No abstract

The t(1;19) chromosomal translocation in acute lymphoblastic leukemias creates chimeric E2a-Pbxl oncoproteins that can act as DNA-binding activators of transcription. A structural analysis of the functional domains of E2a-Pbxl showed that portions of both E2a and Pbxl were essential for transformation of NIH 3T3 cells and transcriptional activation of synthetic reporter genes containing PBX1 consensus binding sites.Hyperexpression of wild-type or experimentally truncated Pbxl proteins was insufficient for transformation, consistent with their inability to activate transcription. When fused with E2a, the Pbx-related proteins Pbx2 and Pbx3 were also transformation competent, demonstrating that all known members of this highly similar subfamily of homeodomain proteins have latent oncogenic potential. The oncogenic contributions of E2a to the chimeras were localized to transactivation motifs AD1 and AD2, as their mutation significantly impaired transformation. Either the homeodomain or Pbxl amino acids flanking this region could mediate transformation when fused to E2a. However, the homeodomain was not essential for transformation, since a mutant E2a-Pbxl protein (E2a-PbxIHD) lacking the homeodomain efficiently transformed fibroblasts and induced malignant lymphomas in transgenic mice. Thus, transformation mediated by the chimeric oncoprotein E2a-Pbxl is absolutely dependent on motifs acquired from E2a but the Pbxl homeodomain is optional. The latter finding suggests that E2a-Pbxl may interact with cellular proteins that assist or mediate alterations in gene expression responsible for oncogenesis even in the absence of homeodomain-DNA interactions.

The E2A gene encodes DNA-binding transcription factors, called E12 and E47, involved in cell specification and maturation. E2A is also involved in a chromosomal translocation that leads to the expression of an oncogenic transcription factor called E2A-PBX1 in cases of acute leukemia. In the work described here, we elucidate the interaction between E2A-PBX1 and transcriptional co-activators. We confirm that the E2A portion can interact with CBP and PCAF and map required elements on E2A and CBP. On CBP, the interaction involves the KIX domain, a well characterized domain that mediates interactions with several other oncogenic transcription factors. On E2A, the interaction with CBP requires conserved ␣-helical domains that reside within activation domains 1 and 2 (AD1 and AD2, respectively). Using purified, recombinant proteins, we show that the E2A-CBP interaction is direct. Notwithstanding the previously demonstrated ability of AD1 and AD2 to function independently, some of our findings suggest functional cooperativity between these two domains. Finally, we show that the CBP/p300-interactive helical domains of E2A are important in the induction of proliferation in cultured primary bone marrow cells retrovirally transduced with E2A-PBX1. Our findings suggest that some aspects of E2A-PBX1 oncogenesis involve a direct interaction with the KIX domain of CBP/p300.

Here we present the Transcription Factor Encyclopedia (TFe), a new web-based compendium of mini review articles on transcription factors (TFs) that is founded on the principles of open access and collaboration. Our consortium of over 100 researchers has collectively contributed over 130 mini review articles on pertinent human, mouse and rat TFs. Notable features of the TFe website include a high-quality PDF generator and web API for programmatic data retrieval. TFe aims to rapidly educate scientists about the TFs they encounter through the delivery of succinct summaries written and vetted by experts in the field. TFe is available at http://www.cisreg.ca/tfe.