Phosphorylation by polo-like kinase 1 induces the tumor-suppressing activity of FADD

College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Korea.
Oncogene (Impact Factor: 8.46). 10/2010; 30(4):471-81. DOI: 10.1038/onc.2010.423
Source: PubMed


Phosphorylation of the Fas-associated death domain (FADD) protein sensitizes cancer cells to various chemotherapeutics. However, the molecular mechanism underlying chemosensitization by phosphorylated FADD (P-FADD) is poorly understood. In this study, we describe the physical interactions and functional interplay between Polo-like kinase 1 (Plk1) and FADD. Plk1 phosphorylates FADD at Ser-194 in response to treatment with taxol. Overexpression of a phosphorylation-mimicking mutant, FADD S194D, caused degradation of Plk1 in an ubiquitin-independent manner, and delayed cytokinesis, consistent with the expected cellular phenotype of Plk1 deficiency. This demonstrates that Plk1 is regulated via a negative feedback loop by its substrate, FADD. Overexpression of FADD S194D sensitized HeLa cells to a low dose of taxol independently of caspase activation, whereas overexpression of FADD S194D resulted in caspase activation in response to a high dose of taxol. Therefore, we examined whether the death potential of P-FADD affected Plk1-mediated tumorigenesis. Transfection of FADD S194D inhibited colony formation by Plk1-overexpressing HeLa cells (HeLa-Plk1). Moreover, overexpression of FADD S194D suppressed tumorigenesis in nude mice xenografted with HeLa-Plk1. Therefore, this study reports the first in vivo validation of tumor-suppressing activity of P-FADD. Collectively, our data demonstrate that in response to taxol, Plk1 endows death-promoting and tumor-suppressor functions to its substrate, FADD.

Full-text preview

Available from:
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Drosophila neuroblasts have served as a model to understand how the balance of stem cell self-renewal versus differentiation is achieved. Drosophila Numb protein regulates this process through its preferential segregation into the differentiating daughter cell. How Numb restricts the proliferation and self-renewal potentials of the recipient cell remains enigmatic. Here, we show that phosphorylation at conserved sites regulates the tumor suppressor activity of Numb. Enforced expression of a phospho-mimetic form of Numb (Numb-TS4D) or genetic manipulation that boosts phospho-Numb levels, attenuates endogenous Numb activity and causes ectopic neuroblast formation (ENF). This effect on neuroblast homeostasis occurs only in the type II neuroblast lineage. We identify Dronc caspase as a novel binding partner of Numb, and demonstrate that overexpression of Dronc suppresses the effects of Numb-TS4D in a non-apoptotic and possibly non-catalytic manner. Reduction of Dronc activity facilitates ENF induced by phospho-Numb. Our findings uncover a molecular mechanism that regulates Numb activity and suggest a novel role for Dronc caspase in regulating neural stem cell homeostasis.
    Preview · Article · Jun 2011 · Development
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Polo-like kinase 1 (Plk1) is a conserved serine/threonine protein kinase that plays pivotal roles during the cell cycle and cell proliferation. Although a number of important targets have been identified, the mechanism of Plk1-regulated pathways and the bulk of the Plk1 interactome are largely unknown. Here, we demonstrate that Plk1 interacts with the DExH/D RNA helicase, UAP56. The protein levels of UAP56 and Plk1 are inversely correlated during the cell cycle. We also show that Plk1 phosphorylates UAP56 in vitro and in vivo and that Plk1-dependent phosphorylation of UAP56 triggers ubiquitination and degradation of UAP56 through proteasomes. This result suggests that Plk1-mediated phosphorylation of UAP56 regulates the stability of UAP56. Our results will be helpful in further understanding mRNA metabolism, cell cycle progression, and the link between mRNA metabolism and cellular function.
    Full-text · Article · Jun 2011 · Molecular Biology Reports
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Administration of the antimitotic chemotherapeutic taxol is known to cause accumulation of the mitotic kinase Aurora-A (Aur-A). Here, we report that Aur-A phosphorylates S203 of the Fas associated with death domain protein (FADD) in response to taxol treatment. In addition, polo-like kinase 1 (Plk1) failed to phosphorylate the Aur-A-unphosphorylatable FADD substitution mutant S203A, indicating that phosphorylation of S203 by Aur-A serves to prime FADD for Plk1-mediated phosphorylation at S194. The double-phosphorylation-mimicking mutant form of FADD, FADD-S194D/S203D (FADD-DD), recruited caspase-8, activating the caspase-dependent cell death pathway. FADD-DD also dissociated the cell death protein RIP1 from FADD, resulting in activation of RIP1 and triggering of caspase-independent cell death. Consistent with its death-promoting potential, FADD-DD showed robust tumor suppressor activity. However, single-phosphorylation-mimicking mutant forms of FADD, FADD-S194D/S203A (FADD-DA) and FADD-S194A/S203D (FADD-AD), were incapable of carrying out such functions, indicating that double phosphorylation of FADD is critical for the execution of cell death and tumor suppression. Collectively, our data show the existence of cooperative actions between Aur-A and Plk1 mitotic kinases in response to taxol, providing a molecular explanation for the action mechanism of taxol.
    Preview · Article · Dec 2011 · Cancer Research
Show more