The cell cycle: a review

Cancer models in Caenorhabditis elegans

Although now dogma, the idea that nonvertebrate organisms such as yeast, worms, and flies could inform, and in some cases even revolutionize, our understanding of oncogenesis in humans was not immediately obvious. Aided by the conservative nature of evolution and the persistence of a cohort of devoted researchers, the role of model organisms as a key tool in solving the cancer problem has, however, become widely accepted. In this review, we focus on the nematode Caenorhabditis elegans and its diverse and sometimes surprising contributions to our understanding of the tumorigenic process. Specifically, we discuss findings in the worm that address a well-defined set of processes known to be deregulated in cancer cells including cell cycle progression, growth factor signaling, terminal differentiation, apoptosis, the maintenance of genome stability, and developmental mechanisms relevant to invasion and metastasis.

Systematic localization of the Arabidopsis core cell cycle proteins reveals novel cell division complexes

Cell division depends on the correct localization of the cyclin-dependent kinases that are regulated by phosphorylation, cyclin proteolysis, and protein-protein interactions. Although immunological assays can define cell cycle protein abundance and localization, they are not suitable for detecting the dynamic rearrangements of molecular components during cell division. Here, we applied an in vivo approach to trace the subcellular localization of 60 Arabidopsis (Arabidopsis thaliana) core cell cycle proteins fused to green fluorescent proteins during cell division in tobacco (Nicotiana tabacum) and Arabidopsis. Several cell cycle proteins showed a dynamic association with mitotic structures, such as condensed chromosomes and the preprophase band in both species, suggesting a strong conservation of targeting mechanisms. Furthermore, colocalized proteins were shown to bind in vivo, strengthening their localization-function connection. Thus, we identified unknown spatiotemporal territories where functional cell cycle protein interactions are most likely to occur.

Direct effects of fascaplysin on human umbilical vein endothelial cells attributing the anti-angiogenesis activity

Novel anti-angiogenesis activity of fascaplysin via VEGF blockage was recently revealed by our previous study in addition to the reported cyclin-dependent kinase 4 (CDK4) selective inhibition. To uncover more details of this pharmacologically prospective property, this study further investigated whether fascaplysin had direct anti-proliferation effects on human umbilical vein endothelial cells (HUVEC), which might be contributing to anti-angiogenesis. The results showed that G1 cell cycle arrest was induced by 2.6 μM fascaplysin in a time-dependent manner, and exhibited more sensitive than hepatocarcinoma cells BeL-7402 and Hela cells. Approximately 56.09 ± 2.63% of the cells were arrested at the G1 phase after 24h, and 64.94 ± 2.07% after 36 h, comparing to the 22.82 ± 1.2% in methanol treated cells. Apoptosis of HUVEC cells was induced by 1.3 μM fascaplysin and indicated by the sub-G1, Hoechst staining, terminal deoxynucleotidyl transferase dUTP-mediated nicked end labeling (TUNEL) assay, and annexin-V and propidium (PI) label. This apoptosis response was further confirmed by the detection of active caspase-3 and by western blotting using antibodies against Bax, Bcl-2, procaspase-8, and Bid, indicating that apoptosis in HUVEC cells may involve a mitochondria pathway, by the demonstration of an increase in the Bax/Bcl-2 ratio. Together, our results suggest that the anti-angiogenesis activity of fascaplysin is through the direct effects of cell cycle arrest and apoptosis on HUVEC.

Squamous cell carcinoma with presence of poxvirus-like inclusions in the foot of a pink-backed pelican (Pelecanus rufescens)

Squamous cell carcinoma (SCC) or avian keratoacanthoma is a neoplastic skin lesion of unknown aetiology that has been well described in birds. Some studies have reported that poxviruses may contribute to the onset of SCC. Here we describe a case of SCC on the underside of a pelican's foot. Histologically, the tumour consisted of irregular cords of pleomorphic epithelial cells that invaded the adjacent tissues. Additionally, keratinized epithelial cells and moderate numbers of keratin pearls were observed. Intracytoplasmic inclusions, a characteristic of this virus, were observed in some of these cells, and viral particles were characterized by electron microscopy. Although the aetiology of the carcinoma in this case may have been secondary to chronic focal trauma, the possibility of a latent or chronic form of fowlpox should be considered in the pathogenesis of the lesion.

The B cell translocation gene (BTG) family in the rat ovary: hormonal induction, regulation, and impact on cell cycle kinetics

The B cell translocation gene (BTG) family regulates gene transcription and cellular differentiation and inhibits proliferation. The present study investigated the spatiotemporal expression pattern of BTG members and their potential role in the rat ovary during the periovulatory period. Immature female rats (22-23 d old) were injected with pregnant mare serum gonadotropin to stimulate follicular development. Ovaries or granulosa cells were collected at various times after hCG administration (n = 3 per time point). Real-time PCR analysis revealed that mRNA for Btg1, Btg2, and Btg3 were highly induced both in intact ovaries and granulosa cells by 4-8 h after hCG treatment, although their temporal expression patterns differed. In situ hybridization analysis demonstrated that Btg1 mRNA expression was highly induced in theca cells at 4 h after hCG, primarily localized to granulosa cells at 8 h, and decreased at 24 h. Btg2 and Btg3 mRNA was also induced in granulosa cells; however, Btg2 mRNA was observed in newly forming corpora lutea. Inhibition of progesterone action and the epidermal growth factor pathway did not change Btg1 and Btg2 mRNA expression, whereas inhibition of prostaglandin synthesis or RUNX activity diminished Btg2 mRNA levels. Overexpression of BTG1 or BTG2 arrested granulosa cells at the G0/G1 phase of the cell cycle and decreased cell apoptosis. In summary, hCG induced Btg1, Btg2, and Btg3 mRNA expression predominantly in the granulosa cell compartment. Our findings suggest that the induction of the BTG family may be important for theca and granulosa cell differentiation into luteal cells by arresting cell cycle progression.

Ginsenoside Rh2-mediated G1 phase cell cycle arrest in human breast cancer cells is caused by p15 Ink4B and p27 Kip1-dependent inhibition of cyclin-dependent kinases

PURPOSE

Present study was undertaken to gain insights into the mechanism of cell cycle arrest by ginseng saponin ginsenoside Rh2 (Rh2) using MCF-7 and MDA-MB-231 breast cancer cells.

METHODS

Cell viability and cell cycle distribution were determined by trypan blue dye exclusion assay and flow cytometry, respectively. Immunoblotting was performed to determine changes in protein levels. Knockdown of desired protein was achieved by transfection with small interfering RNA (siRNA).

RESULTS

Rh2 treatment significantly inhibited viability of both cells in a concentration-dependent manner, which correlated with G(0)/G(1) phase cell cycle arrest. Rh2-mediated cell cycle arrest was accompanied by down-regulation of cyclin-dependent kinases (Cdk) and cyclins leading to decreased interaction between cyclin D1 and Cdk4/Cdk6 and increased recruitment of p15(Ink4B) and p27(Kip1) to cyclin D1/Cdk4 and cyclin D1/Cdk6 complexes. In addition, Rh2 treatment markedly reduced the levels of phosphorylated retinoblastoma protein (P-Rb) and decreased transcriptional activity of E2F1 in luciferase reporter assay. Rh2-induced cell cycle arrest was significantly attenuated by knockdown of p15(Ink4B) and/or p27(Kip1) proteins.

CONCLUSIONS

Rh2-mediated cell cycle arrest in human breast cancer cells is caused by p15(Ink4B) and p27(Kip1)-dependent inhibition of kinase activities of G(1)-S specific Cdks/cyclin complexes.

Flavopiridol reduces the impedance of neural prostheses in vivo without affecting recording quality

We hypothesized that re-entry into the cell cycle may be associated with reactive gliosis surrounding neural prostheses, and that administration of a cell cycle inhibitor (flavopiridol) at the time of surgery would reduce this effect. We investigated the effects of flavopiridol on recording quality and impedance over a 28-day time period and conducted histology at 3 and 28 days post-implantation. Flavopiridol reduced the expression of a cell cycle protein (cyclin D1) in microglia surrounding probes at the 3-day time point. Impedance at 1 kHz was decreased by drug administration across the study period compared to vehicle controls. Correlations between recording (SNR, units) and impedance metrics revealed a small, but statistically significant, inverse relationship between these variables. However, the relationship between impedance and recording quality was not sufficiently strong for flavopiridol to result in an improvement in SNR or the number of units detected. Our data indicate that flavopiridol is an effective, easily administered treatment for reducing impedance in vivo, potentially through inhibiting microglial encapsulation of implanted devices. This strategy may be useful in stimulation applications, where reduced impedance is desirable for achieving activation thresholds and prolonging the lifetime of the implanted power supply. While improvements in recording quality were not observed, a combination of flavopiridol with a second strategy which enhances neuronal signal detection may enhance these results in future studies.

FBA-TPQ, a novel marine-derived compound as experimental therapy for prostate cancer

We recently synthesized a series of novel makaluvamine compounds, and found that the most potent was FBA-TPQ. The effects of FBA-TPQ on human (LNCaP and PC3) and murine (TRAMP C1) prostate cancer cells were evaluated. Potential mechanisms of action of the compound were also determined. FBA-TPQ exhibited dose-dependent cytotoxicity in the low micromolar range, inhibited proliferation, caused cell cycle arrest, and induced apoptosis in prostate cancer cell lines. The compound also decreased the expression of the androgen receptor and PSA. The results presented herein support the further development of FBA-TPQ as a novel agent for prostate cancer.

Effects of low dose quercetin: cancer cell-specific inhibition of cell cycle progression

Quercetin is a flavonoid present in many vegetables, fruits, and beverages. Due to its anti-oxidant, anti-tumor, and anti-inflammatory activity, quercetin has been studied extensively as a chemoprevention agent in several cancer models. Since most of these studies used higher doses of quercetin than clinically achievable, we focused on the effectiveness of physiologically relevant doses of quercetin. A low dose of quercetin exerted cancer cell-specific inhibition of proliferation and this inhibition resulted from cell cycle arrest at the G(1) phase. Quercetin induced p21 CDK inhibitor with a concomitant decrease of phosphorylation of pRb, which inhibits the G(1)/S cell cycle progression by trapping E2F1. A low dose of quercetin induced mild DNA damage and Chk2 activation, which is the main regulator of p21 expression by quercetin. In addition, quercetin down-regulated the cyclin B1 and CDK1, essential components of G(2)/M cell cycle progression. Inhibition of the recruitment of key transcription factor NF-Y to cyclin B1 gene promoter by quercetin led to transcriptional inhibition. This study proved that the chemo-preventive efficacy of a physiologically relevant dose of quercetin can be achievable through the inhibition of cell cycle progression.

Deregulation of the cell cycle machinery by Epstein-Barr virus nuclear antigen 3C

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with a large number of lymphoid and epithelial malignancies. As a successful pathogen it has co-evolved with its human host for millions of years. EBV has the unique ability to establish life-long latent infection in primary human B lymphocytes. During latent infection, a small subset of viral proteins is expressed. These proteins are essential for maintenance of the EBV genome as well as the deregulation of various signaling pathways that facilitate the proliferation and survival of the infected cells. Epstein-Barr nuclear antigen (EBNA)3C is one of the latent proteins shown to be essential for transformation of primary human B lymphocytes in vitro. EBNA3C primarily functions as a transcriptional regulator by interacting with a number of well known cellular and viral transcriptional factors. We have recently identified several binding partners for EBNA3C including proteins that regulate cell cycle and chromatin remodeling. We are actively engaged in discerning the biological significance of these interactions. This review summarizes our current understanding of how EBNA3C usurps cellular pathways that promote B-cell transformation.

p21 is required for atRA-mediated growth inhibition of MEPM cells, which involves RAR

All-trans retinoic acid (atRA), a metabolite of vitamin A, is essential for embryonic development. Thus the spatial and temporal dispersal of RA must be tightly controlled. Previous studies show that excessive atRA led to growth inhibition and p21 accumulation in mouse embryonic palatal mesenchymal (MEPM) cells. We reported here the identification of p21 as a required mediator during atRA-induced growth inhibition. atRA caused a G1 arrest in the cell cycle with an increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S phase. In addition to a marked effect on cell cycling, atRA also triggered DNA fragmentation, reflected by an increase of the fraction of cells in the sub-G(1) population. Western blot analysis revealed that atRA treatment led to an increase in p21 level and a decrease in cyclin D1 protein and Rb phosphorylation. Using luciferase assay with reporter gene regulated by p21 promoter, we showed that atRA increased the reporter activity in a dose-dependent manner; and p21 siRNA blocked the growth inhibition by atRA, suggesting that p21 is required for atRA-mediated growth inhibition. Moreover, the induction of p21 by atRA was partially attenuated when RAR was silenced with specific siRNA. atRA stimulated RARE-driven reporter gene activity dose-dependently. Using chromatin immunoprecipitation, we demonstrated that RAR protein could bind to the p21 promoter. Taken together, our results indicate p21 is responsible for atRA-induced growth inhibition of MEPM cells and RAR plays a role during this process.

Transfection of adult canine Schwann cells and olfactory ensheathing cells at early and late passage with human TERT differentially affects growth factor responsiveness and in vitro growth

Adult canine Schwann cells and olfactory ensheathing cells (OECs) are closely related cell types that are considered attractive candidates for translational studies of neural repair. To establish a reliable cell source by comparing the in vitro properties of immortalized Schwann cells and OECs for transplantation purposes, we transfected both cell types with human telomerase reverse transcriptase (hTERT). Ectopic hTERT expression has been shown to induce immortalization of various cell types without substantial alterations of their phenotypes. Schwann cells and OECs were isolated from adult dogs, transfected with hTERT at early (P4) and late passage (P26), characterized regarding in vitro proliferation, antigenic expression and senescence-associated genes in the presence and absence of fibroblast growth factor-2 (FGF-2). Ectopic hTERT expression in late passage glia treated with but not without FGF-2 prevented the decline in proliferation observed in non-transfected cells. Immortalization did not alter p75(NTR) and GFAP but O4 and A2B5 expression. Contrary to this, early passage hTERT transfection significantly reduced proliferation independent of FGF-2 and lowered expression of O4 and GFAP in both cell types. Transfection did not alter mRNA expression of senescence-associated genes such as p53 and p16. No substantial differences were found between Schwann cells and OECs underscoring the close relationship of both cell types. Taken together, we established a stable source of adult canine Schwann cells and OECs and demonstrated that the effects of hTERT expression on in vitro growth and growth factor responsiveness depend on the replicative age.

Mechanisms of cell cycle control revealed by a systematic and quantitative overexpression screen in S. cerevisiae

Regulation of cell cycle progression is fundamental to cell health and reproduction, and failures in this process are associated with many human diseases. Much of our knowledge of cell cycle regulators derives from loss-of-function studies. To reveal new cell cycle regulatory genes that are difficult to identify in loss-of-function studies, we performed a near-genome-wide flow cytometry assay of yeast gene overexpression-induced cell cycle delay phenotypes. We identified 108 genes whose overexpression significantly delayed the progression of the yeast cell cycle at a specific stage. Many of the genes are newly implicated in cell cycle progression, for example SKO1, RFA1, and YPR015C. The overexpression of RFA1 or YPR015C delayed the cell cycle at G2/M phases by disrupting spindle attachment to chromosomes and activating the DNA damage checkpoint, respectively. In contrast, overexpression of the transcription factor SKO1 arrests cells at G1 phase by activating the pheromone response pathway, revealing new cross-talk between osmotic sensing and mating. More generally, 92%–94% of the genes exhibit distinct phenotypes when overexpressed as compared to their corresponding deletion mutants, supporting the notion that many genes may gain functions upon overexpression. This work thus implicates new genes in cell cycle progression, complements previous screens, and lays the foundation for future experiments to define more precisely roles for these genes in cell cycle progression.

All cells require proper cell cycle regulation; failure leads to numerous human diseases. Cell cycle mechanisms are broadly conserved across eukaryotes, with many key regulatory genes known. Nonetheless, our knowledge of regulators is incomplete. Many classic studies have analyzed yeast loss-of-function mutants to identify cell cycle genes. Studies have also implicated genes based upon their overexpression phenotypes, but the effects of gene overexpression on the cell cycle have not been quantified for all yeast genes. We individually quantified the effect of overexpression on cell cycle progression for nearly all (91%) of yeast genes, and we report the 108 genes causing the most significant and reproducible cell cycle defects, most of which have not been previously observed. We characterize three genes in more detail, implicating one in chromosomal segregation and mitotic spindle formation. A second affects mitotic stability and the DNA damage checkpoint. Curiously, overexpression of a third gene, SKO1, arrests the cell cycle by activating the pheromone response pathway, with cells mistakenly behaving as if mating pheromone is present. These results establish a basis for future experiments elucidating precise cell cycle roles for these genes. Similar assays in human cells could help further clarify the many connections between cell cycle control and cancers.

Experimental therapy of prostate cancer with novel natural product anti-cancer ginsenosides

BACKGROUND

Ginseng and its components exert various biological effects, including antioxidant, anti-carcinogenic, anti-mutagenic, and anti-tumor activity, and recent research has focused on their value in human cancer prevention and treatment. We recently isolated 25-hydroxyprotopanaxadiol (25-OH-PPD) and 25-hydroxyprotopanaxatriol (25-OH-PPT) from Panax ginseng and evaluated their anti-cancer activity in vitro.

METHODS

We compared the effects of the two compounds on human prostate cancer LNCaP and PC3 cells in vitro and in a mouse PC3 xenograft tumor model. We also accomplished a preliminary determination of the mechanisms of action of the compounds.

RESULTS

25-OH-PPD, but not 25-OH-PPT, inhibited prostate cancer cell growth and proliferation, induced apoptosis, and led to arrest in the G1 phase of the cell cycle. In nude mice bearing PC3 xenograft tumors, 25-OH-PPD inhibited tumor growth in a dose-dependent manner and could be safely combined with chemotherapeutic agents (taxotere and gemcitabine) and radiation therapy to improve the anti-tumor effects. Further, in both PC3 and LNCaP cell lines, 25-OH-PPD increased expression of p21, p27, and Bax, induced PARP cleavage and activated caspases. The compound also reduced expression of MDM2, E2F1, Bcl2, cdk2/4/6, and cyclin D1, which correlated with the cell cycle arrest in G1 and the decrease in proliferation. Moreover, 25-OH-PPD demonstrated low toxicity to non-cancer cells and no observable host toxicity in animals either alone or in combination with conventional therapies.

CONCLUSIONS

The newly identified ginsenoside 25-OH-PPD may have potential as a novel prostate cancer therapeutic agent.

Combinatorial modification of human histone H4 quantitated by two-dimensional liquid chromatography coupled with top down mass spectrometry

Quantitative proteomics has focused heavily on correlating protein abundances, ratios, and dynamics by developing methods that are protein expression-centric (e.g. isotope coded affinity tag, isobaric tag for relative and absolute quantification, etc.). These methods effectively detect changes in protein abundance but fail to provide a comprehensive perspective of the diversity of proteins such as histones, which are regulated by post-translational modifications. Here, we report the characterization of modified forms of HeLa cell histone H4 with a dynamic range >10(4) using a strictly Top Down mass spectrometric approach coupled with two dimensions of liquid chromatography. This enhanced dynamic range enabled the precise characterization and quantitation of 42 forms uniquely modified by combinations of methylation and acetylation, including those with trimethylated Lys-20, monomethylated Arg-3, and the novel dimethylated Arg-3 (each <1% of all H4 forms). Quantitative analyses revealed distinct trends in acetylation site occupancy depending on Lys-20 methylation state. Because both modifications are dynamically regulated through the cell cycle, we simultaneously investigated acetylation and methylation kinetics through three cell cycle phases and used these data to statistically assess the robustness of our quantitative analysis. This work represents the most comprehensive analysis of histone H4 forms present in human cells reported to date.

DAP5 promotes cap-independent translation of Bcl-2 and CDK1 to facilitate cell survival during mitosis

DAP5 is an eIF4G protein previously implicated in mediating cap-independent translation in response to cellular stresses. Here we report that DAP5 is crucial for continuous cell survival in nonstressed cells. The knockdown of endogenous DAP5 induced M phase-specific caspase-dependent apoptosis. Bcl-2 and CDK1 were identified by two independent screens as DAP5 translation targets. Notably, the activity of the Bcl-2 IRES was reduced in DAP5 knockdown cells and a selective shift of Bcl-2 mRNA toward light polysomal fractions was detected. Furthermore, a functional IRES was identified in the 5'UTR of CDK1. At the cellular level, attenuated translation of CDK1 by DAP5 knockdown decreased the phosphorylation of its M phase substrates. Ectopic expression of Bcl-2 or CDK1 proteins partially reduced the extent of caspase activation caused by DAP5 knockdown. Thus, DAP5 is necessary for maintaining cell survival during mitosis by promoting cap-independent translation of at least two prosurvival proteins.

Explorative data analysis of MCL reveals gene expression networks implicated in survival and prognosis supported by explorative CGH analysis

Background

Mantle cell lymphoma (MCL) is an incurable B cell lymphoma and accounts for 6% of all non-Hodgkin's lymphomas. On the genetic level, MCL is characterized by the hallmark translocation t(11;14) that is present in most cases with few exceptions. Both gene expression and comparative genomic hybridization (CGH) data vary considerably between patients with implications for their prognosis.

Methods

We compare patients over and below the median of survival. Exploratory principal component analysis of gene expression data showed that the second principal component correlates well with patient survival. Explorative analysis of CGH data shows the same correlation.

Results

On chromosome 7 and 9 specific genes and bands are delineated which improve prognosis prediction independent of the previously described proliferation signature. We identify a compact survival predictor of seven genes for MCL patients. After extensive re-annotation using GEPAT, we established protein networks correlating with prognosis. Well known genes (CDC2, CCND1) and further proliferation markers (WEE1, CDC25, aurora kinases, BUB1, PCNA, E2F1) form a tight interaction network, but also non-proliferative genes (SOCS1, TUBA1B CEBPB) are shown to be associated with prognosis. Furthermore we show that aggressive MCL implicates a gene network shift to higher expressed genes in late cell cycle states and refine the set of non-proliferative genes implicated with bad prognosis in MCL.

Conclusion

The results from explorative data analysis of gene expression and CGH data are complementary to each other. Including further tests such as Wilcoxon rank test we point both to proliferative and non-proliferative gene networks implicated in inferior prognosis of MCL and identify suitable markers both in gene expression and CGH data.

Human immunodeficiency virus infection inhibits granulocyte-macrophage colony-stimulating factor-induced microglial proliferation

It is well known that infection by the human immunodeficiency virus (HIV) dysregulates cell physiology, but little information is available on the consequences of HIV infection in primary macrophages and microglia. The authors examined the relationship between cell proliferation and HIV infection in primary cultures of microglia and in human central nervous system (CNS). In cultures infected with HIV (ADA and BaL), granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated cell proliferation was reduced in productively infected (p24+) cells as compared to p24- cells. The reduction was observed with both Ki67 and BrdU labeling, suggesting a G1/S block. The reduction was insignificant when microglia were infected with a Vpr- mutant virus. In human CNS, proliferating (Ki67+) cells were rare but were increased in the HIV+ and HIV encephalitis (HIVE) groups compared to the HIV- group. A positive correlation between GM-CSF immunoreactivity and Ki67 counts, implicating GM-CSF as a growth factor in human CNS was found. The relationship between total macrophage (CD68+) proliferation and infected macrophage (p24+) proliferation was assessed in HIVE by double labeling. Whereas 1.2% of total CD68+ cells were Ki67+, only 0.5% of HIV p24+ cells were Ki67+ (P < .05). Furthermore, staining for CD45RB (as opposed to CD68) facilitated the identification of Ki67+ microglia, indicating that CD68 could underestimate proliferating microglia. The authors conclude that although there is increased expression of GM-CSF and increased cell proliferation in the CNS of HIV-seropositive individuals, cell proliferation in the productively infected population is actually suppressed. These data suggest that there might be a viral gain in the suppressed host cell proliferation.

Regulation of the cellular DNA double-strand break response

DNA double-strand breaks occur frequently in cycling cells, and are also induced by exogenous sources, including ionizing radiation. Cells have developed integrated double-strand break response pathways to cope with these lesions, including pathways that initiate DNA repair (either via homologous recombination or nonhomologous end joining), the cell-cycle checkpoints (G1-S, intra-S phase, and G2-M) that provide time for repair, and apoptosis. However, before any of these pathways can be activated, the damage must first be recognized. In this review, we will discuss how the response of mammalian cells to DNA double-strand breaks is regulated, beginning with the activation of ATM, the pinnacle kinase of the double-strand break signalling cascade.

CDC-25.1 stability is regulated by distinct domains to restrict cell division during embryogenesis in C. elegans

Cdc25 phosphatases are key positive cell cycle regulators that coordinate cell divisions with growth and morphogenesis in many organisms. Intriguingly in C. elegans, two cdc-25.1(gf) mutations induce tissue-specific and temporally restricted hyperplasia in the embryonic intestinal lineage, despite stabilization of the mutant CDC-25.1 protein in every blastomere. We investigated the molecular basis underlying the CDC-25.1(gf) stabilization and its associated tissue-specific phenotype. We found that both mutations affect a canonical beta-TrCP phosphodegron motif, while the F-box protein LIN-23, the beta-TrCP orthologue, is required for the timely degradation of CDC-25.1. Accordingly, depletion of lin-23 in wild-type embryos stabilizes CDC-25.1 and triggers intestinal hyperplasia, which is, at least in part, cdc-25.1 dependent. lin-23(RNAi) causes embryonic lethality owing to cell fate transformations that convert blastomeres to an intestinal fate, sensitizing them to increased levels of CDC-25.1. Our characterization of a novel destabilizing cdc-25.1(lf) intragenic suppressor that acts independently of lin-23 indicates that additional cues impinge on different motifs of the CDC-25.1 phosphatase during early embryogenesis to control its stability and turnover, in order to ensure the timely divisions of intestinal cells and coordinate them with the formation of the developing gut.

p21-LacZ reporter mice reflect p53-dependent toxic insult

There is an urgent need to discover less toxic and more selective drugs to treat disease. The use of transgenic mice that report on toxic insult-induced transcription can provide a valuable tool in this regard. To exemplify this strategy, we have generated transgenic mice carrying a p21-LacZ transgene. Transgene activity reflected endogenous p21 gene activation in various tissues, displayed compound-specific spatial expression signatures in the brain and immune tissues and enabled p53-dependent and p53-independent responses to be identified. We discuss the application of these mice in delineating the molecular events in normal cellular growth and disease and for the evaluation of drug toxicity.

Insulin and IGF-1 mediated inhibition of apoptosis in CHO cells grown in suspension in a protein-free medium

When Chinese hamster ovary (CHO) cells were grown in suspension and deprived of serum, 40% of them became apoptotic after 72 hours, as determined by flow cytometry analysis of TUNEL-labelled cells. Cell viability, assessed by erythrocin B staining, decreased correspondingly. An increase in the total fraction of cells expressing interleukin converting enzyme (ICE; caspase 1), B-cell lymphoma 2 protein (Bcl-2,) and Bcl-2 associated x protein (Bax) was shown by antibody probing and subsequent flow cytometry. The p53 tumour suppressor gene product level remained low within the cell population. Insulin-like growth factor-1 (IGF-1) inhibited cell death in a concentration-dependent manner, and at 20 ng/ml, cell viability was maintained close to 100% and no apoptotic cells were detected. Also, insulin was shown to inhibit cell death - at 1.0 microg/ml, cell viability was 95%, whereas 10% of the cells stained for apoptosis. At the highest concentrations of IGF-1 and insulin, the expression of ICE, Bcl-2 and Bax was fully suppressed, whereas the p53 product level increased, despite still being detectable in a minority of cells. Under these conditions, IGF-1 may increase p53 expression to restrain abnormal cell proliferation. It is concluded that special attention should be paid to exposure and culture conditions that induce acquired susceptibility to a toxic insult, during the development and validation of cell-based assays.

p53 and retinoblastoma pathways in bladder cancer

A majority of the aggressive, invasive bladder carcinomas have alterations in the p53 and retinoblastoma genes and pathways. Examination of the alterations in the molecules in these pathways that regulate the cell cycle and their effects on the prognosis of bladder cancer are areas of active research. While defects in the p53-Mdm2-p14 axis have been implicated in urothelial cancer, perturbations in the cyclin-dependent kinases and their inhibitors have also been extensively studied in this context. Genetic alterations of the retinoblastoma gene and aberrant post-translational modifications of its protein have also been incriminated in invasive bladder cancer. This article reviews the individual prognostic roles of alterations in these molecules in the context of bladder cancer. Additionally, we review findings from recent studies that are attempting to analyze these markers in combination in an effort to construct molecular panels that can serve as more robust outcome predictors. More importantly, alterations in these molecules are now becoming enticing targets for novel therapeutics. We also review some of these agents that can restore the tumor cells' altered homeostatic mechanisms, thereby having potential in transitional cell carcinoma therapy. Future management of bladder cancer will employ validated marker panels for outcome prediction, and novel genetic and pharmacologic agents that will be able to target molecular alterations in individual tumors based on their respective profiles.

AU-rich-element-mediated upregulation of translation by FXR1 and Argonaute 2

AU-rich elements (AREs), present in mRNA 3'-UTRs, are potent posttranscriptional regulatory signals that can rapidly effect changes in mRNA stability and translation, thereby dramatically altering gene expression with clinical and developmental consequences. In human cell lines, the TNFalpha ARE enhances translation relative to mRNA levels upon serum starvation, which induces cell-cycle arrest. An in vivo crosslinking-coupled affinity purification method was developed to isolate ARE-associated complexes from activated versus basal translation conditions. We surprisingly found two microRNP-related proteins, fragile-X-mental-retardation-related protein 1 (FXR1) and Argonaute 2 (AGO2), that associate with the ARE exclusively during translation activation. Through tethering and shRNA-knockdown experiments, we provide direct evidence for the translation activation function of both FXR1 and AGO2 and demonstrate their interdependence for upregulation. This novel cell-growth-dependent translation activation role for FXR1 and AGO2 allows new insights into ARE-mediated signaling and connects two important posttranscriptional regulatory systems in an unexpected way.

USF inhibits cell proliferation through delay in G2/M phase in FRTL-5 cells

Upstream stimulatory factor (USF) has a negative effect on the cell proliferation in some cell types. However, its effect on thyrocytes is not clear. Therefore, we investigated the effects of USF on the proliferation and function of thyroid follicular cells. Complementary DNAs of the USF-1 and USF-2 were synthesized using RT-PCR from FRTL-5 cells, and each was transfected to FRTL-5 cells and papillary thyroid carcinoma cell lines. Cyclic AMP (cAMP) production and [methyl-3H] thymidine uptake after thyroid stimulating hormone (TSH) treatment were measured in FRTL-5 cells. In the carcinoma cell lines, 5-bromo-2'-deoxyuridine (BrdU) uptake was assayed to evaluate cell proliferation. Apoptosis was tested by Hoechst staining and cell cycle analysis was done using a fluorescence activated cell sorting. Expression of cell cycle regulating genes was evaluated by Northern and Western blotting. Overexpression of USF-1 and USF-2 significantly suppressed TSH-stimulated [methyl-3H] thymidine uptake (p<0.05), while it maintained TSH-stimulated cAMP production in FRTL-5 cells. Overexpression of USF significantly suppressed BrdU uptake in each carcinoma cell line, NPA and TPC-1 cells (p<0.05). It induced delay of cell cycle at the G2/M phase, but did not increase apoptosis in FRTL-5 cells. It was accompanied by a decrease of cyclin B1 and cyclin-dependent kinase (CDK)-1, and an increase of p27 expression. USF-1 and USF-2 suppressed cell proliferation of normal thyrocytes and thyroid carcinoma cells. However, they retained the ability to produce cAMP after TSH stimulation. Their inhibitory effect on cell proliferation might be caused partly by the delay in G2/M phase.

Immunohistochemical analysis for Mdm2 and p53 proteins in methylcholanthrene-induced mouse rhabdomyosarcomas

3-methylcholanthrene (MC)-induced mouse 10 embryonal (ERSs) and 24 pleomorphic rhabdomyosarcomas (PRSs) of the dermis were examined immunohistochemically for nuclear reactivity of Mdm2, p53, and proliferating cell nuclear antigen (PCNA). ERSs were microscopically present in the rhabdium layer of the dermis from 10 to 13 weeks post injection (PI), and PRSs developed from 13 weeks PI. Moderate to marked Mdm2 reactivity was observed in each of the 10 ERSs, and 23 of the 24 PRSs. Moderate to marked p53 reactivity was observed in 5 of the 10 ERSs, and 19 of the 24 PRSs. p53 reactivity increased in PRSs compared with ERSs. The level of Mdm2 expression was significantly higher compared with p53 expression. Discordant Mdm2 overexpression was observed in 5 ERSs and 5 PRSs, and discordant p53 overexpression was observed in 1 PRSs, although co-overexpression of Mdm2 and p53 was observed in 5 ERSs and 18 PRSs. PCNA reactivity significantly increased in PRSs compared with ERSs. These results suggest that Mdm2 overexpression is an important pathogenic event in MC-induced mouse rhabdomyosarcomas, and its expression may be induced by p53-independent pathway.

TACE release of TNF-alpha mediates mechanotransduction-induced activation of p38 MAPK and myogenesis

Skeletal muscle responds to mechanical stimulation by activating p38 MAPK, a key signal for myogenesis. However, the mechanotransduction mechanism that activates p38 is unknown. Here we show that mechanical stimulation of myoblasts activates p38 and myogenesis through stimulating TNF-alpha release by TNF-alpha converting enzyme (TACE). In C2C12 or mouse primary myoblasts cultured in growth medium, static stretch activated p38 along with ERK1/2, JNK and AKT. Disrupting TNF-alpha signaling by TNF-alpha-neutralizing antibody or knocking out TNF-alpha receptors blocked stretch activation of p38, but not ERK1/2, JNK or AKT. Stretch also activated differentiation markers MEF2C, myogenin, p21 and myosin heavy chain in a TNF-alpha- and p38-dependent manner. Stretch stimulated the cleavage activity of TACE. Conversely, TACE inhibitor TAPI or TACE siRNA abolished stretch activation of p38. In addition, conditioned medium from stretched myoblast cultures activated p38 in unstretched myoblasts, which required TACE activity in the donor myoblasts, and TNF-alpha receptors in the recipient myoblasts. These results indicate that posttranscriptional activation of TACE mediates the mechanotransduction that activates p38-dependent myogenesis via the release of TNF-alpha.

N-methylformamide and 9-hydroxystearic acid: two anti-proliferative and differentiating agents with different modes of action in colon cancer cells

N-methylformamide (NMF) is an anti-proliferative, differentiating agent studied in several cell lines as well as in preclinical and clinical trials, whose mechanisms of action are still unclear. 9-Hydroxystearic acid (9-HSA) is an endogenous product of lipid peroxidation recently identified as a new histone deacetylase 1 inhibitor. Both agents show the same anti-proliferative effects by arresting colon cancer cell growth in G0/G1. We addressed two questions. (i) Do they act by regulating G0/G1 checkpoint proteins? (ii) Does 9-HSA have differentiating effects comparable to those of NMF? The effects of NMF and 9-HSA on growth, differentiation and invasiveness of HT29, a colon cancer cell line, have been compared by using immunoprecipitation analysis, confocal microscopy, enzyme assays and invasiveness tests. The results show that the G1 arrest caused by NMF is a cell cycle exit due to p27 induction, whereas 9-HSA has no effect on the induction of this inhibitor. Evidence is presented that the arrest in early G0/G1 induced by 9-HSA is associated with the conversion of HT29 characteristics to those of a more benign phenotype, whereas the arrest in the late G1 in response to NMF is not followed by a decrease in tumorigenicity. The failure of NMF in cancer therapy indicates that both anti-proliferative and differentiating characteristics are required for an anti-tumoral agent to be effective.

TNF-alpha regulates myogenesis and muscle regeneration by activating p38 MAPK

Although p38 MAPK activation is essential for myogenesis, the upstream signaling mechanism that activates p38 during myogenesis remains undefined. We recently reported that p38 activation, myogenesis, and regeneration in cardiotoxin-injured soleus muscle are impaired in TNF-alpha receptor double-knockout (p55(-/-)p75(-/-)) mice. To fully evaluate the role of TNF-alpha in myogenic activation of p38, we tried to determine whether p38 activation in differentiating myoblasts requires autocrine TNF-alpha, and whether forced activation of p38 rescues impaired myogenesis and regeneration in the p55(-/-)p75(-/-) soleus. We observed an increase of TNF-alpha release from C2C12 or mouse primary myoblasts placed in low-serum differentiation medium. A TNF-alpha-neutralizing antibody added to differentiation medium blocked p38 activation and suppressed differentiation markers myocyte enhancer factor (MEF)-2C, myogenin, p21, and myosin heavy chain in C2C12 myoblasts. Conversely, recombinant TNF-alpha added to differentiation medium stimulated myogenesis at 0.05 ng/ml while inhibited it at 0.5 and 5 ng/ml. In addition, differentiation medium-induced p38 activation and myogenesis were compromised in primary myoblasts prepared from p55(-/-)p75(-/-) mice. Increased TNF-alpha release was also seen in cardiotoxin-injured soleus over the course of regeneration. Forced activation of p38 via the constitutive activator of p38, MKK6bE, rescued impaired myogenesis and regeneration in the cardiotoxin-injured p55(-/-)p75(-/-) soleus. These results indicate that TNF-alpha regulates myogenesis and muscle regeneration as a key activator of p38.

The immunomodulator AS101 induces growth arrest and apoptosis in Multiple Myeloma: Association with the Akt/Survivin pathway

Multiple Myeloma (MM) is a clonal B-cell malignancy affecting both the immune and the skeletal systems, and accounts for 10% of all hematological cancers. The immunomodulator ammonium trichloro (dioxoethylene-O,O') tellurate (AS101) is a non-toxic compound which has direct anti-tumoral properties in several tumor models. The present study examined the anti-tumoral activity of AS101 in MM by targeting the Akt/Survivin signaling pathway, crucial for survival. We showed that AS101 inhibites cell proliferation and colonies formation of MM cell lines, in a dose-dependent manner. AS101 induced G(2)/M growth arrest and increased both cyclin-dependent kinase inhibitor p21(waf1) protein levels and Cdk1 (p34(cdc2))-inhibitory phosphorylation. Longer incubation of MM cells with AS101 resulted in accumulation of apoptotic cell population and in increased caspase 9, 3 and 7 activities. We also showed that AS101 down-regulated Akt phosphorylation and decreased expression of the inhibitor of apoptosis, survivin. Since Akt and survivin are potentials targets for MM therapy, we suggest that AS101, currently being used in clinical studies, may have therapeutic implications in myeloma and other hematopoietic malignancies.

Identification of molecular markers and signaling pathway in endometrial cancer in Hong Kong Chinese women by genome-wide gene expression profiling

Endometrial cancer is the third most common gynecologic malignancy and the ninth most common malignancy for females overall in Hong Kong. Approximately 80% or more of these cancers are endometrioid endometrial adenocarcinomas. The aim of this study was to reveal genes contributing to the development of endometrioid endometrial cancer, which may impact diagnosis, prognosis and treatment of the disease. Whole-genome gene expression analysis was completed for a set of 55 microdissected sporadic endometrioid endometrial adenocarcinomas and 29 microdissected normal endometrium specimens using the Affymetrix Human U133 Plus 2.0 oligonucleotide microarray. Selected genes of interest were validated by quantitative real-time-polymerase chain reaction (qRT-PCR). Pathway analysis was performed to reveal gene interactions involved in endometrial tumorigenesis. Unsupervised hierarchical clustering displayed a distinct separation between the endometrioid adenocarcinomas and normal endometrium samples. Supervised analysis identified 117 highly differentially regulated genes (>or=4.0-fold change), which distinguished the endometrial cancer specimens from normal endometrium. Twelve novel genes including DKK4, ZIC1, KIF1A, SAA2, LOC16378, ALPP2, CCL20, CXCL5, BST2, OLFM1, KLRC1 and MBC45780 were deregulated in the endometrial cancer, and further validated in an independent set of 56 cancer and 29 normal samples using qRT-PCR. In addition, 10 genes were differentially regulated in late-stage cancer, as compared to early-stage disease, and may be involved in tumor progression. Pathway analysis of the expression data from this tumor revealed an interconnected network consisting of 21 aberrantly regulated genes involved in angiogenesis, cell proliferation and chromosomal instability. The results of this study highlight the molecular features of endometrioid endometrial cancer and provide insight into the events underlying the development and progression of endometrioid endometrial cancer.

Molecular biology of bladder cancer: prognostic and clinical implications

The role of various molecular determinants involved in the genesis, progression, and outcome of bladder cancer has been the focus of investigations for the past 2 decades. Increasingly, the analysis of the interplay between these molecular factors is taking center stage. We review herein the studies examining the effects of deregulation of the various molecules implicated in the cell cycle, apoptosis, and angiogenesis pathways and analyze the central role of p53 in regulating these pathways. Technological advancements enable detection and quantification of gene transcripts and protein products, helping us move toward achieving the goal of establishing diagnostic, prognostic, and therapeutic marker panels. Recent studies have therefore focused on multiple-marker analyses to generate informative panels that can have greater clinical value for bladder cancer management. The use of molecular marker panels can provide a more objective alternative to clinical parameters for diagnosis and treatment decisions. Clinical trials aimed at treating urothelial carcinoma based on a patient's molecular profile can be predicted to empower clinicians to personalize patient management through increased therapeutic efficacy.

Modulation of astrocyte proliferation by HIV-1: differential effects in productively infected, uninfected, and Nef-expressing cells

Although quiescent in normal brain, reactive astrocytes can proliferate in various disorders. We examined the impact of HIV-1 on astrocyte proliferation in cultures exposed to VSVg env-pseudotyped HIV-1 which yields high levels of infection. HIV-1, while increasing the proliferation of uninfected (p24-) astrocytes, strongly inhibited proliferation of productively infected (p24+) cells. The cell cycle arrest was G1/S rather than G2/M, a type commonly attributed to Vpr. No clear role of Vpr or Nef could be identified. Adenovirus-mediated expression of Nef (a model of "restricted" infection) induced M-phase arrest of astrocytes. We speculate that HIV-1 is a significant modulator of astrocyte proliferation in vivo.

Immunohistochemical expression of Mdm2 and p53 in canine cutaneous mast cell tumours

The objective of this study was to evaluate by immunohistochemical means nuclear reactivity for Mdm2 and p53 proteins in 71 canine cutaneous mast cell tumours. Detectable reactivity for Mdm2 was observed in 17 of 23 grade I tumours, 19 of 27 grade II tumours, and 14 of 21 grade III tumours, the grading method used was that by Patnaik et al. [Vet. Pathol., vol. 21, 1984, p. 469]. Increased reactivity for Mdm2 was detected in grade III tumours compared with grade I tumours. In contrast to Mdm2, detectable reactivity for p53 was observed in 17 tumours. Of 39 cases with moderate or marked Mdm2, 34 showed mild or no detectable p53, although only five showed moderate or marked p53. The results suggest that Mdm2 overexpression plays a crucial role in canine mast cell tumorigenesis and is consistent with the histologic grade, and its expression may be induced without p53 overexpression.

A novel mechanism of FSH regulation of DNA synthesis in the granulosa cells of hamster preantral follicles: involvement of a protein kinase C-mediated MAP kinase 3/1 self-activation loop

The objective was to reveal whether a protein kinase C (PKC [all isozymes])-mediated self-sustaining MAPK3/1 (3/1 extracellular signal regulated kinase 2/1, also known as ERK2/1) activation loop was necessary for FSH- or epidermal growth factor (EGF)-induced DNA synthesis in the granulosa cells of intact preantral follicles. For this purpose, hamster preantral follicles were cultured with FSH or EGF in the presence of selective kinase inhibitors FSH or EGF phosphorylated RAF1, MAP2K1, and MAPK3/1. However, a relatively higher dose of EGF was necessary to sustain the MAPK3/1 activity, which was essential for cyclin-dependent kinase 4 (CDK4) activation and DNA synthesis. In intact preantral follicles, FSH or EGF stimulated DNA synthesis only in the granulosa cells. Sustained activation of MAPK3/1 beyond 3 h was independent of EGFR kinase activity but dependent on PKC activity, which appeared to form a self-sustaining MAPK3/1 activation loop by activating RAF1, MAP2K1, and PLA2G4 (phospholipase A2 [all cytosolic isozymes]). Inhibition of PKC activity as late as 4 h after the administration of FSH or EGF arrested DNA synthesis, which corresponded with attenuated phosphorylation of RAF1 and MAPK3/1, thus suggesting an essential role of PKC in MAPK3/1 activation. Collectively, these data present a novel self-sustaining mechanism comprised of MAPK3/1, PLA2G4, PKC, and RAF1 for CDK4 activation leading to DNA synthesis in granulosa cells. Either FSH or EGF can activate the loop to activate CDK4 and initiate DNA synthesis; however, consistent with our previous findings, FSH effect seems to be mediated by EGF, which initiates the event by stimulating EGFR kinase.

Immunohistochemical Detection of p27 and p21 Proteins in Canine Hair Follicle and Epidermal Neoplasms

Trichoblastomas, trichoepitheliomas, and squamous cell carcinomas in the skin of dogs were analysed by immunohistochemistry for the nuclear expression of p27, p21 and proliferating cell nuclear antigen (PCNA). High levels of p27 were present in trichoepitheliomas and trichoblastomas compared with squamous cell carcinomas. Detectable p21 was found in trichoepitheliomas and squamous cell carcinomas, but trichoblastomas had low level of p21 nuclear reactivity. Low levels of PCNA were detected in trichoepitheliomas and trichoblastomas compared with squamous cell carcinomas. The results suggested that nuclear p27 acts as a cyclin-dependent kinase (CDK) inhibitor in trichoepitheliomas and trichoblastomas. Nuclear p21 expression is involved in the induction of epithelial differentiation and seems to be unrelated to CDK inhibition.

REGULATION OF ROOT APICAL MERISTEM DEVELOPMENT

The establishment of the Angiosperm root apical meristem is dependent on the specification of a stem cell niche and the subsequent development of the quiescent center at the presumptive root pole. Distribution of auxin and the establishment of auxin maxima are early formative steps in niche specification that depend on the expression and distribution of auxin carriers. Auxin specifies stem cell niche formation by directly and indirectly affecting gene activities. Part of the indirect regulation by auxin may involve changes in redox, favoring local, oxidized microenvironments. Formation of a QC is required for root meristem development and elaboration. Many signals likely pass between the QC and the adjacent root meristem tissues. Disappearance of the QC is associated with roots becoming determinate. Given the many auxin feedback loops, we hypothesize that roots evolved as part of an auxin homeostasis mechanism.

Role of TNF-{alpha} signaling in regeneration of cardiotoxin-injured muscle

Recent data suggest a physiological role for the proinflammatory cytokine TNF-alpha in skeletal muscle regeneration. However, the underlying mechanism is not understood. In the present study, we analyzed TNF-alpha-activated signaling pathways involved in myogenesis in soleus muscle injured by cardiotoxin (CTX) in TNF-alpha receptor double-knockout mice (p55(-/-)p75(-/-)). We found that activation of p38MAPK, which is critical for myogenesis, was blocked in CTX-injured p55(-/-)p75(-/-) soleus on day 3 postinjury when myogenic differentiation was being initiated, while activation of ERK1/2 and JNK MAPK, as well as transcription factor NF-kappaB, was not reduced. Consequently, the phosphorylation of transcription factor myocyte enhancer factor-2C, which is catalyzed by p38 and crucial for the expression of muscle-specific genes, was blunted. Meanwhile, expression of p38-dependent differentiation marker myogenin and p21 were suppressed. In addition, expression of cyclin D1 was fivefold that in wild-type (WT) soleus. These results suggest that myogenic differentiation is blocked or delayed in the absence of TNF-alpha signaling. Histological studies revealed abnormalities in regenerating p55(-/-)p75(-/-) soleus. On day 5 postinjury, new myofiber formation was clearly observed in WT soleus but not in p55(-/-)p75(-/-) soleus. To the contrary, p55(-/-)p75(-/-) soleus displayed renewed inflammation and dystrophic calcification. On day 12 postinjury, the muscle architecture of WT soleus was largely restored. Yet, in p55(-/-)p75(-/-) soleus, multifocal areas of inflammation, myofiber death, and myofibers with smaller cross-sectional area were observed. Functional studies demonstrated an attenuated recovery of contractile force in injured p55(-/-)p75(-/-) soleus. These data suggest that TNF-alpha signaling plays a critical regulatory role in muscle regeneration.

The carboxyl-terminal domain of RNA polymerase II is phosphorylated by a complex containing cdk9 and infected-cell protein 22 of herpes simplex virus 1

The infected-cell protein 22 (ICP22), a regulatory protein encoded by the alpha22 gene of herpes simplex virus 1, is required for the optimal expression of a set of late viral proteins that includes the products of the U(S)11, U(L)38, and U(L)41 genes. ICP22 has two activities. Thus, ICP22 and the U(L)13 protein kinase mediate the activation of cdc2 and degradation of its partners, cyclins A and B. cdc2 and its new partner, the DNA polymerase accessory factor (U(L)42), bind topoisomerase IIalpha in an ICP22-dependent manner. In addition, ICP22 and U(L)13 mediate an intermediate phosphorylation of the carboxyl terminus of RNA polymerase II (RNA POL II). Here we report another function of ICP22. Thus, ICP22 physically interacts with cdk9, a constitutively active cyclin-dependent kinase involved in transcriptional regulation. A protein complex containing ICP22 and cdk9 phosphorylates in vitro the carboxyl-terminal domain of RNA POL II in a viral U(S)3 protein kinase-dependent fashion. Finally, the carboxyl-terminal domain of RNA POL II fused to glutathione S-transferase is phosphorylated in reaction mixtures containing complexes pulled down with ICP22 or cdk9 immune precipitated from lysates of wild-type parent virus or deltaU(L)13 but not deltaU(S)3 mutant-infected cells. The experiments described here place ICP22 and cdk9 in a complex with the carboxyl-terminal domain of RNA POL II. At the same time we confirm the requirement of ICP22 and the U(L)13 protein kinase in the posttranslational modification of RNA POL II that alters its electrophoretic mobility, although U(S)3 kinase appears to play a role in a cell-type-dependent fashion.

Protein expression of Mdm2 and p53 in hyperplastic and neoplastic lesions of the canine circumanal gland

Hyperplastic and neoplastic lesions of the circumanal gland in dogs were examined immunohistochemically for nuclear expression of Mdm2 and p53 proteins. Mdm2 nuclear labelling was detected in 64.3% of hyperplastic lesions and 70.7% of adenomas, the immunolabelling being stronger in the latter. Mdm2 reactivity in reserve-like cells in adenomas showed wide variation, the immunoreactive cells ranging from 4 to 80%. No reactivity was shown in 81.9% of adenocarcinomas. In contrast to Mdm2 reactivity, each of 14 hyperplastic lesions and 11 adenocarcinomas, and 60 of 65 adenomas (92.3%) failed to show nuclear p53 reactivity. These results suggest that increased expression of Mdm2 is an early event in circumanal gland tumorigenesis, and may be present in the absence of nuclear p53 protein accumulation.

JAK-STAT signaling involved in phorbol 12-myristate 13-acetate- and dimethyl sulfoxide-induced 2'-5' oligoadenylate synthetase expression in human HL-60 leukemia cells

The JAK-STAT signal transduction cascade participates in various cellular processes, including immune response, cell replication, differentiation and oncogenesis. Here, we report that this cascade is induced in two human myeloid HL-60 leukemia cell variants by the granulocyte differentiation inducer dimethyl sulfoxide (DMSO) and macrophage differentiation inducer phorbol 12-myristate 13-acetate (PMA). DMSO and PMA also induced the expression and catalytic activity of 2'-5' oligoadenylate synthetase (2-5A synthetase), a known interferon (IFN) inducible enzyme. The HL-60 cell variants included HL-205, which is susceptible to DMSO- and PMA-induced differentiation, and HL-525, which is susceptible to DMSO- but not to PMA-induced differentiation. Treatment of HL-205 and HL-525 cells with DMSO and HL-205 cells with PMA-induced JAK1 phosphorylation, JAK1/STAT1 association, formation of STAT1-STAT2 heterodimers, and the binding of the active IFN stimulating growth factor 3 (ISGF3) to the IFN-stimulated response element (ISRE) fragment isolated from the 2-5A synthetase promoter. These events were either reduced or absent in the resistant HL-525 cells treated with PMA. Taken together, our data implicate the above signaling cascade in DMSO- and PMA-induced 2-5A synthetase expression and catalytic activity in the HL-60 cell system.