Growth factor-dependent signaling and cell cycle progression

Acrobatic training prevents learning impairments and astrocyte remodeling in the hippocampus of rats undergoing chronic cerebral hypoperfusion: sex-specific benefits

Background

Chronic cerebral hypoperfusion (CCH) leads to memory and learning impairments associated with degeneration and gliosis in the hippocampus. Treatment with physical exercise carries different therapeutic benefits for each sex. We investigated the effects of acrobatic training on astrocyte remodeling in the CA1 and CA3 subfields of the hippocampus and spatial memory impairment in male and female rats at different stages of the two-vessel occlusion (2VO) model.

Methods

Wistar rats were randomly allocated into four groups of males and females: 2VO acrobatic, 2VO sedentary, sham acrobatic, and sham sedentary. The acrobatic training was performed for 4 weeks prior to the 2VO procedure. Brain samples were collected for morphological and biochemical analysis at 3 and 7 days after 2VO. The dorsal hippocampi were removed and prepared for Western blot quantification of Akt, p-Akt, COX IV, cleaved caspase-3, PARP, and GFAP. GFAP immunofluorescence was performed on slices of the hippocampus to count astrocytes and apply the Sholl's circle technique. The Morris water maze was run after 45 days of 2VO.

Results

Acutely, the trained female rats showed increased PARP expression, and the 2VO-trained rats of both sexes presented increased GFAP levels in Western blot. Training, mainly in males, induced an increase in the number of astrocytes in the CA1 subfield. The 2VO rats presented branched astrocytes, while acrobatic training prevented branching. However, the 2VO-induced spatial memory impairment was partially prevented by the acrobatic training.

Conclusion

Acrobatic training restricted the astrocytic remodeling caused by 2VO in the CA1 and CA3 subfields of the hippocampus. The improvement in spatial memory was associated with more organized glial scarring in the trained rats and better cell viability observed in females.

Effects of different alkylating agents on photoreceptor degeneration and proliferative response of Müller glia

Animal models for retinal degeneration are essential for elucidating its pathogenesis and developing new therapeutic strategies in humans. N-methyl-N-nitrosourea (MNU) has been extensively used to construct a photoreceptor-specific degeneration model, which has served to unveil the molecular process of photoreceptor degeneration as well as the mechanisms regulating the protective responses of remaining cells. Methyl methanesulphonate (MMS), also known to cause photoreceptor degeneration, is considered a good alternative to MNU due to its higher usability; however, detailed pathophysiological processes after MMS treatment remain uncharacterized. Here, we analyzed the time course of photoreceptor degeneration, Müller glial proliferation, and expression of secretory factors after MNU and MMS treatments in rats. While the timing of rod degeneration was similar between the treatments, we unexpectedly found that cones survived slightly longer after MMS treatment. Müller glia reentered the cell cycle at a similar timing after the two treatments; however, the G1/S transition occurred earlier after MMS treatment. Moreover, growth factors such as FGF2 and LIF were more highly upregulated in the MMS model. These data suggest that comparative analyses of the two injury models may be beneficial for understanding the complex regulatory mechanisms underlying the proliferative response of Müller glia.

Transcriptional Fluctuations Govern the Serum-Dependent Cell Cycle Duration Heterogeneities in Mammalian Cells

Mammalian cells exhibit a high degree of intercellular variability in cell cycle period and phase durations. However, the factors orchestrating the cell cycle duration heterogeneities remain unclear. Herein, by combining cell cycle network-based mathematical models with live single-cell imaging studies under varied serum conditions, we demonstrate that fluctuating transcription rates of cell cycle regulatory genes across cell lineages and during cell cycle progression in mammalian cells majorly govern the robust correlation patterns of cell cycle period and phase durations among sister, cousin, and mother-daughter lineage pairs. However, for the overall cellular population, alteration in the serum level modulates the fluctuation and correlation patterns of cell cycle period and phase durations in a correlated manner. These heterogeneities at the population level can be fine-tuned under limited serum conditions by perturbing the cell cycle network using a p38-signaling inhibitor without affecting the robust lineage-level correlations. Overall, our approach identifies transcriptional fluctuations as the key controlling factor for the cell cycle duration heterogeneities and predicts ways to reduce cell-to-cell variabilities by perturbing the cell cycle network regulations.

Wnt signaling regulates hepatocyte cell division by a transcriptional repressor cascade

As a general model for cell cycle control, repressors keep cells quiescent until growth signals remove the inhibition. For S phase, this is exemplified by the Retinoblastoma (RB) protein and its inactivation. It was unknown whether similar mechanisms operate in the M phase. The Wnt signaling pathway is an important regulator of cell proliferation. Here, we find that Wnt induces expression of the transcription factor Tbx3, which in turn represses mitotic inhibitors E2f7 and E2f8 to permit mitotic progression. Such a cascade of transcriptional repressors may be a general mechanism for cell division control. These findings have implications for tissue homeostasis and disease, as the function for Wnt signaling in mitosis is relevant to its widespread role in stem cells and cancer.

Cell proliferation is tightly controlled by inhibitors that block cell cycle progression until growth signals relieve this inhibition, allowing cells to divide. In several tissues, including the liver, cell proliferation is inhibited at mitosis by the transcriptional repressors E2F7 and E2F8, leading to formation of polyploid cells. Whether growth factors promote mitosis and cell cycle progression by relieving the E2F7/E2F8-mediated inhibition is unknown. We report here on a mechanism of cell division control in the postnatal liver, in which Wnt/β-catenin signaling maintains active hepatocyte cell division through Tbx3, a Wnt target gene. The TBX3 protein directly represses transcription of E2f7 and E2f8, thereby promoting mitosis. This cascade of sequential transcriptional repressors, initiated by Wnt signals, provides a paradigm for exploring how commonly active developmental signals impact cell cycle completion.

Mesenchymal stromal cell delivery as a potential therapeutic strategy against COVID-19: Promising evidence from in vitro results

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19) pandemic, which was initiated in December 2019. COVID-19 is characterized by a low mortality rate (< 6%); however, this percentage is higher in elderly people and patients with underlying disorders. COVID-19 is characterized by mild to severe outcomes. Currently, several therapeutic strategies are evaluated, such as the use of anti-viral drugs, prophylactic treatment, monoclonal antibodies, and vaccination. Advanced cellular therapies are also investigated, thus representing an additional therapeutic tool for clinicians. Mesenchymal stromal cells (MSCs), which are known for their immunoregulatory properties, may halt the induced cytokine release syndrome mediated by SARS-CoV-2, and can be considered as a potential stem cell therapy.

AIM

To evaluate the immunoregulatory properties of MSCs, upon stimulation with COVID-19 patient serum.

METHODS

MSCs derived from the human Wharton’s Jelly (WJ) tissue and bone marrow (BM) were isolated, cryopreserved, expanded, and defined according to the criteria outlined by the International Society for Cellular Therapies. Then, WJ and BM-MSCs were stimulated with a culture medium containing 15% COVID-19 patient serum, 1% penicillin-streptomycin, and 1% L-glutamine for 48 h. The quantification of interleukin (IL)-1 receptor a (Ra), IL-6, IL-10, IL-13, transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF)-a, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), and indoleamine-2,3-dioxygenase (IDO) was performed using commercial ELISA kits. The expression of HLA-G1, G5, and G7 was evaluated in unstimulated and stimulated WJ and BM-MSCs. Finally, the interactions between MSCs and patients’ macrophages were established using co-culture experiments.

RESULTS

Thawed WJ and BM-MSCs exhibited a spindle-shaped morphology, successfully differentiated to “osteocytes”, “adipocytes”, and “chondrocytes”, and in flow cytometric analysis were characterized by positivity for CD73, CD90, and CD105 (> 95%) and negativity for CD34, CD45, and HLA-DR (< 2%). Moreover, stimulated WJ and BM-MSCs were characterized by increased cytoplasmic granulation, in comparison to unstimulated cells. The HLA-G isoforms (G1, G5, and G7) were successfully expressed by the unstimulated and stimulated WJ-MSCs. On the other hand, only weak expression of HLA-G1 was identified in BM-MSCs. Stimulated MSCs secreted high levels of IL-1Ra, IL-6, IL-10, IL-13, TGF-β1, FGF, VEGF, PDGF, and IDO in comparison to unstimulated cells (P < 0.05) after 12 and 24 h. Finally, macrophages derived from COVID-19 patients successfully adapted the M2 phenotype after co-culturing with stimulated WJ and BM-MSCs.

CONCLUSION

WJ and BM-MSCs successfully produced high levels of immunoregulatory agents, which may efficiently modulate the over-activated immune responses of critically ill COVID-19 patients.

Synchronization of HeLa Cells to Mitotic Subphases

The cell cycle is a series of events leading to cell replication. When plated at low cell densities in serum-containing medium, cultured cells start to proliferate, moving through the four phases of the cell cycle: G1, S, G2, and M. Mitosis is the most dynamic period of the cell cycle, involving a major reorganization of virtually all cell components. Mitosis is further divided into prophase, prometaphase, metaphase, anaphase, and telophase, which can be easily distinguished from one another by protein markers and/or comparing their chromosome morphology under fluorescence microscope. The progression of the cell cycle through these mitotic subphases is tightly regulated by complicated molecular mechanisms. Synchronization of cells to the mitotic subphases is important for understanding these molecular mechanisms. Here, we describe a protocol to synchronize Hela cells to prometaphase, metaphase, and anaphase/telophase. In this protocol, Hela cells are first synchronized to the early S phase by a double thymidine block. Following the release of the block, the cells are treated with nocodazole, MG132, and blebbistatin to arrest them at prometaphase, metaphase, and anaphase/telophase, respectively. Successful synchronization is assessed using Western blot and fluorescence microscopy.

Regulation of Cell Cycle Progression by Growth Factor-Induced Cell Signaling

The cell cycle is the series of events that take place in a cell, which drives it to divide and produce two new daughter cells. The typical cell cycle in eukaryotes is composed of the following phases: G1, S, G2, and M phase. Cell cycle progression is mediated by cyclin-dependent kinases (Cdks) and their regulatory cyclin subunits. However, the driving force of cell cycle progression is growth factor-initiated signaling pathways that control the activity of various Cdk–cyclin complexes. While the mechanism underlying the role of growth factor signaling in G1 phase of cell cycle progression has been largely revealed due to early extensive research, little is known regarding the function and mechanism of growth factor signaling in regulating other phases of the cell cycle, including S, G2, and M phase. In this review, we briefly discuss the process of cell cycle progression through various phases, and we focus on the role of signaling pathways activated by growth factors and their receptor (mostly receptor tyrosine kinases) in regulating cell cycle progression through various phases.

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.

Effect of quercetin on ovarian cells of pigs and cattle

The bioflavonoid quercetin is a component of food with numerous biological effects, but its function in reproductive processes and mechanisms in various species remain unclear. The aim of this study was to examine the effect of quercetin on ovarian cells isolated from ovaries of two phytophagous mammalian species (i.e. pigs and cattle). There was analysis of the effect of quercetin (0, 1, 10, and 100 ng/mL) on cultured granulosa cells of pigs and cattle. Proliferation (PCNA) and apoptosis (bax) markers and release of progesterone (P4), testosterone (T), estradiol (E2), and IGF-I were quantified using quantitative immunocytochemistry, enzyme immunoassay, or radioimmunoassay. Treatments with quercetin reduced PCNA and bax accumulation and decreased P4 release from both granulosa cells of pigs and cattle. In cells of pigs, treatment with quercetin reduced T output, however, in cells of cattle quercetin increased T release. In cells of pigs, quercetin reduced IGF-I release. In cells of cattle, quercetin at smaller doses (1 or 10 ng/mL), promoted and at a large dose (100 ng/mL) reduced IGF-I secretions. There was no substantial E2 release from granulosa cells of pigs or cattle. These observations are the first to indicate there is a direct action of quercetin on basic ovarian cell functions (proliferation, apoptosis, and hormones release) which can be species-specific.

Spirulina Crude Protein Promotes the Migration and Proliferation in IEC-6 Cells by Activating EGFR/MAPK Signaling Pathway

Spirulina is a type of filamentous blue-green microalgae known to be rich in nutrients and to have pharmacological effects, but the effect of spirulina on the small intestine epithelium is not well understood. Therefore, this study aims to investigate the proliferative effects of spirulina crude protein (SPCP) on a rat intestinal epithelial cells IEC-6 to elucidate the mechanisms underlying its effect. First, the results of wound-healing and cell viability assays demonstrated that SPCP promoted migration and proliferation in a dose-dependent manner. Subsequently, when the mechanisms of migration and proliferation promotion by SPCP were confirmed, we found that the epidermal growth factor receptor (EGFR) and mitogen-activated protein (MAPK) signaling pathways were activated by phosphorylation. Cell cycle progression from G0/G1 to S phase was also promoted by SPCP through upregulation of the expression levels of cyclins and cyclin-dependent kinases (Cdks), which regulate cell cycle progression to the S phase. Meanwhile, the expression of cyclin-dependent kinase inhibitors (CKIs), such as p21 and p27, decreased with SPCP. In conclusion, our results indicate that activation of EGFR and its downstream signaling pathway by SPCP treatment regulates cell cycle progression. Therefore, these results contribute to the research on the molecular mechanism for SPCP promoting the migration and proliferation of rat intestinal epithelial cells.

Two-Pulse Endosomal Stimulation of Receptor Tyrosine Kinases Induces Cell Proliferation

Signals transduced from ligand-activated receptor tyrosine kinases (RTKs) lead to a diverse array of biological outcomes, such as cell proliferation. Strict regulation of RTK activity is therefore necessary to prevent aberrancies in cell signaling that can lead to diseases such as cancer. RTKs are activated at the plasma membrane (PM) upon ligand binding. Contrary to the initial belief, RTK activity does not terminate immediately following endocytosis, instead RTKs remain active while being trafficked in endosomes. Here we describe a two-pulse endosomal stimulation approach which can specifically activate endosome-accumulated EGFR and drive cell proliferation.

The Double-Edged Sword Profile of Redox Signaling: Oxidative Events As Molecular Switches in the Balance between Cell Physiology and Cancer

The intracellular redox state in the cell depends on the balance between the level of reactive oxygen species (ROS) and the activity of defensive systems including antioxidant enzymes. This balance is a dynamic process that can change in relation to many factors and/or stimuli induced within the cell. ROS production is derived from physiological metabolic events. For instance, mitochondria represent the major ROS sources during oxidative phosphorylation, but other systems, such as NADPH oxidase or specific enzymes in certain metabolisms, may account for ROS production as well. Whereas high levels of ROS perturb the cell environment, causing oxidative damage to biological macromolecules, low levels of ROS can exert a functional role in the cell, influencing the activity of specific enzymes or modulating some intracellular signaling cascades. Of particular interest appears to be the role of ROS in tumor systems not only because ROS are known to be tumorigenic but also because tumor cells are able to modify their redox state, regulating ROS production to sustain tumor growth and proliferation. Overall, the scope of this review was to critically discuss the most recent findings pertaining to ROS physiological roles as well as to highlight the controversial involvement of ROS in tumor systems.

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.

Direct effect of glucocorticoids on glucose-activated adult rat β-cells increases their cell number and their functional mass for transplantation

Compounds that increase β-cell number can serve as β-cell replacement therapies in diabetes. In vitro studies have identified several agents that can activate DNA synthesis in primary β-cells but only in small percentages of cells and without demonstration of increases in cell number. We used whole well multiparameter imaging to first screen a library of 1,280 compounds for their ability to recruit adult rat β-cells into DNA synthesis and then assessed influences of stimulatory agents on the number of living cells. The four compounds with highest β-cell recruitment were glucocorticoid (GC) receptor ligands. The GC effect occurred in glucose-activated β-cells and was associated with increased glucose utilization and oxidation. Hydrocortisone and methylprednisolone almost doubled the number of β-cells in 2 wk. The expanded cell population provided an increased functional β-cell mass for transplantation in diabetic animals. These effects are age dependent; they did not occur in neonatal rat β-cells, where GC exposure suppressed basal replication and was cytotoxic. We concluded that GCs can induce the replication of adult rat β-cells through a direct action, with intercellular differences in responsiveness that have been related to differences in glucose activation and in age. These influences can explain variability in GC-induced activation of DNA synthesis in rat and human β-cells. Our study also demonstrated that β-cells can be expanded in vitro to increase the size of metabolically adequate grafts.

Antiphospholipid Antibodies in Patients with Cancer

Antiphospholipid antibodies are generally associated with Antiphospholipid Syndrome, which can occur as a primary disorder or may be secondary to connective tissue disease or tumour. The presence of antiphospholipid antibodies in patients with tumour disease is responsible for thrombotic complications. In a population of 53 tumor patients with positive carcinoembryonic antigen CEA, carbohydrate antigen CA19.9, CA125 and CA15.3 markers, IgM and IgG anticardiolipin and antiphosphatidylinositol were detected by solid-phase immunoassays. Our results show that moderate or high levels of antiphospholipid antibodies are present in a great number of patients with CEA and CA19.9 markers, suggesting a specific association with gastroenteric tumors. By testing for antiphosphatidylinositol antibodies, many patients not evidenced by the standard anticardiolipin assay were found to be antiphospholipid-positive. The analysis of antiphosphatidylinositol antibodies as a diagnostic tool in gastroenteric cancer to highlight patients with the risk of thromboembolic complications is discussed.

Unraveling Growth Factor Signaling and Cell Cycle Progression in Individual Fibroblasts

Cultured cells require the actions of growth factors to enter the cell cycle, but how individual members of a population respond to the same stimulus remains unknown. Here we have employed continuous monitoring by live cell imaging in a dual-reporter cell model to investigate the regulation of short-term growth factor signaling (protein kinase B (PKB/Akt) activity) and longer-term progression through the cell cycle (cyclin-dependent kinase 2 activity). In the total population, insulin-like growth factor-I (IGF-I)-enhanced cell cycle entry by >5-fold compared with serum-free medium (from 13.5 to 78%), but at the single cell level we observed a broad distribution in the timing of G1 exit (4-24 h, mean ∼12 h) that did not vary with either the amount or duration of IGF-I treatment. Cells that failed to re-enter the cell cycle exhibited similar responses to IGF-I in terms of integrated Akt activity and migration distance compared with those that did. We made similar observations with EGF, PDGF-AA, and PDGF-BB. As potential thresholds of growth factor-mediated cell cycle progression appeared to be heterogeneous within the population, the longer-term proliferative outcomes of individual cells to growth factor stimulation could not be predicted based solely on acute Akt signaling responses, no matter how robust these might be. Thus, although we could define a relationship at the population level between growth factor-induced Akt signaling dynamics and cell cycle progression, we could not predict the fate of individual cells.

Kv1.3 channels modulate human vascular smooth muscle cells proliferation independently of mTOR signaling pathway

Phenotypic modulation (PM) of vascular smooth muscle cells (VSMCs) is central to the process of intimal hyperplasia which constitutes a common pathological lesion in occlusive vascular diseases. Changes in the functional expression of Kv1.5 and Kv1.3 currents upon PM in mice VSMCs have been found to contribute to cell migration and proliferation. Using human VSMCs from vessels in which unwanted remodeling is a relevant clinical complication, we explored the contribution of the Kv1.5 to Kv1.3 switch to PM. Changes in the expression and the functional contribution of Kv1.3 and Kv1.5 channels were studied in contractile and proliferating VSMCs obtained from human donors. Both a Kv1.5 to Kv1.3 switch upon PM and an anti-proliferative effect of Kv1.3 blockers on PDGF-induced proliferation were observed in all vascular beds studied. When investigating the signaling pathways modulated by the blockade of Kv1.3 channels, we found that anti-proliferative effects of Kv1.3 blockers on human coronary artery VSMCs were occluded by selective inhibition of MEK/ERK and PLCγ signaling pathways, but were unaffected upon blockade of PI3K/mTOR pathway. The temporal course of the anti-proliferative effects of Kv1.3 blockers indicates that they have a role in the late signaling events essential for the mitogenic response to growth factors. These findings establish the involvement of Kv1.3 channels in the PM of human VSMCs. Moreover, as current therapies to prevent restenosis rely on mTOR blockers, our results provide the basis for the development of novel, more specific therapies.

L-arginine stimulates fibroblast proliferation through the GPRC6A-ERK1/2 and PI3K/Akt pathway

l-Arginine is considered a conditionally essential amino acid and has been shown to enhance wound healing. However, the molecular mechanisms through which arginine stimulates cutaneous wound repair remain unknown. Here, we evaluated the effects of arginine supplementation on fibroblast proliferation, which is a key process required for new tissue formation. We also sought to elucidate the signaling pathways involved in mediating the effects of arginine on fibroblasts by evaluation of extracellular signal-related kinase (ERK) 1/2 activation, which is important for cell growth, survival, and differentiation. Our data demonstrated that addition of 6 mM arginine significantly enhanced fibroblast proliferation, while arginine deprivation increased apoptosis, as observed by enhanced DNA fragmentation. In vitro kinase assays demonstrated that arginine supplementation activated ERK1/2, Akt, PKA and its downstream target, cAMP response element binding protein (CREB). Moreover, knockdown of GPRC6A using siRNA blocked fibroblast proliferation and decreased phosphorylation of ERK1/2, Akt and CREB. The present experiments demonstrated a critical role for the GPRC6A-ERK1/2 and PI3K/Akt signaling pathway in arginine-mediated fibroblast survival. Our findings provide novel mechanistic insights into the positive effects of arginine on wound healing.

The effects of low-dose nepsilon-(carboxymethyl)lysine (CML) and nepsilon-(carboxyethyl)lysine (CEL), two main glycation free adducts considered as potential uremic toxins, on endothelial progenitor cell function

Background

Patients with chronic kidney disease (CKD) are at high risk of cardiovascular disease (CVD). Endothelial progenitor cell (EPCs) dysfunction plays a key role in this pathogenesis. Uremic retention toxins have been reported to be in associated with EPC dysfunction. Advanced glycation end-products (AGEs) free adducts, including Nepsilon-(carboxymethyl)lysine (CML) and Nepsilon-(carboxyethyl)lysine (CEL), are formed by physiological proteolysis of AGEs and released into plasma for urinary excretion. They are retained in CKD patients and are considered to be potential uremic toxins. Though AGEs have been demonstrated to impair EPC function in various ways, the effect of AGE free adducts on EPC function has not been studied. Thus, we examined the role of CML and CEL in the regulation of growth-factor-dependent function in cultured human EPCs and the mechanisms by which they may affect EPC function.

Methods

Late outgrowth EPCs were incubated with different concentrations of CML or CEL for up to 72 hours. Cell proliferation was determined using WST-1 and BrdU assays. Cell apoptosis was tested with annexin V staining. Migration and tube formation assays were used to evaluate EPC function.

Results

Though CML and CEL were determined to have anti-proliferative effects on EPCs, cells treated with concentrations of CML and CEL in the range found in CKD patients had no observable impairment on migration or tube formation. CML and CEL did not induce EPC apoptosis. The reduced growth response was accompanied by significantly less phosphorylation of mitogen-activated protein kinases (MAPKs).

Conclusions

Our study revealed that CML and CEL at uremic concentrations have low biological toxicity when separately tested. The biologic effects of AGE free adducts on the cardiovascular system merit further study.

Regulation of epidermal growth factor receptor signalling by inducible feedback inhibitors

Signalling by the epidermal growth factor receptor (EGFR) controls morphogenesis and/or homeostasis of several tissues from worms to mammals. The correct execution of these programmes requires the generation of EGFR signals of appropriate strength and duration. This is obtained through a complex circuitry of positive and negative feedback regulation. Feedback inhibitory mechanisms restrain EGFR activity in time and space, which is key to ensuring that receptor outputs are commensurate to the cell and tissue needs. Here, we focus on the emerging field of inducible negative feedback regulation of the EGFR in mammals. In mammalian cells, four EGFR inducible feedback inhibitors (IFIs), namely LRIG1, RALT (also known as MIG6 and ERRFI1), SOCS4 and SOCS5, have been discovered recently. EGFR IFIs are expressed de novo in the context of early or delayed transcriptional responses triggered by EGFR activation. They all bind to the EGFR and suppress receptor signalling through several mechanisms, including catalytic inhibition and receptor downregulation. Here, we review the mechanistic basis of IFI signalling and rationalise the function of IFIs in light of gene-knockout studies that assign LRIG1 and RALT an essential role in restricting cell proliferation. Finally, we discuss how IFIs might participate in system control of EGFR signalling and highlight the emerging roles for IFIs in the suppression of EGFR-driven tumorigenesis.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Identification of microRNAs controlling human ovarian cell proliferation and apoptosis

Previous studies have shown that microRNAs (miRNAs) can control steroidogenesis in cultured granulosa cells. In this study we wanted to determine if miRNAs can also affect proliferation and apoptosis in human ovarian cells. The effect of transfection of cultured primary ovarian granulosa cells with 80 different constructs encoding human pre-miRNAs on the expression of the proliferation marker, PCNA, and the apoptosis marker, Bax was evaluated by immunocytochemistry. Eleven out of 80 tested miRNA constructs resulted in stimulation, and 53 miRNAs inhibited expression of PCNA. Furthermore, 11 of the 80 miRNAs tested promoted accumulation of Bax, while 46 miRNAs caused a reduction in Bax in human ovarian cells. In addition, two selected antisense constructs that block the corresponding miRNAs mir-15a and mir-188 were evaluated for their effects on expression of PCNA. An antisense construct inhibiting mir-15a (which precursor suppressed PCNA) increased PCNA, whereas an antisense construct for mir-188 (which precursor did not change PCNA) did not affect PCNA expression. Verification of effects of selected pre-mir-10a, mir-105, and mir-182 by using other markers of proliferation (cyclin B1) and apoptosis (TdT and caspase 3) confirmed specificity of miRNAs effects on these processes. This is the first direct demonstration of the involvement of miRNAs in controlling both proliferation and apoptosis by ovarian granulose cells, as well as the identification of miRNAs promoting and suppressing these processes utilizing a genome-wide miRNA screen.

ICBP90 mediates the ERK1/2 signaling to regulate the proliferation of Jurkat T cells

ERK1/2 activation leads to the release of E2F that could bind to the E2F binding sites in the inverted CCAAT box binding protein (ICBP90) gene promoter. Therefore, in the present study the relationship between ERK1/2 signaling and ICBP90 in the regulation of Jurkat T cell proliferation was explored. Jurkat T cells were treated with different concentrations of various signal pathway inhibitors. The cell viability and cell cycle were determined. Furthermore, the expression of non-phosphorylated and phosphorylated ERK1/2, and ICBP90 was measured by Western blot analysis. All the inhibitors, including PD98059, LY294002, AG490, genistein and GF109203X, suppressed the cell colony formation and proliferation to different extent in a dose-dependent manner. PD98059 could suppress the cell proliferation remarkably, arrested the cell cycle at G1/G0 stage and blocked its entrance from S phase to G2/M phase. Three or 24h after exposure to the inhibitors, all the inhibitors downregulated the level of the phosphorylated ERK1/2, of which the inhibitory roles of PD98059, LY294002 and AG490 were more significant. All the inhibitors had no effect on the expression of ICBP90 after 3h treatment, but downregulated markedly its expression after 24h treatment, especially PD98059, LY294002 and AG490. The expression of ICBP90 was directly proportioned to the level of ERK1/2 phosphorylation and the cell proliferation. Our results demonstrate that ICBP90 might be a pivotal target for the ERK1/2 signaling pathway to control the proliferation of Jurkat T cells.

The effect of obestatin on porcine ovarian granulosa cells

The aim of our in vitro experiments was to investigate the role of obestatin, a newly discovered metabolic hormone produced in the stomach and other tissues, in the direct control of ovarian cell proliferation, apoptosis and secretion. Porcine granulosa cells were cultured in the presence of obestatin (0, 1, 10 and 100ng/ml medium). The expression of intracellular peptides associated with proliferation (PCNA, cyclin B1, MAP kinase), as well as markers of apoptosis (Bax, p53, Caspase 3), were detected using immunocytochemistry and Western immunoblotting. Secretion of progesterone (P4), testosterone (T) and estradiol (E2) was measured by EIA. Addition of obestatin (1-100ng/ml) to the culture medium significantly stimulated the expression of PCNA and resulted in an increase in expression of cyclin B1 and MAPK. It also significantly increased the percentage of cells containing the apoptotic and anti-proliferating peptides p53, Caspase 3 and Bax. At 10 and 100ng/ml, obestatin promoted the secretion of P4, but not T or E2. Our results are the first demonstration that obestatin directly controls porcine ovarian cell functions: it can stimulate proliferation (accumulation of rPCNA, cyclin B1 and MAPK), apoptosis (expression of p53, Caspase 3 and Bax) and the secretion of progesterone.

Poly(ADP-ribosyl)ation is implicated in the G0-G1 transition of resting cells

Poly(ADP-ribosyl)ation, catalysed by a family of poly(ADP-ribose) polymerases (PARPs), plays an important role in a large variety of physiological processes, including cell proliferation, but its role in cell cycle progression is not yet completely defined. As reported here, the examination of early times following serum stimulation of quiescent fibroblasts suggests that poly(ADP-ribosyl)ation is necessary for the transition from the G0 phase to the G1 phase. We show that PARP activity is involved in this step through the regulation of immediate-early response genes, such as c-Fos and c-Myc. This is supported by the finding that exogenous Myc expression substantially restores cell cycle reactivation in the absence of polymer synthesis. Furthermore, using RNA interference, we show that PARP-1 is the PARP family member playing the most prominent role in the upregulation of c-Fos and c-Myc during G0-G1 transition. We report that even in lectin-stimulated peripheral blood mononucleated cells, the inhibition of PARP activity interferes with the upregulation of immediate-early genes and delays the induction of proliferation, suggesting a general role for PARP-1 in linking growth factor signaling with cell cycle entry.

The ERK-RSK1 activation by growth factors at G2 phase delays cell cycle progression and reduces mitotic aberrations

Growth factors accelerate G0 to S progression in the cell cycle, however, the roles of growth factors in other cell cycle phases are largely unknown. Here, we show that treatment of HeLa cells with hepatocyte growth factor (HGF) at G2 phase induced the G2/M transition delay as evidenced by FACS analysis as well as by mitotic index and time-lapse analyses. Growth factors such as epidermal growth factor (EGF) and fibroblast growth factor (FGF) also induced G2/M transition delay like HGF. HGF treatment at G2 phase causes a delayed activation of cyclin B1-associated kinase and a diminished nuclear translocation of cyclin B1. Either U0126, a MAPK kinase (MEK) inhibitor, or kinase-dead mutant of ribosomal S6 kinase (RSK) abolished the delay. Additionally, knockdown of RSK1, but not RSK2, with siRNA abrogated the delay, indicating that the extracellular-regulated protein kinase (ERK)-RSK1 mediates the HGF-induced delay. We further found that the delay in G2/M transition of cells expressing oncogenic HGF receptor, M1268T, was abolished by RSK1 knockdown. Intriguingly, we observed that HGF induced chromosomal segregation defects, and depletion of RSK1, but not RSK2, aggravated these chromosomal aberrations. Taken together, the ERK-RSK1 activation by growth factors delays G2/M transition and this might be required to maintain genomic integrity during growth factor stimulation.

Effects of ghrelin and its analogues on chicken ovarian granulosa cells

The aim of these in vitro experiments was (1) to examine the effects of ghrelin on the basic functions of ovarian cells (proliferation, apoptosis, secretory activity); (2) to determine the possible involvement of the GHS-R1a receptor and PKA- and MAPK-dependent post-receptor intracellular signalling cascades; (3) to identify the active part of the 28-amino acid molecule responsible for the effects of ghrelin on ovarian cells. We compared the effect of full-length ghrelin 1-28, a synthetic activator of GHS-R1a, GHRP6, and ghrelin molecular fragments 1-18 and 1-5 on cultured chicken ovarian cells. Indices of cell apoptosis (expression of the apoptotic peptide bax and the anti-apoptotic peptide bcl-2), proliferation (expression of proliferation-associated peptide PCNA), and expression of protein kinases (PKA and MAPK) within ovarian granulosa cells were analysed by immunocytochemistry. The secretion of progesterone (P(4)), testosterone (T), estradiol (E(2)) and arginine-vasotocin (AVT) by isolated ovarian follicular fragments was evaluated by RIA/EIA. It was observed that accumulation of bax was increased by ghrelin 1-28, GHRP6 and ghrelin 1-18, but not by ghrelin 1-5. Expression of bcl-2 was suppressed by addition of ghrelin 1-28, GHRP6 and ghrelin 1-5, but promoted by ghrelin 1-18. The occurrence of PCNA was reduced by ghrelin 1-28, GHRP6, ghrelin 1-18 and ghrelin 1-5. An increase in the expression of MAPK/ERK1, 2 was observed after addition of ghrelin 1-28, GHRP6 and ghrelin 1-18, but not ghrelin 1-5. The accumulation of PKA decreased after treatment with ghrelin 1-28 and increased after treatment with GHRP6 and ghrelin 1-18 but not ghrelin 1-5. Secretion of P(4) by ovarian follicular fragments was decreased after addition of ghrelin 1-28 or ghrelin 1-5 but stimulated by GHRP6 and ghrelin 1-18. Testosterone secretion was inhibited by ghrelins 1-28 and 1-18, but not by GHRP6 or ghrelin 1-5. Estradiol secretion was reduced after treatment with ghrelin 1-28 but stimulated by ghrelins 1-18 and 1-5; GHRP6 had no effect. AVT secretion was stimulated by ghrelin 1-28, GHRP6 and ghrelin 1-18, but inhibited by ghrelin 1-5. The comparison of the effects of the four ghrelin analogues on nine parameters of ovarian cells suggest (1) a direct effect of ghrelin on basic ovarian functions-apoptosis, proliferation, steroid and peptide hormone secretion; (2) that the majority of these effects can be mediated through GHS-R1a receptors; (3) an effect of ghrelin on MAPK- and PKA-dependent intracellular mechanisms, which can potentially mediate the action of ghrelin at the post-receptor level; (4) that ghrelin residues 5-18 may be responsible for the major effects of ghrelin on the avian ovary.

The increase in retinal cells proliferation induced by FGF2 is mediated by tyrosine and PI3 kinases

Since 1973, multiple effects of basic fibroblast growth factor have been described in a large number of cells. These effects include proliferation, survival and differentiation. The aim of this work was to study the intracellular pathways involved in the basic fibroblast growth factor (FGF2) effect on rat retinal cells proliferation in vitro. Our data show that treatment with FGF2 increases proliferation in a concentration- and time-dependent manner. The effect of 25 ng/ml FGF2 was blocked by 10 microM genistein, a tyrosine kinase inhibitor and by 25 microM LY294002, a PI3 kinase inhibitor. The concomitant treatment with 0.3 microM chelerythrine chloride, a protein kinase C inhibitor, and 6.25 microM LY294002 also inhibited the effect of FGF2. Our results suggest that the proliferative effect of FGF2 on retinal cell cultures involves the activation of distinct kinases.

Leptin directly controls proliferation, apoptosis and secretory activity of cultured chicken ovarian cells

The aim of our in-vitro experiments was to examine, whether leptin can directly control functions of avian ovarian cells and to outline potential intracellular mediators of its effects. Granulosa cells or fragments of ovarian follicular wall were cultured with leptin (0, 1, 10 or 100 ng/mL medium). The expression of peptides involved in apoptosis (TdT, bax, its binding protein, bcl-2, ASK-1 and p53), cell cycle-related peptides (PCNA and cyclin B1), release of hormones (progesterone, testosterone, estradiol, arginine-vasotocin), as well as the expression of protein kinases (PKA, MAPK/ERK1,2 and CDK/p34) in the ovarian cells were examined by using immunocytochemistry, TUNEL, SDS-PAGE-Western immunoblotting, EIA and RIA. It was found that leptin inhibited expression of all markers of cytoplasmic apoptosis (bax, ASK-1 and p53), stimulated expression of anti-apoptotic peptide bcl-2, but did not affect nuclear DNA fragmentation (TdT). Furthermore, leptin inhibited expression of PCNA (marker of S-phase of mitosis), but not of cyclin B1 (marker of G phase of cell cycle). Moreover, it promoted release of progesterone and estradiol, suppressed release of testosterone, but did not affect arginine-vasotocin. Finally, leptin inhibited expression of MAPK/ERK1,2 and CDK/p34 and stimulated expression of PKA. The present observations demonstrate that leptin can directly control basic chicken ovarian functions - inhibit cytoplasmic apoptosis and proliferation (S-phase, but not G-phases of mitosis), regulate secretory activity (release of steroids, but not nonapeptide hormone) and expression of MAPK, PKA and CDC2, which might be potential intracellular mediators of leptin action.

Hepatocyte growth factor at S phase induces G2 delay through sustained ERK activation

The effect of growth factors on the cell cycle progression, except G1/S transition, is poorly understood. Herein, we examined the effect of hepatocyte growth factor (HGF) treated at S phase on the cell cycle progression of HeLa cells. Interestingly, the treatment resulted in G2 delay, evidenced by flow cytometric and mitotic index analyses. The delay corresponded with the delay of degradation of cyclin A and cyclin B, and the delay of decrease of Cdk1/cyclin B and Cdk2/cyclin A kinase activities. As for the signaling responsible, sustained activation of ERK, but neither of p38MAPK nor of JNK, was observed after HGF treatment at S phase. Furthermore, U0126, an inhibitor of MEK1, and DN-MEK partially abrogated the G2 delay, indicating that activation of MEK-ERK pathway is involved. Taken together, HGF treatment of HeLa cells at S phase induces G2 delay partially through sustained activation of ERK signaling.

Two waves of the nuclear phospholipase C activity in serum-stimulated HL-60 cells during G(1) phase of the cell cycle

Phosphatidylinositol-specific phospholipase C (PI-PLC) is activated in cell nuclei during the cell cycle progression. We have previously demonstrated two peaks of an increase in the nuclear PI-PLC activities in nocodazole-synchronized HL-60 cells. In this study, the activity of nuclear PI-PLC was investigated in serum-stimulated HL-60 cells. In serum-starved HL-60 cells, two peaks of the activity of nuclear PI-PLC were detected at 30 min and 11 h after the re-addition of serum with no parallel increase in PLC activity in cytosol, postnuclear membranes or total cell lysates. An increase in the serine phosphorylation of b splicing variant of PI-PLCbeta(1) was detected with no change in the amount of PI-PLCbeta(1b) in nuclei isolated at 30 min and 11 h after the addition of serum. PI-PLC inhibitor ET-18-OCH(3) and MEK inhibitor PD 98059 completely abolished serum-mediated increase at both time-points. The addition of inhibitors either immediately or 6 h after the addition of serum had inhibitory effects on the number of cells entering S phase. These results demonstrate that two waves of nuclear PI-PLCbeta(1b) activity occur in serum-stimulated cells during G(1) phase of the cell cycle and that the later increase in the PLC activity is equally important for the progression into the S phase.

The role of ghrelin and some intracellular mechanisms in controlling the secretory activity of chicken ovarian cells

The general aim of these in-vitro experiments was to determine whether ghrelin controls the secretory activity of chicken ovarian cells and whether its action is mediated by TK-, MAPK-, CDK- or PKA-dependent intracellular mechanisms. We postulated that particular protein kinases could be considered as mediators of ghrelin action (a) if they are controlled by ghrelin, and (b) if blockers of these kinases modify the action of ghrelin. In our in-vitro experiments we investigated whether ghrelin altered the accumulation of TK, MAPK, CDK and PKA in chicken ovarian cells and whether ghrelin, with or without blockers of MAPK, CDK and PKA, affected the secretion of progesterone (P4), testosterone (T), estradiol (E2) or arginine-vasotocin (AVT). In the first series of experiments, the influence of a ghrelin 1-18 analogue (1, 10 or 100 ng/mL) was studied on the expression of TK, MAPK and PKA in cultured chicken ovarian granulosa cells. The percentage of cells containing TK/phosphotyrosine MAPK/ERK1, 2 and PKA was determined using immunocytochemistry. Ghrelin increased the expression of both TK and MAPK. The low concentration of ghrelin (1 ng/mL) increased the accumulation of PKA in ovarian cells whilst the high concentration (100 ng/mL) decreased it. The 10 ng/mL concentration had no effect. In the second series of experiments, the effects of the ghrelin analogue combined with an MAPK blocker (PD98059; 100 ng/mL), a CDK blocker (olomoucine; 1 microg/mL), or a PKA blocker (KT5720; 100 ng/mL), were tested for their effects on the secretion of hormones by cultured fragments of chicken ovarian follicular wall. P4, T, E2 and AVT secretions were measured using RIA and EIA. Ghrelin increased T and decreased E2, but did not affect P4 or AVT secretion. The PKA blocker promoted P4 secretion and suppressed E2 and AVT, but did not affect T secretion. It prevented or even reversed the effect of ghrelin on T and E2, but did not modify its effect on AVT secretion. The MAPK blocker enhanced P4 and T and reduced AVT, but did not affect E2 secretion. It was able to prevent or reverse the effect of ghrelin on T and E, and it induced a stimulatory effect of ghrelin on AVT secretion. The CDK blocker reduced the secretion of AVT, but had no effect on steroid hormone secretion. It induced the stimulatory influence of ghrelin on the secretion of P4 and AVT, but did not modify the effect of ghrelin on other hormones. These observations clearly demonstrate that ghrelin is a potent regulator of the secretory activity of ovarian cells and of TK, MAPK and PKA. Furthermore, they suggest that MAPK-, CDK- and PKA-dependent intracellular mechanisms are involved in the control of ovarian secretion and that they mediate the effects of ghrelin on these processes.

La(3+)-induced extracellular signal-regulated kinase (ERK) signaling via a metal-sensing mechanism linking proliferation and apoptosis in NIH 3T3 cells

The effects of La(3+) on the extracellular signal-regulated kinase (ERK) signaling were investigated to explore the mechanism by which La(3+) results in cell proliferation associated with apoptosis in mouse embryo fibroblast NIH 3T3 cells. Our data showed that La(3+) ions could induce a pulse of phosphorylation of ERK mainly through an unknown metal-sensing mechanism, which is different from the Ca(2+)-sensing receptor . The putative sensor protein showed one binding site for La(3+) with a dissociation constant of approximately 8 nM. Inductions of c-fos, c-myc, and cyclin D1 and phosphorylation of retinoblastoma protein (pRb) were observed after activation of ERK. These results are consistent with our previous observation that La(3+) promotes proliferation by helping the cells pass through the G1/S restriction point and enter S phase. This La(3+)-induced signaling cascade exhibited abnormally sustained c-myc induction and pRb phosphorylation. Furthermore, a continual increase of the p53 level was observed along with the signal transduction, and a significant decrease of B-cell lymphoma/leukemia-2 gene was observed after approximately 18 h of incubation. All of the results were highly correlated with the increase of S-phase population and apoptotic cells. Therefore, the experimental results suggested that La(3+) induced cell proliferation and apoptosis compatible to a p53-related mechanism in NIH 3T3 cells via an ERK-signaling cascade induced by a metal-sensing mechanism.

Novel expression and functional role of ghrelin in chicken ovary

Ghrelin has recently emerged as pleiotropic regulator of a wide array of endocrine and non-endocrine functions. The former likely includes the control of gonadal function, as expression of ghrelin and its putative receptor, the GH secretagogue receptor type 1a (GHS-R1a), has been described in mammalian gonads, and direct effects of ghrelin in the control of testicular secretion and cell proliferation have been reported. Yet, the expression and/or functional role of ghrelin in gonads from non-mammalian species remain to be analyzed. The present study aimed to evaluate the expression of ghrelin and GHS-R genes in the chicken ovary, and to assess the potential involvement of ghrelin in the direct control of chick ovarian function. To this end, RT-PCR assays for ghrelin and GHS-R1a mRNAs were performed in ovarian tissue, and cultures of chicken ovarian cells were conducted in the presence of increasing doses (1, 10 or 100 ng/ml) of the ghrelin analog, ghrelin 1-18. Our results demonstrate that both ghrelin and GHS-R1a mRNAs are expressed in chick ovarian tissue. Moreover, challenge of ovarian granulosa cells with ghrelin 1-18 was able to induce markers of proliferation (i.e. expression of both PCNA and cyclin), and to modulate markers of apoptosis (i.e. decreased expression of caspase-3, bax, bcl-2 and TUNEL-positive cells). Moreover, ghrelin 1-18 increased the expression of PCNA, cyclin, bax and p53 in cultures of ovarian follicular fragments, where it also stimulated the release of progesterone, estradiol, arginine-vasotocin (AVT) and IGF-I, but not of testosterone. In conclusion, our study provides novel evidence for the gonadal expression of the genes encoding ghrelin and its cognate receptor in a non-mammalian species, i.e. the chicken ovary, and unravels the potential involvement of this newly discovered molecule in the control of key gonadal functions in the chick, such as proliferation, apoptosis, and hormone release.

A positive feedback loop couples Ras activation and CD44 alternative splicing

The Ras signaling pathway is important in both cell proliferation and tumor progression. Alternatively spliced isoforms of CD44 containing variable exon 6 (v6) can serve as coreceptors for growth factor receptors that activate Ras. Here we use v6-specific small interfering RNA (siRNA) to investigate the role of CD44 alternative splicing in Ras signaling. We identify a positive feedback loop in which Ras signaling promotes CD44v6 splicing, and CD44v6 then sustains late Ras signaling, which is important for cell cycle progression. These results are the first demonstration of a positive feedback loop linking signaling-dependent alternative splicing to mitogenic progression.

Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

PKC-delta is a serine/threonine kinase that mediates diverse signal transduction pathways. We previously demonstrated that overexpression of PKC-delta slowed the G1 progression of Caco-2 colon cancer cells, accelerated apoptosis, and induced cellular differentiation. In this study, we further characterized the PKC-delta dependent signaling pathways involved in these tumor suppressor actions in Caco-2 cells overexpressing PKC-delta using a Zn2+ inducible expression vector. Consistent with a G1 arrest, increased expression of PKC-delta caused rapid and significant downregulation of cyclin D1 and cyclin E proteins (50% decreases, P<0.05), while mRNA levels remained unchanged. The PKC agonist, phorbol 12-myristate 13-acetate (TPA, 100 nM, 4 h), induced two-fold higher protein and mRNA levels of p21(Waf1), a cyclin-dependent kinase (cdk) inhibitor in PKC-delta transfectants compared with empty vector (EV) transfected cells, whereas the PKC-delta specific inhibitor rottlerin (3 microM) or knockdown of this isoenzyme with specific siRNA oligonucleotides blocked p21(Waf1) expression. Concomitantly, compared to EV control cells, PKC-delta upregulation decreased cyclin D1 and cyclin E proteins co-immunoprecipitating with cdk6 and cdk2, respectively. In addition, overexpression of PKC-delta increased binding of cdk inhibitor p27(Kip1) to cdk4. These alterations in cyclin-cdks and their inhibitors are predicted to decrease G1 cyclin kinase activity. As an independent confirmation of the direct role PKC-delta plays in cell growth and cell cycle regulation, we knocked down PKC-delta using specific siRNA oligonucleotides. PKC-delta specific siRNA oligonucleotides, but not irrelevant control oligonucleotides, inhibited PKC-delta protein by more than 80% in Caco-2 cells. Moreover, PKC-delta knockdown enhanced cell proliferation ( approximately 1.4-2-fold, P<0.05) and concomitantly increased cyclin D1 and cyclin E expression ( approximately 1.7-fold, P<0.05). This was a specific effect, as nontargeted PKC-zeta was not changed by PKC-delta siRNA oligonucleotides. Consistent with accelerated apoptosis in PKC-delta transfectants, compared to EV cells, PKC-delta upregulation increased proapoptotic regulator Bax two-fold at mRNA and protein levels, while antiapoptotic Bcl-2 protein was decreased by 50% at a post-transcriptional level. PKC-delta specific siRNA oligonucleotides inhibited Bax protein expression by more than 50%, indicating that PKC-delta regulates apoptosis through Bax. Taken together, these results elucidate two critical mechanisms regulated by PKC-delta that inhibit cell cycle progression and enhance apoptosis in colon cancer cells. We postulate these antiproliferative pathways mediate an important tumor suppressor function for PKC-delta in colonic carcinogenesis.

Structure-activity studies on a library of potent calix[4]arene-based PDGF antagonists that inhibit PDGF-stimulated PDGFR tyrosine phosphorylation

Platelet-derived growth factor (PDGF) and its receptor PDGFR are required for tumor growth and angiogenesis, so disruption of the PDGF-PDGFR interaction should lead to starvation of tumors and reduction of tumor growth. Potent PDGF antagonists have been discovered through the synthesis of a series of calix[4]arene-based compounds that are designed to bind to the three-loop region of PDGF. The effect of lower-rim alkylation, linker and number of interacting head groups on the calix[4]arene scaffold on PDGF affinity and cellular activity has been investigated.

Antibody-bound amyloid precursor protein upregulates ornithine decarboxylase expression

Alzheimer's disease is a neurodegenerative disorder characterised by extracellular accumulation of the Abeta peptide, derived from the amyloid precursor protein (APP). The function of APP as a cell surface receptor was examined by ligand-mimicking using an antibody against the APP extracellular domain. Alterations in gene expression evoked by antibody-bound APP were analysed using human pathway-finder gene arrays and the largest change in expression levels was found for ornithine decarboxylase (ODC). These results were confirmed by Western blotting which showed even higher upregulation on the protein level. APP knockdown by RNAi verified that upregulation of ODC was APP-mediated. This APP signalling event did not require gamma-secretase cleavage, as it was independent of the presence of presenilin-1 or -2. The induced ODC expression was rapid and biphasic, resembling growth-factor stimulated signalling events. This study shows that antibody-bound APP leads to altered gene expression that may be relevant to AD.

Effects of imatinib and interferon on primitive chronic myeloid leukaemia progenitors

Imatinib has impressive activity against chronic myeloid leukaemia (CML), but does not appear to completely eradicate the disease. Although responses to interferon-alpha (IFN) are slower and less dramatic than those to imatinib, they can be durable even after discontinuation of the drug. Unlike imatinib, the specific mechanisms responsible for IFN's clinical activity in CML are unknown. We found that IFN induced a G1 cell cycle arrest, as well as terminal differentiation, of the CML cell line KT-1 and CML CD34+ cells from clinical specimens. Myeloid growth factors augmented the antileukaemic activity of IFN, and neutralising antibodies directed against myeloid growth factors inhibited IFN's antileukaemic activity. We next directly compared the effects of imatinib and IFN against differentiated and primitive CML progenitors from newly-diagnosed patients. Although less active against CML granulocyte-macrophage colony forming units than imatinib, IFN was significantly more toxic to primitive CML progenitors responsible for the maintenance of long-term cultures. Imatinib and IFN appear to have divergent effects on CML progenitors at different stages of maturation, with imatinib more active against differentiated CML progenitors and IFN more active against primitive CML progenitors. The different target cells for these agents may explain the disparities in the kinetics and durability of their clinical responses. At least part of the clinical effect of IFN in CML appears to result from its ability to differentiate primitive CML progenitors.

The role of protein kinase A and cyclin-dependent (CDC2) kinase in the control of basal and IGF-II-induced proliferation and secretory activity of chicken ovarian cells

The aim of these experiments was to study the role of protein kinase A (PKA), cyclin-dependent kinase 2 (CDC2) and insulin-like growth factor II (IGF-II) in the control of ovarian function in domestic fowl, as well as the role of PKA and CDC2 in mediating the effects of IGF-II on the ovary. For this purpose, we studied the influence of an inhibitor of PKA (KT5720; 50 ng/ml), a CDC2 blocker (olomoucine; 1 microg/ml), IGF-II (0, 1, 10 or 100 ng/ml) and their combinations on cultured fragments of chicken ovarian follicular wall. Accumulation of PKA and CDC2 and secretion of progesterone (P4), testosterone (T), estradiol (E2) and arginine-vasotocin (AVT) were evaluated by using SDS-PAGE-Western blotting and RIA/EIA. IGF-II addition to culture medium stimulated T, E2 and AVT secretion and inhibited P4 secretion. These changes were associated with an increase in PKA and a decrease in CDC2 accumulation. The PKA blocker KT5720, when given alone, increased accumulation of PKA and secretion of T and E2, but not AVT and inhibited P4 secretion. The PKA blocker also prevented and even reversed the effects of IGF-II on PKA and steroid hormones secretion, but enhanced the action of IGF-II on AVT. The inhibitor of CDC2, olomoucine, when given alone, suppressed the expression of CDC2 and the secretion of P4 and AVT (but not T and E2). When given together with IGF-II, it augmented IGF-II-induced suppression of CDC2 and reversed the effects of IGF-II on P4 (but not on T, E2 or AVT). These observations demonstrate the involvement of PKA, CDC2 and IGF-II in regulating the secretory activity of avian ovarian cells. Our data also suggest the involvement of PKA in the mediation of IGF-II effects on P4, T, E2 and AVT secretion. CDC2 can mediate the effects of IGF-II on ovarian P4 secretion but not on other hormones.