Casein kinase 1γ acts as a molecular switch for cell polarization through phosphorylation of the polarity factor Tea1 in fission yeast

Fission yeast undergoes growth polarity transition from monopolar to bipolar during G2 phase, designated NETO (New End Take Off). It is known that NETO onset involves two prerequisites, the completion of DNA replication and attainment of a certain cell size. However, the molecular mechanism remains unexplored. Here, we show that casein kinase 1γ, Cki3 is a critical determinant of NETO onset. Not only did cki3? cells undergo NETO during G1‐ or S‐phase, but they also displayed premature NETO under unperturbed conditions with a smaller cell size, leading to cell integrity defects. Cki3 interacted with the polarity factor Tea1, of which phosphorylation was dependent on Cki3 kinase activity. GFP nanotrap of Tea1 by Cki3 led to Tea1 hyperphosphorylation with monopolar growth, whereas the same entrapment by kinase‐dead Cki3 resulted in converse bipolar growth. Intriguingly, the Tea1 interactor Tea4 was dissociated from Tea1 by Cki3 entrapment. Mass spectrometry identified four phosphoserine residues within Tea1 that were hypophosphorylated in cki3? cells. Phosphomimetic Tea1 mutants showed compromised binding to Tea4 and NETO defects, indicating that these serine residues are critical for protein–protein interaction and NETO onset. Our findings provide significant insight into the mechanism by which cell polarization is regulated in a spatiotemporal manner.     

Endothelin-1 causes a prolonged protein kinase C activation and acts as a co-mitogen in vascular smooth muscle cells

Endothelin-1 (ET-1) is known to act via G-protein coupled receptors. It has therefore been suggested that any mitogenic activity it may possess, is due to activation of phospholipase C and protein kinase C (PKC). We have therefore examined both the ability of ET-1 to act as a mitogen and its ability to activate PKC. We found that ET-1 significantly increased thymidine incorporation and enhanced platelet-derived growth factor-induced DNA synthesis, as well as causing a prolonged translocation of PKC to the cell membrane. ET-1 significantly increased PKC dependent phosphorylation of two specific substrates. The phosphorylation of MBP_4–14 (from myelin basic protein) was partially dependent on extracellular Ca²⁺, implicating activation of PKC-α, whereas phosphorylation of the so called ε-peptide was Ca²⁺-independent and prolonged. This could be due either to the δ or ζ isoform of PKC, known to be present in these cells. However, ET-1 induced little proliferation or PKC activity in a transformed smooth muscle cell line, DDT₁ MF-2, which lacks expression of the PKC-αisoform, but expresses the ζ-isoform. Thus, it would appear that ET-1-induced mitogenicity in smooth muscle cells may be related to the sustained, Ca²⁺-independent activation of PKC-δ.     

Tumor-necrosis-factor-induced fibroblast growth factor-1 acts as a survival factor in a transformed endothelial cell line.

Endothelial cells undergo apoptosis after withdrawal of growth factors, alterations in the extracellular matrix, or exposure to cytokines. Here we report that tumor necrosis factor (TNF)-alpha induces apoptosis of human endothelial cells derived from the umbilical vein in a dose-dependent fashion. Apoptosis is triggered through a pathway that is independent from the levels of Bcl-2. On the contrary, TNF stimulates the growth of spontaneously transformed human umbilical vein endothelial cells. This proliferative effect is mediated through the up-regulation of fibroblast growth factor-1 by TNF. The addition of specific fibroblast growth factor-1 antisense oligonucleotides inhibits TNF-induced fibroblast growth factor-1 expression, thus inhibiting the growth and triggering apoptosis of spontaneously transformed human umbilical vein endothelial cells.     

Stress resistance as a determinate of C. elegans lifespan

It is difficult to exaggerate the progress that has been made in biogerontology over the last 15 years. As with all scientific revolutions, a few experiments in a small number of laboratories have changed the way in which we think about and design experiments. As a result of these experiments, there is much evidence to suggest that a rudimentary understanding of some of the processes that cause aging will be available in the next decade. One particular area of progress is the molecular genetics of lifespan. Although one may draw some distinctions between chronological lifespan and normal aging, extended lifespan remains one of the best indicators that an intervention in an aging process has been made. The isolation of a long-lived variant of a laboratory invertebrate is now essentially a trivial project but the information obtained from this approach is proving invaluable. As with most other biological problems, the most important experimental developments are coming from studying simple organisms in a reductionist fashion.     

The growth factor SVH-1 regulates axon regeneration in C. elegans via the JNK MAPK cascade

The ability of neurons to undergo regenerative growth after injury is governed by cell-intrinsic and cell-extrinsic regeneration pathways. These pathways represent potential targets for therapies to enhance regeneration. However, the signaling pathways that orchestrate axon regeneration are not well understood. In Caenorhabditis elegans, the Jun N-terminal kinase (JNK) and p38 MAP kinase (MAPK) pathways are important for axon regeneration. We found that the C. elegans SVH-1 growth factor and its receptor, SVH-2 tyrosine kinase, regulate axon regeneration. Loss of SVH-1-SVH-2 signaling resulted in a substantial defect in the ability of neurons to regenerate, whereas its activation improved regeneration. Furthermore, SVH-1-SVH-2 signaling was initiated extrinsically by a pair of sensory neurons and functioned upstream of the JNK-MAPK pathway. Thus, SVH-1-SVH-2 signaling via activation of the MAPK pathway acts to coordinate neuron regeneration response after axon injury.     

APPL1 acts as a protective factor against podocytes injury in high glucose environment

APPL1, an intracellular adaptor protein, takes part in numerous metabolic reactions. Although APPL1 plays a key role in glucose metabolism via adiponectin pathway and has been proved associated with type 2 diabetes, little is known about its role in diabetic nephropathy. To explore the role of APPL1 in diabetic nephropathy, we upregulated the expression of APPL1 in cultured mouse podocytes by adenovirus infection and tested the effects of APPL1 overexpression in podocytes treated with high glucose. Here, a mouse podocyte cell line (generated from H-2Kb-tsA58 immortmouse) was cultured and divided into four groups: Group 1 (normal glucose, NG), Group 2 (high glucose, HG), Group 3 (HG and infected with control adenovirus) and Group 4 (HG and infected with Ad-APPL1). Cell vitality of Group 4 is significantly higher than Group 2, but notably lower than Group 1 (P<0.01). The apoptosis rate of Group 4 was much lower (P<0.01) than Group 2 and Group 3. A decrease in phase G0/G1 and an increase in phase S was observed in Group 4 compared with Group 2 (P<0.01). These data suggested the protective role of APPL1 overexpression in high glucose condition. Moreover, the levels of Nephrin, AMPK and p-AMPK were decreased by high-glucose treatment, but increased by APPL1 overexpression. In conclusion, in the experimental high glucose condition, APPL1 acts as a protective factor against podocytes injury through regulating AMPK signaling, and may be a new therapy target for diabetic nephropathy.     

Protein kinase C acts as a molecular detector of firing patterns to mediate sensory gating in Aplysia

Habituation of a behavioral response to a repetitive stimulus enables animals to ignore irrelevant stimuli and focus on behaviorally important events. In Aplysia, habituation is mediated by rapid depression of sensory synapses, which could leave an animal unresponsive to important repetitive stimuli, making it vulnerable to injury. We identified a form of plasticity that prevents synaptic depression depending on the precise stimulus strength. Burst-dependent protection from depression is initiated by trains of 2-4 action potentials and is distinct from previously described forms of synaptic enhancement. The blockade of depression is mediated by presynaptic Ca(2+) influx and protein kinase C (PKC) and requires localization of PKC via a PDZ domain interaction with Aplysia PICK1. During protection from depression, PKC acts as a highly sensitive detector of the precise pattern of sensory neuron firing. Behaviorally, burst-dependent protection reduces habituation, enabling animals to maintain responsiveness to stimuli that are functionally important.     

Prolactin acts as a potent survival factor against C2-ceramide-induced apoptosis in human granulosa cells

BACKGROUND: The role of prolactin in the regulation of ovarian folliculogenesis and corpus luteal function and in particular its relationship to atresia in these structures is as yet unclear. We established a model of apoptosis in which to examine the actions of prolactin. METHOD: Granulosa cells collected from IVF-flush were cultured at 0.1-0.3 x 10(6) cells/well in growth media for 48 h, placed into serum-free media for 24 h prior to dosing for 24 h. Dose responses to C2-ceramide and prolactin were performed. Cells were then treated with an apoptotic dose of C2-ceramide alone, prolactin (100 ng/ml) alone or a combination of the two. Cell death was assessed by Trypan Blue cell counting and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; Thiazolyl Blue] assay and apoptosis confirmed by morphological assessment and flow cytometry. RESULTS: C2-ceramide (0-40 micro mol/l) induced a dose-dependent increase in cell death (63.8% increase at 40 micro mol/l) and, morphologically, cells exhibited classical features of apoptosis. Prolactin alone had no effect on metabolic activity or total cell number. On co- incubation, prolactin alone had no effect on cell death, whereas C2-ceramide induced an approximately 62.6% increase in apoptosis, which was inhibited in the presence of prolactin. CONCLUSIONS: Prolactin may contribute significantly to early corpus luteum formation and survival by acting as a potent antiapoptotic factor for human granulosa cells.     

The SAND domain protein ULTRAPETALA1 acts as a trithorax group factor to regulate cell fate in plants

During development, trithorax group (trxG) chromatin remodeling complexes counteract repression by Polycomb group (PcG) complexes to sustain active expression of key regulatory genes. Although PcG complexes are well characterized in plants, little is known about trxG activities. Here we demonstrate that the Arabidopsis SAND (Sp100, AIRE-1, NucP41/75, DEAF-1) domain protein ULTRAPETALA1 (ULT1) functions as a trxG factor that counteracts the PcG-repressive activity of CURLY LEAF. In floral stem cells, ULT1 protein associates directly with the master homeotic locus AGAMOUS, inducing its expression by regulating its histone methylation status. Our analysis introduces a novel mechanism that mediates epigenetic switches controlling post-embryonic stem cell fates in plants.