Identification of transcription factor related to toxicity of dioxin

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2378-tetrachlorodibenzo-p-dioxin (dioxin) and related compounds exert various toxicities such as teratogenicity and tumor promoting activity, but the mechanisms of gene expression accompanied with emerge of their toxic effect remain to be unclear. Previously, we showed that 3453'4'-pentachlorobiphenyl (PenC) a dioxin related compound, induces the expression of pi class glutathione S-transferase (GSTP1) gene in primary cultured rat liver parenchymal cells.In order to understand the regulation of GSTP1 gene expression, a regulatory element on 5' flanking sequence of this gene was identified by CAT assay. The GPEI element was shown to be required for stimulation of GSTP1 gene expression by PenCB in primary cultured liver parenchymal cells. GPEI is already known to contain a dyad of phorbol ester responsive element-like elements oriented palindromically. It is suggested that a novel signal transduction pathway activated by PenCB contributes to stimulation of GSTP1 expression.Not only PenCB but epidermal growth factor (EGF) induces the expression of GSTP1 gene. GPEI element is also required for the expression of this gene by EGF and TGFα. It is suggested that EGF and TGFα induce GSTP1 by the same signal transduction pathway as PenCB.We intend now to identify the GPEI binding protein using a nuclear extract of immortalized rat liver parenchymal cells which constitutively express GSTP1 as a starting material. GPEI binding proteins in the nucleous were cross-linked with 32P labeled GPEI oligomer by UV irradiation and were separated by 2D gel electrophoresis. Proteins bound to GPEI oligomer were isolated after detecting by autoradiography. After determining the molecular weights of triptic digests of isolated proteins by MALDI-TOF/MS, we have identified the GPEI binding proteins referring with the data base of protein sequences.