Estrogen binding and estrogenic responses in normal human osteoblast‐like cells

A finite human cell line was established from trabecular bone explants obtained from a 48‐year‐old woman. These cells, designated BG688, were characterized as osteoblast‐like in phenotype using the following independent criteria: (1) the presence of histochemically detectable alkaline phosphatase (AP) activity; (2) response to the calciotropic hormone 1,25‐(OH)₂D₃ as assessed by increased AP activity; (3) synthesis and secretion of the osteoblast‐specific marker bone gla protein; and (4) expression of α₁(I)‐procollagen and α₁(III)‐procollagen mRNAs in a pattern similar to that of other osteoblast‐like cell lines. In addition to these classic osteoblast markers, BG688 cells also possess approximately 2400 high‐affinity (K_d = 0.45 nM) 17β‐estradiol (E₂) binding sites per cell. The binding of E₂ to these sites is specific, and of the steroid hormone agonists tested, E₂ and diethylstilbestrol elicited the greatest amount of competition with radiolabeled E₂. BG688 cells were also shown to respond to a physiologic concentration (10 nM) of E₂. In vitro translation products of poly(A)⁺ RNA obtained from control and hormone‐treated cells revealed a pleiotropic influence of E₂ on the relative abundance of several mRNAs as assessed by two‐dimensional gel electrophoretic analysis of their corresponding peptides. E₂ also elicits a twofold increase in the steady‐state concentration of α₁(I)‐procollagen mRNA as demonstrated by northern blot hybridization. Thus, we here extend our previous data obtained in osteoblast‐like osteosarcoma cells to indicate that a normal osteoblastic cell line is a target for the action of estrogen. The E₂ responsiveness of these cells, coupled with their osteoblast‐like phenotype, renders BG688 cells an attractive system in which to investigate the role of estrogens in the regulation of osteoblast function.