Short-listed for Access to Understanding 2013
ovaries, that stimulates the formation of the female sexual characteristics at
puberty. It also triggers the growth of the breast tissues during the
reproductive cycle and during pregnancy. However, oestrogen exposure in a
woman’s lifetime has been linked to breast cancer risk for many years. During
the development of breast cancer, oestrogen feeds the breast tissues and the
tumour indiscriminately and consequently helps its progression. Treatments that
block oestrogen receptors have been successfully used in the clinic, however
the response is difficult to predict and some patients eventually develop
resistance to those drugs. Understanding how oestrogen and its receptor work is
key to developing new effective therapies against breast cancer.
have discovered that the oestrogen receptor (ER) activates a different set of
genes in breast cancer patients who died compared to patients who survived.
This important study could help scientists understand why a disease that
appears superficially identical, has such differing outcomes in terms of
response to treatment and, ultimately, survival.
which means that it can travel to the cell nucleus, when partnered with
oestrogen, and reach the DNA molecules that harbour all our genes. Like all
transcription factors, ER has the capacity to attach to some specific “target”
genes, and lead to their activation or inhibition, which will in turn tell the
cells how to behave. ER is aided in reaching its nuclear targets by the
pathfinder transcription factor FOXA1, which opens up the DNA molecule for easy
access. It is known that this collaboration between ER and FOXA1 involves many
genes and is very dynamic, but the importance of its role in cancer development
is still unclear.
“capture” a transcription factor together with the DNA to which it is bound. It
is then possible to read the DNA sequence obtained from these binding events in
order to identify target genes of specific transcription factors. This
technique, previously used in cancer cell line models, was applied for the
first time by the team in
to biopsies from breast cancer patients that all possessed ER and FOXA1. These
patients were carefully chosen according to how aggressive their cancer was:
eight patients with good prognosis, seven patients with bad prognosis and three
who had a relapse and developed metastases were selected.
compared them between the different groups. The results showed that 484 binding
sites (i.e. spots on the DNA where ER is bound) were common to most of the
patients, but that the strength of the binding was more important in poor
outcome and relapse patients compared to good outcome ones. The experiment also
indicated that the different outcome patients can be well characterised by a
specific set of ER bound genes: 1,192 binding sites were predominantly found in
the poor prognosis group and another, distinct 599 binding sites were
representative of the good outcomes. The authors also observed that the
pathfinder FOXA1 was more often binding near the poor outcome ER binding sites
than the good ones.
for a double whammy; activating the poor outcome genes but also inhibiting the
genes in the good outcome group, meaning that the binding of ER at those
specific binding sites was biologically relevant in term of regulating cell
well established cancer cell line models that were either drug sensitive or
drug resistant, reproducing what is seen in patients. However, contrary to what
they had hypothesised, the drug sensitive cell model was more similar to the
poor outcome patients group, in term of ER binding sites, possibly suggesting
that these models constitute an intermediate category of tumours, with an ER
binding profile resembling more advanced tumours, on their way to acquired drug
resistance. The events that led to this intermediate category might have been
caused by the presence of other stimuli, such as other hormones or growth
factors for instance, in the patients from whom the cell line models were
established. By treating drug sensitive cells with some of these chemical
stimuli, they were able to shift the ER binding profile, and observed an increase
in new FOXA1 binding sites.
critical role in orchestrating the behaviour of breast cancer cells, but the
emergence of FOXA1 as the principal conductor sets the stage for novel
approaches in targeted therapy.
This entry describes research published in the following article, selected by Cancer Research UK:
Access to Understanding entrants are asked to write a plain English summary of a research article. For Access to Understanding 2013 there were 9 articles to choose from, selected by the Europe PMC funders.
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