EGF receptor (EGFR) endocytosis is induced by stress in a manner dependent on the p38 MAPK family. Ligand and stresses such as X-rays, reportedly promote nuclear trafficking of endocytosed EGFR for regulation of gene transcription and DNA repair. We fail to detect EGFR endocytosis or nuclear transport following X-ray treatment of HeLa or head and neck cancer cells, despite extensive DNA damage induction. Apparent nuclear staining with EGFR extracellular domain antibody remained present despite reduced/absent EGFR expression, and so did not represent nuclear EGFR. UVB and UVC, but not X-ray or UVA, treatment induced p38 activation and EGFR endocytosis, although all of these stresses induced DNA damage, indicating that DNA damage alone is not sufficient to induce EGFR endocytosis. Increased reactive oxygen species (ROS) levels following UVB treatment, compared to that seen with X-rays, do not alone explain differences in p38 activation. UVB, like UVC, induced EGFR accumulation predominantly in perinuclear endosomes, rather than in the nucleus. Our morphological techniques identifying major changes in receptor distribution do not exclude the possibility that small but biologically relevant amounts of EGFR enter the nucleus. This study highlights the importance and limitations of morphological analyses of receptor distribution in understanding signaling outcome.

译文

:EGF受体(EGFR)的内吞作用是由应激以依赖于p38 MAPK家族的方式诱导的。据报道,配体和压力(例如X射线)可促进内吞EGFR的核转运,从而调节基因转录和DNA修复。尽管广泛的DNA损伤诱导作用,但在X射线治疗HeLa或头颈部癌细胞后,我们仍未检测到EGFR的内吞作用或核转运。尽管EGFR表达减少/缺失,但仍存在EGFR胞外域抗体的明显核染色,因此并不代表核EGFR。 UVB和UVC处理可诱导p38活化和EGFR内吞作用,而不是X射线或UVA,尽管所有这些压力均可诱导DNA损伤,表明仅DNA损伤不足以诱导EGFR内吞作用。与X射线相比,UVB处理后增加的活性氧(ROS)水平不能单独解释p38活化的差异。与UVC一样,UVB主要诱导EGFR聚集在核周内体中,而不是在细胞核中。我们的鉴定受体分布主要变化的形态学技术并不排除少量但生物学上相关的EGFR进入细胞核的可能性。这项研究强调了受体分布形态分析在理解信号转导结果中的重要性和局限性。

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