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 st eroid-binding protein (SBP-R) in human breast cancer are reported. SBP -R was detected in MCF-7 cells (estrogen receptor positive, ER+), whil e MDA-MB 231 cells (ER-) did not bind SBP. MCF-7 cells treated with SB P and E(2) showed a marked increase of intracellular cAMP, and a signi ficant reduction of both E(2) induced cell proliferation and E(2)-medi ated increase of progesterone receptor (PGR). The inhibition of E(2) e ffects in MCF-7 cells was shown to be highly specific for SBP and medi ated 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 th an negative samples. Our data, thus, suggest that SBP-R and ER could b e functionally related and also that SBP could modulate estrogen actio n at target cell site.