Intranuclear Concentration of Lysosomal Hydrolases in Steroid Target Cells

The present investigation was designed to determine whether the rapid intracellular redistribution of lysosomes to a perinuclear position in reproductive target cells after administration of specific gonadal hormones in vivo was accompanied by evidence of penetration of the nucleoplasm by lysosomal marker enzymes. Nuclei were prepared by conventional isolation and purification procedures from preputial glands or uteri that were excised from gonadectomized rats within 2–15 min after intravenous injection of physiological doses of estradiol‐17β, testosterone or saline control solutions. Control and experimental preparations were essentially “pure”, as judged by routine phase‐contrast microscopic criteria in general use. However, nuclei from target cells of animals given hormone contained substantial activities of representative lysosomal hydrolases, including acid phosphatase, β‐glucuronidase and acid ribonuclease II. In contrast, the samples originating from the target tissue of saline‐treated controls or from non‐target tissues contained minimal concentrations of these enzyme activities. After further purification of the nuclei by removal of the outer nuclear membrane through brief exposure to very low concentrations of Triton X‐100 in the cold, the resultant ‘ultrapurified’ nuclei retained significant concentrations of structurally latent lysosomal marker enzymes after hormonal pretreatment without evidence of appreciable contamination by enzymes of mitochondrial origin. Similar results were obtained with nuclei isolated by non‐aqueous procedures. These combined observations appear to exclude adsorption artifacts. The total activities of lysosomal enzymes in the unfractionated homogenates and the Mg2+‐dependent ribonuclease activity indigenous to the nuclear compartment were unaffected by prior hormone treatment. These results are consistent with the hypothesis that invasion of the nucleoplasm of specific target cells by lysosomal products may serve as a mechanism for triggering genic derepression in steroid hormone‐induced growth.