Multiple novel nonsynonymous CYP2B6 gene polymorphisms in Caucasians: demonstration of phenotypic null alleles

J Pharmacol Exp Ther. 2004 Oct;311(1):34-43. doi: 10.1124/jpet.104.068973. Epub 2004 Jun 9.

Abstract

The human microsomal cytochrome P450, CYP2B6, is involved in the biotransformation of several clinically important drugs. By complete sequence analysis of the human CYP2B6 gene coding regions in selected Caucasian DNA samples, we identified the five novel missense mutations 62A>T (Q21L in exon 1), 136A>G (M46V in exon 1), 12820G>A (G99E in exon 2), 13076G>A (R140Q in exon 3), and 21388T>A (I391N in exon 8). The recently described but functionally uncharacterized variant 13072A>G (K139E) was also observed. Haplotype analysis indicated the presence of at least six novel alleles that code for the protein variants CYP2B6.10 (Q21L, R22C), CYP2B6.11 (M46V), CYP2B6.12 (G99E), CYP2B6.13 (K139E, Q172H, K262R), CYP2B6.14 (R140Q), and CYP2B6.15 (I391N). Heterologous expression in COS-1 cells revealed comparable levels of CYP2B6 apoprotein and bupropion hydroxylase activity for CYP2B6.1 (wild type) and CYP2B6.10, whereas all other variants exhibited reduced expression and/or function. The three amino acid changes M46V, G99E, and I391N resulted in almost unmeasurable (M46V) or undetectable (G99E and I391N) enzyme activity, despite the presence of residual protein. The K139E change led to completely abolished protein expression; as a consequence, no function was detected. Expression in insect cells by recombinant baculoviruses confirmed these results and demonstrated the virtual absence of incorporated heme in these protein variants. The collective allele frequency of the four very low or null activity variants M46V, G99E, K139E, and I391N was 2.6% in a Caucasian study population. These data provide further insight into the genetic variability of CYP2B6 and demonstrate the existence of phenotypic null alleles in this gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Aryl Hydrocarbon Hydroxylases / genetics*
  • Aryl Hydrocarbon Hydroxylases / metabolism
  • Cytochrome P-450 CYP2B6
  • European Continental Ancestry Group / genetics*
  • Haplotypes
  • Humans
  • Liver / metabolism
  • Molecular Sequence Data
  • Oxidoreductases, N-Demethylating / genetics*
  • Oxidoreductases, N-Demethylating / metabolism
  • Polymorphism, Genetic*
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid

Substances

  • Recombinant Proteins
  • Aryl Hydrocarbon Hydroxylases
  • CYP2B6 protein, human
  • Cytochrome P-450 CYP2B6
  • Oxidoreductases, N-Demethylating