title: Uncleaved ApoM signal peptide is required for formation of large ApoM/sphingosine 1-phosphate (S1P)-enriched HDL particles.
abstract: Apolipoprotein M (apoM), a plasma sphingosine 1-phosphate (S1P) carrier, associates with plasma HDL via its uncleaved signal peptide. Hepatocyte-specific apoM overexpression in mice stimulates formation of both larger nascent HDL in hepatocytes and larger mature apoM/S1P-enriched HDL particles in plasma by enhancing hepatic S1P synthesis and secretion. Mutagenesis of apoM glutamine 22 to alanine (apoM(Q22A)) introduces a functional signal peptidase cleavage site. Expression of apoM(Q22A) in ABCA1-expressing HEK293 cells resulted in the formation of smaller nascent HDL particles compared with wild type apoM (apoM(WT)). When apoM(Q22A) was expressed in vivo, using recombinant adenoviruses, smaller plasma HDL particles and decreased plasma S1P and apoM were observed relative to expression of apoM(WT). Hepatocytes isolated from both apoM(WT)- and apoM(Q22A)-expressing mice displayed an equivalent increase in cellular levels of S1P, relative to LacZ controls; however, relative to apoM(WT), apoM(Q22A) hepatocytes displayed more rapid apoM and S1P secretion but minimal apoM(Q22A) bound to nascent lipoproteins. Pharmacologic inhibition of ceramide synthesis increased cellular sphingosine and S1P but not medium S1P in both apoM(WT) and apoM(Q22A) hepatocytes. We conclude that apoM secretion is rate-limiting for hepatocyte S1P secretion and that its uncleaved signal peptide delays apoM trafficking out of the cell, promoting formation of larger nascent apoM- and S1P-enriched HDL particles that are probably precursors of larger apoM/S1P-enriched plasma HDL.
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Mingxia
authors: M
authors: Liu
authors: the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298.
authors: Jeremy
authors: J
authors: Allegood
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Xuewei
authors: X
authors: Zhu
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Jeongmin
authors: J
authors: Seo
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Abraham K
authors: AK
authors: Gebre
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Elena
authors: E
authors: Boudyguina
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Dongmei
authors: D
authors: Cheng
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and.
authors: Chia-Chi
authors: CC
authors: Chuang
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and the Department of Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157 and.
authors: Gregory S
authors: GS
authors: Shelness
authors: the Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298.
authors: Sarah
authors: S
authors: Spiegel
authors: From the Department of Internal Medicine, Section on Molecular Medicine, and the Department of Biochemistry, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157 and jparks@wakehealth.edu.
authors: John S
authors: JS
authors: Parks
mesh_terms: D000818:Animals; D001053:Apolipoproteins / Q000737:chemistry / Q000378:metabolism*; D000075243:Apolipoproteins M; D008075:Lipoproteins, HDL / Q000737:chemistry*; D008246:Lysophospholipids / Q000737:chemistry*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D021382:Protein Sorting Signals; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: C501623:ApoM protein, mouse; D001053:Apolipoproteins; D000075243:Apolipoproteins M; D008075:Lipoproteins, HDL; D008246:Lysophospholipids; D021382:Protein Sorting Signals; C060506:sphingosine 1-phosphate; D013110:Sphingosine
keywords: Apolipoprotein M; Ceramide; Cholesterol; Fumonisin B1; High Density Lipoproteins; Liver; Myriocin; Sphingolipid; Sphingosine 1-Phosphate (S1P)
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