TJP1, TJP2, and TJP3 are closely related scaffolding proteins that link tight junction (TJ) transmembrane proteins such as claudins, junctional adhesion molecules, and occludin to the actin cytoskeleton (PubMed:12021270). The tight junction acts to limit movement of substances through the paracellular space and as a boundary between the compositionally distinct apical and basolateral plasma membrane domains of epithelial and endothelial cells. Binds and recruits PATJ to tight junctions where it connects and stabilizes apical and lateral components of tight junctions (PubMed:12021270). Promotes cell-cycle progression through the sequestration of cyclin D1 (CCND1) at tight junctions during mitosis which prevents CCND1 degradation during M-phase and enables S-phase transition (By similarity). With TJP1 and TJP2, participates in the junctional retention and stability of the transcription factor DBPA, but is not involved in its shuttling to the nucleus (PubMed:24986862). Contrary to TJP2, TJP3 is dispensable for individual viability, embryonic development, epithelial differentiation, and the establishment of TJs, at least in the laboratory environment (By similarity). Heterodimer with TJP1 (PubMed:9531559, PubMed:8408213, PubMed:10575001). Interacts with UBN1 (By similarity). Interacts with occludin OCLN and claudins (PubMed:9531559, PubMed:8408213). Interacts with PATJ (PubMed:12021270). Interacts with FASLG (By similarity). Interacts with CCND1 (By similarity). Exhibits predominant nuclear expression in proliferating cells but is exclusively junctionally expressed after confluence is reached (By similarity). Shows an epithelial-specific tight junction localization in a TJP1/TJP2-dependent fashion (By similarity). Expression is up-regulated by the depletion of the junctional protein paracingulin CGNL1 (PubMed:18653465). Phosphorylated (PubMed:8408213). Belongs to the MAGUK family.