Small GTPase Rab12 Regulates Constitutive Degradation of Transferrin Receptor
Small GTPase Rab12 Regulates Constitutive Degradation of Transferrin Receptor
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DOI：
10.1111/j.1600-0854.2011.01240.x
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发表时间：
2011-10-01
期刊：
影响因子：
4.5
通讯作者：
Fukuda, Mitsunori
中科院分区：
文献类型：
--
作者：
Matsui, Takahide;Itoh, Takashi;Fukuda, Mitsunori
转铁蛋白受体（Transferrin receptor，TfR）是一种在质膜和细胞内膜之间转运的质膜蛋白。虽然TfR本身也会像其他细胞内蛋白一样发生降解，但是否存在特异性的TfR降解途径尚未研究。在这项研究中，我们筛选了小GTTRab蛋白，在所有真核生物的膜交通的共同监管机构，蛋白质，特别是参与TfR降解。我们进行了三个连续的方法，即与TfR的Rab共定位，与溶酶体共定位，Rab敲低的特定的小干扰RNA（siRNA）的筛选，并成功地确定Rab12，一个以前未知的Rab亚型，作为一个主要的候选人中的60人或小鼠Rab筛选。我们发现，Rab12的组成型活性突变体的表达减少了TfR蛋白的量，而通过敲低Rab12本身或其上游激活剂Dennd3来功能性消融Rab12增加了TfR蛋白的量。然而，有趣的是，Rab12的敲低对表皮生长因子受体（EGFR）蛋白的降解没有影响，即对常规降解途径没有影响。我们的研究结果表明，TfR是组成性降解的Rab12依赖的途径（推测从回收内体到溶酶体），这是独立的传统的降解途径。
Transferrin receptor (TfR) is a well-characterized plasma membrane protein that travels between the plasma membrane and intracellular membrane compartments. Although TfR itself should undergo degradation, the same as other intracellular proteins, whether a specific TfR degradation pathway exists has never been investigated. In this study, we screened small GTPase Rab proteins, common regulators of membrane traffic in all eukaryotes, for proteins that are specifically involved in TfR degradation. We performed the screening by three sequential methods, i.e. colocalization of Rab with TfR, colocalization with lysosomes, and knockdown of Rab by specific small interfering RNA (siRNA), and succeeded in identifying Rab12, a previously uncharacterized Rab isoform, as a prime candidate among the 60 human or mouse Rabs screened. We showed that expression of a constitutive active mutant of Rab12 reduced the amount of TfR protein, whereas functional ablation of Rab12 by knockdown of either Rab12 itself or its upstream activator Dennd3 increased the amount of TfR protein. Interestingly, however, knockdown of Rab12 had no effect on the degradation of epidermal growth factor receptor (EGFR) protein, i.e. on a conventional degradation pathway. Our findings indicated that TfR is constitutively degraded by a Rab12-dependent pathway (presumably from recycling endosomes to lysosomes), which is independent of the conventional degradation pathway.