R.C. Hall

Retinoid binding to nuclei and microsomes of rat testes interstitial cells: I — Mediation of retinoid binding by cellular retinoid-binding proteins

Abstract Purified cellular retinol-binding protein (cRBP) and cellular retinoic acid-binding protein (cRABP) mediated the transfer of their respective 3 H-ligands to nuclei and microsomes of retinol-sufficient rat testes interstitial cells in a saturable and reversible manner. Crossover experiments utilizing [ 3 H]retinol·cRBP/retinoic acid·cRABP and [ 3 H]retinoic acid·cRABP/retinol·cRBP did not result in dissociation of the labeled ligand from either the nuclear or microsomal fraction. Further, binding of free [ 3 H]retinol or [ 3 H]retinoic acid was not saturable nor was binding detectably reduced in the presence of unlabeled retinoids. When nuclei and microsomes were prepared from retinol-deficient tissues, cRBP-mediated binding of [ 3 H]retinol was also saturable and reversible. However, total binding was significantly increased in both cell fractions. Similarly, cRABP-mediated binding of [ 3 H]retinoic acid was significantly higher in retinol-deficient nuclei and microsomes. Extraction of cRBP- or cRABP-mediated nuclear-bound 3 H-retinoids with NaCl indicated that 50% of the retinol and retinoic acid were removed with 0.14 M NaCl. Retinol binding in nuclear subfractions including the 0.14 M NaCl fraction was pronasesensitive, RNase and DNase insensitive; retinoic acid was pronase- and RNase-sensitive, and DNase-insensitive. Nuclear binding of free retinoids was

Rat testes interstitial cell nuclei exhibit three distinct receptors for retinoic acid

Purified nuclei from rat testes interstitial cells were incubated with an equimolar complex of [3H]retinoic acid and purified cellular retinoic acid-binding protein (cRABP) and with ATP. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and radiofluorographic analysis of the nuclear fractions indicated the presence of 3 highly labeled receptors for retinoic acid which were distinct from cRABP. These data demonstrate that retinoic acid binds to 3 novel nuclear acceptors of which cRABP does not appear to be a part.