YOSHIOKA Toshimasa Tokyo Women's Medical University, School of Medicine, Associate professor, 医学部, 助教授 (60146438)
MURAKI Takamura Tokyo Women's Medical University, School of Medicine, Professor, 医学部, 教授 (50051446)
|Budget Amount *help
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 2000: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1999: ¥1,500,000 (Direct Cost: ¥1,500,000)
The aryl hydrocarbon receptor (AhR) mediates signal transduction elicited by environmental toxin, e. g. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AhR binds heat shock protein 90 (hsp90) in the cytosol. Upon ligand binding, AhR translocates into nucleus to activate the transcription of target genes and exhibits toxic effects of environmental toxins. Thus, nucleocytoplasmic shuttling of AhR is an important step in the regulation of AhR action. In the present study, we analyzed molecular mechanism of nucleocytoplasmic shuttling and intracellular cross talk of AhR using the cells expressing a fusion protein of green fluorescent protein and AhR.
1. Hsp90 inhibitors significantly inhibited ligand-induced transcriptional activation of AhR.However, Hsp90 inhibitors paradoxically caused a transient nuclear translocation of unliganded AhR.These unliganded nuclear AhR redistributes to cytoplasm without activating gene transcription. The nuclear trafficking of AhR may provoke rapid degradation of the receptor by proteasomes.
2. The effect of molecular chaperones and cochapeornes on the nucleocytoplasmic shuttling of AhR was studied. The overexpression of hsp90, hsc70, p60, hsp40 or p23 did not affect ligand-induced nuclear translocation of AhR.However, the nuclear export of AhR was attenuated by overexpression of nuclear hsp90, hsc70, p60 and hsp40. Thus, nuclear hsp90, hsc70, p60 and hsp40 appear to regulate the nuclear retention of AhR.AhR may cross talk with other nuclear receptors or signal transduction molecules via these molecular chaperones and cochaperones.