The Effect of Dynasore Upon the Negative Interaction Between ENaC and CFTR Channels in Xenopus laevis Oocytes.

Shroom is a family of related proteins linked to the actin cytoskeleton, and one of them, xShroom1, is constitutively expressed in Xenopus laevis oocytes which is required for the expression of the epithelial sodium channel (ENaC). On the other hand, ENaC and the cystic fibrosis transmembrane regulator (CFTR) are co-expressed in many types of cells with a negative or positive interaction depending on the studied tissues. Here, we measured the amiloride-sensitive ENaC currents (INaamil) and CFTR currents (ICFTR) with voltage clamp techniques in oocytes co-injected with ENaC and/or CFTR and xShroom1 antisense oligonucleotides. The objective was to study the mechanism of regulation of ENaC by CFTR when xShroom1 was suppressed and the endocytic traffic of CFTR was blocked. CFTR activation had a measurable negative effect on ENaC and this activation resulted in a greater inhibition of INaamil than with xShroom1 antisense alone. Our results with Dynasore, a drug that acts as an inhibitor of endocytic pathways, suggest that the changes in INaamil by xShroom1 downregulation were probably due to an increment in channel endocytosis. An opposite effect was observed when ICFTR was measured. Thus, when xShroom1 was downregulated, the ICFTR was larger than in the control experiments and this effect is not observed with Dynasore. A speculative explanation could be that xShroom1 exerts a dual effect on the endocytic traffic of ENaC and CFTR and these actions were canceled with Dynasore. In the presence of Dynasore, no difference in either INaamil or ICFTR was observed when xShroom1 was downregulated.

CFTR channel in oocytes from Xenopus laevis and its regulation by xShroom1 protein.

Shroom is a family of related proteins linked to the actin cytoskeleton. xShroom1 is constitutively expressed in Xenopus laevis oocytes, and it is required for the expression of the epithelial sodium channel (ENaC). As there is a close relationship between ENaC and the cystic fibrosis transmembrane regulator (CFTR), we examined the action of xShroom1 on CFTR expression and activity. Biotinylation was used to measure CFTR surface expression, and currents were registered with voltage clamp when stimulated with forskolin and 3-isobutyl-1-methylxanthine. Oocytes were coinjected with CFTR complementary RNAs (cRNAs) and xShroom1 sense or antisense oligonucleotides. We observed an increment in CFTR currents and CFTR surface expression in oocytes coinjected with CFTR and xShroom1 antisense oligonucleotides. MG-132, a proteasome inhibitor, did not prevent the increment in currents when xShroom1 was suppressed by antisense oligonucleotides. In addition, we inhibited the delivery of newly synthesized proteins to the plasma membrane with BFA and we found that the half-life of plasma membrane CFTR was prolonged when coinjected with the xShroom1 antisense oligonucleotides. Chloroquine, an inhibitor of the late endosome/lysosome, did not significantly increase CFTR currents when xShroom1 expression was inhibited. The higher expression of CFTR when xShroom1 is suppressed is in concordance with the functional studies suggesting that the suppression of the xShroom1 protein resulted in an increment in CFTR currents by promoting the increase of the half-life of CFTR in the plasma membrane. The role of xShroom1 in regulating CFTR expression could be relevant in the understanding of the channel malfunction in several diseases.

[CFTR and ENaC functions in cystic fibrosis]. / Funciones de los canales iónicos CFTR y ENAC en la fibrosis quística.

Cystic fibrosis is caused by dysfunction or lack of the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel that has a key role in maintaining ion and water homoeostasis in different tissues. CFTR is a cyclic AMP-activated Cl- channel found in the apical and basal plasma membrane of airway, intestinal, and exocrine epithelial cells. One of CFTR's primary roles in the lungs is to maintain homoeostasis of the airway surface liquid layer through its function as a chloride channel and its regulation of the epithelial sodium channel ENaC. More than 1900 CFTR mutations have been identified in the cftr gene. The disease is characterized by viscous secretions of the exocrine glands in multiple organs and elevated levels of sweat sodium chloride. In cystic fibrosis, salt and fluid absorption is prevented by the loss of CFTR and ENaC is not appropriately regulated, resulting in increased fluid and sodium resorption from the airways and formation of a contracted viscous surface liquid layer. In the sweat glands both Na+ and Cl- ions are retained in the lumen, causing significant loss of electrolytes during sweating. Thus, elevated sweat NaCl concentration is the basis of the classic pilocarpine-induced sweat test as a diagnostic feature of the disease. Here we discuss the ion movement of Cl- and Na+ ions in two tissues, sweat glands and in the air surface as well as the role of ENaC in the pathogenesis of cystic fibrosis.

NCoA3 upregulation in breast cancer­associated adipocytes elicits an inflammatory profile.

Nuclear receptor coactivator 3 (NCoA3) is a transcriptional coactivator of NF­κB and other factors, which is expressed at relatively low levels in normal cells and is amplified or overexpressed in several types of cancer, including breast tumors. NCoA3 levels have been shown to be decreased during adipogenesis; however, its role in tumor­surrounding adipose tissue (AT) remains unknown. Therefore, the present study assessed the modulation of NCoA3 in breast cancer­associated adipocytes and evaluated its association with the expression of inflammatory markers. 3T3­L1 adipocytes were stimulated with conditioned medium from human breast cancer cell lines and the expression levels of NCoA3 were evaluated by reverse transcription­quantitative (q)PCR. NF­κB activation was measured by immunofluorescence, and tumor necrosis factor and monocyte chemoattractant protein 1 levels were analyzed by qPCR and dot blot assays. The results obtained from the in vitro model were supported using mammary AT (MAT) from female mice, MAT adjacent to tumors from patients with breast cancer and bioinformatics analysis. The results revealed that adipocytes expressing high levels of NCoA3 were mainly associated with a pro­inflammatory profile. In 3T3­L1 adipocytes, NCoA3 downregulation or NF­κB inhibition reversed the expression of inflammatory molecules. In addition, MAT from patients with a worse prognosis exhibited high levels of this coactivator. Notably, adipocyte NCoA3 levels could be modulated by inflammatory signals from tumors. The modulation of NCoA3 levels in synergy with NF­κB activity in MAT in a tumor context could be factors required to establish breast cancer­associated inflammation. As adipocytes are involved in the development and progression of breast cancer, this signaling network deserves to be further investigated to improve future tumor treatments.

Funciones de los canales iónicos CFTR y ENAC en la fibrosis quística / CFTR and ENaC functions in cystic fibrosis

La fibrosis quística se debe a la ausencia o defecto del canal transmembrana regulador de la fibrosis quística (CFTR), un canal de cloruro codificado en el gen cftr que juega un papel clave en la homeostasis del agua e iones. El CFTR es activado por el AMPc y se localiza en las membranas apicales y basolaterales de las vías aéreas, intestino y glándulas exocrinas. Una de sus funciones primarias en los pulmones es mantener la capa de líquido superficial a través de su función de canal y regular el canal epitelial de sodio sensible al amiloride (ENaC). Se han identificado más de 1900 mutaciones en el gen cftr. La enfermedad se caracteriza por secreciones viscosas en las glándulas exocrinas y por niveles elevados de cloruro de sodio en el sudor. En la fibrosis quística el CFTR no funciona y el ENaC está desregulado; el resultado es un aumento en la reabsorción de sodio y agua con la formación de un líquido viscoso. En las glándulas sudoríparas tanto el Na+ como el Cl- se retienen en el lumen causando una pérdida de electrolitos durante la sudoración y el NaCl se elimina al sudor. Así, los niveles elevados de NaCl son la base del test del sudor inducido por pilocarpina, un método de diagnóstico para la enfermedad. En esta revisión se discuten los movimientos de Cl- y Na+ en las glándulas sudoríparas y pulmón así como el papel del ENaC en la patogénesis de la enfermedad.(AU)

Cystic fibrosis is caused by dysfunction or lack of the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel that has a key role in maintaining ion and water homoeostasis in different tissues. CFTR is a cyclic AMP-activated Cl- channel found in the apical and basal plasma membrane of airway, intestinal, and exocrine epithelial cells. One of CFTR’s primary roles in the lungs is to maintain homoeostasis of the airway surface liquid layer through its function as a chloride channel and its regulation of the epithelial sodium channel ENaC. More than 1900 CFTR mutations have been identified in the cftr gene. The disease is characterized by viscous secretions of the exocrine glands in multiple organs and elevated levels of sweat sodium chloride. In cystic fibrosis, salt and fluid absorption is prevented by the loss of CFTR and ENaC is not appropriately regulated, resulting in increased fluid and sodium resorption from the airways and formation of a contracted viscous surface liquid layer. In the sweat glands both Na+ and Cl- ions are retained in the lumen, causing significant loss of electrolytes during sweating. Thus, elevated sweat NaCl concentration is the basis of the classic pilocarpine-induced sweat test as a diagnostic feature of the disease. Here we discuss the ion movement of Cl- and Na+ ions in two tissues, sweat glands and in the air surface as well as the role of ENaC in the pathogenesis of cystic fibrosis.(AU)

Funciones de los canales iónicos CFTR y ENAC en la fibrosis quística / CFTR and ENaC functions in cystic fibrosis

La fibrosis quística se debe a la ausencia o defecto del canal transmembrana regulador de la fibrosis quística (CFTR), un canal de cloruro codificado en el gen cftr que juega un papel clave en la homeostasis del agua e iones. El CFTR es activado por el AMPc y se localiza en las membranas apicales y basolaterales de las vías aéreas, intestino y glándulas exocrinas. Una de sus funciones primarias en los pulmones es mantener la capa de líquido superficial a través de su función de canal y regular el canal epitelial de sodio sensible al amiloride (ENaC). Se han identificado más de 1900 mutaciones en el gen cftr. La enfermedad se caracteriza por secreciones viscosas en las glándulas exocrinas y por niveles elevados de cloruro de sodio en el sudor. En la fibrosis quística el CFTR no funciona y el ENaC está desregulado; el resultado es un aumento en la reabsorción de sodio y agua con la formación de un líquido viscoso. En las glándulas sudoríparas tanto el Na+ como el Cl- se retienen en el lumen causando una pérdida de electrolitos durante la sudoración y el NaCl se elimina al sudor. Así, los niveles elevados de NaCl son la base del test del sudor inducido por pilocarpina, un método de diagnóstico para la enfermedad. En esta revisión se discuten los movimientos de Cl- y Na+ en las glándulas sudoríparas y pulmón así como el papel del ENaC en la patogénesis de la enfermedad.

Cystic fibrosis is caused by dysfunction or lack of the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel that has a key role in maintaining ion and water homoeostasis in different tissues. CFTR is a cyclic AMP-activated Cl- channel found in the apical and basal plasma membrane of airway, intestinal, and exocrine epithelial cells. One of CFTR’s primary roles in the lungs is to maintain homoeostasis of the airway surface liquid layer through its function as a chloride channel and its regulation of the epithelial sodium channel ENaC. More than 1900 CFTR mutations have been identified in the cftr gene. The disease is characterized by viscous secretions of the exocrine glands in multiple organs and elevated levels of sweat sodium chloride. In cystic fibrosis, salt and fluid absorption is prevented by the loss of CFTR and ENaC is not appropriately regulated, resulting in increased fluid and sodium resorption from the airways and formation of a contracted viscous surface liquid layer. In the sweat glands both Na+ and Cl- ions are retained in the lumen, causing significant loss of electrolytes during sweating. Thus, elevated sweat NaCl concentration is the basis of the classic pilocarpine-induced sweat test as a diagnostic feature of the disease. Here we discuss the ion movement of Cl- and Na+ ions in two tissues, sweat glands and in the air surface as well as the role of ENaC in the pathogenesis of cystic fibrosis.

Funciones de los canales iónicos CFTR y ENAC en la fibrosis quística. / [CFTR and ENaC functions in cystic fibrosis].

Cystic fibrosis is caused by dysfunction or lack of the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel that has a key role in maintaining ion and water homoeostasis in different tissues. CFTR is a cyclic AMP-activated Cl- channel found in the apical and basal plasma membrane of airway, intestinal, and exocrine epithelial cells. One of CFTRs primary roles in the lungs is to maintain homoeostasis of the airway surface liquid layer through its function as a chloride channel and its regulation of the epithelial sodium channel ENaC. More than 1900 CFTR mutations have been identified in the cftr gene. The disease is characterized by viscous secretions of the exocrine glands in multiple organs and elevated levels of sweat sodium chloride. In cystic fibrosis, salt and fluid absorption is prevented by the loss of CFTR and ENaC is not appropriately regulated, resulting in increased fluid and sodium resorption from the airways and formation of a contracted viscous surface liquid layer. In the sweat glands both Na+ and Cl- ions are retained in the lumen, causing significant loss of electrolytes during sweating. Thus, elevated sweat NaCl concentration is the basis of the classic pilocarpine-induced sweat test as a diagnostic feature of the disease. Here we discuss the ion movement of Cl- and Na+ ions in two tissues, sweat glands and in the air surface as well as the role of ENaC in the pathogenesis of cystic fibrosis.