Demonstration of estrogen and vitamin d receptors in bone marrow-derived stromal cells: Up-regulation ofthe estrogen receptor by l, 25-dihydroxyvitamin-d₃

We have shown earlier that 17β-estradiol inhibits cytokine-induced interleukin-6 (IL-6) production by bone marrow-derived stromal cells as well as osteoblasts, two types of cells with a critical influence on orteoclast development, and that ovariectomy causes an IL-6-mediated up-regulation of osteoclastogenesis in mice. Prompted by this, we have searched here for the presence of estrogen receptors (ERs) in two murine bone marrow-derived stromal cell lines, +/+ LDA11 and MBA 13.2, and the osteoblast-like cell line MC3T3-E1. All three cell lines axhibited high affinity saturable binding for [¹²⁵I] 17β-estradiol with a dissociation constant of approximately 10-¹⁰ M and concentration of binding sites of 260 ± 30, 170 ± 10, and 90 ± 10 sites per cell, respectively. In addition, we amplified complementary DNA from the stromal cell lines by polymerase chain reaction using oligonucleotide primers flanking the DNA binding domain of the murine uterine ER. The amplified product showed an identical nucleotide sequence to the DNA binding domain of the murine uterine receptor. Consistent with the functionality of the ER in stromal cells, and specifically its role in the regulation of IL-6 by 17β-estradiol, we found that the pure estrogen antagonist ICI 164,384 completely prevented the effect of 17β-estradiol on IL-6. All three cell lines also expressed receptors for 1,25-dihydroxyvitamin-D₃ [1,25(OH)₂D₃] (dissociation constant, ∼10^-10 M), with a concentration of binding sites of 490 ± 20, 920 ± 20, and 1110 ± 70 sites per cell, respectively. 1,25(OH)₂D₃ treatment of the stromal cells caused a 2-fold increase in the concentration of ERs and a decrease in cell proliferation. These data establish that bone marrow-derived stromal cells express functional estrogen as well as vitamin D receptors, which serve to mediate actions of their respective ligands on the biosynthetic activity of these cells and presumably the effects of these two steroid hormones on osteoclastogenesis.