Li Muyang, Philantrope Fredrick, Diot Alexandra, Bourdon Jean-Christophe, Thompson Patricia
Department of Pathology, Renaissance School of Medicine, Stony Brook University, New York, NY 11794, USA.
Division of Cancer Research, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland, UK.
Cancers (Basel). 2022 Jul 2;14(13):3255. doi: 10.3390/cancers14133255.
SMG1, a phosphatidylinositol 3-kinase-related kinase (PIKK), essential in nonsense-mediated RNA decay (NMD), also regulates p53, including the alternative splicing of p53 isoforms reported to retain p53 functions. We confirm that SMG1 inhibition in MCF7 tumor cells induces p53β and show p53γ increase. Inhibiting SMG1, but not UPF1 (a core factor in NMD), upregulated several cholesterol pathway genes. SMG1 knockdown significantly increased ABCA1, a cholesterol efflux pump shown to be positively regulated by full-length p53 (p53α). An investigation of RASSF1C, an NMD target, increased following SMG1 inhibition and reported to inhibit miR-33a-5p, a canonical ABCA1-inhibiting miRNA, did not explain the ABCA1 results. ABCA1 upregulation following SMG1 knockdown was inhibited by p53β siRNA with greatest inhibition when p53α and p53β were jointly suppressed, while p53γ siRNA had no effect. In contrast, increased expression of MVD, a cholesterol synthesis gene upregulated in p53 deficient backgrounds, was sensitive to combined targeting of p53α and p53γ. Phenotypically, we observed increased intracellular cholesterol and enhanced sensitivity of MCF7 to growth inhibitory effects of cholesterol-lowering Fatostatin following SMG1 inhibition. Our results suggest deregulation of cholesterol pathway genes following SMG1 knockdown may involve alternative p53 programming, possibly resulting from differential effects of p53 isoforms on cholesterol gene expression.
SMG1是一种磷脂酰肌醇3激酶相关激酶（PIKK），在无义介导的RNA衰变（NMD）中必不可少，它还调节p53，包括据报道保留p53功能的p53异构体的可变剪接。我们证实，在MCF7肿瘤细胞中抑制SMG1会诱导p53β的产生，并显示p53γ增加。抑制SMG1而非UPF1（NMD中的核心因子）会上调多个胆固醇途径基因。SMG1基因敲低显著增加了ABCA1，ABCA1是一种胆固醇流出泵，已证明受全长p53（p53α）正向调节。对RASSF1C（一种NMD靶点）的研究表明，在抑制SMG1后其表达增加，且据报道它能抑制miR-33a-5p（一种典型的抑制ABCA1的miRNA），但这并不能解释ABCA1的结果。SMG1基因敲低后ABCA1的上调被p53β siRNA抑制，当p53α和p53β共同被抑制时抑制作用最大，而p53γ siRNA则没有效果。相比之下，MVD（一种在p53缺陷背景中上调的胆固醇合成基因）的表达增加对p53α和p53γ的联合靶向敏感。从表型上看，我们观察到抑制SMG1后，MCF7细胞内胆固醇增加，且对降低胆固醇的法舒地尔的生长抑制作用的敏感性增强。我们的结果表明，SMG1基因敲低后胆固醇途径基因的失调可能涉及p53的替代编程，这可能是由于p53异构体对胆固醇基因表达的不同影响所致。
