Visualizing surface plasmons with photons, photoelectrons, and electrons

Multidimensional imaging of surface plasmons via hyperspectral dark field optical microscopy, tip-enhanced Raman scattering, nonlinear photoemission electron microscopy, and electron energy loss spectroscopy.

Diethylnitrosamine genotoxicity evaluated in sprague dawley rats using pig-a mutation and reticulocyte micronucleus assays

Diethylnitrosamine (DEN) is a genotoxic carcinogen, but in vivo DNA-damaging activities are not usually evident in hematopoietic cells because the short-lived active metabolite is formed mainly in the liver. DEN therefore represented an interesting case for evaluating the performance characteristics of blood-based endpoints of genotoxicity that have been automated using flow cytometric analysis-frequency of micronucleated reticulocytes and Pig-a mutant phenotype reticulocytes (RET(CD59-) ) and erythrocytes (RBC(CD59-) ). Male Sprague Dawley rats were treated for 28 consecutive days with DEN at levels up to 12.5 mg/kg/day. Serial blood samples were collected and micronucleus frequencies were determined on Days 4 and 29, while RET(CD59-) and RBC(CD59-) frequencies were determined on Days 15, 29, and 42. The Pig-a analyses were conducted with an enrichment step based on immunomagnetic column separation to increase the statistical power of the assay. Modest but significant reductions to reticulocyte frequencies demonstrated that bone marrow was exposed to reactive intermediates. Even so, DEN did not affect micronucleus frequencies at any dose level tested. However, RET(CD59-) frequencies were significantly elevated in the high dose group on Day 29, and RBC(CD59-) were increased at this same dose level on Days 29 and 42. These results demonstrate that the Pig-a assay is sufficiently sensitive to evaluate chemicals for genotoxic potential, even in the case of a promutagen that has traditionally required direct assessment(s) of liver tissue for detection of DNA-damage.

Persistence of cisplatin-induced mutagenicity in hematopoietic stem cells: implications for secondary cancer risk following chemotherapy

Cisplatin is a cytostatic agent used in the treatment of many types of cancer, but its use is associated with increased incidences of secondary leukemia. We evaluated cisplatin's in vivo genotoxic potential by analyzing peripheral blood for Pig-a mutant phenotype erythrocytes and for chromosomal damage in the form of micronuclei. Mutant phenotype reticuloyte and erythrocyte frequencies, based on anti-CD59 antibody labeling and flow cytometric analysis, were determined in male Sprague Dawley rats treated for 28 consecutive days (days 1-28) with up to 0.4 mg cisplatin/kg/day, and sampled on days -4, 15, 29, and 56. Vehicle and highest dose groups were evaluated at additional time points post-treatment up to 6 months. Day 4 and 29 blood samples were also analyzed for micronucleated reticulocyte frequency using flow cytometry and anti-CD71-based labeling. Mutant phenotype reticulocytes were significantly elevated at doses ≥0.1 mg/kg/day, and mutant phenotype erythrocytes were elevated at doses ≥0.05 mg/kg/day. In the 0.4 mg/kg/day group, these effects persisted for the 6 month observation period. Cisplatin also induced a modest but statistically significant increase in micronucleus frequency at the highest dose tested. The prolonged persistence in the production of mutant erythrocytes following cisplatin exposure suggests that this drug mutates hematopoietic stem cells and that this damage may ultimately contribute to the increased incidence of secondary leukemias seen in patients cured of primary malignancies with platinum-based regimens.

Pig-a gene mutation and micronucleated reticulocyte induction in rats exposed to tumorigenic doses of the leukemogenic agents chlorambucil, thiotepa, melphalan, and 1,3-propane sultone

To evaluate whether blood-based genotoxicity endpoints can provide temporal and dose-response data within the low-dose carcinogenic range that could contribute to carcinogenic mode of action (MoA) assessments, we evaluated the sensitivity of flow cytometry-based micronucleus and Pig-a gene mutation assays at and below tumorigenic dose rate 50 (TD50) levels. The incidence of micronucleated reticulocytes (MN-RET) was used to evaluate chromosomal damage, and the frequency of CD59-negative reticulocytes (RET(CD59-) ) and erythrocytes (RBC(CD59-) ) served as phenotypic reporters of mutation at the X-linked Pig-a gene. Several leukemogenic agents with a presumed genotoxic MoA were studied. Specifically, male Sprague Dawley rats were treated via oral gavage for 28 days with chlorambucil, thiotepa, melphalan, and 1,3-propane sultone at doses corresponding to 0.33x, 1x, and 3x TD50, as well as at the maximum tolerated dose. Frequencies of MN-RET were determined at Days 4 and 29, and RET(CD59-) and RBC(CD59-) data were collected pretreatment as well as Days 15/16, 29, and 56/57. Dose-related increases were observed for each endpoint, and time to maximal effect was consistently: MN-RET < RET(CD59-)  < RBC(CD59-) . For each of the chemicals studied, the genotoxic events occurred long before tumors or preneoplastic lesions would be expected. Furthermore, in the case of Pig-a gene mutation, the responses were observed at or below the TD50 dose for three out of the four chemicals studied. These data illustrate the potential for quantitative blood-based analyses to provide dose-response and temporality information that relates genetic damage to cancer induction.

Follicle-stimulating hormone stimulates protein kinase A-mediated histone H3 phosphorylation and acetylation leading to select gene activation in ovarian granulosa cells

We examined the phosphorylation and acetylation of histone H3 in ovarian granulosa cells stimulated to differentiate by follicle-stimulating hormone (FSH). We found that protein kinase A (PKA) mediates H3 phosphorylation on serine 10, based on inhibition exclusively by PKA inhibitors. FSH-stimulated H3 phosphorylation in granulosa cells is not downstream of mitogen-activated protein kinase/extracellular signal-regulated kinase, ribosomal S6 kinase-2, mitogen- and stress-activated protein kinase-1, p38 MAPK, phosphatidylinositol-3 kinase, or protein kinase C. Transcriptional activation-associated H3 phosphorylation on serine 10 and acetylation of lysine 14 leads to activation of serum glucocorticoid kinase, inhibin alpha, and c-fos genes. We propose that phosphorylation of histone H3 on serine 10 by PKA in coordination with acetylation of H3 on lysine 14 results in reorganization of the promoters of select FSH responsive genes into a more accessible configuration for activation. The unique role of PKA as the physiological histone H3 kinase is consistent with the central role of PKA in initiating granulosa cell differentiation.

Developmental regulation of mitogen-activated protein kinase-activated kinases-2 and -3 (MAPKAPK-2/-3) in vivo during corpus luteum formation in the rat

The current study investigates the activation in vivo and regulation of the expression of components of the p38 mitogen-activated protein kinase (MAPK) pathway during gonadotropin-induced formation and development of the rat corpus luteum, employing a sequential PMSG/human CG (hCG) treatment paradigm. We postulated that the p38 MAPK pathway could serve to promote phosphorylation of key substrates during luteal maturation, since maturing luteal cells, thought to be cAMP-nonresponsive, nevertheless maintain critical phosphoproteins. Both p38 MAPK and its upstream activator MAPK kinase-6 (MKK6) were found to be chronically activated during the luteal maturation phase, with activation detected by 24 h post hCG and maintained through 4 days post hCG. The p38 MAPK downstream protein kinase target termed MAPK-activated protein kinase-3 (MAPKAPK-3) was newly induced at both mRNA and protein levels during luteal formation and maturation, while mRNA and protein expression of the closely related MAPKAPK-2 diminished. Two potential substrates for MAPKAPKs, the small heat shock protein HSP-27 and the cAMP regulatory element binding protein CREB, were monitored in vivo for phosphorylation. HSP-27 phosphorylation was not modulated during luteal maturation. In contrast, we observed sustained luteal-phase CREB phosphorylation in vivo, consistent with upstream MKK6/p38 MAPK activation and MAPKAPK-3 induction. MAPKAPK-3-specific immune complex kinase assays provided direct evidence that MAPKAPK-3 was in an activated state during luteal maturation in vivo. Cellular inhibitor studies indicated that an intact p38 MAPK path was required for CREB phosphorylation in a cellular model of luteinization, as treatment of luteinized granulosa cells with the p38 MAPK inhibitor SB 203580 strongly inhibited CREB phosphorylation. Transient transfection studies provided direct evidence that MAPKAPK-3 was capable of signaling to activate CREB transcriptional activity, as assessed by means of GAL4-CREB fusion protein construct coexpressed with GAL4-luciferase reporter construct. Introduction of wild-type, but not kinase-dead mutant, MAPKAPK-3 cDNA, into a mouse ovarian cell line stimulated GAL4-CREB- dependent transcriptional activity approximately 3-fold. Thus MAPKAPK-3 is indeed uniquely poised to support luteal maturation through the phosphorylation and activation of the nuclear transcription factor CREB.

Protein kinase C and meiotic regulation in isolated mouse oocytes

In this study, the possible role of protein kinase C (PKC) in mediating both positive and negative actions on meiotic maturation in isolated mouse oocytes has been examined. When cumulus cell-enclosed oocytes (CEO) were cultured for 17-18 hr in a medium containing 4 mM hypoxanthine (HX) to maintain meiotic arrest, each of the five different activators and five different antagonists of PKC stimulated germinal vesicle breakdown (GVB) in a dose-dependent fashion. One of the activators, phorbol-12-myristate 13-acetate (PMA), also triggered GVB in CEO arrested with isobutylmethylxanthine or guanosine, but not in those arrested with dibutyryl cyclic AMP. When denuded oocytes (DO) were cultured for 3hr in inhibitor-free medium, all PKC activators suppressed maturation (<10% GVB compared to 94% in controls), while the effect of PKC antagonists was negligible. Four of the five antagonists reversed the meiosis-arresting action of HX in DO. PMA transiently arrested the spontaneous maturation of both CEO and DO, with greater potency in DO. The stimulatory action of PMA in HX-arrested oocytes was dependent on cumulus cells, because meiotic induction occurred in CEO but not DO. PKC activators also preferentially stimulated cumulus expansion when compared to antagonists. A cell-cell coupling assay determined that the action of PMA on oocyte maturation was not due to a loss of metabolic coupling between the oocyte and cumulus oophorus. Finally, Western analysis demonstrated the presence of PKCs alpha, beta1, delta, and eta in both cumulus cells and oocytes, but only PKC epsilon was detected in the cumulus cells. It is concluded that direct activation of PKC in the oocyte suppresses maturation, while stimulation within cumulus cells generates a positive trigger that leads to meiotic resumption.

A major, transformation-sensitive PKC-binding protein is also a PKC substrate involved in cytoskeletal remodeling

Protein kinase C (PKC) plays a major role in regulating cell growth, transformation, and gene expression; however, identifying phosphorylation events that mediate these responses has been difficult. We expression-cloned a group of PKC-binding proteins and identified a high molecular weight, heat-soluble protein as the major PKC-binding protein in REF52 fibroblasts (Chapline, C., Mousseau, B., Ramsay, K., Duddy, S., Li, Y., Kiley, S. C., and Jaken, S. (1996) J. Biol. Chem. 271, 6417-6422). In this study, we demonstrate that this PKC-binding protein, clone 72, is also a PKC substrate in vitro and in vivo. Using a combination of phosphopeptide mapping, Edman degradation, and electrospray mass spectrometry, serine residues 283, 300, 507, and 515 were identified as the major in vitro PKC phosphorylation sites in clone 72. Phosphorylation state-selective antibodies were raised against phosphopeptides encompassing each of the four phosphorylation sites. These antibodies were used to determine that phorbol esters stimulate phosphorylation of serines 283, 300, 507, and 515 in cultured cells, indicating that clone 72 is directly phosphorylated by PKC in living cells. Phosphorylated clone 72 preferentially accumulates in membrane protrusions and ruffles, indicating that PKC activation and clone 72 phosphorylation are involved in membrane-cytoskeleton remodeling. These data lend further evidence to the model that PKCs directly interact with, phosphorylate, and modify the functions of a group of substrate proteins, STICKs (substrates that interact with C-kinase).

Follicle stimulating hormone (FSH) activates the p38 mitogen-activated protein kinase pathway, inducing small heat shock protein phosphorylation and cell rounding in immature rat ovarian granulosa cells

This study investigates the possibility that FSH activates the p38 mitogen-activated protein kinase (MAPK) pathway in immature granulosa cells (GC). FSH induced the phosphorylation (activation) of p38 MAPK as evaluated by immunoprecipitation and by phosphorylation-specific immunoblotting. FSH-induced phosphorylation of p38 MAPK was blocked by pretreatment with the protein kinase A (PKA) inhibitor H89 and mimicked by the cAMP generating agonist forskolin, indicating that FSH-induced cAMP production and PKA activation are necessary and sufficient for the activation of p38 MAPK in GC. The small heat shock protein HSP-27 comprises a downstream phosphorylation target for the p38 MAPK pathway. FSH-induced phosphorylation of HSP-27 was blocked by pretreatment with the p38 MAPK inhibitor SB 203580, indicating that p38 MAPK activation is necessary for FSH-induced HSP-27 phosphorylation. FSH-induced GC rounding/aggregation was blocked by pretreatment with SB 203580 indicating that p38 MAPK activation is necessary for FSH-induced GC cell shape change. The results of these experiments show that the p38 MAPK pathway is activated in GC in response to FSH in a cAMP/PKA-dependent manner, and that p38 MAPK activity is required for FSH-induced HSP-27 phosphorylation as well as rounding/aggregation in GC.