Multiple quality control mechanisms monitor yeast chitin synthase folding in the endoplasmic reticulum.

The chitin synthase Chs3 is a multipass membrane protein whose trafficking is tightly controlled. Accordingly, its exit from the endoplasmic reticulum (ER) depends on several complementary mechanisms that ensure its correct folding. Despite its potential failure on its exit, Chs3 is very stable in this compartment, which suggests its poor recognition by ER quality control mechanisms such as endoplasmic reticulum-associated degradation (ERAD). Here we show that proper N-glycosylation of its luminal domain is essential to prevent the aggregation of the protein and its subsequent recognition by the Hrd1-dependent ERAD-L machinery. In addition, the interaction of Chs3 with its chaperone Chs7 seems to mask additional cytosolic degrons, thereby avoiding their recognition by the ERAD-C pathway. On top of that, Chs3 molecules that are not degraded by conventional ERAD can move along the ER membrane to reach the inner nuclear membrane, where they are degraded by the inner nuclear membrane-associated degradation (INMAD) system, which contributes to the intracellular homeostasis of Chs3. These results indicate that Chs3 is an excellent model to study quality control mechanisms in the cell and reinforce its role as a paradigm in intracellular trafficking research.

Exomer complex regulates protein traffic at the TGN through differential interactions with cargos and clathrin adaptor complexes.

Protein sorting at the trans-Golgi network (TGN) usually requires the assistance of cargo adaptors. However, it remains to be examined how the same complex can mediate both the export and retention of different proteins or how sorting complexes interact among themselves. In Saccharomyces cerevisiae, the exomer complex is involved in the polarized transport of some proteins from the TGN to the plasma membrane (PM). Intriguingly, exomer and its cargos also show a sort of functional relationship with TGN clathrin adaptors that is still unsolved. Here, using a wide range of techniques, including time-lapse and BIFC microscopy, we describe new molecular implications of the exomer complex in protein sorting and address its different layers of functional interaction with clathrin adaptor complexes. Exomer mutants show impaired amino acid uptake because it facilitates not only the polarized delivery of amino acid permeases to the PM but also participates in their endosomal traffic. We propose a model for exomer where it modulates the recruitment of TGN clathrin adaptors directly or indirectly through the Arf1 function. Moreover, we describe an in vivo competitive relationship between the exomer and AP-1 complexes for the model cargo Chs3. These results highlight a broad role for exomer in regulating protein sorting at the TGN that is complementary to its role as cargo adaptor and present a model to understand the complexity of TGN protein sorting.

Association of serum uric acid levels to inflammation biomarkers and endothelial dysfunction in obese prepubertal children.

BACKGROUND: High serum uric acid (SUA) levels are present in patients with metabolic syndrome (MetS), when the latter is associated with endothelial dysfunction, inflammation, and hypertension. This increase in SUA levels may have a key role in cardiovascular diseases. OBJECTIVE: We aim to quantify the differences in inflammation biomarkers, endothelial dysfunction, and parameters associated with MetS in obese prepubertal children compared to non-obese children, and determine if there is a relationship between uric acid levels and these variables. METHODS: A cross-sectional study was carried out on obese children (6-9 yr old). The study included 43 obese children and the same number of non-obese children (control group), matched by age and sex. SUA, C-reactive protein (CRP), interleukin-6 (IL-6), soluble intercellular adhesion molecule-1 (sICAM-1), glucose, insulin, lipid profile, and blood pressure were all measured. RESULTS: SUA levels, CRP, and sICAM-1 were significantly higher in obese children. In the obese group, SUA levels showed a positive correlation with body mass index (BMI), insulin, homeostasis model assessment for insulin resistance (HOMA-IR), CRP, IL-6, sICAM-1, and triglycerides (TGs), and correlated negatively with high-density lipoprotein cholesterol (HDL-C) and Apo-AI, but not with Apo-B. When adjusted for age, sex, and creatinine, it was noted that SUA levels are independent predictive factors for sICAM-1, CRP, and IL-6. CONCLUSIONS: Inflammation biomarkers, endothelial dysfunction, and parameters associated with MetS are elevated in obese prepubertal children and correlate to uric acid levels.

Relationship between changes in plasma leptin concentrations and plasminogen activator inhibitor-1 in obese prepubertal children after nine months of treatment.

BACKGROUND/AIMS: The metabolic syndrome (MS) is associated with insulin resistance (IR), inappropriate fibrinolysis and high plasma leptin concentrations. The aim of this study was to quantify fibrinolysis and MS-related variables in obese prepubertal children and to evaluate changes in these variables as a result of improved body mass index (BMI), IR and leptin levels following 9 months of treatment. METHODS: The homeostasis model assessment for insulin resistance (HOMA-IR), leptin, plasminogen activator inhibitor-1 (PAI-1) and lipid profile were studied at baseline in obese (n = 50) and nonobese children (n = 50), and after 9 months of treatment in obese children. RESULTS: In the cross-sectional study the mean values for insulin, HOMA-IR, triglycerides, leptin and PAI-1 were significantly higher in obese children than in controls. High-density lipoprotein cholesterol (HDLc) and apolipoprotein A-1 were significantly lower. In the longitudinal study, after 9 months, children with lowered BMI standard deviation score displayed a significant decrease in insulin, HOMA-IR, PAI-1, leptin and triglyceride levels, and an increase in HDLc. Only leptin proved to be an independent predictive factor for changes in PAI-1 (p = 0.010). CONCLUSION: Obesity-linked disorders appear in obese children prior to puberty; these disorders can be improved by decreasing BMI. Changes in leptin levels were found to independently predict changes in PAI-1 in obese children and can help to diagnose complications associated with the obesity.

Promoter heterozygosity at the Candida albicans CHS7 gene is translated into differential expression between alleles.

A characteristic genetic trait in Candida albicans is diploidism, which is accompanied by a high degree of natural heterozygosity. Here, we describe natural heterozygosity in the promoter of the CaCHS7 gene in the SC5314 strain, associated with a GC-rich sequence of 28 nucleotides. Both alleles are expressed in the wild type and contribute to the total levels of the CaCHS7 mRNA. However, the presence of this region in the promoter (L allele) significantly reduced the transcription of the gene as compared with its absence (S allele). Heterozygous strains containing either allele showed distinct phenotypic characteristics. The HeteroL strain showed reduced levels of chitin, a partial resistance to calcofluor, and a moderate degree of morphogenetic alterations in hypha-inducing media. The HeteroS strain was very similar to the wild type, showing only a modest decrease in chitin that did not appear to confer distinct phenotypic characteristics. This is therefore a new report about allelic heterogeneity in C. albicans, directly translated into differential regulation of both alleles, leading to phenotypic consequences. The allelic heterogeneity reported appears to be strain-specific. However, sequence comparison between strains indicated that this region is prone to genetic divergence, which is probably responsible for the reported allelic heterozygosity of CaCHS7.

Cell integrity signaling activation in response to hyperosmotic shock in yeast.

Current progress highlights the role of the yeast cell wall as a highly dynamic structure that responds to many environmental stresses. Here, we show that hyperosmotic shock transiently activates the PKC signaling pathway, a response that requires previous activation of the HOG pathway. Phosphorylation of Slt2p under such conditions is related to changes in the glycerol turnover and is mostly Mid2p dependent, suggesting that changes in cell turgor, mediated by intracellular accumulation of glycerol, are sensed by PKC sensors to promote the cell integrity response. These observations, together with previous results, suggest that yeast cells respond to changes in cellular turgor by remodeling their cell walls.