Transactivation of a DR-1 PPRE by a human constitutive androstane receptor variant expressed from internal protein translation start sites.
Downstream in-frame start codons produce amino-terminal-truncated human constitutive androstane receptor protein isoforms (DeltaNCARs). The DeltaNCARs are expressed in liver and in vitro cell systems following translation from in-frame methionine AUG start codons at positions 76, 80, 125, 128, 168 and 265 within the full-length CAR mRNA. The resulting CAR proteins lack the N-terminal DNA-binding domain (DBD) of the receptor, yielding DeltaNCAR variants with unique biological function. Although the DeltaNCARs maintain full retinoid X receptor alpha (RXRalpha) heterodimerization capacity, the DeltaNCARs are inactive on classical CAR-inducible direct repeat (DR)-4 elements, yet efficiently transactivate a DR-1 element derived from the endogenous PPAR-inducible acyl-CoA oxidase gene promoter. RXRalpha heterodimerization with CAR1, CAR76 and CAR80 isoforms is necessary for the DR-1 PPRE activation, a function that exhibits absolute dependence on both the respective RXRalpha DBD and CAR activation (AF)-2 domains, but not the AF-1 or AF-2 domain of RXRalpha, nor CAR's DBD. A new model of CAR DBD-independent transactivation is proposed, such that in the context of a DR-1 peroxisome proliferator-activated response element, only the RXRalpha portion of the CAR-RXRalpha heterodimer binds directly to DNA, with the AF-2 domain of tethered CAR mediating transcriptional activation of the receptor complex.
Stoner
Matthew A
MA
Center for Molecular Toxicology & Carcinogenesis, The Pennsylvania State University, University Park, PA 16802, USA.
Auerbach
Scott S
SS
Zamule
Stephanie M
SM
Strom
Stephen C
SC
Omiecinski
Curtis J
CJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D018387:Codon, Initiator; D000090702:Constitutive Androstane Receptor; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D047492:Peroxisome Proliferator-Activated Receptors / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000737:chemistry; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements; D047488:Retinoid X Receptors / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D018387:Codon, Initiator; D000090702:Constitutive Androstane Receptor; D008024:Ligands; D047492:Peroxisome Proliferator-Activated Receptors; D020033:Protein Isoforms; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D047488:Retinoid X Receptors; D014157:Transcription Factors