NORE1A is a Ras senescence effector that controls the apoptotic/senescent balance of p53 via HIPK2.
Bottom Line: We show that NORE1A is a powerful Ras senescence effector and that down-regulation of NORE1A suppresses senescence induction by Ras and enhances Ras transformation.NORE1A acts to suppress its proapoptotic phosphorylation of p53 but enhance its prosenescent acetylation of p53.Thus, we identify a major new Ras signaling pathway that links Ras to the control of specific protein acetylation and show how NORE1A allows Ras to qualitatively modify p53 function to promote senescence.
Affiliation: Department of Medicine, Department of Biochemistry and Molecular Biology, Department of Pharmacology and Toxicology, J.G. Brown Cancer Center, Molecular Targets Group, University of Louisville, Louisville, KY 40202.Show MeSH
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Mentions: HIPK2 is a tumor suppressor that binds p53 and modulates its activity both directly and indirectly (Puca et al., 2010). Thus, HIPK2 is a good candidate for a downstream component of NORE1A senescence signaling. To determine the importance of HIPK2 for NORE1A-mediated senescence, we generated stable clones of A549 cells transfected with shRNAs against HIPK2. Compared with the scrambled shRNA control, the HIPK2 knockdown cells were resistant to NORE1A induced senescence (Fig. 6 a). Suppression of HIPK2 similarly reduced baseline senescence in HBEC-3KT cells (Fig. 6 b). To further confirm the biological importance of the interaction between NORE1A and HIPK2, we used deletion mutagenesis followed by point mutagenesis to identify the minimal domain required for the interaction of NORE1A with HIPK2. Ultimately, Arginines 92–94 of NORE1A were mutated to Alanines. The resultant NORE1AR92-94A mutant (NORE1AR3A) was defective for the interaction with HIPK2 and defective for the induction of senescence in A549 cells (Fig. 6 c) and showed a reduced ability to stabilize HIPK2 (Fig. S1 a). However, it retained WT binding to MST1 and retained WT apoptosis capacity (Fig. 6 d).
Affiliation: Department of Medicine, Department of Biochemistry and Molecular Biology, Department of Pharmacology and Toxicology, J.G. Brown Cancer Center, Molecular Targets Group, University of Louisville, Louisville, KY 40202.