Densin and beta-catenin form a complex and co-localize in cultured podocyte cell junctions

Densin is a member of LAP (leucine-rich repeat and PDZ domain) protein family that localizes in kidney to slit diaphragms, which are essential components of the glomerular filtration barrier. We have previously shown that densin interacts with a crucial slit diaphragm protein, nephrin. Here, we searched for novel binding partners of densin by yeast-two hybrid assay and identified beta-catenin. The interaction was confirmed by reciprocal co-immunoprecipitation assay and the binding site in densin was determined by GST-pull down assays. The GST-tagged densin was also able to pull down P-cadherin together with beta-catenin from human kidney glomerular lysates. Furthermore, densin co-localized with beta-catenin and F-actin in cell-cell contacts in cultured mouse podocytes. During cell-cell contact disruption and reformation densin and beta-catenin were dislocated from and relocated back to plasma membrane in a similar fashion. These and our previous findings suggest that densin may associate with the cadherin-catenin and nephrin complex(es), and may be involved in the formation of the cell-cell contacts including the slit diaphragm.