Mos and the cell cycle

Co-expression analysis identifies neuro-inflammation as a driver of sensory neuron aging in Aplysia californica

Aging of the nervous system is typified by depressed metabolism, compromised proteostasis, and increased inflammation that results in cognitive impairment. Differential expression analysis is a popular technique for exploring the molecular underpinnings of neural aging, but technical drawbacks of the methodology often obscure larger expression patterns. Co-expression analysis offers a robust alternative that allows for identification of networks of genes and their putative central regulators. In an effort to expand upon previous work exploring neural aging in the marine model Aplysia californica, we used weighted gene correlation network analysis to identify co-expression networks in a targeted set of aging sensory neurons in these animals. We identified twelve modules, six of which were strongly positively or negatively associated with aging. Kyoto Encyclopedia of Genes analysis and investigation of central module transcripts identified signatures of metabolic impairment, increased reactive oxygen species, compromised proteostasis, disrupted signaling, and increased inflammation. Although modules with immune character were identified, there was no correlation between genes in Aplysia that increased in expression with aging and the orthologous genes in oyster displaying long-term increases in expression after a virus-like challenge. This suggests anti-viral response is not a driver of Aplysia sensory neuron aging.

MRNA and miRNA expression patterns associated to pathways linked to metal mixture health effects

Metals are a threat to human health by increasing disease risk. Experimental data have linked altered miRNA expression with exposure to some metals. MiRNAs comprise a large family of non-coding single-stranded molecules that primarily function to negatively regulate gene expression post-transcriptionally. Although several human populations are exposed to low concentrations of As, Cd and Pb as a mixture, most toxicology research focuses on the individual effects that these metals exert. Thus, this study aims to evaluate global miRNA and mRNA expression changes induced by a metal mixture containing NaAsO2, CdCl2, Pb(C2H3O2)2·3H2O and to predict possible metal-associated disease development under these conditions. Our results show that this metal mixture results in a miRNA expression profile that may be responsible for the mRNA expression changes observed under experimental conditions in which coding proteins are involved in cellular processes, including cell death, growth and proliferation related to the metal-associated inflammatory response and cancer.

Involvement of polo-like kinase 1 (Plk1) in mitotic arrest by inhibition of mitogen-activated protein kinase-extracellular signal-regulated kinase-ribosomal S6 kinase 1 (MEK-ERK-RSK1) cascade

Cell division is controlled through cooperation of different kinases. Of these, polo-like kinase 1 (Plk1) and p90 ribosomal S6 kinase 1 (RSK1) play key roles. Plk1 acts as a G(2)/M trigger, and RSK1 promotes G(1) progression. Although previous reports show that Plk1 is suppressed by RSK1 during meiosis in Xenopus oocytes, it is still not clear whether this is the case during mitosis or whether Plk1 counteracts the effects of RSK1. Few animal models are available for the study of controlled and transient cell cycle arrest. Here we show that encysted embryos (cysts) of the primitive crustacean Artemia are ideal for such research because they undergo complete cell cycle arrest when they enter diapause (a state of obligate dormancy). We found that Plk1 suppressed the activity of RSK1 during embryonic mitosis and that Plk1 was inhibited during embryonic diapause and mitotic arrest. In addition, studies on HeLa cells using Plk1 siRNA interference and overexpression showed that phosphorylation of RSK1 increased upon interference and decreased after overexpression, suggesting that Plk1 inhibits RSK1. Taken together, these findings provide insights into the regulation of Plk1 during cell division and Artemia diapause cyst formation and the correlation between the activity of Plk1 and RSK1.

MAP kinases regulate unfertilized egg apoptosis and fertilization suppresses death via Ca2+signaling

The default fate for eggs from many species is death by apoptosis and thus, successful fertilization depends upon suppression of the maternal death program. Little is known about the molecular triggers which activate this process or how the fertilization signal suppresses the default maternal apoptotic pathway. The MAP kinase (MAPK) family member, ERK, plays a universal and critical role in several stages of oocyte meiotic maturation, and fertilization results in ERK inactivation. In somatic cells, ERK and other MAPK family members, p38 and JNK, provide opposing signals to regulate apoptosis, however, it is not known whether MAPKs play a regulatory role in egg apoptosis, nor whether suppression of apoptosis by fertilization is mediated by MAPK activity. Here we demonstrate that MAPKs are involved in starfish egg apoptosis and we investigate the relationship between the fertilization induced signaling pathway and MAPK activation. ERK is active in post-meiotic eggs just until apoptosis onset and then p38, JNK and a third kinase are activated, and remain active through execution. Sequential activation of ERK and p38 is necessary for apoptosis, and newly synthesized proteins are required both upstream of ERK and downstream of p38 for activation of the full apoptotic program. Fertilization causes a dramatic rise in intracellular Ca2+, and we report that Ca2+ provides a necessary and sufficient pro-survival signal. The Ca2+ pathway following fertilization of both young and aged eggs causes ERK to be rapidly inactivated, but fertilization cannot rescue aged eggs from death, indicating that ERK inactivation is not sufficient to suppress apoptosis.

Metaphase I arrest of starfish oocytes induced via the MAP kinase pathway is released by an increase of intracellular pH

Reinitiation of meiosis in oocytes usually occurs as a two-step process during which release from the prophase block is followed by an arrest in metaphase of the first or second meiotic division [metaphase I (MI) or metaphase II (MII)]. The mechanism of MI arrest in meiosis is poorly understood, although it is a widely observed phenomenon in invertebrates. The blockage of fully grown starfish oocytes in prophase of meiosis I is released by the hormone 1-methyladenine. It has been believed that meiosis of starfish oocytes proceeds completely without MI or MII arrest, even when fertilization does not occur. Here we show that MI arrest of starfish oocytes occurs in the ovary after germinal vesicle breakdown. This arrest is maintained both by the Mos/MEK/MAP kinase pathway and the blockage of an increase of intracellular pH in the ovary before spawning. Immediately after spawning into seawater, activation of Na+/H+ antiporters via a heterotrimeric G protein coupling to a 1-methyladenine receptor in the oocyte leads to an intracellular pH increase that can overcome the MI arrest even in the presence of active MAP kinase.

Expression of mos in astrocytic tumors and its potential role in neoplastic progression

The c-mos gene and its protein product mos, components of the mitogen-activated protein kinase transduction pathway, are known to be involved in the control of meiosis and mitosis. Apart from a study on lung carcinomas, there is little information about its role in human neoplasia. The aim of this study was to investigate expression of mos in astrocytic tumors and to correlate it with accumulation of p53. We studied expression of mos in 62 cases of supratentorial astrocytic tumor. Intracytoplasmic immunostaining for mos was found in 28 (45%) cases: 3 of 20 (15%) grade 2 astrocytomas, 9 of 20 (45%) grade 3 anaplastic astrocytomas, and 16 of 22 (73%) glioblastomas. Immunopositivity for mos correlated significantly (P < 0.01) with tumor grade but not with p53 expression. In contrast to the findings in relation to lung tumors, immunopositivity for mos in astrocytic tumors did not predict recurrence-free or overall survival time. Cytoplasmic immunostaining was observed in scattered large cortical neurons adjacent to tumors, possibly due to stress-induced abortive entry into the cell cycle. The correlation of mos immunopositivity with tumor grade may reflect the expansion of more malignant mos-positive clones. This study provides evidence that mos may be involved in the neoplastic progression of a proportion of astrocytic tumors.

Assignment of porcine cyclin-dependent kinase 4 (CDK4) and oncogene c-mos (MOS) by nonradioactive nonfluorescence in situ hybridization

Two pig genes, cyclin-dependent kinase 4 (CDK4) and the oncogene c-mos (MOS) were mapped by means of nonradioactive nonfluorescence in situ hybridization. Our approach was based on the detection of hybridized biotinylated probe by peroxidase conjugated extravidin and the reaction of peroxidase with its substrate diaminobenzidine (DAB) resulting in a dark precipitate. To increase the sensitivity of the method in single-copy gene mapping, two amplifications of the peroxidase signal were used: immunological amplification by biotinylated antiavidin, and peroxidase-catalysed deposition of biotinylated tyramide. Using this method, two 2-kb-long probes for the porcine genes CDK4 and MOS were mapped to pig chromosomes 5p12 and 4q14-15, respectively. Non-radioactive nonfluorescence in situ hybridization described here is a method of choice for gene mapping of short probes.

Calcium-mediated inactivation of the MAP kinase pathway in sea urchin eggs at fertilization

We have evaluated the regulation of a 43-kDa MAP kinase in sea urchin eggs. Both MAP kinase and MEK (MAP kinase kinase) are phosphorylated and active in unfertilized eggs while both are dephosphorylated and inactivated after fertilization, although with distinct kinetics. Reactivation of MEK or the 43-kDa MAP kinase prior to or during the first cell division was not detected. Confocal immunolocalization microscopy revealed that phosphorylated (active) MAP kinase is present primarily in the nucleus of the unfertilized egg, with some of the phosphorylated form in the cytoplasm as well. Incubation of unfertilized eggs in the MEK inhibitor U0126 (0.5 microM) resulted in the inactivation of MEK and MAP kinase within 30 min. Incubation in low concentrations of U0126 (sufficient to inactivate MEK and MAP kinase) after fertilization had no effect on progression through the embryonic cell cycle. Microinjection of active mammalian MAP kinase phosphatase (MKP-3) resulted in inactivation of MAP kinase in unfertilized eggs, as did addition of MKP-3 to lysates of unfertilized eggs. Incubation of unfertilized eggs in the Ca(2+) ionophore A23187 led to inactivation of MEK and MAP kinase with the same kinetics as observed with sperm-induced egg activation. This suggests that calcium may be deactivating MEK and/or activating a MAP kinase-directed phosphatase. A cell-free system was used to evaluate the activation of phosphatase separately from MEK inactivation. Unfertilized egg lysates were treated with U0126 to inactivate MEK and then Ca(2+) was added. This resulted in increased MAP kinase phosphatase activity. Therefore, MAP kinase inactivation at fertilization in sea urchin eggs likely is the result of a combination of MEK inactivation and phosphatase activation that are directly or indirectly responsive to Ca(2+).

Germinal vesicle materials are not required for the activation of MAP kinase in porcine oocyte maturation

The requirement of the germinal vesicle (GV) for the normal kinetics of mitogen-activated protein (MAP) kinase activity during porcine oocyte maturation was investigated. Porcine follicular oocytes were enucleated, and the locations of their extracellular signal-regulated kinases 1 and 2 (ERK1/2), major MAP kinases in maturating porcine oocytes, were detected by indirect immunofluorescent microscopy. The MAP kinase activity was assayed as myelin basic protein (MBP) kinase activity, and the phosphorylation states of ERK1/2 were detected by immunoblotting analyses. Translocation of MAP kinase into the GV and association with the spindle were observed in intact oocytes, while MAP kinase in enucleated oocytes was distributed almost uniformly in cytoplasm throughout the culturing period. The phosphorylation and the activation of MAP kinase were induced, and the activity was comparable with that of control denuded oocytes. The high level of activity was maintained through maturation, even in the absence of spindle formation. These results indicate that the presence of nuclear material and translocation into the GV are dispensable for the activation of MAP kinase and that associating with the spindle is not required for maintenance of its activity though porcine oocyte maturation.

c-Mos proteolysis is independent of the CA(2+) rise induced by 6-DMAP in Xenopus oocytes

In Xenopus oocytes, metaphase II arrest is due to a cytostatic factor (CSF) that involves c-Mos, maintaining a high MPF (cdk1/cyclin B) activity in the cell. At fertilization, a rise in intracellular calcium triggers the proteolysis of both cyclin B and c-Mos. The kinase inhibitor 6-dimethylaminopurine (6-DMAP) is also able to release matured Xenopus oocytes from metaphase II block. This is characterized by c-Mos proteolysis without degradation of cyclin B. We hypothesized that 6-DMAP induced an increase in intracellular calcium. Using the calcium-sensitive fluorescent dye Fura-2, we observed a systematic increase in intracellular calcium following 6-DMAP application. In matured oocytes previously microinjected with the calcium chelator BAPTA, no calcium changes occurred after 6-DMAP addition; however, c-Mos was still proteolysed. In oocytes at the GVBD stage, c-Mos proteolysis occurred in response to 6-DMAP but not to calcium ionophore treatment. We suggest that c-Mos proteolysis is rather controlled by a phosphorylation-dependent process.

c-mos immunoreactivity is an indicator of good prognosis in lung cancer

AIMS

Reports concerning the expression of cytoplasmic components of the mitogen-activating protein kinase (MAPK) pathway in lung cancer are limited. One of the molecules participating in this pathway is the product of the c-mos proto-oncogene. In vitro investigations, in somatic cells, have shown that c-mos expression has opposing effects on cell cycle progression suggesting that it may represent an important determinant of aberrant cell function. In this study we analysed, by immunohistochemical means, its status in a series of lung carcinomas and correlated the findings with clinicopathological parameters and survival of the patients.

METHODS AND RESULTS

Sixty cases of lung carcinomas were included in the study. These comprised 52 non-small (NSCLCs) and eight small cell lung carcinomas (SCLCs). Sections from the carcinomas were immunostained with the polyclonal anti-c-mos antibody P-19. Specificity was tested by using the appropriate control peptide and control cell lines. Expression was observed in 63% of the cases, with NSCLCs showing higher reactivity (67%) than SCLCs (37.5%). Staining was observed mainly to the cytoplasm and membranes of the cancerous cells, but some nuclei reacted as well. An intratumour heterogeneous immunoreactivity was noticed. The most interesting and unexpected finding was that c-mos positive staining was associated with better recurrence-free survival in our series, regardless of histological type (P = 0.035). Furthermore, favourable disease-related and recurrence-free survival was observed in the SqC group with c-mos immunoreactivity (P < 0. 001).

CONCLUSIONS

c-mos proto-oncogene is expressed in a significant proportion of lung carcinomas and may play a role in its development. The fact that its expression is associated with a relatively good prognosis may be indicative of a negative impact on tumour growth.

The critical role of the MAP kinase pathway in meiosis II in Xenopus oocytes is mediated by p90(Rsk)

BACKGROUND

During oocyte maturation in Xenopus, progesterone induces entry into meiosis I, and the M phases of meiosis I and II occur consecutively without an intervening S phase. The mitogen-activated protein (MAP) kinase is activated during meiotic entry, and it has been suggested that the linkage of M phases reflects activation of the MAP kinase pathway and the failure to fully degrade cyclin B during anaphase I. To analyze the function of the MAP kinase pathway in oocyte maturation, we used U0126, a potent inhibitor of MAP kinase kinase, and a constitutively active mutant of the protein kinase p90(Rsk), a MAP kinase target.

RESULTS

Even with complete inhibition of the MAP kinase pathway by U0126, up to 90% of oocytes were able to enter meiosis I after progesterone treatment, most likely through activation of the phosphatase Cdc25C by the polo-like kinase Plx1. Subsequently, however, U0126-treated oocytes failed to form metaphase I spindles, failed to reaccumulate cyclin B to a high level and failed to hyperphosphorylate Cdc27, a component of the anaphase-promoting complex (APC) that controls cyclin B degradation. Such oocytes entered S phase rather than meiosis II. U0126-treated oocytes expressing a constitutively active form of p90(Rsk) were able to reaccumulate cyclin B, hyperphosphorylate Cdc27 and form metaphase spindles in the absence of detectable MAP kinase activity.

CONCLUSIONS

The MAP kinase pathway is not essential for entry into meiosis I in Xenopus but is required during the onset of meiosis II to suppress entry into S phase, to regulate the APC so as to support cyclin B accumulation, and to support spindle formation. Moreover, one substrate of MAP kinase, p90(Rsk), is sufficient to mediate these effects during oocyte maturation.

Impaired growth and fertility of cAMP-specific phosphodiesterase PDE4D-deficient mice

In eukaryotic cells, the inactivation of the cyclic nucleotide signal depends on a complex array of cyclic nucleotide phosphodiesterases (PDEs). Although it has been established that multiple PDE isoenzymes with distinct catalytic properties and regulations coexist in the same cell, the physiological significance of this remarkable complexity is poorly understood. To examine the role of a PDE in cAMP signaling in vivo, we have inactivated the type 4 cAMP-specific PDE (PDE4D) gene, a mammalian homologue of the Drosophila dunce. This isoenzyme is involved in feedback regulation of cAMP levels. Mice deficient in PDE4D exhibit delayed growth as well as reduced viability and female fertility. The decrease in fertility of the null female is caused by impaired ovulation and diminished sensitivity of the granulosa cells to gonadotropins. These pleiotropic phenotypes demonstrate that PDE4D plays a critical role in cAMP signaling and that the activity of this isoenzyme is required for the regulation of growth and fertility.

Evidence for an important role of serine 16 and its phosphorylation in the stabilization of c-Mos

The c-Mos serine/threonine protein kinase is an essential component of cytostatic factor (CSF), which is required for metaphase II arrest of eggs in vertebrates. Previously, we showed that c-Mos residue Ser-16 is phosphorylated in the ts110 Mo-MuSV-encoded Gag-Mos fusion protein. Here we provide evidence that Mos is phosphorylated at Ser-16 in transfected COS-1 cells. To investigate the role of this phosphorylation, Ser-16 was substituted with alanine or glutamic acid in full-length v-Mos (an Env-Mos fusion protein that contains 31 additional amino acids at the amino terminus of c-Mos), its mouse c-Mos equivalent version (v-Mos residues 32-374, hereafter referred to as Mos), and mouse c-Mos. Constructs expressing mutant versions of Mos were transfected into COS-1 and NIH3T3 cells in a transient and stable manner, respectively. Synthesis and proteolysis of Mos were evaluated by pulse-chase analysis of 35S-methionine-labeled proteins. Our findings indicate that the S16A mutant of Mos was highly unstable. It accumulated to approximately 10% of the level of wild-type Mos or its S16E mutant. In addition, the S16A mutation but not the S16E mutation inhibited Mos interaction with a cellular protein, p35, suggesting that phosphorylation at Ser-16 may promote Mos interaction with p35. As expected from its destabilizing effect, the S16A mutation caused a dramatic decrease in the cellular transforming activity of Mos (determined by soft-agar colony-formation assay with the stably transfected NIH3T3 cells), which is known to correlate with its CSF function. Efficient ubiquitin-mediated proteolysis of c-Mos requires proline as the second residue from the amino-terminus. In contrast to Mos, neither the stability nor protein kinase activity of v-Mos (in which c-Mos residue Pro-2 becomes Pro-33) was affected by the S16A mutation. To provide further proof that, similar to c-Mos, the S16A mutant is recognized by the proteolysis system through Pro-2, we show that the effect of the S16A mutation is reversed by the Pro-2-Ala mutation. Thus, our results indicate that Ser-16 has an important role in the regulation of c-Mos and that phosphorylation at Ser-16 may inhibit proteolysis of c-Mos.