Cbl-b, a RING-type E3 ubiquitin ligase, targets phosphatidylinositol 3-kinase for ubiquitination in T cells

J Biol Chem. 2001 Feb 16;276(7):4872-8. doi: 10.1074/jbc.M008901200. Epub 2000 Nov 21.

Abstract

Cbl-b is implicated in setting the threshold of T lymphocyte activation. In Cbl-b-deficient T cells, the activation of Vav, a guanine nucleotide exchange factor, is significantly enhanced. The molecular mechanism underlying Cbl-b-regulated Vav activation was unclear. Here it is shown that Cbl-b interacts with and induces ubiquitin conjugation to the p85 regulatory subunit of phosphatidylinositol 3-kinase, an upstream regulator of Vav. A functional RING finger of Cbl-b was essential for p85 ubiquitination. However, a loss of function mutation at the well-conserved amino-terminal variant src homology (SH) 2 domain of Cbl-b did not affect its ligase activity. A distal carboxyl-terminal proline-rich region in Cbl-b was mapped to contain the primary binding sequences for the SH3 domain of p85. Deletion of either the distal proline-rich region in Cbl-b or the SH3 domain of p85 severely reduced ubiquitin conjugation to p85. The data suggest a molecular link for Cbl-b-mediated negative regulation of Vav, with phosphatidylinositol 3-kinase as a direct target for Cbl-b E3 ubiquitin ligase.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Carrier Proteins / chemistry
  • Carrier Proteins / physiology*
  • Humans
  • Jurkat Cells
  • Ligases / physiology
  • Phosphatidylinositol 3-Kinases / chemistry
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoproteins / chemistry
  • Phosphoproteins / physiology*
  • Proline / metabolism
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins c-cbl
  • T-Lymphocytes / enzymology*
  • T-Lymphocytes / immunology*
  • Ubiquitin-Protein Ligases
  • Ubiquitins / metabolism*
  • src Homology Domains

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Phosphoproteins
  • Ubiquitins
  • Proline
  • CBLB protein, human
  • Proto-Oncogene Proteins c-cbl
  • Ubiquitin-Protein Ligases
  • Phosphatidylinositol 3-Kinases
  • Ligases