Smith M, Burke Z, Carter D
Physiology Unit, School of Molecular and Medical Biosciences, MOMED, Cardiff University of Wales, UK.
Mol Cell Endocrinol. 1996 Sep 18;122(2):151-8. doi: 10.1016/0303-7207(96)03878-6.
The AP-1 transcription factor is a variable complex of Fos and Jun nuclear phosphoproteins that is induced in many cell types. AP-1 interacts with transcription factors of different classes, including the nuclear steroid hormone receptors, an interaction that is often mutually antagonistic and thereby serves to integrate different cellular signalling events. In addition to direct, molecular interactions between AP-1 and glucocorticoid receptor (GR), there is also evidence that the two signalling pathways may interact at different levels, but in vivo interactions of this nature have not been well characterized. We have investigated a unique cellular context for GR/AP-1 interactions, namely in the adrenal gland of the rat where the production of glucocorticoids leads to extremely high local levels of glucocorticoids, and where high constitutive AP-1 activity (as determined by in vitro DNA binding activity) has been demonstrated. We have now shown that depletion of glucocorticoid production in rats with the 11-beta-hydroxylase inhibitor, metyrapone, results in increased adrenal AP-1 activity. The demonstrated 5-fold increase is reversed by prior treatment with the glucocorticoid agonist, dexamethasone, and is largely localized to the adrenal medullary region. Further experiments have shown that c-Jun and JunD are the principal components of adrenal AP-1 in the basal state, but a change in jun-B expression appears to underly the metyrapone-induced increase in AP-1 activity. In situ hybridization analysis has shown that glucocorticoid depletion is associated with a dramatic increase in adrenal medullary junB mRNA, and using immunoblotting we have demonstrated a similar increase in nuclear levels of both the 43 kD JunB protein, and an associated phosphorylated JunB. Our use of a pharmacological intervention to demonstrate tonic suppression of adrenal medullary JunB expression by glucocorticoids has provided evidence of a nuclear mechanism that may have physiological relevance as an adaptive response to fluctuating levels of glucocorticoids.
AP-1转录因子是一种由Fos和Jun核磷蛋白组成的可变复合物，在多种细胞类型中被诱导产生。AP-1与不同类别的转录因子相互作用，包括核类固醇激素受体，这种相互作用通常是相互拮抗的，从而有助于整合不同的细胞信号事件。除了AP-1与糖皮质激素受体（GR）之间的直接分子相互作用外，还有证据表明这两种信号通路可能在不同水平上相互作用，但这种性质的体内相互作用尚未得到很好的表征。我们研究了GR/AP-1相互作用的一种独特细胞环境，即在大鼠肾上腺中，糖皮质激素的产生导致局部糖皮质激素水平极高，并且已证明存在高组成型AP-1活性（通过体外DNA结合活性测定）。我们现在已经表明，用11-β-羟化酶抑制剂美替拉酮使大鼠的糖皮质激素产生减少，会导致肾上腺AP-1活性增加。所显示的5倍增加可被糖皮质激素激动剂地塞米松预先处理逆转，并且主要定位于肾上腺髓质区域。进一步的实验表明，c-Jun和JunD是基础状态下肾上腺AP-1的主要成分，但jun-B表达的变化似乎是美替拉酮诱导的AP-1活性增加的基础。原位杂交分析表明，糖皮质激素减少与肾上腺髓质junB mRNA的显著增加有关，并且使用免疫印迹我们已经证明43 kD JunB蛋白以及相关的磷酸化JunB的核水平有类似的增加。我们使用药理学干预来证明糖皮质激素对肾上腺髓质JunB表达的强直性抑制，这提供了一种核机制的证据，该机制可能作为对糖皮质激素水平波动的适应性反应具有生理相关性。
