| Summary: | 碩士 === 中山醫學院 === 毒理學研究所 === 87 === It has been shown that polycyclic aromatic hydrocarbon (PAHs) induce gene expression of cytochrome P450IA1(CYPIA1), cytochrome P450 IB1(CYPIB1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione-s-transferases (GST) and aldehyde dehydrogenase (ALDH) through activation of Aryl hydrocarbon receptor (AhR) and Aryl hydrocarbon receptor nuclear translocator (Arnt). AhR and Arnt are also reported to relate to differentiation and carcinogenesis. The mRNA level of AhR and Arnt were increased during keratinocyte differentiation. Previous studies demonstrated that CYPIA1 induction was suppressed in chemically-induced mouse skin papillomas and squamous cell carcinomas. In the present study, we observed differential CYPIA1 inducibility between a spontaneously immortalized human keratinocyte HaCat cell line and a human skin basal cell carcinoma (BCC) cell line. HaCaT cells presist differentiation ability and express both early and late differentiation markers (K1, K10, and involucrin). However, BCC cells only express early differentiation markers (K1 and K10) and fail to differentiate. In HaCaT cells, treatment with 1 M or 10 M B[a]P for 24 hr reduced viable cell numbers 3 days later. But B[a]P failed to decrease viable cell number in BCC cells. It is known that B[a]P does not only induce CYPIA1 gene expression but are also metabolically activated by CYPIA1. Therefore, we further examined CYPIA1 gene expression and enzyme activity in B[a]P-treated HaCaT and BCC cells. Both CYPIA1 gene expression and enzyme activity are only induced by B[a]P in HaCaT cells, but not in BCC cells. The levels of AhR and Arnt in HaCaT cells were increased during differentiation. When we utilized a gel retardation assay to detect AhR activation, B[a]P induced a Banding with the [32p]-dioxin responsive element in nuclear extract from HaCaT cells, but not in nuclear extract from BCC cells. Pretreatment with tyrocine kinase inhibitor-genistein or herbimycin A 15 minutes increased B[a]P-induced CYPIA1 gene expression to 2.71 or 3.65 fold of control. Our results suggest that certain tyrosine kinases are overexpression in BCC cells, which effected AhR/Arnt-DNA binding ability and downregulated CYPIA1 gene expression.
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