Carlos Sanhueza

Glucose deprivation causes oxidative stress and stimulates aggresome formation and autophagy in cultured cardiac myocytes.

Aggresomes are dynamic structures formed when the ubiquitin-proteasome system is overwhelmed with aggregation-prone proteins. In this process, small protein aggregates are actively transported towards the microtubule-organizing center. A functional role for autophagy in the clearance of aggresomes has also been proposed. In the present work we investigated the molecular mechanisms involved on aggresome formation in cultured rat cardiac myocytes exposed to glucose deprivation. Confocal microscopy showed that small aggregates of polyubiquitinated proteins were formed in cells exposed to glucose deprivation for 6 h. However, at longer times (18 h), aggregates formed large perinuclear inclusions (aggresomes) which colocalized with gamma-tubulin (a microtubule-organizing center marker) and Hsp70. The microtubule disrupting agent vinblastine prevented the formation of these inclusions. Both small aggregates and aggresomes colocalized with autophagy markers such as GFP-LC3 and Rab24. Glucose deprivation stimulates reactive oxygen species (ROS) production and decreases intracellular glutathione levels. ROS inhibition by N-acetylcysteine or by the adenoviral overexpression of catalase or superoxide dismutase disrupted aggresome formation and autophagy induced by glucose deprivation. In conclusion, glucose deprivation induces oxidative stress which is associated with aggresome formation and activation of autophagy in cultured cardiac myocytes.

Helicobacter pylori–Induced Loss of Survivin and Gastric Cell Viability Is Attributable to Secreted Bacterial Gamma-Glutamyl Transpeptidase Activity

Helicobacter pylori is the etiologic agent of a series of gastric pathologies that may culminate in the development of gastric adenocarcinoma. An initial step in this process is the loss of glandular structures in the gastric mucosa, presumably as the consequence of increased apoptosis and reduced cellular regeneration, which may be attributed to the combination of several bacterial and host factors and to an unfavorable proinflammatory environment. In a previous study, we showed that survivin, a member of the inhibitor of apoptosis protein family, is expressed in the normal human gastric mucosa and that its levels decrease in the mucosa of infected patients and in gastric cells exposed in culture to the bacteria, coincident with increased cell death in the latter case. We investigated the bacterial factors responsible for loss of survivin in gastric cells exposed to H. pylori. The results of this study indicated that the loss of survivin due to H. pylori infection involves proteasome-mediated degradation of the protein. Studies with isogenic mutants deficient in either CagA, VacA, lipopolysaccharide, or gamma-glutamyl transpeptidase (GGT) implicated the latter in H. pylori-induced loss of survivin and cell viability. Moreover, experiments with the GGT inhibitor 6-diazo-5-oxo-l-norleucine and purified recombinant GGT protein indicated that secreted bacterial GGT activity was required and sufficient to induce these effects.

Caveolin-1 in Melanoma Progression

Cancer is a leading cause of death world wide and mortality due to this group of diseases has doubled in the last 20 years. With an estimated 3 million cases, skin cancer is currently the third most common human malignancy and global incidence is rising at an alarming rate due to environmental changes. Within that category, melanomas represent the least common, but most dangerous form accounting for the majority of skin cancer-related deaths. In general terms, cancer evolves as the consequence of a multi-factorial process that involves the loss of a cell’s ability to respond in an appropriate fashion to cues provided by the microenvironment. The development of such aberrant, autonomous behavior is caused by both genetic mutations and epigenetic mechanisms. Particularly relevant in the context of melanoma are the Ras/Raf/MEK/Erk, PI3K/PTEN and NF-kB signaling pathways. The Wnt/┚-catenin patway is also implicated, but it s role still remains unclear. Depending on whether changes result in a “gain of function” or a “loss of function”, the molecules involved are classified as either oncogenes or tumor suppressors, examples important in melanomas being NRas and B-Raf or PTEN, respectively. More recently, a new group of molecular participants has begun to emerge, which, depending on the cellular context, display the ability to either block tumor development or favor progression. Very little is still known about the underlying mechanisms that might explain such “ambiguous” behavior. In this respect, work from our laboratory has focused on the study of a scaffolding protein called caveolin-1. This protein is implicated in a large number of cellular processes, including caveolae formation and vesicular transport, cholesterol transport and the regulation of signal transduction. With respect to tumor development, initial reports implicated caveolin-1 as a tumor suppressor. For instance, caveolin-1 expression is reduced in several human tumors including lung, mammary, colon, ovarian carcinoma and sarcomas, as wells as osteosarcomas and re-expression of the protein can reverse characteristics associated with the transformed phenotype. However, evidence to the contrary is also available showing that caveolin-1 promotes more aggressive traits in tumor cells, such as metastasis and multidrug resistance. Importantly, in human melanoma patients high levels of caveolin-1 are detected in exosomes found in the plasma and some data available associate caveolin-1 expression with increased metastatic potential in different human melanoma cell lines. In this chapter, we summarize data available in the literature highlighting the ambiguity of caveolin-1 function in cancer development. Mechanisms that might explain one or the other

Caveolin-1 impairs PKA-DRP1-mediated remodelling of ER–mitochondria communication during the early phase of ER stress

Close contacts between endoplasmic reticulum and mitochondria enable reciprocal Ca2+ exchange, a key mechanism in the regulation of mitochondrial bioenergetics. During the early phase of endoplasmic reticulum stress, this inter-organellar communication increases as an adaptive mechanism to ensure cell survival. The signalling pathways governing this response, however, have not been characterized. Here we show that caveolin-1 localizes to the endoplasmic reticulum–mitochondria interface, where it impairs the remodelling of endoplasmic reticulum–mitochondria contacts, quenching Ca2+ transfer and rendering mitochondrial bioenergetics unresponsive to endoplasmic reticulum stress. Protein kinase A, in contrast, promotes endoplasmic reticulum and mitochondria remodelling and communication during endoplasmic reticulum stress to promote organelle dynamics and Ca2+ transfer as well as enhance mitochondrial bioenergetics during the adaptive response. Importantly, caveolin-1 expression reduces protein kinase A signalling, as evidenced by impaired phosphorylation and alterations in organelle distribution of the GTPase dynamin-related protein 1, thereby enhancing cell death in response to endoplasmic reticulum stress. In conclusion, caveolin-1 precludes stress-induced protein kinase A-dependent remodelling of endoplasmic reticulum–mitochondria communication.

Un lobo marino en controversia. Materialidad, taxonomía y disputa científica (segunda mitad del siglo XIX)

El presente articulo examina, a partir de un estudio de caso, la discusion y controversia internacional en torno al nacimiento de una especie zoologica, hoy conocida bajo la sinonimia de Arctophoca philippii (Peters, 1866) y Arctocephalus philippii (Peters, 1866). Con tal objetivo se estudia el movimiento de los restos de un lobo marino desde Chile hasta Alemania y la discusion que suscito a proposito de su definicion taxonomica. Este trabajo postula que las propiedades materiales del ejemplar movilizado, sus circunstancias de caza, traslado y resguardo entre los museos, como tambien las posibilidades materiales de comparacion y analisis, marcaron los debates internacionales respecto de su clasificacion entre naturalistas de Inglaterra, Alemania, Chile y Argentina.