Kim Sungdae, Nahm Minyeop, Kim Najin, Kwon Yumi, Kim Joohyung, Choi Sukwoo, Choi Eun Young, Shim Jiwon, Lee Cheolju, Lee Seungbok
Interdisciplinary Graduate Program in Genetic Engineering, Seoul National University, Seoul 08826, Korea.
Department of Cell and Developmental Biology and Dental Research Institute, Seoul National University, Seoul 08826, Korea.
Development. 2017 Nov 15;144(22):4159-4172. doi: 10.1242/dev.153288. Epub 2017 Oct 9.
GTPase regulator associated with focal adhesion kinase 1 (GRAF1) is an essential component of the GPI-enriched endocytic compartment (GEEC) endocytosis pathway. Mutations in the human gene are associated with acute myeloid leukemia, but its normal role in myeloid cell development remains unclear. We show that Graf, the ortholog of GRAF1, is expressed and specifically localizes to GEEC endocytic membranes in macrophage-like plasmatocytes. We also find that loss of Graf impairs GEEC endocytosis, enhances EGFR signaling and induces a plasmatocyte overproliferation phenotype that requires the EGFR signaling cascade. Mechanistically, Graf-dependent GEEC endocytosis serves as a major route for EGFR internalization at high, but not low, doses of the predominant EGFR ligand Spitz (Spi), and is indispensable for efficient EGFR degradation and signal attenuation. Finally, Graf interacts directly with EGFR in a receptor ubiquitylation-dependent manner, suggesting a mechanism by which Graf promotes GEEC endocytosis of EGFR at high Spi. Based on our findings, we propose a model in which Graf functions to downregulate EGFR signaling by facilitating Spi-induced receptor internalization through GEEC endocytosis, thereby restraining plasmatocyte proliferation.
与粘着斑激酶1相关的GTP酶调节因子（GRAF1）是富含糖基磷脂酰肌醇的内吞区室（GEEC）内吞途径的重要组成部分。人类基因中的突变与急性髓系白血病有关，但其在髓系细胞发育中的正常作用仍不清楚。我们发现，GRAF1的直系同源基因Graf在巨噬细胞样浆细胞中表达并特异性定位于GEEC内吞膜。我们还发现，Graf的缺失会损害GEEC内吞作用，增强表皮生长因子受体（EGFR）信号传导，并诱导一种需要EGFR信号级联反应的浆细胞过度增殖表型。从机制上讲，依赖Graf的GEEC内吞作用是高剂量而非低剂量的主要EGFR配体Spitz（Spi）时EGFR内化的主要途径，并且对于有效的EGFR降解和信号衰减是不可或缺的。最后，Graf以受体泛素化依赖的方式直接与EGFR相互作用，提示了一种Graf在高Spi水平促进EGFR的GEEC内吞作用的机制。基于我们的发现，我们提出了一个模型，其中Graf通过促进Spi诱导的受体通过GEEC内吞作用内化来下调EGFR信号传导，从而抑制浆细胞增殖。
