De Simone Veronica, Bevivino Gerolamo, Sedda Silvia, Izzo Roberta, Laudisi Federica, Dinallo Vincenzo, Franzè Eleonora, Colantoni Alfredo, Ortenzi Angela, Salvatori Silvia, Rossi Piero, Sica Giuseppe S, Fantini Massimo C, Stolfi Carmine, Monteleone Giovanni
Department of Systems Medicine, University of 'Tor Vergata', Rome, Italy.
Department of Surgery, University of 'Tor Vergata', Rome, Italy.
Cell Death Dis. 2017 Mar 16;8(3):e2681. doi: 10.1038/cddis.2017.103.
Upregulation of Smad7, an inhibitor of transforming growth factor-β1 (TGF-β1), occurs in sporadic colorectal cancer (CRC) and knockdown of Smad7 inhibits CRC cell growth, a phenomenon that associates with decreased expression of cell division cycle 25 homolog A and arrest of cells in the S phase of the cell cycle. These findings occur in CRC cells unresponsive to TGF-β1, thus suggesting the existence of a Smad7-mediated TGF-β1-independent mechanism that controls CRC cell behavior. Here we show that Smad7 inhibition with a specific Smad7 antisense oligonucleotide upregulates eukaryotic translation initiation factor 2α (eIF2α) phosphorylation, a transcription factor involved in the regulation of cell cycle arrest and induction of cell death, and induces activating transcription factor 4 (ATF4) and CCAAT/enhancer binding protein homology protein (CHOP), two downstream targets of eIF2α. Among the upstream kinases that control eIF2α phosphorylation, the serine-threonine protein kinase RNA (PKR), but not general control non-derepressible 2 (GCN2) and protein kinase RNA-like endoplasmic reticulum kinase (PERK), is activated by Smad7 knockdown. PKR silencing abolishes Smad7 antisense-induced eIF2α phosphorylation and ATF4/CHOP induction, thereby preventing Smad7 antisense-driven cell death. Smad7 inhibition diminishes interaction of PKR with protein kinase inhibitor p58 (p58), a cellular inhibitor of PKR, but does not change the expression and/or activity of other factors involved in the control of PKR activation. These findings delineate a novel mechanism by which Smad7 knockdown promotes CRC cell death.
转化生长因子-β1（TGF-β1）抑制剂Smad7在散发性结直肠癌（CRC）中上调，敲低Smad7可抑制CRC细胞生长，这一现象与细胞分裂周期25同源物A表达降低以及细胞周期S期停滞有关。这些发现出现在对TGF-β1无反应的CRC细胞中，因此提示存在一种Smad7介导的不依赖TGF-β1的机制来控制CRC细胞行为。在此我们表明，用特异性Smad7反义寡核苷酸抑制Smad7可上调真核翻译起始因子2α（eIF2α）磷酸化，eIF2α是一种参与细胞周期停滞调节和细胞死亡诱导的转录因子，并诱导eIF2α的两个下游靶点激活转录因子4（ATF4）和CCAAT/增强子结合蛋白同源蛋白（CHOP）。在控制eIF2α磷酸化的上游激酶中，丝氨酸-苏氨酸蛋白激酶RNA（PKR）而非一般控制非抑制性2（GCN2）和蛋白激酶RNA样内质网激酶（PERK）被Smad7敲低激活。PKR沉默消除了Smad7反义诱导的eIF2α磷酸化和ATF4/CHOP诱导，从而阻止了Smad7反义驱动的细胞死亡。Smad7抑制减少了PKR与蛋白激酶抑制剂p58（p58）的相互作用，p58是PKR的一种细胞内抑制剂，但不改变参与PKR激活控制的其他因子的表达和/或活性。这些发现描绘了一种Smad7敲低促进CRC细胞死亡的新机制。
