Abstract
M.Sc.
Heat shock (HS) proteins and HS transcription factors (HSFs) have been coined as the
‘Achilles Heel’ for cancer therapy, since they have been found to be overexpressed in cancer
cells and are required for cell survival during tumour progression and metastasis. Hsp70 and
other members of the Hsp family have been shown to inhibit apoptosis at several different
stages, contributing to resistance to chemotherapy.
NSAIDs, like salicylates and aspirin, are used for the treatment and prevention of cancers
such as breast cancer. SA has been shown to enhance HSF-DNA binding and results in the
increased expression of heat-induced Hsp70 which is antiapoptotic.
We hypothesise that SA treatment can result in the potentiation of Hsp70 in MCF-7 cells
further increasing their resistance to apoptosis and thus the aim of this study was to
investigate the dose-responsive effects of salicylic acid (SA) in the presence and absence of
heat shock on components of the pro and antiapoptotic components of the apoptotic pathway.
MCF-7 cells, which naturally overexpress Hsp70, were treated with several doses of SA in the
presence and absence of a mild heat shock, followed by analysis of Hsp70 and several pro and
antiapoptotic members of intrinsic and extrinsic apoptotic pathways, including Bcl-2, Bax,
caspase 6 and 8, JNK, AIF and APAF-1.
Induced Hsp70 accumulation by the SA treatments in the presence and absence of heat shock
enhanced apoptosis in cells exposed to SA whereas higher concentrations of SA combination
with heat shock induced necrosis and a decrease in Hsp70 accumulation in MCF-7 cells.
Identification of the effects which specific concentrations of SA in the presence and absence
of heat shock had on the apoptotic pathway constituents helped highlight potential pathways
by which cell death could occur in MCF-7 cells through the downregulation of Hsp70. It is
most likely that MCF-7 cell death is occurring due to the release of reactive oxygen species
(ROS) which in turn lead to necrosis or death may be achieved via a cathepsin-B-mediated
cell death pathway where both of these possibilities need to be further investigated.