Direct modulation by androgens of the response of human bone cells (SaOS-2) to human parathyroid hormone (PTH) and PTH-related protein.

We have reported previously that 17 beta-estradiol (E2) inhibits selectively the cAMP response to human (h) PTH and PTH-related protein (hPTHrP), but not to vasoactive intestinal peptide, in human osteoblast-like cells (SaOS-2). We have now extended these studies to investigate the actions of androgens on hPTH-stimulated accumulation of cAMP, and on the roles of new protein synthesis and pertussis toxin (PTox) substrates in the actions of steroid hormones on SaOS-2 cells. Pretreatment with testosterone (T) or 5 alpha-dihydrotestosterone (5 alpha-DHT) for 4-12 h at concentrations of 10(-12) to 10(-8) M inhibited significantly the cAMP response to hPTH by up to 50-70% of control. Like E2, the actions of T and 5 alpha-DHT were selective for hPTH or hPTHrP; there was no inhibition of the stimulatory action of vasoactive intestinal peptide. Two related steroids, 5 beta-DHT and 17 alpha-epitestosterone, did not inhibit the action of hPTH. Pretreatment of cells with cycloheximide, under conditions which inhibited protein synthesis by greater than 90%, reduced the cAMP response to hPTH but did not block the further inhibitory actions of E2, T, or 5 alpha-DHT. Pretreamtent of cells with PTox (100 ng/ml) for 24 h, enhanced the accumulation of cAMP stimulated by hPTH consistent with an action of PTox on Gi; however, the inhibitory actions of E2, T, and 5 alpha-DHT on PTH-stimulated cAMP accumulation were not attenuated by PTox. We conclude that androgens, as well as estrogens, act directly on human bone cells to modulate selectively an early effect of hPTH. The inhibitory actions of these steroid hormones do not appear to depend on new protein synthesis and may not involve a functionally active PTox substrate, presumably Gi.