Toll-like receptor 9 (TLR9) is a cellular
DNA-receptor, which is widely expressed in
cancer. Synthetic TLR9-ligands induce
cancer cell invasion in vitro, but the role of TLR9 in
cancer pathophysiology remains unclear. Increased TLR9 expression has been, however, detected in
estrogen receptor negative (ER-) breast
cancers. In this study, we investigated the effects of ERα expression and
sex steroid hormones on TLR9 expression in human ER+ (MCF-7, T47-D) and ER- (MDA-MB-231)
breast cancer cell lines in vitro. We also studied TLR9
mRNA expression in archival
breast cancer specimens (n = 12) with qRT-PCR, using primer sets that detect only the TLR9A
isoform or the
isoforms A and B (TLR9A/B). The TLR9
mRNA expression was detected in 10/12 specimens with both primer sets, and in 1/12 with only the TLR9A or the TLR9A/B primer sets. The basal TLR9
mRNA expression levels were significantly lower in the ER+ cell lines as compared with the ER- MDA-MB-231 cells. The transfection of ERα
cDNA into MDA-MB-231 cells also resulted in down-regulation of TLR9 expression. While sex
steroids had no effect on TLR9 expression in MCF-7 cells,
testosterone (10(-8) M) induced TLR9 expression in MDA-MB-231 and T47-D cells. Although
bicalutamide blocked this
testosterone effect in MDA-MB-231 cells, in T47-D cells
bicalutamide increased TLR9 expression and only partially blocked the
testosterone effects.
Estradiol (10(-8) M) induced TLR9 expression in T47-D cells. The invasive effects of synthetic TLR9-ligands were augmented by
testosterone in vitro. This effect was lost in TLR9
siRNA MDA-MB-231 cells and also decreased by over-expression of ERα, which also inhibited NF-κB activation by TLR9-ligands. In conclusion, expression of TLR9
isoforms A and B can be detected in clinical
breast cancer specimens. The ERα and
sex steroid hormones regulate TLR9 expression and invasive effects in the
breast cancer cells. Also, the commonly used hormonal
cancer therapy bicalutamide affects TLR9 expression.