Bone-specific expression of the alpha chain of the nascent polypeptide-associated complex, a coactivator potentiating c-Jun-mediated transcription.
The alpha chain of the nascent polypeptide-associated complex (alpha-NAC) coactivator was shown to potentiate the activity of the homodimeric c-Jun activator, while transcription mediated by the c-Fos/c-Jun heterodimer was unaffected. The use of deletion mutants in pull-down assays revealed that alpha-NAC interacted with amino acids 1 to 89 of the c-Jun protein and that the coactivator could interact with both the unphosphorylated and the serine 73-phosphorylated form of c-Jun. N-terminal-deleted c-Jun protein failed to interact with alpha-NAC in mammalian two-hybrid assays, while mutant c-Jun proteins lacking the leucine zipper or the basic domain retained interaction with alpha-NAC in vivo. Kinetics studies with purified c-Jun homodimer and recombinant alpha-NAC proteins allowed determination of the mechanism of coactivation by alpha-NAC: the coactivator stabilized the AP-1 complex formed by the c-Jun homodimer on its DNA recognition sequence through an eightfold reduction in the dissociation constant (kd) of the complex. This effect of alpha-NAC was specific, because alpha-NAC could not stabilize the interactions of JunB or Sp1 with their cognate binding sites. Interestingly, the expression of alpha-NAC was first detected at 14.5 to 15 days postconception, concomitantly with the onset of ossification during embryogenesis. The alpha-NAC protein was specifically expressed in differentiated osteoblasts at the centers of ossification. Thus, the alpha-NAC gene product exhibits the properties of a developmentally regulated, bone-specific transcriptional coactivator.
Moreau
A
A
Shriners Hospital, and Department of Surgery, McGill University, Montréal, Québec, Canada.
Yotov
W V
WV
Glorieux
F H
FH
St-Arnaud
R
R
D000818:Animals; D001665:Binding Sites; D001842:Bone and Bones / Q000196:embryology / Q000378:metabolism; D002460:Cell Line; D019281:Dimerization; D015870:Gene Expression; D051379:Mice; D018832:Molecular Chaperones; D010006:Osteoblasts / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
D018832:Molecular Chaperones; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D018808:Transcription Factor AP-1; C096099:nascent-polypeptide-associated complex