Granulocyte Colony-stimulating Factor-induced Aortitis with Lung Injury, Splenomegaly, and a Rash During Treatment for Recurrent Extraosseous Mucinous Chondrosarcoma.

We herein report a case of aortitis induced by granulocyte colony-stimulating factor (G-CSF) that coincided with lung injury, splenomegaly, and cutaneous manifestations during treatment for recurrent extraosseous mucinous chondrosarcoma. Computed tomography revealed large-vessel vasculitis, splenomegaly, and pulmonary interstitial changes. Treatment with prednisolone was successful. Because sarcoma is a rare disease, this case is valuable for showing clinicians that G-CSF preparations could cause aortitis regardless of the patient's underlying diseases or therapeutic pharmacological backgrounds.

GPR87 mediates lysophosphatidic acid-induced colony dispersal in A431 cells.

We have previously reported that an orphan G protein-coupled receptor GPR87 was activated by lysophosphatidic acid (LPA) and that it induced an increase in the intracellular Ca(2+) levels in the CHO cells genetically engineered to express GPR87-Gα16 fusion protein. Because the Ca(2+) response was blocked by the LPA receptor antagonist Ki16425, GPR87 was suggested to be a putative LPA receptor. However, further studies are required to confirm whether GPR87 is an LPA receptor. A previous study showed that colonies of A431 cells treated with LPA showed rapid and synchronized dissociation. Because A431 cells have been shown to express GPR87, we used these cells to examine whether GPR87 acted as an LPA receptor. When A431 cells were treated with gpr87-specific siRNA, the expression of GPR87 was decreased and LPA-induced colony dispersal was significantly reduced. Treatment of the cells with lpa1 siRNA had an additive effect in decrease in the colony dispersal. Studies on the LPA-mediated signaling pathway in A431 cells indicated that transactivation of the epidermal growth factor receptor (EGFR) by LPA led to cell scattering. PD153035, an inhibitor of tyrosine-kinase of EGFR, and BB94, an inhibitor of metalloprotease which produces a ligand for EGFR, significantly prevented the LPA-induced scattering of A431 cells pretreated with lpa1 or gpr87-siRNA. These results strongly suggested that GPR87 acts as an LPA receptor and induces colony dispersal via the transactivation of EGFR in A431 cells.

Lysophosphatidic acid induces neurite branch formation through LPA3.

Although neurite branching is crucial for neuronal network formation after birth, its underlying mechanisms remain unclear. Here, we demonstrate that lysophosphatidic acid (LPA) stimulates neurite branching through a novel signaling pathway. Treatment of neuronal cell lines with LPA resulted in neurite branch formation when LPA(3) receptor was introduced. The effects of LPA were blocked by inhibition of G(q) signaling. Furthermore, expression of inhibitory mutants of the small GTPase Rnd2/Rho7 or an Rnd2 effector rapostlin abolished LPA(3)-mediated neurite branching. The LPA(3) agonist 2(S)-OMPT or LPA also induced axonal branch formation in hippocampal neurons, which was blocked by G(q) and Rnd2 pathway inhibition or LPA(3) knockdown. These findings suggest that the novel signaling pathway involving LPA(3), G(q), and Rnd2 may play an important role in neuronal network formation.

Coordinated interactions between actin and microtubules through crosslinkers in neurite retraction induced by lysophosphatidic acid.

Neurite development requires rearrangement of cytoskeletal elements, which are mechanically and functionally integrated with each other. Although the process of how an extracellular signal induces rearrangement of a single element has been closely examined, the mechanisms by which the signal regulates cytoskeletal integration during cell shape changes are poorly understood. We previously reported that lysophosphatidic acid (LPA) induces actin polymerization-dependent microtubule (MT) rearrangement, leading to neurite retraction in cultured neurons. Here we examined whether the crosslinker proteins were involved in LPA-induced neurite retraction using immortalized mouse neuroblast TR cells. When the MT-binding domains of MACF (MT actin-crosslinking factor) were exogenously expressed in TR cells, MTs were found to be stabilized and become resistant to exposure to LPA. On the other hand, expression of MT-associated protein 2c showed no effect on LPA-induced neurite retraction. These findings suggest that MACF is involved in actin-dependent MT rearrangement during LPA-induced neurite retraction.

In silico study on the substrate binding manner in human myo-inositol monophosphatase 2.

The human IMPA2 gene encoding myo-inositol monophosphatase 2 is highly implicated with bipolar disorder but the substrates and the reaction mechanism of myo-inositol monophosphatase 2 have not been well elucidated.9 In the present study, we constructed 3D models of three- and two-Mg(2+)-ion bound myo-inositol monophosphatase 2, and studied substrate-binding manners using the docking program AutoDock3. The subsequent study showed that the three-metal-ion model could interact with myo-inositol monophosphates, as follows: The phosphate moiety coordinated three Mg(2+) ions, and the inositol ring formed hydrogen bonds with the amino acids conserved in the family. Furthermore, the OH group vicinal to the phosphate group formed a hydrogen bond with a non-bridging oxygen atom of the phosphate. These interactions have been proposed as crucial for forming the transitional state, bipyramidal structure in the bovine myo-inositol monophosphatase. We therefore propose that the human myo-inositol monophosphatase 2 interacts with myo-inositol monophosphates in the three-metal-ion bound form, and proceeds the dephosphorylation through the three-metal-ion theory.

Lysophosphatidic acid influences initial neuronal polarity establishment.

Neuronal polarity is specified by neurite determination into axons and dendrites. Its establishment requires both extrinsic signals, which regulate axon and dendrite development through repulsive or attractive actions, and intrinsic cellular mechanisms, which include rearrangement and selective transport of the cytoskeleton and localization of intracellular organelles. However, it remains unclear how extrinsic signals activate intrinsic cellular mechanisms to establish neuronal polarity. Here, we examine the effects of lysophosphatidic acid (LPA), a signaling lipid that induces cytoskeletal rearrangement in neuronal cells, on neuronal polarity establishment. In hippocampal neuronal cultures where a concentration gradient of LPA was formed, the bases of axons were located predominantly at the side distal to the LPA source. Furthermore, Golgi apparatus were also positioned distally as early as 1h after exposure to the LPA source, suggesting that LPA signaling is involved in the initial determination of the area where an axon sprouts, and thereby the establishment of neuronal polarity.

Post-translational modifications of tubulin in the nervous system.

Many studies have shown that microtubules (MTs) interact with MT-associated proteins and motor proteins. These interactions are essential for the formation and maintenance of the polarized morphology of neurons and have been proposed to be regulated in part by highly diverse, unusual post-translational modifications (PTMs) of tubulin, including acetylation, tyrosination, detyrosination, Delta2 modification, polyglutamylation, polyglycylation, palmitoylation, and phosphorylation. However, the precise mechanisms of PTM generation and the properties of modified MTs have been poorly understood until recently. Recent PTM research has uncovered the enzymes mediating tubulin PTMs and provided new insights into the regulation of MT-based functions. The identification of tubulin deacetylase and discovery of its specific inhibitors have paved the way to understand the roles of acetylated MTs in kinesin-mediated axonal transport and neurodegenerative diseases such as Huntington's disease. Studies with tubulin tyrosine ligase (TTL)-null mice have shown that tyrosinated MTs are essential in normal brain development. The discovery of TTL-like genes encoding polyglutamylase has led to the finding that polyglutamylated MTs which accumulate during brain development are involved in synapse vesicle transport or neurite outgrowth through interactions with motor proteins or MT-associated proteins, respectively. Here we review current exciting topics that are expected to advance MT research in the nervous system.