Journal
BIOCHEMICAL JOURNAL
Volume 459, Issue -, Pages 47-58Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20131215
Keywords
apolipoprotein B; endoplasmic reticulum; post-Golgi VLDL transport vesicle (PG-VTV); trans-Golgi network (TGN); triacylglycerol; very low-density lipoprotein (VLDL)
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Funding
- NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases) of the NIH (National Institutes of Health) [R01 DK-81413]
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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 degrees 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.
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