title: Sphingomyelin synthases regulate protein trafficking and secretion.
abstract: Sphingomyelin synthases (SMS1 and 2) represent a class of enzymes that transfer a phosphocholine moiety from phosphatidylcholine onto ceramide thus producing sphingomyelin and diacylglycerol (DAG). SMS1 localizes at the Golgi while SMS2 localizes both at the Golgi and the plasma membrane. Previous studies from our laboratory showed that modulation of SMS1 and, to a lesser extent, of SMS2 affected the formation of DAG at the Golgi apparatus. As a consequence, down-regulation of SMS1 and SMS2 reduced the localization of the DAG-binding protein, protein kinase D (PKD), to the Golgi. Since PKD recruitment to the Golgi has been implicated in cellular secretion through the trans golgi network (TGN), the effect of down-regulation of SMSs on TGN-to-plasma membrane trafficking was studied. Down regulation of either SMS1 or SMS2 significantly retarded trafficking of the reporter protein vesicular stomatitis virus G protein tagged with GFP (VSVG-GFP) from the TGN to the cell surface. Inhibition of SMSs also induced tubular protrusions from the trans Golgi network reminiscent of inhibited TGN membrane fission. Since a recent study demonstrated the requirement of PKD activity for insulin secretion in beta cells, we tested the function of SMS in this model. Inhibition of SMS significantly reduced insulin secretion in rat INS-1 cells. Taken together these results provide the first direct evidence that both enzymes (SMS1 and 2) are capable of regulating TGN-mediated protein trafficking and secretion, functions that are compatible with PKD being a down-stream target for SMSs in the Golgi.
authors: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina, United States of America.
authors: Marimuthu
authors: M
authors: Subathra
authors: Asfia
authors: A
authors: Qureshi
authors: Chiara
authors: C
authors: Luberto
mesh_terms: D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015536:Down-Regulation; D015971:Gene Expression Regulation, Enzymologic; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D051381:Rats; D017855:Transferases (Other Substituted Phosphate Groups) / Q000235:genetics / Q000502:physiology*; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: C028391:G protein, vesicular stomatitis virus; D007328:Insulin; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D014759:Viral Envelope Proteins; D049452:Green Fluorescent Proteins; C455440:SGMS1 protein, human; D017855:Transferases (Other Substituted Phosphate Groups); C070186:phosphatidylcholine-ceramide phosphocholine transferase