Ubiquitin-independent entry into the yeast recycling pathway
Ubiquitin-independent entry into the yeast recycling pathway
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DOI：
10.1034/j.1600-0854.2002.030204.x
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发表时间：
2002-02-01
期刊：
影响因子：
4.5
通讯作者：
Davis, NG
中科院分区：
文献类型：
--
作者：
Chen, LY;Davis, NG
酵母α因子受体（Ste3p）受到两种机制上不同的内吞作用模式的影响：组成型配体依赖性途径与受体的液泡降解有关，而配体依赖性摄取途径主要与再循环有关，从而与受体再利用有关。 Ste3p 泛素化触发其摄取进入组成性途径。目前的工作考虑了与 Ste3p 配体依赖性内吞机制相关的受体泛素化的作用。 doa4-Delta 突变降低了细胞内泛素的可用性，从而阻碍了 Ste3p 的本构摄取。然而，Ste3p 配体依赖性回收途径的吸收继续未受影响。通过分析在所有可能的泛素受体位点具有 Lys-to-Arg 取代的受体突变体，进一步表明了 Ste3p 配体依赖性摄取的泛素独立性。同样，配体诱导的内化没有受到损害。此外，对于受体的再循环或缓慢的PEP4依赖性周转没有看到明显的影响（对于通过配体依赖性机制内化的受体，运输到液泡/溶酶体是次要的，是再循环的替代命运）。然而，人们注意到 Lys-to-Arg 突变的一个显着影响。在细胞长时间暴露于α因子配体后，Lys-to-Arg受体没有被递送到液泡腔，而是定位到液泡的限制膜。因此，虽然受体泛素化显然不是α因子依赖性摄取进入再循环途径或再循环本身所必需的，但它确实影响受体到液泡的路径，可能是通过影响通过晚期内体、多囊泡体的路径：泛素化受体可能被选择进入内部、腔囊泡，而未修饰的受体可能留在限制性外膜上。
The yeast a-factor receptor (Ste3p) is subject to two mechanistically distinct modes of endocytosis: a constitutive, ligand-in dependent pathway links to vacuolar degradation of the receptor, while a ligand-dependent uptake pathway links primarily to recycling and thus, receptor reutilization. Ste3p ubiquitination triggers its uptake into the constitutive pathway. The present work considers the role of the receptor ubiquitination associated with the Ste3p ligand-dependent endocytosis mechanism. The doa4-Delta mutation which reduces the cellular availability of ubiquitin blocks the Ste3p constitutive uptake. Uptake into the Ste3p ligand-dependent recycling pathway, however, continues unimpaired. The ubiquitin independence of Ste3p ligand-dependent uptake was further indicated by analysis of receptor mutants having Lys-to-Arg substitutions at all possible ubiquitin acceptor sites. Again, the ligand-induced internalization was unimpaired. Furthermore, no discernible effect was seen on either recycling or on the slow PEP4-dependent turnover of the receptor (for receptor internalized via the ligand-dependent mechanism, trafficking to the vacuole/lysosome is the minor, alternate fate to recycling). However, one striking effect of the Lys-to-Arg mutations was noted. Following a prolonged exposure of the cells to the a-factor ligand, rather than being delivered to the vacuolar lumen, the Lys-to-Arg receptor was found to localize instead to the limiting membrane of the vacuole. Thus, while receptor ubiquitination clearly is not required for either the a-factor-dependent uptake into recycling pathway or for the recycling itself, it does affect the routing of receptor to the vacuole, likely by affecting the routing through the late endosomal, multivesicular body: ubiquitinated receptor may be selected into the internal, lumenal vesicles, while unmodified receptor may be left to reside at the limiting external membrane.