Haugsten Ellen Margrethe, Malecki Jedrzej, Bjørklund Sunniva Maria Stordal, Olsnes Sjur, Wesche Jørgen
Centre for Cancer Biomedicine, Faculty Division Norwegian Radium Hospital, University of Oslo, 0310 Oslo, Norway.
Mol Biol Cell. 2008 Aug;19(8):3390-403. doi: 10.1091/mbc.e07-12-1219. Epub 2008 May 14.
Endocytosis and targeting of growth factor receptors for lysosomal degradation have been associated with ubiquitination of the intracellular part of the receptors. To elucidate the role of receptor ubiquitination in internalization and sorting of fibroblast growth factor receptor (FGFR), we constructed several mutants of FGFR1 in which lysines, potential ubiquitination sites, were substituted for arginines. Substitution of all lysine residues in the intracellular part of FGFR1 resulted in inactivation of the tyrosine kinase domain of the receptor. However, several multilysine FGFR1 mutants, where up to 26 of 29 lysines in the intracellular part of the receptor were mutated, retained tyrosine kinase activity. The active multilysine mutants were poorly ubiquitinated, but internalized normally, indicating that ubiquitination of the receptor is not required for endocytosis. In contrast, degradation of the multilysine mutants was dramatically reduced as the mutants were inefficiently transported to lysosomes but rather sorted to recycling endosomes. The altered sorting resulted in sustained signaling. The duration of FGFR1 signaling seems to be tightly regulated by receptor ubiquitination and subsequent sorting to the lysosomes for degradation.
内吞作用以及生长因子受体靶向溶酶体降解与受体胞内部分的泛素化有关。为了阐明受体泛素化在成纤维细胞生长因子受体（FGFR）内化和分选过程中的作用，我们构建了FGFR1的几个突变体，其中潜在的泛素化位点赖氨酸被精氨酸取代。FGFR1胞内部分所有赖氨酸残基的取代导致受体酪氨酸激酶结构域失活。然而，几个多赖氨酸FGFR1突变体，其中受体胞内部分29个赖氨酸中有多达26个发生突变，仍保留酪氨酸激酶活性。活性多赖氨酸突变体的泛素化程度较低，但能正常内化，这表明受体的泛素化对于内吞作用并非必需。相反，多赖氨酸突变体的降解显著减少，因为这些突变体不能有效地转运至溶酶体，而是被分选至再循环内体。分选的改变导致信号持续存在。FGFR1信号传导的持续时间似乎受到受体泛素化以及随后分选至溶酶体进行降解的严格调控。
