title: NUMB phosphorylation destabilizes p53 and promotes self-renewal of tumor-initiating cells by a NANOG-dependent mechanism in liver cancer.
abstract: Stem cell populations are maintained through self-renewing divisions in which one daughter cell commits to a particular fate whereas the other retains the multipotent characteristics of its parent. The NUMB, a tumor suppressor, in conjunction with another tumor-suppressor protein, p53, preserves this property and acts as a barrier against deregulated expansion of tumor-associated stem cells. In this context, NUMB-p53 interaction plays a crucial role to maintain the proper homeostasis of both stem cells, as well as differentiated cells. Because the molecular mechanism governing the assembly and stability of the NUMB-p53 interaction/complex are poorly understood, we tried to identify the molecule(s) that govern this process. Using cancer cell lines, tumor-initiating cells (TICs) of liver, the mouse model, and clinical samples, we identified that phosphorylations of NUMB destabilize p53 and promote self-renewal of TICs in a pluripotency-associated transcription factor NANOG-dependent manner. NANOG phosphorylates NUMB by atypical protein kinase C zeta (aPKCζ), through the direct induction of Aurora A kinase (AURKA) and the repression of an aPKCζ inhibitor, lethal (2) giant larvae. By radioactivity-based kinase activity assays, we showed that NANOG enhances kinase activities of both AURKA and aPKCζ, an important upstream process for NUMB phosphorylation. Phosphorylation of NUMB by aPKCζ destabilizes the NUMB-p53 interaction and p53 proteolysis and deregulates self-renewal in TICs.
  
  
  CONCLUSIONS
  Post-translational modification of NUMB by the NANOG-AURKA-aPKCζ pathway is an important event in TIC self-renewal and tumorigenesis. Hence, the NANOG-NUMB-p53 signaling axis is an important regulatory pathway for TIC events in TIC self-renewal and liver tumorigenesis, suggesting a therapeutic strategy by targeting NUMB phosphorylation. Further in-depth in vivo and clinical studies are warranted to verify this suggestion.
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA.
authors.forename: Hifzur R
authors.initials: HR
authors.lastname: Siddique
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Feldman
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA.
authors.forename: Chia-Lin
authors.initials: CL
authors.lastname: Chen
authors.affiliation: Norris Comprehensive Cancer Center, University of Southern California, Keck School of Medicine, Los Angeles, CA.
authors.forename: Vasu
authors.initials: V
authors.lastname: Punj
authors.affiliation: Division of Medical Bioengineering, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tokumitsu
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA.|Southern California Research Center for Alcoholic Liver and Pancreatic Diseases (ALPD) and Cirrhosis, Los Angeles, CA.
authors.forename: Keigo
authors.initials: K
authors.lastname: Machida
mesh_terms: D000071916:AC133 Antigen; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D064096:Aurora Kinase A / Q000235:genetics; D006023:Glycoproteins / Q000032:analysis; D056945:Hep G2 Cells; D018398:Homeodomain Proteins / Q000502:physiology*; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D000071317:Nanog Homeobox Protein; D014411:Neoplastic Stem Cells / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010455:Peptides / Q000032:analysis; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000502:physiology*; D000099221:Protein Kinase C zeta
chemical_list: D000071916:AC133 Antigen; D015703:Antigens, CD; D064096:Aurora Kinase A; D006023:Glycoproteins; D018398:Homeodomain Proteins; D008565:Membrane Proteins; D000071317:Nanog Homeobox Protein; D009419:Nerve Tissue Proteins; D010455:Peptides; D011493:Protein Kinase C; D016159:Tumor Suppressor Protein p53; D000099221:Protein Kinase C zeta; C486780:NANOG protein, human; C113026:NUMB protein, human; C495901:TP53 protein, human; C576917:AURKA protein, human