CLDN1 and cancer: Detail analyses indicated that SUMOylation could enhance the transcriptional repression activity of Slug by recruiting more corepressors (like Sin3A, CtBP, HDAC1 or HDAC2), decreasing its downstream target gene expressions (such as E-cadherin, claudin 1 and occludin) and promoting cancer cell migration, invasion, and metastasis (Fig. 7).