Eberhard Yanina, Gronda Marcela, Hurren Rose, Datti Alessandro, MacLean Neil, Ketela Troy, Moffat Jason, Wrana Jeffrey L, Schimmer Aaron D
Princess Margaret Hospital, Ontario Cancer Institute, Toronto, ON, Canada.
Oncotarget. 2011 Mar;2(3):186-96. doi: 10.18632/oncotarget.239.
Evasion of death receptor ligand-induced apoptosis contributs to cancer development and progression. To better understand mechanisms conferring resistance to death ligands, we screened an siRNA library to identify sequences that sensitize resistant cells to fas activating antibody (CH-11). From this screen, we identified the Sterol-Regulatory Element-Binding Protein 1 (SREBP1), a transcription factor, which regulates genes involved in cholesterol and fatty acid synthesis including fatty acid synthase. Inhibition of SREBP1 sensitized PPC-1 and HeLa to the death receptor ligands CH-11 and TRAIL. In contrast, DU145 prostate cancer cells that are resistant to death ligands despite expressing the receptors on their cell surface remained resistant to CH-11 and TRAIL after knockdown of SREBP1. Consistent with the effects on cell viability, the addition of CH-11 activated caspases 3 and 8 in HeLa but not DU145 cells with silenced SREBP1. We demonstrated that knockdown of SREBP1 produced a marked decrease in fatty acid synthase expression. Furthermore, genetic or chemical inhibition of fatty acid synthase with shRNA or orlistat, respectively, recapitulated the effects of SREBP1 inhibition and sensitized HeLa but not DU145 cells to CH-11 and TRAIL. Sensitization to death receptor ligands by inhibition of fatty acid synthase was associated with activation of caspase 8 prior to caspase 9. Neither silencing of SREBP1 or fatty acid synthase changed basal expression of the core death receptor components Fas, caspase 8, FADD, caspase 3 or FLIP. Thus, inhibition of SREBP1 or its downstream target fatty acid synthase sensitizes resistant cells to death ligands.
逃避死亡受体配体诱导的细胞凋亡有助于癌症的发生和发展。为了更好地理解赋予对死亡配体抗性的机制，我们筛选了一个小干扰RNA文库，以鉴定使抗性细胞对Fas激活抗体（CH-11）敏感的序列。通过该筛选，我们鉴定出了固醇调节元件结合蛋白1（SREBP1），一种转录因子，它调节参与胆固醇和脂肪酸合成的基因，包括脂肪酸合酶。抑制SREBP1使PPC-1和HeLa细胞对死亡受体配体CH-11和TRAIL敏感。相反，DU145前列腺癌细胞尽管在其细胞表面表达受体，但对死亡配体具有抗性，在敲低SREBP1后，对CH-11和TRAIL仍具有抗性。与对细胞活力的影响一致，添加CH-11可激活HeLa细胞中的半胱天冬酶3和8，但对SREBP1沉默的DU145细胞则无此作用。我们证明敲低SREBP1会导致脂肪酸合酶表达显著降低。此外，分别用短发夹RNA或奥利司他对脂肪酸合酶进行基因或化学抑制，重现了SREBP1抑制的效果，并使HeLa细胞而非DU145细胞对CH-11和TRAIL敏感。通过抑制脂肪酸合酶使细胞对死亡受体配体敏感与半胱天冬酶8在半胱天冬酶9之前的激活有关。沉默SREBP1或脂肪酸合酶均未改变核心死亡受体成分Fas、半胱天冬酶8、FADD、半胱天冬酶3或FLIP的基础表达。因此，抑制SREBP1或其下游靶标脂肪酸合酶可使抗性细胞对死亡配体敏感。
