FAPP2 is involved in the transport of apical cargo in polarized MDCK cells

Phosphatidylinositol-4-phosphate ( PI( 4) P) is the main phosphoinositide in the Golgi complex and has been reported to play a pleiotropic role in transport of cargo from the trans-Golgi network to the plasma membrane ( PM) in polarized Madin-Darby canine kidney (MDCK) cells. Overexpression of the chimeric fluorescent protein encoding the pleckstrin homology domain, which is specific for PI( 4) P, inhibited both apical and basolateral transport pathways. The transport of apical cargo from the Golgi was shown to be specifically decreased by adenovirus-mediated RNA interference directed against PI( 4) P adaptor protein ( FAPP) 2. FAPP1 depletion had no effect on transport. On the other hand, FAPP2 was not involved in the Golgi-to-PM transport of cargo that was targeted to the basolateral membrane domain. Thus, we conclude that FAPP2 plays a specific role in apical transport in MDCK cells.