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Nuclear translocation of CAR is dependent on ubiquitination and proteasome‐mediated degradation of CAR cytoplasmic retention protein (CCRP)
Author(s) -
Timsit Yoav E.,
Negishi Masahiko
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a657-c
Subject(s) - mg132 , constitutive androstane receptor , microbiology and biotechnology , proteasome , ubiquitin , chemistry , cytoplasm , proteasome inhibitor , cytosol , nuclear export signal , hsp90 , biochemistry , transcription factor , biology , cell nucleus , nuclear receptor , gene , heat shock protein , enzyme
The constitutive active/androstane receptor (CAR) plays an important role as a coordinate transcription factor in the regulation of various hepatic metabolic pathways for chemicals such as drugs, glucose, fatty acids, bilirubin, and bile acids. Currently, it is known that in its inactive state, CAR is retained in the cytoplasm in a protein complex with Hsp90 and the tetratricopeptide repeat protein CAR cytosolic retention protein (CCRP). Upon activation by phenobarbital (PB) or the PB‐like inducer 1,4‐bis[2‐(3,5‐dichloropyridyloxy)]‐benzene (TCPOBOP), CAR translocates into the nucleus. We have identified ubiquitin‐dependent degradation of CCRP as an important signal for the nuclear translocation of CAR. Treatment with the proteasome inhibitor MG132 (5 μM) causes CAR to accumulate in the cytosol of transfected HepG2 cells. In the presence of MG132, TCPOBOP increases CCRP ubiquitination in HepG2 cells co‐expressing CAR, while CAR itself is not ubiquitinated. Moreover, immunoprecipitation experiments show that in the presence of MG132, CAR remains bound to CCRP. Consistent with continued retention of CAR by CCRP upon activator treatment in the presence of MG132, we observe the attenuation of CAR‐mediated transcriptional activation on both reporter constructs and the endogenous CYP2B6 gene in HepG2 cells. Collectively, these data suggest that ubiquitin‐proteasomal regulation of CCRP is an important determinant for the ability of CAR to respond to PB or PB‐like inducers.