Sheppard K E, Hourigan S, Li K X, Krozowski Z S
Baker Medical Research Institute, Monash University Medical School, Prahran, Victoria, Australia 3181.
Am J Physiol Gastrointest Liver Physiol. 2000 Sep;279(3):G536-42. doi: 10.1152/ajpgi.2000.279.3.G536.
When small intestinal epithelial cells are incubated with [(3)H]corticosterone, nuclear binding is displaced neither by aldosterone nor RU-28362, suggesting that [(3)H]corticosterone is binding to a site distinct from mineralocorticoid receptor and glucocorticoid receptor. Saturation and Scatchard analysis of nuclear [(3)H]corticosterone binding demonstrate a single saturable binding site with a relatively low affinity (49 nM) and high capacity (5 fmol/microg DNA). Competitive binding assays indicate that this site has a unique steroid binding specificity, which distinguishes it from other steroid receptors. Steroid specificity of nuclear binding mirrors inhibition of the low 11beta-dehydrogenase activity, suggesting that binding may be to an 11beta-hydroxysteroid dehydrogenase (11betaHSD) isoform, although 11betaHSD1 is not present in small intestinal epithelia and 11betaHSD2 does not colocalize intracellularly with the binding site. In summary, a nuclear [(3)H]corticosterone binding site is present in small intestinal epithelia that is distinct from other steroid receptors and shares steroid specificity characteristics with 11betaHSD2 but is distinguishable from the latter by its distinct intracellular localization.
当小肠上皮细胞与[³H]皮质酮一起孵育时，醛固酮和RU - 28362均不能取代其核结合，这表明[³H]皮质酮结合的位点不同于盐皮质激素受体和糖皮质激素受体。对核[³H]皮质酮结合进行的饱和及Scatchard分析显示，存在一个单一的可饱和结合位点，其亲和力相对较低（49 nM），容量较高（5 fmol/μg DNA）。竞争性结合试验表明，该位点具有独特的类固醇结合特异性，这使其有别于其他类固醇受体。核结合的类固醇特异性反映出低11β - 脱氢酶活性受到抑制，这表明结合可能是与一种11β - 羟基类固醇脱氢酶（11βHSD）同工型，尽管小肠上皮中不存在11βHSD1，且11βHSD2在细胞内并不与该结合位点共定位。总之，小肠上皮中存在一个核[³H]皮质酮结合位点，它不同于其他类固醇受体，与11βHSD2具有相同的类固醇特异性特征，但因其独特的细胞内定位而与后者不同。
