CYP2D7 splice variants in human liver and brain: Does CYP2D7 encode functional protein?

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Abstract

A CYP2D7 brain-specific protein metabolizing codeine and encoded by an alternate mRNA has recently been described in Indian subjects. To examine its potential presence in other ethnic backgrounds, CYP2D7 and CYP2D6 full-length splice products were analyzed in liver and brain. CYP2D7 splice variant-specific PCR on 13 subjects revealed the previously reported partial intron 6-containing transcript encoding CYP2D7 in both tissues as a minor variant. This transcript is not predicted to encode functional protein as a frame-shift-reverting deletion in CYP2D7 exon 1 (138delT) was not detected in any transcript or in 285 additional genotyped subjects. The g.14408G > C SNP required for functional transcript also was not observed; all transcripts and individuals genotyped as g.14408G/G that causes a premature stop codon in any splice variants that contain the 57 bp intron 6 insertion. Therefore, no evidence for functional CYP2D7 transcripts was observed in Asian, Caucasian or African American individuals.

Section snippets

Methods

Source of DNA and RNA. Tissue samples were obtained through NICHD-supported tissue retrieval programs, the University of Maryland Brain and Tissue Bank for Developmental Disorders (Baltimore, MD), and the Central Laboratory for Human Embryology at the University of Washington (Seattle, WA). RNA from 26 liver specimens (n = 3, prenatal; n = 23, postnatal) was used for the study. Of six subjects, brain tissue was also available (n = 3, prenatal; n = 3 postnatal). The use of these tissues was approved by

Cloning and identification of splice variants

Amplification of full-length CYP2D7 and CYP2D6 cDNA from liver and brain revealed multiple PCR products (Fig. 1). While fragments larger than full-length cDNA were visible in all subjects for liver, a shift towards larger bands (>2 kb) was especially evident in brain. In these latter cases, almost all amplicons were considerably larger than the expected 1.6 kb transcript. Since these initial results confirmed the existence of numerous alternative splice products, full-length liver and brain cDNA

Discussion

A recent report describing a functional CYP2D7 protein expressed in brain with kinetic characteristics distinct from those of CYP2D6 offers promise for novel therapeutic strategies targeting opiate receptors in the treatment of pain [3]. Other potential applications can be envisioned within the context of drug abuse and other areas where a role for CYP2D6 involvement is suggested or implied, such as the serotonin salvage pathway [2] and personality traits [19]. Moreover, the presence of

Acknowledgments

We gratefully acknowledge the technical assistance of Darren W. Baker and Liliane Ndjountché.

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    This work was supported by RO1 ES10855-04 from the National Institute of Environmental Health Sciences.

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