THE RECEPTOR, METABOLISM AND EFFECTS OF ANDROGEN IN OSTEOBLASTIC MC3T3-E1 CELLS

We investigated the androgen receptor (AR), metabolism and effects of androgens in osteoblastic MC3T3-E1 cells. AR was proved as a transcrip t of a IO-kb mRNA and as a 110-kDa protein. An immunocytochemical stud y showed that AR was located mainly in the nuclei. Specific binding of [H-3]DHT was observed in both the nuclear and cytosol fractions. MC3T 3-E1 cells possessed approximately 1190 binding sites per cell and mos t of the sites (1150 sites) situated in the nucleus. The apparent K-d value in the nuclear fraction was 1.35 nM for [H-3]DHT binding, and it was similar to that for [H-3]testosterone. In the competition analysi s, there was not much difference in the displacement of the [H-3] DHT binding from AR between the addition of radioinert DHT and testosteron e. In studies of 5 alpha-reductase activity and aromatase activity of the cells, both activities were lower than the respective values in cl assical androgen target tissues. Androgens stimulated the incorporatio n of [H-3]thymidine into the cell, and DHT and testosterone had a simi lar potency on the cell proliferation. Thus, these results suggest tes tosterone itself acts mainly on the osteoblasts without conversion to DHT.