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At least 253 records · Page 14Linked to original sources
PubMed2007

All-trans retinoic acid induces proliferation of an irradiated stem cell supporting stromal cell line AFT024.

OBJECTIVE: We have previously shown that all-trans retinoic acid (ATRA) enhanced the maintenance of early human hematopoietic progenitor cells (HPCs) in the presence of an irradiated stromal cell line AFT024. In this study, we examined the effects of ATRA on the stromal cell component with particular reference to cellular proliferation and gene expression. METHODS: Irradiated AFT024 cells were cultured in Dulbecco's Modified Eagle's Medium supplemented with fetal bovine serum and were incubated with ATRA at 1 mumol/L up to 21 days. The cells were examined in terms of immunostaining for proliferative cell nuclear antigen (PCNA) and BrdU incorporation, apoptosis assay, cell cycle analysis, and gene expression using semiquantitative reverse-transcriptase polymerase chain reaction. RESULTS: In the control experiments, AFT024 cells lost their confluence in culture after 15-Gy irradiation and were arrested in G2/M phase on days 7 and 21. ATRA restored the cellular confluence with an increase in proliferation on day 21 (BrdU incorporation: 20.6-fold; PCNA staining: 51.7-fold) with reversal of cell cycle arrest (S phase: 2.7-fold increase; G2/M phase: 2.0-fold decrease). There was no effect on apoptosis as shown by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. ATRA significantly upregulated the expression of cell cycle genes for checkpoint transition, including cyclin A2, B2, and aurora kinase B, as well as genes associated with a putative role in HPC maintenance, including osteopontin, HoxA5, enhancer of zeste homolog 2, and peroxisome proliferator-activated receptor gamma. CONCLUSION: We concluded that ATRA induced cellular proliferation of irradiated AFT024 cells and expression of a number of genes whose relevance to HPC homeostasis would have to be further examined.

Animals↗
PubMed2004

Spatial and temporal gene expression profiling of the contused rat spinal cord.

Microarray technology was used to examine gene expression changes following contusive injury of the adult rat spinal cord. To obtain a global understanding of the changes triggered by the injury, differential gene expression was examined spatially, using tissue samples from the epicenter of injury as well as 1 cm rostral and 1 cm caudal to the epicenter, and temporally, at 3 h, 24 h, 7 days, and 35 days post-injury. To filter out gene expression changes that were due to the laminectomy, samples of contused tissue were compared to laminectomy-only controls. We took advantage of four different, complementary methods of data analysis to detect differentially expressed genes. We have identified functional groups of genes that are differentially regulated in our model, including those associated with apoptosis, cell cycle, inflammation, and cholesterol metabolism. Our analysis has led to the identification of novel potential therapeutic targets within each group of genes that is discussed.

Animals↗
PubMed2006

Acute injury directs the migration, proliferation, and differentiation of solid organ stem cells: evidence from the effect of hypoxia-ischemia in the CNS on clonal "reporter" neural stem cells.

Clonal neural cells with stem-like features integrate appropriately into the developing and degenerating central and peripheral nervous system throughout the neuraxis. In response to hypoxic-ischemic (HI) injury, previously engrafted, integrated, and quiescent clonal neural stem cells (NSCs) transiently re-enter the cell cycle, migrate preferentially to the site of ischemia, and differentiate into neurons and oligodendrocytes, the neural cell types typically lost following HI brain injury. They also replenish the supply of immature uncommitted resident stem/progenitor cells. Although they yield astrocytes, scarring is inhibited. These responses appear to occur most robustly within a 3-7 day "window" following HI during which signals are elaborated that upregulate genetic programs within the NSC that mediate proliferation, migration, survival, and differentiation, most of which appear to be terminated once the "window closes" and the chronic phase ensues, sending the NSCs into a quiescent state. These insights derived from using the stem cell in a novel role--as a "reporter" cell--to both track and probe the activity of endogenous stem cells as well as to "interrogate" and "report" the genes differentially induced by the acutely vs. chronically injured milieu. NSCs may be capable of the replacement of cells, genes, and non-diffusible factors in both a widespread or more circumscribed manner (depending on the therapeutic demands of the clinical situation). They may be uniquely responsive to some types of neurodegenerative conditions. We submit that these various capabilities are simply the normal expression of the basic homeostasis-preserving biologic properties and attributes of a stem cell which, if used rationally and in concert with this biology, may be exploited for therapeutic ends.

Animals↗
PubMed2004

Mitochondria damage checkpoint in apoptosis and genome stability.

Mitochondria perform multiple cellular functions including energy production, cell proliferation and apoptosis. Studies described in this paper suggest a role for mitochondria in maintaining genomic stability. Genomic stability appears to be dependent on mitochondrial functions involved in maintenance of proper intracellular redox status, ATP-dependent transcription, DNA replication, DNA repair and DNA recombination. To further elucidate the role of mitochondria in genomic stability, I propose a mitochondria damage checkpoint (mitocheckpoint) that monitors and responds to damaged mitochondria. Mitocheckpoint can coordinate and maintain proper balance between apoptotic and anti-apoptotic signals. When mitochondria are damaged, mitocheckpoint can be activated to help cells repair damaged mitochondria, to restore normal mitochondrial function and avoid production of mitochondria-defective cells. If mitochondria are severely damaged, mitocheckpoint may not be able to repair the damage and protect cells. Such an event triggers apoptosis. If damage to mitochondria is continuous or persistent such as damage to mitochondrial DNA resulting in mutations, mitocheckpoint may fail which can lead to genomic instability and increased cell survival in yeast. In human it can cause cancer. In support of this proposal we provide evidence that mitochondrial genetic defects in both yeast and mammalian systems lead to impaired DNA repair, increased genomic instability and increased cell survival. This study reveals molecular genetic mechanisms underlying a role for mitochondria in carcinogenesis in humans.

Adenosine Triphosphate↗
PubMed2004

Ability of human CDC25B phosphatase splice variants to replace the function of the fission yeast Cdc25 cell cycle regulator.

CDC25 phosphatases are essential and evolutionary-conserved actors of the eukaryotic cell cycle control. To examine and compare the properties of three splicing variants of human CDC25B, recombinant fission yeast strains expressing the human proteins in place of the endogenous Cdc25 were generated and characterized. We report, that the three CDC25B variants: (i) efficiently replace the yeast counterpart in vegetative growth, (ii) partly restore the gamma and UV radiation DNA damage-activated checkpoint, (iii) fail to restore the DNA replication checkpoint activated by hydroxyurea. Although these yeast strains do not reveal the specific functions of the human CDC25B variants, they should provide useful screening tools for the identification of new cell cycle regulators and pharmacological inhibitors of CDC25 phosphatase.

Alternative Splicing↗
PubMed2004

The early impact of genetics on our understanding of cell cycle regulation in Aspergillus nidulans.

The application of genetic analysis was crucial to the rapid progress that has been made in cell cycle research. Ron Morris, one of the first to apply genetics to cell cycle research, developed Aspergillus nidulans into an important model system for the analysis of many aspects of cell biology. Within the area of cell cycle research, Ron's laboratory is noted for development of novel cell biological and molecular genetic approaches as well as seminal insights regarding the regulation of mitosis, checkpoint regulation of the cell cycle, and the role of microtubule-based motors in chromosome segregation. In this special edition of FGB dedicated to Ron Morris, and in light of the recent progress in fungal genomics, we review the outstanding contributions his work made to our understanding of mitotic regulation. Indeed, his efforts have provided many mutants and experimental tools along with the conceptual framework for current and future studies of mitosis in A. nidulans.

Aspergillus nidulans↗
PubMed2004

The role of endogenous and exogenous DNA damage and mutagenesis.

The field of DNA damage responsiveness in general, and the consequences of endogenous and exogenous base damage in DNA, in particular, has made new and exciting contributions to our increasing understanding of the initiation and progression of neoplasia in humans. This article presents some of the highlights in this area of investigation, with a particular emphasis on DNA repair, the tolerance of DNA damage and its contribution to mutagenesis, and DNA damage checkpoint regulation.

Bacteriocins↗
PubMed2004

DNA damage tumor suppressor genes and genomic instability.

Disruption of the mechanisms that regulate cell-cycle checkpoints, DNA repair, and apoptosis results in genomic instability and the development of cancer in multicellular organisms. The protein kinases ATM and ATR, as well as their downstream substrates Chk1 and Chk2, are central players in checkpoint activation in response to DNA damage. Histone H2AX, ATRIP, as well as the BRCT-motif-containing molecules 53BP1, MDC1, and BRCA1 function as molecular adapters or mediators in the recruitment of ATM or ATR and their targets to sites of DNA damage. The increased chromosomal instability and tumor susceptibility apparent in mutant mice deficient in both p53 and either histone H2AX or proteins that contribute to the nonhomologous end-joining mechanism of DNA repair indicate that DNA damage checkpoints play a pivotal role in tumor suppression.

Animals↗
PubMed2006

Is genomic evaluation feasible in endoscopic studies of Barrett's esophagus? A pilot study.

BACKGROUND: The global gene expression in Barrett's esophagus (BE) in comparison to adjacent or histologically similar tissues has not been extensively studied. OBJECTIVE: To test the feasibility of conducting gene arrays in endoscopically obtained mucosal specimens. DESIGN: Cross-sectional feasibility study. SETTING: The Houston Department of Veterans Affairs Medical Center. PATIENTS: We collected endoscopic biopsies from BE, normal esophagus, antrum, duodenum, and sigmoid colon from 5 patients with BE. RNA was extracted and subjected to cDNA microarrays and gene expression was compared between BE and control tissues. Reverse transcription-PCR was conducted to confirm some of the findings. MAIN OUTCOME MEASUREMENTS: Gene expression profiles in BE tissues and 4 control sites: squamous esophagus, antrum, duodenum, sigmoid colon. RESULTS: On average, 2 biopsies by disposable jumbo biopsy forceps provided approximately 5 microg required for microarrays. From the original number of 22,283 gene probes, 13,805 genes had a quality score of P < .05 and were subjected to further comparison. BE gene expression clustered most closely with that of antrum and least closely with squamous esophagus. Of the 587 genes that had significantly different expression between BE and duodenum, 246 were upregulated and 341 were downregulated in BE. The expression of genes involved in apoptosis, negative regulation of apoptosis, and inflammatory response was significantly lower in BE compared to squamous esophagus. None of the gene groups were significantly overexpressed in BE compared to squamous esophagus or antrum. The reverse transcription-PCR confirmed the results of microarrays. LIMITATIONS: Small sample size. CONCLUSIONS: Microarray-based studies are feasible in endoscopically obtained tissues. Differences in gene expression could identify potential markers and shed light on the pathogenesis of BE.

Aged↗
PubMed2005

Growth arrest of thyrotropic tumors by thyroid hormone is correlated with novel changes in Wnt-10A.

The molecular mechanism underlying thyroid hormone inhibition of thyrotrope cell growth is poorly understood. A comprehensive screen for T3-regulated genes involved in thyrotrope cell regulation was performed by Affymetrix MGU74A Genechip microarray analyses, which compared total RNA from hypothyroid versus 24 h T3-treated TtT-97 tumors. Of the 13,000 genes screened, a number of novel, T3-responsive candidate genes were identified. Within the Wnt family of growth factors, only Wnt-10A transcripts were abundantly expressed in hypothyroid TtT-97 tumors, and were down-regulated with T3 by 6 h of treatment. In addition, nuclear beta-catenin, which is a downstream mediator of canonical Wnt signaling, was decreased at the protein and functional levels. TtT-97 growth suppression was associated with decreased cyclin A transcript levels. We conclude that treatment of thyrotropic TtT-97 tumors with T3 resulted in the decreased expression of Wnt-10A, and that thyroid hormone may inhibit growth via cyclin A regulation.

Animals↗
PubMed2003

Cell cycle timing and developmental checkpoints in Caulobacter crescentus.

Development in Caulobacter reflects a level of complexity once thought only to exist in eukaryotic cells. The cell cycle and development are not isolated from each other, but are interdependent processes. Checkpoints are in place to ensure that both cell cycle and developmental processes are completed accurately before the next stage is initiated. The timing of these processes is regulated by signal transduction networks that integrate signals from DNA replication, cell division and development. These signal transduction networks achieve precise timing of the cell cycle and development by regulating temporal gene expression, and protein activity by dynamic spatial localization within the cell and timed proteolysis.

Caulobacter crescentus↗
PubMed2004

Polo-like kinase-1 controls recovery from a G2 DNA damage-induced arrest in mammalian cells.

DNA damage triggers multiple checkpoint pathways to arrest cell cycle progression. Less is known about the mechanisms that allow resumption of the cell cycle once checkpoint signaling is silenced. Here we show that while in undamaged cells several redundant pathways can promote the onset of mitosis, this redundancy is lost in cells recovering from a DNA damage-induced arrest. We demonstrate that Plk1 is crucial for mitotic entry following recovery from DNA damage. However, Plk1 is no longer required in cells depleted of Wee1, and we could show that Plk1 is involved in the degradation of Wee1 at the onset of mitosis. Thus, our data show that the cell cycle machinery is reset in response to DNA damage and that cells become critically dependent on Plk1-mediated degradation of Wee1 for their recovery.

Cell Cycle Proteins↗
PubMed2004

Phosphorylation of Cdc20 by Bub1 provides a catalytic mechanism for APC/C inhibition by the spindle checkpoint.

To ensure the fidelity of chromosome segregation, the spindle checkpoint blocks the ubiquitin ligase activity of APC/C(Cdc20) in response to a single chromatid not properly attached to the mitotic spindle. Here we show that HeLa cells depleted for Bub1 by RNA interference are defective in checkpoint signaling. Bub1 directly phosphorylates Cdc20 in vitro and inhibits the ubiquitin ligase activity of APC/C(Cdc20) catalytically. A Cdc20 mutant with all six Bub1 phosphorylation sites removed is refractory to Bub1-mediated phosphorylation and inhibition in vitro. Upon checkpoint activation, Bub1 itself is hyperphosphorylated and its kinase activity toward Cdc20 is stimulated. Ectopic expression of the nonphosphorylatable Cdc20 mutant allows HeLa cells to escape from mitosis in the presence of spindle damage. Therefore, Bub1-mediated phosphorylation of Cdc20 is required for proper checkpoint signaling. We speculate that inhibition of APC/C(Cdc20) by Bub1 in a catalytic fashion may partly account for the exquisite sensitivity of the spindle checkpoint.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2004

Differential basal expression of genes associated with stress response, damage control, and DNA repair among mouse tissues.

Efficient recognition and repair of DNA damage is essential for maintaining genomic integrity. Tissues and cell types within tissues appear to vary in both DNA damage susceptibilities and cancer incidences, yet the molecular mechanisms underlying these differences are not well understood. The purpose of this study was to characterize the baseline transcription profiles of selected genes involved in DNA damage recognition and repair processes among several tissues of healthy adult B6C3F1 mice (testis, brain, liver, spleen and heart), which are routinely used by the National Toxicology Program (NTP) to conduct long-term chemical carcinogenicity studies. Stress response, damage control and DNA repair-associated genes were differentially expressed among the tissues examined. Overall, stress response genes exhibited the greatest variation among tissues with the highest expression in liver and heart while DNA repair genes exhibited the least variation. Damage control genes associated with cell cycle regulation and DNA repair genes generally had the highest expression in testis. The expression levels of several genes were rank correlated with the spontaneous cancer incidences among these tissues. Variations in basal expression of DNA damage recognition and repair-associated genes among healthy tissues may contribute to their differential response to genotoxic agents and susceptibility to genetic disease.

Animals↗
PubMed2005

Distinct disease mechanisms in peripheral neuropathies due to altered peripheral myelin protein 22 gene dosage or a Pmp22 point mutation.

Point mutations affecting PMP22 can cause hereditary demyelinating and dysmyelinating peripheral neuropathies. In addition, duplication and deletion of PMP22 are associated with Charcot-Marie-Tooth disease Type 1A (CMT1A) and Hereditary Neuropathy with Liability to Pressure Palsy (HNPP), respectively. This study was designed to elucidate disease processes caused by misexpression of Pmp22 and, at the same time, to gain further information on the controversial molecular function of PMP22. To this end, we took advantage of the unique resource of a set of various Pmp22 mutant mice to carry out comparative expression profiling of mutant and wild-type sciatic nerves. Tissues derived from Pmp22-/- ("knockout"), Pmp22tg (increased Pmp22 copy number), and Trembler (Tr; point mutation in Pmp22) mutant mice were analyzed at two developmental stages: (i) at postnatal day (P)4, when normal myelination has just started and primary causative defects of the mutations are expected to be apparent, and (ii) at P60, with the goal of obtaining information on secondary disease effects. Interestingly, the three Pmp22 mutants exhibited distinct profiles of gene expression, suggesting different disease mechanisms. Increased expression of genes involved in cell cycle regulation and DNA replication is characteristic and specific for the early stage in Pmp22-/- mice, supporting a primary function of PMP22 in the regulation of Schwann cell proliferation. In the Tr mutant, a distinguishing feature is the high expression of stress response genes. Both Tr and Pmp22tg mice show strongly reduced expression of genes important for cholesterol synthesis at P4, a characteristic that is common to all three mutants at P60. Finally, we have identified a number of candidate genes that may play important roles in the disease process or in myelination per se.

Animals↗
PubMed2005

Molecular mechanisms of hydroxyurea(HU)-induced apoptosis in the mouse fetal brain.

Hydroxyurea (HU), a potent mammalian teratogen, affects proliferating embryonic cells and inhibits DNA synthesis. The teratogenic potential of HU has been well known in experimental animals for several decades. In this study, we investigated molecular mechanisms of HU-induced apoptosis in the telencephalon of the fetal brain by exposing pregnant mice to HU on day 13 of gestation. The number of TUNEL-positive cells began to increase at 3 h, peaked at 12 h, and rapidly decreased at 24 h. Although changes of p53 mRNA expression were not observed by RT-PCR, a p53-positive reaction was detected immunohistochemically in the nuclei of neuroepithelial cells from 1 h to 6 h, and p53-protein expression was simultaneously identified by Western blot analysis. The expression of p53-target genes was detected at both the mRNA and protein. The mRNA levels of apotosis-related genes (fas, fasL, and bax) and cell cycle-related genes (mdm2 and p21) were significantly elevated, and the degree to and sequence in which these target genes expressed was similar to those for fas, fasL, mdm2 and p21. Flow-cytometric and Western blot analyses of cell cycle-related proteins suggested that neuroepithelial cells are arrested at the S checkpoint from 3 to 6 h and at the G2/M checkpoint at 12 h, respectively. HU-induced apoptosis is considered to be mediated by p53 in the fetal brain.

Animals↗
PubMed2006

Genes associated with early development, apoptosis and cell cycle regulation define a gene expression profile of adenoid cystic carcinoma.

Adenoid cystic carcinoma (ACC) is an uncommon salivary gland malignancy characterized by indolent yet relentless growth that exhibits inherent resistance to systemic chemotherapy, surgical salvage and conventional radiotherapy. We used microarray analysis to characterize gene expression changes associated with ACC. Eight ACC patient specimens were compared with normal parotid gland tissue and the ACC3 cell line. Differentially expressed genes were identified (512 total) using supervised analysis methods and functional categories assigned using OntoExpress. Genes associated with morphogenesis, neurogenesis, proliferation and apoptosis characterized ACC tumors. Genes associated with saliva production and immune response characterized normal parotid tissues while the ACC3 cell line expressed genes primarily associated with proliferation, chromosome maintenance and the cell cycle. These results demonstrate that ACC tumors express genes associated with early developmental processes including morphogenesis and neurogenesis implicating oncogenic events that result in dedifferentiation of normal salivary glands.

Adult↗