The lysosomal trafficking regulator interacting protein-5 localizes mainly in epithelial cells

Endocytosis, subsequent protein sorting into multivesicular bodies (MVBs), and eventual degradation in lysosomes compose an important mechanism for controlling protein expression on the plasma membrane. The lysosomal trafficking regulator interacting protein-5 (LIP5) is part of the complex protein machinery involved in MVB biosynthesis. LIP5 interacts with other players of the ESCRT machinery as well as with two known cargo proteins, AQP2 and EGFR, whose degradation is affected upon reduction of LIP5 expression. To investigate the expression and localization pattern of LIP5, we studied LIP5 protein expression in a mouse tissue panel and subjected various rodent and human tissues to immunohistochemistry. Immunoblotting revealed that, except for jejunum, LIP5 is expressed as a 42 kDa protein in all mouse tissues tested. Alternatively-spliced gene products could not be detected. Immunohistochemical studies revealed that in tissues positive for LIP5, LIP5 is detected in virtually all epithelial cells of the examined rodent and human tissues. The observed LIP5 expression in epithelial tissues suggests that LIP5 is of particular importance in the MVB sorting and degradation of proteins expressed in polarized cells.