Cytoplasmic accumulation of the nuclear receptor CAR by a tetratricopeptide repeat protein in HepG2 cells.
The nuclear constitutive active receptor (CAR) is a key transcription factor regulating phenobarbital (PB)-inducible transcription of various hepatic genes that encode xenobiotic/steroid-metabolizing enzymes. CAR is retained in the cytoplasm of noninduced livers and translocates into the nucleus after PB induction. HepG2 cells lack the capability of retaining CAR in the cytoplasm; thus, the receptor spontaneously accumulates in the nucleus. We have now cloned and characterized a tetratricopeptide repeat (TPR) protein, designated cytoplasmic CAR retention protein (CCRP), for its ability to accumulate the receptor in the cytoplasm of cotransfected HepG2 cells. CCRP directly interacts with the ligand-binding domain of CAR and mediates the formation of a cytoplasmic CAR-CCRP-90-kDa heat shock protein (hsp90) ternary complex. Simultaneous expression of fluorescent protein-tagged CAR and CCRP reveals their colocalization with tubulin in mouse liver in vivo. Thus, these results indicate that CCRP may be a component of the CAR-hsp90 complex and involved in retaining the receptor in the cytoplasm of both HepG2 cells and probably in vivo liver cells.
Kobayashi
Kaoru
K
National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Sueyoshi
Tatsuya
T
Inoue
Kaoru
K
Moore
Rick
R
Negishi
Masahiko
M
D000818:Animals; D001665:Binding Sites; D003001:Cloning, Molecular; D000090702:Constitutive Androstane Receptor; D003600:Cytosol / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D008099:Liver / Q000378:metabolism*; D051379:Mice; D018832:Molecular Chaperones; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D000090702:Constitutive Androstane Receptor; C478938:Dnajc7 protein, mouse; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors