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The hormone 1alpha,25(OH)(2)-vitamin D(3) (125D) binds to its nuclear receptor (VDR) to stimulate gene transcription activity. Inversion of configuration at C-20 of the side chain to generate 20-epi-1alpha,25(OH)(2)D(3) (20E-125D) increases transcription 200-5000-fold over 125D with its 20-normal (20N) side chain. This enhancement has been attributed to the VDR ligand-binding domain (LBD) having different contact sites for 20N and 20E side chains that generate different VDR conformations. We synthesized 1alpha, 25-dihydroxy-21-(3-hydroxy-3-methylbutyl)vitamin D(3) (Gemini) with two six-carbon side chains (both 20N and 20E orientations). Energy minimization calculations indicate the Gemini side chain possesses significantly more energy minima than either 125D or 20E-125D (2346, 207, and 127 minima, respectively). We compared activities of 125D, 20E-125D, and Gemini, respectively, in several assays: binding to wild-type (100%, 147%, and 38%) and C-terminal-truncated mutant VDR; transcriptional activity (of the transfected osteopontin promoter in ROS 17/2.8 cells: ED(50) 10, 0.005, and 1.0 nM); mediation of conformational changes in VDR assessed by protease clipping (major trypsin-resistant fragment of 34, 34, and 28 kDa). For inhibition of cellular clonal growth of human leukemia (HL-60) and breast cancer (MCF7) cell lines, the ED(50)(125D)/ED(50)(Gem) was respectively 380 and 316. We conclude that while Gemini readily binds to the VDR and generates unique conformational changes, none of them is able to permit a superior gene transcription activity despite the presence of a 20E side chain.

We examined the mechanism of accelerated proteolysis in denervated rat soleus muscles. The soleus was denervated by severing either the tibial nerve (proximal, short stump) or sciatic nerve (distal, long stump) at 24, 48, 72, or 96 h before excision. Twenty-four hours after denervation, the extent of atrophy was similar for proximal and distal denervation, although lysosomal latency declined in both groups. After 48 and 72 h, denervation resulted in a decline in protein content, an increase in in vitro protein degradation, and a decline in lysosomal latency, all of which were greater in proximally denervated than in contralateral distally denervated muscles. These differences between acute responses of proximally and distally denervated muscles suggest the retention of some factor in the longer nerve stump that attenuates atrophy. After 96 h, total protein loss, protein degradation, and lysosomal latency were similar for proximal and distal denervation, suggesting the loss of axoplasmic flow from the long nerve stump.