Trimerization and genotype-phenotype correlation of COL4A5 mutants in Alport syndrome

INTRODUCTION: Alport syndrome is a hereditary glomerulonephritis that results from the disruption of collagen α345(IV) heterotrimerization caused by mutation in METHODS: We selected 9 α5(IV) missense mutants with typical glycine substitutions that clinically differed in disease progression. To quantify the trimerization of each mutant, split nanoluciferase-fused α3/α5 mutants and α4 were transfected into the cells, and intracellular and secreted heterotrimer were detected by luminescence using an assay that we developed previously. RESULTS: Trimer formation and secretion patterns tended to be similar to the wild type in most of the mutations that did not show proteinuria at a young age. On the other hand, trimer secretion was significantly reduced in all the mutations that showed proteinuria and early onset of renal failure. One of these mutants has low ability of intracellular trimer formation, and the others had the defect of low-level secretion. In addition, the mutant that is assumed to be nonpathogenic has similar trimer formation and secretion pattern as wild-type α5(IV). CONCLUSION: The result of cell-based α345(IV) heterotrimer formation assay was largely correlated with clinical genotype-phenotype. These trimerization assessments provide additional phenotypic considerations and may help to distinguish between pathogenic and nonpathogenic mutations

Bafilomycin A1-sensitive pathway is required for the maturation of cystic fibrosis transmembrane conductance regulator

AbstractCystic fibrosis (CF) is the most common lethal genetic disease in Caucasians caused by the trafficking defects of CF transmembrane conductance regulator (CFTR), which is a cAMP-dependent Cl− channel at the plasma membrane. The trafficking pathway of CFTR is thought to be non-conventional because CFTR maturation is inhibited by the dysfunction of syntaxin 13, which is involved in protein recycling via endosomal pathway. In this study, to clarify whether the endosomal trafficking is required for CFTR maturation, we utilized a specific vacuolar H+-ATPase inhibitor, bafilomycin A1 (BafA1), which inhibits the protein trafficking from early endosome. Our data showed that low concentration of BafA1 (50nM) decreased the expression of mature CFTR but induced the accumulation of immature CFTR in the juxta-nuclear region containing an early endosome marker. Pulse-chase analysis showed that BafA1 inhibited the maturation of CFTR, but it slightly stabilized immature CFTR. These results indicate that BafA1-sensitive pathway is required for CFTR maturation and emphasize that endosomal trafficking pathway might be involved in the maturation of CFTR

MEF/ELF4 transactivation by E2F1 is inhibited by p53

Myeloid elf-1-like factor (MEF) or Elf4 is an E-twenty-six (ETS)-related transcription factor with strong transcriptional activity that influences cellular senescence by affecting tumor suppressor p53. MEF downregulates p53 expression and inhibits p53-mediated cellular senescence by transcriptionally activating MDM2. However, whether p53 reciprocally opposes MEF remains unex-plored. Here, we show that MEF is modulated by p53 in human cells and mice tissues. MEF expression and promoter activity were suppressed by p53. While we found that MEF promoter does not contain p53 response elements, intriguingly, it contains E2F consensus sites. Subsequently, we determined that E2F1 specifically binds to MEF promoter and transactivates MEF. Nevertheless, E2F1 DNA binding and transactivation of MEF promoter was inhibited by p53 through the association between p53 and E2F1. Furthermore, we showed that activation of p53 in doxorubicin-induced senescent cells increased E2F1 and p53 interaction, diminished E2F1 recruitment to MEF promoter and reduced MEF expression. These observations suggest that p53 downregulates MEF by associating with and inhibiting the binding activity of E2F1, a novel transcriptional activator of MEF. Together with previous findings, our present results indicate that a negative regulatory mechanism exists between p53 and MEF

Inhibition of post-translational N-glycosylation by HRD1 that controls the fate of ABCG5/8 transporter

N-glycosylation of proteins in endoplasmic reticulum is critical for protein quality control. We showed here a post-translational N-glycosylation affected by the HRD1 E3 ubiquitin ligase. Both WT- and E3-defective C329S-HRD1 decreased the level of high mannose form of ABCG8, a protein that heterodimerizes with ABCG5 to control sterol balance. Meanwhile, HRD1 increased the non-glycosylated ABCG8 regardless of its E3 activity, thereby suppressing full maturation of ABCG5/8 transporter. Pulse chase and mutational analysis indicated that HRD1 inhibits STT3B-dependent post-translational N-glycosylation of ABCG8. Whereas, HRD1 had only slight effect on the N-glycosylation status of ABCG5; rather it accelerated ABCG5 degradation in an E3 activity-dependent manner. Finally, RMA1, another E3 ubiquitin ligase, accelerated the degradation of both ABCG5 and ABCG8 via E3 activity-dependent manner. HRD1 and RMA1 may therefore be negative regulators of disease-associated transporter ABCG5/ABCG8. The findings also highlight the unexpected E3 activity-independent role of HRD1 in the regulation of N-glycosylation

Posttranslational negative regulation of glycosylated and non-glycosylated BCRP expression by Derlin-1

Human breast cancer resistance protein (BCRP)/MXR/ABCG2 is a well-recognized ABC half-transporter that is highly expressed at the apical membrane of many normal tissues and cancer cells. BCRP facilitates disposition of endogenous and exogenous harmful xenobiotics to protect cells/tissues from xenobiotic-induced toxicity. Despite the enormous impact of BCRP in the physiological and pathophysiological regulation of the transport of a wide variety of substrates, little is known about the factors that regulate posttranslational expression of BCRP. Here, we identified Derlin-1, a member of a family of proteins that bears homology to yeast Der1p, as a posttranslational regulator of BCRP expression. Overexpression of Derlin-1 suppressed ER to Golgi transport of wild-type (WT) BCRP that is known to be efficiently trafficked to the plasma membrane. On the other hand, protein expression of N596Q variant of BCRP, N-linked glycosylation- deficient mutant that preferentially undergoes ubiquitin-mediated ER-associated degradation (ERAD), was strongly suppressed by the overexpression of Derlin-1, whereas knockdown of Derlin-1 stabilized N596Q protein, suggesting a negative regulatory role of Derlin-1 for N596Q protein expression. Notably, knockdown of Derlin-1 also stabilized the expression of tunicamycin-induced deglycosylated WT BCRP protein, implying the importance of glycosylation state for the recognition of BCRP by Derlin- 1. Thus, our data demonstrate that Derlin-1 is a negative regulator for both glycosylated and non-glycosylated BCRP expression and provide a novel posttranslational regulatory mechanism of BCRP by Derlin-1

The DsbA-L gene is associated with respiratory function of the elderly via its adiponectin multimeric or antioxidant properties

Oxidative stress and inflammation play a key role in the age-related decline in the respiratory function. Adipokine in relation to the metabolic and inflammatory systems is attracting growing interest in the field of respiratory dysfunction. The present clinical and experimental studies investigated the role of the disulfide bond-forming oxidoreductase A-like protein (DsbA-L) gene, which has antioxidant and adiponectin multimeric (i.e. activation) properties, on the respiratory function of the elderly. We performed a retrospective longitudinal genotype-phenotype relationship analysis of 318 Japanese relatively elderly participants (mean age ± standard deviation: 67.0 ± 5.8 years) during a health screening program and an in vitro DsbA-L knock-down evaluation using 16HBE14o-cells, a commonly evaluated human airway epithelial cell line. The DsbA-L rs1917760 polymorphism was associated with a reduction in the ratio of forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) and %FEV1 and with the elevation of the prevalence of FEV1/FVC < 70%. We also confirmed that the polymorphism was associated with a decreased respiratory function in relation to a decrease in the ratio of high-molecular-weight adiponectin/total adiponectin (as a marker of adiponectin multimerization) and an increase in the oxidized human serum albumin (as an oxidative stress marker). Furthermore, we clarified that DsbA-L knock-down induced oxidative stress and up-regulated the mucus production in human airway epithelial cells. These findings suggest that the DsbA-L gene may play a role in protecting the respiratory function of the elderly, possibly via increased systemic adiponectin functions secreted from adipocytes or through systemic and/or local pulmonary antioxidant properties

DNA demethylation-dependent enhancement of toll-like receptor-2 gene expression in cystic fibrosis epithelial cells involves SP1-activated transcription

<p>Abstract</p> <p>Background</p> <p>The clinical course of cystic fibrosis (CF) is characterized by recurrent pulmonary infections and chronic inflammation. We have recently shown that decreased methylation of the toll-like receptor-2 (TLR2) promoter leads to an apparent CF-related up-regulation of TLR2. This up-regulation could be responsible, in part, for the CF-associated enhanced proinflammatory responses to various bacterial products in epithelial cells. However, the molecular mechanisms underlying DNA hypomethylation-dependent enhancement of TLR2 expression in CF cells remain unknown.</p> <p>Results</p> <p>The present study indicates that there is a specific CpG region (CpG#18-20), adjacent to the SP1 binding site that is significantly hypomethylated in several CF epithelial cell lines. These CpGs encompass a minimal promoter region required for basal TLR2 expression, and suggests that CpG#18-20 methylation regulates TLR2 expression in epithelial cells. Furthermore, reporter gene analysis indicated that the SP1 binding site is involved in the methylation-dependent regulation of the TLR2 promoter. Inhibition of SP1 with mithramycin A decreased TLR2 expression in both CF and 5-azacytidine-treated non-CF epithelial cells. Moreover, even though SP1 binding was not affected by CpG methylation, SP1-dependent transcription was abolished by CpG methylation.</p> <p>Conclusion</p> <p>This report implicates SP1 as a critical component of DNA demethylation-dependent up-regulation of TLR2 expression in CF epithelial cells.</p

Mild Electrical Stimulation with Heat Shock Ameliorates Insulin Resistance via Enhanced Insulin Signaling

Low-intensity electrical current (or mild electrical stimulation; MES) influences signal transduction and activates phosphatidylinositol-3 kinase (PI3K)/Akt pathway. Because insulin resistance is characterized by a marked reduction in insulin-stimulated PI3K-mediated activation of Akt, we asked whether MES could increase Akt phosphorylation and ameliorate insulin resistance. In addition, it was also previously reported that heat shock protein 72 (Hsp72) alleviates hyperglycemia. Thus, we applied MES in combination with heat shock (HS) to in vitro and in vivo models of insulin resistance. Here we show that 10-min treatment with MES at 5 V (0.1 ms pulse duration) together with HS at 42°C increased the phosphorylation of insulin signaling molecules such as insulin receptor substrate (IRS) and Akt in HepG2 cells maintained in high-glucose medium. MES (12 V)+mild HS treatment of high fat-fed mice also increased the phosphorylation of insulin receptor β subunit (IRβ) and Akt in mice liver. In high fat-fed mice and db/db mice, MES+HS treatment for 10 min applied twice a week for 12–15 weeks significantly decreased fasting blood glucose and insulin levels and improved insulin sensitivity. The treated mice showed significantly lower weight of visceral and subcutaneous fat, a markedly improved fatty liver and decreased size of adipocytes. Our findings indicated that the combination of MES and HS alleviated insulin resistance and improved fat metabolism in diabetes mouse models, in part, by enhancing the insulin signaling pathway