The E3 ubiquitin ligase Mule acts through the ATM-p53 axis to maintain B lymphocyte homeostasis

J Exp Med. 2012 Jan 16;209(1):173-86. doi: 10.1084/jem.20111363. Epub 2012 Jan 2.

Abstract

Cellular homeostasis is controlled by pathways that balance cell death with survival. Mcl-1 ubiquitin ligase E3 (Mule) is an E3 ubiquitin ligase that targets the proapoptotic molecule p53 for polyubiquitination and degradation. To elucidate the role of Mule in B lymphocyte homeostasis, B cell-specific Mule knockout (BMKO) mice were generated using the Cre-LoxP recombination system. Analysis of BMKO mice showed that Mule was essential for B cell development, proliferation, homeostasis, and humoral immune responses. p53 transactivation was increased by two- to fourfold in Mule-deficient B cells at steady state. Genetic ablation of p53 in BMKO mice restored B cell development, proliferation, and homeostasis. p53 protein was increased in resting Mule-deficient mouse embryonic fibroblasts (MEFs) and embryonic stem (ES) cells. Loss of Mule in both MEFs and B cells at steady state resulted in increased levels of phospho-ataxia telangiectasia mutated (ATM) and the ATM substrate p53. Under genotoxic stress, BMKO B cells were resistant to apoptosis, and control MEFs exhibited evidence of a physical interaction between Mule and phospho-ATM. Phospho-ATM, phospho-p53, and Brca1 levels were reduced in Mule-deficient B cells and MEFs subjected to genotoxic stress. Thus, Mule regulates the ATM-p53 axis to maintain B cell homeostasis under both steady-state and stress conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Ataxia Telangiectasia Mutated Proteins
  • B-Lymphocytes / cytology
  • B-Lymphocytes / enzymology*
  • B-Lymphocytes / immunology
  • Cell Cycle Proteins / metabolism*
  • Cell Differentiation / genetics
  • Cell Differentiation / immunology
  • Cell Line
  • Cell Proliferation
  • DNA Damage / immunology
  • DNA-Binding Proteins / metabolism*
  • Female
  • Gene Order
  • Gene Targeting
  • Homeostasis / genetics
  • Homeostasis / immunology
  • Immunity, Humoral / genetics
  • Immunoglobulin Class Switching / genetics
  • Immunoglobulin Isotypes / blood
  • Lymphocyte Activation / genetics
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Protein Serine-Threonine Kinases / metabolism*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism*
  • Tumor Suppressor Proteins / metabolism*
  • Ubiquitin-Protein Ligases / deficiency
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Immunoglobulin Isotypes
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • Huwe1 protein, mouse
  • Ubiquitin-Protein Ligases
  • Ataxia Telangiectasia Mutated Proteins
  • Atm protein, mouse
  • Protein Serine-Threonine Kinases