PhDTamoxifen remains a widely used hormone therapy for pre and postmenopausal
women with hormone receptor positive breast cancer in both
adjuvant and metastatic disease settings. Resistance to this well tolerated
and cost-effective drug limits its use. Only an improved understanding of the
mechanisms of tamoxifen resistance will provide the basis for overcoming this
phenomenon.
Expression profiles from tamoxifen-resistant and sensitive MCF7
derived breast cancer cell lines were prepared, using Affymetrix HG_U133A
cDNA microarrays. The data generated was analysed to identify novel
pathways and genes associated with tamoxifen resistance or sensitivity.
Selected genes, whose expression correlates with response to tamoxifen,
were validated using RT-PCR in cell lines and following this, in situ
hybridisation and immunohistochemistry on cell lines. Functional analyses of
these genes were carried out: genes that were down-regulated in tamoxifen
resistant MCF7 cells (HRASLS3, CTSD, CAXII) were selectively knocked
down using RNA interference. Cell lines stably over-expressing genes upregulated
in the tamoxifen resistant MCF7s (ATP1B1, SOCS2, NR4A2) were
selected. These manipulated cells were subsequently tested for their
response to anti-oestrogen treatment.
Another major marker in breast cancer is the ERBB2 proto-oncogene;
overexpressed in 20% of breast carcinomas, it is associated with poor
prognosis and hormone resistance. The transcriptional deregulation of
ERBB2 in breast cancer may in part be mediated by the transcription factors
AP-2 and . Previous studies have shown that ERBB2 expression is
repressed by oestrogen activated oestrogen receptor and that AP-2 binding
sites within the ERBB2 promoter and the intronic enhancer are required for
this oestrogenic repression.
Using RNA interference, AP-2 and were successfully knocked down
in breast cancer cell lines MCF7, T47D and ZR75-1. These have been used
to investigate the effect of AP-2 loss on ERBB2 expression in hormonally
manipulated cells
