TY - JOUR
T1 - Apolipoprotein A-1-simulated apolipoprotein E secretion from human macrophages is independent of cholesterol efflux
AU - Kockx, M
AU - Rye, Kerry-Anne
AU - Gaus, K
AU - Quinn, Carmel
AU - Wright, Janelle
AU - Sloan, Timothy
AU - Sviridov, Dimitri
AU - Fu, Ying
AU - Sullivan, David
AU - Burnett, John
AU - Rust, Stephan
AU - Assmann, Gerd
AU - Anantharamaiah, G
AU - Palgunachari, Mayakonda
AU - Katz, Sissel
AU - Phillips, Michael
AU - Dean, Roger
AU - Jessup, Wendy
AU - Kritharides, Leonard
PY - 2004
Y1 - 2004
N2 - Apolipoprotein A-I (apoA-I)-mediated cholesterol efflux involves the binding of apoA-I to the plasma membrane via its C terminus and requires cellular ATP-binding cassette transporter (ABCA1) activity. ApoA-I also stimulates secretion of apolipoprotein E (apoE) from macrophage foam cells, although the mechanism of this process is not understood. In this study, we demonstrate that apoA-I stimulates secretion of apoE independently of both ABCA1-mediated cholesterol efflux and of lipid binding by its C terminus. Pulse-chase experiments using 35S-labeled cellular apoE demonstrate that macrophage apoE exists in both relatively mobile (Em) and stable (Es) pools, that apoA-I diverts apoE from degradation to secretion, and that only a small proportion of apoA-I-mobilized apoE is derived from the cell surface. The structural requirements for induction of apoE secretion and cholesterol efflux are clearly dissociated, as C-terminal deletions in recombinant apoA-I reduce cholesterol efflux but increase apoE secretion, and deletion of central helices 5 and 6 decreases apoE secretion without perturbing cholesterol efflux. Moreover, a range of 11- and 22-mer α-helical peptides representing amphipathic α-helical segments of apoA-I stimulate apoE secretion whereas only the C-terminal α-helix (domains 220–241) stimulates cholesterol efflux. Other α-helix-containing apolipoproteins (apoA-II, apoA-IV, apoE2, apoE3, apoE4) also stimulate apoE secretion, implying a positive feedback autocrine loop for apoE secretion, although apoE4 is less effective. Finally, apoA-I stimulates apoE secretion normally from macrophages of two unrelated subjects with genetically confirmed Tangier Disease (mutations C733R and c.5220–5222delTCT; and mutations A1046D and c.4629–4630insA), despite severely inhibited cholesterol efflux. We conclude that apoA-I stimulates secretion of apoE independently of cholesterol efflux, and that this represents a novel, ABCA-1-independent, positive feedback pathway for stimulation of potentially anti-atherogenic apoE secretion by α-helix-containing molecules including apoA-I and apoE.
AB - Apolipoprotein A-I (apoA-I)-mediated cholesterol efflux involves the binding of apoA-I to the plasma membrane via its C terminus and requires cellular ATP-binding cassette transporter (ABCA1) activity. ApoA-I also stimulates secretion of apolipoprotein E (apoE) from macrophage foam cells, although the mechanism of this process is not understood. In this study, we demonstrate that apoA-I stimulates secretion of apoE independently of both ABCA1-mediated cholesterol efflux and of lipid binding by its C terminus. Pulse-chase experiments using 35S-labeled cellular apoE demonstrate that macrophage apoE exists in both relatively mobile (Em) and stable (Es) pools, that apoA-I diverts apoE from degradation to secretion, and that only a small proportion of apoA-I-mobilized apoE is derived from the cell surface. The structural requirements for induction of apoE secretion and cholesterol efflux are clearly dissociated, as C-terminal deletions in recombinant apoA-I reduce cholesterol efflux but increase apoE secretion, and deletion of central helices 5 and 6 decreases apoE secretion without perturbing cholesterol efflux. Moreover, a range of 11- and 22-mer α-helical peptides representing amphipathic α-helical segments of apoA-I stimulate apoE secretion whereas only the C-terminal α-helix (domains 220–241) stimulates cholesterol efflux. Other α-helix-containing apolipoproteins (apoA-II, apoA-IV, apoE2, apoE3, apoE4) also stimulate apoE secretion, implying a positive feedback autocrine loop for apoE secretion, although apoE4 is less effective. Finally, apoA-I stimulates apoE secretion normally from macrophages of two unrelated subjects with genetically confirmed Tangier Disease (mutations C733R and c.5220–5222delTCT; and mutations A1046D and c.4629–4630insA), despite severely inhibited cholesterol efflux. We conclude that apoA-I stimulates secretion of apoE independently of cholesterol efflux, and that this represents a novel, ABCA-1-independent, positive feedback pathway for stimulation of potentially anti-atherogenic apoE secretion by α-helix-containing molecules including apoA-I and apoE.
U2 - 10.1074/jbc.M401177200
DO - 10.1074/jbc.M401177200
M3 - Article
SN - 0021-9258
VL - 279
SP - 25966
EP - 25977
JO - The Journal of Biological Chemistry
JF - The Journal of Biological Chemistry
IS - 25
ER -