Faculty Collaboration Database

Quality control in the apoA-I secretory pathway: deletion of apoA-I helix 6 leads to the formation of cytosolic phospholipid inclusions. J Lipid Res 2004 Jul;45(7):1207-20

Date

04/03/2004

Pubmed ID

15060083

DOI

10.1194/jlr.M300498-JLR200

Scopus ID

2-s2.0-3042651483 (requires institutional sign-in at Scopus site)   10 Citations

Abstract

From a total of 47 known apolipoprotein A-I (apoA-I) mutations, only 18 are linked to low plasma HDL apoA-I concentrations, and 78% of these map to apoA-I helices 6 and 7 (residues 143-186). Gene transfer and transgenic mouse studies have shown that several helix 6 apoA-I mutations have reduced hepatic HDL production. Our objective was to examine the impact of helix 6 modifications on intracellular biosynthetic processing and secretion of apoA-I. Cells were transfected with wild-type or mutant apoA-I, radiolabeled with [(35)S]Met/Cys, and then placed in unlabeled medium for up to 4 h. Results show that >90% of newly synthesized wild-type apoA-I was secreted by 60 min. Over the same length of time, only 20% of helix 6 deletion mutant (Delta 6 apoA-I) was secreted, whereas 80% remained cell associated. Microscopic and biochemical studies revealed that cell-associated Delta 6 apoA-I was located predominantly within the cytoplasm as lipid-protein inclusions, whereas wild-type apoA-I was localized in the endoplasmic reticulum/Golgi. Results using other helix deletions or helix 6 substitution mutations indicated that only complete removal of helix 6 resulted in massive cytoplasmic accumulation. These data suggest that alterations in native apoA-I conformation can lead to aberrant trafficking and accumulation of apolipoprotein-phospholipid structures. Thus, conformation-dependent alterations in intracellular trafficking and turnover may underlie the reduced plasma HDL concentrations observed in individuals harboring deletion mutations within helix 6.

Author List

Bhat S, Zabalawi M, Willingham MC, Shelness GS, Thomas MJ, Sorci-Thomas MG

Authors

Mary Sorci Thomas PhD Professor in the Medicine department at Medical College of Wisconsin
Michael J. Thomas PhD Professor in the Pharmacology and Toxicology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Apolipoprotein A-I
Cell Line, Tumor
Cytosol
Endoplasmic Reticulum
Golgi Apparatus
Humans
Inclusion Bodies
Lipoproteins, HDL
Phospholipids
Protein Structure, Secondary
Protein Transport
Sequence Deletion
Transfection