Association with Hrs is required for the early endosomal localization, stability, and function of STAM
Association with Hrs is required for the early endosomal localization, stability, and function of STAM
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DOI：
10.1093/jb/mvh046
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发表时间：
2004-03-01
影响因子：
2.7
通讯作者：
Komada, M
中科院分区：
文献类型：
--
作者：
Mizuno, E;Kawahata, K;Komada, M
STAM1和STAM2是STAM1蛋白家族的成员，通过它们的盘绕区与Hrs相关。Hrs和STAM都能结合泛素和。参与内体对转运到溶酶体的泛素化货物蛋白的分选。本文研究了STAM与Hrs结合的生物学意义。内源性STAM1和STAM2主要定位于早期核内体，提示它们是常驻核内体蛋白。相比之下，STAM2突变体缺乏卷曲卷曲区，不结合Hrs，在细胞质上定位错误。位于盘绕区n端且在STAM2蛋白中保守的区域的缺失也严重影响了Hrs的结合和STAM2的内体定位，表明该区域也参与了这些活动。通过RNA干扰减少内源性Hrs同样会导致外源表达的STAM2在细胞质中的错误定位。这些结果表明，STAM。是本地化。通过与靶膜上的Hrs结合而进入早期内体。此外，内源性STAM蛋白的表达水平在Hrs缺失的细胞中急剧降低，表明STAM通过与Hrs结合而稳定。最后，缺乏Hrs结合活性的STAM2突变体在引起早期内体增大、在这种异常细胞器上积累泛素化蛋白以及抑制配体激活的表皮生长因子受体的降解方面存在缺陷，这表明与Hrs的关联是STAM功能的先决条件。
Members of the STAM family of proteins, STAM1 and STAM2, are associated with Hrs through their coiled-coil regions. Both Hrs and STAM bind ubiquitin and. are involved in endosomal sorting of ubiquitinated cargo proteins for trafficking to the lysosome. Here we examined the biological significance of STAM binding to Hrs. Endogenous STAM1 and STAM2 were mostly localized on the early endosome, suggesting that they are resident endosomal proteins. A STAM2 mutant that lacks the coiled-coil region and does not bind Hrs, in contrast, mislocalized to the cytoplasm. Deletion of a region located N-terminal to the coiled-coil region and conserved among STAM proteins also severely affected Hrs binding and the endosomal localization of STAM2, suggesting that this region is also involved in these activities. Depletion of endogenous Hrs by RNA interference similarly caused the mislocalization of exogenously expressed STAM2 to the cytoplasm. These results indicate that STAM. is localized. to the early endosome by binding to Hrs on the target membrane. In addition, the expression level of endogenous STAM proteins was drastically reduced in Hrs-depleted cells, suggesting that STAM is stabilized by binding to Hrs. Finally, STAM2 mutants lacking the Hrs-binding activity were defective in causing the enlargement of early endosomes, accumulating ubiquitinated proteins on this aberrant organelle, and inhibiting the degradation of ligand-activated epidermal growth factor receptors, suggesting that the association with Hrs is a prerequisite for STAM function.