[The Molecular Functions of Claudins in Cancer Development and Progression].

Claudins(CLDNs)are essential components of tight junctions, which are the most apical elements of apical junctional complexes. The family consists of more than 20 members in humans and shows distinct expression patterns in a tissue- and cell-type-specific manner. Recently, many studies have shown that CLDNs overexpressed in cancer cells positively regulate their malignant behavior. First, fusion genes between CLDNs and signaling molecules produce chimeric proteins that act as drivers. Second, cancer and non-cancer cells form heterocellular adhesions via CLDNs and they act as a metastatic niche. Third, CLDNs enhance cancer cell nutrition by conjugating with amino acid transporters on the cell membrane. Fourth, CLDN acts as an activation trigger for signalling cascades. In this review, we present these 4 representative examples of how CLDNs positively regulate cancer progression.