Specific and nonspecific membrane-binding determinants cooperate in targeting phosphatidylinositol transfer protein β-isoform to the mammalian trans-golgi network

Phosphatidylinositol transfer proteins (PITPs) regulate the interface between lipid metabolism and specific steps in membrane trafficking through the secretory pathway in eukaryotes. Herein, we describe the cis-acting information that controls PITP,6 localization in mammalian cells. We demonstrate PITP beta localizes predominantly to the trans-Golgi network (TGN) and that this localization is independent of the phospholipid-bound state of PITP beta. Domain mapping analyses show the targeting information within PITP beta consists of three short C-terminal specificity elements and a nonspecific membrane-binding element defined by a small motif consisting of adjacent tryptophan residues (the W202W203 motif). Combination of the specificity elements with the W202W203 motif is necessary and sufficient to generate an efficient TGN-targeting module. Finally, we demonstrate that PITP beta association with the TGN is tolerant to a range of missense mutations at residue serine 262, we describe the TGN localization of a novel PITP beta isoform with a naturally occurring S(262)Q polymorphism, and we find no other genetic or pharmacological evidence to support the concept that PITP beta localization to the TGN is obligately regulated by conventional protein kinase C (PKC) or the Golgi-localized PKC isoforms delta or epsilon. These latter findings are at odds with a previous report that conventional PKC-mediated phosphorylation of residue Ser(262) is required for PITP beta targeting to Golgi membranes.