In this review article, we summarized the known roles of Skp2 both in health and disease states in relation to the UPS.

CCNE1 Amplification as a Predictive Biomarker of Chemotherapy Resistance in Epithelial Ovarian Cancer

Ovarian cancer is the most-deadly gynecologic malignancy, with greater than 14,000 women expected to succumb to the disease this year in the United States alone. In the front-line setting, patients are treated with a platinum and taxane doublet. Although 40–60% of patients achieve complete clinical response to first-line chemotherapy, 25% are inherently platinum-resistant or refractory with a median overall survival of about one year. More than 80% of women afflicted with ovarian cancer will recur. Many attempts have been made to understand the mechanism of platinum and taxane based chemotherapy resistance. However, despite decades of research, few predictive markers of chemotherapy resistance have been identified. Here, we review the current understanding of one of the most common genetic alterations in epithelial ovarian cancer, CCNE1 (cyclin E1) amplification, and its role as a potential predictive marker of cytotoxic chemotherapy resistance. CCNE1 amplification has been identified as a primary oncogenic driver in a subset of high grade serous ovarian cancer that have an unmet clinical need. Understanding the interplay between cyclin E1 amplification and other common ovarian cancer genetic alterations provides the basis for chemotherapeutic resistance in CCNE1 amplified disease. Exploration of the effect of cyclin E1 amplification on the cellular machinery that causes dysregulated proliferation in cancer cells has allowed investigators to explore promising targeted therapies that provide the basis for emerging clinical trials.

A hybrid stochastic model of the budding yeast cell cycle

The growth and division of eukaryotic cells are regulated by complex, multi-scale networks. In this process, the mechanism of controlling cell-cycle progression has to be robust against inherent noise in the system. In this paper, a hybrid stochastic model is developed to study the effects of noise on the control mechanism of the budding yeast cell cycle. The modeling approach leverages, in a single multi-scale model, the advantages of two regimes: (1) the computational efficiency of a deterministic approach, and (2) the accuracy of stochastic simulations. Our results show that this hybrid stochastic model achieves high computational efficiency while generating simulation results that match very well with published experimental measurements.

Non-Thermal Atmospheric Pressure Bio-Compatible Plasma Stimulates Apoptosis via p38/MAPK Mechanism in U87 Malignant Glioblastoma

Nonthermal plasma is a promising novel therapy for the alteration of biological and clinical functions of cells and tissues, including apoptosis and inhibition of tumor progression. This therapy generates reactive oxygen and nitrogen species (RONS), which play a major role in anticancer effects. Previous research has verified that plasma jets can selectively induce apoptosis in various cancer cells, suggesting that it could be a potentially effective novel therapy in combination with or as an alternative to conventional therapeutic methods. In this study, we determined the effects of nonthermal air soft plasma jets on a U87 MG brain cancer cell line, including the dose- and time-dependent effects and the physicochemical and biological correlation between the RONS cascade and p38/mitogen-activated protein kinase (MAPK) signaling pathway, which contribute to apoptosis. The results indicated that soft plasma jets efficiently inhibit cell proliferation and induce apoptosis in U87 MG cells but have minimal effects on astrocytes. These findings revealed that soft plasma jets produce a potent cytotoxic effect via the initiation of cell cycle arrest and apoptosis. The production of reactive oxygen species (ROS) in cells was tested, and an intracellular ROS scavenger, N-acetyl cysteine (NAC), was examined. Our results suggested that soft plasma jets could potentially be used as an effective approach for anticancer therapy.

Lessons from equilibrium statistical physics regarding the assembly of protein complexes

In order to carry out their functions, most proteins assemble into multicomponent complexes. In the process of assembly, complexes need to discriminate their specific components from a mixture of hundreds of different proteins present in the cell. To assess some of the implications of this requirement, we develop a minimal model of self-assembly based on equilibrium statistical physics. We argue that the need to assemble reliably imposes fundamental constraints on the characteristics of complexes, which we support with analysis of available structural and compositional data. Our work constitutes only a step toward future theory of protein complex assembly, which will have to incorporate also nonequilibrium and kinetic aspects of this fundamental and rich, yet theoretically neglected, problem.

Cellular functions are established through biological evolution, but are constrained by the laws of physics. For instance, the physics of protein folding limits the lengths of cellular polypeptide chains. Consequently, many cellular functions are carried out not by long, isolated proteins, but rather by multiprotein complexes. Protein complexes themselves do not escape physical constraints, one of the most important being the difficulty of assembling reliably in the presence of cellular noise. In order to lay the foundation for a theory of reliable protein complex assembly, we study here an equilibrium thermodynamic model of self-assembly that exhibits 4 distinct assembly behaviors: diluted protein solution, liquid mixture, “chimeric assembly,” and “multifarious assembly.” In the latter regime, different protein complexes can coexist without forming erroneous chimeric structures. We show that 2 conditions have to be fulfilled to attain this regime: 1) The composition of the complexes needs to be sufficiently heterogeneous, and 2) the use of the set of components by the complexes has to be sparse. Our analysis of publicly available databases of protein complexes indicates that cellular protein systems might have indeed evolved so as to satisfy both of these conditions.

Chemical Regeneration of Wound Defects: Relevance to the Canine Palatal Mucosa and Cell Cycle Up-Regulation in Human Gingival Fibroblasts

Background

Trichloroacetic acid (TCA) is an agent widely applied in dermatology for skin regeneration. To test whether TCA can offer an advantage for the regeneration of oral soft tissue defects, the cellular events following TCA application were explored in vitro and its influence on the oral soft tissue wound healing was evaluated in a canine palate model.

Methods

The cytotoxicity and growth factor gene expression in human gingival fibroblasts were tested in vitro following the application of TCA at four concentrations (0.005%, 0.05%, 0.5% and 1%) with different time intervals (0, 3, 9 and 21 h). One concentration of TCA was selected to screen the genes differentially expressed using DNA microarray and the associated pathways were explored. TCA was injected in open wound defects of the palatal mucosa from beagle dogs (n = 3) to monitor their healing and regeneration up to day 16-post-administration.

Results

While the 0.5-1% concentration induced the cytoxicity, a significantly higher expression of growth factor genes was observed after 3 and 9 h following the 0.5% TCA application in comparison to other groups. DNA microarray analysis in 0.5% TCA group showed 417 genes with a significant 1.5-fold differential expression, involving pathways of cell cycle, FoxO signaling, p53 signaling, ubiquitin mediated proteolysis and cAMP signaling. In vivo results showed a faster reepithelialization of TCA-treated wounds as compared to spontaneous healing.

Conclusion

TCA promoted the healing and regeneration of oral soft tissue wound defects by up-regulating the cell cycle progression, cell growth, and cell viability, particularly at a concentration of 0.5%.

3-(3-Methoxyphenyl)-6-(3-amino-4-methoxyphenyl)-7H-[1,2,4] triazolo [3,4-b][1,3,4] thiadiazine, a novel tubulin inhibitor, evokes G2/M cell cycle arrest and apoptosis in SGC-7901 and HeLa cells

Gastric cancer and cervical cancer are two major malignant tumors that threaten human health. The novel chemotherapeutic drugs are needed urgently to treat gastric cancer and cervical cancer with high anticancer activity and metabolic stability. Previously we have reported the synthesis, characterization and identification of a novel combretastatin A-4 analog, 3-(3-methoxyphenyl)-6-(3-amino-4- methoxyphenyl) -7H-[1,2,4]triazolo[3,4-b][1,3,4] thiadiazine (XSD-7). In this study, we sought to investigate its anticancer mechanisms in a human gastric cancer cell line (SGC-7901 cells) and human cervical carcinoma cell line (HeLa cells). The 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay showed that XSD-7 induced cytotoxicity in SGC-7901 and HeLa cells with inhibitory concentration 50 values of 0.11 ± 0.03 and 0.12 ± 0.05 µM, respectively. Immunofluorescence studies proved that XSD-7 inhibited microtubule polymerization during cell division in SGC-7901 and HeLa cells. Then, these cells were arrested at G2/M cell cycle and subsequently progressed into apoptosis. In further study, mitochondrial membrane potential analysis and Western blot analysis demonstrated that XSD-7 treatment-induced SGC-7901 cell apoptosis via both the mitochondria-mediated pathway and the death receptor-mediated pathway. In contrast, XSD-7 induced apoptosis in HeLa cells mainly via the mitochondria-mediated pathway. Hence, our data indicate that XSD-7 exerted antiproliferative activity by disrupting microtubule dynamics, leading to cell cycle arrest, and eventually inducing cell apoptosis. XSD-7 with novel structure has the potential to be developed for therapeutic treatment of gastric cancer and cervical cancer.

Cell cycle dynamics in the reprogramming of cellular identity

Reprogramming of cellular identity is fundamentally at odds with replication of the genome: cell fate reprogramming requires complex multidimensional epigenomic changes, whereas genome replication demands fidelity. In this review, we discuss how the pace of the genome's replication and cell cycle influences the way daughter cells take on their identity. We highlight several biochemical processes that are pertinent to cell fate control, whose propagation into the daughter cells should be governed by more complex mechanisms than simple templated replication. With this mindset, we summarize multiple scenarios where rapid cell cycle could interfere with cell fate copying and promote cell fate reprogramming. Prominent examples of cell fate regulation by specific cell cycle phases are also discussed. Overall, there is much to be learned regarding the relationship between cell fate reprogramming and cell cycle control. Harnessing cell cycle dynamics could greatly facilitate the derivation of desired cell types.

Cullin Ring Ubiquitin Ligases (CRLs) in Cancer: Responses to Ionizing Radiation (IR) Treatment

Treatment with ionizing radiation (IR) remains the cornerstone of therapy for multiple cancer types, including disseminated and aggressive diseases in the palliative setting. Radiotherapy efficacy could be improved in combination with drugs that regulate the ubiquitin-proteasome system (UPS), many of which are currently being tested in clinical trials. The UPS operates through the covalent attachment of ATP-activated ubiquitin molecules onto substrates following the transfer of ubiquitin from an E1, to an E2, and then to the substrate via an E3 enzyme. The specificity of ubiquitin ligation is dictated by E3 ligases, which select substrates to be ubiquitylated. Among the E3s, cullin ring ubiquitin ligases (CRLs) represent prototypical multi-subunit E3s, which use the cullin subunit as a central assembling scaffold. CRLs have crucial roles in controlling the cell cycle, hypoxia signaling, reactive oxygen species clearance and DNA repair; pivotal factors regulating the cancer and normal tissue response to IR. Here, we summarize the findings on the involvement of CRLs in the response of cancer cells to IR, and we discuss the therapeutic approaches to target the CRLs which could be exploited in the clinic.