A sequence upstream of canonical PDZ-binding motif within CFTR COOH-terminus enhances NHERF1 interaction

CFTR bearing variant p.Phe312del exhibits function inconsistent with phenotype and negligible response to ivacaftor

The chloride channel dysfunction caused by deleterious cystic fibrosis transmembrane conductance regulator (CFTR) variants generally correlates with severity of cystic fibrosis (CF). However, 3 adults bearing the common severe variant p.Phe508del (legacy: F508del) and a deletion variant in an ivacaftor binding region of CFTR (p.Phe312del; legacy: F312del) manifested only elevated sweat chloride concentration (sw[Cl-]; 87-105 mEq/L). A database review of 25 individuals with F312del and a CF-causing variant revealed elevated sw[Cl-] (75-123 mEq/L) and variable CF features. F312del occurs at a higher-than-expected frequency in the general population, confirming that individuals with F312del and a CF-causing variant do not consistently develop overt CF features. In primary nasal cells, CFTR bearing F312del and F508del generated substantial chloride transport (66.0% ± 4.5% of WT-CFTR) but did not respond to ivacaftor. Single-channel analysis demonstrated that F312del did not affect current flow through CFTR, minimally altered gating, and ablated the ivacaftor response. When expressed stably in CF bronchial epithelial (CFBE41o-) cells, F312del-CFTR demonstrated residual function (50.9% ± 3.3% WT-CFTR) and a subtle decrease in forskolin response compared with WT-CFTR. F312del provides an exception to the established correlation between CFTR chloride transport and CF phenotype and informs our molecular understanding of ivacaftor response.

The role of CDX2 in renal tubular lesions during diabetic kidney disease

Renal tubules are vulnerable targets of various factors causing kidney injury in diabetic kidney disease (DKD), and the degree of tubular lesions is closely related to renal function. Abnormal renal tubular epithelial cells (RTECs) differentiation and depletion of cell junction proteins are important in DKD pathogenesis. Caudal-type homeobox transcription factor 2 (CDX2), represents a key nuclear transcription factor that maintains normal proliferation and differentiation of the intestinal epithelium. The present study aimed to evaluate the effects of CDX2 on RTECs differentiation and cell junction proteins in DKD. The results demonstrated that CDX2 was mainly localized in renal tubules, and downregulated in various DKD models. CDX2 upregulated E-cadherin and suppressed partial epithelial-mesenchymal transition (EMT), which can alleviate hyperglycemia-associated RTECs injury. Cystic fibrosis transmembrane conductance regulator (CFTR) was regulated by CDX2 in NRK-52E cells, and CFTR interfered with β-catenin activation by binding to Dvl2, which is an essential component of Wnt/β-catenin signaling. CFTR knockdown abolished the suppressive effects of CDX2 on Wnt/β-catenin signaling, thereby upregulating cell junction proteins and inhibiting partial EMT in RTECs. In summary, CDX2 can improve renal tubular lesions during DKD by increasing CFTR amounts to suppress the Wnt/β-catenin signaling pathway.

A Peptide-Nucleic Acid Targeting miR-335-5p Enhances Expression of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Gene with the Possible Involvement of the CFTR Scaffolding Protein NHERF1

(1) Background: Up-regulation of the Cystic Fibrosis Transmembrane Conductance Regulator gene (CFTR) might be of great relevance for the development of therapeutic protocols for cystic fibrosis (CF). MicroRNAs are deeply involved in the regulation of CFTR and scaffolding proteins (such as NHERF1, NHERF2 and Ezrin). (2) Methods: Content of miRNAs and mRNAs was analyzed by RT-qPCR, while the CFTR and NHERF1 production was analyzed by Western blotting. (3) Results: The results here described show that the CFTR scaffolding protein NHERF1 can be up-regulated in bronchial epithelial Calu-3 cells by a peptide-nucleic acid (PNA) targeting miR-335-5p, predicted to bind to the 3′-UTR sequence of the NHERF1 mRNA. Treatment of Calu-3 cells with this PNA (R8-PNA-a335) causes also up-regulation of CFTR. (4) Conclusions: We propose miR-335-5p targeting as a strategy to increase CFTR. While the efficiency of PNA-based targeting of miR-335-5p should be verified as a therapeutic strategy in CF caused by stop-codon mutation of the CFTR gene, this approach might give appreciable results in CF cells carrying other mutations impairing the processing or stability of CFTR protein, supporting its application in personalized therapy for precision medicine.

Phospholipase C controls chloride-dependent short-circuit current in human bronchial epithelial cells

Chloride secretion by airway epithelial cells is primordial for water and ion homeostasis and airways surface prevention of infections. This secretion is impaired in several human diseases, including cystic fibrosis, a genetic pathology due to CFTR gene mutations leading to chloride channel defects. A potential therapeutic approach is aiming at increasing chloride secretion either by correcting the mutated CFTR itself or by stimulating non-CFTR chloride channels at the plasma membrane. Here, we studied the role of phospholipase C in regulating the transepithelial chloride secretion in human airway epithelial 16HBE14o- and CFBE cells over-expressing wild type (WT)- or F508del-CFTR. Western blot analysis shows expression of the three endogenous phospholipase C (PLC) isoforms, namely, PLCδ1, PLCγ1, and PLCβ3 in 16HBE14o- cells. In 16HBE14o- cells, we performed Ussing chamber experiments after silencing each of these PLC isoforms or using the PLC inhibitor U73122 or its inactive analogue U73343. Our results show the involvement of PLCβ3 and PLCγ1 in CFTR-dependent short-circuit current activated by forskolin, but not of PLCδ1. In CFBE-WT CFTR and corrected CFBE-F508del CFTR cells, PLCβ3 silencing also inhibits CFTR-dependent current activated by forskolin and UTP-activated calcium-dependent chloride channels (CaCC). Our study supports the importance of PLC in maintaining CFTR-dependent chloride secretion over time, getting maximal CFTR-dependent current and increasing CaCC activation in bronchial epithelial cells.

Treatment of human airway epithelial Calu-3 cells with a peptide-nucleic acid (PNA) targeting the microRNA miR-101-3p is associated with increased expression of the cystic fibrosis Transmembrane Conductance Regulator () gene

Since the identification of microRNAs (miRNAs) involved in the regulation of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, miRNAs known to down-regulate the expression of the CFTR and associated proteins have been investigated as potential therapeutic targets. Here we show that miR-101-3p, targeting the 3'-UTR sequence of the CFTR mRNA, can be selectively inhibited by a peptide nucleic acid (PNA) carrying a full complementary sequence. With respect to clinical relevance of microRNA targeting, it is expected that reduction in concentration of miRNAs (the anti-miRNA approach) could be associated with increasing amounts of target mRNAs. Consistently to this hypothesis, we report that PNA-mediated inhibition of miR-101-3p was accompanied by CFTR up-regulation. Next Generation Sequencing (NGS) was performed in order to verify the effects of the anti-miR-101-3p PNA on the Calu-3 miRNome. Upon inhibition of miR-101-3p we observed a fold change (FC) expression <2 of the majority of miRNAs (403/479, 84.13%), whereas we identified a list of dysregulated miRNAs, suggesting that specific miRNA inhibition (in our case miR-101-3p) might be accompanied by alteration of expression of other miRNAs, some of them known to be involved in Cystic Fibrosis (CF), such as miR-155-5p and miR-125b-5p.

Integrated Transcriptomic and Proteomic Analysis of Human Eccrine Sweat Glands Identifies Missing and Novel Proteins

The eccrine sweat gland is an exocrine gland that is involved in the secretion of sweat for control of temperature. Malfunction of the sweat glands can result in disorders such as miliaria, hyperhidrosis and bromhidrosis. Understanding the transcriptome and proteome of sweat glands is important for understanding their physiology and role in diseases. However, no systematic transcriptome or proteome analysis of sweat glands has yet been reported. Here, we isolated eccrine sweat glands from human skin by microdissection and performed RNA-seq and proteome analysis. In total, ∼138,000 transcripts and ∼6,100 proteins were identified. Comparison of the RNA-seq data of eccrine sweat glands to other human tissues revealed the closest resemblance to the cortex region of kidneys. The proteome data showed enrichment of proteins involved in secretion, reabsorption, and wound healing. Importantly, protein level identification of the calcium ion channel TRPV4 suggests the importance of eccrine sweat glands in re-epithelialization of wounds and prevention of dehydration. We also identified 2 previously missing proteins from our analysis. Using a proteogenomic approach, we identified 7 peptides from 5 novel genes, which we validated using synthetic peptides. Most of the novel proteins were from short open reading frames (sORFs) suggesting that many sORFs still remain to be annotated in the human genome. This study presents the first integrated analysis of the transcriptome and proteome of the human eccrine sweat gland and would become a valuable resource for studying sweat glands in physiology and disease.

Characterization of Δ(G970-T1122)-CFTR, the most frequent CFTR mutant identified in Japanese cystic fibrosis patients

A massive deletion over three exons 16-17b in the CFTR gene was identified in Japanese CF patients with the highest frequency (about 70% of Japanese CF patients definitely diagnosed). This pathogenic mutation results in a deletion of 153 amino acids from glycine at position 970 (G970) to threonine at 1122 (T1122) in the CFTR protein without a frameshift. We name it Δ(G970-T1122)-CFTR. In the present study, we characterized the Δ(G970-T1122)-CFTR expressed in CHO cells using immunoblots and a super resolution microscopy. Δ(G970-T1122)-CFTR proteins were synthesized and core-glycosylated but not complex-glycosylated. This observation suggests that the Δ(G970-T1122) mutation can be categorized into the class II mutation like ΔF508. However, VX-809 a CFTR corrector that can help maturation of ΔF508, had no effect on Δ(G970-T1122). Interestingly C-terminal FLAG tag seems to partially rescue the trafficking defect of Δ(G970-T1122)-CFTR; however the rescued Δ(G970-T1122)-CFTR proteins do not assume channel function. Japanese, and perhaps people in other Asian nations, carry a class II mutation Δ(G970-T1122) with a higher frequency than previously appreciated. Further study of the Δ(G970-T1122)-CFTR is essential for understanding CF and CFTR-related diseases particularly in Asian countries.

The epithelial sodium channel (ENaC) as a therapeutic target for cystic fibrosis

Cystic fibrosis (CF) is a monogenic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR dysfunction is characterized by abnormal mucociliary transport due to a dehydrated airway surface liquid (ASL) and hyperviscous mucus, among other pathologies of host defense. ASL depletion is caused by the absence of CFTR mediated chloride secretion along with continued activity of the epithelial sodium channel (ENaC) activity, which can also be affected by CFTR mediated anion conductance. Therefore, ENaC has been proposed as a therapeutic target to ameliorate ASL dehydration and improve mucus transport. Inhibition of ENaC has been shown to restore ASL hydration and enhance mucociliary transport in induced models of CF lung disease. To date, no therapy inhibiting ENaC has successfully translated to clinical efficacy, in part due to concerns regarding off-target effects, systemic exposure, durability of effect, and adverse effects. Recent efforts have been made to develop novel, rationally designed therapeutics to produce-specific, long-lasting inhibition of ENaC activity in the airways while simultaneously minimizing off target fluid transport effects, systemic exposure and side effects. Such approaches comprise next-generation small molecule direct inhibitors, indirect channel-activating protease inhibitors, synthetic peptide analogs, and oligonucleotide-based therapies. These novel therapeutics represent an exciting step forward in the development of ENaC-directed therapies for CF.

Capitalizing on the heterogeneous effects of CFTR nonsense and frameshift variants to inform therapeutic strategy for cystic fibrosis

CFTR modulators have revolutionized the treatment of individuals with cystic fibrosis (CF) by improving the function of existing protein. Unfortunately, almost half of the disease-causing variants in CFTR are predicted to introduce premature termination codons (PTC) thereby causing absence of full-length CFTR protein. We hypothesized that a subset of nonsense and frameshift variants in CFTR allow expression of truncated protein that might respond to FDA-approved CFTR modulators. To address this concept, we selected 26 PTC-generating variants from four regions of CFTR and determined their consequences on CFTR mRNA, protein and function using intron-containing minigenes expressed in 3 cell lines (HEK293, MDCK and CFBE41o-) and patient-derived conditionally reprogrammed primary nasal epithelial cells. The PTC-generating variants fell into five groups based on RNA and protein effects. Group A (reduced mRNA, immature (core glycosylated) protein, function <1% (n = 5)) and Group B (normal mRNA, immature protein, function <1% (n = 10)) variants were unresponsive to modulator treatment. However, Group C (normal mRNA, mature (fully glycosylated) protein, function >1% (n = 5)), Group D (reduced mRNA, mature protein, function >1% (n = 5)) and Group E (aberrant RNA splicing, mature protein, function > 1% (n = 1)) variants responded to modulators. Increasing mRNA level by inhibition of NMD led to a significant amplification of modulator effect upon a Group D variant while response of a Group A variant was unaltered. Our work shows that PTC-generating variants should not be generalized as genetic 'nulls' as some may allow generation of protein that can be targeted to achieve clinical benefit.

Roles of NHERF Family of PDZ-Binding Proteins in Regulating GPCR Functions

Multicellular organisms are equipped with an array of G-protein-coupled receptors (GPCRs) that mediate cell-cell signaling allowing them to adapt to environmental cues and ultimately survive. This is mechanistically possible through complex intracellular GPCR machinery that encompasses a vast network of proteins. Within this network, there is a group called scaffolding proteins that facilitate proper localization of signaling proteins for a quick and robust GPCR response. One protein family within this scaffolding group is the PSD-95/Dlg/ZO-1 (PDZ) family which is important for GPCR localization, internalization, recycling, and downstream signaling. Although the PDZ family of proteins regulate the functions of several receptors, this chapter focuses on a subfamily within the PDZ protein family called the Na⁺/H⁺ exchanger regulatory factors (NHERFs). Here we extensively review the predominantly characterized roles of NHERFs in renal phosphate absorption, intestinal ion regulation, cancer progression, and immune cell functions. Finally, we discuss the future perspectives and possible clinical application of targeting NHERFs in several disorders.