CLDN4 and cancer: Some of the tight junction proteins including Claudin-1 (Dhawan et al, 2005; Soini and Talvensaari-Mattila, 2006) and Claudin-4 (de Oliveira et al, 2005; Morin, 2005; Soini and Talvensaari-Mattila, 2006) are upregulated in several cancers.