Fig. 2.

An overview of VLDL assembly and secretion. Step 1: In the rough ER, ApoB is lipidated by MTP, leading to the formation of pre-VLDL, then VLDL₂ by further lipidation. VLDL₂ exits the ER compartment via Sar1/COPII vesicles, which are directed to the Golgi apparatus. ARF-1 is involved in VLDL₂ trafficking between the ER and the Golgi apparatus. Step 2: In the Golgi apparatus, VLDL₂ is converted into larger VLDL₁ by the addition of lipids. This step is promoted by phospholipase D1 and extracellular signal-regulated kinase 2 (ERK2). At this stage degradation by PERPP may occur. COPII, coat protein II; FA, fatty acid; MTP, microsomal triglyceride transfer protein; TAG, triacylglycerol