Submitted on October 29, 2007
Accepted on December 5, 2007
SOX-18 controls endothelial-specific Claudin-5 gene expression and barrier function
Ruud D Fontijn1, Oscar L Volger1, Joost O Fledderus1, Arie Reijerkerk2, Helga E de vries2, and Anton J Horrevoets1*
1 Medical Biochemistry, Academic Medical Center-University of Amsterdam, Amsterdam, Netherlands
2 Molecular Cell Biology and Immunology, VU Medical Center, amsterdam, Netherlands
* To whom correspondence should be addressed. E-mail: a.j.horrevoets{at}amc.uva.nl.
Members of the claudin family constitute tight junction strands and are major determinants in specificity and selectivity of paracellular barriers. Transcriptional control of claudin gene expression is essential to establish individual claudin expression patterns and barrier properties. Using full genome expression profiling we now identify SRY (sex determining region Y)-box 18 (SOX18), a member of the SOX family of high mobility group (HMG) box transcription factors, as one of the most differentially induced genes during establishment of the endothelial barrier. We show that overexpression of SOX-18 and a dominant negative mutant thereof, as well as SOX18 silencing, greatly affects levels of claudin-5 (CLDN5). The relevance of an evolutionary conserved SOX-binding site in the CLDN5 promoter is shown using sequential promoter deletions as well as point mutations. Furthermore, SOX18 silencing abrogates endothelial barrier function as measured by Electric Cell-Substrate Impedance Sensing (ECIS). Thus, an obligatory role for SOX-18 in the regulation of CLDN5 gene expression in an endothelial-specific and cell-density dependent manner is established, as well as a crucial, non-redundant role for specifically SOX-18 in formation of the endothelial barrier.
