Regulation of Renal Epithelial Tight Junctions by the von Hippel-Lindau Tumor Suppressor Gene Involves Occludin and Claudin 1 and Is Independent of E-Cadherin

Abstract

Epithelial-to-mesenchymal transitions (EMT) are important in renal development, fibrosis, and cancer. Loss of function of the tumor suppressor VHL leads to many features of EMT, and it has been hypothesized that the pivotal mediator is down-regulation of the adherens junction (AJ) protein E-cadherin. Here we show that VHL loss-of-function also has striking effects on the expression of the tight junction (TJ) components occludin and claudin 1 in vitro in VHL-defective clear cell renal cell carcinoma (CCRCC) cells and in vivo in VHL-defective sporadic CCRCCs (compared with normal kidney). Occludin is also down-regulated in premalignant foci in kidneys from patients with germline VHL mutations, consistent with a contribution to CCRCC initiation. Reexpression of E-cadherin was sufficient to restore AJ but not TJ assembly, indicating that the TJ defect is independent of E-cadherin down-regulation. Additional experiments show that activation of hypoxia inducible factor (HIF) contributes to both TJ and AJ abnormalities, thus the VHL/HIF pathway contributes to multiple aspects of the EMT phenotype that are not interdependent. Despite the independent nature of the defects, we show that treatment with the histone deacetylase inhibitor sodium butyrate, which suppresses HIF activation, provides a method for reversing EMT in the context of VHL inactivation. INTRODUCTIONA key characteristic of epithelial surfaces is the formation of specialized intercellular junctions at points of cell-cell contact. It is increasingly appreciated that these junctions have extensive roles beyond their function in cellular cohesion including determination of epithelial permeability and providing inputs modulating proliferation and differentiation. Two important types of intercellular junctions in the kidney epithelium are the tight junction (TJ) and adherens junction (AJ; Tsukita et al., 2001;Conacci-Sorrell et al., 2002;Matter and Balda, 2003). AJs are formed on the basolateral cell membrane and are composed of transmembrane cadherins linked to intracellular catenin proteins (Conacci-Sorrell et al., 2002). AJs are involved in cell-cell adhesion and also regulate ␤-catenin availability (Nelson and Nusse, 2004). TJs are formed on the apical surface of the lateral membrane and are analagous in structure to AJs, with specific transmembrane proteins (occludin and claudins), which are linked to the actin cytoskeleton via intracellular adaptor proteins, the zona occludens (ZO) family of proteins (Tsukita et al., 2001). In addition to its traditional roles in maintaining apical-basal polarity and controlling paracellular permeability the TJ is also now recognized as a signaling hub. TJ regulation of pathways involving raf kinase, rho GTPase, and the Y-box transcription factor ZONAB control important cellular processes such as cell proliferation, gene transcription, and cellular differentiation (Braga, 2002;Matter and Balda, 2003;Gonzalez-Mariscal et al., 2007;Guillemot et al., 2008).VHL is a classical tumor suppressor gene which acts as a gatekeeper i...

Protein Kinase D Promotes Airway Epithelial Barrier Dysfunction and Permeability through Down-regulation of Claudin-1

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