Casale G P, Cheng Z, Liu J n, Cavalieri E L, Singhal M
Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha 68198-6805, USA.
Mol Carcinog. 2000 Feb;27(2):125-40. doi: 10.1002/(sici)1098-2744(200002)27:2<125::aid-mc8>3.0.co;2-0.
The potent carcinogenicity of dibenzo[a,l]pyrene (DB[a,l]P) in mouse skin is associated with an inflammatory response and a striking epidermal hyperplasia. The mechanism of these tissue responses is not known. However, a recent study has shown DB[a,l]P to be a contact sensitizer. In view of the programmed expression of cytokines during induction of contact hypersensitivity (CHS) and elicitation of CHS reactions, we analyzed cytokine mRNAs in treated skin and draining lymph nodes of SENCAR mice, at selected times after a single, epicutaneous application of DB[a,l]P or dimethylbenz[a]anthracene (DMBA), a substantially weaker carcinogen and a weaker contact sensitizer than DB[a,l]P. Cytokine mRNAs were quantified by first-strand DNA synthesis with reverse transcriptase (RT) and DNA amplification by the polymerase chain reaction (PCR). Histopathology of treated skin was determined in the same experiments. Time-response profiles of interferon (IFN) gamma and interleukin (IL) 2 in the DLN and IL1beta, IL10, tumor necrosis factor (TNF) alpha, and IL4 mRNAs in the skin of mice treated with 200 nmol of DB[a,l]P were in remarkable agreement with established profiles in mice treated with conventional contact sensitizers, e.g., oxazolone or dinitrochlorobenzene. Strong upregulation of DLN IFNgamma mRNA coupled with little change in IL 2 mRNA suggested a CD8(+) T-cell response characteristic of CHS induction. Coordinate expression of epidermal IL1beta, TNFalpha, and IL10 mRNAs, 24 h after DB[a,l]P treatment, was also characteristic of CHS induction. IL1beta and IL10 are upregulated by allergens and not by chemical irritants. Time-response profiles of epidermal IL1beta, TNFalpha, IL10, and IL4 mRNAs, 3-14 d after DB[a,l]P treatment, corresponded with expression of these cytokines during elicitation of CHS reactions. Epidermal IL4 is specifically upregulated during CHS reactions. Cytokine mRNA responses were dose-dependent (50, 100, and 200 nmol of DB[a,l]P) and markedly weaker in animals treated with 400 nmol of DMBA. Significantly, the intensity of epidermal hyperplasia correlated with the strength of the cytokine mRNA signals in DLN and skin. In conclusion, our data support carcinogen-specific CHS as a mechanism by which the very potent carcinogen DB[a,l]P induces epidermal hyperplasia, a requirement for tumor promotion in mouse skin.
二苯并[a,l]芘（DB[a,l]P）对小鼠皮肤具有很强的致癌性，这与炎症反应和显著的表皮增生有关。这些组织反应的机制尚不清楚。然而，最近的一项研究表明DB[a,l]P是一种接触性致敏剂。鉴于在接触性超敏反应（CHS）诱导和CHS反应激发过程中细胞因子的程序性表达，我们在单次经皮涂抹DB[a,l]P或二甲基苯并[a]蒽（DMBA，一种致癌性比DB[a,l]P弱得多且接触致敏性也较弱的物质）后的选定时间，分析了SENCAR小鼠处理过的皮肤和引流淋巴结中的细胞因子mRNA。通过逆转录酶（RT）进行第一链DNA合成和聚合酶链反应（PCR）进行DNA扩增来定量细胞因子mRNA。在相同实验中确定处理过的皮肤的组织病理学。用200 nmol DB[a,l]P处理的小鼠的引流淋巴结中干扰素（IFN）γ和白细胞介素（IL）2以及皮肤中IL1β、IL10、肿瘤坏死因子（TNF）α和IL4 mRNA的时间反应谱与用传统接触致敏剂（如恶唑酮或二硝基氯苯）处理的小鼠中已确定的谱显著一致。引流淋巴结IFNγ mRNA的强烈上调以及IL 2 mRNA的几乎无变化表明了CHS诱导的CD8(+) T细胞反应特征。DB[a,l]P处理后24小时，表皮IL1β、TNFα和IL10 mRNA的协同表达也是CHS诱导的特征。IL1β和IL10由变应原上调，而非化学刺激物。DB[a,l]P处理后3 - 14天，表皮IL1β、TNFα、IL10和IL4 mRNA的时间反应谱与CHS反应激发过程中这些细胞因子的表达一致。表皮IL4在CHS反应期间特异性上调。细胞因子mRNA反应呈剂量依赖性（50、100和200 nmol DB[a,l]P），在用400 nmol DMBA处理的动物中明显较弱。重要的是，表皮增生的强度与引流淋巴结和皮肤中细胞因子mRNA信号的强度相关。总之，我们的数据支持致癌物特异性CHS作为一种机制，通过该机制，极强的致癌物DB[a,l]P诱导表皮增生，这是小鼠皮肤肿瘤促进的一个必要条件。
