Lipschutz Joshua H, Li Shixiong, Arisco Amy, Balkovetz Daniel F
Department of Medicine & Cell and Molecular Biology Graduate Group, University of Pennsylvania and Veterans Affairs Medical Center, Philadelphia, Pennsylvania 19104, USA.
J Biol Chem. 2005 Feb 4;280(5):3780-8. doi: 10.1074/jbc.M408122200. Epub 2004 Nov 29.
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 approximately 20-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.
上皮细胞的紧密连接决定了跨上皮细胞旁通透性的特征。最近的研究表明，紧密连接蛋白claudin家族是调节上皮组织细胞旁通透性特性的分子成分的主要候选者。Madin-Darby犬肾（MDCK）I型和II型细胞是研究紧密连接的模型，基于跨上皮电阻（TER），分别含有“紧密”和“渗漏”的紧密连接。过表达研究表明，这两种MDCK细胞株的紧密连接渗漏是由紧密连接蛋白claudin-2的表达所致。用肝细胞生长因子处理MDCK II型细胞激活细胞外信号调节激酶（ERK）1/2，可抑制claudin-2的表达并使TER短暂升高。这一过程被ERK 1/2抑制剂U0126阻断。将组成型活性丝裂原活化蛋白激酶/细胞外信号调节激酶激酶转染到MDCK II型细胞中也可抑制claudin-2的表达并增加TER。MDCK I型细胞的活性ERK 1/2水平高于MDCK II型细胞。用U0126处理MDCK I型细胞可降低活性ERK 1/2水平，诱导claudin-2蛋白表达，并使TER降低约20倍。U0126处理还可诱导高电阻小鼠皮质集合管细胞系（94D）中claudin-2的表达并降低TER。这些数据首次表明，ERK 1/2信号通路对哺乳动物肾上皮细胞中claudin-2的表达具有负调控作用，并为通过紧密连接复合物中claudin组成变化调节紧密连接细胞旁转运提供了证据。
