Cbl ubiquitination of p85 is essential for Epo-induced EpoR endocytosis
Cbl ubiquitination of p85 is essential for Epo-induced EpoR endocytosis
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DOI：
10.1182/blood-2013-05-506212
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发表时间：
2013-12-05
期刊：
影响因子：
20.3
通讯作者：
Huang, Lily Jun-shen
中科院分区：
文献类型：
--
作者：
Bulut, Gamze B.;Sulahian, Rita;Huang, Lily Jun-shen
促红细胞生成素（Epo）与Epo受体（EpoR）结合，激发下游信号传导，这对红细胞生成至关重要。Epo诱导的EpoR的内吞和降解是Epo信号转导的一个重要的负调控机制。这种机制的缺陷在原发性家族性和先天性红细胞增多症（PFCP）中红细胞过度生成中起关键作用。在这里，我们已经确定了一种新的机制，介导EpoR依赖EpoR的内化。Epo诱导PI 3 K的p85调节亚基的Cbl依赖性泛素化，其结合EpoR上的磷酸酪氨酸。泛素化允许p85与内吞蛋白epsin-1相互作用，从而驱动EpoR内吞作用。Cbl的敲除、其显性负性形式的表达或缺乏泛素相互作用基序的epsin-1突变体的表达都损害了Epo诱导的EpoR内化。模拟PFCP患者的突变EpoR不能结合p85，与epsin-1共定位，或在Epo刺激下内化，并表现出Epo超敏性。类似地，Cbl的敲低也引起原代红系祖细胞中的Epo超敏性。恢复p85与PFCP受体的结合拯救了Epo诱导的epsin-1共定位和EpoR内化，并使Epo超敏性正常化。我们的研究结果揭示了一种新的Cbl/p85/epsin-1途径在EpoR内吞作用，并表明，在这一途径的缺陷，导致过量的Epo信号和红系细胞过度增殖PFCP。（血。2013;122（24）：3964-3972）
Erythropoietin (Epo) binding to the Epo receptor (EpoR) elicits downstream signaling that is essential for red blood cell production. One important negative regulatory mechanism to terminate Epo signaling is Epo-induced EpoR endocytosis and degradation. Defects in this mechanism play a key role in the overproduction of erythrocytes in primary familial and congenital polycythemia (PFCP). Here we have identified a novel mechanism mediating Epo-dependent EpoR internalization. Epo induces Cbl-dependent ubiquitination of the p85 regulatory subunit of PI3K, which binds to phosphotyrosines on EpoR. Ubiquitination allows p85 to interact with the endocytic protein epsin-1, thereby driving EpoR endocytosis. Knockdown of Cbl, expression of its dominant negative forms, or expression of an epsin-1 mutant devoid of ubiquitin-interacting motifs all compromise Epo-induced EpoR internalization. Mutated EpoRs mimicking those from PFCP patients cannot bind p85, colocalize with epsin-1, or internalize on Epo stimulation and exhibit Epo hypersensitivity. Similarly, knockdown of Cbl also causes Epo hypersensitivity in primary erythroid progenitors. Restoring p85 binding to PFCP receptors rescues Epo-induced epsin-1 colocalization and EpoR internalization and normalizes Epo hypersensitivity. Our results uncover a novel Cbl/p85/epsin-1 pathway in EpoR endocytosis and show that defects in this pathway contribute to excessive Epo signaling and erythroid hyperproliferation in PFCP. (Blood. 2013;122(24):3964-3972)