title: Mature VLDL triggers the biogenesis of a distinct vesicle from the trans-Golgi network for its export to the plasma membrane.
abstract: Post-Golgi trafficking of mature VLDL (very-low-density lipoprotein) is crucial in maintaining normal TAG (triacylglycerol) homoeostasis of hepatocytes; however, the mechanism that regulates the exit of mature VLDL from the TGN (trans-Golgi network) is not known. We developed an in vitro TGN-budding assay that allowed us to examine the formation of secretory vesicles from the TGN in primary rat hepatocytes. We isolated TAG-rich PG-VTVs (post-TGN VLDL transport vesicles) using a continuous sucrose density gradient. PG-VTVs were distributed in low-density fractions, whereas protein transport vesicles were present in relatively higher-density fractions of the same sucrose gradient. EM revealed large intact PG-VTVs ranging 300-350 nm in size. The biogenesis of PG-VTVs from the TGN required cytosol, ATP, GTP hydrolysis and incubation at 37°C. PG-VTVs concentrated the VLDL proteins: apolipoproteins apoB100, apoAIV, apoAI and apoE, but did not contain either albumin or transferrin. Proteinase K treatment did not degrade VLDL core proteins, suggesting that PG-VTVs were sealed. PG-VTVs were able to fuse with and deliver VLDL to the PM (plasma membrane) in a vectorial manner. We conclude that we have identified a new TGN-derived vesicle, the PG-VTV, which specifically transports mature VLDL from the TGN to the PM.
authors.affiliation: *Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
authors.forename: Tanvir
authors.initials: T
authors.lastname: Hossain
authors.affiliation: *Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
authors.forename: Aladdin
authors.initials: A
authors.lastname: Riad
authors.affiliation: *Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
authors.forename: Shaila
authors.initials: S
authors.lastname: Siddiqi
authors.affiliation: *Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
authors.forename: Sampath
authors.initials: S
authors.lastname: Parthasarathy
authors.affiliation: *Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32827, U.S.A.
authors.forename: Shadab A
authors.initials: SA
authors.lastname: Siddiqi
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D022142:Secretory Vesicles / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D008079:Lipoproteins, VLDL