Glucose‐regulated protein 78: A new partner of p53 in trophoblast

Although wild‐type p53 protein is overexpressed in first trimester trophoblast, it is inactive towards its target genes Metalloproteinase 2 and 9. This seems to be due to a complex mechanism of inactivation and stabilization of p53 relying on the formation of protein complexes involving the N‐terminus of p53. To detect the proteins associated with this sequence, we incubated biotinylated p53 N‐terminal peptide in cytotrophoblastic cell medium 24 h before lysis of cells. We purified the proteins retained on biotinylated peptide using a neutravidin affinity column. Proteins were then identified by peptide mass finger printing followed or not by peptide fragmentation sequencing. Among these proteins, we identified glucose‐regulated protein 78 (GRP78) and verified its interaction with p53 in trophoblastic cells by immunoprecipitation and Western blot analysis. Moreover, the decreased expression of GRP78 induced by GRP78siRNA or versipelostatin decreased the formation of high molecular weight p53 complexes and p53 monomer and increased trophoblastic invasion. These results suggest that GRP78 is involved in inactivation and stabilization of p53 and in the regulation of trophoblastic invasion.     

Sulforaphane as an inducer of glutathione prevents oxidative stress-induced cell death in a dopaminergic-like neuroblastoma cell line

The total GSH depletion observed in the substantia nigra (SN) appears to be responsible for subsequent oxidative stress (OS), mitochondrial dysfunction, and dopaminergic cell loss in patients with Parkinson's disease. A strategy to prevent the OS of dopaminergic cells in the SN may be the use of chemopreventive agents as inducers of endogenous GSH, antioxidant and phase 2 enzymes. In this study, we demonstrated that treatment of the dopaminergic-like neuroblastoma SH-SY5Y cell line with sulforaphane (SF), a cruciferous vegetables inducer, resulted in significant increases of total GSH level, NAD(P)H : quinone oxidoreductase-1, GSH-transferase and -reductase, but not GSH-peroxidase, catalase and superoxide dismutase activities. Further, the elevation of GSH levels, GSH-transferase and NAD(P)H:quinone oxidoreductase-1 activities was correlated to an increase of the resistance of SH-SY5Y cells to toxicity induced by H₂O₂ or 6-hydroxydopamine (6-OHDA). The pre-treatment of SH-SY5Y cells with SF was also shown to prevent various apoptotic events (mitochondrial depolarization, caspase 9 and 3 activation and DNA fragmentation) and necrosis elicited by 6-OHDA. Further, the impairment of antioxidant capacity and reactive oxygen species formation at intracellular level after exposure to 6-OHDA was effectively counteracted by pre-treatment with SF. Last, both the cytoprotective and antioxidant effects of SF were abolished by the addition of buthionine sulfoximine supporting the main role of GSH in the neuroprotective effects displayed by SF. These findings show that SF may play a role in preventing Parkinson's disease.     

Adenosine A2A receptors enable the synaptic effects of cannabinoid CB1 receptors in the rodent striatum

Adenosine A_2A, cannabinoid CB₁ and metabotropic glutamate 5 (mGlu₅) receptors are all highly expressed in the striatum. The aim of the present work was to investigate whether, and by which mechanisms, the above receptors interact in the regulation of striatal synaptic transmission. By extracellular field potentials (FPs) recordings in corticostriatal slices, we demonstrated that the ability of the selective type 1 cannabinoid receptor (CB₁R) agonist WIN55,212-2 to depress synaptic transmission was prevented by the pharmacological blockade or the genetic inactivation of A_2ARs. Such a permissive effect of A_2ARs towards CB₁Rs does not seem to occur pre-synaptically as the ability of WIN55,212-2 to increase the R2/R1 ratio under a protocol of paired-pulse stimulation was not modified by ZM241385. Furthermore, the effects of WIN55,212-2 were reduced in slices from mice lacking post-synaptic striatal A_2ARs. The selective mGlu₅R agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) potentiated the synaptic effects of WIN55,212-2, and such a potentiation was abolished by A_2AR blockade. Unlike the synaptic effects, the ability of WIN55,212-2 to prevent NMDA-induced toxicity was not influenced by ZM241385. Altogether, these results show that the state of activation of A_2ARs regulates the synaptic effects of CB₁Rs and that A_2ARs may control CB₁ effects also indirectly, namely through mGlu₅Rs.     

A Non-sulfated Chondroitin Stabilizes Membrane Tubulation in Cnidarian Organelles

Membrane tubulation is generally associated with rearrangements of the cytoskeleton and other cytoplasmic factors. Little is known about the contribution of extracellular matrix components to this process. Here, we demonstrate an essential role of proteoglycans in the tubulation of the cnidarian nematocyst vesicle. The morphogenesis of this extrusive organelle takes place inside a giant post-Golgi vesicle, which topologically represents extracellular space. This process includes the formation of a complex collagenous capsule structure that elongates into a long tubule, which invaginates after its completion. We show that a non-sulfated chondroitin appears as a scaffold in early morphogenesis of all nematocyst types in Hydra and Nematostella. It accompanies the tubulation of the vesicle membrane forming a provisional tubule structure, which after invagination matures by collagen incorporation. Inhibition of chondroitin synthesis by β-xylosides arrests nematocyst morphogenesis at different stages of tubule outgrowth resulting in retention of tubule material and a depletion of mature capsules in the tentacles of hydra. Our data suggest a conserved role of proteoglycans in the stabilization of a membrane protrusion as an essential step in organelle morphogenesis.     

From yeast to neurodegenerative diseases: ten years of exploration of mitochondrial dynamic disorders

Ten years ago, OPA1 was identified as the major gene responsible for hereditary optic nerve degeneration, evidencing the first defect in mitochondrial network dynamics as the princeps pathophysiological mechanism in a mitochondriopathy. Later, alterations in other genes involved in mitochondrial fusion or fission, such as MFN2, DRP1 and GDAP1, were also associated with inherited neurological diseases, mainly affecting peripheral nerves. More recently, altered mitochondrial plasticity was also demonstrated in common age-related neurodegenerative disorders, as Alzheimer and Parkinson diseases, thus substantiating the critical role of mitochondrial dynamics in neurons as a key element governing the efficiency of oxidative respiration and its distribution along the axons.     

The Aurora-A/TPX2 complex: A novel oncogenic holoenzyme?

The Aurora-A kinase regulates cell division by phosphorylating multiple downstream targets in the mitotic apparatus. Aurora-A is frequently overexpressed in tumor cells and it is therefore regarded as a novel candidate target in anti-cancer therapy. Its actual contribution to cell transformation, however, is not entirely clarified; furthermore, its transforming ability has been found to vary broadly depending on the systems and experimental conditions in which it was assayed. This variability suggests that Aurora-A overexpression requires the concomitant deregulation of partner factor(s) to fully elicit its oncogenic potential. Molecular and structural studies indicate that the full activation and correct mitotic localisation of Aurora-A require its interaction with the spindle regulator TPX2. In this review we propose a brief reappraisal of Aurora-A intrinsic oncogenic features. We then present literature screening data indicating that TPX2 is also overexpressed in many tumor types, and, furthermore, that Aurora-A and TPX2 are frequently co-overexpressed. We therefore propose that the association of Aurora-A and TPX2 gives rise to a novel functional unit with oncogenic properties. We also suggest that some of the roles that are conventionally attributed to Aurora-A in cell transformation and tumorigenesis could in fact be a consequence of the oncogenic activation of this unit.