Rescue of Murine F508del CFTR Activity in Native Intestine by Low Temperature and Proteasome Inhibitors

Most patients with Cystic Fibrosis (CF) carry at least one allele with the F508del mutation, resulting in a CFTR chloride channel protein with a processing, gating and stability defect, but with substantial residual activity when correctly sorted to the apical membranes of epithelial cells. New therapies are therefore aimed at improving the folding and trafficking of F508del CFTR, (CFTR correctors) or at enhancing the open probability of the CFTR chloride channel (CFTR potentiators). Preventing premature breakdown of F508del CFTR is an alternative or additional strategy, which is investigated in this study. We established an ex vivo assay for murine F508del CFTR rescue in native intestinal epithelium that can be used as a pre-clinical test for candidate therapeutics. Overnight incubation of muscle stripped ileum in modified William's E medium at low temperature (26°C), and 4 h or 6 h incubation at 37°C with different proteasome inhibitors (PI: ALLN, MG-132, epoxomicin, PS341/bortezomib) resulted in fifty to hundred percent respectively of the wild type CFTR mediated chloride secretion (forskolin induced short-circuit current). The functional rescue was accompanied by enhanced expression of the murine F508del CFTR protein at the apical surface of intestinal crypts and a gain in the amount of complex-glycosylated CFTR (band C) up to 20% of WT levels. Sustained rescue in the presence of brefeldin A shows the involvement of a post-Golgi compartment in murine F508del CFTR degradation, as was shown earlier for its human counterpart. Our data show that proteasome inhibitors are promising candidate compounds for improving rescue of human F508del CFTR function, in combination with available correctors and potentiators

Endogenous type II cGMP-dependent protein kinase exists as a dimer in membranes and can Be functionally distinguished from the type I isoforms

In mammalian tissues two types of cGMP-dependent protein kinase (cGK) have been identified. In contrast to the dimeric cGK I, cGK II purified from pig intestine was shown previously to behave as a monomer. However, recombinant rat cGK II was found to have hydrodynamic parameters indicative of a homodimer. Chemical cross-linking studies showed that pig cGK II in intestinal membranes h

cGMP stimulation of cystic fibrosis transmembrane conductance regulator Cl- channels co-expressed with cGMP-dependent protein kinase type II but not type Ibeta

In order to investigate the involvement of cGMP-dependent protein kinase (cGK) type II in cGMP-provoked intestinal Cl- secretion, cGMP-dependent activation and phosphorylation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels was analyzed after expression of cGK II or cGK Ibeta in intact cells. An intestinal cell line which stably expresses CFTR (IEC-CF7) but contains no detectable endogenous cGK II was infected with a recombinant adenoviral vector containing the cGK II coding region (Ad-cGK II) resulting in co-expression of active cGK II. In these cells, CFTR was activated by membrane-permeant analogs of cGMP or by the cGMP-elevating hormone atrial natriuretic peptide as measured by 125I- efflux assays and whole-cell patch clamp analysis. In contrast, infection with recombinant adenoviruses expressing cGK Ibeta or luciferase did not convey cGMP sensitivity to CFTR in IEC-CF7 cells. Concordant with the activation of CFTR by only cGK II, infection with Ad-cGK II but not Ad-cGK Ibeta enabled cGMP analogs to increase CFTR phosphorylation in intact cells. These and other data provide evidence that endogenous cGK II is a key mediator of cGMP-provoked activation of CFTR in cells where both proteins are co-localized, e. g. intestinal epithelial cells. Furthermore, they demonstrate that neither the soluble cGK Ibeta nor cAMP-dependent protein kinase are able to substitute for cGK II in this cGMP-regulated function

Regulation of chloride transport in cultured normal and cystic fibrobis keratinocytes

Abstract Cultured normal (N) and cystic fibrosis (CF) keratinocytes were evaluated for their Cl−-transport properties by patch-clamp-, Ussing chamber- and isotopic efflux-measurements. Special attention was paid to a 32 pS outwardly rectifying Cl− channel which has been reported to be activated upon activation of cAMP-dependent pathways in N, but not in CF cells. This depolarization-induced Cl− channel was found with a similar incidence in N and CF apical keratininocyte membranes. However, activation of this channel in excised patches by protein kinase (PK)-A or PK-C was not successfull in either N or CF keratinocytes. Forskolin was not able to activate Cl− channels in N and CF cell-attached patches. The Ca2+-ionophore A23187 activated in cell-attached patches a linear 17 pS Cl− channel in both N and CF cells. This channel inactivated upon excision. No relationship between the cell-attached 17 pS and the excised 32 pS channel could be demonstrated. Returning to the measurement of Cl− transport at the macroscopic level, we found that a drastic rise in intracellular cAMP induced by forskolin did in N as well as CF cells not result in a change in the short-circuit current (Isc) or the fractional efflux rates of 36Cl− and 125I−. In contrast, addition of A23187 resulted in an increase of the Isc and in the isotopic anion efflux rates in N and CF cells. We conclude that Cl−-transport in cultured human keratinocytes can be activated by Ca2+, but not by cAMP-dependent pathways

Differential thermostability and response to cystic fibrosis transmembrane conductance regulator potentiators of human and mouse F508del-CFTR

Cross-species comparative studies have highlighted differences between human and mouse cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial Cl− channel defective in cystic fibrosis (CF). Here, we compare the impact of the most common CF mutation F508del on the function of human and mouse CFTR heterologously expressed in mammalian cells and their response to CFTR modulators using the iodide efflux and patch-clamp techniques. Once delivered to the plasma membrane, human F508del-CFTR exhibited a severe gating defect characterized by infrequent channel openings and was thermally unstable, deactivating within minutes at 37°C. By contrast, the F508del mutation was without effect on the gating pattern of mouse CFTR, and channel activity demonstrated thermostability at 37°C. Strikingly, at all concentrations tested, the clinically approved CFTR potentiator ivacaftor was without effect on the mouse F508del-CFTR Cl− channel. Moreover, eight CFTR potentiators, including ivacaftor, failed to generate CFTR-mediated iodide efflux from CHO cells expressing mouse F508del-CFTR. However, they all produced CFTR-mediated iodide efflux with human F508del-CFTR-expressing CHO cells, while fifteen CFTR correctors rescued the plasma membrane expression of both human and mouse F508del-CFTR. Interestingly, the CFTR potentiator genistein enhanced CFTR-mediated iodide efflux from CHO cells expressing either human or mouse F508del-CFTR, whereas it only potentiated human F508del-CFTR Cl− channels in cell-free membrane patches, suggesting that its action on mouse F508del-CFTR is indirect. Thus, the F508del mutation has distinct effects on human and mouse CFTR Cl− channels

DOC1-Dependent Recruitment of NURD Reveals Antagonism with SWI/SNF during Epithelial-Mesenchymal Transition i

The Nucleosome Remodeling and Deacetylase (NURD) complex is a key regulator of cell differentiation that has also been implicated in tumorigenesis. Loss of the NURD subunit Deleted in Oral Cancer 1 (DOC1) is associated with human oral squamous cell carcinomas (OSCCs). Here, we show that restoration of DOC1 expression in OSCC cells leads to a reversal of epithelial-mesenchymal transition (EMT). This is caused by the DOC1-dependent targeting of NURD to repress key transcriptional regulators of EMT. NURD recruitment drives extensive epigenetic reprogramming, including eviction of the SWI/SNF remodeler, formation of inaccessible chromatin, H3K27 deacetylation, and binding of PRC2 and KDM1A, followed by H3K27 methylation and H3K4 demethylation. Strikingly, depletion of SWI/SNF mimics the effects of DOC1 re-expression. Our results suggest that SWI/SNF and NURD function antagonistically to control chromatin state and transcription. We propose that disturbance of this dynamic equilibrium may lead to defects in gene expression that promote oncogenesis

Toward an internally consistent astronomical distance scale

Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press (chapter 8 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

Controlling bias and inflation in epigenome- and transcriptome-wide association studies using the empirical null distribution

We show that epigenome- and transcriptome-wide association studies (EWAS and TWAS) are prone to significant inflation and bias of test statistics, an unrecognized phenomenon introducing spurious findings if left unaddressed. Neither GWAS-based methodology nor state-of-the-art confounder adjustment methods completely remove bias and inflation. We propose a Bayesian method to control bias and inflation in EWAS and TWAS based on estimation of the empirical null distribution. Using simulations and real data, we demonstrate that our method maximizes power while properly controlling the false positive rate. We illustrate the utility of our method in large-scale EWAS and TWAS meta-analyses of age and smoking

A high-quality human reference panel reveals the complexity and distribution of genomic structural variants

Structural variation (SV) represents a major source of differences between individual human genomes and has been linked to disease phenotypes. However, the majority of studies provide neither a global view of the full spectrum of these variants nor integrate them into reference panels of genetic variation. Here, we analyse whole genome sequencing data of 769 individuals from 250 Dutch families, and provide a haplotype-resolved map of 1.9 million genome variants across 9 different variant classes, including novel forms of complex indels, and retrotransposition-mediated insertions of mobile elements and processed RNAs. A large proportion are previously under reported variants sized between 21 and 100 bp. We detect 4 megabases of novel sequence, encoding 11 new transcripts. Finally, we show 191 known, trait-associated SNPs to be in strong linkage disequilibrium with SVs and demonstrate that our panel facilitates accurate imputation of SVs in unrelated individuals

WGS-based telomere length analysis in Dutch family trios implicates stronger maternal inheritance and a role for RRM1 gene

Telomere length (TL) regulation is an important factor in ageing, reproduction and cancer development. Genetic, hereditary and environmental factors regulating TL are currently widely investigated, however, their relative contribution to TL variability is still understudied. We have used whole genome sequencing data of 250 family trios from the Genome of the Netherlands project to perform computational measurement of TL and a series of regression and genome-wide association analyses to reveal TL inheritance patterns and associated genetic factors. Our results confirm that TL is a largely heritable trait, primarily with mother’s, and, to a lesser extent, with father’s TL having the strongest influence on the offspring. In this cohort, mother’s, but not father’s age at conception was positively linked to offspring TL. Age-related TL attrition of 40 bp/year had relatively small influence on TL variability. Finally, we have identified TL-associated variations in ribonuclease reductase catalytic subunit M1 (RRM1 gene), which is known to regulate telomere maintenance in yeast. We also highlight the importance of multivariate approach and the limitations of existing tools for the analysis of TL as a polygenic heritable quantitative trait