Oxygen-regulated and transactivating domains in endothelial PAS protein 1: comparison with hypoxia-inducible factor-1alpha.
Endothelial PAS protein 1 (EPAS1) is a basic helix-loop-helix Per-AHR-ARNT-Sim transcription factor related to hypoxia-inducible factor-1alpha (HIF-1alpha). To analyze EPAS1 domains responsible for transactivation and oxygen-regulated function, we constructed chimeric fusions of EPAS1 with a GAL4 DNA binding domain, plus or minus the VP16 activation domain. Two transactivation domains were defined in EPAS1; a C-terminal domain (amino acids 828-870), and a larger internal domain (amino acids 517-682). These activation domains were interspersed by functionally repressive sequences, several of which independently conveyed oxygen-regulated activity. Two types of activity were defined. Sequences lying N-terminal to and overlapping the internal transactivation domain conferred regulated repression on the VP16 transactivator. Sequences lying C-terminal to this internal domain conveyed repression and oxygen-regulated activity on the native EPAS1 C-terminal activation domain, but not the Gal/VP16 fusion. Fusions containing internal but not C-terminal regulatory domains manifested regulation of fusion protein level. Comparison of EPAS1 with HIF-1alpha demonstrated a similar organization for both proteins, and for the C terminus defined a conserved RLL motif critical for inducibility. Overall, EPAS1 sequences were less inducible than those of HIF-1alpha, and inducibility was strikingly reduced as their expression level was increased. Despite these quantitative differences, EPAS1 regulation appeared similar to HIF-1alpha, conforming to a model involving the modulation of both protein level and activity, through distinct internal and C-terminal domains.
O'Rourke
J F
JF
Erythropoietin Group, Room 425, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, United Kingdom.
Tian
Y M
YM
Ratcliffe
P J
PJ
Pugh
C W
CW
D051792:Basic Helix-Loop-Helix Proteins; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D010100:Oxygen; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000099162:Endothelial PAS Domain-Containing Protein 1; C052130:GAL4 protein, S cerevisiae