17 beta-estradiol and parathyroid hormone potentiate each other's stimulatory effects on alkaline phosphatase activity in SaOS-2 cells in a differentiation-dependent manner.

We studied the effects of 17 beta-estradiol (E2) and PTH on alkaline phosphatase activity in SaOS-2 cells that had been passaged and grown continually in the presence (SaOS + Dex) or absence (SaOS - Dex) of 10(-8) M dexamethasone (Dex). We showed that the more differentiated SaOS + Dex cells had higher alkaline phosphatase activity and PTH-responsive adenylate cyclase than the less differentiated SaOS - Dex cells. In SaOS - Dex cells, E2 or PTH (1 x 10(-11)-1 x 10(-6) M) had no effect on alkaline phosphatase activity. On the other hand, in SaOS + Dex cells, PTH and E2 each had small but very significant stimulatory effects on alkaline phosphatase activity. The combined effects of PTH and E2 resulted in potentiation which was dose dependent for PTH and E2. 17 alpha-estradiol and tamoxifen (1 x 10(-11)-1 x 10(-6) M) had no effect on PTH-stimulated alkaline phosphatase activity in SaOS + Dex cells, but the latter inhibited the E2 effect, clearly demonstrating its specificity. In conclusion, we have shown that in more differentiated osteoblastic cells, E2 and PTH have interactive effects on alkaline phosphatase activity.