Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima 727-0023, Japan.
Biochem Biophys Res Commun. 2010 Aug 20;399(2):232-7. doi: 10.1016/j.bbrc.2010.07.060. Epub 2010 Jul 21.
ESCRT-I, which mediates the sorting of ubiquitinated cargo protein from the plasma membrane to the endosomal vesicle, comprises a heterotetramer of TSG101 (Vps23), Vps28, Vps37 and MVB12 protein. In humans, the structurally similar subtypes MVB12A and MVB12B are subunits of ESCRT-I. However, no functional description of these proteins has been described. Here we show the differing effects of tyrosine phosphorylation and ubiquitination of both MVB12 proteins on their respective functions. As noted in our previous study, Tyr204 phosphorylation of MVB12A in response to epidermal growth factor (EGF) stimulation affects binding to CD2AP, which regulates the amounts of EGF receptor bound to ESCRT-I. Strikingly, ubiquitination of Lys264 and Lys290 of MVB12B was induced and led to the instability and inclusion of MVB12B in COS-7 cells. These ubiquitinations increased upon EGF stimulation, which was regulated by the phosphorylations of Tyr241 and Tyr243 of MVB12B. Furthermore, MVB12A was also involved in the aggregation-prone proteins of MVB12B. These results suggest that the expression of MVB12B may be normally suppressed through the ubiquitin-proteasome pathway that simultaneously regulates the fate of MVB12A and the functions of ESCRT-I.
ESCRT-I 介导泛素化货物蛋白从质膜到内体小泡的分拣，由 TSG101（Vps23）、Vps28、Vps37 和 MVB12 蛋白组成异四聚体。在人类中，结构相似的亚型 MVB12A 和 MVB12B 是 ESCRT-I 的亚基。然而，这些蛋白质的功能尚未被描述。在这里，我们展示了 MVB12 蛋白的酪氨酸磷酸化和泛素化对其各自功能的不同影响。如我们之前的研究所示，MVB12A 的 Tyr204 磷酸化对表皮生长因子（EGF）刺激的反应影响了与 CD2AP 的结合，CD2AP 调节与 ESCRT-I 结合的 EGF 受体的数量。引人注目的是，MVB12B 的 Lys264 和 Lys290 的泛素化被诱导，并导致 MVB12B 在 COS-7 细胞中的不稳定性和包含。这些泛素化在 EGF 刺激下增加，受 MVB12B 的 Tyr241 和 Tyr243 磷酸化的调节。此外，MVB12A 也参与了 MVB12B 的聚集倾向蛋白。这些结果表明，MVB12B 的表达可能通过同时调节 MVB12A 的命运和 ESCRT-I 的功能的泛素蛋白酶体途径正常受到抑制。
