Understanding how pioneer factors regulate estrogen receptor function in breast cancer cells
Jason S Carroll, Kelly A Holmes
Cancer Research UK/Cambridge Research Institute, Cambridge, UK
BACR/AstraZeneca Frank Rose Young Scientist Award
Background
Estrogen
Receptor (ER) regulation of target gene transcription is a significant factor
in breast cancer development and progression. Recent work in characterising ER
transcriptional activity has suggested that ER regulates gene expression from
distal cis-regulatory elements and uses a large number of co-factors for
modulating chromatin. We recently showed that ER binding to chromatin requires
a novel class of proteins called Pioneer factors. FoxA1 and GATA3 were shown to
be Pioneer factors, required for ER to maintain binding to the DNA at a select
number of tested regions. Recent work has suggested that Groucho/TLE proteins
may have Pioneer properties.
Methods
We
use genomic technologies, such as high throughput sequencing (Solexa
sequencing) in combination with Chromatin Immunoprecipitations (ChIP) and DNase
sensitivity assays. This allows us to map transcription factor binding sites
and chromatin structure on a global level.
Results
We
now show that the Groucho protein TLE1 is an ER Pioneer factor required for ER
DNA interactions. Our data suggest that TLE1 is necessary for ER to bind to
more than half the ER binding sites within the genome and for estrogen mediated
transcriptional activity. Furthermore, TLE1 is essential for efficient
estrogen-mediated cell cycle progression and can predict outcome in ER positive
breast cancer patients. We also confirm on a genome-wide level that FoxA1 and
GATA3 are critical determinants of ER binding to the chromatin and overall
chromatin structure.
Conclusion
These
data provide insight into the mechanisms by which ER maintains chromatin
interactions and suggests that Pioneer factors may be critical determinants of
ER function in breast cancer cells.
