The use of
platinum complexes for the
therapy of
breast cancer is an emerging new treatment modality. To gain insight into the mechanisms underlying
cisplatin resistance in
breast cancer, we used
estrogen receptor-positive MCF-7 cells as a model system. We generated
cisplatin-resistant MCF-7 cells and determined the functional status of
epidermal growth factor receptor (EGFR), MAPK, and AKT signaling pathways by phosphoreceptor
tyrosine kinase and phospho-MAPK arrays. The
cisplatin-resistant MCF-7 cells are characterized by increased EGFR phosphorylation, high levels of AKT1
kinase activity, and ERK1 phosphorylation. In contrast, the JNK and
p38 MAPK modules of the MAPK signaling pathway were inactive. These conditions were associated with inactivation of the p53 pathway and increased BCL-2 expression. We investigated the expression of genes encoding the
ligands for the ERBB signaling cascade and found a selective up-regulation of
amphiregulin expression, which occurred at later stages of
cisplatin resistance development.
Amphiregulin is a specific
ligand of the EGFR (ERBB1) and a potent
mitogen for epithelial cells. After exposure to
cisplatin, the resistant MCF-7 cells secreted
amphiregulin protein over extended periods of time, and knockdown of
amphiregulin expression by specific
short interfering RNA resulted in a nearly complete reversion of the resistant phenotype. To demonstrate the generality and importance of our findings, we examined
amphiregulin expression and
cisplatin resistance in a variety of human
breast cancer cell lines and found a highly significant correlation. In contrast,
amphiregulin levels did not significantly correlate with
cisplatin resistance in a panel of
lung cancer cell lines. We have thus identified a novel function of
amphiregulin for
cisplatin resistance in human
breast cancer cells.