Developmental lung expression and transcriptional regulation of Claudin-6 by TTF-1, Gata-6, and FoxA2

Abstract

BackgroundClaudins are transmembrane proteins expressed in tight junctions that prevent paracellular transport of extracellular fluid and a variety of other substances. However, the expression profile of Claudin-6 (Cldn6) in the developing lung has not been characterized.Methods and resultsCldn6 expression was determined during important periods of lung organogenesis by microarray analysis, qPCR and immunofluorescence. Expression patterns were confirmed to peak at E12.5 and diminish as lung development progressed. Immunofluorescence revealed that Cldn6 was detected in cells that also express TTF-1 and FoxA2, two critical transcriptional regulators of pulmonary branching morphogenesis. Cldn6 was also observed in cells that express Sox2 and Sox9, factors that influence cell differentiation in the proximal and distal lung, respectively. In order to assess transcriptional control of Cldn6, 0.5, 1.0, and 2.0-kb of the proximal murine Cldn6 promoter was ligated into a luciferase reporter and co-transfected with expression vectors for TTF-1 or two of its important transcriptional co-regulators, FoxA2 and Gata-6. In almost every instance, TTF-1, FoxA2, and Gata-6 activated gene transcription in cell lines characteristic of proximal airway epithelium (Beas2B) and distal alveolar epithelium (A-549).ConclusionsThese data revealed for the first time that Cldn6 might be an important tight junctional component expressed by pulmonary epithelium during lung organogenesis. Furthermore, Cldn6-mediated aspects of cell differentiation may describe mechanisms of lung perturbation coincident with impaired cell junctions and abnormal membrane permeability.

Conditional pulmonary over-expression of Claudin 6 during embryogenesis delays lung morphogenesis

“…We have already published in vitro research that specifies Cldn6 regulatory programs mediated by TTF-1, Gata-6, and FoxA2 (Jimenez et al, 2014). This work expands the impact of previous in vitro work by demonstrating potential feedback between these factors and Cldn6 availability in vivo.…”

“…In addition, FoxA2 is required for normal airway epithelial differentiation and lung organogenesis (Wan et al, 2004). Thus, Cldn6 augmentation during lung organogenesis may directly or indirectly impact fundamental processes including cell population expansion and differentiation (Jimenez et al, 2014).…”

“…During murine lung morphogenesis, Cldn6 is highly expressed between embryonic day (E) 10.5 to E 16.5. A general theme exists wherein higher expression occurs during early stages of lung development with diminished expression as lung morphogenesis proceeds (Jimenez et al, 2014;Troy et al, 2009;Turksen and Troy, 2002).…”

“…During murine lung morphogenesis, Cldn6 is highly expressed between embryonic day (E) 10.5 to E 16.5. A general theme exists wherein higher expression occurs during early stages of lung development with diminished expression as lung morphogenesis proceeds (Jimenez et al, 2014;Troy et al, 2009;Turksen and Troy, 2002).Given the diversity and complexity of Cldn family members, conditional transgenic overexpression and knock-down models of maturing pulmonary airspaces. Understanding the role of Cldn6 should shed light on the functions of TJs during lung development and in conditions where compromised lung development predisposes individuals to hypoplastic lung complications.…”

Claudins and cancer: Fall of the soldiers entrusted to protect the gate and keep the barrier intact

“…EGF-stimulation also regulates claudin-4 transcription in MDCK-II cells in Stat-3-dependent manner while Twist-1 suppresses claudin-4 expression in esophageal cancer cells [94]. On the other hand, expression of claudin-6, which was recently recognized as a marker of the mouse pluripotent stem cells, is regulated by TTF, GATA-6 and FoxA2 transcription factors [95]. Claudin-18, on the other hand, is frequently downregulated in gastric and hepatocellular carcinoma and is a direct target of T/EBP/NKX2.1 homeodomain transcription factor.…”