In Situ Hybridization and Immunohistochemical Analysis of Cytochrome P450 1B1 Expression in Human Normal TissuesLevan Muskhelishvilia, Patricia A. Thompsonb, Donna F. Kusewitta, Charles Wangb, and Fred F. Kadlubarba Pathology Associates International, Jefferson, Arkansas b Division of Molecular Epidemiology of National Center for Toxicological Research, Jefferson, Arkansas Correspondence to: Levan Muskhelishvili, Pathology Associates International, 3900 NCTR Rd., MC 923, Jefferson, AR 72079. E-mail: lmuskhelishvili@nctr.fda.gov
Cytochrome P450 1B1 (CYP1B1) is a recently cloned dioxin-inducible form of the cytochrome P450 supergene family of xenobiotic-metabolizing enzymes. CYP1B1 is constitutively expressed mainly in extrahepatic tissues and is inducible by aryl hydrocarbon receptor ligands. Human CYP1B1 is involved in activation of chemically diverse human procarcinogens, including polycyclic aromatic hydrocarbons and some aromatic amines, as well as the endogenous hormone 17ß-estradiol. The metabolism of 17ß-estradiol by CYP1B1 forms 4-hydroxyestradiol, a product believed to be important in estrogen-induced carcinogenesis. Although the distribution of CYP1B1 mRNA and protein in a number of human normal tissues has been well documented, neither the cells expressing CYP1B1 in individual tissue nor the intracellular localization of the enzyme has been thoroughly characterized. In this study, using nonradioactive in situ hybridization and immunohistochemistry, we examined the cellular localization of CYP1B1 mRNA and protein in a range of human normal tissues. CYP1B1 mRNA and protein were expressed in most samples of parenchymal and stromal tissue from brain, kidney, prostate, breast, cervix, uterus, ovary, and lymph nodes. In most tissues, CYP1B1 immunostaining was nuclear. However, in tubule cells of kidney and secretory cells of mammary gland, immunoreactivity for CYP1B1 protein was found in both nucleus and cytoplasm. This study demonstrates for the first time the nuclear localization of CYP1B1 protein. Moreover, the constitutive expression and wide distribution of CYP1B1 mRNA and protein in many human normal tissues suggest functional roles for CYP1B1 in the bioactivation of xenobiotic procarcinogens and endogenous substrates such as estrogens. (J Histochem Cytochem 49:229236, 2001) Key Words: cytochrome p450, CYP1B1, in situ hybridization, immunohistochemistry
Cytochromes P450 (CYPs) are a multigene family of constitutively expressed and inducible enzymes involved in the oxidative metabolic activation and detoxification of many endogenous and exogenous compounds (
Studies on human uterine myometrium, MCF-7 cells, and a human lymphoblastoid cell line demonstrated that CYP1B1 protein is involved in the metabolism of 17ß-estradiol and testosterone (
The wide distribution of CYP1B1 in human organs and its involvement in biotransformation of exogenous compounds as well as endogenous substrates, such as steroid hormones, suggest that this enzyme may have a significant role in tumorigenesis and in endogenous hormone metabolism. Although the distribution of CYP1B1 mRNA and protein in number of human normal tissues has been well documented ( In this study, using in situ hybridization (ISH) and immunohistochemical (IHC) techniques, we show the following: (a) CYP1B1 mRNA and protein are expressed in a variety of human normal tissues; (b) CYP1B1 mRNA and protein are expressed in parenchymal and stromal cells of tissues examined; and (c) CYP1B1 protein is localized mainly in the nuclei of the cells, although in some cell types it is also present in cytoplasm.
Tissue Samples
CYP1B1 Antisense RNA Probe
In Situ Hybridization
Anti-CYP1B1 Antibody
Immunohistochemistry For evaluation of CYP1B1 expression in astrocytes of human brain cortex, immunostaining of brain sections with CYP1B1 antibodies was followed by immunohistochemical detection of glial fibrillary acidic protein (GFAP). Briefly, GFAP antibodies (mouse monoclonal anti-human GFAP; Lab Vision, Fremont, CA) were used at 1:50 dilution. Nonspecific staining was blocked with 5% normal goat serum (Sigma). The brain sections were incubated with biotinylated goat anti-mouse antibodies and ExtrAvidin-conjugated alkaline phosphatase (Sigma). Staining was developed with New Fuchsin substrate (Biogenex; San Ramon, CA). For inhibition of endogenous alkaline phosphatase activity, 0.6 mg/ml levamisole (Sigma) was added to the substrate mix. Sections were counterstained with hematoxylin. Normal mouse serum or PBS replaced GFAP antibodies in negative controls.
In Situ Hybridization
Immunohistochemistry
In human brain cortex, strong nuclear immunostaining of the majority of neurons was observed in all samples examined (Table 1; Fig 2A). Double labeling of brain sections with CYP1B1 and GFAP antibodies demonstrated that CYP1B1 protein was also expressed in the nuclei of a majority of astrocytes (Table 1; Fig 2B).
In the kidney, strong CYP1B1 immunoreactivity was detected in both nuclei and cytoplasm of distal tubules. However, weak nuclear and cytoplasmic immunostaining was also observed in some of the proximal tubules (Table 1; Fig 2C). Immunostaining of mammary epithelia was not even. In the same sample, secretory cells of some lobules displayed only nuclear immunostaining, whereas cells in other lobules exhibited both nuclear and cytoplasmic immunoreactivity (Table 1; Fig 2D). Epithelial cells of prostate, cervix, and uterus, oocytes and follicular cells in ovary, and lymphoid cells and macrophages in lymph nodes exhibited only nuclear immunostaining, which ranged from weak to strong in different samples (Table 1; Fig 2E2J). Stromal cells and muscle cells of organs such as uterus and cervix were also positively stained; the protein was expressed mostly in nuclei (Table 1; Fig 2K). Only three of nine liver samples examined were CYP1B1-positive. Two of them exhibited mild cytoplasmic immunostaining, and in the third sample both nuclei and cytoplasm were weakly immunoreactive (Table 1; Fig 2L).
The present results demonstrated that CYP1B1 mRNA and protein are expressed in different types of human normal tissues (Fig 1 and Fig 2). These results are not consistent with a previous study that found CYP1B1 protein only in tumor tissues (
Earlier, it had been shown that CYP1B1 mRNA was present in human brain tissue ( According to ISH analysis and immunohistochemistry with CYP1B1 antibodies, the main cellular subset expressing CYP1B1 in human brain is neurons. Morphologically, however, astrocytes are hardly distinguishable from small neurons. To determine if astrocytes also express CYP1B1 protein, we performed double immunolabeling with CYP1B1 and GFAP antibodies. The double labeling clearly demonstrated that most astrocytes also express CYP1B1 protein and that in these cells the enzyme is also localized in the nucleus. The intracellular pattern of CYP1B1 immunostaining in other tissues was mostly similar to that in brain cells: epithelial cells of prostate, uterus, and cervix, oocytes and follicular cells in the ovary, lymphoid cells and macrophages in lymph nodes, and stromal and muscle cells in different organs displayed mostly nuclear staining. However, in tubule cells of the kidney and secretory cells of the mammary gland, immunostaining for CYP1B1 was observed in both nucleus and cytoplasm. The present study demonstrates for the first time nuclear localization of CYP1B1 protein, suggesting a functional role in the nucleus.
The human liver exhibits the lowest levels of CYP1B1 mRNA (
The constitutive expression and wide distribution of CYP1B1 mRNA and protein in human normal tissues supports the possibility of an important regulational role and suggests its involvement in local metabolism of xenobiotics. Human CYP1B1 is capable of activation of chemically diverse human procarcinogens (
Received for publication August 17, 2000; accepted August 23, 2000.
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