Background: Positive expression of estrogen receptor (ER) beta is correlated with a favorable prognosis for patients with epidermal growth factor receptor (EGFR) mutations and predicts a good clinical outcome for patients with lung cancer after treatment with an EGFR-tyrosine kinase inhibitor (TKI), suggesting that it may be a candidate surrogate marker. The molecular mechanism underlying the apparent link between EGFR mutations and ER beta expression in lung cancer cell lines was investigated.
Materials and methods: Four different human lung cancer cell lines were used, including one with an exon19 delE746-A750, one with a substitution of Leu for Arg at codon 858 in exon 21 (L858R), one with a L858R+ threonine-to-methionine mutation at codon 790 of EGFR (T790M) and one with wild-type EGFR. The EGFR mutations were investigated by direct sequencing. The expression levels of ER beta in the cell lines, in tumors from SCID mice and in primary human tissue specimens were evaluated by immunohistochemistry. Cell growth was compared after treatment with 17-beta-estradiol. The proliferative activity following knockdown of ER beta by siRNA was also examined. Furthermore, the cell inhibition assay was performed for cells treated with gefitinib after knockdown of ER beta. To investigate the relevant pathways for ER beta, the expression of apoptosis-related molecules was evaluated by Western blotting analysis.
Results: All the cell lines showed positive expression of ER beta, the cancer cells from SCID mice, and the original primary tumors showed positive expression of ER beta. All of the cell lines revealed a similar proliferative pattern, regardless of the presence of EGFR mutations. Although the suppression of ER beta slightly increased the proliferative activity, no statistically significant effect on proliferation was observed in any of the cell lines. Moreover, no significant changes in any cell signaling or apoptosis-related molecules were observed following ER beta knockdown.
Conclusion: A direct association between EGFR mutations and ER beta expression in lung cancer cell lines is lacking. Further investigation will be necessary to clarify the role of the ER in the EGFR signaling pathway.