Mature VLDL Triggers the Biogenesis of a Distinct Vesicle from the Trans Golgi Network for its Export to the Plasma Membrane

Post-Golgi trafficking of mature VLDL is crucial in maintaining the normal triacylglycerol (TAG) homeostasis of hepatocytes; however, the mechanism that regulates the exit of mature VLDL from the trans-Golgi network (TGN) 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 post-TGN VLDL transport vesicles (PG-VTV) 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. Electron microscopy 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 oC. PG-VTVs concentrated the VLDL proteins: 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 plasma membrane (PM) 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.

Source: BJ Cell - January 16, 2014 Category: Biochemistry Authors: T Hossain, A Riad, S Siddiqi, S Parthasarathy, S A. Siddiqi Tags: BJ Cell Source Type: research