Mori S, Rönnstrand L, Claesson-Welsh L, Heldin C H
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
J Biol Chem. 1994 Feb 18;269(7):4917-21.
The importance of tyrosine residues in ligand-mediated endocytosis of the platelet-derived growth factor beta-receptor was analyzed using a series of tyrosine residue-mutated beta-receptors, which together cover all of the tyrosine residues in the juxtamembrane segment, the kinase insert, and the carboxyl-terminal tail; also certain of the tyrosine residues within the first and second parts of the kinase domain were examined. Of all of these tyrosine residues, only Tyr-579 seemed to be important for internalization, since mutation of this residue resulted in substantial reduction in the rate of ligand-induced receptor internalization (approximately 60% of the wild-type level). Replacement of Tyr-579 by either an aromatic (Phe) or a nonaromatic (Asp) residue reduced the efficiency of the mutant receptors in internalization to the same extent, suggesting that the role of Tyr-579 in the beta-receptor is different from that of the previously described tyrosine-based internalization motifs, which were first determined for the low density lipoprotein receptor. Tyr-579 has been found to be an autophosphorylation site in the beta-receptor. Moreover, the internalization rate of a kinase negative receptor mutant was not altered by the additional mutation of Tyr-579. Thus, it is likely that phosphorylation of Tyr-579 is important for ligand-induced internalization of the beta-receptor.
利用一系列酪氨酸残基突变的β受体分析了酪氨酸残基在血小板衍生生长因子β受体的配体介导内吞作用中的重要性，这些突变体共同覆盖了近膜段、激酶插入区和羧基末端尾巴中的所有酪氨酸残基；同时也检测了激酶结构域第一和第二部分内的某些酪氨酸残基。在所有这些酪氨酸残基中，只有Tyr-579似乎对内化作用很重要，因为该残基的突变导致配体诱导的受体内化速率大幅降低（约为野生型水平的60%）。用芳香族（苯丙氨酸）或非芳香族（天冬氨酸）残基取代Tyr-579会使突变受体的内化效率降低到相同程度，这表明Tyr-579在β受体中的作用与先前描述的基于酪氨酸的内化基序不同，后者最初是在低密度脂蛋白受体中确定的。已发现Tyr-579是β受体中的一个自磷酸化位点。此外，激酶阴性受体突变体的内化速率不会因Tyr-579的额外突变而改变。因此，Tyr-579的磷酸化可能对配体诱导的β受体内化很重要。
