Distinct mRNA, protein expression patterns and distribution of oestrogen receptors α and β in human primary breast cancer: Correlation with proliferation marker Ki-67 and clinicopathological factors

To elucidate the molecular profile of oestrogen receptors α and β (ERα, ERβ) we studied ERα and ERβ expression at the mRNA and protein levels using real-time polymerase chain reaction (RT-PCR), Western blot analysis and immunohistochemical (IHC) methods in 41 primary breast cancers and surrounding tissues. ERα mRNA and ERβ mRNA were detected in all of the breast cancer and normal matched tissues analysed. ERα mRNA levels showed greater diversity than ERβ mRNA levels and the range of amount of ERβ transcripts was far smaller than that of ERα. At the protein level, the percentage of ERα- or ERβ-positive cases changed. Seventy percent of the tumours studied produced full-length 65kDa ERα protein in Western blot analysis and 67% of assessed cases were positive in IHC. Full-length 57kDa ERβ protein was detected by Western blotting in 97% of analysed breast cancers, while 67% were ERβ-positive using IHC. ERα was localised in the nucleus, while cytoplasmic and perinuclear localisation of ERβ was observed in normal as well as in breast cancer cells. The amount of ERα (but not ERβ) increased with age. The expression of ERα correlated positively with progesterone receptor and negatively with proliferation marker Ki-67. These results confirm the previous observations that the lack of ERα protein expression is not due to lack of ERα gene expression or methylation of ERα promoter, but due to post-transcriptional or post-translational mechanisms. Our investigation also suggests that ERα is more dysregulated in breast cancer, and thereby ERβ is more tightly regulated in the tumour.