PKCζ Is Required for Microtubule-Based Motility of Vesicles Containing the ntcp Transporter

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Intracellular trafficking regulates the abundance and therefore activity of transporters present at the plasma membrane. The transporter, Na+-taurocholate co-transporting polypeptide (ntcp), is increased at the plasma membrane upon treatment of cells with cAMP, for which microtubules (MTs) are required and the PI3K pathway and PKCζ have been implicated. However, trafficking of ntcp on MTs has not been demonstrated directly and the regulation and intracellular localization of ntcp is not well understood. Here, we utilize in vitro and whole-cell immunofluorescence microscopy assays to demonstrate that ntcp is present on intracellular vesicles that bind MTs and move bidirectionally, using kinesin-1 and dynein. These vesicles co-localize with markers for recycling endosomes and early but not late endosomes. They frequently undergo fission, providing a mechanism for the exclusion of ntcp from late endosomes. PI(3,4,5)P3 activates PKCζ and enhances motility of the ntcp vesicles and overcomes the partial inhibition produced by a PI3-kinase inhibitor. Specific inhibition of PKCζ blocks the motility of ntcp-containing vesicles but has no effect on late vesicles as shown both in vitro and in living cells transfected with ntcp-GFP. These data indicate that PKCζ is required specifically for the intracellular movement of vesicles that contain the ntcp transporter.

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