The golgi-associated PDZ domain protein PIST/GOPC stabilizes the β1-adrenergic receptor in intracellular compartments after internalization

Many G-protein-coupled receptors carry C-terminal ligand motifs for PSD-95/discs large/ZO-1 (PDZ) domains; via interaction with PDZ domain-containing scaffold proteins, this allows for integration of receptors into signaling complexes. However, the presence of PDZ domain proteins attached to intracellular membranes suggests that PDZ-type interactions may also contribute to subcellular sorting of receptors. The protein interacting specifically with Tc10 (PIST; also known as GOPC) is a trans-Golgi-associated protein that interacts through its single PDZ domain with a variety of cell surface receptors. Here we show that PIST controls trafficking of the interacting β1-adrenergic receptor both in the anterograde, biosynthetic pathway and during postendocytic recycling. Overexpression and knockdown experiments show that PIST leads to retention of the receptor in the trans-Golgi network (TGN), to the effect that overexpressed PIST reduces activation of the MAPK pathway by β1-adrenergic receptor (β1AR) agonists. Receptors can be released from retention in the TGN by coexpression of the plasma membrane-associated scaffold PSD-95, which allows for transport of receptors to the plasma membrane. Stimulation of β1 receptors and activation of the cAMP pathway lead to relocation of PIST from the TGN to an endosome-like compartment. Here PIST colocalizes with SNX1 and the internalized β1AR and protects endocytosed receptors from lysosomal degradation. In agreement, β1AR levels are decreased in hippocampi of PIST-deficient mice. Our data suggest that PIST contributes to the fine-tuning of β1AR sorting both during biosynthetic and postendocytic trafficking.

Subcellular sorting of the G-protein coupled mouse somatostatin receptor 5 by a network of PDZ-domain containing proteins

PSD-95/discs large/ZO-1 (PDZ) domain proteins integrate many G-protein coupled receptors (GPCRs) into membrane associated signalling complexes. Additional PDZ proteins are involved in intracellular receptor trafficking. We show that three PDZ proteins (SNX27, PIST and NHERF1/3) regulate the mouse somatostatin receptor subtype 5 (SSTR5). Whereas the PDZ ligand motif of SSTR5 is not necessary for plasma membrane targeting or internalization, it protects the SSTR5 from postendocytic degradation. Under conditions of lysosomal inhibition, recycling of the SSTR5 to the plasma membrane does not depend on the PDZ ligand. However, recycling of the wild type receptor carrying the PDZ binding motif depends on SNX27 which interacts and colocalizes with the receptor in endosomal compartments. PIST, implicated in lysosomal targeting of some membrane proteins, does not lead to degradation of the SSTR5. Instead, overexpressed PIST retains the SSTR5 at the Golgi. NHERF family members release SSTR5 from retention by PIST, allowing for plasma membrane insertion. Our data suggest that PDZ proteins act sequentially on the GPCR at different stages of its subcellular trafficking.

A general approach toward shape-controlled synthesis of silicon nanowires

Controlling the morphology, electronic properties, and growth direction of nanowires (NWs) is an important aspect regarding their integration into devices on technologically relevant scales. Using the vapor-solid-solid (VSS) approach, with Ni as a catalyst and octachlorotrisilane (Si(3)Cl(8), OCTS) as a precursor, we achieved epitaxial growth of rectangular-shaped Si-NWs, which may have important implications for electronic mobility and light scattering in NW devices. The process parameters were adjusted to form cubic α-NiSi(2) particles which further act as the shaping element leading to prismatic Si-NWs. Along with the uncommon shape, also different crystallographic growth directions, namely, [100] and [110], were observed on the very same sample. The growth orientations were determined by analysis of the NWs' azimuths on the Si (111) substrates as well as by detailed transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigations.

Regional and subcellular distribution of the receptor-targeting protein PIST in the rat central nervous system

Protein interacting specifically with Tc10, PIST, is a Golgi-associated sorting protein involved in regulating cell-surface targeting of plasma membrane receptors. The present study provides the first comprehensive description of PIST distribution in the mammalian central nervous system and of its subcellular localization by immunocytochemistry. PIST is distributed widely throughout the neuraxis, predominantly associated with neuronal cell bodies and dendrites. In hippocampal neurons, in vitro and in situ, PIST displayed a patchy subcellular distribution in an area surrounding the nucleus and extending into one of the major dendrites. By colocalization with the trans-Golgi marker TGN38, we were able to show that PIST is associated largely but not exclusively with the trans-Golgi network in central neurons. High or moderate to high levels of PIST-like immunoreactivity were found in cortical areas, in particular in layer V of the neocortex. The motor cortex was most strongly labeled. Also, the piriform and insular cortices displayed strong PIST labeling. In the hippocampus, CA2 but not CA1 or CA3 pyramidal cells displayed strong PIST-labeling, extending into their apical dendrites. In the thalamus, ventrolateral and laterodorsal nuclei were most strongly stained, whereas in the hypothalamus the supraoptic nucleus stood out with strong immunoreactivity. Strikingly, in the brainstem all cranial nerve motor nuclei were PIST-positive at varying levels, which is in keeping with the prominent expression of PIST in forebrain motor areas. This selective distribution of PIST suggests that the protein serves distinctive roles in specific neuronal populations, establishing functionally distinct zones, for instance, in the hippocampus.

Subeutectic synthesis of epitaxial Si-NWs with diverse catalysts using a novel Si precursor

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl(4) as precursor, OCTS provides Si without the addition of H(2). By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation.

A moment closure model for sexually transmitted disease transmission through a concurrent partnership network

A moment closure model of sexually transmitted disease spread through a concurrent partnership network is developed. The model employs pair approximations of higher-order correlations to derive equations of motion in terms of numbers of pairs and singletons. The model is derived from an underlying stochastic process of partnership network formation and disease transmission. The model is analysed numerically; and the final size and time evolution are considered for various levels of concurrency, as measured by the concurrency index kappa3 of Kretzschmar and Morris. Additionally, a new way of calculating R0 for spatial network models is developed. It is found that concurrency significantly increases R0 and the final size of a sexually transmitted disease, with some interesting exceptions.

Fecal bacterial activity in symptomatic carbohydrate malabsorption: effect on the fecal short-chain fatty acid ratio

BACKGROUND

It is still not clear why only some patients with carbohydrate malabsorption experience symptoms. In a previous study on healthy fructose malabsorbers an increased degradation of fructose in anaerobic fecal cultures from symptomatic malabsorbers was found, indicating increased bacterial activity. In the present study, the same investigation was repeated in patients with nonspecific abdominal complaints and fructose malabsorption. Moreover fecal short-chain fatty acids (SCFA), products of colonic bacterial fermentation of carbohydrates were measured.

PATIENTS AND METHODS

A standard quantity of fructose (500 mg) was added to anaerobic fecal cultures from 25 patients (nine men, 16 women; median of age 53 years, range 36-69 years). The fructose degradation rate was assessed using photometry, and interpreted as representing bacterial activity in the colon. In 14 of the patients, SCFA levels were also measured using chromatography on a capillary column.

RESULTS

10 of the 25 patients had a history of symptoms after ingesting fructose-containing foods, and also showed symptoms during the test; 6 patients had symptoms either in their history or during the test; and the remaining 9 were free of symptoms. There were no differences in the H2 increase. The fructose degradation rate was higher in symptomatic malabsorbers (255 mg vs. 217 mg), but the difference was not significant. However, there was a strong inverse correlation between this bacterial activity and the acetate level, with r = -0.822 (P = 0.000) and r = -0.868 (P = 0.000) in the rank correlation. The correlation for propionate was r = 0.479 (P = 0.083), and that for butyrate was r = 0.599 (P = 0.024).

CONCLUSIONS

This study failed to confirm a significant correlation between fecal bacterial activity and the occurrence of symptoms in patients with fructose malabsorption. However, the interesting correlation with the SCFA raises questions regarding possible connections between colonic bacteria, carbohydrate malabsorption, and the beneficial effect of this pattern of SCFA in several colonic diseases.

LAT2, a new basolateral 4F2hc/CD98-associated amino acid transporter of kidney and intestine

Glycoprotein-associated amino acid transporters (gpaAT) are permease-related proteins that require heterodimerization to express their function. So far, four vertebrate gpaATs have been shown to associate with 4F2hc/CD98 for functional expression, whereas one gpaAT specifically associates with rBAT. In this study, we characterized a novel gpaAT, LAT2, for which mouse and human cDNAs were identified by expressed sequence tag data base searches. The encoded ortholog proteins are 531 and 535 amino acids long and 92% identical. They share 52 and 48% residues with the gpaATs LAT1 and y(+)LAT1, respectively. When mouse LAT2 and human 4F2hc cRNAs were co-injected into Xenopus oocytes, disulfide-linked heterodimers were formed, and an L-type amino acid uptake was induced, which differed slightly from that produced by LAT1-4F2hc: the apparent affinity for L-phenylalanine was higher, and L-alanine was transported at physiological concentrations. In the presence of an external amino acid substrate, LAT2-4F2hc also mediated amino acid efflux. LAT2 mRNA is expressed mainly in kidney and intestine, whereas LAT1 mRNA is expressed widely. Immunofluorescence experiments showed colocalization of 4F2hc and LAT2 at the basolateral membrane of kidney proximal tubules and small intestine epithelia. In conclusion, LAT2 forms with LAT1 a subfamily of L-type gpaATs. We propose that LAT1 is involved in cellular amino acid uptake, whereas LAT2 plays a role in epithelial amino acid (re)absorption.

Luminal heterodimeric amino acid transporter defective in cystinuria

Mutations of the glycoprotein rBAT cause cystinuria type I, an autosomal recessive failure of dibasic amino acid transport (b(0,+) type) across luminal membranes of intestine and kidney cells. Here we identify the permease-like protein b(0,+)AT as the catalytic subunit that associates by a disulfide bond with rBAT to form a hetero-oligomeric b(0,+) amino acid transporter complex. We demonstrate its b(0,+)-type amino acid transport kinetics using a heterodimeric fusion construct and show its luminal brush border localization in kidney proximal tubule. These biochemical, transport, and localization characteristics as well as the chromosomal localization on 19q support the notion that the b(0,+)AT protein is the product of the gene defective in non-type I cystinuria.