Mechanism of gene expression by androgen receptor in rat and mouse submandibular glands

类固醇受体从非转化状态到转化状态的转化被认为是类固醇激素作用的关键过程。转化的受体激活靶细胞中的特定基因。类固醇激素受体从dna非结合状态到dna结合状态的转化可以通过短暂加热、暴露于盐或ATP和凝胶层析来诱导。一般来说，通过添加硫酸鱼精蛋白选择性地沉淀非转化受体。我们发现，负责非转化受体与鱼精蛋白相交的成分是一个88-kDa蛋白，该88-kDa蛋白的氨基酸组成与hela细胞和酵母的热休克蛋白90几乎相同。类固醇转化受体复合物与核受体位点相互作用，但染色质结构如何改变基因表达尚不清楚。[^3H]雄激素预标记的细胞质雄激素受体与小鼠颌下腺粗核相互作用，受体的激活是这种相互作用的先决条件。雌性小鼠体内给予[^3H]雄激素后，从颌下腺组织纯化的核中发现放射活性，[^3H]雄激素标记的纯化核被微球菌核酸酶进一步消化。雄激素受体是在溶解的、活性的染色质组分中发现的，这些染色质组分含有单核和二核小体。通过体外交换实验，在微球菌核酸酶消化后的可溶性部分中发现了与完整雄性体内染色质结合位点相关的内源性雄激素受体复合物，而在雌性体内则没有发现这种复合物。这些结果表明雄激素受体转移到细胞核并与染色质相关，并且这种关联对微球菌核酸酶优先敏感。

Conversion of steroid receptors from the nontransformed to transformed state, called transformation, is thought to be a key process of the steroid hormone action. Transformed receptors activate the specific genes in target cells. Transformation of steroid hormone receptor from a DNA-unbound state to a DNA-bound state can be induced by brief heating, exposure to salt, or ATP, and gel chromatography. IN general, nontransformed receptor is precipitated selectively by the addition of protamine sulfate. We found that the component responsible for the interection between the nontransformed receptor and protamine is an 88-kDa protein and this 88-kDa protein is almost the same as those of heat-shock protein 90 of hela cells and yeast for the amino acid composition.The steroid-transformed receptor complex interacts with nuclear acceptor sites, but it remains unclear how the structure of chromatin is changed for gene expression. Cytosol androgen receptor prelabeled with [^3H]androgen interacted with the crude nuclei in mouse submandibular gland and activation of the receptor was prerequisite for this interaction. After in vivo administration of [^3H]androgen to female mice, redioactivities were found in the nuclei purified from submandibular gland tissues and the [^3H]androgen-labeled purified nuclei were further digested with micrococcal nuclease. the androgen receptor was found in solubilized, active chromatin fractions which contained mono- and dinucleosomes. By an in vitro exchange assay, endogenous androgen-receptor complexes associated with chromatin binding sites in intact males were found in the solubilized fraction after micrococcal nuclease digestion, whereas such complexes were not found in females. These results suggest that the androgen receptors translocated to the nuclei and became associated with chromatin and that this association preferentially sensitive to micrococcal nuclease.