Farnesol Stimulates Differentiation in Epidermal Keratinocytes via PPARα

doi:10.1074/jbc.275.15.11484

Farnesol Stimulates Differentiation in Epidermal Keratinocytes via PPARα*

From the ^‡Departments of Dermatology,^‡Medicine, and ^§§Pediatrics, University of California San Francisco, School of Medicine, California 94143; the ^§Dermatology and ^‖Medical Services, Department of Veterans Affairs Medical Center, San Francisco, California 94121; and ^**Institut de Génétique et Biologie Moleculaire et Cellulaire, 67404 Illkirck, France

Abstract

The isoprenoids farnesol and juvenile hormone III (JH), metabolites of the cholesterol biosynthetic pathway, have been shown to stimulate fetal epidermal development in rodents. In this study we determined whether this effect might be attributed to a direct induction of keratinocytes differentiation and examined the mechanisms responsible for these effects. Rates of cornified envelope formation, a marker of keratinocyte terminal differentiation, as well as protein and mRNA levels of two proteins required for cornified envelope formation, involucrin (INV) and transglutaminase, increased 2- to 3-fold in normal human keratinocytes (NHK) treated with either farnesol or JH, even at low calcium concentrations (0.03 mm), which otherwise inhibit differentiation. In contrast, neither cholesterol nor mevalonate affected INV or transglutaminase mRNA levels. Effects of farnesol and JH on INV and transglutaminase mRNA levels were additive with high calcium concentrations (1.2 mm) that independently stimulate keratinocyte differentiation. In contrast, keratinocyte DNA synthesis was inhibited by these compounds. Both farnesol and JH stimulated INV and transglutaminase promoter activity, suggesting regulation at the transcriptional level. A series of truncation and deletion experiments revealed a farnesol-responsive region (−2452 to −1880 base pairs (bp)) in the INV gene. This region contained an AP-1 site. A single base pair mutation of the AP-1 site at −2116 to −2110 bp abolished farnesol responsiveness, identical to effects by peroxisome proliferator-activated receptor (PPARα) activators. Farnesoid X-activated receptor mRNA was not detected in NHK, but farnesol treatment increased activities of both a PPAR response element and PPARα mRNA levels in NHK. Furthermore, the increase in PPRE activity by farnesol was dependent upon PPARα in CV-1 cells. Finally, topical applications of farnesol increased mRNA and protein levels of the differentiation-specific genes, profilaggrin and loricrin, determined by immunohistochemistry and in situhybridization, in wild-type but not in PPARα−/− murine epidermis. These findings suggest a novel role for selected isoprenoid cholesterol intermediates in the regulation of differentiation-specific gene transcription and a convergence of PPARα with the cholesterol synthetic pathway.

Footnotes

↵* This study was supported by National Institutes of Health Grants HD29706, AR39639, AR29706, and AR39448; by the Medical Research Service, Department of Veterans Affairs Medical Center; by Association pour la Recherche contre le Cancer Grant ARC9943 (to J. A.); and by Human Frontier Science Program Grant RG 0041/1999-M (to J. A.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¶ To whom correspondence should be addressed: Dermatology Service (190), Department of Veterans Affairs Medical Center, 4150 Clement St., San Francisco, CA 94121. Tel.: 415-750-2091; Fax: 415-751-3927; E-mail: kh1111@hotmail.com.
↵2 K. Hanley, L. G. Kömüves, D. C. Ng, K. Schoonjans, S. S. He, P. Lau, D. D. Bikle, M. L. Williams, P. M. Elias, J. Auwerx, and K. R. Feingold, unpublished observations.
↵3 Communication with T. Willson, Glaxo-Wellcome.
Abbreviations:

INV

involucrin

NHK

normal human keratinocyte

PPARα

peroxisome proliferator-activated receptor α

PPRE

peroxisome proliferator response element

JH

juvenile hormone III

FXR

farnesoid-X-activated receptor

CE

cornified envelope

AP-1

activator protein-1

RAR

retinoic acid receptor

KGM

keratinocyte growth medium

CMF-PBS

calcium- and magnesium-free phosphate-buffered saline

TG'ase

transglutaminase

kb

kilobase(s)

bp

base pair(s)

RT-PCR

reverse transcriptase-polymerase chain reaction

DIG

digoxigenin

SREBP

sterol regulatory element binding protein

Wy-14643

4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (pirinixic acid)
- Received September 17, 1999.
- Revision received January 18, 2000.
The American Society for Biochemistry and Molecular Biology, Inc.