Effects of mutations in the post-translational modification sites on the trafficking of hyaluronan synthase 2 (HAS2).

Vesicular trafficking of hyaluronan synthases (HAS1-3) from endoplasmic reticulum (ER) through Golgi to plasma membrane (PM), and either back to endosomes and lysosomes, or out into extracellular vesicles, is important for their activities. We studied how post-translational modifications affect the trafficking of HAS2 by mutagenesis of the sites of ubiquitination (K190R), phosphorylation (T110A) and O-GlcNAcylation (S221A), using Dendra2- and EGFP-HAS2 transfected into COS1 cells. Confocal microscopy showed HAS2 wild type (wt) and its K190R and S221A mutants in ER, Golgi and extracellular vesicles, while the T110A mutant remained mostly in the ER. HA synthesis was reduced by S221A, while completely blocked by K190R and T110A. Cell-surface biotinylation indicated that T110A was absent from PM, while S221A was close to the level of wt, and K190R was increased in PM. TIRF microscopy analysis gave similar results. Rab10 silencing increased HA secretion by HAS2, likely by inhibiting endocytosis of the enzyme from PM, as reported before for HAS3. Green-to-red photo-conversion of Dendra2-HAS2 constructs suggested slower decay of K190R and S221A than HAS2 wt, while T110A was barely degraded at all. S221D and S221E, the phosphomimetic mutants of this site, decayed faster and blocked hyaluronan synthesis, suggesting alternative O-GlcNAc/-PO4 substitution to regulate the stability of the enzyme. Probing the role of dynamic O-GlcNAcylation at S221 by adding glucosamine increased the half-life of only HAS2 wt. The Dendra2·HAS2 disappearance from Golgi was slower for K190R. Of the two inactive constructs, K190R co-transfected with HAS2 wt suppressed, whereas T110A had no effect on HA synthesis. Interestingly, the HAS2-stimulated shedding of extracellular vesicles was dependent on HAS residence in PM but independent of HA synthesis. The results indicate that post-translational modifications control the trafficking of HAS2, and that trafficking is an integral part of the post-translational regulation of HAS2 activity.

[Is good old minocycline a new neuroprotective drug?]. / Es la vieja minociclina un nuevo fármaco neuroprotector?

INTRODUCTION: During the last decade, the neuroprotective effects of minocycline have been a matter of an intense debate. A broad amount of contradictory studies can be found in the scientific literature, going from neuroprotection to the exacerbation of toxicity in diverse experimental models. Such differences could be the result of minocycline acting on multiple pharmacological targets. DEVELOPMENT: In the present review we will go over these pharmacological targets and the effects derived from their modulation by minocycline. Among others, its antioxidant activity derived from its chemical structure or its modulator effect on several enzymes such as nitric oxide synthase will be reviewed. Furthermore, the effects of minocycline on the intracellular pathways implicated in neurodegenerative processes including apoptosis stages, activation decision and execution will be addressed. CONCLUSIONS: All the mechanisms described herein have not escaped to a scientific community needed of new therapeutic drugs for the treatment of neurodegenerative conditions. However, the sparse clinical trials carried out so far are mainly aimed at assessing its tolerability and safety or are still in progress. We believe that more studies, both clinical and pre-clinical, should be carried out in order to ascertain the therapeutic window and the neurodegenerative disorders in which minocycline could be useful.

Reactive oxygen species and p38 mitogen-activated protein kinase activate Bax to induce mitochondrial cytochrome c release and apoptosis in response to malonate.

Malonate, an inhibitor of mitochondrial complex II, is a widely used toxin to study neurodegeneration in Huntington's disease and ischemic stroke. We have shown previously that malonate increased reactive oxygen species (ROS) production in human SH-SY5Y neuroblastoma cells, leading to oxidative stress, cytochrome c release, and apoptotic cell death. Expression of a green fluorescent protein-Bax fusion protein in SH-SY5Y neuroblastoma cells demonstrated a Bax redistribution from the cytosol to mitochondria after 12 to 24 h of malonate treatment that coincided with mitochondrial potential collapse and chromatin condensation. Inhibition of Bax translocation using furosemide, as well as Bax gene deletion, afforded significant protection against malonate-induced apoptosis. Further experiments revealed that malonate induced a prominent increase in the level of activated p38 mitogen-activated protein (MAP) kinase and that treatment with the p38 MAP kinase inhibitor SKF86002 potently blocked malonate-induced Bax translocation and apoptosis. Treatment with vitamin E diminished ROS production, reduced the activation status of p38 MAP kinase, inhibited Bax translocation, and protected against malonate-induced apoptosis. Our data suggest that malonate-induced ROS production and subsequent p38 MAP kinase activation mediates the activation of the pro-apoptotic Bax protein to induce mitochondrial membrane permeabilization and neuronal apoptosis.