Molecular Determinants of the Human a 2C -Adrenergic Receptor Temperature-Sensitive Intracellular Traffic s

ABSTRACT The human a 2C -adrenergic receptor (a 2C -AR) is localized intracellularly at physiologic temperature. Decreasing the environmental temperature strongly stimulates the receptor transport to the cell surface. In contrast, rat and mouse a 2C -AR plasma membrane levels are less sensitive to decrease in temperature, whereas the opossum a 2C -AR cell surface levels are not changed in these conditions. Structural analysis demonstrated that human a 2C -AR has a high number of arginine residues in the third intracellular loop and in the C-terminus, organized as putative RXR motifs. Although these motifs do not affect the receptor subcellular localization at 37°C, deletion of the arginine clusters significantly enhanced receptor plasma membrane levels at reduced temperature. We found that this exaggerated transport of the human receptor is mediated by two functional arginine clusters, one in the third intracellular loop and one in the C-terminus. This effect is mediated by interactions with COPI vesicles, but not by 14-3-3 proteins. In rat a 2C -AR, the arginine cluster from the third intracellular loop is shifted to the left due to three missing residues. Reinsertion of these residues in the rat a 2C -AR restored the same temperature sensitivity as in the human receptor. Proteomic and coimmunoprecipitation experiments identified pontin as a molecule having stronger interactions with human a 2C -AR compared with rat a 2C -AR. Inhibition of pontin activity enhanced human receptor plasma membrane levels and signaling at 37°C. Our results demonstrate that human a 2C -AR has a unique temperature-sensitive traffic pattern within the G protein-coupled receptor class due to interactions with different molecular chaperones, mediated in part by strict spatial localization of specific arginine residues

A comprehensive analysis of sialolith proteins and the clinical implications.

BackgroundSialolithiasis or salivary gland stones are associated with high clinical morbidity. The advances in the treatment of sialolithiasis has been limited, however, by our understanding of their composition. More specifically, there is little information regarding the formation and composition of the protein matrix, the role of mineralogical deposition, or the contributions of cell epithelium and secretions from the salivary glands. A better understanding of these stone characteristics could pave the way for future non-invasive treatment strategies.MethodsTwenty-nine high-quality ductal stone samples were analyzed. The preparation included successive washings to avoid contamination from saliva and blood. The sialoliths were macerated in liquid nitrogen and the maceration was subjected to a sequential, four-step, protein extraction. The four fractions were pooled together, and a standardized aliquot was subjected to tandem liquid chromatography mass spectrometry (LCMS). The data output was subjected to a basic descriptive statistical analysis for parametric confirmation and a subsequent G.O.-KEGG data base functional analysis and classification for biological interpretation.ResultsThe LC-MS output detected 6934 proteins, 824 of which were unique for individual stones. An example of our sialolith protein data is available via ProteomeXchange with the identifier PXD012422. More important, the sialoliths averaged 53% homology with bone-forming proteins that served as a standard comparison, which favorably compared with 62% homology identified among all sialolith sample proteins. The non-homologous protein fraction had a highly variable protein identity. The G.O.-KEGG functional analysis indicated that extracellular exosomes are a primary cellular component in sialolithiasis. Light and electron microscopy also confirmed the presence of exosomal-like features and the presence of intracellular microcrystals.ConclusionSialolith formation presents similarities with the hyperoxaluria that forms kidney stones, which suggests the possibility of a common origin. Further verification of a common origin could fundamentally change the way in which lithiasis is studied and treated

A comprehensive analysis of sialolith proteins and the clinical implications.

Background:Sialolithiasis or salivary gland stones are associated with high clinical morbidity. The advances in the treatment of sialolithiasis has been limited, however, by our understanding of their composition. More specifically, there is little information regarding the formation and composition of the protein matrix, the role of mineralogical deposition, or the contributions of cell epithelium and secretions from the salivary glands. A better understanding of these stone characteristics could pave the way for future non-invasive treatment strategies. Methods:Twenty-nine high-quality ductal stone samples were analyzed. The preparation included successive washings to avoid contamination from saliva and blood. The sialoliths were macerated in liquid nitrogen and the maceration was subjected to a sequential, four-step, protein extraction. The four fractions were pooled together, and a standardized aliquot was subjected to tandem liquid chromatography mass spectrometry (LCMS). The data output was subjected to a basic descriptive statistical analysis for parametric confirmation and a subsequent G.O.-KEGG data base functional analysis and classification for biological interpretation. Results:The LC-MS output detected 6934 proteins, 824 of which were unique for individual stones. An example of our sialolith protein data is available via ProteomeXchange with the identifier PXD012422. More important, the sialoliths averaged 53% homology with bone-forming proteins that served as a standard comparison, which favorably compared with 62% homology identified among all sialolith sample proteins. The non-homologous protein fraction had a highly variable protein identity. The G.O.-KEGG functional analysis indicated that extracellular exosomes are a primary cellular component in sialolithiasis. Light and electron microscopy also confirmed the presence of exosomal-like features and the presence of intracellular microcrystals. Conclusion:Sialolith formation presents similarities with the hyperoxaluria that forms kidney stones, which suggests the possibility of a common origin. Further verification of a common origin could fundamentally change the way in which lithiasis is studied and treated

Disruption of the Putative Ribosome-Binding Motif of a Scaffold Protein Impairs Cytochrome c Oxidase Subunit Expression in Leishmania major

Leishmania parasites are trypanosomatid protozoans that persist in infected human hosts to cause a spectrum of pathologies, from cutaneous and mucocutaneous manifestations to visceral leishmaniasis caused by Leishmania donovani. The latter is usually fatal if not treated. Persistence of L. major in the mammalian host depends upon maintaining gene-regulatory programs to support essential parasite metabolic functions. These include expression and assembly of mitochondrial L. major cytochrome c oxidase (LmCOX) subunits, important for Leishmania ATP production. Significantly, under mammalian conditions, WT levels of LmCOX subunits require threshold levels of the Leishmania ribosome-associated scaffold protein, LACK. Unexpectedly, we find that although disruption of LACK’s putative ribosome-binding motif does not grossly perturb ribosome association or global protein synthesis, it nonetheless impairs COX subunit expression, mitochondrial function, and virulence. Our data indicate that the quality of LACK’s interaction with Leishmania ribosomes is critical for LmCOX subunit expression and parasite mitochondrial function in the mammalian host. Collectively, these findings validate LACK’s ribosomal interactions as a potential therapeutic target.During their parasitic life cycle, through sandflies and vertebrate hosts, Leishmania parasites confront strikingly different environments, including abrupt changes in pH and temperature, to which they must rapidly adapt. These adaptations include alterations in Leishmania gene expression, metabolism, and morphology, allowing them to thrive as promastigotes in the sandfly and as intracellular amastigotes in the vertebrate host. A critical aspect of Leishmania metabolic adaptation to these changes is maintenance of efficient mitochondrial function in the hostile vertebrate environment. Such functions, including generation of ATP, depend upon the expression of many mitochondrial proteins, including subunits of cytochrome c oxidase (COX). Significantly, under mammalian temperature conditions, expression of Leishmania major COX subunit IV (LmCOX4) and virulence are dependent upon two copies of LACK, a gene that encodes the ribosome-associated scaffold protein, LACK (Leishmania ortholog of RACK1 [receptor for activated C kinase]). Targeted replacement of an endogenous LACK copy with a putative ribosome-binding motif-disrupted variant (LACKR34D35G36→LACKD34D35E36) resulted in thermosensitive parasites that showed diminished LmCOX4 expression, mitochondrial fitness, and replication in macrophages. Surprisingly, despite these phenotypes, LACKD34D35E36 associated with monosomes and polysomes and showed no major impairment of global protein synthesis. Collectively, these data suggest that wild-type (WT) LACK orchestrates robust LmCOX4 expression and mitochondrial fitness to ensure parasite virulence, via optimized functional interactions with the ribosome

In vitro Characterization of a novel murine model of cancerous progression

To evaluate a potentially valuable tool to study cancer progression and metastasis, we characterized a novel murine model composed of a parental oncogene-transformed embryonic fibroblast line and five cell lines isolated from progressively advanced tumors. Lines derived from distant metastases displayed significantly greater rates of motility, invasiveness, and extracellular acidification than lines derived from a primary tumor or local metastases. A comprehensive proteomic analysis of these cells showed numerous oncogenes to be upregulated and tumor suppressors to be downregulated in the advanced lines, and provided novel targets for future examination. The first cell line capable of extravasation displayed particularly high proteomic variation, which could provide insight into its epithelial to mesenchymal transition. The proteomic variation was less than that of an established human breast cancer model, indicating that the observed differences are more likely contributive to tumorigenesis. In total, we validated a novel cell model for the study of tumorigenesis, while providing a robust proteomic data set to guide future research