Role of ADP ribosylation factor 1 in the assembly and secretion of ApoB-100-containing lipoproteins.

Objective: We investigated the role of ADP ribosylation factor 1 (ARF1) in the assembly of very-low-density lipoproteins (VLDLs).
Methods and Results: The dominant-negative ARF1 mutant, T31N, decreased the assembly of apoB-100 VLDL 1 (Svedberg floatation units [Sf] 60 to 400) by 80%. The decrease coincided with loss of coatamer I (COPI) from the Golgi apparatus and inhibition of anterograde transport, as demonstrated by time-lapse studies of the vesicular stomatitis virus G protein. The VLDL 1 assembly was also completely inhibited at 15 degrees C. Thus, the antegrade transport is essential for the assembly of VLDL 1. Intracellular localization of N-acetylgalactosaminyl transferase 2 indicated that the Golgi apparatus was at least partly intact when the VLDL assembly was inhibited. Transient transfection with phospholipase D 1 increased the assembly of VLDL 1 and VLDL 2 (Sf 20 to 60). Overexpression of ARF1 in stably transfected McA-RH7777 cells increased the secretion of VLDL 2 but not of VLDL 1, which was dependent on the availability of oleic acid. Secretion of VLDL 1 increased with increasing amounts of oleic acid, and VLDL 2 secretion decreased simultaneously.
Conclusions: Overexpression of ARF1 increased the assembly of VLDL 2 but not of VLDL 1, whose production was dependent on both anterograde transport and the availability of fatty acids.