Overexpression of the trk tyrosine kinase rapidly accelerates nerve growth factor-induced differentiation.

To investigate the role of the gp140trk receptor tyrosine kinase in nerve growth factor (NGF)-induced differentiation, we have overexpressed gp140trk in the NGF-responsive PC12 cell line. Here we demonstrate that overexpression of gp140trk results in marked changes in NGF-induced differentiation. Whereas PC12 cells elaborated neurites after 2 days of continuous exposure to NGF, PC12 cells overexpressing gp140trk by 20-fold(trk-PC12) began this process within hours. Compared with wild-type PC12 cells, trk-PC12 exhibited an increase in both high and low affinity NGF-binding sites. Furthermore, trk-PC12 cells displayed an enhanced level of NGF-dependent gp140trk autophosphorylation, and this activity was sustained for many hours following ligand binding. The tyrosine phosphorylation or activity of several cellular proteins, such as PLC-gamma 1, PI-3 kinase, and Erk1 and the expression of the mRNA for the late response gene transin were also sustained as a consequence of gp140trk overexpression. The data indicate that overexpression of gp140trk in PC12 cells markedly accelerates NGF-induced differentiation pathways, possibly through the elevation of gp140trk tyrosine kinase activity.     

Rho-associated kinase connects a cell cycle-controlling anchorage signal to the mammalian target of rapamycin pathway

When deprived of anchorage to the extracellular matrix, fibroblasts arrest in G(1) phase at least in part due to inactivation of G(1) cyclin-dependent kinases. Despite great effort, how anchorage signals control the G(1)-S transition of fibroblasts remains highly elusive. We recently found that the mammalian target of rapamycin (mTOR) cascade might convey an anchorage signal that regulates S phase entry. Here, we show that Rho-associated kinase connects this signal to the TSC1/TSC2-RHEB-mTOR pathway. Expression of a constitutively active form of ROCK1 suppressed all of the anchorage deprivation effects suppressible by tsc2 mutation in rat embryonic fibroblasts. TSC2 contains one evolutionarily conserved ROCK target-like sequence, and an alanine substitution for Thr(1203) in this sequence severely impaired the ability of ROCK1 to counteract the anchorage loss-imposed down-regulation of both G(1) cell cycle factors and mTORC1 activity. Moreover, TSC2 Thr(1203) underwent ROCK-dependent phosphorylation in vivo and could be phosphorylated by bacterially expressed active ROCK1 in vitro, providing biochemical evidence for a direct physical interaction between ROCK and TSC2.     

The CDP-ethanolamine pathway and phosphatidylserine decarboxylation generate different phosphatidylethanolamine molecular species

In mammalian cells, phosphatidylethanolamine (PtdEtn) is mainly synthesized via the CDP-ethanolamine (Kennedy) pathway and by decarboxylation of phosphatidylserine (PtdSer). However, the extent to which these two pathways contribute to overall PtdEtn synthesis both quantitatively and qualitatively is still not clear. To assess their contributions, PtdEtn species synthesized by the two routes were labeled with pathway-specific stable isotope precursors, d(3)-serine and d(4)-ethanolamine, and analyzed by high performance liquid chromatography-mass spectrometry. The major conclusions from this study are that (i) in both McA-RH7777 and Chinese hamster ovary K1 cells, the CDP-ethanolamine pathway was favored over PtdSer decarboxylation, and (ii) both pathways for PtdEtn synthesis are able to produce all diacyl-PtdEtn species, but most of these species were preferentially made by one pathway. For example, the CDP-ethanolamine pathway preferentially synthesized phospholipids with mono- or di-unsaturated fatty acids on the sn-2 position (e.g. (16:0-18:2)PtdEtn and (18:1-18:2)PtdEtn), whereas PtdSer decarboxylation generated species with mainly polyunsaturated fatty acids on the sn-2 position (e.g. (18:0-20:4)PtdEtn and (18:0-20:5)PtdEtn in McArdle and (18: 0-20:4)PtdEtn and (18:0-22:6)PtdEtn in Chinese hamster ovary K1 cells). (iii) The main PtdEtn species newly synthesized from the Kennedy pathway in the microsomal fraction appeared to equilibrate rapidly between the endoplasmic reticulum and mitochondria. (iv) Newly synthesized PtdEtn species preferably formed in the mitochondria, which is at least in part due to the substrate specificity of the phosphatidylserine decarboxylase, seemed to be retained in this organelle. Our data suggest a potentially essential role of the PtdSer decarboxylation pathway in mitochondrial functioning.     

Overexpression of SERCA2a accelerates repolarisation in rabbit ventricular myocytes

Overexpression of the sarcoplasmic reticulum Ca ATPase (SERCA2a) produces positive inotropism and it has been proposed as a promising strategy to counteract defective excitation-contraction coupling in the failing heart. However, the effects of overexpressing SERCA2a on action potential duration (APD), which can affect diastolic parameters in the heart, is unknown. We, therefore, investigated the relationship between SERCA2a overexpression and APD in adult rabbit ventricular myocytes which were cultured for 48 h. Overexpression of SERCA2a was achieved by infection with an adenovirus carrying both SERCA2a and GFP independently driven by CMV promoters, Ad.SERCA2a. Myocytes infected with Ad.GFP only and/or non-infected myocytes were used as controls. Electrophysiological measurements were taken using switch clamping with 15-25 M Omega resistance microelectrodes. In Ad.SERCA2a infected myocytes, APD was significantly reduced compared with both groups of control cells at 0.5 Hz (APD50 (ms) non-infected: 481+/-98, n=12; Ad.GFP: 464+/-85, n=11; Ad.SERCA2a: 285+/-69, n=13 (mean+/-S.E.M.) and at 1 Hz (APD50 (ms) non-infected: 375+/-64, n=22; Ad.GFP: 363+/-47, n=18; Ad.SERCA2a: 231+/-54, n=24). Using AP voltage-clamping, we recorded a 0.2 mM Cd-sensitive current which can be ascribed to Ca current flowing during the AP. The integral of this current was reduced in Ad.SERCA2a myocytes compared with control (non-infected charge (pC): 27.5+/-4.2, n=8; Ad.SERCA2a: 15.5+/-4.1, n=11; P<0.01). Using AP clamping during the loading protocol, to take into account changes in APD, SR Ca content (assessed by integrating a 20 mM caffeine-induced inward current) was significantly larger in Ad.SERCA2a compared with both controls (SR Ca content (microM/l non-mitochondrial volume): non-infected: 25.5+/-7, n=8; Ad.GFP: 25.7+/-11, n=6; Ad.SERCA2a: 80.5+/-19, n=8). In conclusion, this study shows that SR Ca content is increased despite decreased Ca entry after overexpression of SERCA2a, and this can lead to positive inotropism. This effect coupled with shorter APD may be a useful therapeutic modality in heart failure.     

Interplay between CDC2 kinase and MAP kinase pathway during maturation of mammalian oocytes

Two principal kinases, p34cdc2 kinase and MAP kinase play a pivotal role in maturation of mammalian oocytes. In the porcine and bovine oocytes both kinases are activated around the time of germinal vesicle breakdown (GVBD). Butyrolactone I (BL I), a specific inhibitor of cdk kinases, prevents effectively and reversibly resumption of meiosis in the porcine and bovine oocytes. Neither p34cdc2 kinase nor MAP kinase are activated in oocytes inhibited in the GV stage. The bovine oocytes maintained for 48 h in the medium supplemented with BL I, progress subsequently to metaphase II in 91%, their cumuli expand optimally and after in vitro fertilization they possess two pronuclei. When the cdc2 kinase is blocked in the porcine oocytes by BL I, MAP kinase, activated by okadaic acid treatment, is able to substitute cdc2 kinase and induce GVBD. The histone H1 kinase activity sharply decreases in the metaphase II oocytes treated by BL I and one or two female pronuclei are formed. These data indicate that BL I is a useful tool either for the two step in vitro culture of mammalian oocytes or for their activation in nuclear transfer experiments.     

The mammalian formin FHOD1 interacts with the ERK MAP kinase pathway

Formin homology 2 domain containing protein (FHOD1), a mammalian formin, regulates cytoskeletal architecture, enhances cell migration, and induces gene expression from the serum response element. In this study, we describe co-precipitation of FHOD1 with components of the ERK MAP kinase pathway while co-precipitation of FHOD1 with p38 MAP kinase and JNK was not observed. In addition, FHOD1 co-localized to lamellipodia with Raf-1 and to stress fibers with MEK. FHOD1-induced gene expression from the serum response element was dependent on ERK MAP kinase activation, and the native skeletal actin promoter were activated by FHOD1 through the SRF site. However, FHOD1-induced stress-fiber formation and gene expression from the skeletal actin promoter was independent of ERK activation. These novel data demonstrate that FHOD1-ERK MAP kinase interaction regulates key aspects of FHOD1 biology.     

Biosynthesis of phosphatidylethanolamine via the CDP-ethanolamine route is an important pathway in isolated rat hepatocytes

In the present study pulse-label and pulse-chase experiments with isolated rat hepatocytes in suspension were designed to investigate the effects of the presence of either serine or ethanolamine in the medium on the rate of phosphatidylethanolamine synthesis via the CDPethanolamine pathway and by decarboxylation of phosphatidylserine. Addition of serine to the medium did not affect the incorporation of [1,2-14C]ethanolamine into phosphatidylethanolamine. Pulse-label experiments showed that the incorporation of [3H]serine into phosphatidylserine decreased in the presence of ethanolamine with a corresponding decrease of the incorporation of label into the ethanolamine base moiety of phosphatidylethanolamine. However, the radioactivity in the diacylglycerol part of phosphatidylethanolamine was considerably higher in the presence of ethanolamine than in its absence. Pulse-chase experiments with labelled serine demonstrated that the conversion of phosphatidylserine to phosphatidylethanolamine was not affected by varying concentrations of ethanolamine. Our observations indicate that in the presence of ethanolamine the biosynthesis of phosphatidylethanolamine via the CDPethanolamine pathway is enhanced relative to the synthesis by decarboxylation of phosphatidylserine.     

Sli2 (Ypk1), a homologue of mammalian protein kinase SGK, is a downstream kinase in the sphingolipid-mediated signaling pathway of yeast

ISP-1 is a new type of immunosuppressant, the structure of which is homologous to that of sphingosine. In a previous study, ISP-1 was found to inhibit mammalian serine palmitoyltransferase, the primary enzyme involved in sphingolipid biosynthesis, and to reduce the intracellular pool of sphingolipids. ISP-1 induces the apoptosis of cytotoxic T cells, which is triggered by decreases in the intracellular levels of sphingolipids. In this study, the inhibition of yeast (Saccharomyces cerevisiae) proliferation by ISP-1 was observed. This ISP-1-induced growth inhibition was also triggered by decreases in the intracellular levels of sphingolipids. In addition, DNA duplication without cytokinesis was detected in ISP-1-treated yeast cells on flow cytometry analysis. We have cloned multicopy suppressor genes of yeast which overcome the lethal sphingolipid depletion induced by ISP-1. One of these genes, SLI2, is synonymous with YPK1, which encodes a serine/threonine kinase. Kinase-dead mutants of YPK1 did not show any resistance to ISP-1, leading us to predict that the kinase activity of the Ypk1 protein should be essential for this resistance to ISP-1. Ypk1 protein overexpression had no effect on sphingolipid biosynthesis by the yeast. Furthermore, both the phosphorylation and intracellular localization of the Ypk1 protein were regulated by the intracellular sphingolipid levels. These data suggest that the Ypk1 protein is a downstream kinase in the sphingolipid-mediated signaling pathway of yeast. The Ypk1 protein was reported to be a functional homologue of the mammalian protein kinase SGK, which is a downstream kinase of 3-phosphoinositide-dependent kinase 1 (PDK1). PDK1 phosphotidylinositol (PI) is regulated by PI-3,4,5-triphosphate and PI-3,4-bisphosphate through the pleckstrin homology (PH) domain. Overexpression of mammalian SGK also overcomes the sphingolipid depletion in yeast. Taking both the inability to produce PI-3,4, 5-triphosphate and PI-3,4-bisphosphate and the lack of a PH domain in the yeast homologue of PDK1, the Pkh1 protein, into account, these findings further suggest that yeast may use sphingolipids instead of inositol phospholipids as lipid mediators.     

Overexpression of Helicard,a CARD-containing helicase cleaved during apoptosis,accelerates DNA degradation

Apoptotic cell death is characterized by several morphological nuclear changes, such as chromatin condensation and extensive fragmentation of chromosomal DNA. These alterations are primarily triggered through the activation of caspases, which subsequently cleave nuclear substrates. Caspase-3 induces processing of Acinus, which leads to chromatin condensation. DNA fragmentation is dependent on the DNase CAD, which is released from its inhibitor, ICAD, upon cleavage by caspase-3. DNA degradation is also induced by AIF and endonuclease G, which are both released from mitochondria upon death stimuli but do not require prior processing by caspases for their DNase activity. Here we report the identification of a widely expressed helicase designated Helicard, which contains two N-terminal CARD domains and a C-terminal helicase domain. Upon apoptotic stimuli, Helicard is cleaved by caspases, thereby separating the CARD domains from the helicase domain. While Helicard localizes in the cytoplasm, the helicase-containing fragment is found in the nucleus. Helicard accelerates Fas ligand-mediated DNA degradation, whereas a noncleavable or a helicase-dead Helicard mutant does not, implicating Helicard in the nuclear remodeling occurring during apoptosis.     

alpha-Synuclein affects the MAPK pathway and accelerates cell death

Insoluble alpha-synuclein accumulates in Parkinson's disease, diffuse Lewy body disease, and multiple system atrophy. However, the relationship between its accumulation and pathogenesis is still unclear. Recently, we reported that overexpression of alpha-synuclein affects Elk-1 phosphorylation in cultured cells, which is mainly performed by mitogen-activated protein kinases (MAPKs). We further examined the relationship between MAPK signaling and the effects of alpha-synuclein expression on ecdysone-inducible neuro2a cell lines and found that cells expressing alpha-synuclein had less phosphorylated MAPKs. Moreover, they showed significant cell death when the concentration of serum in the culture medium was reduced. Under normal serum conditions, the addition of the MAPK inhibitor U0126 also caused cell death in alpha-synuclein-expressing cells. Transfection of constitutively active MEK-1 resulted in MAPK phosphorylation in alpha-synuclein-expressing cells and improved cell viability even under reduced serum conditions. Thus, we conclude that alpha-synuclein regulates the MAPK pathway by reducing the amount of available active MAPK. Our findings suggest a mechanism for pathogenesis and thus offer therapeutic insight into synucleinopathies.     

Overexpression of calmodulin induces cardiac hypertrophy by a calcineurin-dependent pathway

The possible role of calcineurin in cardiac hypertrophy induced by calmodulin (CaM) overexpression in the heart was investigated. CaM transgenic (CaM-TG) mice developed marked cardiac hypertrophy and exhibited up-regulation of atrial natriuretic factor (ANF) and beta-myosin heavy chain gene expression in the heart during the first 2 weeks after birth. The activity of calcineurin in the heart was also significantly increased in CaM-TG mice compared with wild-type littermates. Treatment of CaM-TG mice with the calcineurin inhibitor FK506 (1mg/kg per day) prevented the increase in the heart-to-body weight ratio as well as that in cardiomyocyte width. FK506 also inhibited the induction of fetal-type cardiac gene expression in CaM-TG mice. Overexpression of CaM in cultured rat cardiomyocytes activated the ANF gene promoter in a manner sensitive to FK506. Activation of a calcineurin-dependent pathway thus contributes to the development of cardiac hypertrophy induced by CaM overexpression in the heart.     

Overexpression of AtBMI1C, a polycomb group protein gene, accelerates flowering in Arabidopsis

Polycomb group protein (PcG)-mediated gene silencing is emerging as an essential developmental regulatory mechanism in eukaryotic organisms. PcGs inactivate or maintain the silenced state of their target chromatin by forming complexes, including Polycomb Repressive Complex 1 (PRC1) and 2 (PRC2). Three PRC2 complexes have been identified and characterized in Arabidopsis; of these, the EMF and VRN complexes suppress flowering by catalyzing the trimethylation of lysine 27 on histone H3 of FLOWER LOCUS T (FT) and FLOWER LOCUS C (FLC). However, little is known about the role of PRC1 in regulating the floral transition, although AtRING1A, AtRING1B, AtBMI1A, and AtBMI1B are believed to regulate shoot apical meristem and embryonic development as components of PRC1. Moreover, among the five RING finger PcGs in the Arabidopsis genome, four have been characterized. Here, we report that the fifth, AtBMI1C, is a novel, ubiquitously expressed nuclear PcG protein and part of PRC1, which is evolutionarily conserved with Psc and BMI1. Overexpression of AtBMI1C caused increased H2A monoubiquitination and flowering defects in Arabidopsis. Both the suppression of FLC and activation of FT were observed in AtBMI1C-overexpressing lines, resulting in early flowering. No change in the H3K27me3 level in FLC chromatin was detected in an AtBMI1C-overexpressing line. Our results suggest that AtBMI1C participates in flowering time control by regulating the expression of FLC; moreover, the repression of FLC by AtBMI1C is not due to the activity of PRC2. Instead, it is likely the result of PRC1 activity, into which AtBMI1C is integrated.     

Overexpression of transglutaminase 2 accelerates the erythroid differentiation of human chronic myelogenous leukemia K562 cell line through PI3K/Akt signaling pathway

Transglutaminase 2 (TG2) is a GTP-binding protein with transglutaminase activity. Despite advances in the characterization of TG2 functions and their impact on cellular processes, the role of TG2 in Human chronic myelogenous leukemia K562 cell line is still poorly understood. To understand the biological significance of TG2 during the differentiation of K562 cells, we established and characterized K562 cells that specifically express TG2. Non-transfected K562 cells showed the increase of membrane-bound-TG2 level after 3 days in the response to Hemin and all trans-retinoic acid (tRA), indicating that membrane recruitment of TG2 is occurred during the erythroid differentiation. However, membrane recruitment of TG2 in TG2-transfected cells revealed within earlier time period, compared with that in vector-transfected cells. The ability of membrane-bound-TG2 to be photoaffinity-labeled with [alpha-32P]GTP was also increased in TG2-transfected cells. TG2-transfected cells activated Akt phosphorylation and inactivated ERK1/2 phosphorylation, compared with vector-transfected cells. Furthermore, phosphorylation of CREB, one of the Akt substrates, was increased in TG2-transfected cells and this phenomenon was confirmed by RT-PCR analysis of several marker genes related with erythroid lineage in the absence of PI3K specific inhibitor, Wortmannin, indicating that PI3K/Akt signaling pathway also involved in the differentiation of the cell. Finally, as results of benzidine positive staining as well as hemoglobinization analysis, overexpression of TG2 revealed acceleration of the erythroid differentiation of K562 cells. Taken together, there was no increased TG2 expression level in the response of Hemin/tRA and delayed differentiation in vector transfected cells than in TG2-transfected cells, suggesting that suppression of TG2 expression may retard the erythroid differentiation of K562 cells. Therefore, our study may give a new insight for another aspect of the development of this disease.     

Overexpression of CNP in chondrocytes rescues achondroplasia through a MAPK-dependent pathway

Achondroplasia is the most common genetic form of human dwarfism, for which there is presently no effective therapy. C-type natriuretic peptide (CNP) is a newly identified molecule that regulates endochondral bone growth through GC-B, a subtype of particulate guanylyl cyclase. Here we show that targeted overexpression of CNP in chondrocytes counteracts dwarfism in a mouse model of achondroplasia with activated fibroblast growth factor receptor 3 (FGFR-3) in the cartilage. CNP prevented the shortening of achondroplastic bones by correcting the decreased extracellular matrix synthesis in the growth plate through inhibition of the MAPK pathway of FGF signaling. CNP had no effect on the STAT-1 pathway of FGF signaling that mediates the decreased proliferation and the delayed differentiation of achondroplastic chondrocytes. These results demonstrate that activation of the CNP-GC-B system in endochondral bone formation constitutes a new therapeutic strategy for human achondroplasia.     

Overexpression of Dd PK2 protein kinase causes rapid development and affects the intracellular cAMP pathway of Dictyostelium discoideum.

The Dd PK2 gene codes for a putative protein of 648 amino acids with a C-terminal half sharing high homology with protein kinase A catalytic subunits from other organisms. In order to find out more about the physiological role of the Dd PK2 kinase, its gene, and a version having a frame shift mutation in the middle of the catalytic region, were overexpressed in developing Dictyostelium cells. Both the intact gene (K-) and the frame shift mutant (Kdel-) caused rapid development with spores formed in 16-18 hours compared to the 24 hours required by their parent. This result was confirmed by the pattern of expression of some developmentally regulated genes. Other rapid developing strains (rde) are activated in the cAMP second messenger system. Both K- and Kdel-containing strains have lower cAMP levels than the parental strain during late development, thus resembling rdeC mutants. K-cells (but not Kdel-cells) produced bizarre fruiting bodies with many prostrate forms. The parallel with rde mutants was confirmed by demonstrating that K-cells are able to form spores in submerged monolayer culture. Furthermore, K-cells have about four times more protein kinase A (cAPK) activity than wild-type cells. These results indicate that the N-terminal domain of Dd PK2 is sufficient to influence cAMP levels and to provoke rapid development, whereas kinase activity seems to be required for the sporogenous phenotype. The association between elevated cAPK and Dd PK2 overexpression phenotype further indicates a role for cAPK in the formation of spores.