Properties and compartmentalization of the testicular receptor for 1,25-dihydroxyvitamin D3.
Adult rat testis contains a specific, high-affinity, low-capacity binding protein for 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) with properties similar to 1,25-(OH)2D3 receptors in other tissues. The receptor sediments at 3.5 +/- 0.2 S20,w in high-salt sucrose density gradients, but aggregates in low-salt gradients. Binding of 1,25-(OH)2D3 was abolished by trypsin, but not by DNase or RNase. Binding was also heavily reduced by the sulfhydryl alkylating agent, N-ethylmaleimide, and by the mercurial reagent, mersalyl, showing that free, reduced SH-groups are necessary for hormone-binding activity. The receptor shows high affinity for 1,25-(OH)2D3 (Kd = 3 X 10(-11) M), but low capacity (Nmax = 8 fmol/mg protein) and is specific for 1,25-(OH)2D3 (Affinity: 1,25-(OH)2D3 greater than 1,24(R),25-(OH)3D3 greater than 25-OH-D3 greater than 1 alpha-OH-D3 greater than 24(R),25-(OH)2D3 much greater than 17 beta-estradiol, testosterone, dexamethasone, R5020, progesterone). With 0.6 nM [3H]1,25-(OH)2D3 and at 0 degrees C, maximum specific binding was achieved after 4 h, and the occupied receptors were stable for more than 24 h. The dissociation of hormone-receptor complexes was temperature-dependent and very slow at low temperature (t1/2 (0 degrees C) much greater than 48 h). At 0 degrees C, the second order association rate constant and the pseudo-first order dissociation rate constant were 2.7 X 10(7) M-1 min-1 and 2 X 10(-5) min-1, respectively. Receptors for 1,25-(OH)2D3 are present in similar amounts in isolated seminiferous tubules and interstitial tissue of adult rats. No specific binding of [3H]1,25-(OH)2D3 could be detected in cultured immature Sertoli cells, cultured immature peritubular (myoid) cells or crude germ cells.
Levy
F O
FO
Eikvar
L
L
Jutte
N H
NH
Frøysa
A
A
Tvermyr
S M
SM
Hansson
V
V
D000818:Animals; D002117:Calcitriol / Q000378:metabolism; D002451:Cell Compartmentation; D002499:Centrifugation, Density Gradient; D003851:Deoxyribonucleases / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D008297:Male; D008634:Mersalyl / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism; D013737:Testis / Q000166:cytology* / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D008634:Mersalyl; D003851:Deoxyribonucleases; D012260:Ribonucleases; D014357:Trypsin; D002117:Calcitriol; D005033:Ethylmaleimide