Reduced expression of PNUTS leads to activation of Rb-phosphatase and caspase-mediated apoptosis.
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.
De Leon
Gabriel
G
Department of Biology and Health Science, Pace University, Pleasantville, New York 10570, USA.
Sherry
Tara C
TC
Krucher
Nancy A
NA
D017209:Apoptosis; D053181:Caspase 8 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004789:Enzyme Activation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000860:Hypoxia; D009687:Nuclear Proteins / Q000096:biosynthesis*; D010766:Phosphorylation; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000096:biosynthesis*; D016160:Retinoblastoma Protein / Q000096:biosynthesis*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C110225:PPP1R10 protein, human; D016601:RNA-Binding Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D053181:Caspase 8; D020169:Caspases