Reduced expression of PNUTS leads to activation of Rb-phosphatase and caspase-mediated apoptosis
Reduced expression of PNUTS leads to activation of Rb-phosphatase and caspase-mediated apoptosis
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DOI：
10.4161/cbt.7.6.5839
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发表时间：
2008-06-01
影响因子：
3.6
通讯作者：
Krucher, Nancy A.
中科院分区：
文献类型：
--
作者：
De Leon, Gabriel;Sherry, Tara C.;Krucher, Nancy A.
大量证据表明，视网膜母细胞瘤（Retinoblastoma, Rb）活性在细胞增殖和凋亡的调控中起重要作用。Rb蛋白的可逆磷酸化是由周期蛋白依赖激酶和蛋白磷酸酶1 （PP1）进行的，调节其功能。PP1相互作用蛋白PNUTS（磷酸酶核靶向亚单位）被认为是Rb磷酸化的调节因子。在本研究中，PNUTS敲低MCF7、SKA和HCT116癌细胞会导致细胞凋亡增加，从而导致生存能力降低。然而，正常细胞（乳腺MCF10A和结肠CCD-18Co）在PNUTS表达减少时不表现出活力降低。PNUTS敲低对Rb-null Saos-2细胞无影响。然而，当Rb在Saos-2细胞中稳定表达时，PNUTS敲低会减少细胞数量。PNUTS在p53(-/-) HCT116细胞中敲低表明p53在诱导凋亡中是不可或缺的。PNUTS表达缺失导致Rb-磷酸酶活性增加和Rb去磷酸化。在PNUTS缺失的细胞中，E2F1与Rb分离，由此导致的凋亡依赖于caspase-8。这些结果表明Rb磷酸化状态可以通过靶向Rb磷酸酶活性来控制，并提示PNUTS可能是促凋亡治疗策略的潜在靶点。
There is abundant evidence that Retinoblastoma (Rb) activity is important in the control of cell proliferation and apoptosis. Reversible phosphorylation of the Rb protein that is carried out by cyclin dependent kinases and Protein phosphatase 1 (PP1) regulates its functions. A PP1 interacting protein, PNUTS (Phosphatase Nuclear Targeting Subunit) is proposed to be a regulator of Rb phosphorylation. In this study, PNUTS knockdown in MCF7, SKA and HCT116 cancer cells causes a reduction in viability due to increased apoptosis. However, normal cells (MCF10A breast and CCD-18Co colon) do not exhibit reduced viability when PNUTS expression is diminished. PNUTS knockdown has no effect in Rb-null Saos-2 cells. However, when Rb is stably expressed in Saos-2 cells, PNUTS knockdown reduces cell number. Knockdown of PNUTS in p53(-/-) HCT116 cells indicates that p53 is dispensable for the induction of apoptosis. Loss of PNUTS expression results in increased Rb-phosphatase activity and Rb dephosphorylation. E2F1 dissociates from Rb in cells depleted of PNUTS and the resulting apoptosis is dependent on caspase-8. These results indicate that Rb phosphorylation state can be manipulated by targeting Rb phosphatase activity and suggest that PNUTS may be a potential target for therapeutic pro-apoptotic strategies.