Ian R. Phillips

The effect of terpenoid compounds on cytochrome P-450 levels in rat liver.

We have investigated the ability of camphor, menthol, pinene, limonene and myrcene to induce in rats members of a cytochrome P-450 sub-family termed PB P-450. These proteins have recently been designated as members of the P450IIB sub-family. None of these naturally occurring terpenoids significantly changed the total content of cytochromes P-450 or cytochrome b5. Radioimmunoassay results showed that PB P-450 was induced 6-fold by camphor and to a lesser extent by menthol and pinene. The induction was confirmed by Western blotting. It was shown by nucleic acid hybridization that induction of PB P-450 by terpenoids was mediated by an increase in the amount of the corresponding mRNA. Analysis of the denaturation of mRNA-cDNA hybrids demonstrated that the mRNA induced by the terpenoids was encoded by a member of the P450IIB sub-family. None of the terpenoids had an effect on the amount of mRNA coding for P450IA2 (a cytochrome P-450 inducible by beta-naphthoflavone and isosafrole). The results indicate that cytochromes P-450 induced by a synthetic compound, phenobarbital, may have originally evolved in response to terpenoid compounds normally present in the environment.

Isolation of a human cytochrome P‐450 reductase cDNA clone and localization of the corresponding gene to chromosome 7q11.2

We have isolated and sequenced cDNA clones that code for rat and human NADPH dependent cytochrome P‐450 reductase. The cDNA coding for the human protein was used to analyse, by Southern blot hybridization, DNA isolated from a panel of 8 independent humanrodent somatic cell hybrids. The results indicate that cytochrome P‐450 reductase is encoded by a single gene (POR) located on human chromosome 7(pter‐q22). Analysis of human metaphase chromosomes by hybridization in situ confirmed the results and refined the localization to 7q11.2. Northern blot hybridization revealed that in human liver the expression of the gene varies by less than 3‐fold between different individuals.

The major phenobarbital‐inducible cytochrome P‐450 gene subfamily (P450IIB) mapped to the long arm of human chromosome 19

We have recently isolated a cloned cDNA that codes for a human orthologue of the major phenobarbital‐inducible cytochrome P450IIB subfamily of rodents. The cloned human cDNA was used to analyse, by Southern blot hybridization, DNA extracted from a panel of 9 independent human‐rodent somatic cell hybrids. The results indicate that all members of the P450IIB gene subfamily of man are located on chromosome 19. Evidence from hybrids containing different regions of human chromosome 19 localizes this cytochrome P‐450 gene subfamily further to the long arm of chromosome 19 in the region cen‐q13.3. We propose the designation CYP2B for this locus.

Cloning and chromosomal mapping of human cytochrome b5 reductase (DIA1)

We have isolated a cDNA clone that codes for human cytochrome b5 reductase. The cDNA was used to analyse, by Southern‐blot hybridization, DNA isolated from a panel of 11 independent human‐rodent somatic cell hybrids. The results indicate that cytochrome b5 reductase is encoded by a single gene located on human chromosome 22.

Cloning, expression and chromosomal localization of a member of the human cytochrome P450IIC gene sub-family.

We have isolatd and sequenced a cDNA clone (pB8) that codes for a novel member of the dcytochrome P450IIC sub‐family of man. Analysis, by Southern blot hybridization, of DNA isolated from a panel of nine independent human‐rodent somatic cell hybrids demonstrated that the corresponding gene (CYP2C) is located on human chromosome 10. Northern blot hybridization of RNA isolated from human livers revealed a 10‐fold inter‐indicidual variation in the expression of the gene.