Sex steroid binding protein receptor (SBP-R) is related to a reduced proliferation rate in human breast cancer

In the last years, an increasing amount of studies described a membrane receptor for the Sex Steroid Binding Protein (SEP) on several androgen-estrogen dependent tissues. One of the suggested biological roles of the interaction between SEP and its receptor seems to be a negative control of the E(2) induced proliferation of human breast cancer cells through the cAMP pathway. In the present work, SEP membrane receptor was evaluated on human breast cancer specimens with a radio-binding assay. Each tissue sample was also evaluated for ER and PGR status. Cytosol Thymidine Kinase levels were measured in tissue samples in order to evaluate cell proliferation rate. SBP binding to membranes of ER+/PGR+ samples was time and temperature dependent, specific and at high affinity. In addition, SBP recognized on breast cancer membranes two sites at different affinity, as previously described for other human tissues and cultured cells. Membrane SBP-R was detected in a significantly higher number of samples positive for both ER and PGR than in negative samples. SBP-R positive samples showed a significantly lower proliferation rate than SBP-R negative samples as demonstrated by TK activity. The present study contains evidences for the existence of a specific membrane receptor for SEP in breast cancer sample membranes and the presence of SBP-R seems to be strictly related to a lower proliferation rate of the sample.