Alternative splicing of Bim and Erk-mediated Bim(EL) phosphorylation are dispensable for hematopoietic homeostasis in vivo

Cell Death Differ. 2012 Jun;19(6):1060-8. doi: 10.1038/cdd.2011.198. Epub 2012 Jan 13.

Abstract

The pro-apoptotic BH3-only protein Bim has a major role in hematopoietic homeostasis, particularly in the lymphocyte compartment, where it strongly affects immune function. The three major Bim isoforms (Bim(EL), Bim(L) and Bim(S)) are generated by alternative splicing. Bim(EL), the most abundant isoform, contains a unique sequence that has been reported to be the target of phosphorylation by several MAP kinases. In particular, Erk1/2 has been shown to interact with Bim(EL) through the DEF2 domain of Bim(EL) and specifically phosphorylate this isoform, thereby targeting it for ubiquitination and proteasomal degradation. To examine the physiological importance of this mechanism of regulation and of the alternative splicing of Bim, we have generated several Bim knock-in mouse strains and analyzed their hematopoietic system. Although mutation in the DEF2 domain reduces Bim(EL) degradation in some circumstances, this mutation did not significantly increase Bim's pro-apoptotic activity in vivo nor impact on the homeostasis of the hematopoietic system. We also show that Bim(EL) and Bim(L) are interchangeable, and that Bim(S) is dispensable for the function of Bim. Hence, we conclude that physiological regulation of Bim relies on mechanisms independent of its alternative splicing or the Erk-dependent phosphorylation of Bim(EL).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing
  • Animals
  • Apoptosis
  • Apoptosis Regulatory Proteins / chemistry
  • Apoptosis Regulatory Proteins / genetics
  • Apoptosis Regulatory Proteins / metabolism*
  • Bcl-2-Like Protein 11
  • Gene Knock-In Techniques
  • Hematopoiesis / physiology
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Mitogen-Activated Protein Kinase 3 / metabolism*
  • Mitogen-Activated Protein Kinases / metabolism*
  • Phosphorylation
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins / chemistry
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • T-Lymphocytes / immunology
  • T-Lymphocytes / metabolism
  • Thymocytes / metabolism

Substances

  • Apoptosis Regulatory Proteins
  • Bcl-2-Like Protein 11
  • Bcl2l11 protein, mouse
  • Membrane Proteins
  • Protein Isoforms
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases