Identification of the human cytochrome P450, P450RAI-2, which is predominantly expressed in the adult cerebellum and is responsible for all- trans -retinoic acid metabolism

Identification of the human cytochrome P450, P450RAI-2, which is predominantly expressed in the adult cerebellum and is responsible for all-trans-retinoic acid metabolism

^*Cytochroma Incorporated, Biosciences Complex, 116 Barrie Street, and Departments of ^†Biochemistry, ^‡Medicine, and ^§Pathology, Queen's University, Kingston, ON, K7L 3N6, Canada

Communicated by Hector F. DeLuca, University of Wisconsin, Madison, WI (received for review January 28, 2000)

Abstract

Retinoids, particularly all-trans-retinoic acid (RA), are potent regulators of cell differentiation, cell proliferation, and apoptosis. The role of all-trans-RA during development and in the maintenance of adult tissues has been well established. The control of all-trans-RA levels in cells and tissues is regulated by the balance between its biosynthesis and its catabolism to inactive metabolites. The cytochrome P450 enzyme P450RAI (herein renamed P450RAI-1) is partially responsible for this inactivation of all-trans-RA. In this report, we describe the identification, molecular cloning, and characterization of a second related enzyme, P450RAI-2, which is also involved in the specific inactivation of all-trans-RA. Transiently transfected P450RAI-2 can convert all-trans-RA to more polar metabolites including 4-oxo-, 4-OH-, and 18-OH-all-trans-RA. Competition experiments with other retinoids suggest that all-trans-RA is the preferred substrate. The high level of expression of P450RAI-2, particularly in the cerebellum and pons of human adult brain, suggests a unique role for this enzyme in the protection of specific tissues from exposure to retinoids.

Footnotes

↵ ¶ To whom reprint requests should be addressed at: Cancer Research Laboratories, Room 355, Botterell Hall, Queen's University, Kingston, ON, K7L 3N6, Canada. E-mail: petkovic{at}post.queensu.ca.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession no. AF252297).
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.120161397.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.120161397
↵ ‖ For information regarding reagents, e-mail info{at}cytochroma.com.
Abbreviations:

RA,

retinoic acid;

RAR,

RA receptor;

RXR,

retinoid X receptor;

4-OH-RA,

4-OH-all-trans-RA;

4-oxo-RA,

4-oxo-all-trans-RA;

18-OH-RA,

18-OH-all-trans-RA;

EST,

expressed sequence tag;

ALDH-1,

aldehyde dehydrogenase-1;

RALDH-2,

retinaldehyde dehydrogenase-2