Differential regulation of retinoblastoma tumor suppressor protein by G(1) cyclin-dependent kinase complexes in vivo

Clinical considerations of CDK4/6 inhibitors in HER2 positive breast cancer

Deregulation of cell cycles can result in a variety of cancers, including breast cancer (BC). In fact, abnormal regulation of cell cycle pathways is often observed in breast cancer, leading to malignant cell proliferation. CDK4/6 inhibitors (CDK4/6i) can block the G1 cell cycle through the cyclin D-cyclin dependent kinase 4/6-inhibitor of CDK4-retinoblastoma (cyclinD-CDK4/6-INK4-RB) pathway, thus blocking the proliferation of invasive cells, showing great therapeutic potential to inhibit the spread of BC. So far, three FDA-approved drugs have been shown to be effective in the management of advanced hormone receptor positive (HR+) BC: palbociclib, abemaciclib, and ribociclib. The combination strategy of CDK4/6i and endocrine therapy (ET) has become the standard therapeutic regimen and is increasingly applied to advanced BC patients. The present study aims to clarify whether CDK4/6i can also achieve a certain therapeutic effect on Human epidermal growth factor receptor 2 positive (HER2+) BC. Studies of CDK4/6i are not limited to patients with estrogen receptor positive/human epidermal growth factor receptor 2 negative (ER+/HER2-) advanced BC, but have also expanded to other types of BC. Several pre-clinical and clinical trials have demonstrated the potential of CDK4/6i in treating HER2+ BC. Therefore, this review summarizes the current knowledge and recent findings on the use of CDK4/6i in this type of BC, and provides ideas for the discovery of new treatment modalities.

Exploring the Role of microRNAs in Glioma Progression, Prognosis, and Therapeutic Strategies

Gliomas, which arise from glial cells in the brain, remain a significant challenge due to their location and resistance to traditional treatments. Despite research efforts and advancements in healthcare, the incidence of gliomas has risen dramatically over the past two decades. The dysregulation of microRNAs (miRNAs) has prompted the creation of therapeutic agents that specially target them. However, it has been reported that they are involved in complex signaling pathways that contribute to the loss of expression of tumor suppressor genes and the upregulation of the expression of oncogenes. In addition, numerous miRNAs promote the development, progression, and recurrence of gliomas by targeting crucial proteins and enzymes involved in metabolic pathways such as glycolysis and oxidative phosphorylation. However, the complex interplay among these pathways along with other obstacles hinders the ability to apply miRNA targeting in clinical practice. This highlights the importance of identifying specific miRNAs to be targeted for therapy and having a complete understanding of the diverse pathways they are involved in. Therefore, the aim of this review is to provide an overview of the role of miRNAs in the progression and prognosis of gliomas, emphasizing the different pathways involved and identifying potential therapeutic targets.

A novel CDK4/6 inhibitor combined with irradiation demonstrates potent anti-tumor efficacy in diffuse midline glioma

OBJECTIVE

Diffuse midline glioma, H3 K27-altered (DMG) is a lethal pediatric brainstem tumor. Despite numerous efforts to improve survival benefits, its prognosis remains poor. This study aimed to design and synthesize a novel CDK4/6 inhibitor YF-PRJ8-1011, which exhibited more potent antitumor activity against a panel of patient-derived DMG tumor cells in vitro and in vivo compared with palbociclib.

METHODS

Patient-derived DMG cells were used to assess the antitumor efficacy of YF-PRJ8-1011 in vitro. The liquid chromatography tandem-mass spectrometry method was used to measure the activity of YF-PRJ8-1011 passing through the blood-brain barrier. DMG patient-derived xenograft models were established to detect the antitumor efficacy of YF-PRJ8-1011.

RESULTS

The results showed that YF-PRJ8-1011 could inhibit the growth of DMG cells both in vitro and in vivo. YF-PRJ8-1011 could well penetrate the blood-brain barrier. It also significantly inhibited the growth of DMG tumors and prolonged the overall survival of mice compared with vehicle or palbociclib. Most notably, it exerted potent antitumor efficacy in DMG in vitro and in vivo compared with palbociclib. In addition, we also found that YF-PRJ8-1011 combined with radiotherapy also showed more significant inhibition of DMG xenograft tumor growth than radiotherapy alone.

CONCLUSION

Collectively, YF-PRJ8-1011 is a novel, safe, and selective CDK4/6 inhibitor for DMG treatment.

OTX1 silencing suppresses ovarian cancer progression through inhibiting the JAK/STAT signaling

BACKGROUND

The aim of our study was to investigate the roles and the underlying mechanisms of orthodenticle homolog 1 (OTX1) in ovarian cancer.

METHODS

OTX1 expression was obtained from TCGA database. OTX1 expression in ovarian cancer cells was detected using qRT-PCR and western blot assay. The cell viability and proliferation was detected by CCK-8 and EdU assays. Cell invasion and migration were detected by transwell assay. Flow cytometry was utilized to determine cell apoptosis and cycle. In addition, western blot assay was used to detect the expression of cell cycle related protein (Cyclin D1 and p21), epithelial-mesenchymal transition (EMT) related protein (E-cadherin, N-cadherin, Vimentin, and Snail), apoptosis related protein (Bcl-2, Bax, and cleaved caspase-3), and JAK/STAT pathway related protein (p-JAK2, JAK2, STAT3, and p-STAT3).

RESULTS

OTX1 was highly expressed in ovarian cancer tissues and cells. OTX1 silencing blocked the cell cycle and repressed cell viability, proliferation, invasion, and migration, while OTX1 silencing facilitated the apoptosis of OVCAR3 and Caov3 cells. OTX1 silencing increased the protein levels of p21, E-cadherin, Bax, and cleaved caspase-3, while the protein levels of Cyclin D1, Bcl-2, N-cadherin, Vimentin, and Snail were decreased by OTX1 silencing. Furthermore, OTX1 silencing suppressed the protein levels of p-JAK2/JAK2 and p-STAT3/STAT3 in OVCAR3 and Caov3 cells. Moreover, overexpression of OTX1 promoted cell proliferation and invasion and inhibited apoptosis in Caov3 cells, but AG490 (an inhibitor of JAK/STAT pathway) reversed the influences on cell biological behavior induced by overexpression of OTX1.

CONCLUSIONS

OTX1 silencing repressed ovarian cancer cell proliferation, invasion, and migration and induced cell apoptosis, which might be involved in JAK/STAT signaling pathway. OTX1 may be considered as a novel therapeutic target for ovarian cancer.

Bridged Proteolysis Targeting Chimera (PROTAC) Enables Degradation of Undruggable Targets

Proteolysis Targeting Chimeras (PROTACs) are attractive therapeutic modalities for degrading disease-causing proteins. While many PROTACs have been developed for numerous protein targets, current small-molecule PROTAC approaches cannot target undruggable proteins that do not have small-molecule binders. Here, we present a novel PROTAC approach, termed bridged PROTAC, which utilizes a small-molecule binder of the target protein's binding partner to recruit the protein complex into close proximity with an E3 ubiquitin ligase to target undruggable proteins. Applying this bridged PROTAC strategy, we discovered MS28, the first-in-class degrader of cyclin D1, which lacks a small-molecule binder. MS28 effectively degrades cyclin D1, with faster degradation kinetics and superior degradation efficiency than CDK4/6, through recruiting the CDK4/6-cyclin D1 complex to the von Hippel-Lindau E3 ligase. MS28 also suppressed the proliferation of cancer cells more effectively than CDK4/6 inhibitors and degraders. Altogether, the bridged PROTAC strategy could provide a generalizable platform for targeting undruggable proteins.

DNASE1L3 inhibits hepatocellular carcinoma by delaying cell cycle progression through CDK2

PURPOSE

Dysregulated cell cycle targeting is a well-established therapeutic strategy against hepatocellular carcinoma (HCC). Dissecting the underlying mechanism may improve the efficacy of HCC therapy.

METHODS

HCC data from TCGA and new clinical samples were used for DNASE1L3 expression analysis and for assessing its correlation with HCC development. The in vitro function of DNASE1L3 in HCC cell proliferation, colony formation, migration and invasion was assessed using RTCA, CCK-8 and transwell assays and the in vivo function in subcutaneous tumor formation in a xenograft nude mouse model. The role of DNASE1L3 in HCC tumorigenesis was further verified in AKT/NRASV12-induced and DEN/CCl₄-induced primary liver cancers in wildtype and Dnase1l3^-/- mice. Finally, RNA-Seq analysis followed by biochemical methods including cell cycle, immunofluorescence, co-immunoprecipitation and Western blotting assays were employed to reveal the underlying mechanism.

RESULTS

We found that DNASE1L3 was significantly downregulated and served as a favorable prognostic factor in HCC. DNASE1L3 dramatically attenuated HCC cell proliferation, colony formation, migration and invasion in vitro and reduced subcutaneous tumor formation in nude mice in vivo. Furthermore, DNASE1L3 overexpression dampened AKT/NRASV12-induced mouse liver cancer in wildtype mice and DNASE1L3 deficiency worsened DEN/CCl₄-induced liver cancer in Dnase1l3^-/- mice. Systemic analysis revealed that DNASE1L3 impaired HCC cell cycle progression by interacting with CDK2 and inhibiting CDK2-stimulated E2F1 activity. C-terminal deletion (DNASE1L3^ΔCT) diminished the interaction with CDK2 and abrogated the inhibitory function against HCC.

CONCLUSION

Our study unveils DNASE1L3 as a novel HCC cell cycle regulator and tumor suppressor. DNASE1L3 impairs HCC tumorigenesis by delaying cell cycle progression possibly through disrupting the positive E2F1-CDK2 regulatory loop. DNASE1L3 may serve as a target for the development of novel therapeutic strategies against HCC.

The Four Homeostasis Knights: In Balance upon Post-Translational Modifications

A cancer outcome is a multifactorial event that comes from both exogenous injuries and an endogenous predisposing background. The healthy state is guaranteed by the fine-tuning of genes controlling cell proliferation, differentiation, and development, whose alteration induces cellular behavioral changes finally leading to cancer. The function of proteins in cells and tissues is controlled at both the transcriptional and translational level, and the mechanism allowing them to carry out their functions is not only a matter of level. A major challenge to the cell is to guarantee that proteins are made, folded, assembled and delivered to function properly, like and even more than other proteins when referring to oncogenes and onco-suppressors products. Over genetic, epigenetic, transcriptional, and translational control, protein synthesis depends on additional steps of regulation. Post-translational modifications are reversible and dynamic processes that allow the cell to rapidly modulate protein amounts and function. Among them, ubiquitination and ubiquitin-like modifications modulate the stability and control the activity of most of the proteins that manage cell cycle, immune responses, apoptosis, and senescence. The crosstalk between ubiquitination and ubiquitin-like modifications and post-translational modifications is a keystone to quickly update the activation state of many proteins responsible for the orchestration of cell metabolism. In this light, the correct activity of post-translational machinery is essential to prevent the development of cancer. Here we summarize the main post-translational modifications engaged in controlling the activity of the principal oncogenes and tumor suppressors genes involved in the development of most human cancers.

Explaining Redundancy in CDK-Mediated Control of the Cell Cycle: Unifying the Continuum and Quantitative Models

In eukaryotes, cyclin-dependent kinases (CDKs) are required for the onset of DNA replication and mitosis, and distinct CDK–cyclin complexes are activated sequentially throughout the cell cycle. It is widely thought that specific complexes are required to traverse a point of commitment to the cell cycle in G1, and to promote S-phase and mitosis, respectively. Thus, according to a popular model that has dominated the field for decades, the inherent specificity of distinct CDK–cyclin complexes for different substrates at each phase of the cell cycle generates the correct order and timing of events. However, the results from the knockouts of genes encoding cyclins and CDKs do not support this model. An alternative “quantitative” model, validated by much recent work, suggests that it is the overall level of CDK activity (with the opposing input of phosphatases) that determines the timing and order of S-phase and mitosis. We take this model further by suggesting that the subdivision of the cell cycle into discrete phases (G0, G1, S, G2, and M) is outdated and problematic. Instead, we revive the “continuum” model of the cell cycle and propose that a combination with the quantitative model better defines a conceptual framework for understanding cell cycle control.

Post-translational modifications on the retinoblastoma protein

The retinoblastoma protein (pRb) functions as a cell cycle regulator controlling G1 to S phase transition and plays critical roles in tumour suppression. It is frequently inactivated in various tumours. The functions of pRb are tightly regulated, where post-translational modifications (PTMs) play crucial roles, including phosphorylation, ubiquitination, SUMOylation, acetylation and methylation. Most PTMs on pRb are reversible and can be detected in non-cancerous cells, playing an important role in cell cycle regulation, cell survival and differentiation. Conversely, altered PTMs on pRb can give rise to anomalies in cell proliferation and tumourigenesis. In this review, we first summarize recent findings pertinent to how individual PTMs impinge on pRb functions. As many of these PTMs on pRb were published as individual articles, we also provide insights on the coordination, either collaborations and/or competitions, of the same or different types of PTMs on pRb. Having a better understanding of how pRb is post-translationally modulated should pave the way for developing novel and specific therapeutic strategies to treat various human diseases.

Tumor Suppressors Having Oncogenic Functions: The Double Agents

Cancer progression involves multiple genetic and epigenetic events, which involve gain-of-functions of oncogenes and loss-of-functions of tumor suppressor genes. Classical tumor suppressor genes are recessive in nature, anti-proliferative, and frequently found inactivated or mutated in cancers. However, extensive research over the last few years have elucidated that certain tumor suppressor genes do not conform to these standard definitions and might act as “double agents”, playing contrasting roles in vivo in cells, where either due to haploinsufficiency, epigenetic hypermethylation, or due to involvement with multiple genetic and oncogenic events, they play an enhanced proliferative role and facilitate the pathogenesis of cancer. This review discusses and highlights some of these exceptions; the genetic events, cellular contexts, and mechanisms by which four important tumor suppressors—pRb, PTEN, FOXO, and PML display their oncogenic potentials and pro-survival traits in cancer.

Overexpression of LINC00852 promotes prostate cancer cell proliferation and metastasis

AIM

Long noncoding RNAs play a key role in the development and progression of various human cancers. Recently, LINC00852 has been reported to be associated with spinal metastasis lung adenocarcinoma. However, the role and potential mechanisms of LINC00852 in prostate cancer cells remain largely unknown.

METHODS

LINC00852 expression in prostate cancer cells was examined by quantitative real-time polymerase chain reaction. Western blotting was used to detect protein expressions in prostate cancer cells. Cell cycle was analyzed by flow cytometric analysis. Cell proliferation was measured by cck-8 assay. The migration and invasion capabilities were determined using transwell assays.

RESULTS

In this study, we found that LINC00852 was highly expressed in prostate cancer tissues based on the TCGA database. Overexpression of LINC00852 mediated by lentivirus significantly reinforced the proliferation and colony formation abilities of prostate cancer cell linePC3. The migration and invasion capabilities were also augmented by overexpression of LINC00852. Flow cytometric analysis revealed that LINC00852 overexpression resulted in a decrease of cells in G0/G1 phase. Moreover, overexpression of LINC00852 affected the expression of epithelial-mesenchymal transition-related proteins.

CONCLUSIONS

Our data collectively demonstrate that LINC00852 contributes to prostate cancer proliferation and metastasis, indicating that LINC00852is a new promising diagnostic and therapeutic target for treatment of prostate cancer.

Citrus hystrix Extracts Protect Human Neuronal Cells against High Glucose-Induced Senescence

Citrus hystrix (CH) is a beneficial plant utilized in traditional folk medicine to relieve various health ailments. The antisenescent mechanisms of CH extracts were investigated using human neuroblastoma cells (SH-SY5Y). Phytochemical contents and antioxidant activities of CH extracts were analyzed using a gas chromatograph–mass spectrometer (GC-MS), 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay and 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) assay. Effects of CH extracts on high glucose-induced cytotoxicity, reactive oxygen species (ROS) generation, cell cycle arrest and cell cycle-associated proteins were assessed using a 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tetrazolium (MTT) assay, non-fluorescent 2′, 7′-dichloro-dihydrofluorescein diacetate (H₂DCFDA) assay, flow cytometer and Western blot. The extracts protected neuronal senescence by inhibiting ROS generation. CH extracts induced cell cycle progression by releasing senescent cells from the G1 phase arrest. As the Western blot confirmed, the mechanism involved in cell cycle progression was associated with the downregulation of cyclin D1, phospho-cell division cycle 2 (pcdc2) and phospho-Retinoblastoma (pRb) proteins. Furthermore, the Western blot showed that extracts increased Surtuin 1 (SIRT1) expression by increasing the phosphorylation of Glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Collectively, CH extracts could protect high glucose-induced human neuronal senescence by inducing cell cycle progression and up-regulation of SIRT1, thus leading to the improvement of the neuronal cell functions.

Restriction point regulation at the crossroads between quiescence and cell proliferation

The coordination of cell proliferation with reversible cell cycle exit into quiescence is crucial for the development of multicellular organisms and for tissue homeostasis in the adult. The decision between quiescence and proliferation occurs at the restriction point, which is widely thought to be located in the G1 phase of the cell cycle, when cells integrate accumulated extracellular and intracellular signals to drive this binary cellular decision. On the molecular level, decision-making is exerted through the activation of cyclin-dependent kinases (CDKs). CDKs phosphorylate the retinoblastoma (Rb) transcriptional repressor to regulate the expression of cell cycle genes. Recently, the classical view of restriction point regulation has been challenged. Here, we review the latest findings on the activation of CDKs, Rb phosphorylation and the nature and position of the restriction point within the cell cycle.

SPH3643: A novel cyclin-dependent kinase 4/6 inhibitor with good anticancer efficacy and strong blood-brain barrier permeability

The cyclin‐dependent kinase (CDK)4/6‐cyclin D1‐Rb‐p16/ink4a pathway is responsible for regulating cell progression past the G₁ restriction point during the cell cycle. The development of a majority of human tumors is associated with dysregulation of this pathway, resulting in increased cancer cell proliferation. Both CDK4 and CDK6, well‐validated cancer drug targets, function primarily as catalytic enzymes that mediate the phosphorylation of retinoblastoma protein (Rb). Here, we determined that SPH3643 is a novel potent antiproliferative agent that inhibits CDK4/6 kinase activity. In biochemical assays, SPH3643 showed more potent inhibition of both CDK4 and CDK6 than did 2 published CDK4/6 inhibitors, LY2835219 and palbociclib, and had better selectivity than LY2835219. Further in vitro study revealed that SPH3643 blocked Cdk/Rb signaling by inhibiting the phosphorylation of Rb^Ser780 and arrested the MCF‐7 cancer cells at G₀/G₁ phase, resulting in marked inhibition of the proliferation of Rb‐positive cancer cell lines. In vivo SPH3643 treatment in mice bearing xenograft tumor models of breast cancer, colon cancer, acute myelocytic leukemia, and glioblastoma resulted in significant decreases in tumor growth. SPH3643 was able to particularly strongly inhibit glioblastoma (U87‐MG) cell growth in the brains of orthotopic carcinoma xenograft mice due to its high degree of intracerebral penetration and significant persistence in this setting. Together these results revealed that SPH3643 is a potent, orally active small‐molecule inhibitor of CDK4/6 with robust anticancer efficacy and a high degree of blood‐brain barrier permeability.

Working on Genomic Stability: From the S-Phase to Mitosis

Fidelity in chromosome duplication and segregation is indispensable for maintaining genomic stability and the perpetuation of life. Challenges to genome integrity jeopardize cell survival and are at the root of different types of pathologies, such as cancer. The following three main sources of genomic instability exist: DNA damage, replicative stress, and chromosome segregation defects. In response to these challenges, eukaryotic cells have evolved control mechanisms, also known as checkpoint systems, which sense under-replicated or damaged DNA and activate specialized DNA repair machineries. Cells make use of these checkpoints throughout interphase to shield genome integrity before mitosis. Later on, when the cells enter into mitosis, the spindle assembly checkpoint (SAC) is activated and remains active until the chromosomes are properly attached to the spindle apparatus to ensure an equal segregation among daughter cells. All of these processes are tightly interconnected and under strict regulation in the context of the cell division cycle. The chromosomal instability underlying cancer pathogenesis has recently emerged as a major source for understanding the mitotic processes that helps to safeguard genome integrity. Here, we review the special interconnection between the S-phase and mitosis in the presence of under-replicated DNA regions. Furthermore, we discuss what is known about the DNA damage response activated in mitosis that preserves chromosomal integrity.

ASC-1 Is a Cell Cycle Regulator Associated with Severe and Mild Forms of Myopathy

OBJECTIVE

Recently, the ASC-1 complex has been identified as a mechanistic link between amyotrophic lateral sclerosis and spinal muscular atrophy (SMA), and 3 mutations of the ASC-1 gene TRIP4 have been associated with SMA or congenital myopathy. Our goal was to define ASC-1 neuromuscular function and the phenotypical spectrum associated with TRIP4 mutations.

METHODS

Clinical, molecular, histological, and magnetic resonance imaging studies were made in 5 families with 7 novel TRIP4 mutations. Fluorescence activated cell sorting and Western blot were performed in patient-derived fibroblasts and muscles and in Trip4 knocked-down C2C12 cells.

RESULTS

All mutations caused ASC-1 protein depletion. The clinical phenotype was purely myopathic, ranging from lethal neonatal to mild ambulatory adult patients. It included early onset axial and proximal weakness, scoliosis, rigid spine, dysmorphic facies, cutaneous involvement, respiratory failure, and in the older cases, dilated cardiomyopathy. Muscle biopsies showed multiminicores, nemaline rods, cytoplasmic bodies, caps, central nuclei, rimmed fibers, and/or mild endomysial fibrosis. ASC-1 depletion in C2C12 and in patient-derived fibroblasts and muscles caused accelerated proliferation, altered expression of cell cycle proteins, and/or shortening of the G0/G1 cell cycle phase leading to cell size reduction.

INTERPRETATION

Our results expand the phenotypical and molecular spectrum of TRIP4-associated disease to include mild adult forms with or without cardiomyopathy, associate ASC-1 depletion with isolated primary muscle involvement, and establish TRIP4 as a causative gene for several congenital muscle diseases, including nemaline, core, centronuclear, and cytoplasmic-body myopathies. They also identify ASC-1 as a novel cell cycle regulator with a key role in cell proliferation, and underline transcriptional coregulation defects as a novel pathophysiological mechanism. ANN NEUROL 2020;87:217-232.

Epstein-Barr Virus Nuclear Antigen 3C Facilitates Cell Proliferation by Regulating Cyclin D2

Cell cycle regulation is one of the hallmarks of virus-mediated oncogenesis. Epstein-Barr virus (EBV)-induced lymphomas express a repertoire of essential viral latent proteins that regulate expression of cell cycle-related proteins to dysregulate this process, thereby facilitating the proliferation of infected cells. We now demonstrate that the essential EBV latent protein 3C (EBNA3C) stabilizes cyclin D2 to regulate cell cycle progression. More specifically, EBNA3C directly binds to cyclin D2 and they colocalize together in nuclear compartments. We show that EBNA3C regulates the promoter of cyclin D2 through cooperation with master transcription factor Bcl6 and enhances its stability by inhibiting its ubiquitin-dependent degradation. EBNA3C also promoted cell proliferation in the presence of cyclin D2, suggesting that cyclin D2 contributes to EBNA3C-mediated cell cycle progression. These results provide new clues as to the role of this essential viral latent protein and its ability to regulate expression of cellular factors, which drives the oncogenic process.IMPORTANCE Epstein-Barr virus (EBV) is the first identified human tumor virus and is associated with a range of human cancers. During EBV-induced lymphomas, the essential viral latent proteins modify the expression of cell cycle-related proteins to disturb the cell cycle process, thereby facilitating the proliferative process. The essential EBV nuclear antigen 3C (EBNA3C) plays an important role in EBV-mediated B-cell transformation. Here we show that EBNA3C stabilizes cyclin D2 to regulate cell cycle progression. More specifically, EBNA3C directly binds to cyclin D2, and they colocalize together in nuclear compartments. EBNA3C enhances cyclin D2 stability by inhibiting its ubiquitin-dependent degradation and significantly promotes cell proliferation in the presence of cyclin D2. Our results provide novel insights into the function of EBNA3C on cell progression by regulating the cyclin D2 protein and raise the possibility of the development of new anticancer therapies against EBV-associated cancers.

Dowregulation of OTX1 attenuates gastric cancer cell proliferation, migration and invasion

Orthodenticle homolog 1 (OTX1) has previously been revealed to be tightly associated with the development and progression of several human tumors. However, the functional roles and underlying molecular mechanisms of OTX1 in gastric cancer (GC) remain poorly understood. In the present study, we observed that OTX1 was highly expressed in GC tissues compared with adjacent non-tumor tissues based on a large cohort of samples from The Cancer Genome Atlas (TCGA) database. An immunohistochemical analysis indicated that OTX1 levels were increased in tumors that became metastatic compared with those in tumors that did not. This finding was significantly associated with patients who had shorter overall survival times. The knockdown of OTX1 significantly inhibited the proliferation, migration and invasion of SGC-7901 and MGC-803 cells. Furthermore, the knockdown of OTX1 induced cell cycle arrest in the G₀/G₁ phase and reduced the expression of cyclin D1. In addition, the inhibition of OTX1 led to increased GC cell apoptosis by upregulating cleaved PARP, cleaved caspase-3 and Bax. In conclusion, our data indicated that OTX1 functions as a key regulator in tumor growth and metastasis of GC cells. Thus, OTX1 may be a promising novel target for molecular therapy directed toward GC.

Activation of FOXO3a reverses 5-Fluorouracil resistance in human breast cancer cells

Breast cancer is the most frequently diagnosed tumor type and the primary leading cause of cancer deaths in women worldwide. Drug resistance is the major obstacle for breast cancer treatment improvement. TRAIL-inducing compound 10 (Tic10), a novel activator of FOXO3, exhibits potent antitumor efficacy both in vitro and in vivo. In the present study, we investigated the resistance reversal effect of Tic10 on multidrug-resistant breast cancer cells T47D/5Fu derived from T47D breast cancer cells. We found that FOXO3a was significantly decreased in T47D/5-Fu cells, whereas treatment of Tic10 enhances FOXO3a expression and nuclear translocation. Moreover, treatment of Tic10 could reverses 5-Fluorouracil resistance of T47D/5-Fu cells via induction of G0/G1 cell cycle arrest and apoptosis. Furthermore, we found that Tic10 decreased the expression of CDK4 via FOXO3a-dependment mechanism. In addition, our data showed that Tic10 could sensitize drug resistant T47D/5-Fu cells to 5-Fu in vivo. Taken together, these data suggested Tic10 as capable of restoring sensitivity for drug-resistant breast cancer cells.

Knockdown of KIF26B inhibits breast cancer cell proliferation, migration, and invasion

Background

Kinesin family member 26B (KIF26B) plays a key role in the development and progression of many human cancers. However, the role and underlying mechanisms of KIF26B in breast cancer cells remain unknown.

Materials and methods

In this study, we inhibited the expression of KIF26B in MDA-MB-231 and MCF-7 cells using lentivirus-delivered shRNA.

Results

Lentivirus-mediated KIF26B knockdown significantly suppressed cell proliferation, colony formation, migration, and invasion. Furthermore, cell cycle analyses revealed that the percentage of cells in the G0/G1 phase was significantly increased in KIF26B knockdown cells. Moreover, the knockdown of KIF26B significantly promoted cell apoptosis via the upregulation of cleaved caspase-3 and Bax.

Conclusion

Our data indicate that KIF26B plays a pivotal role in tumor growth and metastasis in breast cancer cells and may be a potential therapeutic target for treating breast cancer.

The innovative regularity and role of p16 methylation in blood during HCC development

Purpose: This study was performed to examine the regularity and role of p16 methylation in hepatocellular carcinoma (HCC) blood.

Methods: Big data of the case-control studies due to blood p16 methylation detection were collected in English and Chinese Journals. The risk of HCC's histologic process was investigated using both Meta-analysis and the quantitative correlation analysis.

Results: p16 methylation frequencies in blood were gradually increased from 0 % in normal to 10 % in benign disease, and to 60 % in HCC development. Based on p16 methylation of normal control blood, p16 methylation between normal and benign disease had no risk, and the methylation risk in HCC was significantly increased from normal to HCC through benign disease OR, 95% CI =16.23 ( 11.66, 22.58 ). Compared with the benign disease matched by HCC patient, the methylation risk of p16 in HCC was found, with the pooled OR value of 10.06 (95% IC = 7.64, 13.21) in blood. In addition, the regulatory mechanism affecting p16 methylation risk in normal blood had no role, and the strength of p16 methylation risk was rapidly increased between benign diseases and HCC blood. p16 methylation risk started from the patients with benign disease in blood. These results in blood and tissue detection were basically consistent.

Conclusions: HCC pathogenesis affecting p16 methylation don't work during normal blood, when from benign diseases to HCC bloods, can produce powerful role. The transcriptional inactivation associated with p16 methylation might start from benign liver disease, and might be increased from benign liver disease to HCC process. p16 methylation in blood can be used as a promising non-invasive biomarker to HCC's prediction and diagnosis.

Quantitative Cell Cycle Analysis Based on an Endogenous All-in-One Reporter for Cell Tracking and Classification

Cell cycle kinetics are crucial to cell fate decisions. Although live imaging has provided extensive insights into this relationship at the single-cell level, the limited number of fluorescent markers that can be used in a single experiment has hindered efforts to link the dynamics of individual proteins responsible for decision making directly to cell cycle progression. Here, we present fluorescently tagged endogenous proliferating cell nuclear antigen (PCNA) as an all-in-one cell cycle reporter that allows simultaneous analysis of cell cycle progression, including the transition into quiescence, and the dynamics of individual fate determinants. We also provide an image analysis pipeline for automated segmentation, tracking, and classification of all cell cycle phases. Combining the all-in-one reporter with labeled endogenous cyclin D1 and p21 as prime examples of cell-cycle-regulated fate determinants, we show how cell cycle and quantitative protein dynamics can be simultaneously extracted to gain insights into G1 phase regulation and responses to perturbations.

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Endogenous mRuby-PCNA as an all-in-one cell cycle reporter

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Automated image analysis pipeline to segment, track, and classify based on PCNA

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Quantitative analysis of cyclin oscillations during a complete cell cycle

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Cyclin D1 maintains G1 phase and prevents the transition into quiescence

An In Vitro Model of Cellular Quiescence in Primary Human Dermal Fibroblasts

Cellular quiescence is a reversible mode of cell cycle exit that allows cells and organisms to withstand unfavorable stress conditions. The factors that underlie the entry, exit, and maintenance of the quiescent state are crucial for understanding normal tissue development and function as well as pathological conditions such as chronic wound healing and cancer. In vitro models of quiescence have been used to understand the factors that contribute to quiescence under well-controlled experimental conditions. Here, we describe an in vitro model of quiescence that is based on neonatal human dermal fibroblasts. The fibroblasts are induced into quiescence by antiproliferative signals, contact inhibition, and serum-starvation (mitogen withdrawal). We describe the isolation of fibroblasts from skin, methods for inducing quiescence in isolated fibroblasts, and approaches to manipulate the fibroblasts in proliferating and quiescent states to determine critical regulators of quiescence.

Distinct molecular subtypes of uterine leiomyosarcoma respond differently to chemotherapy treatment

Background

Uterine leiomyosarcoma (ULMS) is an aggressive form of soft tissue tumors. The molecular heterogeneity and pathogenesis of ULMS are not well understood.

Methods

Expression profiling data were used to determine the possibility and optimal number of ULMS molecular subtypes. Next, clinicopathological characters and molecular pathways were analyzed in each subtype to prospect the clinical applications and progression mechanisms of ULMS.

Results

Two distinct molecular subtypes of ULMS were defined based on different gene expression signatures. Subtype I ULMS recapitulated low-grade ULMS, the gene expression pattern of which resembled normal smooth muscle cells, characterized by overexpression of smooth muscle function genes such as LMOD1, SLMAP, MYLK, MYH11. In contrast, subtype II ULMS recapitulated high-grade ULMS with higher tumor weight and invasion rate, and was characterized by overexpression of genes involved in the pathway of epithelial to mesenchymal transition and tumorigenesis, such as CDK6, MAPK13 and HOXA1.

Conclusions

We identified two distinct molecular subtypes of ULMS responding differently to chemotherapy treatment. Our findings provide a better understanding of ULMS intrinsic molecular subtypes, and will potentially facilitate the development of subtype-specific diagnosis biomarkers and therapy strategies for these tumors.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3568-y) contains supplementary material, which is available to authorized users.

The antiviral cytokine interferon-gamma restricts neural stem/progenitor cell proliferation through activation of STAT1 and modulation of retinoblastoma protein phosphorylation

Neural stem/progenitor cells (NPSCs) express receptors for many inflammatory cytokines, with varying effects on differentiation and proliferation depending on the stage of development and the milieu of inflammatory mediators. In primary neurons and astrocytes, we recently showed that interferon gamma (IFNγ), a potent antiviral cytokine that is required for the control and clearance of many central nervous system (CNS) infections, could differentially affect cell survival and cell cycle progression depending upon the cell type and the profile of activated intracellular signaling molecules. Here, we show that IFNγ inhibits proliferation of primary NSPCs through dephosphorylation of the tumor suppressor Retinoblastoma protein (pRb), which is dependent on activation of signal transducers and activators of transcription‐1 (STAT1) signaling pathways. Our results show i) IFNγ inhibits neurosphere growth and proliferation rate in a dose‐dependent manner; ii) IFNγ blocks cell cycle progression through a late‐stage G1/S phase restriction; iii) IFNγ induces phosphorylation and expression of STAT1 and STAT3; iv) IFNγ decreases cyclin E/cdk2 expression and reduces phosphorylation of cyclin D1 and pRb on serine residue 795; and v) the effects of IFNγ on NSPC proliferation, cell cycle protein expression, and pRb phosphorylation are STAT1‐dependent. These data define a mechanism by which IFNγ could contribute to a reduction in NSPC proliferation in inflammatory conditions. Further delineation of the effects of inflammatory cytokines on NSPC growth could improve our understanding of how CNS infections and other inflammatory events disrupt brain development and NSPC function. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Schisandrin B inhibits cell proliferation and induces apoptosis in human cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is the second most common hepatic cancer with high resistance to current chemotherapies and extremely poor prognosis. The present study aimed to examine the effects of schisandrin B (Sch B) on CCA cells both in vitro and in vivo and to examine its underlying mechanism. We found that Sch B inhibited the viability and proliferation of CCA cells in a dose- and time-dependent manner as assessed by MTT and colony formation assays. The flow cytometric assay revealed G0/G1 phase arrest in the Sch B-treated HCCC-9810 and RBE cells. In addition, Sch B induced intrahepatic cholangiocarcinoma apoptosis as shown by the results of Annexin V/PI double staining. Rhodamine 123 staining revealed that Sch B decreased the mitochondrial membrane potential (ΔΨm) in a dose-dependent manner. Mechanistically, western blot analysis indicated that Sch B induced apoptosis by upregulating Bax, cleaved caspase-3, cleaved caspase-9 and cleaved PARP, and by downregulating cyclin D1, Bcl-2 and CDK-4. Moreover, Sch B significantly inhibited HCCC-9810 xenograft growth in athymic nude mice. In summary, these findings suggest that Sch B exhibited potent antitumor activities via the induction of CCA apoptosis and that Sch B may be a promising drug for the treatment of CCA.

SENP1-modulated sumoylation regulates retinoblastoma protein (RB) and Lamin A/C interaction and stabilization

The retinoblastoma tumor suppressor protein (RB) plays a critical role in cell proliferation and differentiation and its inactivation is a frequent underlying factor in tumorigenesis. While the regulation of RB function by phosphorylation is well studied, proteasome-mediated RB protein degradation is emerging as an important regulatory mechanism. Although our understanding of RB turnover is currently limited, there is evidence that the nuclear lamina filament protein Lamin A/C protects RB from proteasomal degradation. Here we show that SUMO1 conjugation of RB and Lamin A/C is modulated by the SUMO protease SENP1 and that sumoylation of both proteins is required for their interaction. Importantly, this SUMO1-dependent complex protects both RB and Lamin A/C from proteasomal turnover.

SUMOylation of Rb enhances its binding with CDK2 and phosphorylation at early G1 phase

Retinoblastoma protein (Rb) is a prototypical tumor suppressor that is vital to the negative regulation of the cell cycle and tumor progression. Hypo-phosphorylated Rb is associated with G0/G1 arrest by suppressing E2F transcription factor activity, whereas Rb hyper-phosphorylation allows E2F release and cell cycle progression from G0/G1 to S phase. However, the factors that regulate cyclin-dependent protein kinase (CDK)-dependent hyper-phosphorylation of Rb during the cell cycle remain obscure. In this study, we show that throughout the cell cycle, Rb is specifically small ubiquitin-like modifier (SUMO)ylated at early G1 phase. SUMOylation of Rb stimulates its phosphorylation level by recruiting a SUMO-interaction motif (SIM)-containing kinase CDK2, leading to Rb hyper-phosphorylation and E2F-1 release. In contrast, a SUMO-deficient Rb mutant results in reduced SUMOylation and phosphorylation, weakened CDK2 binding, and attenuated E2F-1 sequestration. Furthermore, we reveal that Rb SUMOylation is required for cell proliferation. Therefore, our study describes a novel mechanism that regulates Rb phosphorylation during cell cycle progression.

Differentiation resistance through altered retinoblastoma protein function in acute lymphoblastic leukemia: in silico modeling of the deregulations in the G1/S restriction point pathway

BACKGROUND

As in many cancer types, the G1/S restriction point (RP) is deregulated in Acute Lymphoblastic Leukemia (ALL). Hyper-phosphorylated retinoblastoma protein (hyper-pRb) is found in high levels in ALL cells. Nevertheless, the ALL lymphocyte proliferation rate for the average patient is surprisingly low compared to its normal counterpart of the same maturation level. Additionally, as stated in literature, ALL cells possibly reside at or beyond the RP which is located in the late-G1 phase. This state may favor their differentiation resistant phenotype. A major phenomenon contributing to this fact is thought to be the observed limited redundancy in the phosphorylation of retinoblastoma protein (pRb) by the various Cyclin Dependent Kinases (Cdks). The latter may result in partial loss of pRb functions despite hyper-phosphorylation.

RESULTS

To test this hypothesis, an in silico model aiming at simulating the biochemical regulation of the RP in ALL is introduced. By exploiting experimental findings derived from leukemic cells and following a semi-quantitative calibration procedure, the model has been shown to satisfactorily reproduce such a behavior for the RP pathway. At the same time, the calibrated model has been proved to be in agreement with the observed variation in the ALL cell cycle duration.

CONCLUSIONS

The proposed model aims to contribute to a better understanding of the complex phenomena governing the leukemic cell cycle. At the same time it constitutes a significant first step in the creation of a personalized proliferation rate predictor that can be used in the context of multiscale cancer modeling. Such an approach is expected to play an important role in the refinement and the advancement of mechanistic modeling of ALL in the context of the emergent and promising scientific domains of In Silico Oncology and more generally In Silico Medicine.

Protein kinase Cζ exhibits constitutive phosphorylation and phosphatidylinositol-3,4,5-triphosphate-independent regulation

Atypical protein kinase C (aPKC) isoenzymes are key modulators of insulin signalling, and their dysfunction correlates with insulin-resistant states in both mice and humans. Despite the engaged interest in the importance of aPKCs to type 2 diabetes, much less is known about the molecular mechanisms that govern their cellular functions than for the conventional and novel PKC isoenzymes and the functionally-related protein kinase B (Akt) family of kinases. Here we show that aPKC is constitutively phosphorylated and, using a genetically-encoded reporter for PKC activity, basally active in cells. Specifically, we show that phosphorylation at two key regulatory sites, the activation loop and turn motif, of the aPKC PKCζ in multiple cultured cell types is constitutive and independently regulated by separate kinases: ribosome-associated mammalian target of rapamycin complex 2 (mTORC2) mediates co-translational phosphorylation of the turn motif, followed by phosphorylation at the activation loop by phosphoinositide-dependent kinase-1 (PDK1). Live cell imaging reveals that global aPKC activity is constitutive and insulin unresponsive, in marked contrast to the insulin-dependent activation of Akt monitored by an Akt-specific reporter. Nor does forced recruitment to phosphoinositides by fusing the pleckstrin homology (PH) domain of Akt to the kinase domain of PKCζ alter either the phosphorylation or activity of PKCζ. Thus, insulin stimulation does not activate PKCζ through the canonical phosphatidylinositol-3,4,5-triphosphate-mediated pathway that activates Akt, contrasting with previous literature on PKCζ activation. These studies support a model wherein an alternative mechanism regulates PKCζ-mediated insulin signalling that does not utilize conventional activation via agonist-evoked phosphorylation at the activation loop. Rather, we propose that scaffolding near substrates drives the function of PKCζ.

Transcriptomic characterization of fibrolamellar hepatocellular carcinoma

Fibrolamellar hepatocellular carcinoma (FLHCC) tumors all carry a deletion of ∼ 400 kb in chromosome 19, resulting in a fusion of the genes for the heat shock protein, DNAJ (Hsp40) homolog, subfamily B, member 1, DNAJB1, and the catalytic subunit of protein kinase A, PRKACA. The resulting chimeric transcript produces a fusion protein that retains kinase activity. No other recurrent genomic alterations have been identified. Here we characterize the molecular pathogenesis of FLHCC with transcriptome sequencing (RNA sequencing). Differential expression (tumor vs. adjacent normal tissue) was detected for more than 3,500 genes (log2 fold change ≥ 1, false discovery rate ≤ 0.01), many of which were distinct from those found in hepatocellular carcinoma. Expression of several known oncogenes, such as ErbB2 and Aurora Kinase A, was increased in tumor samples. These and other dysregulated genes may serve as potential targets for therapeutic intervention.

The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling

The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.

Simultaneous measurement of passage through the restriction point and MCM loading in single cells

Passage through the Retinoblastoma protein (RB1)-dependent restriction point and the loading of minichromosome maintenance proteins (MCMs) are two crucial events in G1-phase that help maintain genome integrity. Deregulation of these processes can cause uncontrolled proliferation and cancer development. Both events have been extensively characterized individually, but their relative timing and inter-dependence remain less clear. Here, we describe a novel method to simultaneously measure MCM loading and passage through the restriction point. We exploit that the RB1 protein is anchored in G1-phase but is released when hyper-phosphorylated at the restriction point. After extracting cells with salt and detergent before fixation we can simultaneously measure, by flow cytometry, the loading of MCMs onto chromatin and RB1 binding to determine the order of the two events in individual cells. We have used this method to examine the relative timing of the two events in human cells. Whereas in BJ fibroblasts released from G0-phase MCM loading started mainly after the restriction point, in a significant fraction of exponentially growing BJ and U2OS osteosarcoma cells MCMs were loaded in G1-phase with RB1 anchored, demonstrating that MCM loading can also start before the restriction point. These results were supported by measurements in synchronized U2OS cells.

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed “senescence,” can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells’ heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

Antiproliferative and apoptosis-inducing activity of schisandrin B against human glioma cells

Background

Malignant glioma is the most devastating and aggressive tumour in the brain and is characterised by high morbidity, high mortality and extremely poor prognosis. The main purpose of the present study was to investigate the effects of schisandrin B (Sch B) on glioma cells both in vitro and in vivo and to explore the possible anticancer mechanism underlying Sch B-induced apoptosis and cell cycle arrest.

Methods

The anti-proliferative ability of Sch B on glioma cells were assessed by MTT and clony formation assays. Flow cytometric analysis was used to detect cell cycle changes. Apoptosis was determined by Hoechst 33342 staining and annexin V/PI double-staining assays. The mitochondrial membrane potential was detected by Rhodamine 123 staining. The in vivo efficacy of Sch B was measured using a U87 xenograft model in nude mice. The expressions of the apoptosis-related and cell cycle-related proteins were analysed by western blot. Student’s t-test was used to compare differences between treated groups and their controls.

Results

We found that Sch B inhibited growth in a dose- and time-dependent manner as assessed by MTT assay. In U87 and U251 cells, the number of clones was strongly suppressed by Sch B. Flow cytometric analysis revealed that Sch B induced cell cycle arrest in glioma cells at the G0/G1 phase. In addition, Sch B induced glioma cell apoptosis and reduced mitochondrial membrane potential (ΔΨm) in a dose-dependent manner. Mechanically, western blot analysis indicated that Sch B induced apoptosis by caspase-3, caspase-9, PARP, and Bcl-2 activation. Moreover, Sch B significantly inhibited tumour growth in vivo following the subcutaneous inoculation of U87 cells in athymic nude mice.

Coclusions

In summary, Sch B can reduce cell proliferation and induce apoptosis in glioma cells and has potential as a novel anti-tumour therapy to treat gliomas.

Lunasin inhibits cell proliferation via apoptosis and reduces the production of proinflammatory cytokines in cultured rheumatoid arthritis synovial fibroblasts

Lunasin, a peptide with 43 amino acid residues and initially isolated and identified in soybean cotyledon, has gained extensive attention due to its anti-inflammatory and anticancer properties. However, its treatment efficacy on rheumatoid arthritis (RA) and corresponding mechanisms have not been reported. Herein, the synovial fibroblasts harvested and isolated from patients with RA were treated with lunasin at various concentrations to examine the proliferation, apoptosis status, and corresponding cell cycle of cultured RA synovial fibroblasts. Meanwhile, the underlying mechanisms of lunasin for RA treatment are explored through Western blot, real-time PCR, ELISA, and luciferase reporter assays. Lunasin significantly inhibited the proliferation and induced the apoptosis of cultured RA synovial fibroblasts. In addition, lunasin reduced the production of interleukin-6 (IL-6), IL-8, and matrix metalloproteinase-3 (MMP-3) and suppressed the activation of NF-κB in cultured RA synovial fibroblasts but did not reveal obvious modulation on the secretion and gene expression of MMP-1. Therefore, lunasin will have promising potential as a novel nutritional supplement or drug candidate for RA due to its potency of suppressing synovial cell proliferation and decreasing the production of proinflammatory cytokines and MMPs in synovial cells.

Association between CCNE1 polymorphisms and the risk of breast cancer in a sample of southeast Iranian population

Cyclin E1 (CCNE1) is a key proto-oncogene. The present study aimed to investigate the effects of single nucleotide polymorphisms in CCNE1 on the risk of breast cancer (BC) in an Iranian population in southeast of Iran. A total of 491 subjects including 266 BC patients and 225 healthy control women were participated in the study. Genotyping of CCNE1 rs3218073 and 72010703 polymorphisms was done using allele-specific polymerase chain reaction (AS-PCR) and rs1406 by PCR-RFLP method.Our findings showed that rs1406 C/A polymorphism increased the risk of BC in codominant (OR 1.60, 95% CI 1.05-2.43, p=0.032 CA vs CC; OR 2.35, 95% CI 1.23-4.49, p=0.011 AA vs CC) and dominant (OR 1.69, 95% CI 1.22-2.56, p=0.012 CA+AA vs CC) inheritance models. The rs1406 A allele increased the risk of BC (OR 1.37, 95% CI 1.06-1.76, p=0.019) in comparison with C allele. On the other hand, CCNE1 rs72010703 (4-bp I/D) and rs3218073 polymorphisms did not show any significant association with BC. This study indicates that CCNE1 rs1406 polymorphism may contribute to BC risk.

Double homeobox gene, Duxbl, promotes myoblast proliferation and abolishes myoblast differentiation by blocking MyoD transactivation

Homeobox genes encode transcription factors that regulate embryonic development programs including organogenesis, axis formation and limb development. Previously, we identified and cloned a mouse double homeobox gene, Duxbl, whose homeodomain exhibits the highest identity (67 %) to human DUX4, a candidate gene of facioscapulohumeral muscular dystrophy (FSHD). Duxbl proteins have been shown to be expressed in elongated myocytes and myotubes of trunk and limb muscles during embryogenesis. In this study, we found that Duxbl maintained low expression levels in various adult muscles. Duxbl proteins were induced to express in activated satellite cells and colocalized with MyoG, a myogenic differentiating marker. Furthermore, Duxbl proteins were not detected in quiescent satellite cells but detected in regenerated myocytes and colocalized with MyoD and MyoG following cardiotoxin-induced muscle injury. Ectopic Duxbl overexpressions in C2C12 myoblast cells promoted cell proliferation through mainly enhancing cyclin D1 and hyper-phosphorylated retinoblastoma protein but reducing p21 expression. However, Duxbl overexpression in C2C12 cells inhibited myogenic differentiation by decreasing MyoD downstream gene expressions, including M-cadherin, MyoG, p21 and cyclin D3 but not MyoD itself. Duxbl overexpressions also promoted cell proliferation but blocked MyoD-induced myogenic conversion in multipotent mesenchymal C3H10T1/2 cells. In addition, results of a luciferase reporter assay suggest that Duxbl negatively regulated MyoG promoter activity through the proximal two E boxes. In conclusion, these results indicate that Duxbl may play a crucial role in myogenesis and postnatal muscle regeneration by activating and proliferating satellite and myoblast cells.

Cyclin D activates the Rb tumor suppressor by mono-phosphorylation

The widely accepted model of G₁ cell cycle progression proposes that cyclin D:Cdk4/6 inactivates the Rb tumor suppressor during early G₁ phase by progressive multi-phosphorylation, termed hypo-phosphorylation, to release E2F transcription factors. However, this model remains unproven biochemically and the biologically active form(s) of Rb remains unknown. In this study, we find that Rb is exclusively mono-phosphorylated in early G₁ phase by cyclin D:Cdk4/6. Mono-phosphorylated Rb is composed of 14 independent isoforms that are all targeted by the E1a oncoprotein, but show preferential E2F binding patterns. At the late G₁ Restriction Point, cyclin E:Cdk2 inactivates Rb by quantum hyper-phosphorylation. Cells undergoing a DNA damage response activate cyclin D:Cdk4/6 to generate mono-phosphorylated Rb that regulates global transcription, whereas cells undergoing differentiation utilize un-phosphorylated Rb. These observations fundamentally change our understanding of G₁ cell cycle progression and show that mono-phosphorylated Rb, generated by cyclin D:Cdk4/6, is the only Rb isoform in early G₁ phase.

DOI:http://dx.doi.org/10.7554/eLife.02872.001

Cells go through a tightly controlled, multi-step procedure before they divide. This cell division program—the cell cycle—is necessary for preventing unrestrained cellular growth, which may lead to cancer. Proteins called cyclins control the progression through each of the phases of the cell cycle, with different cyclins working during different phases.

During the G1 phase of the cell cycle, cells grow in size and produce the proteins that are required to copy DNA. Once a cell passes a checkpoint called the 'restriction point' at the end of the G1 phase, it is committed to dividing. It is therefore particularly important to keep events during G1 phase in check.

The Retinoblastoma tumor suppresor protein (Rb) is a key player in regulating the G1 phase. Rb sequesters transcription factors that are essential for the cell cycle to progress. Previously, it was thought that a complex called cyclin D added more and more phosphates to the Rb protein during the G1 phase. This process predicted a slow release of transcription factors, which attach to DNA and start the process of DNA replication. While many studies have presented data that is consistent with this model, direct biochemical evidence of these events is lacking.

Narasimha, Kaulich, Shapiro et al. now present biochemical analyses of Rb proteins that show—completely unexpectedly—that the cyclin D complex adds just one phosphate group to Rb during the G1 phase, although this group can be added to one of fourteen different sites. The resulting 'mono-phosphorylated' Rb varieties can each sequester different transcription factors and stop them working.

At the restriction point, many more phosphate groups are then rapidly added, and the Rb protein is inactivated by a different cyclin. This cyclin—called Cyclin E—then drives cells into the next phase of the cell cycle. Establishing how cyclin E is activated is a priority for future research.

DOI:http://dx.doi.org/10.7554/eLife.02872.002

Cell cycle regulators cyclin D1 and CDK4/6 have estrogen receptor-dependent divergent functions in breast cancer migration and stem cell-like activity

Cyclin D1 and its binding partners CDK4/6 are essential regulators of cell cycle progression and are implicated in cancer progression. Our aim was to investigate a potential regulatory role of these proteins in other essential tumor biological characteristics. Using a panel of breast cancer cell lines and primary human breast cancer samples, we have demonstrated the importance of these cell cycle regulators in both migration and stem-like cell activity. siRNA was used to target cyclin D1 and CDK4/6 expression, having opposing effects on both migration and stem-like cell activity dependent upon estrogen receptor (ER) expression. Inhibition of cyclin D1 or CDK4/6 increases or decreases migration and stem-like cell activity in ER-ve (ER-negative) and ER+ve (ER-positive) breast cancer, respectively. Furthermore, overexpressed cyclin D1 caused decreased migration and stem-like cell activity in ER-ve cells while increasing activity in ER+ve breast cancer cells. Treatment of breast cancer cells with inhibitors of cyclin D1 and CDK4/6 (Flavopiridol/PD0332991), currently in clinical trials, mimicked the effects observed with siRNA treatment. Re-expression of ER in two ER-ve cell lines was sufficient to overcome the effects of either siRNA or clinical inhibitors of cyclin D1 and CDK4/6.   In conclusion, cyclin D1 and CDK4/6 have alternate roles in regulation of migration and stem-like cell activity. Furthermore, these effects are highly dependent upon expression of ER. The significance of these results adds to our general understanding of cancer biology but, most importantly, could be used diagnostically to predict treatment response to cell cycle inhibition in breast cancer.

Posttranslational modifications of the retinoblastoma tumor suppressor protein as determinants of function

The retinoblastoma tumor suppressor protein (pRB) plays an integral role in G1-S checkpoint control and consequently is a frequent target for inactivation in cancer. The RB protein can function as an adaptor, nucleating components such as E2Fs and chromatin regulating enzymes into the same complex. For this reason, pRB's regulation by posttranslational modifications is thought to be critical. pRB is phosphorylated by a number of different kinases such as cyclin dependent kinases (Cdks), p38 MAP kinase, Chk1/2, Abl, and Aurora b. Although phosphorylation of pRB by Cdks has been extensively studied, activities regulated through phosphorylation by other kinases are just starting to be understood. As well as being phosphorylated, pRB is acetylated, methylated, ubiquitylated, and SUMOylated. Acetylation, methylation, and SUMOylation play roles in pRB mediated gene silencing. Ubiquitinylation of pRB promotes its degradation and may be used to regulate apoptosis. Recent proteomic data have revealed that pRB is posttranslationally modified to a much greater extent than previously thought. This new information suggests that many unknown pathways affect pRB regulation. This review focuses on posttranslational modifications of pRB and how they influence its function. The final part of the review summarizes new phosphorylation sites from accumulated proteomic data and discusses the possibilities that might arise from this data.

Regulation of human endometrial stromal proliferation and differentiation by C/EBPβ involves cyclin E-cdk2 and STAT3

During each menstrual cycle, the human uterus undergoes a unique transformation, known as decidualization, which involves endometrial stromal proliferation and differentiation. During this process, the stromal cells are transformed into decidual cells, which produce factors that prepare the uterus for potential embryo implantation. We previously identified the transcription factor CCAAT/enhancer-binding protein (C/EBP)β as a regulator of endometrial stromal proliferation and differentiation in mice. In this study, we addressed the role of C/EBPβ in human endometrial decidualization. Using small interfering RNA targeted to C/EBPβ mRNA, we demonstrated that C/EBPβ controls the proliferation of primary human endometrial stromal cells (HESCs) by regulating the expression of several key cell cycle-regulatory factors during the G(1)-S phase transition. Additionally, loss of C/EBPβ expression blocked the differentiation of HESCs in response to estrogen, progesterone, and cyclic AMP. Gene expression profiling of normal and C/EBPβ-deficient HESCs revealed that the receptor for the cytokine IL-11 and its downstream signal transducer signal transducer and activator of transcription 3 (STAT3) are targets of regulation by C/EBPβ. Chromatin immunoprecipitation analysis indicated that C/EBPβ controls the expression of STAT3 gene by directly interacting with a distinct regulatory sequence in its 5'-flanking region. Attenuation of STAT3 mRNA expression in HESCs resulted in markedly reduced differentiation of these cells, indicating an important role for STAT3 in decidualization. Gene expression profiling, using STAT3-deficient HESCs, showed an extensive overlap of pathways downstream of STAT3 and C/EBPβ during stromal cell differentiation. Collectively, these findings revealed a novel functional link between C/EBPβ and STAT3 that is a critical regulator of endometrial differentiation in women.

Gap 1 phase length and mouse embryonic stem cell self-renewal

In somatic cells, the length of the G1 phase of the cell cycle is tightly linked to differentiation, and its elongation can drive differentiation in many cases. Although it has been suggested that the situation is very similar in embryonic stem cells (ESCs), where a rapid cell cycle and a short G1 phase maintain the pluripotent state, evidence has been contradictory. Here we show that, in murine ESCs, elongation of the cell cycle and elongation of G1 are compatible with their pluripotent state. Multiple methods that lengthen the cell cycle and that target cyclin-dependent kinase, retinoblastoma protein, and E2F activity all fail to induce differentiation on their own or even to facilitate differentiation. The resistance of murine ESCs to differentiation induced by lengthening G1 and/or the cell cycle could allow for separate control of these events and provide new opportunities for investigation and application.

Yang-Dan-Tang, Identified from 15 Chinese Herbal Formulae, Inhibits Human Lung Cancer Cell Proliferation via Cell Cycle Arrest

Lung cancer has long been one of the most deadly forms of cancer. The majority of lung cancers are of the non-small-cell lung cancer (NSCLC) type. Here we used the non-small-cell lung carcinoma cell line A549 to screen 15 different traditional Chinese herbal medicine (CHM) formulae to explore the possible mechanisms of alternative medicine in lung cancer therapy. We identified three formulae (Formulae 3, 5, and 14) that substantially decreased the survival of A549 cells but did not affect MRC5 normal lung tissue cells. Formula 14, Yang-Dan-Tang, a modified decoction of Ramulus Cinnamomi Cassiae, was chosen for further characterization. Flow cytometry analysis showed that treatment of Formula 14 induced cell cycle arrest in G1 and G2 phase without causing significant cell death. These results were also confirmed by Western blot analysis, with decreased expression of G1/S and G2/M promoting cell cycle machinery including cyclin D3, cyclin B1, CDK4, and CDK6. This study provides further insight into the possible working mechanism of Yang-Dan-Tang in patients.

Antitumor activity of cell-permeable p18(INK4c) with enhanced membrane and tissue penetration

Practical methods to deliver proteins systemically in animals have been hampered by poor tissue penetration and inefficient cytoplasmic localization of internalized proteins. We therefore pursued the development of improved macromolecule transduction domains (MTDs) and tested their ability to deliver therapeutically active p18(INK4c). MTD103 was identified from a screen of 1,500 signal peptides; tested for the ability to promote protein uptake by cells and tissues; and analyzed with regard to the mechanism of protein uptake and the delivery of biologically active p18(INK4c) into cancer cells. The therapeutic potential of cell-permeable MTD103p18(INK4c) (CP-p18(INK4c)) was tested in the HCT116 tumor xenograft model. MTD103p18(INK4c) appeared to traverse plasma membranes directly, was transferred from cell-to-cell and was therapeutically effective against cancer xenografts, inhibiting tumor growth by 86-98% after 5 weeks (P < 0.05). The therapeutic responses to CP-p18(INK4c) were accompanied by high levels of apoptosis in tumor cells. In addition to enhancing systemic delivery of CP-p18(INK4c) to normal tissues and cancer xenografts, the MTD103 sequence delayed protein clearance from the blood, liver and spleen. These results demonstrate that macromolecule intracellular transduction technology (MITT), enabled by MTDs, may provide novel protein therapies against cancer and other diseases.

Pokemon silencing leads to Bim-mediated anoikis of human hepatoma cell QGY7703

Pokemon is an important proto-oncogene that plays a critical role in cellular oncogenic transformation and tumorigenesis. Anoikis, which is regulated by Bim-mediated apoptosis, is critical to cancer cell invasion and metastasis. We investigated the role of Pokemon in anoikis, and our results show that Pokemon renders liver cells resistant to anoikis via suppression of Bim transcription. We knocked-down Pokemon in human hepatoma cells QGY7703 with small interfering RNAs (siRNA). Knockdown of Pokemon alone did not significantly affect the growth and survival of QGY7703 cells but notably enhanced their sensitivity to apoptotic stress due to the presence of chemical agents or cell detachment, thereby inducing anoikis, as evidenced by flow cytometry and caspase-3 activity assays. In contrast, ectopic expression of Pokemon in HL7702 cells led to resistance to anoikis. Dual-luciferase reporter and ChIP assays illustrated that Pokemon suppressed Bim transcription via direct binding to its promoter. Our results suggest that Pokemon prevents anoikis through the suppression of Bim expression, which facilitates tumor cell invasion and metastasis. This Pokemon-Bim pathway may be an effective target for therapeutic intervention for cancer.

Strategic cell-cycle regulatory features that provide mammalian cells with tunable G1 length and reversible G1 arrest

Transitions between consecutive phases of the eukaryotic cell cycle are driven by the catalytic activity of selected sets of cyclin-dependent kinases (Cdks). Yet, their occurrence and precise timing is tightly scheduled by a variety of means including Cdk association with inhibitory/adaptor proteins (CKIs). Here we focus on the regulation of G1-phase duration by the end of which cells of multicelled organisms must decide whether to enter S phase or halt, and eventually then, differentiate, senesce or die to obey the homeostatic rules of their host. In mammalian cells, entry in and progression through G1 phase involve sequential phosphorylation and inactivation of the retinoblastoma Rb proteins, first, by cyclin D-Cdk4,6 with the help of CKIs of the Cip/Kip family and, next, by the cyclin E-Cdk2 complexes that are negatively regulated by Cip/Kip proteins. Using a dynamical modeling approach, we show that the very way how the Rb and Cip/Kip regulatory modules interact differentially with cyclin D-Cdk4,6 and cyclin E-Cdk2 provides to mammalian cells a powerful means to achieve an exquisitely-sensitive control of G1-phase duration and fully reversible G1 arrests. Consistently, corruption of either one of these two modules precludes G1 phase elongation and is able to convert G1 arrests from reversible to irreversible. This study unveils fundamental design principles of mammalian G1-phase regulation that are likely to confer to mammalian cells the ability to faithfully control the occurrence and timing of their division process in various conditions.