LB54
The identification of transcriptional targets of TBX2 and their role in breast cancer proliferation
Keara Redmond, Nyree Crawford, Hannah Farmer, Zenobia D'Costa, Niamh Buckley, Caoimhe Nic An tSaoir, Dorota Tkocz, Paul Mullan
Queen's University Belfast, UK
Background
TBX2 is a member of a family of genes encoding developmental transcription
factors which play a crucial role in the development of many tissues. TBX2 is a
transcriptional repressor and has been shown in vitro to repress a
number of key growth regulatory genes such as p14ARF, p21WAF1 and Connexin 43.
Previous work has shown that the TBX2 locus is found on a region of chromosome
17 (17q23) which is amplified in up to 20% of primary breast cancers, and this
has been shown to result in TBX2 overexpression. TBX2 is associated with highly
aggressive breast cancer and with hereditary breast cancers.
Method and Results
We have found that knockdown of TBX2 by siRNA or the induction of a TBX2
dominant-negative protein leads to profound growth inhibition in a number of
breast cancer cell lines. We carried out a microarray with TBX2 siRNA which
identified 600 genes that are potential transcriptional targets of TBX2. We
have validated a number of these targets by real-time PCR and Northern blotting,
and have performed luciferase promoter studies for one target gene, NDRG1,
which is consistently upregulated with TBX2 siRNA. Using NDRG1 promoter
constructs we have identified a mode of action of TBX2, through an EGR1
dependent mechanism. Co-IP experiments have shown the interaction of TBX2 with
EGR1, and ChIP assays have shown that TBX2 requires EGR1 in order to localize
to the NDRG1 promoter.
Conclusion
We have identified a novel mode of transcriptional repression by the oncogene
TBX2, which is dependent of the interaction of TBX2 with the transcription
factor EGR1. This interaction is necessary in order for TBX2 to repress target
genes involved in growth control.
