Fortunati N, Raineri M, Cignetti A, Hammond G L, Frairia R
Laboratorio di Endocrinologia, Azienda Ospedaliera S.Giovanni B.ta, Torino, Italy.
Steroids. 1998 May-Jun;63(5-6):282-4. doi: 10.1016/s0039-128x(98)00021-x.
The interaction between plasma sex hormone-binding globulin (SHBG) and its receptor (SHBG-R) inhibits estradiol-induced proliferation of MCF-7 cells (human estrogen-dependent breast cancer) through cAMP and PKA. Thus, SHBG can modulate estradiol action in breast cancer, but the implications of this require a more detailed knowledge of the SHBG-R. To this end, we have transfected MCF-7 cells with an expression vector carrying the human SHBG cDNA (S-MCF-7) and studied the effects of this on both SHBG-R binding and cell proliferation. Control cells were parental MCF-7 (P-MCF-7) and MCF-7 cells transfected with the beta-galactosidase gene (B-MCF-7). Transfections were mediated by lipofectin followed by selection of transfected cells with G418. The amounts of SHBG in culture medium were evaluated by IRMA assay, with only S-MCF-7 cells shown to secrete SHBG; SHBG-R levels were evaluated by tracer binding technique. In P-MCF-7 and B-MCF-7 cells, SHBG-R was detectable as a two-binding site receptor, but no binding of SHBG was observed in S-MCF-7 cells. Proliferation of cells treated with estradiol was evaluated by [3H]thymidine incorporation in the three cell lines and in cells pretreated with SHBG (1 nM) purified from human serum or with conditioned medium from S-MCF-7 cells (medium S). In all three lines, cell proliferation increased after estradiol treatment. Preincubation with purified SHBG was effective in reducing estrogen-induced cell proliferation to basal levels in P-MCF-7 and B-MCF-7 but not in S-MCF-7 cells. The estradiol effect was also inhibited in P-MCF-7 cells treated with medium S. In conclusion, 1) SHBG inhibits estradiol-induced proliferation in cells containing a functional SHBG-R, whereas it has no detectable effect in cells in which the SHBG-R is either absent or not available to bind SHBG; and 2) S-MCF-7 cells are insensitive to SHBG (locally produced or exogenous) because their SHBG-R is occupied by SHBG.
血浆性激素结合球蛋白（SHBG）与其受体（SHBG-R）之间的相互作用通过环磷酸腺苷（cAMP）和蛋白激酶A（PKA）抑制雌二醇诱导的MCF-7细胞（人雌激素依赖性乳腺癌细胞）增殖。因此，SHBG可调节乳腺癌中雌二醇的作用，但这一作用的具体影响需要对SHBG-R有更详细的了解。为此，我们用携带人SHBG cDNA的表达载体转染MCF-7细胞（S-MCF-7），并研究其对SHBG-R结合及细胞增殖的影响。对照细胞为亲本MCF-7（P-MCF-7）和用β-半乳糖苷酶基因转染的MCF-7细胞（B-MCF-7）。转染由脂质体介导，随后用G418筛选转染细胞。通过免疫放射分析（IRMA）测定培养基中SHBG的含量，结果显示只有S-MCF-7细胞分泌SHBG；通过示踪剂结合技术评估SHBG-R水平。在P-MCF-7和B-MCF-7细胞中，SHBG-R可检测为双结合位点受体，但在S-MCF-7细胞中未观察到SHBG的结合。通过[3H]胸腺嘧啶核苷掺入法评估三种细胞系以及用从人血清中纯化的SHBG（1 nM）或S-MCF-7细胞的条件培养基（培养基S）预处理的细胞中雌二醇处理后的细胞增殖情况。在所有三种细胞系中，雌二醇处理后细胞增殖均增加。用纯化的SHBG预孵育可有效将P-MCF-7和B-MCF-7细胞中雌激素诱导的细胞增殖降低至基础水平，但对S-MCF-7细胞无效。用培养基S处理的P-MCF-7细胞中雌二醇的作用也受到抑制。总之，1）SHBG抑制含有功能性SHBG-R的细胞中雌二醇诱导的增殖，而在SHBG-R缺失或无法结合SHBG的细胞中未观察到可检测的作用；2）S-MCF-7细胞对SHBG（内源性或外源性）不敏感，因为其SHBG-R被SHBG占据。
