Elsevier

Biochemical Pharmacology

Volume 57, Issue 12, 15 June 1999, Pages 1407-1413
Biochemical Pharmacology

Gene Expression and Development
Expression of CYP2A genes in human liver and extrahepatic tissues

https://doi.org/10.1016/S0006-2952(99)00015-5Get rights and content

Abstract

Members of the human cytochrome P450 2A (CYP2A) subfamily are known to metabolize several promutagens, procarcinogens, and pharmaceuticals. In this study, the expression of the three genes found in the human CYP2A gene cluster was investigated in the liver and several extrahepatic tissues by gene-specific reverse transcriptase-polymerase chain reaction (RT-PCR). All three transcripts (CYP2A6, CYP2A7, and CYP2A13) were found to be present in liver. Quantitative RT-PCR analysis showed that CYP2A6 and CYP2A7 mRNAs were present at roughly equal levels in the liver, while CYP2A13 was expressed at very low levels. Two putative splicing variants of CYP2A7 were found in the liver. Nasal mucosa contained a low level of CYP2A6 and a relatively high level of CYP2A13 transcripts. Kidney, duodenum, lung, alveolar macrophages, peripheral lymphocytes, placenta, and uterine endometrium were negative for all transcripts. This survey gives a comprehensive picture of the expression pattern of CYP2A genes in liver and extrahepatic tissues and constitutes a basis for a search for functional CYP2A forms and their roles in chemical toxicity in liver and nasal mucosa.

Section snippets

Tissue samples

Surplus liver tissue was obtained from elective liver surgery at the Department of Surgery, University Hospital of Oulu, Finland. Nasal mucosa samples were obtained during surgery for diseases of nasal cavity or sinuses at the Department of Otolaryngology, University Hospital of Oulu. The nasal mucosa samples were taken from respiratory areas of the nasal cavity. Placental samples were from the repository kept at the Department of Pharmacology and Toxicology, University of Oulu. Uterine

Screening of CYP2A transcripts in liver and extrahepatic tissues

To ensure the quality and integrity of cDNA preparations, tissue samples were first analyzed for the presence of β-actin transcripts, and, where possible, for the presence of mRNA corresponding to CYP forms known to be expressed in each tissue. Only samples with detectable β-actin transcripts and positive CYP controls were subjected to assay with CYP2A-specific primers.

All three CYP2A mRNAs were detected in the liver by qualitative RT-PCR. Analysis of the PCR products in ethidium

Discussion

This study shows that all three CYP2A genes are transcribed in human liver, and that out of several extrahepatic tissues and organs studied, only nasal mucosa appears to contain detectable levels of CYP2A13 and CYP2A6 mRNA. It is well established that the RT-PCR technique can detect extremely small amounts of mRNA, often present at levels that may not be physiologically meaningful. On the other hand, a clear merit of this methodology is its high level of specificity, ensuring that only correct

Acknowledgements

We thank Risto Tuimala, Sirpa Rintala, and Teuvo Tammela (University of Tampere, Finland) for providing kidney samples, and Gerhard Bookjans and Peter Munzel (Institute of Toxicology, University of Tubingen, Germany) for providing duodenal samples. Pauli Wirta and Markku Pasanen helped in obtaining endometrium and placental samples. Financial support was provided by The Academy of Finland [Contracts 34555 and 29456].

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