SUMOylation of claudin-2: SUMOylation of claudin-2

The C‐terminal cytoplasmic tails of claudins are likely sites for interaction with proteins that regulate their function. We performed a yeast two‐hybrid screen with the tail of human claudin‐2 against a human kidney cDNA library and identified interactions with the PDZ3 domain of ZO‐2 as well as ubiquitin‐conjugating enzyme E2I (SUMO ligase‐1) and E3 SUMO‐protein ligase PIAS; the first is a predicted interaction, while the latter two are novel and suggest that claudin‐2 is a substrate for SUMOylation. Using an in vitro SUMOylation assay, we identified K218 as a conjugation site on claudin‐2; mutation of that lysine to arginine blocked SUMOylation. Stable expression of inducible GFP‐SUMO‐1 in MDCK cells resulted in decreased levels of claudin‐2 protein by immunoblot and decreased claudin‐2 membrane expression by immunofluorescence microscopy. We conclude that the cellular levels of claudin‐2 may be modulated by SUMOylation, warranting further investigation of cellular pathways that regulate this modification in vivo.