Abstract:
The Brn-3a POU family transcription factor is able to induce the
expression of a number of neuronally-expressed genes as well as to enhance neuronal
differentiation and inhibit apoptosis. Many of these effects are mediated by
the C-terminal POU domain of Brn-3a which acts both as a DNA binding domain
and a transcriptional activation domain. To identify the mechanisms by which
this domain acts, we carried out a yeast two hybrid assay to identify proteins
which interact with it. We show that both full length Brn-3a and the isolated
POU domain interact with the EWS transcription factor and its oncogenic derivative
EWS-Fli1. Moreover, EWS can block Brn-3a-mediated activation of the Bcl-x promoter
whereas this effect is lost in EWS-Fli1. The significance of this novel interaction
is discussed in terms of the manner in which Brn-3a regulates its target promoters
and the mechanism of oncogenic transformation by EWS-Fli1.