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The expression of oestrogen receptor (ER)- (cid:1) and its variants, but not ER (cid:2) , in adult human mammary ﬁbroblasts

Whilst oestrogen receptor (ER)- (cid:1) and ER (cid:2) have been shown to be important in the development of the mammary gland, the cell-speciﬁc expression pattern of these two receptors within the human breast is not clear. Although it is well established that in the developing rodent mammary gland stromal ER (cid:1) mediates the secretion of growth factors which stimulate the proliferation of the ductal epithelium, the expression of ER (cid:1) in human adult breast stromal ﬁbroblasts is controversial, and the expression of ER (cid:2) has not been properly deﬁned. In the present study, we have evaluated the expression of ER (cid:1) and ER (cid:2) by immunohistochemistry in normal tissue samples, and in puriﬁed human breast ﬁbroblasts by Western blotting, RT-PCR analysis and ligand-binding sucrose gradient assay. Our data clearly demonstrated that ER (cid:2) variants, including ER (cid:2) 1, ER (cid:2) 2, ER (cid:2) 5, ER (cid:2)(cid:3) and ER (cid:2) ins, but not ER (cid:1) , are expressed in human adult mammary ﬁbroblasts. These results are supported by the ﬁndings that an ER (cid:2) -selective ligand, BAG, but not the ER (cid:1) high-affinity ligand oestradiol, can induce ﬁbroblast growth factor-7 release and activate transcription from an oestrogen-responsive element promoter in these adult human mammary ﬁbroblasts. Together, these observations revealed that, in the adult breast and in breast cancer, the proliferative signals derived from the stroma of adult mammary glands in response to oestrogen are not mediated by ER (cid:1) and provide new insights into the nature of stromal–epithelial interactions in the adult mammary gland. In addition, the expression of these ER (cid:2) variants in cells where there is no ER (cid:1) suggested that these ER (cid:2) splice forms may have functions other than that of modulating ER (cid:1) activity.