Shi Biao, Isseroff R Rivakh
Department of Dermatology, University of California Davis School of Medicine, Davis, CA, USA.
Exp Dermatol. 2005 Jul;14(7):519-27. doi: 10.1111/j.0906-6705.2005.00317.x.
The proliferative responses of cells to mitogens decrease during aging, and this may result from age-related defects in signal transduction in response to mitogens. In this study, we have investigated the age-related alteration of responses to epidermal growth factor (EGF) in cultured human keratinocytes that were senesced in vitro by repeated passage. The stimulation with EGF increased the DNA-binding activity of activator protein 1 (AP-1), an important transcription factor for cell proliferation, in young keratinocytes, whereas the binding activity showed little or slight change in the senescent cells. The induced DNA-binding activity of AP-1 in young cells was inhibited by PD 98059, an inhibitor of MEK, and partially inhibited by GF 109203X, an inhibitor of protein kinase C. Western blot analysis demonstrated that EGF induced dramatic increase in the phosphorylation of EGF receptor (EGFR) and extracellular signal-regulated kinases (ERK) in young cells, while this phosphorylation was much less profound in senescent cells. Finally, the application of EGF to young cells resulted in increased phosphorylation of Fra-2, a Fos protein component of the Jun/Fos heterodimer AP-1 complex. This EGF-induced Fra-2 phosphorylation was attenuated in senescent cells. Taken together, our study suggests that the signal transduction mediated by EGF/ERK pathway is altered in senescent human keratinocytes, and this change may be attributed, in part, to the decreased AP-1 transcription activity observed in senescent keratinocytes.
细胞对有丝分裂原的增殖反应在衰老过程中会降低，这可能是由于对有丝分裂原的信号转导出现与年龄相关的缺陷所致。在本研究中，我们调查了通过反复传代在体外衰老的培养人角质形成细胞中对表皮生长因子（EGF）反应的年龄相关变化。用EGF刺激可增加年轻角质形成细胞中活化蛋白1（AP-1）的DNA结合活性，AP-1是细胞增殖的重要转录因子，而在衰老细胞中该结合活性几乎没有变化或仅有轻微变化。年轻细胞中AP-1的诱导DNA结合活性被MEK抑制剂PD 98059抑制，并被蛋白激酶C抑制剂GF 109203X部分抑制。蛋白质印迹分析表明，EGF可诱导年轻细胞中表皮生长因子受体（EGFR）和细胞外信号调节激酶（ERK）的磷酸化显著增加，而在衰老细胞中这种磷酸化程度要低得多。最后，将EGF应用于年轻细胞导致Fra-2磷酸化增加，Fra-2是Jun/Fos异二聚体AP-1复合物的Fos蛋白成分。这种EGF诱导的Fra-2磷酸化在衰老细胞中减弱。综上所述，我们的研究表明，衰老的人角质形成细胞中EGF/ERK途径介导的信号转导发生了改变，这种变化可能部分归因于衰老角质形成细胞中观察到的AP-1转录活性降低。
