Functional relationships between golgi dynamics and lipid metabolism and transport

The Golgi apparatus is a sorting nexus for protein and lipids exported from theendoplasmic reticulum (ER) to other organelles and for secretion. The lipids and sterolsthat delineate the vesicular/tubular transport carriers and cisternae that constitute theGolgi transport apparatus are just packaging materials but participate directly inmembrane fusion, cargo sorting and polarized transport. Low abundance lipids, such asdiacylglycerol (DAG), phosphatidic acid (PtdOH), lyso-phospholipids andphosphatidylinositol phosphates, contribute to these processes by localized synthesis andinterconversion. These lipids alter the structure of membranes by assisting in induction ofpositive and negative curvature required for carrier assembly, and regulate the activity ofproteins that temporally and spatially regulate fusion and fission events. The Golgiapparatus is especially enriched in phosphatidylinositol 4-phosphate (PtdIns(4)P), wherelocalized metabolism by Golgi-associated PtdIns 4-kinases (PI4K) and phosphatasescontrols PtdIns(4)P pools that recruit proteins involved in lipid transport and vesiculartrafficking. DAG and ceramide conversion in the late Golgi and trans-Golgi network(TGN) by sphingomyelin (SM) synthase regulates Golgi trafficking by recruiting andactivating protein kinase D (PKD) for phosphorylation of targets such a PI4KIIIβ. SMand glycosphingolipids (GSL) synthesized in the Golgi apparatus condenses withcholesterol into nanoscale assemblies called lipid rafts. These platforms function inmembrane signaling and regulate trans-Golgi network (TGN)-sorting machinery. There isan increasing appreciation for the role of lipid and sterol transfer proteins in modulationof Golgi apparatus function. In particular, site-directed ceramide and sterol transfer proteins that communicate lipid status, and regulate cholesterol, SM and GSLmetabolism. Here we will review the highly integrated lipid metabolic and signalingpathways housed in the Golgi apparatus that control secretory activity and membraneassembly.