STRUCTURE-FUNCTION STUDIES OF 1,25-DIHYDROXYVITAMIN-D3 AND THE VITAMIN-D ENDOCRINE SYSTEM - 1,25-DIHYDROXY-PENTADEUTERIO-PREVITAMIN-D3 (AS A 6-S-CIS ANALOG) STIMULATES NONGENOMIC BUT NOT GENOMIC BIOLOGICAL RESPONSES

The hormone 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) generates biologic al responses via both genomic and nongenomic mechanisms. This article addresses activity differences between the 6-s-trans (extended) and th e 6-s-cis (steroid-like) conformation of 1,25-(OH)2D3 to initiate thes e responses. Because of facile interconversion of the 6-s-trans and 6- s-cis conformers of 1,25-(OH)2D3, kinetically competent amounts of bot h conformers exist to interact with any potential receptors for 1,25-( OH)2D3. We have chemically synthesized 1,25-(OH)2-9,14,19,19,19-pentad euterio-pre-D3 (1,25-(OH)2-d5-pre-D3), an analog of the 6-s-cis confor mation of 1,25-(OH)2D3. We found that 1,25-(OH)2-d5-pre-D3 and 1,25-(O H)2D3 were equivalently active in two nongenomic systems (transcaltach ia as measured in the perfused chick intestine and Ca-45(2+ uptake thr ough voltage-gated Ca2+ channels in ROS 17/2.8 cells). 1,25-(OH)2-d5-p re-D3 was significantly less active both in binding in vitro to the pl asma vitamin D-binding protein (7%) and to the chick (10%) and pig (4% ) intestinal nuclear 1,25-(OH)2D3 receptors generating genomic biologi cal responses in vivo (induction of plasma levels of osteocalcin, < 5% ) or in cultured cells (inhibition of HL-60 cell differentiation, < 5% ; inhibition of MG-63 proliferation, < 2%; and induction of osteocalci n, < 2%). These results suggest that the genomic and nongenomic respon ses are mediated by separate receptors. Further, the 6-s-cis form (ste roid-like conformation) of the natural hormone, 1,25-(OH)2D3, may be s electively responsible for its nongenomic function(s).