Sex steroid-binding protein and its membrane receptor in estrogen-dependent breast cancer: Biological and pathophysiological impact

Data obtained in our laboratory about the membrane receptor for sex steroid-binding protein (SBP-R) in human breast cancer are reported. SBP-R was detected in MCF-7 cells (estrogen receptor positive, ER+), while MDA-MB 231 cells (ER-) did not bind SBP. MCF-7 cells treated with SBP and E(2) showed a marked increase of intracellular cAMP, and a significant reduction of both E(2) induced cell proliferation and E(2)-mediated increase of progesterone receptor (PGR). The inhibition of E(2) effects in MCF-7 cells was shown to be highly specific for SBP and mediated by protein kinase A, the target of cAMP. Membrane SBP-R was also evaluated in primary breast cancers. SBP-R was detectable only on ER+/PR+ samples and SBP-R+ samples presented a lower proliferation rate than negative samples. Our data, thus, suggest that SBP-R and ER could be functionally related and also that SBP could modulate estrogen action at target cell site.