Distinct cell cycle timing requirements for extracellular signal-regulated kinase and phosphoinositide 3-kinase signaling pathways in somatic cell mitosis

Cell cycle regulation by ADP and IGF-1 in cultured late developing glia progenitors of the avian retina

In the avian retina, ADP induces the proliferation of late developing glia progenitors. Here, we show that in serum-containing retinal cell cultures, ADP-induced increase in [3H]-thymidine incorporation can be prevented by the IGF-1 receptor antagonists AG1024 and I-OMe-Tyrphostin AG 538, suggesting the participation of IGF-1 in ADP-mediated progenitor proliferation. In contrast, no increase in [3H]-thymidine incorporation is observed in retinal cultures treated only with IGF-1. Under serum starvation, while no increase in cell proliferation is detected in cultures treated only with ADP or IGF-1, a significant increase in [3H]-thymidine incorporation and number of PCNA expressing cells is observed in cultures treated concomitantly with ADP plus IGF-1, suggesting that both molecules are required to induce proliferation of retinal progenitors. In serum-starved cultures, although an increase in cell viability is detected by MTT assays in IGF-1-treated cultures, no significant increase in viability of [3H]-thymidine labeled progenitors is observed, suggesting that IGF-1 may contribute to survival of postmitotic cells in culture. While only ADP increases intracellular calcium, only IGF-1 induces the phosphorylation of Akt in the retinal cultures. IGF-1 through the PI3K/Akt pathway induces a significant increase in the transcription and expression of CDK1 with a decrease in phospho-histone H3 expression that is concomitant with an increase in the expression of cyclins D1 and E and CDK2. These findings suggest that IGF-1 stimulates CDK-1 mRNA and protein expression that enable progenitors to progress through the cell cycle. However, signaling of ADP in the presence IGF-I seems to be required for DNA synthesis.

FoxO3 normalizes Smad3-induced arterial smooth muscle cell growth

Transition of arterial smooth muscle (ASM) from a quiescent, contractile state to a growth-promoting state is a hallmark of cardiovascular disease (CVD), a leading cause of death and disability in the United States and worldwide. While many individual signals have been identified as important mechanisms in this phenotypic conversion, the combined impact of the transcription factors Smad3 and FoxO3 in ASM growth is not known. The purpose of this study was to determine that a coordinated, phosphorylation-specific relationship exists between Smad3 and FoxO3 in the control of ASM cell growth. Using a rat in vivo arterial injury model and rat primary ASM cell lysates and fractions, validated low and high serum in vitro models of respective quiescent and growth states, and adenoviral (Ad-) gene delivery for overexpression (OE) of individual and combined Smad3 and/or FoxO3, we hypothesized that FoxO3 can moderate Smad3-induced ASM cell growth. Key findings revealed unique cellular distribution of Smad3 and FoxO3 under growth conditions, with induction of both nuclear and cytosolic Smad3 yet primarily cytosolic FoxO3; Ad-Smad3 OE leading to cytosolic and nuclear expression of phosphorylated and total Smad3, with almost complete reversal of each with Ad-FoxO3 co-infection in quiescent and growth conditions; Ad-FoxO3 OE leading to enhanced cytosolic expression of phosphorylated and total FoxO3, both reduced with Ad-Smad3 co-infection in quiescent and growth conditions; Ad-FoxO3 inducing expression and activity of the ubiquitin ligase MuRF-1, which was reversed with concomitant Ad-Smad3 OE; and combined Smad3/FoxO3 OE reversing both the pro-growth impact of singular Smad3 and the cytostatic impact of singular FoxO3. A primary takeaway from these observations is the capacity of FoxO3 to reverse growth-promoting effects of Smad3 in ASM cells. Additional findings lend support for reciprocal antagonism of Smad3 on FoxO3-induced cytostasis, and these effects are dependent upon discrete phosphorylation states and cellular localization and involve MuRF-1 in the control of ASM cell growth. Lastly, results showing capacity of FoxO3 to normalize Smad3-induced ASM cell growth largely support our hypothesis, and overall findings provide evidence for utility of Smad3 and/or FoxO3 as potential therapeutic targets against abnormal ASM growth in the context of CVD.

Silencing of KNTC1 inhibits hepatocellular carcinoma cells progression via suppressing PI3K/Akt pathway

Kinetochore associated 1 (KNTC1) encodes a kinetochore component in Rod-Zwilch-ZW10 (RZZ) complex which is essential for the segregation of sister chromatids during mitosis and participates in the spindle checkpoint. Recent research demonstrated that kinetochore proteins may be potential biomarkers and may contribute to the development of human malignancies. Our immunohistochemistry experiment showed that KNTC1 was highly expressed in hepatocellular carcinoma (HCC) tissues and correlated with terrible prognosis, indicating that KNTC1 acts a pivotal role in HCC development. Furthermore, lentivirus delivered short hairpin RNA (shRNA) KNTC1 (Lv-shKNTC1) was applied to infect BEL-7404 and SK-HEP-1 to identify roles of KNTC1 on HCC. Lv-shKNTC1 cells showed reduced proliferation ability, increased apoptosis and decreased migration ability. In vivo experiments suggested that xenografts grow significantly slower upon the silencing of KNTC1. Mechanistically, the protein levels of PIK3CA, p-Akt, CCND1, CDK6 are all down-regulated in Lv-KNTC1 cells and the Lv-shKNTC1 tumor tissues of nude mice. Therefore, KNTC1 may affect the biological activity of HCC cells through PI3K/Akt signaling pathway. Further studies revealed that ZW10 is a pivotal protein that participates in KNTC1-induced regulation of PI3K/Akt signaling pathway. In summary, the key finding of this report highlighted the significance of KNTC1 in tumor regression of HCC, demonstrating KNTC1 as an innovative target for adjuvant treatment of HCC.

SGK1 is essential for meiotic resumption in mammalian oocytes

In mammalian females, oocytes are stored in the ovary and meiosis is arrested at the diplotene stage of prophase I. When females reach puberty oocytes are selectively recruited in cycles to grow, overcome the meiotic arrest, complete the first meiotic division and become mature (ready for fertilization). At a molecular level, the master regulator of prophase I arrest and meiotic resumption is the maturation-promoting factor (MPF) complex, formed by the active form of cyclin dependent kinase 1 (CDK1) and Cyclin B1. However, we still do not have complete information regarding the factors implicated in MPF activation. In this study we document that out of three mammalian serum-glucocorticoid kinase proteins (SGK1, SGK2, SGK3), mouse oocytes express only SGK1 with a phosphorylated (active) form dominantly localized in the nucleoplasm. Further, suppression of SGK1 activity in oocytes results in decreased CDK1 activation via the phosphatase cell division cycle 25B (CDC25B), consequently delaying or inhibiting nuclear envelope breakdown. Expression of exogenous constitutively active CDK1 can rescue the phenotype induced by SGK1 inhibition. These findings bring new insights into the molecular pathways acting upstream of MPF and a better understanding of meiotic resumption control by presenting a new key player SGK1 in mammalian oocytes.

Cell Cycle Synchronization of Primary and Cultured Articular Chondrocytes

Cell cycle synchronization allows cells in a culture, originally at different stages of the cell cycle, to be brought to the same phase. It is normally performed by applying cell cycle arresting chemical agents to cells cultured in monolayer. While effective, isolated chondrocytes tend to dedifferentiate when cultured in monolayer and typically require 3D culturing methods to ensure phenotypic stability. Here, we describe both the conventional cell cycle synchronization method for cells in monolayer culture and an adapted method of synchronizing primary chondrocytes directly during the cell isolation process to limit potential dedifferentiation. Different methods including serum-starvation and treatment with thymidine, nocodazole, aphidicolin, and RO-3306 can synchronize the chondrocytes at different discrete phases. A cell purity of more than 90% in the S phase can be achieved with simultaneous cell isolation and synchronization using double thymidine treatment, generating a population of synchronized chondrocytes that show increased matrix synthesis when subsequently cultured in 3D.

Temporal and Spatial Transcriptomic Dynamics across Brain Development in Xenopus laevis tadpoles

Amphibian metamorphosis is a transitional period that involves significant changes in the cell type populations and biological processes occurring in the brain. Analysis of gene expression dynamics during this process may provide insight into the molecular events underlying these changes. We conducted differential gene expression analyses of the developing X. laevis tadpole brain during this period in two ways: first, over stages of development in the midbrain, and second, across regions of the brain at a single developmental stage. We found that genes pertaining to positive regulation of neural progenitor cell proliferation as well as known progenitor cell markers were upregulated in the midbrain prior to metamorphic climax; concurrently, expression of cell cycle timing regulators decreased across this period, supporting the notion that cell cycle lengthening contributes to a decrease in proliferation by the end of metamorphosis. We also found that at the start of metamorphosis, neural progenitor populations appeared to be similar across the fore-, mid-, and hindbrain regions. Genes pertaining to negative regulation of differentiation were upregulated in the spinal cord compared to the rest of the brain, however, suggesting that a different program may regulate neurogenesis there. Finally, we found that regulation of biological processes like cell fate commitment and synaptic signaling follow similar trajectories in the brain across early tadpole metamorphosis and mid- to late-embryonic mouse development. By comparing expression across both temporal and spatial conditions, we have been able to illuminate cell type and biological pathway dynamics in the brain during metamorphosis.

Cell Cycle Synchronization of Primary Articular Chondrocytes Enhances Chondrogenesis

OBJECTIVE

Although tissue engineering is a promising option for articular cartilage repair, it has been challenging to generate functional cartilaginous tissue. While the synthetic response of chondrocytes can be influenced by various means, most approaches treat chondrocytes as a homogeneous population that would respond similarly. However, isolated cells heterogeneously progress through the cell cycle, which can affect macromolecular biosynthesis. As it is possible to synchronize cells within discrete cell cycle phases, the purpose of this study was to investigate the effects of cell cycle synchronization on the chondrogenic potential of primary articular chondrocytes.

DESIGN

Different methods of cell synchronization (serum starvation, thymidine, nocodazole, aphidicolin, and RO-3306) were tested for their ability to synchronize primary articular chondrocytes during the process of cell isolation. Cells (unsynchronized and synchronized) were then encapsulated in alginate gels, cultured for 4 weeks, and analyzed for their structural and biochemical properties.

RESULTS

The double-thymidine method yielded the highest level of cell purity, with cells synchronized in S phase. While the cells started to lose synchronization after 24 hours, tissue constructs developed from initially S phase synchronized cells had significantly higher glycosaminoglycan and collagen II amounts than those developed using unsynchronized cells.

CONCLUSIONS

Initial synchronization led to long-term changes in cartilaginous tissue formation. This effect was postulated to be due to the rapid auto-induction of TGF-βs by actively dividing S phase cells, thereby stimulating chondrogenesis. Cell synchronization methods may also be applied in conjunction with redifferentiation methods to improve the chondrogenic potential of dedifferentiated or diseased chondrocytes.

Cell-intrinsic mechanisms of drug tolerance to systemic therapies in cancer

In cancer patients with metastatic disease, the rate of complete tumor response to systemic therapies is low, and residual lesions persist in the majority of patients due to early molecular adaptation in cancer cells. A growing body of evidence suggests that a subpopulation of drug-tolerant « persister » cells - a reversible phenotype characterized by reduced drug sensitivity and decreased cell proliferation - maintains residual disease and may serve as a reservoir for resistant phenotypes. The survival of these residual tumor cells can be caused by reactivation of specific signaling pathways, phenotypic plasticity (i.e., transdifferentiation), epigenetic or metabolic reprogramming, downregulation of apoptosis as well as transcriptional remodeling. In this review, we discuss the molecular mechanisms that enable adaptive survival in drug-tolerant cells. We describe the main characteristics and dynamic nature of this persistent state, and highlight the current therapeutic strategies that may be used to interfere with the establishment of drug-tolerant cells, as an alternative to improve objective response to systemic therapies and delay the emergence of resistance to improve long-term survival.

Spatiotemporal control of pathway sensors and cross-pathway feedback regulate a differentiation MAPK pathway in yeast

Mitogen-activated protein kinase (MAPK) pathways control cell differentiation and the response to stress. In Saccharomyces cerevisiae, the MAPK pathway that controls filamentous growth (fMAPK) shares components with the pathway that regulates the response to osmotic stress (HOG). Here, we show that the two pathways exhibit different patterns of activity throughout the cell cycle. The different patterns resulted from different expression profiles of genes encoding mucin sensors that regulate the pathways. Cross-pathway regulation from the fMAPK pathway stimulated the HOG pathway, presumably to modulate fMAPK pathway activity. We also show that the shared tetraspan protein Sho1p, which has a dynamic localization pattern throughout the cell cycle, induced the fMAPK pathway at the mother-bud neck. A Sho1p-interacting protein, Hof1p, which also localizes to the mother-bud neck and regulates cytokinesis, also regulated the fMAPK pathway. Therefore, spatial and temporal regulation of pathway sensors, and cross-pathway regulation, control a MAPK pathway that regulates cell differentiation in yeast.

Abnormal function of telomere protein TRF2 induces cell mutation and the effects of environmental tumor‑promoting factors (Review)

Recent studies have found that somatic gene mutations and environmental tumor-promoting factors are both indispensable for tumor formation. Telomeric repeat-binding factor (TRF)2 is the core component of the telomere shelterin complex, which plays an important role in chromosome stability and the maintenance of normal cell physiological states. In recent years, TRF2 and its role in tumor formation have gradually become a research hot topic, which has promoted in-depth discussions into tumorigenesis and treatment strategies, and has achieved promising results. Some cells bypass elimination, due to either aging, apoptosis via mutations or abnormal prolongation of the mitotic cycle, and enter the telomere crisis period, where large-scale DNA reorganization occurs repeatedly, which manifests as the precancerous cell cycle. Finally, at the end of the crisis cycle, the mutation activates either the expression level of telomerase or activates the alternative lengthening of telomere mechanism to extend the local telomeres. Under the protection of TRF2, chromosomes are gradually stabilized, immortal cells are formed and the stagewise mutation-driven transformation of normal cells to cancer cells is completed. In addition, TRF2 also shares the characteristics of environmental tumor-promoting factors. It acts on multiple signal transduction pathway-related proteins associated with cell proliferation, and affects peripheral angiogenesis, inhibits the immune recognition and killing ability of the microenvironment, and maintains the stemness characteristics of tumor cells. TRF2 levels are abnormally elevated by a variety of tumor control proteins, which are more conducive to the protection of telomeres and the survival of tumor cells. In brief, the various regulatory mechanisms which tumor cells rely on to survive are organically integrated around TRF2, forming a regulatory network, which is conducive to the optimization of the survival direction of heterogeneous tumor cells, and promotes their survival and adaptability. In terms of clinical application, TRF2 is expected to become a new type of cancer prognostic marker and a new tumor treatment target. Inhibition of TRF2 overexpression could effectively cut off the core network regulating tumor cell survival, reduce drug resistance, or bypass the mutation under the pressure of tumor treatment selection, which may represent a promising therapeutic strategy for the complete eradication of tumors in the clinical setting. Based on recent research, the aim of the present review was to systematically elaborate on the basic structure and functional characteristics of TRF2 and its role in tumor formation, and to analyze the findings indicating that TRF2 deficiency or overexpression could cause severe damage to telomere function and telomere shortening, and induce DNA damage response and chromosomal instability.

Cracking the context-specific PI3K signaling code

Specificity in signal transduction is determined by the ability of cells to "encode" and subsequently "decode" different environmental signals. Akin to computer software, this "signaling code" governs context-dependent execution of cellular programs through modulation of signaling dynamics and can be corrupted by disease-causing mutations. Class IA phosphoinositide 3-kinase (PI3K) signaling is critical for normal growth and development and is dysregulated in human disorders such as benign overgrowth syndromes, cancer, primary immune deficiency, and metabolic syndrome. Despite decades of PI3K research, understanding of context-dependent regulation of the PI3K pathway and of the underlying signaling code remains rudimentary. Here, we review current knowledge on context-specific PI3K signaling and how technological advances now make it possible to move from a qualitative to quantitative understanding of this pathway. Insight into how cellular PI3K signaling is encoded or decoded may open new avenues for rational pharmacological targeting of PI3K-associated diseases. The principles of PI3K context-dependent signal encoding and decoding described here are likely applicable to most, if not all, major cell signaling pathways.

Ailanthone Induces Cell Cycle Arrest and Apoptosis in Melanoma B16 and A375 Cells

Malignant melanoma is the most lethal type of skin cancer. Previous studies have shown that ailanthone has potent antitumor activity in a variety of cell lines. However, the anti-tumor effect of ailanthone on malignant melanoma remains unclear. To investigate the anti-tumor mechanisms of ailanthone in human melanoma B16 and mouse melanoma A375 cells, the cell counting kit-8 assay, colony formation assay, DNA content analysis, Hoechst 33258, and Annexin V-FITC/PI staining were used to assess cell proliferation, cell cycle distribution, and cell apoptosis, respectively. Western blotting was performed to evaluate the expression of cell cycle- and apoptosis-related proteins and regulatory molecules. The results showed that ailanthone significantly inhibited melanoma B16 and A375 cell proliferation as well as remarkably induced cell cycle arrest at the G0–G1 phase in B16 cells and the G2–M phase in A375 cells in a dose-dependent manner. Further investigation revealed that ailanthone promoted the expression of p21 and suppressed the expression of cyclin E in B16 cells or cyclin B in A375 cells through the PI3K-Akt signaling pathway. In addition, ailanthone induced B16 and A375 cell apoptosis via a caspase-dependent mechanism. Further studies showed that ailanthone remarkably downregulated Bcl-2 and upregulated Apaf-1 and Bax, and subsequently increased mitochondrial membrane permeabilization and released cytochrome c from the mitochondria in B16 cells and A375 cells. Taken together, ailanthone induces cell cycle arrest via the PI3K-Akt signaling pathway as well as cell apoptosis via the mitochondria-mediated apoptotic signaling pathway. Ailanthone may be potentially utilized as an anti-tumor agent in the management of malignant melanoma.

ERK1/2/MAPK pathway-dependent regulation of the telomeric factor TRF2

Telomere stability is a hallmark of immortalized cells, including cancer cells. While the telomere length is maintained in most cases by the telomerase, the activity of a protein complex called Shelterin is required to protect telomeres against unsuitable activation of the DNA damage response pathway. Within this complex, telomeric repeat binding factor 2 (TRF2) plays an essential role by blocking the ataxia telangiectasia-mutated protein (ATM) signaling pathway at telomeres and preventing chromosome end fusion. We showed that TRF2 was phosphorylated in vitro and in vivo on serine 323 by extracellular signal-regulated kinase (ERK1/2) in both normal and cancer cells. Moreover, TRF2 and activated ERK1/2 unexpectedly interacted in the cytoplasm of tumor cells and human tumor tissues. The expression of non-phosphorylatable forms of TRF2 in melanoma cells induced the DNA damage response, leading to growth arrest and tumor reversion. These findings revealed that the telomere stability is under direct control of one of the major pro-oncogenic signaling pathways (RAS/RAF/MEK/ERK) via TRF2 phosphorylation.

Functional role of AKT signaling in bovine early embryonic development: potential link to embryotrophic actions of follistatin

BACKGROUND

TGF-β signaling pathways regulate several crucial processes in female reproduction. AKT is a non-SMAD signaling pathway regulated by TGF-β ligands essential for oocyte maturation and early embryonic development in the mouse, but its regulatory role in bovine early embryonic development is not well established. Previously, we demonstrated a stimulatory role for follistatin (a binding protein for specific members of TGF-β superfamily) in early bovine embryonic development. The objectives of the present studies were to determine the functional role of AKT signaling in bovine early embryonic development and embryotrophic actions of follistatin.

METHODS

We used AKT inhibitors III and IV as pharmacological inhibitors of AKT signaling pathway during the first 72 h of in vitro embryo culture. Effects of AKT inhibition on early embryonic development and AKT phosphorylation were investigated in the presence or absence of exogenous follistatin.

RESULTS

Pharmacological inhibition of AKT signaling resulted in a significant reduction in early embryo cleavage, and development to the 8- to 16-cell and blastocyst stages (d7). Treatment with exogenous follistatin increased AKT phosphorylation and rescued the inhibitory effect of AKT inhibitors III and IV on AKT phosphorylation and early embryonic development.

CONCLUSIONS

Collectively, results suggest a potential requirement of AKT for bovine early embryonic development, and suggest a potential role for follistatin in regulation of AKT signaling in early bovine embryos.

DUSP3/VHR: A Druggable Dual Phosphatase for Human Diseases

Protein tyrosine kinases (PTK), discovered in the 1970s, have been considered master regulators of biological processes with high clinical significance as targets for human diseases. Their actions are countered by protein tyrosine phosphatases (PTP), enzymes yet underrepresented as drug targets because of the high homology of their catalytic domains and high charge of their catalytic pocket. This scenario is still worse for some PTP subclasses, for example, for the atypical dual-specificity phosphatases (ADUSPs), whose biological functions are not even completely known. In this sense, the present work focuses on the dual-specificity phosphatase 3 (DUSP3), also known as VH1-related phosphatase (VHR), an uncommon regulator of mitogen-activated protein kinase (MAPK) phosphorylation. DUSP3 expression and activities are suggestive of a tumor suppressor or tumor-promoting enzyme in different types of human cancers. Furthermore, DUSP3 has other biological functions involving immune response mediation, thrombosis, hemostasis, angiogenesis, and genomic stability that occur through either MAPK-dependent or MAPK-independent mechanisms. This broad spectrum of actions is likely due to the large substrate diversity and molecular mechanisms that are still under scrutiny. The growing advances in characterizing new DUSP3 substrates will allow the development of pharmacological inhibitors relevant for possible future clinical trials. This review covers all aspects of DUSP3, since its gene cloning and crystallographic structure resolution, in addition to its classical and novel substrates and the biological processes involved, followed by an update of what is currently known about the DUSP3/VHR-inhibiting compounds that might be considered potential drugs to treat human diseases.

Kinases Involved in Both Autophagy and Mitosis

Both mitosis and autophagy are highly regulated dynamic cellular processes and involve various phosphorylation events catalysed by kinases, which play vital roles in almost all physiological and pathological conditions. Mitosis is a key event during the cell cycle, in which the cell divides into two daughter cells. Autophagy is a process in which the cell digests its own cellular contents. Although autophagy regulation has mainly been studied in asynchronous cells, increasing evidence indicates that autophagy is in fact tightly regulated in mitosis. Here in this review, we will discuss kinases that were originally identified to be involved in only one of either mitosis or autophagy, but were later found to participate in both processes, such as CDKs (cyclin-dependent kinases), Aurora kinases, PLK-1 (polo-like kinase 1), BUB1 (budding uninhibited by benzimidazoles 1), MAPKs (mitogen-activated protein kinases), mTORC1 (mechanistic target of rapamycin complex 1), AMPK (AMP-activated protein kinase), PI3K (phosphoinositide-3 kinase) and protein kinase B (AKT). By focusing on kinases involved in both autophagy and mitosis, we will get a more comprehensive understanding about the reciprocal regulation between the two key cellular events, which will also shed light on their related therapeutic investigations.

Transient Arrest of Germinal Vesicle Breakdown Improved In Vitro Development Potential of Buffalo (Bubalus Bubalis) Oocytes

Germinal vesicle breakdown (GVBD) is the first milestone that an oocyte needs to achieve toward completing the maturation and gaining potential to fertilize. Significantly lower in vitro embryo production rate in buffaloes can be attributed to heterogeneity of GVBD occurrence among oocytes obtained from abattoir derived ovaries. Evidence from our earlier work had suggested that different qualities of buffalo oocytes differ significantly in their timing of GVBD. Besides, these oocytes also differ in terms of volume of Akt phosphorylation, which initiates the process of GVBD. With objective of synchronizing the oocytes for GVBD, immature buffalo oocytes were subjected to a two-step culture protocol, initially in the presence of GVBD inhibitors and subsequently, in vitro maturation (IVM) with added SC79 (activates Akt). Expression of developmentally important genes was assessed along with embryo development rate and blastocyst health to interpret the consequences. Oocytes subjected to a short GVBD inhibition period of 6 h followed by IVM with SC79 resulted in improved cleavage and blastocyst rates. Resultant blastocysts also possessed higher ICM: TE ratio. Further, GVBD inhibited oocytes displayed a sustained cytoplasmic maturation status in terms of reorganization of cortical granules (CGs), mitochondrial membrane potential, and glutathione levels during the period of inhibition. We conclude that a temporary GVBD arrest of buffalo oocytes and modulation of Akt improves the in vitro embryo development rate as well as quality of resultant embryos. Besides, our meiotic arrest protocol does not affect the cytoplasmic maturation. J. Cell. Biochem. 119: 278-289, 2018. © 2017 Wiley Periodicals, Inc.

Litchi seed extract inhibits epidermal growth factor receptor signaling and growth of Two Non-small cell lung carcinoma cells

BACKGROUND

Litchi seeds possess rich amounts of phenolics and have been shown to inhibit proliferation of several types of cancer cells. However, the suppression of EGFR signaling in non-small cell lung cancer (NSCLC) by litchi seed extract (LCSE) has not been fully understood.

METHODS

In this study, the effects of LCSE on EGFR signaling, cell proliferation, the cell cycle and apoptosis in A549 adenocarcinoma cells and NCI- H661 large-cell carcinoma cells were examined.

RESULTS

The results demonstrated that LCSE potently reduced the number of cancer cells and induced growth inhibition, cell-cycle arrest in the G1 or G2/M phase, and apoptotic death in the cellular experiment. Only low cytotoxicity effect was noted in normal lung MRC-5 cells. LCSE also suppressed cyclins and Bcl-2 and elevated Kip1/p27, Bax and caspase 8, 9 and 3 activities, which are closely associated with the downregulation of EGFR and its downstream Akt and Erk-1/-2 signaling.

CONCLUSION

The results implied that LCSE suppressed EGFR signaling and inhibited NSCLC cell growth. This study provided in vitro evidence that LCSE could serve as a potential agent for the adjuvant treatment of NSCLC.

ErbB Receptors and Cancer

The ErbB receptor family, also known as the EGF receptor family or type I receptor family, includes the epidermal growth factor (EGF) receptor (EGFR) or ErbB1/Her1, ErbB2/Her2, ErbB3/Her3, and ErbB4/Her4. Among all RTKs, EGFR was the first RTK identified and the first one linked to cancer. Thus, EGFR has also been the most intensively studied among all RTKs. ErbB receptors are activated after homodimerization or heterodimerization. The ErbB family is unique among the various groups of receptor tyrosine kinases (RTKs) in that ErbB3 has impaired kinase activity, while ErbB2 does not have a direct ligand. Therefore, heterodimerization is an important mechanism that allows the activation of all ErbB receptors in response to ligand stimulation. The activated ErbB receptors bind to many signaling proteins and stimulate the activation of many signaling pathways. The specificity and potency of intracellular signaling pathways are determined by positive and negative regulators, the specific composition of activating ligand(s), receptor dimer components, and the diverse range of proteins that associate with the tyrosine phosphorylated C-terminal domain of the ErbB receptors. ErbB receptors are overexpressed or mutated in many cancers, especially in breast cancer, ovarian cancer, and non-small cell lung cancer. The overexpression and overactivation of ErbB receptors are correlated with poor prognosis, drug resistance, cancer metastasis, and lower survival rate. ErbB receptors, especially EGFR and ErbB2 have been the primary choices as targets for developing cancer therapies.

Comparison of melatonin with growth factors in promoting precursor cells proliferation in adult mouse subventricular zone

Melatonin, secreted mainly by the pineal gland, plays roles in various physiological functions including protecting cell death. We showed in previous study that the proliferation and differentiation of precursor cells from the adult mouse subventricular zone (SVZ) can be modulated by melatonin via the MT1 melatonin receptor. Since melatonin and epidermal growth factor receptor (EGFR) share some signaling pathway components, we investigated whether melatonin can promote the proliferation of precursor cells from the adult mouse SVZ via the extracellular signal-regulated protein kinase /mitogen-activated protein kinase (ERK/MAPK) pathways in comparison with epidermal growth factor (EGF). Melatonin-induced ERK/MAPK pathways compared with EGF were measured by using in vitro and vivo models. We used neurosphere proliferation assay, immunocytochemistry, and immuno-blotting to analyze significant differences between melatonin and growth factor treatment. We also used specific antagonist and inhibitors to confirm the exactly signaling pathway including luzindole and U0126. We found that significant increase in proliferation was observed when two growth factors (EGF+bFGF) and melatonin were used simultaneously compared with EGF + bFGF or compared with melatonin alone. In addition, the present result suggested the synergistic effect occurred of melatonin and growth factors on the activating the ERK/MAPK pathway. This study exhibited that melatonin could act as a trophic factor, increasing proliferation in precursor cells mediated through the melatonin receptor coupled to ERK/MAPK signaling pathways. Understanding the mechanism by which melatonin regulates precursor cells may conduct to the development of novel strategies for neurodegenerative disease therapy.

Reduced levels of Dusp3/Vhr phosphatase impair normal spindle bipolarity in an Erk1/2 activity-dependent manner

Dual specificity phosphatase-3 (Dusp3/Vhr) regulates cell cycle progression by counteracting the effects of mitogen-activated protein kinases (Mapk) Erk1/2 and Jnk. Despite the known upregulation of Dusp3 at M phase in mammalian cells, its mitotic functions are poorly characterized. Here, we report that loss of Dusp3 by RNAi leads to the formation of multipolar spindles in human mitotic cancer cells in an Erk1/2-dependent manner. In the phosphatase-silenced cells, the normal bipolar spindle structure was restored by chemical inhibition of Erk1/2 and ectopic overexpression of Dusp3. We propose that at M phase Dusp3 keeps Erk1/2 activity in check to facilitate normal mitosis.

8-60hIPP5(m)-induced G2/M cell cycle arrest involves activation of ATM/p53/p21(cip1/waf1) pathways and delayed cyclin B1 nuclear translocation

Protein phosphatase 1 (PP1) is a major serine/threonine phosphatase that controls gene expression and cell cycle progression. The active mutant IPP5 (8-60hIPP5(m)), the latest member of the inhibitory molecules for PP1, has been shown to inhibit the growth of human cervix carcinoma cells (HeLa). In order to elucidate the underlying mechanisms, the present study assessed overexpression of 8-60hIPP5(m) in HeLa cells. Flow cytometric and biochemical analyses showed that overexpression of 8-60hIPP5(m) induced G2/M-phase arrest, which was accompanied by the upregulation of cyclin B1 and phosphorylation of G2/M-phase proteins ATM, p53, p21(cip1/waf1) and Cdc2, suggesting that 8-60hIPP5(m) induces G2/M arrest through activation of the ATM/p53/p21(cip1/waf1)/Cdc2/ cyclin B1 pathways. We further showed that overexpression of 8-60hIPP5(m) led to delayed nuclear translocation of cyclin B1. 8-60hIPP5(m) also could translocate to the nucleus in G2/M phase and interact with pp1α and Cdc2 as demonstrated by co-precipitation assay. Taken together, our data demonstrate a novel role for 8-60hIPP5(m) in regulation of cell cycle in HeLa cells, possibly contributing to the development of new therapeutic strategies for cervix carcinoma.

ERK Plays a Role in Chromosome Alignment and Participates in M-Phase Progression

Cell division, a prerequisite for cell proliferation, is a process in which each daughter cell inherits one complete set of chromosomes. The mitotic spindle is a dedicated apparatus for the alignment and segregation of chromosomes. Extracellular signal-regulated kinase (ERK) 1/2 plays crucial roles in cell cycle progression, particularly during M-phase. Although, association with the mitotic spindle has been reported, the precise roles played by ERK in the dynamics of the mitotic spindle and in M-phase progression remain to be elucidated. In this study, we used MEK inhibitors U0126 and GSK1120212 to dissect the roles of ERK in M-phase progression and chromosome alignment. Fluorescence microscopy revealed that ERK is localized to the spindle microtubules in a manner independent of Src kinase, which is one of the kinases upstream of ERK at mitotic entry. ERK inhibition induces an increase in the number of prophase cells and a decrease in the number of anaphase cells. Time-lapse imaging revealed that ERK inhibition perturbs chromosome alignment, thereby preventing cells from entering anaphase. These results suggest that ERK plays a role in M-phase progression by regulating chromosome alignment and demonstrate one of the mechanisms by which the aberration of ERK signaling may produce cancer cells.

Trajectories of cell-cycle progression from fixed cell populations

An accurate dissection of sources of cell-to-cell variability is crucial for quantitative biology at the single-cell level but has been challenging for the cell cycle. We present Cycler, a robust method that constructs a continuous trajectory of cell-cycle progression from images of fixed cells. Cycler handles heterogeneous microenvironments and does not require perturbations or genetic markers, making it generally applicable to quantifying multiple sources of cell-to-cell variability in mammalian cells.

Rational Combinations of Targeted Agents in AML

Despite modest improvements in survival over the last several decades, the treatment of AML continues to present a formidable challenge. Most patients are elderly, and these individuals, as well as those with secondary, therapy-related, or relapsed/refractory AML, are particularly difficult to treat, owing to both aggressive disease biology and the high toxicity of current chemotherapeutic regimens. It has become increasingly apparent in recent years that coordinated interruption of cooperative survival signaling pathways in malignant cells is necessary for optimal therapeutic results. The modest efficacy of monotherapy with both cytotoxic and targeted agents in AML testifies to this. As the complex biology of AML continues to be elucidated, many “synthetic lethal” strategies involving rational combinations of targeted agents have been developed. Unfortunately, relatively few of these have been tested clinically, although there is growing interest in this area. In this article, the preclinical and, where available, clinical data on some of the most promising rational combinations of targeted agents in AML are summarized. While new molecules should continue to be combined with conventional genotoxic drugs of proven efficacy, there is perhaps a need to rethink traditional philosophies of clinical trial development and regulatory approval with a focus on mechanism-based, synergistic strategies.

Selective CREB-dependent cyclin expression mediated by the PI3K and MAPK pathways supports glioma cell proliferation

The cyclic-AMP response element binding (CREB) protein has been shown to have a pivotal role in cell survival and cell proliferation. Transgenic rodent models have revealed a role for CREB in higher-order brain functions, such as memory and drug addiction behaviors. CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours. It is the central position of CREB, downstream from key developmental and growth signalling pathways, which gives CREB this ability to influence a spectrum of cellular activities, such as cell survival, growth and differentiation, in both normal and cancer cells. We show that CREB is highly expressed and constitutively activated in patient glioma tissue and that this activation closely correlates with tumour grade. The mechanism by which CREB regulates glioblastoma (GBM) tumour cell proliferation involves activities downstream from both the mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K) pathways that then modulate the expression of three key cell cycle factors, cyclin B, D and proliferating cell nuclear antigen (PCNA). Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms. The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself. Given that CREB sits at the hub of key cancer cell signalling pathways, understanding the role of glioma-specific CREB function may lead to improved novel combinatorial anti-tumour therapies, which can complement existing PI3K-specific drugs undergoing early phase clinical trials.

Inhibitory effects of Pericarpium zanthoxyli extract on adipocyte differentiation

Obesity is a risk factor associated with numerous disorders, such as type 2 diabetes, hypertension, dyslipidemia and coronary heart disease. In this study, we investigated the inhibitory effects of Pericarpium zanthoxyli extract (PZE) on the adipocytic differentiation of OP9 cells. During adipocyte differentiation, the OP9 cells were treated with 0, 10 and 20 µg/ml of PZE at various time intervals, followed by the examination of lipid droplet formation and the mRNA expression of adipogenesis-related genes. The cells treated with PZE during the early period (days 0-2) showed a significant reduction in the accumulation of lipid droplets, which were induced by a standard adipogenic cocktail, as well as a decrease in the expression of the adipogenesis-related transcription factor, peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ-target genes, such as adipocyte protein 2 (aP2), fatty acid synthase (FAS) and other adipocyte markers. Adipocyte differentiation was not inhibited by treatment with PZE during the late stage of differentiation (days 3-5). Thus, the inhibitory effects of PZE on adipocyte differentiation occurred during the early stages of adipogenesis, which was confirmed by the decrease in the levels of CCAAT/enhancer-binding protein β (C/EBPβ) in a dose-dependent manner when the OP9 cells were exposed to PZE. Taken together, our results indicate that PZE inhibit the early stages of adipogenic differentiation by inhibiting C/EBPβ expression.

Targeting SRC and tubulin in mucinous ovarian carcinoma

PURPOSE

To investigate the antitumor effects of targeting Src and tubulin in mucinous ovarian carcinoma.

EXPERIMENTAL DESIGN

The in vitro and in vivo effects and molecular mechanisms of KX-01, which inhibits Src pathway and tubulin polymerization, were examined in mucinous ovarian cancer models.

RESULTS

In vitro studies using RMUG-S and RMUG-L cell lines showed that KX-01 inhibited cell proliferation, induced apoptosis, arrested the cell cycle at the G2-M phase, and enhanced the cytotoxicity of oxaliplatin in the KX-01-sensitive cell line, RMUG-S. In vivo studies showed that KX-01 significantly decreased tumor burden in RMUG-S and RMUG-L mouse models relative to untreated controls, and the effects were greater when KX-01 was combined with oxaliplatin. KX-01 alone and in combination with oxaliplatin significantly inhibited tumor growth by reducing cell proliferation and inducing apoptosis in vivo. PTEN knock-in experiments in RMUG-L cells showed improved response to KX-01. Reverse phase protein array analysis showed that in addition to blocking downstream molecules of Src family kinases, KX-01 also activated acute stress-inducing molecules.

CONCLUSION

Our results showed that targeting both the Src pathway and tubulin with KX-01 significantly inhibited tumor growth in preclinical mucinous ovarian cancer models, suggesting that this may be a promising therapeutic approach for patients with mucinous ovarian carcinoma.

EGFR/MEK/ERK/CDK5-dependent integrin-independent FAK phosphorylated on serine 732 contributes to microtubule depolymerization and mitosis in tumor cells

FAK is a non-receptor tyrosine kinase contributing to migration and proliferation downstream of integrin and/or growth factor receptor signaling of normal and malignant cells. In addition to well-characterized tyrosine phosphorylations, FAK is phosphorylated on several serines, whose role is not yet clarified. We observed that phosphorylated FAK on serine 732 (P-FAKSer732) is present at variable levels in vitro, in several melanoma, ovarian and thyroid tumor cell lines and in vivo, in tumor cells present in fresh ovarian cancer ascites. In vitro P-FAKSer732 was barely detectable during interphase while its levels strongly increased in mitotic cells upon activation of the EGFR/MEK/ERK axis in an integrin-independent manner. P-FAKSer732 presence was crucial for the maintenance of the proliferation rate and its levels were inversely related to the levels of acetylated α-tubulin. P-FAKSer732 localized at the microtubules (MTs) of the spindle, biochemically associated with MTs and contributed to MT depolymerization. The lack of the phosphorylation on Ser732 as well as the inhibition of CDK5 activity by roscovitine impaired mitotic spindle assembly and correct chromosome alignment during mitosis. We also identified, for the first time, that the EGF-dependent EGFR activation led to increased P-FAKSer732 and polymerized MTs. Our data shed light on the multifunctional roles of FAK in neoplastic cells, being involved not only in integrin-dependent migratory signaling but also in integrin-independent MT dynamics and mitosis control. These findings provide a new potential target for inhibiting the growth of tumor cells in which the EGFR/MEK/ERK/CDK5 pathway is active.

RSK promotes G2/M transition through activating phosphorylation of Cdc25A and Cdc25B

Activation of the mitogen-activated protein kinase (MAPK) cascade in mammalian cell lines positively regulates the G2/M transition. The molecular mechanism underlying this biological phenomenon remains poorly understood. Ribosomal S6 kinase (RSK) is a key downstream element of the MAPK cascade. Our previous studies established roles of RSK2 in Cdc25C activation during progesterone-induced meiotic maturation of Xenopus oocytes. In this study we demonstrate that both recombinant RSK and endogenous RSK in Xenopus egg extracts phosphorylate all three isoforms of human Cdc25 at a conserved motif near the catalytic domain. In human HEK293 and PC-3mm2 cell lines, RSK preferentially phosphorylates Cdc25A and Cdc25B in mitotic cells. Phosphorylation of the RSK sites in these Cdc25 isoforms increases their M-phase-inducing activities. Inhibition of RSK-mediated phosphorylation of Cdc25 inhibits G2/M transition. Moreover, RSK is likely to be more active in mitotic cells than in interphase cells, as evidenced by the phosphorylation status of T359/S363 in RSK. Together, these findings indicate that RSK promotes G2/M transition in mammalian cells through activating phosphorylation of Cdc25A and Cdc25B.

HER2 stabilizes survivin while concomitantly down-regulating survivin gene transcription by suppressing Notch cleavage

In breast cancer, the HER2 (human epidermal growth factor receptor 2) receptor tyrosine kinase is associated with extremely poor prognosis and survival. Notch signalling has a key role in cell-fate decisions, especially in cancer-initiating cells. The Notch intracellular domain produced by Notch cleavage is translocated to the nucleus where it activates transcription of target genes. To determine the combinatory effect of HER2 and Notch signalling in breast cancer, we investigated the effect of HER2 on Notch-induced cellular phenomena. We found the down-regulation of Notch-dependent transcriptional activity by HER2 overexpression. Also, the HER2/ERK (extracellular-signal-regulated kinase) signal pathway down-regulated the activity of γ-secretase. When we examined the protein level of Notch target genes in HER2-overexpressing cells, we observed that the level of survivin, downstream of Notch, increased in HER2 cells. We found that activation of ERK resulted in a decrease in XAF1 [XIAP (X-linked inhibitor of apoptosis)-associated factor 1] which reduced the formation of the XIAP-XAF1 E3 ligase complex to ubiquitinate survivin. In addition, Thr(34) of survivin was shown to be the most important residue in determining survivin stability upon phosphorylation after HER2/Akt/CDK1 (cyclin-dependent kinase 1)-cyclin B1 signalling. The results of the present study show the combinatorial effects of HER2 and Notch during breast oncogenesis.

Inhibition of AKT enhances mitotic cell apoptosis induced by arsenic trioxide

Accumulated evidence has revealed a tight link between arsenic trioxide (ATO)-induced apoptosis and mitotic arrest in cancer cells. AKT, a serine/threonine kinase frequently over-activated in diverse tumors, plays critical roles in stimulating cell cycle progression, abrogating cell cycle checkpoints, suppressing apoptosis, and regulating mitotic spindle assembly. Inhibition of AKT may therefore enhance ATO cytotoxicity and thus its clinical utility. We show that AKT was activated by ATO in HeLa-S3 cells. Inhibition of AKT by inhibitors of the phosphatidyl inositol 3-kinase/AKT pathway significantly enhanced cell sensitivity to ATO by elevating mitotic cell apoptosis. Ectopic expression of the constitutively active AKT1 had no effect on ATO-induced spindle abnormalities but reduced kinetochore localization of BUBR1 and MAD2 and accelerated mitosis exit, prevented mitotic cell apoptosis, and enhanced the formation of micro- or multi-nuclei in ATO-treated cells. These results indicate that AKT1 activation may prevent apoptosis of ATO-arrested mitotic cells by attenuating the function of the spindle checkpoint and therefore allowing the formation of micro- or multi-nuclei in surviving daughter cells. In addition, AKT1 activation upregulated the expression of aurora kinase B (AURKB) and survivin, and depletion of AURKB or survivin reversed the resistance of AKT1-activated cells to ATO-induced apoptosis. Thus, AKT1 activation suppresses ATO-induced mitotic cell apoptosis, despite the presence of numerous spindle abnormalities, probably by upregulating AURKB and survivin and attenuating spindle checkpoint function. Inhibition of AKT therefore effectively sensitizes cancer cells to ATO by enhancing mitotic cell apoptosis.

KIFC1 is essential for bipolar spindle formation and genomic stability in the primary human fibroblast IMR-90 cell

Kinesin family member C1 (KIFC1) is the only member of the minus-end-directed kinesin-14 family in human cells. In cancer cells, KIFC1 plays an essential role in bipolar spindle formation by clustering the multiple poles during mitosis. However, it has not been clearly demonstrated whether KIFC1 also functions to mediate bipolar spindle formation and to maintain genomic stability in normal cells. In this study, by using human primary lung fibroblast IMR-90 cells, we showed that KIFC1 knock-down with lentiviral KIFC1 shRNA induced 17% of cells with multiple microtubule organizing centers (MTOCs) and delayed cyclin A degradation for more than 2 hr in early mitosis. However, these cells eventually carried out mitosis, resulting in 24% of cells with lagging chromosomes and 9% of cells with micronuclei after mitosis. Karyotyping of KIFC1-depleted IMR-90 cells demonstrated that cells with various abnormal numbers of chromosomes are produced. When IMR-90 cells treated with KIFC1 or the control shRNA for 60 hr were compared, 20% less cells were observed in KIFC1-depleted cells without an obvious immediate cell death. As reported for Mad2 depletion in IMR-90 cells, KIFC1-depleted IMR-90 cells showed typical features of senescence, like senescence-associated (SA) β-galactosidase expression, when incubated 6 days or more. However, IMR-90 cells knocked down with both KIFC1 and Mad2 underwent apoptosis, suggesting that KIFC1 and Mad2 likely function in different pathways during mitosis. Taken together, we suggest that KIFC1 plays an essential role for bipolar MTOC formation and maintaining chromosomal stability in the mitosis of human primary fibroblast IMR-90.

Inhibition of PI3K/Akt pathway impairs G2/M transition of cell cycle in late developing progenitors of the avian embryo retina

PI3K/Akt is an important pathway implicated in the proliferation and survival of cells in the CNS. Here we investigated the participation of the PI3K/Akt signal pathway in cell cycle of developing retinal progenitors. Immunofluorescence assays performed in cultures of chick embryo retinal cells and intact tissues revealed the presence of phosphorylated Akt and 4E-BP1 in cells with typical mitotic profiles. Blockade of PI3K activity with the chemical inhibitor LY 294002 (LY) in retinal explants blocked the progression of proliferating cells through G2/M transition, indicated by an expressive increase in the number of cells labeled for phosphorylated histone H3 in the ventricular margin of the retina. No significant level of cell death could be detected at this region. Retinal explants treated with LY for 24 h also showed a significant decrease in the expression of phospho-Akt, phospho-GSK-3 and the hyperphosphorylated form of 4E-BP1. Although no change in the expression of cyclin B1 was detected, a significant decrease in CDK1 expression was noticed after 24 h of LY treatment both in retinal explants and monolayer cultures. Our results suggest that PI3K/Akt is an active pathway during proliferation of retinal progenitors and its activity appears to be required for proper CDK1 expression levels and mitosis progression of these cells.

Inhibition of IGF-IR increases chemosensitivity in human colorectal cancer cells through MRP-2 promoter suppression

The emergence of multidrug resistance (MDR) in cancer cells has made many of the currently available chemotherapeutic agents ineffective. However, the mechanism involved in mediating this effect is not yet fully understood. Here, we found the overexpression of type I insulin-like growth factor receptor (IGF-IR) in established colorectal MDR cells. Specific siRNA of IGF-IR decreases cell proliferation, exert synergistic effect with anticancer drugs. The downstream signaling of IGF-IR, PI3K/AKT pathway, was altered upon IGF-IR silencing. The expression of multidrug-resistance-associated protein 2 (MRP-2) was suppressed due to the nuclear translocation of nuclear factor-like 2 (Nrf2). Then the intracellular drug concentration was increased and the drug-resistant phenotype was reversed. Our findings improve current understanding of the biology of IGF-IR and MDR and have significant therapeutic implications on colorectal MDR cancer.

Extracellular signal-regulated kinase 2 (ERK2) mediates phosphorylation and inactivation of nuclear interaction partner of anaplastic lymphoma kinase (NIPA) at G2/M

NIPA is an F-box-like protein that contributes to the timing of mitotic entry. It targets nuclear cyclin B1 for ubiquitination in interphase, whereas in G(2)/M phase, NIPA is inactivated by phosphorylation to allow for cyclin B1 accumulation, a critical event for proper G(2)/M transition. We recently specified three serine residues of NIPA and demonstrated a sequential phosphorylation at G(2)/M, where initial Ser-354 and Ser-359 phosphorylation is most crucial for SCF(NIPA) inactivation. In this study, we identified ERK2 as the kinase responsible for this critical initial phosphorylation step. Using in vitro kinase assays, we found that both ERK1 and ERK2 phosphorylated NIPA with high efficiency. Mutation of either Ser-354 or Ser-359 abolished ERK-dependent NIPA phosphorylation. Pharmacologic inhibition of ERK1/2 in cell lines resulted in decreased NIPA phosphorylation at G(2)/M. By combining cell cycle synchronization with stable expression of shRNA targeting either ERK1 or ERK2, we showed that ERK2 but not ERK1 mediated NIPA inactivation at G(2)/M. ERK2 knockdown led to a delay at the G(2)/M transition, a phenotype also observed in cells expressing a phospho-deficient mutant of NIPA. Thus, our data add to the recently described divergent functions of ERK1 and ERK2 in cell cycle regulation, which may be due in part to the differential ability of these kinases to phosphorylate and inactivate NIPA at G(2)/M.

Differential regulation of Smad3 and of the type II transforming growth factor-β receptor in mitosis: implications for signaling

The response to transforming growth factor-β (TGF-β) depends on cellular context. This context is changed in mitosis through selective inhibition of vesicle trafficking, reduction in cell volume and the activation of mitotic kinases. We hypothesized that these alterations in cell context may induce a differential regulation of Smads and TGF-β receptors. We tested this hypothesis in mesenchymal-like ovarian cancer cells, arrested (or not) in mitosis with 2-methoxyestradiol (2ME2). In mitosis, without TGF-β stimulation, Smad3 was phosphorylated at the C-terminus and linker regions and localized to the mitotic spindle. Phosphorylated Smad3 interacted with the negative regulators of Smad signaling, Smurf2 and Ski, and failed to induce a transcriptional response. Moreover, in cells arrested in mitosis, Smad3 levels were progressively reduced. These phosphorylations and reduction in the levels of Smad3 depended on ERK activation and Mps1 kinase activity, and were abrogated by increasing the volume of cells arrested in mitosis with hypotonic medium. Furthermore, an Mps1-dependent phosphorylation of GFP-Smad3 was also observed upon its over-expression in interphase cells, suggesting a mechanism of negative regulation which counters increases in Smad3 concentration. Arrest in mitosis also induced a block in the clathrin-mediated endocytosis of the type II TGF-β receptor (TβRII). Moreover, following the stimulation of mitotic cells with TGF-β, the proteasome-mediated attenuation of TGF-β receptor activity, the degradation and clearance of TβRII from the plasma membrane, and the clearance of the TGF-β ligand from the medium were compromised, and the C-terminus phosphorylation of Smad3 was prolonged. We propose that the reduction in Smad3 levels, its linker phosphorylation, and its association with negative regulators (observed in mitosis prior to ligand stimulation) represent a signal attenuating mechanism. This mechanism is balanced by the retention of active TGF-β receptors at the plasma membrane. Together, both mechanisms allow for a regulated cellular response to TGF-β stimuli in mitosis.

Sulforaphane inhibits mitotic clonal expansion during adipogenesis through cell cycle arrest

Obesity is a risk factor for numerous metabolic disorders such as type 2 diabetes, hypertension, and coronary heart disease. Adipocyte differentiation is triggered by adipocyte hyperplasia, which leads to obesity. In this study, the inhibitory effect of sulforaphane, an isothiocyanate, on adipogenesis in 3T3-L1 cells was investigated. Sulforaphane decreased the accumulation of lipid droplets stained with Oil Red O and inhibited the elevation of triglycerides in the adipocytes (half-maximal inhibitory concentration = 7.3 µmol/l). The expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), major transcription factors for adipocyte differentiation, was significantly reduced by sulforaphane. The major effects of sulforaphane on the inhibition of adipocyte differentiation occurred during the early stage of adipogenesis. Thus, the expression of C/EBPβ, an early-stage biomarker of adipogenesis, decreased in a concentration-dependent manner when the adipocytes were exposed to sulforaphane (0, 5, 10, and 20 µmol/l). The proliferation of adipocytes treated with 20 µmol/l sulforaphane for 24 and 48 h was also suppressed. These results indicate that sulforaphane may specifically affect mitotic clonal expansion to inhibit adipocyte differentiation. Sulforaphane arrested the cell cycle at the G(0)/G(1) phase, increased p27 expression, and decreased retinoblastoma (Rb) phosphorylation. Additionally, sulforaphane modestly decreased the phosphorylation of ERK1/2 and Akt. Our results indicate that the inhibition of early-stage adipocyte differentiation by sulforaphane may be associated with cell cycle arrest at the G(0)/G(1) phase through upregulation of p27 expression.

Human corneal endothelial cells employ phosphorylation of p27(Kip1) at both Ser10 and Thr187 sites for FGF-2-mediated cell proliferation via PI 3-kinase

PURPOSE

FGF-2 stimulates cell proliferation of rabbit corneal endothelial cells (rCECs) by degrading the cyclin-dependent kinase inhibitor p27(Kip1) (p27) through its phosphorylation mechanism. The authors investigated whether the cell proliferation of human CECs (hCECs) is also induced by FGF-2 stimulation through the p27 phosphorylation pathway.

METHODS

Expression and activation of protein were analyzed by immunoblotting. Cell proliferation was measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. Transfection of hCECs with small interference RNA (siRNA) was performed using a transfection reagent.

RESULTS

FGF-2 stimulated cell proliferation in hCECs; the FGF-2 action was completely blocked by pathway-specific inhibitors for PI 3-kinase (LY294002) and MEK1/2 (U0126), respectively. Using immunoblotting, the authors showed that FGF-2 induced phosphorylation of p27 at both serine 10 (Ser10) and threonine 187 (Thr187) sites. These effects were also completely blocked by LY294002 or U0126. The authors then determined cross-talk between PI 3-kinase and extracellular signal-regulated kinase (ERK)1/2; blocking of ERK1/2 activation by LY294002 indicated that in hCECs ERK1/2 works as a downstream effector to PI 3-kinase for cell proliferation induced by FGF-2, whereas the ERK1/2 pathway in rCECs is parallel to the PI 3-kinase pathway. However, the downstream mechanism involved in cell cycle progression in hCECs is identical to that of rCECs: phosphorylation of p27 at Ser10 was mediated by kinase-interacting stathmin (KIS), confirmed with siRNA to KIS, and phosphorylation of p27 at Thr187 was mediated by cell division cycle 25A (Cdc25A), confirmed using Cdc25A inhibitor. CONCLUSIONS; FGF-2 stimulates proliferation of hCECs through PI 3-kinase and its downstream target ERK1/2 pathways. This linear signal transduction significantly downregulates p27 through its phosphorylation at both Ser10 and Thr187 sites mediated by KIS and Cdc25A, respectively.

Mechanisms of aneuploidy induction by RAS and RAF oncogenes

Most cancers progress with the accumulation of genetic mutations with time and this is frequently associated with the acquisition of genomic instability in the form of whole chromosome changes, chromosomal rearrangements, gene amplifications or smaller changes at the nucleotide level. Whole chromosome instability (W-CIN), characterised by aneuploidy, is a major form of genomic instability observed in human cancers and several lines of evidence now support the argument that W-CIN is a promoter of tumourigenesis rather than being a passenger event. The primary mechanism proposed for evolution of CIN is abnormalities in mitosis/cytokinesis. However, mutations in genes directly involved in controlling mitosis/cytokinesis are rare in human cancers and so the mechanisms underpinning the evolution of CIN in cancers are not currently clear. On the other hand, mutations in RAS or BRAF are frequently found in human cancers, many of which demonstrate CIN, suggesting a possible link between deregulated signaling through the RAS/RAF/MEK/ERK pathway and CIN. In this review, we focus on a potential relationship between deregulated RAS/RAF signaling and CIN, and discuss possible mechanisms connecting the two.

Loss of c-Met disrupts gene expression program required for G2/M progression during liver regeneration in mice

Background

Previous work has established that HGF/c-Met signaling plays a pivotal role in regulating the onset of S phase following partial hepatectomy (PH). In this study, we used Met^fl/fl;Alb-Cre^+/− conditional knockout mice to determine the effects of c-Met dysfunction in hepatocytes on kinetics of liver regeneration.

Methodology/Principal Finding

The priming events appeared to be intact in Met^fl/fl;Alb-Cre^+/− livers. Up-regulation of stress response (MAFK, IKBZ, SOCS3) and early growth response (c-Myc, c-Jun, c-Fos, DUSP1 and 6) genes as assessed by RT-qPCR and/or microarray profiling was unchanged. This was consistent with an early induction of MAPK/Erk and STAT3. However, after a successful completion of the first round of DNA replication, c-Met deficient hepatocytes were blocked in early/mid G2 phase as shown by staining with phosphorylated form of histone H3. Furthermore, loss of c-Met in hepatocytes diminished the subsequent G1/S progression and delayed liver recovery after partial hepatectomy. Upstream signaling pathways involved in the blockage of G2/M transition included lack of persistent Erk1/2 activation and inability to up-regulate the levels of Cdk1, Plk1, Aurora A and B, and Mad2 along with a defective histone 3 phosphorylation and lack of chromatin condensation. Continuous supplementation with EGF in vitro increased proliferation of Met^fl/fl;Alb-Cre^+/− primary hepatocytes and partially restored expression levels of mitotic cell cycle regulators albeit to a lesser degree as compared to control cultures.

Conclusion/Significance

In conclusion, our results assign a novel non-redundant function for HGF/c-Met signaling in regulation of G2/M gene expression program via maintaining a persistent Erk1/2 activation throughout liver regeneration.

Prevention of in vitro hepatic stellate cells activation by the adenosine derivative compound IFC305

We have previously shown that adenosine and the aspartate salt of adenosine (IFC305) reverse pre-established CCl(4)-induced cirrhosis in rats. However, their molecular mechanism of action is not clearly understood. Hepatic stellate cells (HSC) play a pivotal role in liver fibrogenesis leading to cirrhosis, mainly through their activation, changing from a quiescent adipogenic state to a proliferative myofibrogenic condition. Therefore, we decided to investigate the effect of IFC305 on primary cultured rat HSC. Our results reveal that this compound suppressed the activation of HSC, as demonstrated by the maintenance of a quiescent cell morphology, including lipid droplets content, inhibition of α-smooth muscle actin (α-SMA) and collagen α1(I) expression, and up-regulation of MMP-13, Smad7, and PPARγ expression, three key antifibrogenic genes. Furthermore, IFC305 was able to repress the platelet-derived growth factor (PDGF)-induced proliferation of HSC. This inhibition was independent of adenosine receptors stimulation; instead, IFC305 was incorporated into cells by adenosine transporters and converted to AMP by adenosine kinase. On the other hand, addition of pyrimidine ribonucleoside as uridine reversed the suppressive effect of IFC305 on the proliferation and activation of HSC, suggesting that intracellular pyrimidine starvation would be involved in the molecular mechanism of action of IFC305. In conclusion, IFC305 inhibits HSC activation and maintains their quiescence in vitro; these results could explain in part the antifibrotic liver beneficial effect previously described for this compound on the animal model.

Mitogen-activated protein/extracellular signal-regulated kinase kinase 1act/tubulin interaction is an important determinant of mitotic stability in cultured HT1080 human fibrosarcoma cells

Activation of the mitogen-activated protein kinase (MAPK) pathway plays a major role in neoplastic cell transformation. Using a proteomics approach, we identified alpha tubulin and beta tubulin as proteins that interact with activated MAP/extracellular signal-regulated kinase kinase 1 (MEK1), a central MAPK regulatory kinase. Confocal analysis revealed spatiotemporal control of MEK1-tubulin colocalization that was most prominent in the mitotic spindle apparatus in variant HT1080 human fibrosarcoma cells. Peptide arrays identified the critical role of positively charged amino acids R108, R113, R160, and K157 on the surface of MEK1 for tubulin interaction. Overexpression of activated MEK1 caused defects in spindle arrangement, chromosome segregation, and ploidy. In contrast, chromosome polyploidy was reduced in the presence of an activated MEK1 mutant (R108A, R113A) that disrupted interactions with tubulin. Our findings indicate the importance of signaling by activated MEK1-tubulin in spindle organization and chromosomal instability.