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Journal of Lipid Research, Vol. 47, 2248-2258, October 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

* Metabolism Section, Veterans Affairs Medical Center, Northern California Institute for Research and Education, University of California at San Francisco, San Francisco, CA 94121
Dermatology Service, Veterans Affairs Medical Center, Northern California Institute for Research and Education, University of California at San Francisco, San Francisco, CA 94121
Published, JLR Papers in Press, July 6, 2006.
1 To whom correspondence should be addressed. e-mail: kfngld{at}itsa.ucsf.edu
Keratinocytes require abundant cholesterol for cutaneous permeability barrier function; hence, the regulation of cholesterol homeostasis is of great importance. ABCA1 is a membrane transporter responsible for cholesterol efflux and plays a pivotal role in regulating cellular cholesterol levels. We demonstrate that ABCA1 is expressed in cultured human keratinocytes (CHKs) and murine epidermis. Liver X receptor (LXR) activation markedly stimulates ABCA1 mRNA and protein levels in CHKs and mouse epidermis. In addition to LXR, activators of peroxisome proliferator-activated receptor (PPAR)
, PPARß/
, and retinoid X receptor (RXR), but neither PPAR
nor retinoic acid receptor, also increase ABCA1 expression in CHKs. Increases in cholesterol supply induced by LDL or mevalonate stimulate ABCA1 expression, whereas inhibiting cholesterol synthesis with statins or cholesterol sulfate decreases ABCA1 expression in CHKs. After acute permeability barrier disruption by either tape-stripping or acetone treatment, ABCA1 expression declines, and this attenuates cellular cholesterol efflux, making more cholesterol available for regeneration of the barrier. In addition, during fetal epidermal development, ABCA1 expression decreases at days 1822 of gestation (term = 22 days), leaving more cholesterol available during the critical period of barrier formation. Together, our results show that ABCA1 is expressed in keratinocytes, where it is negatively regulated by a decrease in cellular cholesterol levels or altered permeability barrier requirements and positively regulated by activators of LXR, PPARs, and RXR or increases in cellular cholesterol levels.
Supplementary key words ATP binding cassette transporter 1 liver X receptor peroxisome proliferator-activated receptor
peroxisome proliferator-activated receptor
peroxisome proliferator-activated receptor
cultured human keratinocyte
Abbreviations: ATRA, all-trans-retinoic acid; 8-Br-cAMP, 8-bromoadenosine-3',5'-cyclic monophosphate; CHK, cultured human keratinocyte; 9-cis-RA, 9-cis-retinoic acid; CS, cholesterol sulfate; LXR, liver X receptor; 25(OH), 25-hydroxycholesterol; PPAR, peroxisome proliferator-activated receptor; 22R, 22(R)-hydroxycholesterol; RXR, retinoid X receptor; TO, TO901317
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