Several mechanisms have evolved to ensure the survival of cells under adverse conditions. The heat shock response is one such evolutionarily conserved survival mechanism. Heat shock factor-1 (HSF1) is a transcriptional regulator of the heat shock response. By the very nature of its prosurvival function, HSF1 may contribute to the pathogenesis of
cancer. The current study investigates the role of HSF1 in the pathogenesis of pancreatobiliary
tumors. HSF1 was downregulated in
pancreatic cancer (MIA PaCa-2 and S2-013) and
cholangiocarcinoma (KMBC and KMCH) cell lines by HSF1-specific
small interfering RNA (
siRNA). Nonsilencing
siRNA was used as control. The effect of HSF1 downregulation on viability and apoptosis parameters, i.e.,
annexin V,
terminal deoxynucleotidyl transferase dUTP-mediated nick end labeling (TUNEL), and
caspase-3, was measured. To evaluate the
cancer-specific effects of HSF1, the effect of HSF1 downregulation on normal human pancreatic ductal cells was also evaluated. HSF1 is abundantly expressed in human pancreatobiliary
cancer cell lines, as well as in
pancreatic cancer tissue, as demonstrated by Western blot and immunohistochemistry, respectively. Inhibition of HSF1 expression by the HSF1
siRNA sequences leads to time-dependent death in pancreatic and
cholangiocarcinoma cell lines. Downregulation of HSF1 expression induces
annexin V and TUNEL positivity and
caspase-3 activation, suggesting activation of a
caspase-dependent apoptotic pathway. Although
caspase-3 inhibition protects against cell death induced by HSF1 expression, it does not completely prevent it, suggesting a role for
caspase-independent cell death. HSF1 plays a prosurvival role in the pathogenesis of pancreatobiliary
tumors. Modulation of HSF1 activity could therefore emerge as a novel therapeutic strategy for
cancer treatment.