Truncation mutations in ABCA1 suppress normal upregulation of full-length ABCA1 by 9-cis-retinoic acid and 22-R-hydroxycholesterol.
Mutations in ABCA1 uniformly decrease plasma HDL-cholesterol (HDL-C) and reduce cholesterol efflux, yet different mutations in ABCA1 result in different phenotypic effects in heterozygotes. For example, truncation mutations result in significantly lower HDL-C and apoliprotein A-I (apoA-I) levels in heterozygotes compared with nontruncation mutations, suggesting that truncation mutations may negatively affect the wild-type allele. To specifically test this hypothesis, we examined ABCA1 protein expression in response to 9-cis-retinoic acid (9-cis-RA) and 22-R-hydroxycholesterol (22-R-OH-Chol) in a collection of human fibroblasts representing eight different mutations and observed that truncation mutations blunted the response to oxysterol stimulation and dominantly suppressed induction of the remaining full-length allele to 5-10% of wild-type levels. mRNA levels between truncation and nontruncation mutations were comparable, suggesting that ABCA1 expression was suppressed at the protein level. Dominant negative activity of truncated ABCA1 was recapitulated in an in vitro model using transfected Cos-7 cells. Our results suggest that the severe reduction of HDL-C in patients with truncation mutations may be at least partly explained by dominant negative suppression of expression and activity of the remaining full-length ABCA1 allele. These data suggest that ABCA1 requires a physical association with itself or other molecules for normal function and has important pharmacogenetic implications for individuals with truncation mutations.
Wellington
Cheryl L
CL
Centre for Molecular Medicine and Therapeutics, Childrens' and Women's Hospital, University of British Columbia, 980 West 28th Avenue, Vancouver, British Columbia, Canada.
Yang
Yu-Zhou
YZ
Zhou
Stephen
S
Clee
Susanne M
SM
Tan
Bing
B
Hirano
Kenichi
K
Zwarts
Karin
K
Kwok
Anita
A
Gelfer
Allison
A
Marcil
Michel
M
Newman
Scott
S
Roomp
Kirsten
K
Singaraja
Roshni
R
Collins
Jennifer
J
Zhang
Lin-Hua
LH
Groen
Albert K
AK
Hovingh
Kees
K
Brownlie
Alison
A
Tafuri
Sherrie
S
Genest
Jacques
J
Kastelein
John J P
JJ
Hayden
Michael R
MR
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D000077556:Alitretinoin; D000483:Alleles; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D005347:Fibroblasts; D005799:Genes, Dominant; D006579:Heterozygote; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology*; D008075:Lipoproteins, HDL / Q000032:analysis; D008264:Macrophages; D051379:Mice; D009154:Mutation / Q000235:genetics*; D014212:Tretinoin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects*
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D006888:Hydroxycholesterols; D008075:Lipoproteins, HDL; C003585:22-hydroxycholesterol; D000077556:Alitretinoin; D014212:Tretinoin