Nuclear interactions of retinoic acid-binding protein in chemically induced mammary adenocarcinoma

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Abstract
Cellular retinoic acid-binding protein (CRABP) was detected in the nuclear fraction of N-methyl-N-nitrosourea-induced [rat] mammary cancers after the incubation of cytosol containing [3H]retinoic acid (RA)-bound CRABP with isolated nuclei. CRABP extracted from the nuclei in buffer containing 0.4 .MU.-KCl sedimented as a 2 S component when subjected to sucorse-density-gradient analysis. [3H]RA-CRABP was found to be a prerequisite for the detection of nuclear binding, since the incubation of isolated nuclei or 0.4 M-KCl extract of the nuclei with [3H]RA did not result in any significant binding. Incubation of [3H]RA-CRABP at 25.degree. or 30.degree. C before incubation with the nuclei neither altered the sedimentation coefficient nor enhanced the nuclear binding compared with 0.degree. C incubation. The tumor nuclei contained a saturable number of binding sites with a Kd of 1.6 .times. 10-9 M. The action of retinoic acid in the target organ may be mediated by its interaction with the nuclei.