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.
National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Kaoru
K
Kobayashi
Tatsuya
T
Sueyoshi
Kaoru
K
Inoue
Rick
R
Moore
Masahiko
M
Negishi
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