C. Garrido et al., HSP27 AS A MEDIATOR OF CONFLUENCE-DEPENDENT RESISTANCE TO CELL-DEATH INDUCED BY ANTICANCER DRUGS, Cancer research, 57(13), 1997, pp. 2661-2667
Resistance of colorectal cancer cells to chemotherapeutic drugs increa
ses as cells reach confluence. Here we show that the small stress prot
ein HSP27, which has been described to block necrotic and apoptotic ce
ll death, accumulates in confluent human colorectal cancer cell lines
HT-29 and Caco2. Cell confluence also induces HSP27 phosphorylation an
d changes in its intracellular distribution. We also show that overexp
ression of human HSP27 by transfection of HT-29 cells increased the re
sistance of cells to doxorubicin or cisplatin and prevented drug-induc
ed apoptosis. Interestingly, nonconfluent HSP27-transfected cells and
confluent control cells in which HSP27 is expressed at the same level
displayed a similar drug resistance. HSP27-transfected cells did not e
xhibit an enhanced resistance when they reached confluence, nor was th
ere an increased accumulation of HSP27. We have previously shown that
HSP27 expression blocks tumor necrosis factor-induced cell death as a
result of decreasing intracellular reactive oxygen species (ROS). Here
we show that HSP27 overexpression in HT-29 cells, obtained either by
transfection or by growing the cells at high density, correlated with
a significant ROS decrease. We conclude that cell confluent-dependent
HSP27 accumulation, probably due to its ability to decrease ROS levels
, is essential for the establishment of the resistance of colorectal c
ancer cells when reaching confluence.