Department of Human Anatomy and Cell Science, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
Neoplasia. 2012 May;14(5):396-409. doi: 10.1596/neo.111514.
The cytoplasmic domains of EGF-like ligands, including EGF cytoplasmic domain (EGFcyt), have important biological functions. Using specific constructs and peptides of human EGF cytoplasmic domain, we demonstrate that EGFcyt facilitates lysosomal and proteasomal protein degradation, and this coincided with growth inhibition of human thyroid and glioma carcinoma cells. EGFcyt and exon 22-23-encoded peptide (EGF22.23) enhanced procathepsin B (procathB) expression and procathB-mediated lysosomal degradation of EGFR/ErbB1 as determined by inhibitors for procathB and the lysosomal ATPase inhibitor BafA1. Presence of mbEGFctF, EGFcyt, EGF22.23, and exon 23-encoded peptides suppressed the expression of the deubiqitinating enzyme ubiquitin C-terminal hydrolase-L1 (UCH-L1). This coincided with hyperubiquitination of total cellular proteins and ErbB1/2 and reduced proteasome activity. Upon small interfering RNA-mediated silencing of endogenously expressed UCH-L1, a similar hyperubiquitinylation phenotype, reduced ErbB1/2 content, and attenuated growth was observed. The exon 23-encoded peptide region of EGFcyt was important for these biologic actions. Structural homology modeling of human EGFcyt showed that this molecular region formed an exposed surface loop. Peptides derived from this EGFcyt loop structure may aid in the design of novel peptide therapeutics aimed at inhibiting growth of cancer cells.
EGF 样配体的细胞质结构域，包括 EGF 细胞质结构域（EGFcyt），具有重要的生物学功能。使用人 EGF 细胞质结构域的特定构建体和肽，我们证明 EGFcyt 促进溶酶体和蛋白酶体蛋白降解，这与人类甲状腺和神经胶质瘤癌细胞的生长抑制相一致。EGFcyt 和外显子 22-23 编码的肽（EGF22.23）增强了组织蛋白酶 B 前体（procathB）的表达，并通过 procathB 和溶酶体 ATP 酶抑制剂 BafA1 确定了 procathB 介导的 EGFR/ErbB1 溶酶体降解。mbEGFctF、EGFcyt、EGF22.23 和外显子 23 编码的肽存在时，抑制去泛素化酶泛素 C 末端水解酶-L1（UCH-L1）的表达。这与总细胞蛋白和 ErbB1/2 的泛素化增加以及蛋白酶体活性降低相一致。在用小干扰 RNA 介导沉默内源性表达的 UCH-L1 后，观察到类似的泛素化表型、减少的 ErbB1/2 含量和减弱的生长。EGFcyt 的外显子 23 编码肽区对于这些生物学作用很重要。人 EGFcyt 的结构同源建模表明，该分子区域形成了一个暴露的表面环。源自该 EGFcyt 环结构的肽可能有助于设计旨在抑制癌细胞生长的新型肽治疗剂。
