Kim Gun-Hwa, Park Eunjoo, Kong Young-Yun, Han Jin-Kwan
Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31, Hyoja Dong, Pohang, Kyungbuk, 790-784, Republic of Korea.
Cell Signal. 2006 Apr;18(4):553-63. doi: 10.1016/j.cellsig.2005.05.026. Epub 2005 Aug 9.
POSH (plenty of SH3s) acts as a scaffold that links activated Rac1 and downstream c-Jun N-terminal kinase (JNK) signaling modules. However, it is unknown whether it's functional domain-mediated roles including the interesting RING-finger domain or its cellular function. Here, we provide evidence that subcellular localization of POSH is regulated by a particular domain of the protein and POSH was colocalized with hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) on early endosomes via interaction of Hrs with POSH's two rear SH3 domains. Moreover, the RING domain of POSH specifically regulates the stability of Hrs, but not of JNK1, via a ubiquitin-proteasomal degradation pathway. Finally, we demonstrate that JNK1 does not interact with Hrs under the conditions of POSH interacted with Hrs, but instead reduces the POSH-catalyzed ubiquitination of Hrs and their reciprocal interaction. Together, these data suggest that POSH has a distinct role as a specific E3 ubiquitin ligase for Hrs on early endosomes, and there exists a relationship between its separate activities as a scaffold and as an E3.
富含SH3结构域蛋白（POSH）作为一种支架蛋白，连接活化的Rac1和下游的c-Jun氨基末端激酶（JNK）信号模块。然而，其功能结构域介导的作用，包括有趣的环指结构域或其细胞功能，尚不清楚。在这里，我们提供证据表明，POSH的亚细胞定位受该蛋白特定结构域的调控，并且通过Hrs与POSH的两个后端SH3结构域相互作用，POSH与早期内体上的肝细胞生长因子调节的酪氨酸激酶底物（Hrs）共定位。此外，POSH的环指结构域通过泛素-蛋白酶体降解途径特异性调节Hrs的稳定性，而不调节JNK1的稳定性。最后，我们证明在POSH与Hrs相互作用的条件下，JNK1不与Hrs相互作用，而是减少POSH催化的Hrs泛素化及其相互作用。总之，这些数据表明，POSH在早期内体上作为Hrs的特异性E3泛素连接酶具有独特作用，并且其作为支架蛋白和作为E3的不同活性之间存在关联。
