We have already identified a novel Rab8 binding protein (Rab8BP), and we have tested the subcellular localization and this revealed that Rab8 and Rab8BP were co-localized on endocytic recycling compartment (ERC.), we further analyzed the Rab8BP function on the membrane transport in polarized and non-polarized cells. First we assed the possibility whether Rab8BP binds to another protein. By pull down assay using GST-fused Rab8BP recombinant protein and mouse tissue lysate, we identified one protein which was specifically interact with Rab8BP, namely Rab8BP interacting protein (Rab8BPIP.)

Second, RabBP and Rab8BPIP were knocked down by shRNA in non-polarized HeLa cells, and polarized primary small intestinal epithelial cells. Although we did not be able to observe any defect on the transport in the HeLa cells, we observed apical-directed transport defect in intestinal epithelial cells. The same defect was also observed in primary small intestinal epithelial cells isolated from Rab8 knockout mice. Our result suggests that Rab8-Rab8BP-Rab8BPIP complex regulates apical cargo transport from ERC in epithelial cells (unpublished.)