Identification of the Retinoic Acid-inducible All-trans-retinoic Acid 4-Hydroxylase

doi:10.1074/jbc.271.47.29922

Identification of the Retinoic Acid-inducible All-trans-retinoic Acid 4-Hydroxylase*

From the ^‡ Cancer Research Laboratories, Departments of
^§ Pathology,
^¶ Biochemistry, and
^∥ Medicine, Queen's University, Kingston, Ontario, K7L 3N6 Canada

**To whom correspondence should be addressed:
Cancer Research Laboratories, Rm. 355, Botterell Hall, Queen's University, Kingston, Ontario, K7L 3N6 Canada.
Tel.: 613-545-6791; Fax: 613-545-6830; E-mail: petkovic{at}post.queensu.ca.

Abstract

Retinoic acid (RA) metabolites of vitamin A are key regulators of gene expression involved in embryonic development and maintenance of epithelial tissues. The cellular effects of RA are dependent upon the complement of nuclear receptors expressed (RARs and RXRs), which transduce retinoid signals into transcriptional regulation, the presence of cellular retinoid-binding proteins (CRABP and CRBP), which may be involved in RA metabolism, and the activity of RA metabolizing enzymes. We have been using the zebrafish as a model to study these processes. To identify genes regulated by RA during exogenous RA exposure, we utilized mRNA differential display. We describe the isolation and characterization of a cDNA, P450RAI, encoding a novel member of the cytochrome P450 family. mRNA transcripts for P450RAI are expressed normally during gastrulation, and in a defined pattern in epithelial cells of the regenerating caudal fin in response to exogenous RA. In COS-1 cells transfected with the P450RAI cDNA, all-trans-RA is rapidly metabolized to more polar metabolites. We have identified 4-oxo-RA and 4-OH-RA as major metabolic products of this enzyme. P450RAI represents the first enzymatic component of RA metabolism to be isolated and characterized at the molecular level and provides key insight into regulation of retinoid homeostasis.

Footnotes

↵* This work was supported by grants from the Medical Research Council of Canada (to G. J. and M. P.). 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.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U68234[GenBank].
↵¹ The abbreviations used are:

RA

retinoic acid

4-OH-RA

4-hydroxy-retinoic acid

4-oxo-RA

4-oxo-retinoic acid

RAR

retinoic acid receptor

RXR

retinoid-X-receptor

CRBP

cellular retinoid binding protein

PCR

polymerase chain reaction

HPLC

high performance liquid chromatography.
↵²J. A. White and M. Petkovich, unpublished data.
↵³J. White and M. Petkovich, manuscript in preparation.
- Received July 25, 1996.
- Revision received August 30, 1996.