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GTPBP3 is an evolutionary conserved protein presumably involved in mitochondrial tRNA (mt-tRNA) modification. In humans, GTPBP3 mutations cause hypertrophic cardiomyopathy with lactic acidosis, and have been associated with a defect in mitochondrial translation, yet the pathomechanism remains unclear. Here we use a GTPBP3 stable-silencing model (shGTPBP3 cells) for a further characterization of the phenotype conferred by the GTPBP3 defect. We experimentally show for the first time that GTPBP3 depletion is associated with an mt-tRNA hypomodification status, as mt-tRNAs from shGTPBP3 cells were more sensitive to digestion by angiogenin than tRNAs from control cells. Despite the effect of stable silencing of GTPBP3 on global mitochondrial translation being rather mild, the steady-state levels and activity of Complex I, and cellular ATP levels were 50% of those found in the controls. Notably, the ATPase activity of Complex V increased by about 40% in GTPBP3 depleted cells suggesting that mitochondria consume ATP to maintain the membrane potential. Moreover, shGTPBP3 cells exhibited enhanced antioxidant capacity and a nearly 2-fold increase in the uncoupling protein UCP2 levels. Our data indicate that stable silencing of GTPBP3 triggers an AMPK-dependent retrograde signaling pathway that down-regulates the expression of the NDUFAF3 and NDUFAF4 Complex I assembly factors and the mitochondrial pyruvate carrier (MPC), while up-regulating the expression of UCP2. We also found that genes involved in glycolysis and oxidation of fatty acids are up-regulated. These data are compatible with a model in which high UCP2 levels, together with a reduction in pyruvate transport due to the down-regulation of MPC, promote a shift from pyruvate to fatty acid oxidation, and to an uncoupling of glycolysis and oxidative phosphorylation. These metabolic alterations, and the low ATP levels, may negatively affect heart function.

Two major mechanisms of intracellular protein degradation, autophagy and the ubiquitin-proteasome pathway, operate in mammalian cells. PTEN, which is frequently mutated in glioblastomas, is a tumor suppressor gene that encodes a dual specificity phosphatase that antagonizes the phosphatidylinositol 3-kinase class I/AKT/mTOR pathway, which is a key regulator of autophagy. Here, we investigated in U87MG human glioma cells the role of PTEN in the regulation of autophagy and the ubiquitin-proteasome pathway, because both are functionally linked and are relevant in cancer progression. Since U87MG glioma cells lack a functional PTEN, we used stable clones that express, under the control of a tetracycline-inducible system (Tet-on), wild-type PTEN and two of its mutants, G129E-PTEN and C124S-PTEN, which, respectively, lack the lipid phosphatase activity only and both the lipid and the protein phosphatase activities of this protein. Expression of PTEN in U87MG glioma cells decreased proteasome activity and also reduced protein ubiquitination. On the contrary, expression of PTEN increased the autophagic flux and the lysosomal mass. Interestingly, and although PTEN negatively regulates the phosphatidylinositol 3-kinase class I/AKT/mTOR signaling pathway by its lipid phosphatase activity, both effects in U87MG cells were independent of this activity. These results suggest a new mTOR-independent signaling pathway by which PTEN can regulate in opposite directions the main mechanisms of intracellular protein degradation.

La epibiosis es una estrategia común en muchos organismos acuáticos, y puede constituir una herramienta de estudio muy valiosa en ecología y conservación. Las ballenas barbadas conforman un taxón muy vulnerable a las pesquerías, lo que exige grandes esfuerzos para su preservación. El varamiento de un ejemplar macho de Balaenoptera physalus en aguas del nororiente venezolano permitió evaluar puntualmente el fenómeno epibiótico. El tegumento del cetáceo fue evaluado in situ, trasladándose algunas barbas al laboratorio para su estudio pormenorizado. El único epibionte observado, aunque en número muy abundante, fue el copépodo harpacticoide Balaenophilus unisetus. Se describen los diferentes estadios de desarrollo detectados: adulto, copepoditos (cinco) y nauplios (tres), acompañándose de ilustraciones y las mediciones pertinentes. Se presentan y discuten aspectos morfológicos, biogeográficos y de hospedero. Resalta de este estudio: la expansión del ámbito geográfico del copépodo, siendo el primer registro en aguas del Atlántico Occidental, caribeñas y venezolanas; la observación de algunos pocos caracteres morfológicos discrepantes a los previamente descritos, los cuales pudieran referir a distintos morfotipos del epibionte; y la primera detección de un tercer estadio naupliar para B. unisetus.

In lung vasculature, reversible constriction of smooth muscle cells exists in response to acute decrease in oxygenlevels (hypoxia). Progressive and irreversible structural remodeling that reduces blood vessel lumen takesplace in response to chronic hypoxia and results in pulmonary hypertension. Several studies have shown a roleof serotonin in regulating acute and chronic hypoxic responses. In this review the contribution of serotonin, itsreceptors and transporter in lung hypoxic responses is discussed. Hypoxic conditions modify plasma levels ofserotonin, serotonin transporter activity, and expression of 5-HT1B and 5-HT2B receptors. These appear to berequired for pulmonary vascular cell proliferation, which depends on the ratio between reactive oxygen speciesand nitric oxide. A heterozygous mutation was identified in the 5-HT2B receptor gene of a patient who developedpulmonary hypertension after fenfluramines anorexigen treatment. This C-terminus truncated 5-HT2Bmutant receptor presents lower nitric oxide coupling, and higher cell proliferation capacity than the wild-typereceptor. Under low oxygen tension, cells increase the transcription of specific genes via stabilization of the transcriptionfactor hypoxia-inducible factor (HIF)-1. Factors such as angiotensin II or thrombin that can also controlHIF-1 pathway contribute to pulmonary vascular remodeling. The 5-HT2B receptor via phosphatidylinositol-3kinase/Akt activates nuclear factor-κB, which is involved in the regulation of HIF-1 expression. Acontrol of HIF-1 by 5-HT2B receptors explains why expression of pulmonary vascular remodeling factors, such as endothelin-1or transforming growth factor-β, which is HIF-1-α regulated, is not modified in hypoxic 5-HT2B receptor mutantmice. Understanding the detailed mechanisms involved in lung hypoxic responses may provide general insightinto pulmonary hypertension pathogenesis. [ABSTRACT FROM AUTHOR]