A reversible arrest point in the late G1 phase of the mammalian cell cycle

Potential immunomodulatory response associated with L-mimosine in male Wistar rats

Leucaena leucocephala is a plant that is used as animal and human food worldwide. This plant contains the toxic compound namely L-mimosine. The main mechanism of action of this compound involves its ability to chelate metal ions, which may interfere with the proliferative activity of cells and being studied for the treatment of cancer. However, little is known about the effect of L-mimosine on immune responses. Thus, the aim of this study was to evaluate the effects of L-mimosine on immune responses in Wistar rats. Different doses of L-mimosine (25, 40 and 60 mg/kg body weight/day) were administered orally by gavage to adult rats for 28 days. No clinical signs of toxicity were observed in animals, but a decrease in the T-dependent response to sheep red blood cells (SRBC) in animals treated with 60 mg/kg L-mimosine and an increase in the intensity of S. aureus phagocytosis by macrophages in animals treated with 40 or 60 mg/kg L-mimosine were observed. Therefore, these findings suggest that L-mimosine did not compromise macrophage activity and inhibited T-dependent clonal expansion during the immune response.

Influence of the Nonprotein Amino Acid Mimosine in Peptide Conformational Propensities from Novel Amber Force Field Parameters

Mimosine is a nonprotein amino acid derived from plants known for its ability to bind to divalent and trivalent metal cations such as Zn²⁺, Ni²⁺, Fe²⁺, or Al³⁺. This results in interesting antimicrobial and anticancer properties, which make mimosine a promising candidate for therapeutic applications. One possibility is to incorporate mimosine into synthetic short peptide drugs. However, how this amino acid affects the peptide structure is not well understood, reducing our ability to design effective therapeutic compounds. In this work, we used computer simulations to understand this question. We first built parameters for the mimosine residue to be used in combination with two classical force fields of the Amber family. Then, we used atomistic molecular dynamics simulations with the resulting parameter sets to evaluate the influence of mimosine in the structural propensities for this amino acid. We compared the results of these simulations with homologous peptides, where mimosine is replaced by either phenylalanine or tyrosine. We found that the strong dipole in mimosine induces a preference for conformations where the amino acid rings are stacked over more extended conformations. We validated our results using quantum mechanical calculations, which provide a robust foundation for the outcome of our classical simulations.

Biochemistry of plants N-heterocyclic non-protein amino acids

Plants catalyze the biosynthesis of a large number of non-protein amino acids, which are usually toxic for other organisms. In this review, the chemistry and metabolism of N-heterocyclic non-protein amino acids from plants are described. These N-heterocyclic non-protein amino acids are composed of β-substituted alanines and include mimosine, β-pyrazol-1-yl-L-alanine, willardiine, isowillardiine, and lathyrine. These β-substituted alanines consisted of an N-heterocyclic moiety and an alanyl side chain. This review explains how these individual moieties are derived from their precursors and how they are used as the substrate for biosynthesizing the respective N-heterocyclic non-protein amino acids. In addition, known catabolism and possible role of these non-protein amino acids in the actual host is explained.

Epithelial tissue geometry directs emergence of bioelectric field and pattern of proliferation

Patterns of proliferation are templated by both gradients of mechanical stress as well as by gradients in membrane voltage (Vm), which is defined as the electric potential difference between the cytoplasm and the extracellular medium. Either gradient could regulate the emergence of the other, or they could arise independently and synergistically affect proliferation within a tissue. Here, we examined the relationship between endogenous patterns of mechanical stress and the generation of bioelectric gradients in mammary epithelial tissues. We observed that the mechanical stress gradients in the tissues presaged gradients in both proliferation and depolarization, consistent with previous reports correlating depolarization with proliferation. Furthermore, disrupting the Vm gradient blocked the emergence of patterned proliferation. We found that the bioelectric gradient formed downstream of mechanical stresses within the tissues and depended on connexin-43 (Cx43) hemichannels, which opened preferentially in cells located in regions of high mechanical stress. Activation of Cx43 hemichannels was necessary for nuclear localization of Yap/Taz and induction of proliferation. Together, these results suggest that mechanotransduction triggers the formation of bioelectric gradients across a tissue, which are further translated into transcriptional changes that template patterns of growth.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents

Mimosine is a non-protein amino acid that can be used as a building block in peptides with metal coordination ability.

Molecular characterization of mimosinase and cystathionine β-lyase in the Mimosoideae subfamily member Mimosa pudica

Mimosinase degrades the non-protein amino acid mimosine and is thought to have evolved from cystathionine β-lyase (CBL) via gene duplication. However, no study has, to date, compared the molecular characteristics of mimosinase and CBL. We therefore cloned mimosinase and CBL from the Mimosoideae subfamily member Mimosa pudica (Mp) and explored the molecular relationship between mimosinase and CBL for the first time. The recombinant Mp mimosinase degraded both mimosine and cystathionine with a much higher turnover number (k_cat) for mimosine compared with cystathionine, and Mp CBL utilized only cystathionine as a substrate. The critical residues implicated in the substrate binding of Arabidopsis thaliana CBL (Tyr-127, Arg-129, Tyr-181, and Arg-440) were highly conserved in both Mp mimosinase and CBL. However, homology modeling and molecular simulation of these enzymes predicted variations in the residues that interact with substrates. A mutation experiment on Mp mimosinase revealed that the disruption of a disulfide bond in the vicinity of the pyridoxal-5'-phosphate domain increased the enzyme's preference toward cystathionine. Treatment of Mp mimosinase with a disulfide-cleavage agent also decreased mimosinase activity. Furthermore, mutation near the conserved binding residue altered the substrate preference between mimosine and cystathionine. Molecular dynamics simulations of Mp mimosinase suggested a closer coordination of the residues that interact with mimosine at the active site compared with cystathionine, indicating a more compact pocket size for mimosine degradation. This study thus may provide new insights into the molecular diversification of CBL, a C-S lyase, into the C-N lyase mimosinase in the Mimosoideae subfamily.

In silico design of mimosine containing peptides as new efficient chelators of aluminum

The design of new and efficient chelators that can remove aluminium(iii), a metal with increasing recognition as a potential toxic agent, from biological systems is an area of high therapeutic relevance. In the present paper, we present an extensive computational study of a new promising type of these chelators based on mimosine containing peptides. The reason to choose mimosine is that the sidechain of this residue is similar to deferiprone, a ligand known to tightly interact with highly-valent metals, and in particular with Al(iii). In this article we analyze systematically, using a combination of methods that include QM/MM MD simulations, how the size and sequence of the polypeptides can alter the fundamental binding patterns to aluminum, in comparison with the binding to deferiprone. Particular attention is given towards the identification of the smallest peptide that interacts efficiently with aluminum, since polypeptide size is a fundamental factor to allow a given polypeptide to efficiently cross the cell membrane. The results indicate that the longest peptides, with 8 or 9 amino acids, show no difficulties interacting with Al(iii) in an optimum arrangement. By contrast, when the peptide contains five or six amino acids Al(iii) is pentacoordinated, reducing the stability of the resultant complex. In summary, our study demonstrates that the mimosine containing peptides can efficiently coordinate highly valent metals such as Al(iii), with a subtle dependence of the binding on the specific chain-lengths of the polypeptide. We believe that the present study sheds light on the adequacy of this new type of chelator towards aluminum binding.

A novel chelator of aluminum is presented, a peptide containing three mimosine residues.

Cytosolic Cysteine Synthase Switch Cysteine and Mimosine Production in Leucaena leucocephala

In higher plants, multiple copies of the cysteine synthase gene are present for cysteine biosynthesis. Some of these genes also have the potential to produce various kinds of β-substitute alanine. In the present study, we cloned a 1275-bp cDNA for cytosolic O-acetylserine(thiol)lyase (cysteine synthase) (Cy-OASTL) from Leucaena leucocephala. The purified protein product showed a dual function of cysteine and mimosine synthesis. Kinetics studies showed pH optima of 7.5 and 8.0, while temperature optima of 40 and 35 °C, respectively, for cysteine and mimosine synthesis. The kinetic parameters such as apparent K_m, k_cat were determined for both cysteine and mimosine synthesis with substrates O-acetylserine (OAS) and Na₂S or 3-hydroxy-4-pyridone (3H4P). From the in vitro results with the common substrate OAS, the apparent k_cat for Cys production is over sixfold higher than mimosine synthesis and the apparent K_m is 3.7 times lower, suggesting Cys synthesis is the favored pathway.

L‑mimosine induces caspase‑9‑mediated apoptosis in human osteosarcoma cells

L-mimosine is a rare plant amino acid extracted from Mimosa or Leucaena spp., and it has been reported to exhibit antitumor activity in a number of types of cancer. However, the underlying mechanisms remain to be clarified. In the present study, the effect of L‑mimosine was investigated in human osteosarcoma cells. A Cell Counting Kit‑8 assay and flow cytometry were used for toxicity detection. Hoechst staining and transmission electron microscopy (TEM), in addition to western blot analysis, were used for the examination of the associated mechanisms. The results of the present study indicated that L‑mimosine significantly inhibited cell proliferation by inducing cellular apoptosis in osteosarcoma cells. The Hoechst staining results and TEM revealed that nuclear damage increased with the concentration increase in L‑mimosine, as did the formation of apoptotic bodies. Additionally, the results of the western blot analysis confirmed that the treatment of cells with L‑mimosine was accompanied by increasing expression of cleaved caspase‑9. L‑mimosine‑induced apoptosis was inhibited by the caspase‑9 inhibitor Z‑LEHD‑FMK. In addition, the extracellular signal‑regulated kinase (ERK) signaling pathway was suppressed following treatment with L‑mimosine. In conclusion, the results of the present study suggested that L‑mimosine induced apoptosis via the mitochondrial apoptotic pathway. The ERK signaling pathway was indicated to be an additional mechanism underlying apoptosis induction. The results provided evidence for the use of L‑mimosine as a promising candidate for osteosarcoma therapy.

LINE-1 protein localization and functional dynamics during the cell cycle

LINE-1/L1 retrotransposon sequences comprise 17% of the human genome. Among the many classes of mobile genetic elements, L1 is the only autonomous retrotransposon that still drives human genomic plasticity today. Through its co-evolution with the human genome, L1 has intertwined itself with host cell biology. However, a clear understanding of L1’s lifecycle and the processes involved in restricting its insertion and intragenomic spread remains elusive. Here we identify modes of L1 proteins’ entrance into the nucleus, a necessary step for L1 proliferation. Using functional, biochemical, and imaging approaches, we also show a clear cell cycle bias for L1 retrotransposition that peaks during the S phase. Our observations provide a basis for novel interpretations about the nature of nuclear and cytoplasmic L1 ribonucleoproteins (RNPs) and the potential role of DNA replication in L1 retrotransposition.

Only two percent of our genetic material or genome are occupied by genes, while between 60-70 percent are made up of hundreds of thousands of copies of very similar DNA sequences. These repetitive sequences evolved from genetic elements called transposons.

Transposons are often referred to as ‘jumping genes’, as they can randomly move within the genome and thereby create dangerous mutations that may lead to cancer or other genetic diseases. LINE-1 is the only remaining active transposon in humans, and it expands by copying and pasting itself to new locations via a process called 'retrotransposition'. To do so, it is first transcribed into RNA – the molecules that help to make proteins – and then converted back into identical DNA sequences.

Previous research has shown that LINE-1 can form complexes with a series of proteins, including the two encoded by LINE-1 RNA itself: ORF1p and ORF2p. The LINE-1 complexes can enter the nucleus of the cell and insert a new copy of LINE-1 into the genome. However, until now it was not known how they do this. To investigate this further, Mita et al. used human cancer cells grown in the lab and tracked LINE-1 during the different stages of the cell cycle.

The results showed that LINE-1 enters the nucleus as the cell starts to divide and the membrane of the nucleus breaks down. The LINE-1 complexes are then retained in the nucleus while the membrane of the nucleus reforms. Later, as the cell duplicates its genetic material, LINE-1 starts to copy and paste itself. Mita et al., together with another group of researchers, also found that during this process, only LINE-1 RNA and ORF2p were found in the nucleus.

This shows that the cell cycle dictates both where the LINE-1 complexes gather and when LINE-1 is active. A next step will be to further investigate how the ‘copy and paste’ mechanisms of LINE-1 and the two LINE-1 proteins are regulated during the cell cycle. In future, this may help to identify LINE-1’s role in processes like aging or in diseases such as cancer.

Cell Synchronization by Rapamycin Improves the Developmental Competence of Porcine SCNT Embryos

The cell cycle stage of donor cells influences the success of somatic cell nuclear transfer (SCNT). This study investigated the effects of rapamycin treatment on synchronization of porcine fibroblasts in comparison with control and serum-starved cells, SCNT donor cell viability, and SCNT-derived embryo development. Porcine fibroblasts were treated with 0.1, 1, 10, and 100 μM rapamycin for 1 or 3 days. The proportion of cells in G0/G1 phase was significantly higher among cells treated with 1 μM rapamycin for 3 days (D3-1R) than among control and serum-starved cells (p < 0.05). In comparison with control cells, rapamycin-treated cells exhibited reduced proliferation, similar to serum-starved cells. The viability (as assessed by the MTT assay) of D3-1R-treated cells was good, similar to control cells, showing their quality was maintained. To confirm nutrient regulation by rapamycin treatment, we checked the transcript levels of nutrient transporter genes (SLC2A2, SLC2A4, SLC6A14, and SLC7A1). These levels were significantly lower in D3-1R-treated cells than in control cells (p < 0.01). We performed SCNT with D3-1R-treated cells (SCNT(D3-1R)) to confirm the effect of cell cycle synchronization by rapamycin treatment. Although SCNT(D3-1R) embryos did not have an increased fusion rate, their cleavage and blastocyst formation rates were significantly higher than those of control embryos (p < 0.05). Regarding embryo quality, the numbers of total and apoptotic cells per blastocyst were increased and decreased, respectively, in SCNT(D3-1R) blastocysts. The mRNA levels of developmental (CDX2 and CDH1) and proapoptotic (FAS and CASP3) genes were significantly higher and lower, respectively, in SCNT(D3-1R) blastocysts than in control blastocysts (p < 0.05). These results demonstrate that rapamycin treatment affects the cell cycle synchronization of donor cells and enhances the developmental potential of porcine SCNT embryos.

YM155 inhibits topoisomerase function

YM155 (sepantronium bromide) has been evaluated in clinical trials as a survivin suppressant, but despite positive signals from early work, later studies were negative. Clarification of the mechanism of action of YM155 is important for its further development. YM155 affects cells in a cell cycle-specific manner. When cells are in G1, YM155 prevented their progression through the S phase, leaving the cells at G1/S when exposed to YM155. Passage through mitosis from G2 is also defective following YM155 exposure. In this study, YM155 did not behave like a typical DNA intercalator in viscosity, circular dichroism, and absorption spectroscopy studies. In addition, molecular modeling experiments ruled out YM155 DNA interaction to produce DNA intercalation. We show that YM155 inhibited topoisomerase 2α decatenation and topoisomerase 1-mediated cleavage of DNA, suggesting that YM155 inhibits the enzyme function. Consistent with these findings, DNA double-strand break repair was also inhibited by YM155.

Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols

The gene expression program of the cell cycle represents a critical step for understanding cell cycle-dependent processes and their role in diseases such as cancer. Cell cycle-regulated gene expression analysis depends on cell synchronization into specific phases. Here we describe a method utilizing two complementary synchronization protocols that is commonly used for studying periodic variation of gene expression during the cell cycle. Both procedures are based on transiently blocking the cell cycle in one defined point. The synchronization protocol by hydroxyurea (HU) treatment leads to cellular arrest in late G1/early S phase, and release from HU-mediated arrest provides a cellular population uniformly progressing through S and G2/M. The synchronization protocol by thymidine and nocodazole (Thy-Noc) treatment blocks cells in early mitosis, and release from Thy-Noc mediated arrest provides a synchronized cellular population suitable for G1 phase and S phase-entry studies. Application of both procedures requires monitoring of the cell cycle distribution profiles, which is typically performed after propidium iodide (PI) staining of the cells and flow cytometry-mediated analysis of DNA content. We show that the combined use of two synchronization protocols is a robust approach to clearly determine the transcriptional profiles of genes that are differentially regulated in the cell cycle (i.e. E2F1 and E2F7), and consequently to have a better understanding of their role in cell cycle processes. Furthermore, we show that this approach is useful for the study of mechanisms underlying drug-based therapies (i.e. mitomycin C, an anticancer agent), because it allows to discriminate genes that are responsive to the genotoxic agent from those solely affected by cell cycle perturbations imposed by the agent.

Inhibition of MCP-1 and MIP-2 Chemokines in Murine Trichinellosis: Effect of the Anti-Inflammatory Compound L-Mimosine

Mimosine, is a plant amino-acid which has been reported to block DNA replication in mammalian cells and to arrest cells reversibly towards the end of the G1 phase or at the beginning of the S phase. In this study, 42 mice were infected with T. spiralis, a nematode parasite, and treated with the anti-inflammatory compound L-mimosine, to determine if any alteration in the chronic inflammatory state occurred, by investigating the host's immunological response. MCP-1, a C-C chemokine and MIP-2, a C-X-C chemokine were tested and measured in the sera of infected animals, after 1, 10, 20, 30, 40, 50 and 60 days postinfection, by ELISA method. The diaphragm/muscle and the masseters of the infected mice, were tested for inflammatory response. We found that MCP-1 was partially inhibited by L-mimosine, while MIP-2 was totally inhibited. Moreover, in sections of the diaphragm and masseters, the infiltration of inflammatory cells such as macrophages, lymphocytes and eosinophils were more intense in untreated animals compared to those treated with L-mimosine. These findings show, that L-mimosine may have an inhibitory effect on MCP-1 and MIP-2 serum levels in Trichinellosis and may influence the recruitment of inflammatory cells and the intensity of the inflammatory reaction in this parasitic disease.

The Chemistry and Biological Activities of Mimosine: A Review

Mimosine [β-[N-(3-hydroxy-4-oxypyridyl)]-α-aminopropionic acid] is a non-protein amino acid found in the members of Mimosoideae family. There are a considerable number of reports available on the chemistry, methods for estimation, biosynthesis, regulation, and degradation of this secondary metabolite. On the other hand, over the past years of active research, mimosine has been found to have various biological activities such as anti-cancer, antiinflammation, anti-fibrosis, anti-influenza, anti-virus, herbicidal and insecticidal activities, and others. Mimosine is a leading compound of interest for use in the development of RAC/CDC42-activated kinase 1 (PAK1)-specific inhibitors for the treatment of various diseases/disorders, because PAK1 is not essential for the growth of normal cells. Interestingly, the new roles of mimosine in malignant glioma treatment, regenerative dentistry, and phytoremediation are being emerged. These identified properties indicate an exciting future for this amino acid. The present review is focused on the chemistry and recognized biological activities of mimosine in an attempt to draw a link between these two characteristics. Copyright © 2016 John Wiley & Sons, Ltd.

Microtubule-stabilizing properties of the avocado-derived toxins (+)-(R)-persin and (+)-(R)-tetrahydropersin in cancer cells and activity of related synthetic analogs

The avocado toxin (+)-R-persin (persin) is active at low micromolar concentrations against breast cancer cells and synergizes with the estrogen receptor modulator 4-hydroxytamoxifen. Previous studies in the estrogen receptor-positive breast cancer cell line MCF-7 indicate that persin acts as a microtubule-stabilizing agent. In the present study, we further characterize the properties of persin and several new synthetic analogues in human ovarian cancer cells. Persin and tetrahydropersin cause G2M cell cycle arrest and increase intracellular microtubule polymerization. One analog (4-nitrophenyl)-deshydroxypersin prevents cell proliferation and blocks cells in G1 of the cell cycle rather than G2M, suggesting an additional mode of action of these compounds independent of microtubules. Persin can synergize with other microtubule-stabilizing agents, and is active against cancer cells that overexpress the P-glycoprotein drug efflux pump. Evidence from Flutax-1 competition experiments suggests that while the persin binding site on β-tubulin overlaps the classical taxoid site where paclitaxel and epothilone bind, persin retains activity in cell lines with single amino acid mutations that affect these other taxoid site ligands. This implies the existence of a unique binding location for persin at the taxoid site.

Activating transcription factor 5 enhances radioresistance and malignancy in cancer cells

Radiotherapy is effective for treating various types of tumors. However, some cancer cells survive after irradiation and repopulate tumors with highly malignant phenotypes that correlate with poor prognosis. It is not known how cancer cells survive and generate malignant tumors after irradiation. Here, we show that activating transcription factor 5 (ATF5) promotes radioresistance and malignancy in cancer cells after irradiation. In the G1-S phase of the cell cycle, cancer cells express high levels of ATF5, which promotes cell cycle progression and thereby increases radioresistance. Furthermore, ATF5 increases malignant phenotypes, such as cell growth and invasiveness, in cancer cells in vitro and in vivo. We have identified a new mechanism for the regeneration of highly malignant tumors after irradiation and shown that ATF5 plays a key role in the process.

Heterologous Expression and Characterization of Mimosinase from Leucaena leucocephala

Heterologous expression of eukaryotic genes in bacterial system is an important method in synthetic biology to characterize proteins. It is a widely used method, which can be sometimes quite challenging, as a number of factors that act along the path of expression of a transgene to mRNA, and mRNA to protein, can potentially affect the expression of a transgene in a heterologous system. Here, we describe a method for successful cloning and expression of mimosinase-encoding gene from Leucaena leucocephala (leucaena) in E. coli as the heterologous host. Mimosinase is an important enzyme especially in the context of metabolic engineering of plant secondary metabolite as it catalyzes the degradation of mimosine, which is a toxic secondary metabolite found in all Leucaena and Mimosa species. We also describe the methods used for characterization of the recombinant mimosinase.

A carbon-nitrogen lyase from Leucaena leucocephala catalyzes the first step of mimosine degradation

The tree legume Leucaena leucocephala contains a large amount of a toxic nonprotein aromatic amino acid, mimosine, and also an enzyme, mimosinase, for mimosine degradation. In this study, we isolated a 1,520-bp complementary DNA (cDNA) for mimosinase from L. leucocephala and characterized the encoded enzyme for mimosine-degrading activity. The deduced amino acid sequence of the coding region of the cDNA was predicted to have a chloroplast transit peptide. The nucleotide sequence, excluding the sequence for the chloroplast transit peptide, was codon optimized and expressed in Escherichia coli. The purified recombinant enzyme was used in mimosine degradation assays, and the chromatogram of the major product was found to be identical to that of 3-hydroxy-4-pyridone (3H4P), which was further verified by electrospray ionization-tandem mass spectrometry. The enzyme activity requires pyridoxal 5'-phosphate but not α-keto acid; therefore, the enzyme is not an aminotransferase. In addition to 3H4P, we also identified pyruvate and ammonia as other degradation products. The dependence of the enzyme on pyridoxal 5'-phosphate and the production of 3H4P with the release of ammonia indicate that it is a carbon-nitrogen lyase. It was found to be highly efficient and specific in catalyzing mimosine degradation, with apparent Km and Vmax values of 1.16×10(-4) m and 5.05×10(-5) mol s(-1) mg(-1), respectively. The presence of other aromatic amino acids, including l-tyrosine, l-phenylalanine, and l-tryptophan, in the reaction did not show any competitive inhibition. The isolation of the mimosinase cDNA and the biochemical characterization of the recombinant enzyme will be useful in developing transgenic L. leucocephala with reduced mimosine content in the future.

Activation of the prereplication complex is blocked by mimosine through reactive oxygen species-activated ataxia telangiectasia mutated (ATM) protein without DNA damage

Mimosine is an effective cell synchronization reagent used for arresting cells in late G1 phase. However, the mechanism underlying mimosine-induced G1 cell cycle arrest remains unclear. Using highly synchronous cell populations, we show here that mimosine blocks S phase entry through ATM activation. HeLa S3 cells are exposed to thymidine for 15 h, released for 9 h by washing out the thymidine, and subsequently treated with 1 mM mimosine for a further 15 h (thymidine → mimosine). In contrast to thymidine-induced S phase arrest, mimosine treatment synchronizes >90% of cells at the G1-S phase boundary by inhibiting the transition of the prereplication complex to the preinitiation complex. Mimosine treatment activates ataxia telangiectasia mutated (ATM)/ataxia telangiectasia and Rad3-related (ATR)-mediated checkpoint signaling without inducing DNA damage. Inhibition of ATM activity is found to induce mimosine-arrested cells to enter S phase. In addition, ATM activation by mimosine treatment is mediated by reactive oxygen species (ROS). These results suggest that, upon mimosine treatment, ATM blocks S phase entry in response to ROS, which prevents replication fork stalling-induced DNA damage.

Mimosine As Well As Serum Starvation Can Be Used for Cell Cycle Synchronization of Sheep Granulosa Cells

This study was evaluated the effect of different synchronization protocols such as serum starvation for 1–3 days, confluency and chemical inhibitors on synchronization accuracy at G0/G1, apoptosis, and DNA synthesis in sheep granulosa cells. The cells were obtained from ovarian antral follicles of slaughtered sheep and used at first and fifth passages. Flow cytometry analysis showed that confluent cells, serum starvation for 24, 48, and 72 hours, and mimosine treatment significantly increased G0/G1 phase cells when compared to normally growing cells (P<0.05). Nocodazole treatment increased the cell population in the G0/G1 stage when compared with the control group but did not change the G2/M stage population. Treatment of cells with mimosine, nocodazole, and serum starvation in three groups resulted in proliferation arrest (P<0.05). Serum starvation for 72 hours significantly promoted apoptosis in granulosa cells (P<0.05). The results of the primary culture and 5th passage were the same. The use of 48-hour serum starvation and mimosine treatments has been recommended because cell death in these groups was very similar to the control group.

Synthesis, pharmacophores, and mechanism study of pyridin-2(1H)-one derivatives as regulators of translation initiation factor 3A

Twenty-seven 1,5-disubstituted-pyridin-2(1H)-one derivatives were synthesized and evaluated for their anti-cancer and anti-fibrosis activity by A549 and NIH3T3 cell viability assays, respectively. To study the selectivity between the cancer and fibrosis cell lines, pharmacophore models (F1-F4) were built in advance for compounds with pyridin-2(1H)-one scaffold, which revealed the relationship between the occupation of the aromatic sub-site F4 and potent anti-cancer activity. The relationship between structure and anti-cancer activity for all target compounds is also reported herein: 1-Phenyl-5-((m-tolylamino)methyl)pyridine-2(1H)-one (22) displayed both potency and selectivity (IC50=0.13 mM) toward the A549 cell line through the inhibition of translation initiation, especially by eIF3a suppression, and can be treated as a lead for the design of novel eIF3a regulators and anti-lung cancer agents.

Active demethylation of the Foxp3 locus leads to the generation of stable regulatory T cells within the thymus

Stable expression of Foxp3 in regulatory T cells (Tregs) depends on DNA demethylation at the Treg-specific demethylated region (TSDR), a conserved, CpG-rich region within the Foxp3 locus. The TSDR is selectively demethylated in ex vivo Tregs purified from secondary lymphoid organs, but it is unclear at which stage of Treg development demethylation takes place. In this study, we show that commitment to a stable lineage occurred during early stages of murine thymic Treg development by engraving of lineage-specific epigenetic marks in parallel with establishment of a Treg-specific gene expression profile. TSDR demethylation was achieved through an active mechanism and involved enzymes of the ten-eleven-translocation family and hydroxylation of methylated cytosines, a modification that is implicated as an initiating step of mitosis-independent DNA demethylation pathways and has not yet been observed at specific loci during immune cell differentiation. Together, our results demonstrate that initiating TSDR demethylation during early stages of thymic Treg development commences stabilization of Foxp3 expression and guarantees full functionality and long-term lineage stability of Tregs.

Role of the cell cycle in regression of the corpus luteum

The corpus luteum contains differentiated steroidogenic cells that have exited the cell cycle of proliferation. In some tissues, deletion of quiescent, differentiated cells by apoptosis in response to injury or pathology is preceded by reentry into the cell cycle. We tested whether luteal cells reenter the cell cycle during the physiological process of luteolysis. Ovaries were obtained after injection of cows with a luteolytic dose of prostaglandin F(2)(α) (PGF). In luteal sections, cells co-staining for markers of cell proliferation (MKI67) and apoptosis (cPARP1) increased 24  h after PGF, indicating that cells that reenter the cell cycle undergo apoptosis. The percent of steroidogenic cells (CYP11A1-positive) co-staining for MKI67 increased after PGF, while co-staining of non-steroidogenic cells did not change. Dispersed luteal cells were stained with Nile Red to distinguish lipid-rich steroidogenic cells from nonsteroidogenic cells and co-stained for DNA. Flow cytometry showed that the percent of steroidogenic cells progressing through the cell cycle and undergoing apoptosis increased after PGF. Culturing luteal cells induced reentry of steroidogenic cells into the cell cycle, providing a model to test the influence of the cell cycle on susceptibility to apoptosis. Blocking cells early in the cell cycle using inhibitors reduced cell death in response to treatment with the apoptosis-inducing protein, Fas ligand (FASL). Progesterone treatment reduced progression through the cell cycle and decreased FASL-induced apoptosis. In summary, steroidogenic cells reenter the cell cycle upon induction of luteal regression. While quiescent cells are resistant to apoptosis, entry into the cell cycle promotes susceptibility to apoptosis.

Mechanism of the antitumoral activity of deferasirox, an iron chelation agent, on mantle cell lymphoma

Mantle cell lymphoma (MCL) characterized by the t(11;14)(q13;q32) translocation, resulting in cyclin D1 overexpression, is one of the most challenging lymphomas to treat. Iron chelators, such as deferasirox, have previously been shown to exhibit anti-proliferative properties; however, their effect on MCL cells has never been investigated. We showed that deferasirox exhibited antitumoral activity against the MCL cell lines HBL-2, Granta-519 and Jeko-1, with 50% inhibitory concentration (IC(50)) values of 7.99 ± 2.46 μM, 8.93 ± 2.25 μM and 31.86 ± 7.26 μM, respectively. Deferasirox induced apoptosis mediated through caspase-3 activation and decreased cyclin D1 protein levels resulting from increased proteasomal degradation. We also demonstrated down-regulation of phosphor-RB (Ser780) expression, which resulted in increasing levels of the E2F/RB complex and G(1)/S arrest. Finally, we showed that deferasirox activity was dependent on its iron chelating ability. The present data indicate that deferasirox, by down-regulating cyclin D1 and inhibiting its related signals, may constitute a promising adjuvant therapeutic molecule in the strategy for MCL treatment.

Acidic nucleoplasmic DNA-binding protein (And-1) controls chromosome congression by regulating the assembly of centromere protein A (CENP-A) at centromeres

The centromere is an epigenetically designated chromatin domain that is essential for the accurate segregation of chromosomes during mitosis. The incorporation of centromere protein A (CENP-A) into chromatin is fundamental in defining the centromeric loci. Newly synthesized CENP-A is loaded at centromeres in early G(1) phase by the CENP-A-specific histone chaperone Holliday junction recognition protein (HJURP) coupled with other chromatin assembly factors. However, it is unknown whether there are additional HJURP-interacting factor(s) involving in this process. Here we identify acidic nucleoplasmic DNA-binding protein 1 (And-1) as a new factor that is required for the assembly of CENP-A nucleosomes. And-1 interacts with both CENP-A and HJURP in a prenucleosomal complex, and the association of And-1 with CENP-A is increased during the cell cycle transition from mitosis to G(1) phase. And-1 down-regulation significantly compromises chromosome congression and the deposition of HJURP-CENP-A complexes at centromeres. Consistently, overexpression of And-1 enhances the assembly of CENP-A at centromeres. We conclude that And-1 is an important factor that functions together with HJURP to facilitate the cell cycle-specific recruitment of CENP-A to centromeres.

The involvement of acidic nucleoplasmic DNA-binding protein (And-1) in the regulation of prereplicative complex (pre-RC) assembly in human cells

DNA replication in all eukaryotes starts with the process of loading the replicative helicase MCM2-7 onto chromatin during late mitosis of the cell cycle. MCM2-7 is a key component of the prereplicative complex (pre-RC), which is loaded onto chromatin by the concerted action of origin recognition complex, Cdc6, and Cdt1. Here, we demonstrate that And-1 is assembled onto chromatin in late mitosis and early G(1) phase before the assembly of pre-RC in human cells. And-1 forms complexes with MCM2-7 to facilitate the assembly of MCM2-7 onto chromatin at replication origins in late mitosis and G(1) phase. We also present data to show that depletion of And-1 significantly reduces the interaction between Cdt1 and MCM7 in G(1) phase cells. Thus, human And-1 facilitates loading of the MCM2-7 helicase onto chromatin during the assembly of pre-RC.

Bp44mT: an orally active iron chelator of the thiosemicarbazone class with potent anti-tumour efficacy

BACKGROUND AND PURPOSE

Our previous studies demonstrated that a thiosemicarbazone iron chelator (di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone; Dp44mT) possesses potent and selective anti-cancer activity but led to cardiotoxicity at non-optimal doses. In this study, we examined the in vivo anti-tumour efficacy and tolerability of a new-generation 2-benzoylpyridine thiosemicarbazone iron chelator (2-benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone; Bp44mT) administered via the oral or i.v. routes.

EXPERIMENTAL APPROACH

BpT chelators were tested in vitro against human lung cancer cells (DMS-53) and in vivo in DMS-53 tumour xenografts in mice. The toxicity of Bp44mT in vivo and its effects on the expression of iron-regulated molecules involved in growth and cell cycle control were investigated.

KEY RESULTS

Administration of Bp44mT by either route resulted in marked dose-dependent inhibition of tumour growth. When administered at 50 mg·kg(-1) via oral gavage three times per week for 23 days, the net xenograft growth was inhibited by 75%, compared with vehicle-treated mice. Toxicological examination showed reversible alterations including slight reduction of RBC count, with a decrease of liver and splenic iron levels, which confirmed iron chelation in vivo. Importantly, in contrast to Dp44mT, the chelator-treated mice did not show cardiac histological abnormalities. There was also no significant weight loss in mice, suggesting oral administration of Bp44mT was well tolerated.

CONCLUSIONS AND IMPLICATIONS

This is the first study to show that Bp44mT can be given orally with potent anti-tumour efficacy. Oral administration of a novel and effective chemotherapeutic agent provides the benefits of convenience for chronic dosing regimens.

Global DNA demethylation during mouse erythropoiesis in vivo

In the mammalian genome, 5'-CpG-3' dinucleotides are frequently methylated, correlating with transcriptional silencing. Genome-wide demethylation is thought to occur only twice during development, in primordial germ cells and in the pre-implantation embryo. These demethylation events are followed by de novo methylation, setting up a pattern inherited throughout development and modified only at tissue-specific loci. We studied DNA methylation in differentiating mouse erythroblasts in vivo by using genomic-scale reduced representation bisulfite sequencing (RRBS). Demethylation at the erythroid-specific β-globin locus was coincident with global DNA demethylation at most genomic elements. Global demethylation was continuous throughout differentiation and required rapid DNA replication. Hence, DNA demethylation can occur globally during somatic cell differentiation, providing an experimental model for its study in development and disease.

A key commitment step in erythropoiesis is synchronized with the cell cycle clock through mutual inhibition between PU.1 and S-phase progression

Hematopoietic progenitors undergo differentiation while navigating several cell division cycles, but it is unknown whether these two processes are coupled. We addressed this question by studying erythropoiesis in mouse fetal liver in vivo. We found that the initial upregulation of cell surface CD71 identifies developmentally matched erythroblasts that are tightly synchronized in S-phase. We show that DNA replication within this but not subsequent cycles is required for a differentiation switch comprising rapid and simultaneous committal transitions whose precise timing was previously unknown. These include the onset of erythropoietin dependence, activation of the erythroid master transcriptional regulator GATA-1, and a switch to an active chromatin conformation at the β-globin locus. Specifically, S-phase progression is required for the formation of DNase I hypersensitive sites and for DNA demethylation at this locus. Mechanistically, we show that S-phase progression during this key committal step is dependent on downregulation of the cyclin-dependent kinase p57(KIP2) and in turn causes the downregulation of PU.1, an antagonist of GATA-1 function. These findings therefore highlight a novel role for a cyclin-dependent kinase inhibitor in differentiation, distinct to their known function in cell cycle exit. Furthermore, we show that a novel, mutual inhibition between PU.1 expression and S-phase progression provides a "synchromesh" mechanism that "locks" the erythroid differentiation program to the cell cycle clock, ensuring precise coordination of critical differentiation events.

The translational regulator eIF3a: the tricky eIF3 subunit!

Regulation of gene expression is a fundamental step in cellular physiology as abnormalities in this process may lead to de-regulated growth and cancer. Translation of mRNA is mainly regulated at the rate-limiting initiation step, where many eukaryotic initiation factors (eIFs) are involved. The largest and most complex initiation factor is eIF3 which plays a role in translational regulation, cell growth and cancer. The largest subunit of eIF3 is eIF3a, although it is not required for the general function of eIF3 in translation initiation. However, eIF3a may play a role as a regulator of a subset of mRNAs and has been demonstrated to regulate the expression of p27(kip1), tyrosinated α-tubulin and ribonucleotide reductase M2 subunit. These molecules have a pivotal role in the regulation of the cell cycle. Moreover, the eIF3a mRNA is ubiquitously expressed in all tissues at different levels and is found elevated in a number of cancer types. eIF3a can modulate the cell cycle and may be a translational regulator for proteins important for entrance into S phase. The expression of eIF3a is decreased in differentiated cells in culture and the suppression of eIF3a expression can reverse the malignant phenotype and change the sensitivity of cells to cell cycle modulators. However, the role of eIF3a in cancer is still unclear. In fact, some studies have identified eIF3a to be involved in cancer development, while other results indicate that it could provide protection against evolution into higher malignancy. Together, these findings highlight the "tricky" and interesting nature of eIF3a.

A winding road to origin discovery

Studies in our laboratory over the last three decades have shown that the Chinese hamster dihydrofolate reductase (DHFR) origin of replication corresponds to a broad zone of inefficient initiation sites distributed throughout the spacer between the convergently transcribed DHFR and 2BE2121 genes. It is clear from mutational analysis that none of these sites is genetically required for controlling origin activity. However, the integrity of the promoter of the DHFR gene is needed to activate the downstream origin, while the 3' processing signals prevent invasion and inactivation of the downstream origin by transcription forks. Several other origins in metazoans have been shown to correspond to zones of inefficient sites, while a different subset appears to be similar to the fixed replicators that characterize origins in S. cerevisiae and lower organisms. These observations have led us to suggest a model in which the mammalian genome is dotted with a hierarchy of degenerate, redundant, and inefficient replicators at intervals of a kilobase or less, some of which may have evolved to be highly circumscribed and efficient. The activities of initiation sites are proposed to be largely regulated by local transcription and chromatin architecture. Recently, we and others have devised strategies for identifying active origins on a genome-wide scale in order to define their distributions between fixed and dispersive origin types and to detect relationships among origins, genes, and epigenetic markers. The global pictures emerging are suggestive but far from complete and appear to be plagued by some of the same uncertainties that have led to conflicting views of individual origins in the past (particularly DHFR). In this paper, we will trace the history of origin discovery in mammalian genomes, primarily using the well-studied DHFR origin as a model, because it has been analyzed by nearly every available origin mapping technique in several different laboratories, while many origins have been identified by only one. We will address the strengths and shortcomings of the various methods utilized to identify and characterize origins in complex genomes and will point out how we and others were sometimes led astray by false assumptions and biases, as well as insufficient information. The goal is to help guide future experiments that will provide a truly comprehensive and accurate portrait of origins and their regulation. After all, in the words of George Santayana, "Those who do not learn from history are doomed to repeat it."

Effects of hydroxyurea on monoclonal antibody production induced by anti-mIgG and LPS stimulation on murine B cell hybridomas

Chemical treatment with hydroxyurea (HU) has been selected as a simple and low cost strategy to generate a cell population enriched for the G1 phase. After the chemical treatment with HU, cells were stimulated with anti-mIgG to test if the positive effects of anti-mIgG on CD40 expression and specific IgG2a production rate were improved upon a cell population with a higher percentage of cells in G1 phase at the beginning of the cell culture. In addition, other treatments assayed in this work were the cell stimulation with Lipopolysaccharide (LPS) both before and after the HU treatment. It has been observed that the use of HU under conditions able to maintain the cells in viable state (0.1 mM for 20 h), has a negative effect on CD40 expression and specific IgG2a production rate induced by anti-mIgG. The positive effect of LPS on cell stimulation induced by anti-mIgG is reduced on cells treated with HU.

A role for BAF57 in cell cycle-dependent transcriptional regulation by the SWI/SNF chromatin remodeling complex

The SWI/SNF complex is an ATP-dependent chromatin remodeling complex that plays pivotal roles in gene regulation and cell cycle control. In the present study, we explored the molecular functions of the BAF57 subunit of SWI/SNF in cell cycle control via transcriptional regulation of cell cycle-related genes. We affinity purified SWI/SNF from HeLa cells stably expressing FLAG-tagged BAF47/Ini1 with or without stable short hairpin RNA-mediated knockdown of BAF57. The subunit composition of the holo-SWI/SNF and BAF57-depleted SWI/SNF complexes from these cells was determined using a quantitative SILAC (stable isotope labeling by amino acids in cell culture)-based proteomic approach. Depletion of BAF57 resulted in a significant codepletion of BAF180 from the SWI/SNF complex without decreasing total cellular BAF180 levels. In biochemical assays of SWI/SNF activity, the holo-SWI/SNF and BAF57/BAF180-depleted SWI/SNF complexes exhibited similar activities. However, in cell proliferation assays using HeLa cells, knockdown of BAF57 resulted in an accumulation of cells in the G(2)-M phase, inhibition of colony formation, and impaired growth in soft agar. Knockdown of BAF57 also caused transcriptional misregulation of various cell cycle-related genes, especially genes involved in late G(2). Collectively, our results have identified a new role for BAF57 within the SWI/SNF complex that is required for (a) maintaining the proper subunit composition of the complex and (b) cell cycle progression through the transcriptional regulation of a subset of cell cycle-related genes.

Transcriptional regulation of p21/CIP1 cell cycle inhibitor by PDEF controls cell proliferation and mammary tumor progression

The Ets family of transcription factors control a myriad of cellular processes and contribute to the underlying genetic loss of cellular homeostasis resulting in cancer. PDEF (prostate-derived Ets factor) has been under investigation for its role in tumor development and progression. However, the role of PDEF in cancer development has been controversial. Some reports link PDEF to tumor promoter, and others show tumor-suppressing functions in various systems under different conditions. So far, there has been no conclusive evidence from in vivo experiments to prove the role of PDEF. We have used both in vitro and in vivo systems to provide a conclusive role of PDEF in the progression process. PDEF-expressing cells block the cell growth rate, and this retardation was reversible when PDEF expression was silenced with PDEF-specific small interfering RNA. When these PDEF-expressing cells were orthotopically implanted into the mouse mammary gland, tumor incidence and growth rate were significantly retarded. Cell cycle analysis revealed that PDEF expression partially blocked cell cycle progression at G(1)/S without an effect on apoptosis. PDEF overexpression resulted in an increase in p21/CIP1 at both the mRNA and protein levels, resulting in decreased Cdk2 activity. Promoter deletion analysis, electrophoresis mobility shift assays, and chromatin immunoprecipitation studies identified the functional Ets DNA binding site at -2118 bp of the p21/CIP1 gene promoter. This site is capable of binding and responding to PDEF. Furthermore, we silenced p21/CIP1 expression in PDEF-overexpressing cells by small interfering RNA. p21-silenced PDEF cells exhibited significantly increased cell growth in vitro and in vivo, demonstrating the p21 regulation by PDEF as a key player. These experiments identified PDEF as a new transcription factor that directly regulates p21/CIP1 expression under non-stressed conditions. This study conclusively proves that PDEF is a breast tumor suppressor for the first time using both in vitro and in vivo systems. PDEF can be further developed as a target for designing therapeutic intervention of breast cancer.

Methods for synchronizing cells at specific stages of the cell cycle

Exponentially growing cells are asynchronous with respect to the cell cycle stage. Detection of cell cycle-related events is improved by enriching the culture for cells at the stage during which the particular event occurs. Methods for synchronizing cells are provided here, including those based on morphological features of the cell (mitotic shake-off), cellular metabolism (thymidine inhibition, isoleucine depravation), and chemical inhibitors of cell progression in G1 (lovastatin), S (aphidicolin, mimosine), and G2/M (nocodazole). Applications of these methods and the advantages and disadvantages of each are described.

S-phase progression stimulates both the mutagenic KU-independent pathway and mutagenic processing of KU-dependent intermediates, for nonhomologous end joining

We used intrachromosomal substrates to directly monitor the effect of the cell cycle on the efficiency and the accuracy of nonhomologous end joining (NHEJ) in mammalian cells. We show that both KU and KU-independent (KU-alt) pathways are efficient when maintaining cells in G1/S, in G2/M or during dynamic progression through S phase. In addition, the accuracy of NHEJ is barely altered when the cells are blocked in G1/S or in G2/M. However, progression through S phase increases the frequency of deletions, which is a hallmark of the KU-alt pathway. Moreover, we show that the intermediates that are generated by the KU-dependent end joining of non-fully complementary ends, and which contain mismatches, nicks or gap intermediates, are less accurately processed when the cells progress through S phase. In conclusion, both KU and KU-alt processes are active throughout the cell cycle, but the repair is more error prone during S phase, both by increasing the mutagenic KU-alt pathway and decreasing the accuracy of the repair of the intermediates generated by the KU-dependent pathway.

Influence of Chromatin Structure on Induction of Double-Strand Breaks in Mammalian Cells Irradiated with DNA-Incorporated125I

In this study the induction of double-strand breaks (DSBs) was investigated in Chinese hamster V79-379A cells irradiated with the Auger-electron emitter (125)I incorporated into DNA. The role of chromatin organization was studied by pulse-labeling synchronized cells with (125)IdU before decay accumulation in early or late S phase. Pulsed-field gel electrophoresis and fragment-size analysis were used to quantify the distribution of DNA fragments in irradiated intact cells and naked DNA as well as in DNA from asynchronously labeled cultures in a different scavenging environment. The results show that in intact cells, after accumulation of decays at -70 degrees C in the presence of 10% DMSO, almost four times more DSBs were induced in late S phase compared with early S phase and the fragment distribution was clearly non-random with an excess of fragments <0.2 Mbp. The DSB yield was 0.6 DSB/cell and decay for cells irradiated in early S phase and 2.3 DSBs/cell and decay for cells irradiated in late S phase. When similar experiments were performed on naked genomic DNA or intact cells irradiated with gamma rays, the difference in yield was not as prominent. These data imply a role of chromatin organization in the induction of DSBs by DNA-incorporated (125)I. In summary, the results presented here suggest that the yield of DSBs as well as the fragment distribution induced by (125)IdU decay may vary significantly depending on the chromatin organization during S phase and the labeling procedure used.

Inhibition of CDK4 impairs proliferation of pancreatic cancer cells and sensitizes towards TRAIL-induced apoptosis via downregulation of survivin

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in Western countries with an average survival after diagnosis of 3-6 months and a five-year survival rate under 5%. Because of the lack of effective therapies, there is the need to characterize new molecular treatment strategies. Abnormal regulation of the cell cycle is a hallmark of neoplasia. Cyclin-dependent kinase 4 (CDK4), a key regulator of G1-phase of the cell cycle, has been shown to be overexpressed in pancreatic cancer. Until now, the contribution of CDK4 to tumor maintenance of pancreatic cancer has not been investigated. In this study, we used the chemical CDK4 inhibitor 2-bromo-12,13-dihydro-5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione, as well as RNA interference, to investigate the function of CDK4 in pancreatic cancer cells. Both approaches led to a reduction of pancreatic cancer cell proliferation due to G1-phase cell cycle arrest and Rb activation. Furthermore, we observed increased sensitivity of G1-arrested pancreatic cancer cells towards TRAIL-induced apoptosis. Sensitization towards TRAIL was due to the transcriptional downregulation of survivin. These findings show that a combined sensitizer/inducer strategy may be a potential therapeutic strategy for pancreatic ductal adenocarcinoma.

Phosphatidylcholine catabolism in the MCF-7 cell cycle

The catabolism of phosphatidylcholine (PtdCho) appears to play a key role in regulating the net accumulation of the lipid in the cell cycle. Current protocols for measuring the degradation of PtdCho at specific cell-cycle phases require prolonged periods of incubation with radiolabelled choline. To measure the degradation of PtdCho at the S and G2 phases in the MCF-7 cell cycle, protocols were developed with radiolabelled lysophosphatidylcholine (lysoPtdCho), which reduces the labelling period and minimizes the recycling of labelled components. Although most of the incubated lysoPtdCho was hydrolyzed to glycerophosphocholine (GroPCho) in the medium, the kinetics of the incorporation of label into PtdCho suggests that the labelled GroPCho did not contribute significantly to cellular PtdCho formation. A protocol which involved exposing the cells twice to hydroxyurea, was also developed to produce highly synchronized MCF-7 cells with a profile of G1:S:G2/M of 90:5:5. An analysis of PtdCho catabolism in the synchronized cells following labelling with lysoPtdCho revealed that there was increased degradation of PtdCho in early to mid-S phase, which was attenuated in the G2/M phase. The results suggest that the net accumulation of PtdCho in MCF-7 cells may occur in the G2 phase of the cell cycle.

Selective determination of mimosine and its dihydroxypyridinyl derivative in plant systems

Our observations on the growth stimulatory nature of mimosine, (beta-(3-hydroxy-4-pyridon-1-yl)-L-alanine), the toxic non-protein plant amino acid, in some model experimental systems, warranted sensitive and selective routine estimations. For the determination of both mimosine and DHP, an indirect spectrophotometric method was developed based on their individual reaction with known excess of DZSAM and by estimating the remaining DZSAM with N-(1-naphthyl)ethylene-diamine (NEDA). The resultant decrease in the secondary coupled product was measured at 540 nm. On equimolar basis, DHP had 40% of the reactivity of mimosine while interference from other relevant compounds was 15-35%. The determination of mimosine and DHP in tissue samples under different physiological conditions was effected after paper chromatographic separation of mimosine and DHP with distinctly differing Rf, from other compounds. The indirect method is superior in terms of absolute selectivity, sensitivity and ease of applicability with linear decreases in absorbance, proportional to increasing concentrations of mimosine from 0.1 to 0.75 microM or DHP from 0.2 to 1.5 microM and with recoveries of 99.2 to 100.5%.

Newt orthologue ofGrowth arrest-specific 6 (NvGas6) is implicated in stress response during newt forelimb regeneration

Red-spotted newts are capable of regenerating various structures and organs through the process of epimorphic regeneration. Receptor tyrosine kinases (RTKs) and their ligands are important for normal cellular development and physiology but most have not yet been characterised during regeneration. We have isolated a newt orthologue of Growth arrest-specific 6 (NvGas6), and examined its expression during forelimb regeneration and within a blastema cell line (B1H1). During limb regeneration, NvGas6 expression increases upon amputation, peaks during maximal blastema cell proliferation, and is subsequently downregulated during redifferentiation. Transcripts are localised to the wound epithelium and distal mesenchymal cells during dedifferentiation and proliferative phases, and scattered within redifferentiating tissues during later stages. In B1H1 cultures, NvGas6 is upregulated under reduced serum conditions and myogenesis. Treatment with mimosine and colchicine or exposure to heat shock or anoxia results in upregulation of NvGas6 expression. Taken together, our findings suggest that during regeneration, NvGas6 expression may be upregulated in response to cellular stress.

Enhanced repair of DNA interstrand crosslinks in S phase

Hela cells synchronized in G1 and S phases of the cell cycle were transfected with pEGFP crosslinked with trioxsalen. Twelve hours later the number of fluorescent cells was determined by fluorescent microscopy. Cells in S phase have repaired 0.2-0.3 ICL/kb over the 12h period, while cells in G1 phase repaired interstrand crosslinks much more poorly. The crosslinked plasmids were efficiently recruited to the nuclear matrix both in G1 phase and S-phase, which showed that the poor repair of G1 cells was a result of a lack of DNA replication rather than of a lack of matrix attachment.

Visualization of bidirectional initiation of chromosomal DNA replication in a human cell free system

Initiation of DNA replication is tightly controlled during the cell cycle to maintain genome integrity. In order to directly study this control we have previously established a cell-free system from human cells that initiates semi-conservative DNA replication. Template nuclei are isolated from cells synchronized in late G₁ phase by mimosine. We have now used DNA combing to investigate initiation and further progression of DNA replication forks in this human in vitro system at single molecule level. We obtained direct evidence for bidirectional initiation of divergently moving replication forks in vitro. We assessed quantitatively replication fork initiation patterns, fork movement rates and overall fork density. Individual replication forks progress at highly heterogeneous rates (304 ± 162 bp/min) and the two forks emanating from a single origin progress independently from each other. Fork progression rates also change at the single fork level, suggesting that replication fork stalling occurs. DNA combing provides a powerful approach to analyse dynamics of human DNA replication in vitro.

Expression profiling of human hepatoma cells reveals global repression of genes involved in cell proliferation, growth, and apoptosis upon infection with parvovirus H-1

Autonomous parvoviruses are characterized by their stringent dependency on host cell S phase and their cytopathic effects on neoplastic cells. To better understand the interactions between the virus and its host cell, we used oligonucleotide arrays that carry more than 19,000 unique human gene sequences to profile the gene expression of the human hepatocellular carcinoma cell line QGY-7703 at two time points after parvovirus H-1 infection. At the 6-h time point, a single gene was differentially expressed with a >2.5-fold change. At 12 h, 105 distinct genes were differentially expressed in virus-infected cells compared to mock-treated cells, with 93% of these genes being down-regulated. These repressed genes clustered mainly into classes involved in transcriptional regulation, signal transduction, immune and stress response, and apoptosis, as exemplified by genes encoding the transcription factors Myc, Jun, Fos, Ids, and CEBPs. Quantitative real-time reverse transcription-PCR analysis on selected genes validated the array data and allowed the changes in cellular gene expression to be correlated with the accumulation of viral transcripts and NS1 protein. Western blot analysis of several cellular proteins supported the array results and substantiated the evidence given by these and other data to suggest that the H-1 virus kills QGY-7703 cells by a nonapoptotic process. The promoter regions of most of the differentially expressed genes analyzed fail to harbor any motif for sequence-specific binding of NS1, suggesting that direct binding of NS1 to cellular promoters may not participate in the modulation of cellular gene expression in H-1 virus-infected cells.

pyd genes of Rhizobium sp. strain TAL1145 are required for degradation of 3-hydroxy-4-pyridone, an aromatic intermediate in mimosine metabolism

Rhizobium sp. strain TAL1145 degrades the Leucaena toxin mimosine and its degradation product 3-hydroxy-4-pyridone (HP). The aim of this investigation is to characterize the Rhizobium genes for HP degradation and transport. These genes were localized by subcloning and mutagenesis on a previously isolated cosmid, pUHR263, containing mid genes of TAL1145 required for mimosine degradation. Two structural genes, pydA and pydB, encoding a metacleavage dioxygenase and a hydrolase, respectively, are required for degradation of HP, and three genes, pydC, pydD, and pydE, encoding proteins of an ABC transporter, are involved in the uptake of HP by TAL1145. These genes are induced by HP, although both pydA and pydB show low levels of expression without HP. pydA and pydB are cotranscribed, while pydC, pydD, and pydE are each transcribed from separate promoters. PydA and PydB show no homology with other dioxygenases and hydrolases in Sinorhizobium meliloti, Mesorhizobium loti, and Bradyrhizobium japonicum. Among various root nodule bacteria, the ability to degrade mimosine or HP is unique to some Leucaena-nodulating Rhizobium strains.

G1/S cell cycle arrest provides anoikis resistance through Erk-mediated Bim suppression

Proper attachment to the extracellular matrix is essential for cell survival. Detachment from the extracellular matrix results in an apoptotic process termed anoikis. Anoikis induction in MCF-10A mammary epithelial cells is due not only to loss of survival signals following integrin disengagement, but also to consequent downregulation of epidermal growth factor (EGFR) and loss of EGFR-induced survival signals. Here we demonstrate that G(1)/S arrest by overexpression of the cyclin-dependent kinase inhibitors p16(INK4a), p21(Cip1), or p27(Kip1) or by treatment with mimosine or aphidicolin confers anoikis resistance in MCF-10A cells. G(1)/S arrest-mediated anoikis resistance involves suppression of the BH3-only protein Bim. Furthermore, in G(1)/S-arrested cells, Erk phosphorylation is maintained in suspension and is necessary for Bim suppression. Following G(1)/S arrest, known proteins upstream of Erk, including Raf and Mek, are not activated. However, retained Erk activation under conditions in which Raf and Mek activation is lost is observed, suggesting that G(1)/S arrest acts at the level of Erk dephosphorylation. Thus, anoikis resistance by G(1)/S arrest is mediated by a mechanism involving Bim suppression through maintenance of Erk activation. These results provide a novel link between cell cycle arrest and survival, and this mechanism could contribute to the survival of nonreplicating, dormant tumor cells that avert apoptosis during early stages of metastasis.