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Bcl3, an IkappaB protein, stimulates activating protein-1 transactivation and cellular proliferation.

Bcl3, an IkappaB protein, was originally isolated as a putative proto-oncogene in a subset of B cell chronic lymphocytic leukemias. Bcl3 was subsequently shown to associate tightly with and transactivate the NFkappaB p50 or p52 homodimer. Herein, we show that Bcl3 stimulates the activating protein-1 (AP-1) transactivation, either alone or in conjunction with transcription integrators steroid receptor coactivator-1 and CREB-binding protein/p300. The C-terminal 158 residues of Bcl3 exhibited an autonomous transactivation function and interacted with specific subregions of the AP-1 components c-Jun and c-Fos, CREB-binding protein/p300, and steroid receptor coactivator-1, as demonstrated by the yeast and mammalian two-hybrid tests as well as glutathione S-transferase pull-down assays. In addition, anti-HA antibody co-precipitated c-Jun from HeLa cells co-expressing c-Jun and HA-tagged Bcl3, consistent with the idea that Bcl3 directly associates with AP-1 in vivo. Furthermore, microinjection of Bcl3 expression vector into Rat-1 fibroblast cells significantly enhanced DNA synthesis and expression of c-jun, one of the cellular target genes of AP-1. These results suggest that Bcl3 may directly participate in the tumorigenesis processes as a novel transcription coactivator of the mitogenic transcription factor AP-1 in vivo.

Pubmed ID: 10497212


  • Na SY
  • Choi JE
  • Kim HJ
  • Jhun BH
  • Lee YC
  • Lee JW


The Journal of biological chemistry

Publication Data

October 1, 1999

Associated Grants


Mesh Terms

  • Animals
  • Cell Division
  • Cell Line
  • DNA Replication
  • Humans
  • I-kappa B Proteins
  • Protein Binding
  • Proto-Oncogene Proteins
  • Transcription Factor AP-1
  • Transcription Factors
  • Transcriptional Activation