Hyperosmolarity-induced up-regulation of claudin-4 mediated by NADPH oxidase-dependent H2O2 production and Sp1/c-Jun cooperation.

Claudin-4 is exclusively localized in the tight collecting ducts in the renal tubule. We examined what molecular mechanism is involved in the regulation of claudin-4 expression. In Madin-Darby canine kidney cells, hyperosmolarity increased the expression level of claudin-4 and the production of reactive oxygen species, which were inhibited by diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, and manganese (III) tetrakis (4-benzoic acid)porphyrin (MnTBAP), a scavenger of H2O2.

Enhancement of cell-cell contact by claudin-4 in renal epithelial Madin-Darby canine kidney cells.

Claudin-4 regulates ion permeability via a paracellular pathway in renal epithelial cells, but its other physiological functions have not been examined. We found that hyperosmotic stress increases claudin-4 expression in Madin-Darby canine kidney cells. Here, we examined whether claudin-4 affects cell motility, cell association, and the intracellular distribution of endogenous junctional proteins.

Epidermal growth factor increases clathrin-dependent endocytosis and degradation of claudin-2 protein in MDCK II cells.

Epidermal growth factor (EGF) decreases the mRNA and protein levels of claudin-2 (CLDN2) in Madin-Darby canine kidney (MDCK) II cells. Here we examined whether EGF affects the stability and intracellular distribution of CLDN2 protein. EGF decreased surface and total levels of CLDN2, which was inhibited by U0126, a MEK inhibitor.

Claudin-2 knockdown decreases matrix metalloproteinase-9 activity and cell migration via suppression of nuclear Sp1 in A549 cells.

Aims: Claudin expression is altered in lung cancer, but the pathophysiological role of claudin is not well understood. We examined the effect of claudin-2 expression on cell migration using human adenocarcinoma A549 cells.

Main Methods: The mRNA level was measured by real time polymerase chain reaction.

Decrease in claudin-2 expression enhances cell migration in renal epithelial Madin-Darby canine kidney cells.

Migration of renal epithelial cells increases after renal tubular damage, but its mechanism has not been clarified in detail. Hyperosmotic stress increased a cellular injury concomitant with a decrease in mRNA and protein expression of claudin-2 in renal tubular epithelial Madin-Darby canine kidney cells. We hypothesized that claudin-2 is involved in the regulation of cell migration.

Magnesium deprivation inhibits a MEK-ERK cascade and cell proliferation in renal epithelial Madin-Darby canine kidney cells.

Aims: Loss of magnesium (Mg(2+)) inhibits cell proliferation and augments nephrotoxicant-induced renal injury, but the role of Mg(2+) has not been clarified in detail. We examined the effect of extracellular Mg(2+) deprivation on a MEK-ERK cascade and cell proliferation using a renal epithelial cell line, Madin-Darby canine kidney (MDCK) cells.

Main Methods: MDCK cells were cultured in Mg(2+)-containing or Mg(2+)-free media.

Extracellular Mg(2+) regulates the tight junctional localization of claudin-16 mediated by ERK-dependent phosphorylation.

Claudin-16 is involved in the paracellular reabsorption of Mg(2+) in the thick ascending limb of Henle. Little is known about the mechanism regulating the tight junctional localization of claudin-16. Here, we examined the effect of Mg(2+) deprivation on the distribution and function of claudin-16 using Madin-Darby canine kidney (MDCK) cells expressing FLAG-tagged claudin-16.

Epidermal growth factor increases claudin-4 expression mediated by Sp1 elevation in MDCK cells.

Epidermal growth factor (EGF) increases claudin-4 expression in Madin-Darby canine kidney (MDCK) cells. Here we examined what regulatory mechanisms are involved in the EGF-induced claudin-4 elevation. EGF transiently increased claudin-4 mRNA at 3h and persistently increased its protein for 24h without affecting claudin-1 expression.