Specific and nonspecific membrane-binding determinants cooperate in targeting phosphatidylinositol transfer protein beta-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 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 W(202)W(203) motif). Combination of the specificity elements with the W(202)W(203) 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 we 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.
Phillips
Scott E
SE
Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7090, USA.
Ile
Kristina E
KE
Boukhelifa
Malika
M
Huijbregts
Richard P H
RP
Bankaitis
Vytas A
VA
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D049294:Phospholipid Transfer Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D014162:Transfection; D021601:trans-Golgi Network / Q000378:metabolism*
D049294:Phospholipid Transfer Proteins; C493471:Pitpnb protein, mouse; D049452:Green Fluorescent Proteins