van Kerkhof Peter, Vallon Erica, Strous Ger J
Department of Cell Biology and Institute of Biomembranes, University Medical Centre Utrecht, Heidelberglaan 100, AZU-G02.525, The Netherlands.
Mol Cell Endocrinol. 2003 Mar 28;201(1-2):57-62. doi: 10.1016/s0303-7207(02)00434-3.
The number of growth hormone receptors (GHRs) per cell are regulated and this feature plays a major role in the hormone responsiveness of the body. We previously observed in transfected Chinese hamster lung cells that GHR availability is determined by three factors: endocytosis (75%), shedding (10%), and other undetermined mechanisms (15%). The endocytosis depends on an active ubiquitin conjugation system. In addition, this process is ligand-independent. Here, we show that this principle is useful to increase the abundance of GHRs at the cell surface of cells using a combination of inhibitors. In theory, an inhibitor that targets the ubiquitin conjugation specific for the GHR, would suffice, as almost 80% of the removal rate depends on this mechanism. As the molecular mechanism is unknown yet, we used a general inhibitor of proteasome action. Unfortunately, such an inhibitor stimulates the shedding process severalfold. Our data show that the combination of a general proteasome inhibitor and a matrix metalloprotease inhibitor results in an almost twofold increase in functional GHRs at the cell surface, and generate new perspectives to increase the sensitivity of cells for growth hormone.
每个细胞中生长激素受体（GHR）的数量受到调控，这一特性在机体对该激素的反应中起主要作用。我们之前在转染的中国仓鼠肺细胞中观察到，GHR的可利用性由三个因素决定：内吞作用（75%）、脱落（10%）和其他未明确的机制（15%）。内吞作用依赖于一个活跃的泛素偶联系统。此外，这个过程不依赖配体。在此，我们表明，利用抑制剂组合，这一原理有助于增加细胞表面GHR的丰度。理论上，一种针对GHR特异性泛素偶联的抑制剂就足够了，因为几乎80%的去除率取决于这一机制。由于分子机制尚不清楚，我们使用了一种蛋白酶体作用的通用抑制剂。不幸的是，这种抑制剂会使脱落过程增加数倍。我们的数据表明，通用蛋白酶体抑制剂和基质金属蛋白酶抑制剂的组合可使细胞表面功能性GHR增加近两倍，并为提高细胞对生长激素的敏感性带来了新的前景。
