Beta(2)-adrenergic receptor down-regulation. Evidence for a pathway that does not require endocytosis.

Sustained activation of most G protein-coupled receptors causes a time-dependent reduction of receptor density in intact cells. This phenomenon, known as down-regulation, is believed to depend on a ligand-promoted change of receptor sorting from the default endosome-plasma membrane recycling pathway to the endosome-lysosome degradation pathway. This model is based on previous studies of epidermal growth factor (EGF) receptor degradation and implies that receptors need to be endocytosed to be down-regulated. In stable clones of L cells expressing beta(2)-adrenergic receptors (beta(2)ARs), sustained agonist treatment caused a time-dependant decrease in both beta(2)AR binding sites and immuno-detectable receptor. Blocking beta(2)AR endocytosis with chemical treatments or by expressing a dominant negative mutant of dynamin could not prevent this phenomenon. Specific blockers of the two main intracellular degradation pathways, lysosomal and proteasome-associated, were ineffective in preventing beta(2)AR down-regulation. Further evidence for an endocytosis-independent pathway of beta(2)AR down-regulation was provided by studies in A431 cells, a cell line expressing both endogenous beta(2)AR and EGF receptors. In these cells, inhibition of endocytosis and inactivation of the lysosomal degradation pathway did not block beta(2)AR down-regulation, whereas EGF degradation was inhibited. These data indicate that, contrary to what is currently postulated, receptor endocytosis is not a necessary prerequisite for beta(2)AR down-regulation and that the inactivation of beta(2)ARs, leading to a reduction in binding sites, may occur at the plasma membrane.     

Polymorphism and signalling of melatonin receptors.

Melatonin receptors belong to the superfamily of G protein-coupled receptors. Cloning of Mel1c receptors expressed in Xenopus skin revealed the existence of a polymorphism for these receptors. Heterologous expression of the two allelic isoforms, called Mel1c(alpha) and Mel1c(beta), indicated functional differences in their signalling properties. Both isoforms are coupled to the cAMP and cGMP pathways. However, the alpha isoform is preferentially coupled to the cAMP pathway, whereas the beta isoform couples preferentially to the cGMP pathway. Coupling differences may be explained by the fact that five of the six amino acid substitutions between the two isoforms are localized within intracellular receptor regions potentially involved in G protein coupling. Allelic isoforms were also observed for Mel1a receptors expressed in ovine pars tuberalis, suggesting that polymorphism is a general feature of the melatonin receptor family. We also evaluated the potential of the two human melatonin receptor subtypes, Mel1a and Mel1b, to modulate the cGMP pathway. Melatonin inhibited intracellular cGMP levels in a dose-dependent manner in HEK293 cells transfected with the human Mel1b receptor. This was not the case for HEK293 cells transfected with the human Mel1a receptor. In conclusion, our results indicate that the expression of receptor subtypes and isoforms may permit differential signalling between melatonin receptors.     

Endothelins Stimulate c-fos and Nerve Growth Factor Expression in Astrocytes and Astrocytoma

Abstract: Endothelin receptors have been identified on astrocytes and astrocytoma, but their physiological significance has remained elusive. It is shown here that endothelins induce c- fos in primary cultures of mouse embryo astrocytes, as well as in two subclones of rat astrocytoma C6 cells, although with different kinetics. In addition, nerve growth factor expression is stimulated, as seen by mRNA accumulation and protein secretion, in primary astrocytes and one of the two C6 subclones, with an apparent correlation with the transience of c- fos induction. The activation of protein kinase C appears as an obligatory step during these processes, because (a) inhibition of protein kinase C by staurosporine blocks the induction by endothelin or phorbol esters of both c- fos and nerve growth factor, and (b) phorbol esterevoked down-regulation of protein kinase C completely abolishes the c- fos induction by endothelin, but not that by the β-adrenergic agonist isoproterenol, a known activator of the cyclic AMP-dependent pathway. Our results support the hypothesis that c- fos product might be implicated in nerve growth factor expression by astrocytes, and also suggest that endothelins may participate in vivo in the modulation of the glial neurotrophic activity during brain development or wound healing.     

Twenty years of human research ethics committees in the Baltic States

Two decades have passed since the first attempts were made to establish systematic ethical review of human research in the Baltic States. Legally and institutionally much has changed. In this paper we provide an historical and structural overview of ethical review of human research and identify some problems related to the role of ethical review in establishing quality research environment in these countries. Problems connected to (a) public availability of information, (b) management of conflicts of interest, (c) REC composition and motivation of REC members, and (d) differing levels of stringency of ethical review for different types of studies, are identified. Recommendations are made to strengthen cooperation among the Baltic RECs.     

New small molecule inhibitors of hepatitis C virus

New small molecule inhibitors of HCV were discovered by screening a small library of indoline alkaloid-type compounds. An automated assay format was employed which allowed identification of dimerization inhibitors of core, the capsid protein of the virus. These compounds were subsequently shown to block production of infectious virus in hepatoma cells.     

Galvechelone lopezmartinezae gen. et sp. nov., a new cryptodiran turtle in the Lower Cretaceous of Europe

Abstract: The Spanish town of Galve (Teruel) is notable because of the abundance of Upper Jurassic and, especially, Lower Cretaceous vertebrates recorded there. Although most groups have been studied in detail, information on turtles is very limited even though the material is relatively abundant. So far, no turtle taxa have been identified at the generic level. The only Lower Cretaceous articulated specimen from Galve is analysed here. It is identified as a representative of Cryptodira, Galvechelone lopezmartinezae gen. et sp. nov. Galvechelone lopezmartinezae is determined as a taxon belonging to the node that groups the turtles traditionally assigned to ‘Macrobaenidae’ and ‘Sinemydidae’, and other taxa such as the members of Panchelonioidea. This node, very abundant in the Lower Cretaceous of Asia, and with a broad subsequent distribution, has recently been recognized in the Lower Cretaceous of Europe. The diversity of basal members of Eucryptodira in the European Late Jurassic (represented by Thalassemydidae, Plesiochelyidae and Eurysternidae) was high. Owing to a relative scarcity of well‐preserved early Cretaceous turtles from Europe, the knowledge of this group of reptiles is limited. The study of the new turtle from Galve, together with the recently described Hoyasemys jimenezi, and the recently completed review of the enigmatic Chitracephalus dumonii demonstrate that members of the cryptodiran node grouping ‘Macrobaenidae’, ‘Sinemydidae’ and Panchelonioidea were also very diverse in this period.