van Kerkhof Peter, Smeets Mirjam, Strous Ger J
Department of Cell Biology and Institute of Biomembranes, Interuniversity Cardiology Institute of the Netherlands, University Medical Center Utrecht, Heidelberglaan 100, Utrecht, The Netherlands.
Endocrinology. 2002 Apr;143(4):1243-52. doi: 10.1210/endo.143.4.8755.
GH promotes not only longitudinal growth in children but is active throughout life in protein, fat, and carbohydrate metabolism. The multiple actions of GH start when GH binds to the cell surface-expressed GH receptor. Effectiveness of the hormone depends both on its presence in the circulation and the availability of receptors at the cell surface of target cells. In this study, we examined the role of the ubiquitin-proteasome pathway in regulating GH receptor availability. We show that receptor turnover is rapid, and almost 3-fold prolonged in the internalization-deficient mutant GH receptor (F327A). Using a monovalent GH antagonist, B2036, we could quantify the internalization of the nonactivated receptor. By comparing internalization of the receptor with shedding of the GH-binding protein, we show that in Chinese hamster lung cell lines, internalization followed by lysosomal degradation is the major pathway for receptor degradation and that the ubiquitin-proteasome pathway controls this process. Inhibition of endocytosis resulted in a 200% increase in receptor availability at the cell surface at steady state.
生长激素（GH）不仅促进儿童的纵向生长，而且在整个生命过程中对蛋白质、脂肪和碳水化合物代谢都有作用。当生长激素与细胞表面表达的生长激素受体结合时，生长激素的多种作用就开始了。该激素的有效性既取决于其在循环中的存在，也取决于靶细胞表面受体的可用性。在本研究中，我们研究了泛素 - 蛋白酶体途径在调节生长激素受体可用性中的作用。我们发现受体周转迅速，而在内化缺陷型突变生长激素受体（F327A）中周转几乎延长了3倍。使用单价生长激素拮抗剂B2036，我们可以量化未活化受体的内化。通过比较受体的内化与生长激素结合蛋白的脱落，我们发现在中国仓鼠肺细胞系中，内化后经溶酶体降解是受体降解的主要途径，并且泛素 - 蛋白酶体途径控制这一过程。内吞作用的抑制导致稳态时细胞表面受体可用性增加200%。
