Cyclosporin A decreases apolipoprotein E secretion from human macrophages via a protein phosphatase 2B-dependent and ATP-binding cassette transporter A1 (ABCA1)-independent pathway.
Cyclosporin A (CsA) is an immunosuppressant that inhibits protein phosphatase 2B (PP2B/calcineurin) and is associated with hyperlipidemia, decreased cholesterol efflux via ATP-binding cassette transporter A1 (ABCA1), and increased risk of atherosclerosis. Apolipoprotein E (apoE) is an important regulator of lipid metabolism and atherosclerosis, the secretion of which from human macrophages is regulated by the serine/threonine protein kinase A (PKA) and intracellular calcium (Ca(2+)) (Kockx, M., Guo, D. L., Huby, T., Lesnik, P., Kay, J., Sabaretnam, T., Jary, E., Hill, M., Gaus, K., Chapman, J., Stow, J. L., Jessup, W., and Kritharides, L. (2007) Circ. Res. 101, 607-616). As PP2B is Ca(2+)-dependent and has been linked to PKA-dependent processes, we investigated whether CsA modulated apoE secretion. CsA dose- and time-dependently inhibited secretion of apoE from primary human macrophages and from Chinese hamster ovary cells stably transfected with human apoE and increased cellular apoE levels without affecting apoE mRNA. [(35)S]Met kinetic modeling studies showed that CsA inhibited both secretion and degradation of apoE, increasing the half-life of cellular apoE 2-fold. CsA also inhibited secretion from primary human Tangier disease macrophages and from mouse macrophages deficient in ABCA1, indicating that the effect is independent of the known inhibition of ABCA1 by CsA. The role of PP2B in mediating apoE secretion was confirmed using additional peptide and chemical inhibitors of PP2B. Importantly, kinetic modeling, live-cell imaging, and confocal microscopy all indicated that CsA inhibited apoE secretion by mechanisms quite distinct from those of PKA inhibition, most likely inducing accumulation of apoE in the endoplasmic reticulum compartment. Taken together, these results establish a novel mechanism for the pro-atherosclerotic effects of CsA, and establish for the first time a role for PP2B in regulating the intracellular transport and secretion of apoE.
Kockx
Maaike
M
Centre for Vascular Research, School of Medical Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia.
Guo
Dongni Lily
DL
Traini
Mathew
M
Gaus
Katharina
K
Kay
Jason
J
Wimmer-Kleikamp
Sabine
S
Rentero
Carles
C
Burnett
John R
JR
Le Goff
Wilfried
W
Van Eck
Miranda
M
Stow
Jennifer L
JL
Jessup
Wendy
W
Kritharides
Leonard
L
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006949:Hyperlipidemias / Q000235:genetics / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007700:Kinetics; D008264:Macrophages / Q000378:metabolism*; D008954:Models, Biological; D013631:Tangier Disease / Q000235:genetics / Q000378:metabolism
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D001057:Apolipoproteins E; D007166:Immunosuppressive Agents; D016572:Cyclosporine; D017868:Cyclic AMP-Dependent Protein Kinases; D019703:Calcineurin