Metabolism and protein binding of sex steroids in target organs: an approach to the mechanism of hormone action

The common 90-kd protein component of non-transformed '8S' steroid receptors is a heat-shock protein

Non-transformed steroid receptors have an approximately 8S sedimentation coefficient that corresponds to an oligomeric structure of 250-300 kd which includes a non-hormone binding 90-kd protein. A monoclonal antibody BF4 raised against the purified, molybdate-stabilized, 8S progesterone receptor (8S-PR) from chick oviduct, recognizes 8S forms of all steroid hormone receptors. BF4 was found specific for a 90-kd protein present in great abundance in all chicken tissues, including that present in 8S-forms of steroid receptors. Here, using immunological and biochemical techniques, we demonstrate that this ubiquitous BF4-positive 90-kd protein is in fact the chicken 90 kd heat-shock protein (hsp 90): it increased in heat-shocked chick embryo fibroblasts, and displayed identical migration in two-dimensional gel electrophoresis and the same V8 peptide map as the already described hsp 90. We discuss the possibility that the interaction between hsp 90 and steroid hormone-binding subunits may play a role in keeping the receptor in an inactive form.

Ultrastructural modifications of renal cells in the three-spined stickleback (Gasterosteus aculeatus L.) after castration

The mechanisms of cellular autophagy have been studied in the renal epithelium of male sticklebacks (Gasterosteus aculeatus L.) following castration. Two main types of alteration are described at the level of the proximal tubule cells. At first, the formation of endoplasmic reticulum whorls is observed, followed immediately by the secretion of lacunar progranules and by nucleolar modifications. These alterations lead to a progressive decrease of the glandular activity of the cells. The other main effect of castration is a general involution of the secretory granules still present in the cells. The involutive processes which lead to the complete destruction of the secretory material and, sometimes, of entire proximal cells, are described. In the collecting tubules, a marked and rapid decrease in glandular activity occurs, followed by disappearance of the mucous secretions. Small dense granules, supposedly lysosomes, are present. The processes described also appear to be characteristic of the normal involution of the renal cells occurring at the end of the breeding period. The findings strongly suggest that the male sex hormone may exert a double control on the renal cells in the stickleback, at both the cytoplasmic and nucleolar levels.

Intranuclear localization and receptor proteins for 1,25-dihydroxycholecalciferol in chick intestine

1. The intranuclear distribution of cholecalciferol and its metabolites was studied in the intestine of rachitic chicks. 2. At high doses of cholecalciferol the nuclei contain the vitamin and its 25-hydroxy metabolite, but over 80% of this is localized on the nuclear membranes. The hormone, 1,25-dihydroxycholecalciferol, is found within the cell nuclei irrespective of the intake of cholecalciferol, but significant amounts could not be found with chromatin isolated free of nuclear membranes. 3. 1,25-Dihydroxycholecalciferol is associated in the nucleus with an acidic protein. Since one of the actions of 1,25-dihydroxycholecalciferol is to control the synthesis of mRNA for calcium-binding protein it was to be expected that the hormone would be bound to chromatin, as with the other steroid hormones. It is suggested that the hormone-receptor complex exists as part of an equilibrium mixture of the complex bound to the DNA and in a free form. 4. A protein extract of nuclei was obtained, which when incubated at 4 degrees C for 1h took up the 1,25-dihydroxycholecalciferol. The nature of this binding was studied. 5. There appear to be two nuclear proteins able to bind the hormone one of which is the intestinal nuclear receptor. The binding sites on this protein are saturable with the hormone, have an association constant of 2x10(9)m(-1) and show a high chemical specificity for the 1,25-dihydroxycholecalciferol. The number of nuclear binding sites for the hormone provided by this receptor is similar to the maximum intestinal hormone concentration so far observed. Its sedimentation coefficient is 3.5S, and is very close to that observed for the nuclear protein to which is attached the 1,25-dihydroxycholecalciferol formed in vivo from vitamin D. 6. The cytoplasmic protein has an association constant of 1x10(9)m(-1)and a sedimentation coefficient of 3.0S, but its relation with the nuclear receptor is not yet clear.

The transporting proteins of cholecalciferol and 25-hydroxycholecalciferol in serum of chicks and other species. Partial purification and characterization of the chick proteins

Chick serum contains two cholecalciferol-binding proteins, one of which binds mainly cholecalciferol (cholecalciferol-binding protein) and the other binds 25-hydroxycholecalciferol (25-hydroxycholecalciferol-binding protein). By means of Cohn fractionation, (NH(4))(2)SO(4) precipitation, gel filtration on Sephadex G-200, ion-exchange chromatography on DEAE-Sephadex and an additional gel-filtration step on Sephadex G-100, these two binding proteins were purified. Both proteins possess beta-globulin mobility on analytical polyacrylamide-disc-gel electrophoresis, a sedimentation coefficient of 3.5S and approximate molecular weights of 60000 for the cholecalciferol-binding protein and 54000 for the 25-hydroxycholecalciferol-binding protein. Sera obtained from rat, pig, human and monkey were shown to contain a single binding protein that is responsible for the transport of both cholecalciferol and 25-hydroxycholecalciferol. In the toad the lipoproteins are used for the transport of these two steroids.