Specific and Nonspecific Membrane-binding Determinants Cooperate in Targeting Phosphatidylinositol Transfer Protein -Isoform to the Mammalian trans-Golgi Network

Phillips SE, Ile KE, Boukhelifa M, Huijbregts RP, Bankaitis VA
Source: Mol Biol Cell
Publication Date: (2006)
Issue: 17(6): 2498-2512
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Embryonic fibroblast, mouse (MEF) immort
Species: mouse
Tissue Origin: embryo
Nucleofector® I/II/2b
SMonitoring Editor: Reid Gilmore 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 PITPbeta localization in mammalian cells. We demonstrate PITPbeta localizes predominantly to the trans-Golgi Network (TGN), and that this localization is independent of the phospholipid-bound state of PITPbeta. Domain mapping analyses show the targeting information within PITPbeta 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 PITPbeta association with the TGN is tolerant to a range of missense mutations at residue serine 262, we describe the TGN-localization of a novel PITPbeta isoform with a naturally occurring S262Q polymorphism, and find no other genetic or pharmacological evidence to support the concept that PITPbeta 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 Ser262 is required for PITPbeta targeting to Golgi membranes.