Izumi H, Ono M, Ushiro S, Kohno K, Kung H F, Kuwano M
Department of Biochemistry, Kyushu University School of Medicine, Fukuoka, Japan.
Exp Cell Res. 1994 Oct;214(2):654-62. doi: 10.1006/excr.1994.1303.
Our previous studies imply that tumor necrosis factor-alpha (TNF-alpha) and epidermal growth factor (EGF) might share a common signal transduction pathway in human omental microvascular endothelial (HOME) cells. Exposure of cultured HOME cells to TNF-alpha for 10 min enhanced EGF receptor phosphorylation at a rate comparable to EGF. Apparent phosphorylation of tyrosine residues was observed in addition to serine/threonine of the EGF receptor by EGF, but only a slightly if any tyrosine phosphorylation by TNF-alpha. In vitro kinase activity of EGF receptor was also enhanced by TNF-alpha as well as by EGF. Furthermore, expression of the c-fos gene was enhanced in response to either EGF or TNF-alpha. Pretreatment of HOME cells with EGF for 12 h almost completely blocked the induction of the c-fos gene by EGF and partially blocked the c-fos induction by TNF-alpha. TNF-alpha-induced c-fos gene expression appeared to be partly due to its transactivation of EGF receptor. EGF and TNF-alpha could enhance c-fos gene expression when protein kinase C was down-regulated by phorbol ester myristate (PMA). Gel retardation assay with the NF-kappa B consensus sequence showed that NF-kappa B binding activity was dramatically activated by TNF-alpha, but not by EGF or PMA. The binding of another transcription factor, AP-1 (Jun/Fos), was enhanced by EGF, TNF-alpha, and PMA, whereas TNF-alpha could still activate AP-1 after longer exposure to EGF. TNF-alpha-induced activation of c-fos gene appears to be mediated through pleiotropic mechanisms and partly through a common signal with EGF, possibly through EGF receptor in microvascular endothelial cells.
我们之前的研究表明，肿瘤坏死因子-α（TNF-α）和表皮生长因子（EGF）可能在人网膜微血管内皮（HOME）细胞中共享一条共同的信号转导途径。将培养的HOME细胞暴露于TNF-α 10分钟，可增强表皮生长因子受体的磷酸化，其速率与EGF相当。EGF除了使表皮生长因子受体的丝氨酸/苏氨酸磷酸化外，还观察到酪氨酸残基的明显磷酸化，但TNF-α引起的酪氨酸磷酸化即便有也很轻微。TNF-α以及EGF均可增强表皮生长因子受体的体外激酶活性。此外，c-fos基因的表达可因EGF或TNF-α而增强。用EGF预处理HOME细胞12小时，几乎可完全阻断EGF对c-fos基因的诱导，并部分阻断TNF-α对c-fos的诱导。TNF-α诱导的c-fos基因表达似乎部分归因于其对表皮生长因子受体的反式激活作用。当蛋白激酶C被佛波酯肉豆蔻酸酯（PMA）下调时，EGF和TNF-α可增强c-fos基因表达。用NF-κB共有序列进行凝胶阻滞分析表明，TNF-α可显著激活NF-κB结合活性，但EGF或PMA则不能。另一种转录因子AP-1（Jun/Fos）的结合可被EGF、TNF-α和PMA增强，而在长时间暴露于EGF后，TNF-α仍可激活AP-1。TNF-α诱导的c-fos基因激活似乎是通过多效机制介导的，部分是通过与EGF的共同信号，可能是通过微血管内皮细胞中的表皮生长因子受体。
