The tight junction of the epithelial cell determines the characteristics of paracellular permeability across epithelium. Recent work points toward the claudin family of tight junction proteins as leading candidates for the molecular components that regulate paracellular permeability properties in epithelial tissues. Madin-Darby canine kidney (MDCK) strain I and II cells are models for the study of tight junctions and based on transepithelial electrical resistance (TER) contain "tight" and "leaky" tight junctions, respectively. Overexpression studies suggest that tight junction leakiness in these two strains of MDCK cells is conferred by expression of the tight junction protein claudin-2. Extracellular signal-regulated kinase (ERK) 1/2 activation by hepatocyte growth factor treatment of MDCK strain II cells inhibited claudin-2 expression and transiently increased TER. This process was blocked by the ERK 1/2 inhibitor U0126. Transfection of constitutively active mitogen-activated protein kinase/extracellular signal-regulated kinase kinase into MDCK strain II cells also inhibited claudin-2 expression and increased TER. MDCK strain I cells have higher levels of active ERK 1/2 than do MDCK strain II cells. U0126 treatment of MDCK strain I cells decreased active ERK 1/2 levels, induced expression of claudin-2 protein, and decreased TER by ϳ20-fold. U0126 treatment also induced claudin-2 expression and decreased TER in a high resistance mouse cortical collecting duct cell line (94D). These data show for the first time that the ERK 1/2 signaling pathway negatively controls claudin-2 expression in mammalian renal epithelial cells and provide evidence for regulation of tight junction paracellular transport by alterations in claudin composition within tight junction complexes.

Ultrathin β-In2S3 nanobelts have been successfully synthesized via a facile improved solvothermal route. The crystal phase, morphology, crystal lattice and composition of as-prepared products were characterized by XRD, FESEM, TEM, HRTEM and EDS, respectively. Results revealed that the as-synthesized β-In2S3 nanobelts are in cubic structure 50−90 nm in width, 13 ± 2 nm in thickness, and the overall length even up to several microns. A possible shape evolution and crystal growth mechanism was suggested, and the formation of β-In2S3 nanobelts resulted from the preferential growth along the ⟨220⟩ direction and enclosed by {202} and {022̅} crystallographic facets. The strong quantum confinement effect in UV−vis spectra and the blue emission in photoluminescence spectra imply the as-synthesized β-In2S3 nanobelts as a promising candidate for phosphor in display devices. Furthermore, the good photocatalytic effects indicate that these β-In2S3 nanobelts are likely to be applied as a new kind of photocatalyst in the future.

Regulating the synthesis of photocatalytic materials at the molecular level could affect the absorption of light and guide the synthesis of highly efficient photocatalysts for the photocatalytic degradation organic pollutants.