Interaction of Syndecan-1 cytoplasmic domain with CASK PDZ domain

Syndecans are integral membrane proteoglycans which have important cellular functions. They are thought to function as co-receptors for various extracellular ligands like extracellular matrix molecules, cell-cell adhesion molecules, and growth fectors. It is shown that they modulate cell proliferation, cell adhesion, cell motility, and cell fate upon such interactions. Recent studies indicated that they also modulate signal transduction events by their core protein interactions. Most of these interactions are through their highly conserved cytoplasmic domains. They contain PDZ domain binding site at their carboxy terminal end, and identification of PDZ protein interactions of Syndecans may be important to explain their role in signaling. We aimed to identify a protein-protein interaction between Syndecan-1 cytoplasmic domain and PDZ domains of CASK and AF-6 proteins with yeast two-hybrid technique. We showed that there is a detectable interaction between CASK and Syndecan-1 through these domains. Our results indicated that CASK PDZ domain binds to Syndecan-1 cytoplasmic domain when expressed in yeast, and this interaction may have important functions in signaling events.