[Relation between c-erbB1, c-erbB2, MAPK expression and resistance to tamoxifen in breast cancer cells in vitro].

OBJECTIVE: To study the growth regulation pathway and the mechanism of acquired resistance to tamoxifen (TAM) in breast cancer cells.

METHODS: TAM was used to induce wild-type MCF-7 human breast cancer cell line and establish a tamoxifen-resistant (TAM-R) cell line. RT-PCR, Western blot and immuocytochemical techniques were used to detect and compare mRNA and protein of c-erbB1, cerbB2, c-erbB3, c-erbB4 in wild-type MCF-7 and TAM-R MCF-7 cell lines.

RESULTS: Compared with wild-type MCF-7 cells, the mRNA of c-erbB1 increased 6 times (P < 0.05) and the protein 3 times higher (P < 0.05), and the mRNA of c-erbB2 increased 3 times (P < 0.05) and the protein 1.5 times higher (P < 0.05) in TAM-R MCF-7 cells. However, comparable levels of c-erbB3 mRNA and protein were expressed in both cell lines. c-erbB4 could not be detected. Under basic conditions, phosphorylated c-erbB1/c-erbB2 and c-erbB1/c-erbB3 heterodimers but not c-erbB2/c-erbB3 receptor heterodimers were detected in TAM-R cells in association with increased level of phosphorylated MAPK.

CONCLUSION: Our findings demonstrated that the development of TAM-resistance in MCF-7 cells is related with the autocrine release and action of an c-erbB1-specific ligand inducing preferential c-erbB1/c-erbB2 dimerization and downstream activation of the MAPK pathway.